UBC Theses and Dissertations

UBC Theses Logo

UBC Theses and Dissertations

Central and peripheral analgesic properties of local anesthetics : effects of lidocaine on thalamic neurons… Schwarz, Stephan 2002

Your browser doesn't seem to have a PDF viewer, please download the PDF to view this item.

Item Metadata

Download

Media
831-ubc_2002-732444.pdf [ 8.98MB ]
Metadata
JSON: 831-1.0090645.json
JSON-LD: 831-1.0090645-ld.json
RDF/XML (Pretty): 831-1.0090645-rdf.xml
RDF/JSON: 831-1.0090645-rdf.json
Turtle: 831-1.0090645-turtle.txt
N-Triples: 831-1.0090645-rdf-ntriples.txt
Original Record: 831-1.0090645-source.json
Full Text
831-1.0090645-fulltext.txt
Citation
831-1.0090645.ris

Full Text

Central and Peripheral Analgesic Properties of Local Anesthetics Effects of Lidocaine on Thalamic Neurons and Efficacy of Ropivacaine in Femoral 3-in-1 Nerve Blockade by S T E P H A N S C H W A R Z M . D . (Ar^tliche Prufung), Georg-August-Universitat Gottingen, 1995 Dr. med., Georg-August-Universitat Gottingen, 1998 A THESIS S U B M I T T E D I N P A R T I A L F U L F I L M E N T O F T H E R E Q U I R E M E N T S F O R T H E D E G R E E O F D O C T O R O F P H I L O S O P H Y in < T H E F A C U L T Y O F G R A D U A T E STUDIES (Department of Pharmacology & Therapeutics) We accept this thesis as conforming to the required standard T H E U N I V E R S I T Y O F BRITISH C O L U M B I A March 2002 © Stephan Schwarz, 2002 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department of f ^ ^ t o ^ / j K' The University of British Columbia Vancouver, Canada Date / W - S ^ ~ZOO^_ DE-6 (2/88) S. S C H W A R Z i i Abstract This thesis is dedicated to the pharmacology & therapeutics of local anesthetics, with a specific focus on their analgesic properties. In the first section, laboratory studies emphasize central mechanisms of the prototype agent, lidocaine, whereas clinical studies in the second section investigate the analgesic efficacy of the recently introduced aminoamide, ropivacaine, when administered peripherally for nerve blockade in knee surgery. The specific objective of the laboratory studies was to define the concentration-dependent effects of lidocaine on the membrane properties and excitability of neurons in the ventral posterior lateral thalamic nucleus (VPL), a major somatosensory and nociceptive relay station that plays a central role in pain states. Lidocaine produces central analgesia and sedation when present in the systemic circulation at low concentrations, and evidence implicates V P L neurons in these actions. Differential interference contrast infrared (DIC-IR) videomicroscopy-guided whole-cell patch clamp techniques were used to record from V P L neurons in rat brain slice preparations. Low, analgesic lidocaine concentrations (10 fiM) significantly decreased neuronal input resistance (ft), which shunted action potentials, increased current thresholds, and reduced tonic firing. The effects were not associated with the classic signs of N a + conductance blockade. The G A B A A receptor antagonist, bicuculline, had no effect on the lidocaine-induced shunt. Higher lidocaine concentrations (> 300 uM; clinically CNS-toxic) did not decrease Ri but reversibly unmasked high threshold C a 2 + spikes (HTSs), susceptible to blockade by C d 2 + . S. S C H W A R Z iii Extracellular QX-314, a quaternary lidocaine analogue, increased rather than decreased Ri. Similarly, neither procainamide nor bupivacaine reduced Ri. In summary, these studies identified novel actions of lidocaine in the thalamus, distinct from the classic effects on N a + conductance. Low concentrations produced a shunting type of inhibition, likely a result of interaction with an intracellular target that does not involve G A B A A receptors. These findings serve as an attractive and plausible mechanism for the systemic analgesic and sedative actions of lidocaine in vivo and may provide a basis for the development of novel, selective, and effective agents for the treatment of acute and chronic pain. The observation of an unmasking of high threshold C a 2 + spikes is in contrast to previous studies in other tissues showing that lidocaine blocks C a 2 + conductances, and is of potential significance for the mechanisms of local anesthetic CNS toxicity. The purpose of the clinical studies was to test i f postoperative pain control in patients undergoing arthroscopic anterior cruciate ligament reconstruction (ACLR) under general anesthesia is improved by addition of a preincisional femoral 3-in-l block with ropivacaine 0.2% to standard intra-articular instillation at the end of surgery. In a prospective, randomized, controlled, double-blind trial (RCT), 44 patients scheduled for inpatient A C L R were studied. Prior to surgery, the treatment group (» = 22) received a femoral 3-in-l block with 40 ml of ropivacaine 0.2%, augmented by additional peri-incisional infiltrations (20 ml) at the end of the procedure. The control group [n — 22) received saline 0.9% instead of ropivacaine. A l l patients received an intra-articular instillation with 30 ml of ropivacaine 0.2% at the end of surgery. The primary efficacy variable was 24 h morphine consumption postoperatively standardized by weight, S. S C H W A R Z iv administered intravenously via a patient-controlled analgesia (PCA) pump. There was no significant difference between both groups in the primary efficacy variable. N o difference was found in visual analog scale pain scores, adverse events, or vital signs. More patients in the treatment group did not require any morphine than in the control group, but this difference was not statistically significant. In conclusion, the clinical studies demonstrated no significant effect in an R C T of a femoral 3-in-l block with ropivacaine 0.2% on postoperative analgesic consumption, compared to intra-articular instillation alone, in patients undergoing A C L R under general anesthesia. S. S C H W A R Z V Table of Contents Abstract ii Table of Contents v List of Tables ix List of Figures x Acknowledgements xii Scope of the Topic and Approach to Research 1 S E C T I O N I: L A B O R A T O R Y STUDIES 5 1.1 Introduction • 6 1.1.1 Overall aim and specific objective 6 1.1.2 Background. 6 1.2 Materials and Methods 16 1.2.1 Ethics 16 1.2.2 Preparation of brain slices 16 1.2.3 Electrophysiological recordings 17 1.2.4 Drugs 21 1.2.5 Statistical analyses 22 1.3 Results 24 1.3.1 Basting membrane properties of VPL neurons 24 1.3.2 Postnatal development of resting membrane properties 26 1.3.3 Current-voltage relationships 28 S. S C H W A R Z vi 1.3.4 Active membrane properties: tonic and burst firing 29 1.3.5 Effects of lidocaine on resting membrane properties 30 1.3.6 Effects of lidocaine on current-voltage relationships 33 1.3.7 Effects of lidocaine on tonic repetitive firing . 35 1.3.8 Effects of lidocaine on burst firing and low threshold spikes 39 1.3.9 Effects of lidocaine on high threshold spikes 39 1.3.10 Effects of GABA.A receptor blockade by bicuculline on lidocaine actions 48 1.3.11 Effects of other local anesthetic agents on membrane properties 51 1.3.11.1 QX-314 ...53 1.3.11.2 Procainamide 56 1.3.11.3 Bupivacaine 62 1.4 Discussion : 66 1.4.1 Shunting inhibition: a novel effect of low lidocaine concentrations in the CNS 66 1.4.1.1 Clinical relevance of concentrations 67 1.4.1.2 Previous investigations 68 1.4.1.3 Physiological significance 69 1.4.1.4 Effects of G A B A A receptor blockade : 74 1.4.1.5 Molecular and cellular actions of lidocaine 76 1.4.1.6 Lidocaine and E E G spindle waves 80 1.4.2 Effects of high lidocaine concentrations 81 1.4.2.1 Effects on high threshold C a 2 + spikes 84 1.4.3 Effects ofprocainamide on membrane properties 86 1.4.4 Limitations and future outlook 87 1.4.5 Summary and conclusions 88 S. S C H W A R Z vii S E C T I O N II: C L I N I C A L STUDIES 89 II. 1 Introduction 90 II. 1.1 Overall aim and specific objective 90 II. 1.2 Background 90 II. 1.3 Femoral 3-in-1 block 91 II. 1.4 Choice of local anesthetic. 95 II. 1.5 Primary hypothesis..... 96 11.2 Materials and Methods 97 11.2.1 Ethics • 97 11.2.2 Study design ; 97 II. 2.3 Inclusion criteria, exclusion criteria, and patient withdrawal. 98 II. 2.4 Treatment interventions 99 II.2.5 Outcome variables 102 II. 2.6 Study drugs and blinding. 102 II.2.7 Statistical analyses ....103 11.3 Results.... 105 II. 3.1 Demographics 105. II. 3.2 Primary efficacy variable 106 11.3.3 Secondary efficacy variables 108 II. 3.4 Adverse events 110 11.4 Discussion 112 II.4.1 Summary and conclusions 119 S. S C H W A R Z viii Overall Conclusion and Closing Remarks 121 Appendix I , 125 Appendix II 127 Appendix III '. 131 Abbreviations 132 Bibliography 139 V S. S C H W A R Z ix List of Tables Table 1 Overview of pain syndromes responsive to systemic lidocaine 9 Table 2 Postnatal development of resting membrane properties 28 Table 3 Effects of lidocaine on input resistance and membrane time constant 33 Table 4 Overview of reported molecular and cellular actions of local anesthetics 77 Table 5 Patient demographics, preoperative vital signs, and surgical data 105 Table 6 Timing of treatment interventions 106 Table 7 Postoperative analgesic consumption (intention-to-treat analysis) 107 Table 8 Number of patients not requiring morphine postoperatively 107 Table 9 Postoperative morphine consumption (patients requiring morphine) 107 Table 10 Incidence of common adverse events I l l S. S C H W A R Z x List of Figures Figure 1 Structural formula of lidocaine 7 Figure 2 The path of sensation according to Descartes 10 Figure 3 Location of the thalamus in the mammalian brain 15 Figure 4 Location of the V P L nucleus in the thalamus 15 Figure 5 DIC-IR images of a V P L neuron 21 Figure 6 Resting membrane properties: frequency distributions, and correlations 25 Figure 7 Postnatal development of resting membrane properties 27 Figure 8 Effects of lidocaine on input resistance, membrane time constant, and resting membrane potential.... 32 Figure 9 Effects of lidocaine on current-voltage relationships 34 Figure 10 Effects of a low concentration of lidocaine on tonic repetitive firing 36 Figure 11 Effects of a low concentration of lidocaine on injected current 37 Figure 12 Effects of high concentrations of lidocaine on tonic repetitive firing 38 Figure 13 Low threshold spikes and the effects of lidocaine on burst firing 40 Figure 14 Time-dependent effects of a high concentration of lidocaine on repetitive spikes 42 Figure 15 Lidocaine unmasks high threshold spikes not blocked by T T X 43 Figure 16 Effects of lidocaine on high threshold spikes in the presence of T T X 45 Figure 17 Effects of C a 2 + free extracellular solution and C d 2 + on the high threshold spikes unmasked by lidocaine 47 S. S C H W A R Z xi Figure 18 Effects of bicuculline on the decrease in tonic firing due to lidocaine 50 Figure 19 Effects of bicuculline on the decrease in input resistance due to lidocaine... 52 Figure 20 Structural formula of QX-314 54 Figure 21 Effects of QX-314 on membrane properties 55 Figure 22 Structural formula of procainamide 57 Figure 23 Effects of procainamide on membrane properties 58 Figure 24 Effects of procainamide on tonic and burst firing 61 Figure 25 Structural formula of bupivacaine 63 Figure 26 Effects of bupivacaine on input resistance 65 Figure 27 Sensory innervation of the lower extremities 92 Figure 28 Structural formula of ropivacaine 96 Figure 29 Treatment interventions 101 Figure 30 Postoperative morphine consumption (patients with no morphine consumption excluded) 108 Figure 31 Postoperative V A S pain scores at rest over time 109 Figure 32 Postoperative blood pressure over time 109 Figure 33 Postoperative heart rate over time 110 S. S C H W A R Z xii Acknowledgements Research is always a collaborative effort. I would not have been able to prepare this combined laboratory and clinical research thesis without the many individuals who directly or indirectly gifted me with their inspiration, ideas, ideals, or other forms of help. First and foremost, I would like to thank my two co-supervisors, Drs. Bernard A . MacLeod and Ernie Puil, for their unfailing support, patience, extraordinary generosity, and outstanding supervision of this thesis, during which they always treated me as a colleague and taught me by providing space and opportunity for independent inquiry and critical thought. I thank Dr. Morley C. Sutter for serving on my supervisory committee, where he offered his invaluable input and experience in bridging clinical and laboratory research and provided a role model for being a physician-scientist. I am grateful to Drs. Frank Tennigkeit and Craig Ries for die generous sharing of their expertise in the laboratory and countless discussions, Stefan Reinker for his collaboration in the studies, on procainamide, and Dr. Richard Neuman, Prof. Walter Stiihmer, and my father, Dr. Dietrich W. F. Schwarz, for their valuable advice and constructive comments. Lance Corey, Jens Haeusser, and Patricia Rust provided technical aid and help with computer-related problems, and Silvia Fu assisted with some of the experiments. I owe my gratitude to Dr. Michael J. A . Walker for his kind gifts of procainamide and Barolo, time for discussions about statistical analyses, and his sense of humour. Dr. Ryan J. Huxtable repeatedly provided financial support for attending the meetings of the Western Pharmacology Society as well as general scholarly guidance, including lessons in English poetry and his perspective on Vinum Columbium Britannicum. S. S C H W A R Z xi i i The clinical section o f these studies would not have been possible without the involved nursing staff at U B C Hospital ( O R suite, P A C U , and wards 1 C / D ) , for whose collaboration and patience I am grateful. Furthermore, I would like to thank L u i Franciosi, Debbie Cannon, and Drs . A l l e n Bain, Chris Bates, Pat McConkey , Ross Davidson, Br ian Day, R o b Eger, N a o m i Kron i tz , Dav id Lea, M i k e Moul t , B o b Purdy, B i l l Regan, and Theo Weideman for their invaluable help. The clinical studies were conducted i n co-operation with Astra Pharma Inc., Canada (Mississauga, O N ) , o f w h o m I would like to representatively acknowledge Rris ta N e v i n , Heather Burt, and Vadna Sime. Sergio Escobedo was helpful in statistical issues and provided assistance with some analyses using SAS software. The U B C Department o f Anesthesia was instrumental i n the completion o f this thesis through extraordinary and ongoing support. In particular, I would like to express my sincerest gratitude to Drs . Jamie Renwick, Eleanor Reimer, and D a v i d R. Bevan (now i n Toronto), without w h o m I would not be where I am today. M y thanks also go to D r . D a v i d Parsons for his kind financial aid for presenting at the Sixth International Conference on Molecular and Basic Mechanisms of Anesthesia. O n a very special note, I am indebted to D r . R o d McTaggart for his mentorship i n Anesthesiology, thoughtful comments on the manuscript for publication o f the clinical section o f this thesis, and his friendship. Funding for this work was provided by a Pharmacia & Upjohn Special University Award , a Bri t ish Columbia Medical Services Foundation ( B C M S F ) Fellowship, a Medical Research Counc i l o f Canada ( M R C ) Fellowship, and the generosity o f my supervisors through their grants from the M R C / C I H R (Canadian Institutes o f Health Research) for the laboratory studies (Dr. Ernie Puil) and Astra Pharma Inc., Canada for the clinical studies (Dr. Bernard A . MacLeod) . The most important support o f all came from Linda , whose unfailing and tireless patience, tolerance, and love words cannot express. S. S C H W A R Z 1 Scope of the T o p i c and A p p r o a c h to Research Modern anesthesiology is a discipline that faces tremendous challenges in a time of rapid progress in other medical specialties and our continuously changing society. In order to be able to provide excellence in patient care for a growing elderly and multiethnic population, there is an imminent need to develop novel pharmacological and therapeutic strategies that are effective and overcome the shortcomings, pitfalls, and untoward events of those available at present. A major therapeutic challenge today remains the mastering of acute and chronic pain. Pain is the most frequent symptom encountered in clinical medicine and among the most common causes of disability in industrialized nations. Economically, acute and chronic pain burdens our society more than heart disease and cancer combined, a fact often escaping our awareness (Thompson 1997). More than one out of three adults in North America report pain symptoms (Bonica 1980, 1990). In the United States alone, 70 million people have chronic pain, many of whom are permanently disabled (Osterweis et al. 1987). A prominent study in the United Kingdom estimated that as many as 46.5% of the general population suffer from chronic pain (Elliott et al. 1999). If poorly treated or left untreated, even acute pain (e.g., acute postoperative pain) can quickly turn into chronic pain (Katz et al. 1996). Historically, there has been a sharp discrepancy between the overall magnitude and scope of the problem on the one hand and the degree of progress and innovation in analgesic pharmacology & therapeutics on the other hand. The level of funding and overall support for pain research has been a fraction of that designated for cardiovascular disease, cancer, or other areas of health S. S C H W A R Z 2 care. O n l y very recently, in 1996, the U.S . National Institutes o f Health ( N I H ) established a Pain Research Consort ium under its aegis, some 23 years after John Joseph (originally born as " G i o v a n n i Guiseppe") Bonica spearheaded the creation o f an international society dedicated to pain research, which became the International Associat ion o f the Study o f Pain (IASP). Whereas the Canadian Institutes o f Health Research (CIHR) thus far lack an institute or consortium specifically committed to pain or anesthesia research, their co-sponsorship o f the recently introduced " D r . Ronald Melzack Pain Research A w a r d " and one (1) postdoctoral fellowship in "clinical or basic science as it relates to Anesthesia, Perioperative Medicine, Pain Medicine and/or Critical Care Medic ine" illustrates the growing awareness o f the needs i n this area. Nevertheless, i n the "disease funding table" o f the N I H for the fiscal years 2000—2002, neither pain nor anesthesia are listed as a research initiative/program o f interest, in contrast to such areas as chronic fatigue syndrome, diagnostic radiology, or topical microbicides ( N I H 2001). The most effective analgesic agents today continue to be opioids, non-steroidal anti-inflammatory drugs (NSAIDs) , and local anesthetics. A l l o f those have been i n use by ancient societies for as long as 5000 years i n the form o f extracts from opium poppy (Papaver somniferum), wi l low bark (Salix spp.), and coca leaves (Erythroxylon cocci), respectively (for reviews o f the history o f analgesia, see Brandt et al. 1997; Hami l ton and Baskett 1999, 2000). The efficacy o f newer groups o f agents, particularly i n the treatment o f chronic pain, is often modest at best, to the disappointment o f both patients and health care providers (Ashburn and Staats 1999). While detailed knowledge now exists on the mechanisms that underlie analgesia due to peripheral nerve blockade by local S. S C H W A R Z 3 anesthetics (reviewed i n Butterworth and Sttichartz 1990), how and where precisely drugs such as opioids and N S A I D s act to produce acute pain relief following systemic application is, despite significant progress (reviewed in Pasternak 1993; M c C o r m a c k 1994; Cashman 1996; Porreca etal. 1997; Ingram 2000), far from being fully understood. Similarly, the specific sites and mechanisms o f action i n the brain for drugs to alleviate chronic pain remain largely unknown. Hence, there is a vital need to shed more light on the cellular and molecular actions o f existing agents on the one hand, and to identify novel therapeutic strategies that are effective, specific, and well tolerated on the other hand. In order to successfully face these challenges and to be able to ensure the quality o f life o f our patients, the logical consequence is an integrated research approach that bridges laboratory and clinical science. The present thesis has been prepared wi th the motivation to pursue this path. W i t h the specific focus on the pharmacology & therapeutics o f the analgesic properties o f local anesthetics, this dissertation explores specific questions about both cellular pharmacological action and clinical therapeutic efficacy o f this group o f agents. In approaching the research questions, an effort was made to address diverse aspects within the wide spectrum o f this topic. A t one end o f this spectrum, the first section o f the thesis focuses on laboratory studies on the possible mechanisms for the central analgesic actions o f a well-established local anesthetic agent, i.e., lidocaine. A t the other end, the second section concentrates on clinical investigation to study the analgesic efficacy o f a newly introduced agent, ropivacaine, when administered peripherally for nerve plexus blockade i n knee surgery. Together, the results provide new knowledge about the diverse properties o f local anesthetics and illustrate the needs for S. S C H W A R Z 4 and benefits o f conducting research i n this area. It is hoped that this work may serve as a small step toward the final goal: to provide the best possible care for our patients today and i n the future. ) S. S C H W A R Z 5 SECTION I: LABORATORY STUDIES Effects of lidocaine on membrane properties and excitability of neurons in the ventral posterior lateral thalamic nucleus of the rat in vitro Results from this section o f the thesis have appeared i n the following publications: Schwarz S K W , Pu i l E : Analgesic and sedative concentrations o f lignocaine shunt tonic and burst firing i n thalamocortical neurones. Br] Pharmacol 1998, 124: 1633-1642. Schwarz S K W , Pu i l E : Lidocaine produces a shunt i n thalamocortical neurons, unaffected by G A B A A receptor blockade. Neurosci Lett 1999, 269: 25-28. Schwarz S K W , Pu i l E : Lidocaine unmasks high threshold C a 2 + spikes i n thalamocortical neurons. Soc Neurosci Abstr 1999, 25: 723. Reinker S, Schwarz S K W , Pu i l E : Effects o f procainamide on membrane properties o f thalamocortical neurons. Proc West Pharmacol Soc2001, 44: 89-92. S. S C H W A R Z 6 1.1 Introduction 1.1.1 Overall aim and specific objective This section o f the thesis focuses on laboratory studies on central actions o f the local anesthetic, lidocaine. The overall aim o f these studies was to identify the mechanisms by which lidocaine produces central analgesia and alterations in consciousness, including sedation and anesthesia. The specific objective here was to define the concentration-dependent effects o f lidocaine on the membrane properties and excitability o f neurons i n a part o f the brain that is crucial for such effects — the thalamus. 1.1.2 Background Lidocaine is the most frequently employed local anesthetic in clinical medicine and represents the prototype agent o f this class o f drugs (Figure 1). Its well-known peripheral actions to block the propagation o f action potentials along nerve fibres are widely exploited for surgical regional anesthesia. When present in the systemic circulation as a result o f local absorption or intravascular injection, however, local anesthetics exhibit effects that imply additional central action (Koppanyi 1962; Garfield and Gugino 1987; Biella and Sotgiu 1993). Such effects reflect central nervous system (CNS) toxicity as well as valuable therapeutic uses. The most frequently observed symptoms o f lidocaine's C N S toxicity are sedation, drowsiness, and alterations in sensorium (Covino 1987; Wallace et al. 1997b). These are associated with low, "subconvulsive" plasma concentrations, typically S. S C H W A R Z 7 between 1 and 5 ug /ml . The same range o f low concentrations produce the therapeutic effects o f lidocaine (see below and de Jong 1994 for review). Aromatic head Amide linkage Amine tail Figure 1 Structural formula o f lidocaine It has been well known for decades that local anesthetics have central analgesic properties (Peterson 1955). Administered systemically at low doses, lidocaine produces analgesia i n acute (inflammatory) pain syndromes such as acute postoperative pain. Lidocaine and other local anesthetics have been used in the maintenance o f general anesthesia, with analgesic effects comparable to those o f nitrous oxide (de Jong 1994). Moreover and perhaps more importantly, systemic lidocaine is effective in the treatment o f chronic pain syndromes such as neuropathic and central pain, which are notoriously difficult to treat and largely resistant to conventional analgesic therapy. There even exists evidence that the analgesia resulting from peripheral nerve blockade used for the management o f chronic pain is at least in part due to the central analgesic properties o f local anesthetics (Arner et al. 1990). In addition to lidocaine, its derivative, mexiletine, administered orally, has been used successfully i n the treatment o f chronic neuropathic S. S C H W A R Z 8 pain syndromes (Dejgard et al. 1988; Chabal et al. 1992). The magnitude o f pain relief from an intravenous (IV) lidocaine infusion provides a tool to predict the response to long-term mexiletine treatment (Galer et al. 1996). Cancer pain has been alleviated with lidocaine and also mexiletine (Sloan et al. 1999). Finally, lidocaine is one o f the few identified agents that are useful for the relief o f tinnitus, which is viewed by many as a form o f chronic pain (Simpson and Davies 1999; Huxtable 2000). Table 1 provides an overview wi th corresponding references o f pain syndromes reported to be responsive to systemic lidocaine. Fo r neuropathic pain, the effective lidocaine plasma concentrations range between 0.62 and 5.0 u g / m l i n humans (Mao and Chen 2000). In a recent study on non-neuropathic pain i n human volunteers, lidocaine selectively reduced secondary hyperalgesia i n a heat/capsaicin sensitization model (Dirks et al. 2000). Another group independently made similar observations and reported substantial reductions i n the development o f secondary hyperalgesia at lidocaine plasma concentrations between 1.5 and 3 p g / m l (Holthusen et al. 2000). A n i m a l studies confirm these observations; for example, i n rodent models o f both acute nociception and chronic pain, lidocaine administered systemically produces antinociception (Courteix et al. 1994; R igon and Takahashi 1996). S. S C H W A R Z 9 Table 1 Overview o f pain syndromes responsive to systemic lidocaine Acute pain Acute postoperative pain (Bartlett and Hutaserani 1961; Cassuto et al. 1985) And-GD2-ganglioside therapy-induced pain (Wallace et al. 1997a) Chronic pain Neuropathic pain (Boas et al. 1982; Marchettini et al. 1992; Ferrante et al. 1996) Diabetic neuropathy (Kastrup et al. 1987; Bach et al. 1990) Postherpetic neuralgia (Rowbotham et al. 1991) Central pain (Edmondson et al. 1993) Phantom limb pain (Lee and Donovan 1995) Complex regional pain syndrome (Wallace et al. 2000) Migraine (Burke 1989; Lewis 1992;* Maizels et al. 1996t) Chronic daily headache (Kaube et al. 1994; Hand and Stark 2000) Fibromyalgia (Sorensen et al. 1995) Cancer pain (Brose and Cousins 1991) Tinnitus* (Melding et al. 1978; Martin and Colman 1980; Israel et al. 1982; den Hartigh et al. 1993) Rectal administration (Xyloproct® suppositories, not marketed in North America; contain 60 mg lidocaine each) tlntranasal administration *Sce page 8 > In contrast to their peripheral effects, relatively little is known about the mechanisms and sites o f the central actions o f local anesthetics. Exis t ing work on this topic has focused on the spinal cord and left supraspinal actions largely unexplored (Mao and Chen 2000). However, several lines o f evidence implicate the thalamus as a crucial supraspinal site in the C N S where local anesthetics such as lidocaine act to produce their systemic analgesic and sedative effects. Descartes already emphasized the significance o f supraspinal centres in nociceptive signalling more than three centuries ago, albeit i n terms that since have been modified and updated (Figure 2). Chronic pain per se was first described as the "thalamic syndrome" in 1906 by Dejerine and Roussy i n their classic paper (1906). Recent studies emphasize the central role o f the thalamus (Figure 3) S. S C H W A R Z 10 and signal transmission by thalamocortical neurons in acute and chronic pain as well as in analgesia (Di Piero etal. 1991; Jeanmonod etal. 1993; Rosen etal. 1994; Peyron etal. 1998; Brunton and Charpak 1998; Apkarian etal. 2000; for reviews, see Albe-Fessard et al. 1985; Willis 1997; L e n 2 and Dougherty 1997). Figure 2 The path of sensation according to Descartes "Iffor example fire (A.) comes near the foot (B), the minute particles of this fire, which as you know move with great velocity, have the power to set in motion the spot on the skin of the foot which they touch, and by this means pulling upon the delicate thread CC, which is attached to the spot of the skin, they open up at the same instant the pore, d, e, against which the delicate thread ends, just as by pulling at one end of a rope one makes to strike at the same instant a bell which hangs at the other end." (1664) (Adapted from Melzack and Wal l 1965) S. S C H W A R Z 11 Thalamocortical neurons relay afferent sensory and nociceptive signals and encode stimulus intensity into firing frequency and spike patterns. They are endowed with complex membrane electrical properties that serve to fulfill their physiological functions (McCormick 1992). In particular, they exhibit two distinct, voltage-dependent action potential firing modes — tonic repetitive firing at depolarized and burst firing at hyperpolarized membrane potentials (Deschenes et al. 1984; Jahnsen and Llinas 1984a) (cf. 1.3.4, 1.3.8, and 1.4.1.). Thalamocortical neurons contribute to the generation o f conscious states and are critical for the production o f the electroencephalographic ( E E G ) rhythms associated with the different states o f awareness and sleep, e.g., the slow-wave activity and spindles o f drowsiness, sedation, and n o n - R E M sleep (Steriade et al. 1990).* L o c a l anesthetics infused at subconvulsive doses produce spindling and increased slow wave (delta- and theta-) activity in the E E G o f humans and other mammals, associated wi th sedation and reduced responsiveness to noxious stimuli (Acheson et al. 195.6; Er iksson and Persson 1966; Wagman et al. 1968; Sakabe et al. 197'A; Seo et al. 1982; Shibata et al. 1994). O n the other hand, abnormal thalamic burst firing occurs i n patients suffering from chronic pain syndromes (Lenz et al. 1987, 1989; Tsoukatos et al. 1997), i n w h o m lidocaine is particularly efficacious as a systemic analgesic (cf. Table 1). *A remarkable clinical illustration of the thalamus' central role in the' generation of spindles and drug-induced synchronized E E G activity is provided by the report of a 53-ycar-old male with fatal familial insomnia (Lugaresi et al. 1986). In this patient, barbiturates and benzodiazepines failed to produce E E G spindles. Post mortem, the autopsy showed degeneration of the anterior and dorsomedial thalamic nuclei. S. S C H W A R Z 12 The ventral posterior lateral nucleus (Nucleus ventralis posterolateralis thalami, V P L ; Le Gros Clark 1930) (Figure 4), located in the ventrobasal complex (VJ3)* of the dorsal thalamus, is the major relay station for somatosensory signals and has a significant role in the transmission of nociceptive signals (reviewed in Jones 1985; Steriade et al. 1997). Specifically, V P L has been associated with the sensory and discriminatory aspects of acute pain perception (Head and Holmes 1911; Melzack and Casey 1968; Albe-Fessard et al. 1985; Lenz et al. 1994a; Apkarian and Shi 1994). Consistent with the former, V P L neurons precisely encode the intensity, location, and time of peripheral stimuli and project specifically and somatotopically to the primary (SI) and secondary (SH) somatosensory cortex (Mountcastle et al. 1963; Poggio and Mountcastle 1963; Kenshalo et al. 1980; Casey and Morrow 1983). V P L neurons receive ascending inputs from the dorsal column pathways via the medial lemniscus, and the spinothalamic tract (Ma et al. 1987; Ferrington et al. 1988; Al-Chaer et al. 1996). Additional inputs include descending feedback projections from the cortex, inhibitory GABAergic fibres from the thalamic reticular nucleus, and modulatory afferents from the brainstem & basal forebrain (cholinergic), Locus coeruleus (noradrenergic), raphe nuclei (serotoninergic), and *VB (also known as ventral posterior nucleus, VP) is comprised of V P L and its medial neighbour, V P M (Jones 1985, pp. 47-48), which receives sensory input from the face. In humans, according to old terminology, V P L corresponds to the Nuclei ventro-caudales posterior externus et anterior externus (V.c.p.c. & V.c.a.e.; Hassler 1959; Jones 1997), and, combined with V P M , to the vcntrocaudal nucleus (Vc) (Hirai and Jones 1989). S. S C H W A R Z 13 hypothalamic tuberomammillary nucleus (histaminergic) (McCormick 1992; Steriade et al. 1997). In contrast to medial and thalamic nuclei, the receptive fields o f V P L neurons are relatively small and somatotopically organized (for review, see Chudler and Bonica 2001). The different body regions are represented within V P L mediolaterally by parasaggital lamellae (Lenz and Dougherty 1997). Consistent with this are the observations that neurons responding to noxious stimuli are found in every region o f the V B complex i n the rat (Guilbaud et al. 1980) and the V P L nucleus in the monkey (Morrow and Casey 1992), and that such neurons may constitute over 50% o f V P L ' s neuronal population (data also from monkey; Chung et al. 1986). The single-unit and network properties o f nociceptive neurons in the V P L nucleus have recently been characterized (Apkarian and Shi 1994; Apkar ian etal. 2000). Classic evidence for the role o f V P L in chronic pain comes from lesion studies, where destruction o f tissue i n the lateral thalamus has been successfully used for treatment o f intractable chronic pain syndromes (Talairach et al. 1949; Ramamurthi and Kalyanaraman 1966; Richardson 1967). Patients with chronic pain demonstrate pathological changes i n V P L , which in addition to the abnormal burst firing mentioned earlier includes alterations in the somatotopic organization (Lenz et al. 1994b). The pivotal involvement o f V P L neurons in chronic pain also is illustrated by in vivo studies on nociceptive transmission i n rat models o f polyarthritic chronic pain and mechanical hyperalgesia following peripheral nerve injury (Gautron and Gui lbaud 1982; M i k i et al. 2000). S. S C H W A R Z 14 A wide variety of analgesic agents from different pharmacological classes have been shown to depress the nociceptive activity of neurons in V B thalamus (Guilbaud et al. 1982; Braga etal. 1985; Carlsson et al. 1988). This section of the thesis considers the possibility that lidocaine could produce its central analgesic effects as well as alterations in sensorium and conscious state at low, subconvulsive concentrations by actions on V P L neurons. However, the cellular effects of local anesthetics on thalamocortical neurons are unknown. Hence, the objective of these studies was to define the concentration-dependent effects of lidocaine on the membrane properties and excitability of V P L neurons in vitro. Here, a novel action of lidocaine in the CNS is reported. Some preliminary results of these studies have been subject of a previous dissertation (Schwarz 1998). S. S C H W A R Z 15 Figure 3 Locat ion o f the thalamus i n the mammalian brain Shown are schematic illustrations of median-saggital sections through the cerebri of different mammals. The thalamus, also known as the "gateway to scnsorium", emerges as the central (hatched) structure in the diencephalon. Note that the images are scaled differently for the different species. (Modified from Sherman and Guillery 2001) Figure 4 Locat ion o f the V P L nucleus in the thalamus (A) Bright-field image of a coronal section of rat thalamus containing the ventrobasal complex with the V P L nucleus laterally and V P M medially (adapted & modified from Desbois and Villanueva 2001). (B) Schematic illustration of a corresponding section from squirrel monkey {Saimiri sciureus). Illustrated is the location of nine neurons (black dots) that responded differentially to noxious mechanical stimulation of the skin in an awake animal (figure & data from Casey and Morrow 1983) (CL, central lateral nucleus; C M , central medial nucleus; L D , lateral dorsal nucleus; LP , lateral posterior nucleus; M D , mediodorsal nucleus; PF, parafascicular nucleus; PO, oral pulvinar nucleus [ = anterior pulvinar nucleus (Burton and Jones 1976)]; V L , ventral lateral nucleus; VPI, ventral posterior inferior nucleus). S. S C H W A R Z 16 1.2 Materials and Methods 1.2.1 Ethics The results presented in this section o f the thesis were obtained from experiments utilizing rat brain slice preparations (see below). The experimental protocol was approved by the Committee on A n i m a l Care o f The University o f Brit ish Columbia, which issued an appropriate A n i m a l Care Certificate (Protocol Number A95-027). A l l animal experiments were conducted in accordance with the guidelines by the Canadian Counci l on A n i m a l Care on the ethical use o f animals ( C C A C 1993), and all efforts were made to minimize the suffering, and, wherever possible, the number o f animals used. 1.2.2 Preparation of brain slices Experiments were conducted with Sprague-Dawley rats aged between postnatal days 10 and 20 (P10-P20), with a majority o f the data obtained from animals aged P14 {of. 1.3.2). The animals were decapitated under deep halothane (Wyeth-Ayerst Canada, Inc.; Montreal , Q C , Canada) anesthesia. The cerebrum was rapidly removed and submerged for 1 m i n i n cold (1-4 °C) artificial cerebrospinal fluid (ACSF) . The A C S F , prepared freshly on each experimental day, contained (in m M ) : N a C l , 124; K C 1 , 4; KH2PO4, 1.25; C a C b , 2; M g C k , 2; NaHCC>3, 26; glucose, 10. The measured osmolarity was 310 m O s m (Advanced Digimatic Osmometer 3DII , Advanced Instruments, Inc., Needham Heights, M A , U.S .A. ) ; saturation with 95% O a / 5 % CO2 for > 1 h yielded a p H of 7.4 (measured at 20-26 °C with a p H meter model 05669-20, Cole-Parmer Instrument S. S C H W A R Z 17 Company, V e r n o n Hi l l s , IL , U.S .A. ) . The brain was dissected into two blocks, each containing the thalamic tissue o f one cerebral hemisphere. After fixation o f a tissue block on a Tef lon stage with cyanoacrylate adhesive (Accu-Flo™ super glue, Lepage, Boucherville, Quebec, Canada) and submersion i n cold A C S F , coronal slices o f 300-500 u m thickness and containing the V P L were prepared wi th a Vibrosl ice (Campden Instruments L td . , L o n d o n , England). In the course o f the experimental work for this thesis, the A C S F for above steps was replaced by a solution containing (in m M ) : sucrose, 125; K C 1 , 2.5; N a H 2 P 0 4 , 1.25; CaCfe, 2; M g C l 2 , 2; N a H C O s , 26; glucose, 25 (Forsythe 1994). Immediately after cutting, the slices were incubated i n normal A C S F , which, except for some experiments performed i n the initial phase o f the work for this thesis, was heated to 37 °C (monitored with a Tele-Thermometer, Y e l l o w Springs Instrument Co . , Y e l l o w Springs, O H , U.S .A) with a Standard Heatblock ( V W R Scientific Products, West Chester, P A , U.S .A. ) . Pr ior to recording, the slices were incubated for at least 1 h i n the A C S F and continuously aerated with 95% Oil5% CO2. 1.2.3 Electrophysiological recordings Whole-cel l patch-clamp recordings (Hamill et al. 1981) were conducted i n the bridge mode using an Axoc lamp 2 A or 2B amplifier (Axon Instruments, Inc., Foster City, C A , U .S .A . ) , allowing direct current (DC) injection to simulate afferent stimulation and test membrane properties. The recording electrodes were prepared from thin-walled borosilicate glass (World Precision Instruments, Inc., Sarasota, F L , U.S .A. ) using a PP-83 two-stage electrode puller (Narishige Scientific Instrument Lab. , Tokyo , Japan). They S. S C H W A R Z 18 were filled with a solution containing (in m M ) K-gluconate, 140; ethylene glycol-bis((3-aminoethyl ether)-N,N,N',N'-tetraacetic acid, 10; K C L 5; N a C l , 4; M g C b , 3; N-[2-hydroxyethyl]piperazine-N'-[2-ethanesulfonic acid] (free acid), 10; C a C b , 1; adenosine-5'-triphosphate (disodium salt), 3; guanosine-5'-triphosphate (sodium salt), 0.3. The solution was titrated to p H 7.3 with 10% gluconic acid and K O H . The approximate concentrations o f free C a 2 + and M g 2 + ions, calculated for p H 7.3 and 25 °C with the use o f W i n M A X C Software, version 1.60 (Chris Patton, Stanford University, Hopkins Marine Station, Pacific Grove, C A , U.S .A. ) , were 11.2 n M and 354 u M , respectively. The estimated electrode resistances were typically ~8 MQ. (range, 6—11 M O ) . Fo r recording, the slices were transferred into a submersion type chamber with a volume o f 1.2 or 1.5 ml , covered with polypropylene or nylon mesh for fixation, and continuously perfused with oxygenated A C S F (95% 02 / 5% CO2) at a flow rate o f 1.5-2.5 m l / m i n (controlled by a M A S T E R F L E X ® C/L™ pump, Cole-Parmer Instrument Company, V e r n o n Hil ls , IL , U.S .A. ) . The temperature o f the perfusing medium i n the chamber was 22-27 °C. The V P L nucleus was identified by aid o f a W i l d 5 M 5 A microscope (Wild, Heerbrugg, Switzerland) or a Zeiss Axioskop FS (Carl Zeiss, Gottingen, Germany) under transmitted light illumination. The atlas by Palkovits & Brownstein (1988) was used as a reference. Except for the initial phase o f experimentation, where whole-cell recording was carried out employing the "b l ind" technique (Blanton et al. 1989), the neurons for recording were visualized using differential interference contrast infrared (DIC-IR) videomicroscopy (Stuart et al. 1993; D o d t and Zieglgansberger 1994) (Figure 5). F o r this S. S C H W A R Z 19 technique, the slices were transferred into a glass-bottom recording chamber mounted on the headstage o f the Zeiss Axioskop FS. The microscope was equipped with a high numerical aperture (NA) water immersion objective (Zeiss Achroplan 4 0 x / 0.75 W ; working distance, 1.9 mm), D I C optics, and a 0.9 N A condenser. The slices were illuminated with a 12 V / 1 0 0 W halogen lamp powered by a 12 V / 1 0 0 W D C power supply (Carl Zeiss, I n c . / L u d l Electronic Products L td . , Hawthorne, N Y , U.S .A . ) . Infrared light was obtained by placing a Schott R G 9 glass filter (Schott Glas, Mainz , Germany; Xmax = 780 nm) in the light path. The images were recorded with a Hamamatsu C2400—07ER video camera system (Hamamatsu Photonics K . K . , Hamamatsu, Japan) and displayed on a video monitor (Black and White Moni to r SSM-175, Sony Corporation, Tokyo , Japan). The electrodes were mounted on the Axoclamp amplifier headstage and advanced wi th a Nano-Stepper Type B (Scientific Precision Instruments G m b H , Oppenheim, Germany) or a low-drift three-dimensional water hydraulic micromanipulator model M H W - 3 (Narishige Scientific Instrument Lab., Tokyo, Japan). After submersion o f the electrode tip i n the A C S F , the measured potential difference was set to 0 m V with a D C offset adjustment. Cel l membranes were ruptured when high resistance ("tight"/"gigaohm-") seals were achieved. After obtaining the whole-cell configuration, access resistance compensation was performed employing bridge balance techniques. Membrane potentials were corrected for a measured liquid junction potential o f 11 m V (cf. Hutcheon et al. 1996), and the offset potential measured on withdrawal o f the electrode from the neuron. Depending on the experimental protocol, injection o f S. S C H W A R Z 20 continuous positive or negative D C was used to manually clamp, hyper-, or depolarize the membrane potential (Vm) via the Axoclamp's " D C Current Command" . The data were filtered at 10 k H z and recorded on chart (Gould Brush 220 Recorder or Brush Recorder M a r k 280, Brush Instruments, Cleveland, Oh io , U .S .A . ) , and, after conversion wi th a Lab Master D M A 40 k H z analog/digital/analog converter (Scientific Solutions, Inc., Solon, O h i o , U.S .A. ) and p C L A M P software, version 5.5 (Axon Instruments, Inc., Foster City, C A , U.S .A. ) , on the hard disk o f an IBM-compatible personal computer. p C L A M P files were imported into C o r e l D R A W software (Corel Corporation, Ottawa, O N , Canada) for creation o f figures depicting experimental data; for clarity o f presentation, spikes were truncated in some figures. Fo r recording on video cassette ( S L - H F 750 super Beta hi-fi V ideo Cassette Recorder, Sony Corporation, Tokyo , Japan), the analog signal was digitally converted by a 44 k H z P C M - 1 Digi ta l V C R -Instrumentation Recorder Adaptor (Medical Systems Corp., Greenvale, N Y , . U . S . A . ) or a P C M - 5 0 1 E S Digi tal A u d i o Processor (Sony Corporation, Tokyo , Japan). The voltage traces were monitored on-line with a Nicolet 310 (Nicolet Instruments Corporation, Madison, W I , U.S .A. ) or K ikusu i C O S 5020™ (Kikusui Electronics Corp. , Yokohama, Japan) oscilloscope. S. S C H W A R Z 21 A B Figure 5 D I C - I R images o f a V P L neuron Shown is a neuron in the V P L nucleus before (A) and during (B) approach with the recording electrode for establishment of the whole-cell configuration of the patch-clamp technique. The figure depicts photographs taken from the image on a video monitor obtained by aid of infrared differential contrast videomicrocopy using an Achroplan 40X/0.75 W water immersion objective (sec text). 1.2.4 Drugs Lidocaine hydrochloride was purchased from Research Biochemicals International (Natick, M A , U.S .A. ) . The powder was dissolved i n fresh A C S F to prepare a concentrated stock solution o f 5 m M , stored in aliquots o f 2.2 m l at —22 °C. Procainamide hydrochloride, bupivacaine hydrochloride, and tetrodotoxin ( T T X ) were obtained from Sigma-Aldrich Canada L t d . (Mississauga, O N , Canada). Q X - 3 1 4 bromide S. S C H W A R Z 22 was obtained from Alomone Labs (Jerusalem, Israel). Stock solutions for procainamide, bupivacaine, and Q X - 3 1 4 were prepared i n a fashion similar to lidocaine. F r o m the citrate-buffered T T X , a 300 u M stock solution was prepared with distilled water and stored i n 500 p i aliquots at —22 °C. Bicuculline methobromide was obtained from Precision Biochemicals, Inc. (Vancouver, B . C . , Canada) and dissolved i n distilled water to produce a 50 m M stock solution, which was also stored at —22 °C. Pr ior to application o f the agents, required aliquots were defrosted and dissolved in A C S F to obtain the respective concentrations. D r u g applications i n the bath were performed by switching from the control perfusate (normal A C S F ) to A C S F containing a desired drug concentration. Unless specifically stated otherwise, reported results represent steady-state responses. Results are reported for one neuron per slice subject to drug application only. 1.2.5 Statistical analyses Statistical analyses were carried out with the use o f Student's t tests for comparisons o f two groups and testing for differences from a theoretical mean, and one-way analysis o f variance ( A N O V A ) for multisample analyses. A s post hoc tests, the Bonferroni test for pairwise multiple comparisons and the Dunnett test for comparisons to control were employed. Differences were considered significant at P < 0.05. A l l data are expressed as mean + S E M , n = sample size (number o f neurons), unless mentioned otherwise. Where feasible, concentration-response relationships were constructed using nonlinear S. S C H W A R Z 23 regression analyses by means o f fitting the data to a four-parameter logistic equation* using the least sum-of-squares method. The data were analyzed using Pr i sm version 2.01 and 3.02 software (GraphPad, San Diego, C A , U.S .A. ) , Microsoft E x c e l 97/2000 software (Microsoft Corporation, Redmond, W A , U.S .A. ) , and the Clampan and Clampfit components o f p C L A M P software version 6 and 8 (Axon Instruments, Inc., Foster City, C A , U .S .A . ) . Bottom + (Top - Bottom) j _l_ -jQ(logEC50-JC) Hi l l slope For normalized data, the value for "Bottom" was fixed at 1.0 (100%), reflecting the control (baseline) response. V = 7,———,,.„ , , where x = logarithm of concentration and y = response. J J _)_ j Q (log ECso-X) Hi l l slope > t> J f S. S C H W A R Z 24 1.3 Results 1.3.1 Resting membrane properties of VPL neurons The results reported here are from recordings of 107 neurons in the V P L nucleus. A l l neurons accepted for analysis had overshooting action potentials and stable resting membrane potentials (Vt) < —50 mV, lasting for up to 4 hours of recording. The neurons had a mean Vt of —68.0 ± 1 . 0 mV (n — 68), consistent with the results of previous investigations on rat V B neurons (cf. Ries and Puil 1999a,b). Input resistances (Ri), determined from the steady-state voltage displacements (AVm) of < —10 mV elicited by injection of hyperpolarizing current pulses of 500 ms duration, averaged 263 ± 21 M Q . The mean membrane time constant (xm; see Abbreviations for definition), estimated from single exponential fits to the AVm, was 34.6 ± 2.0 ms. Input capacitances were calculated according to C\ — x m / R and averaged 156 ± 8 pF. A l l data were normally distributed. Analyses of relative frequency distribution of these parameters were indicative of a uniform population of neurons (Figure 6, A—D), consistent with previous observations that the neuronal population in rodent dorsal thalamic nuclei is almost exclusively comprised of thalamocortical relay neurons and practically devoid of interneurons (Harris and Hendrickson 1987; Steriade et al. 1997). There was an extremely significant (P < 0.0001) positive correlation between Ri and %m (r2 = 0.50; Figure 6E), indicating behaviour of the data in accordance with x m — R C N o strong correlation was found between the calculated C\ (see above) and Vt (r2 = 0.06; Figure 6E). S. S C H W A R Z 25 100n 75 50' 25 r • r2 = 0.50 (P< 0.0001) 250 500 Ri (MO) 750 1000 -40--50-| -60-| -70 H -80 -90 0 • 0.06 100 200 300 Q (pF) 400 500 Figure 6 Resting membrane properties: frequency distributions and correlations (A)-(D) Relative frequency distribution of resting membrane potential {Vr [A]), input capacitance (Ci [B]), input resistance (Ri [C]), and membrane time constant (xm \D]). Bin width for VT, 2 m V ; G , 20 pF; Ri, 50 Mil; and xm , 5 ms. (E) A highly significant correlation was observed between Ri and x m (r2 = 0.50; P < 0.0001). (F) N o strong correlation was found between Ci and Vt (r2 = 0.06; P = 0.04). S. S C H W A R Z 26 1.3.2 Postnatal development of resting membrane properties A s mentioned in 1.2.2, the data presented i n this section o f the thesis largely was obtained from animals i n the age range o f P10-P20 , with a majority o f the animals aged P14. Whi le it was not a primary objective o f these studies to perform an in-depth investigation o f postnatal development o f the resting membrane properties o f V P L neurons, the available data offered the opportunity for a limited analysis within the above age range and comparison o f the results to the existing literature. Consistent with previously published findings on thalamocortical neurons i n V B (Perez Velazquez and Carlen 1996) and the medial geniculate body ( M G B ; Tennigkeit et al. 1998b), the input resistance o f the V P L neurons decreased i n the course o f postnatal development. This decrease reached a plateau, such that the difference in Ri between animals aged P14 and P I 5—20 was no longer statistically significant (Bonferroni's multiple comparison test following A N O V A , P > 0.05; Table 2). Input capacitance increased concomitantly, indicative o f an increase in neuronal membrane surface area associated with cell growth (Figure 7A). Similar to the observations by Tennigkeit et al, there were small decreases in membrane time constant with age that did not reach statistical significance (Figure 7B). There were no significant changes i n resting membrane potential with increasing postnatal age (Figure 7C). This observation i n V P L appears i n contrast to M G B but is likely explained by the fact that no animals < P10 were studied here: i n M G B , for example, Vt decreases with increasing age but reaches a plateau after - P 1 0 - P 1 2 (Tennigkeit etal. 1998b). S. S C H W A R Z 27 Q . O 500-400-300-200-100H • • 0 . 2 0 ; P < 0 . 0 0 0 1 B 10 100-12 —i— 14 — i — 1 6 Age (d) — i — 1 8 — i — 2 0 75-^ = 0 . 0 1 E 50-2 5 -: ! 5 » * — r . 1 • • • • — i — 16 — i — 1 8 — i — 20 10 12 14 Age (d) Age (d) 1 0 11 1 2 1 3 1 4 1 5 1 6 1 7 1 8 1 9 2 0 Figure 7 Postnatal development o f resting membrane properties S. S C H W A R Z 28 Table 2 Postnatal development o f resting membrane properties Ri (Mn) O (pF) Tm (ms) Yr (mV) n PI 0-13 389 ± 67 124 ± 1 2 41.6 ± 6 . 0 -68.7 ± 2 . 5 • 15 PH 253 ± 25 147 ± 1 1 33.7 ± 3 . 0 -66.2 ± 1.6 29 P15-20 193 ± 2 4 196 ± 1 9 32.2 ± 2.5 -69.3 ± 1 . 4 22 P value* 0.0028 0.0052 0.22 0.36 *One-way A N O V A 1.3.3 Current-voltage relationships Typically, the I-V relationships for the V P L neurons were approximately linear (i.e., ohmic) at membrane potentials positive to — 9 0 m V (cf. Figure 9). A t more hyperpolarized voltages, neurons exhibited some inward (depolarizing) rectification (cf. Jahnsen and Llinas 1984b; Hutcheon et al. 1996; Tennigkeit et al. 1996), consistent wi th activation o f the inwardly rectifying K + current, Ini (Constanti and Galvan 1983; Sutor and Habli tz 1993) and the hyperpolarization-activated mixed cationic current, Ih (McCormick and Pape 1990b; Pape 1996; Williams et al. 1997b). Similar to other whole-cell investigations o f rat thalamocortical neurons (Puil et al. 1994; Tennigkeit et al. 1996; Ries and Pu i l 1999a), neurons i n the present study did not routinely exhibit i n the hyperpolarizing responses the depolarizing membrane potential "sags" that are characteristic for Ih. Other investigators have observed sags in intracellular recordings o f thalamocortical neurons in the cat and guinea pig (McCormick and Pape 1990b; S. S C H W A R Z 29 Pirchio et al. 1997). Tennigkeit et al. (1996) demonstrated an unmasking o f sags i n rats by application o f B a 2 + , a selective blocker o f IIR (Travagli and Gil l is 1994). It is possible in the present study that the gluconate in the electrode (intracellular) solution (cf. 1.2.3) inhibited Jh (Velumian et al. 1997). However, some neurons did exhibit sags. Whereas the precise reasons for these discrepancies remain unclear, other factors likely play a role; these include differences in recording technique, the species investigated, and the developmental state o f the animals. 1.3.4 Active membrane properties: tonic and burst firing A l l neurons exhibited the voltage-dependent firing patterns characteristic for thalamocortical relay neurons (cf. Deschenes et al. 1984; Jahnsen and Llinas 1984a). Injection o f suprathreshold depolarizing current pulses into neurons near rest elicited repetitive tonic firing (blocked by 600 n M T T X ; cf. Figure 16), whereas on hyperpolarizing Vm (typically to values between —80 and —90 m V ) by D C injection, depolarization elicited burst firing on top o f a low threshold spike (LTS), a slow envelope o f depolarization (see Figure 13B in chapter 1.3.8). Rebound L T S bursts also could be evoked from a Vm near rest by hyperpolarizing current pulses (Figure 13A), known to de-inactivate the underlying T-type C a 2 + current, IT* (Jahnsen and Llinas 1984a). A s previously reported by others, the bursts consisted o f ~1—7 high frequency action *Also known as low threshold- or low voltage-activated (LVA) C a 2 + current S. S C H W A R Z 30 potentials (here, ~> 80 Hz) that were blocked by T T X (not illustrated), indicating that they were mainly carried by N a + . The L T S s themselves were not blocked by T T X but disappeared when the superfusing A C S F contained zero C a 2 + , indicative o f their generation by IT (cf. 1.3.9). The finding by M c C o r m i c k and Pape (1988) that L T S s are absent i n interneurons recorded from cat lateral geniculate nucleus ( L G N ) provided additional indication that the neurons recorded here (cf. 1.3.1, page 24) were thalamocortical relay neurons. 1.3.5 Effects of lidocaine on resting membrane properties Appl ica t ion o f lidocaine decreased the Ri o f the V P L neurons i n a reversible manner (Figure 8A). The time for an application to produce a steady-state response was typically ~5 m i n (range, 2.5—7 min). This effect exhibited a distinct, non-classical concentration dependence. Whereas the maximal decrease i n Ri occurred at a low concentration (10 u M ; decrease in Ri up to 28% o f control), the magnitude o f this effect decreased with higher concentrations, and no reduction in Ri occurred at 300 pM—1 m M (Figure 8B). These multiphasic relationships implied the presence o f multiple actions o f lidocaine that affect Ri i n an overlapping fashion. The data did not fit conventional concentration-response models (e.g., a four-parameter logistic equation, cf. 1.2.5) for construction o f a meaningful classic sigmoid curve. Concomitant with the effect on Ri , lidocaine administration caused reductions in x m wi th a similar concentration dependence (Figure 8C). The maximum reduction in x m at 10 u M lidocaine was 34% o f control. The respective input capacitances, calculated according to C\ = x m / R (cf. 1.3.1) were not S. S C H W A R Z 31 significantly different from the control values over the range from 0.6-600 u M (data not shown), indicating a primary effect o f lidocaine on membrane conductance (of. Figure 8B and Figure 8C). The reversal potentials for the increased conductances (1/Ri), determined from current-voltage (I-V) curves (see 1.3.6), were typically between Vr and ~ - 5 0 m V . A summary o f the numerical data on the concentration-dependent effects o f lidocaine on Ri and X m is given in Table 3. Lidocaine at concentrations < 10 u M did not produce consistent changes in membrane potential except for 2 out o f 11 neurons where application o f 10 u M was associated with depolarizations (7 and 9 m V , respectively). A t 30 or 100 u M , lidocaine depolarized 6 out o f 12 neurons (Figure 8D). The time required to reach a maximal depolarization was typically 2 to 3 min. The depolarizing response observed at 30 u M ranged between 5 and 12 m V i n 2 out o f 6 neurons, and, at 100 u M , between 6 and 9 m V i n 4 out o f 6 neurons. Repolarization to resting values was seen usually after 4—5 m i n on terminating the application. Higher concentrations (300 uM—1 m M ) again had no consistent effects on Vt. N o hyperpolarizations were seen as a result o f lidocaine application. In neurons where application o f T T X (600 nM) completely abolished action potentials, lidocaine produced small decreases i n Ri that were reversible and associated with variable changes in Vt. Fo r example, 10 u M lidocaine reduced Ri to a level o f 82.0 ± 5.8% o f control values (P = 0.04, n = 5). S. S C H W A R Z 32 Figure 8 Effects o f lidocaine on input resistance, membrane time constant, and resting membrane potential (A) A low concentration of lidocaine (10 u M ; 8 min application) significantly decreased input resistance (Rj), evident as a decreased amplitude of the steady-state voltage response to hyperpolarizing current injection (pulse duration, 500 ms). The magnitude of the decrease in Rj in the neuron was 51% (400 MCI to 196 M Q ) . The effects were completely reversed after 10 min washout. (B) & (C) Concentration-response curves for the effects of lidocaine on Ri and membrane time constant (xm; for each concentration, n = 4—11; cf. Table 3). Note the multiphasic character of the relationships (see text). The maximum reduction in Rj occurred with 10 u M lidocaine. (D) Lidocaine application (100 uM) depolarized a V P L neuron from —69 m V to —64 mV. The downward deflections in the voltage trace represent responses to hyperpolarizing current pulses (-40 pA, 500 ms); the positive deflections represent rebound L T S bursts (cf. Figure 13). Near the peak response, Vm was manually clamped at the control (Vr) level through D C injection for assessment of a change in input resistance. Close to full recovery was reached after 4 min of washout. S. S C H W A R Z 33 Table 3 Effects o f lidocaine on input resistance and membrane time constant [Lidocaine] R/ P value P value n (% of control) (% of control) 0.6 81.1 ± 1 3 . 3 0.21 81.9 ± 1 6 . 4 0.32 6 1 82.6 + 17.0 0.35 81.0 ± 1 7 . 4 0.32 6 ' 3 80.6 ± 1 6 . 9 0.30 81.8 ± 2 3 . 7 0.48 6 10 70.5 ± 7 . 3 0.002 75.3 ± 8 . 3 0.01 11 30 76.6 ± 1 3 . 4 0.14 74.5 ± 6 . 5 0.01 6 100 72.4 ± 7 . 8 0.02 81.1 ± 6 . 9 0.04 6 300 86.1 ± 17.0 0.47 88.7 ± 9.2 0.31 4 600 9,8.2 ± 12.1 0.89 111.7 ± 1 1 . 2 0.34 7 1000 100.4 ± 14.8 0.98 88.7 ± 1 1 . 4 0.39 4 1.3.6 Effects of lidocaine on current-voltage relationships Figure 9 shows the effects o f lidocaine on the I-V curves and corresponding voltage traces o f a representative neuron clamped at —61 m V with D C injection. A low concentration o f lidocaine (10 pM) , which caused the greatest reduction i n Ri, markedly reduced the slope resistance over a wide voltage range (—125 m V to threshold or — 5 0 m V ) . The values for Vm where control I- V curves intersected wi th those obtained under lidocaine application (i.e., the reversal potential for the conductance changes; Vc not clamped) typically ranged between Vt and — 5 0 m V (cf. page 31). F u l l recovery from these effects usually was reached —10 min after washout with normal A C S F . Lidocaine had no consistent effect on the inward rectification o f the neurons (tf. 1.3.1). S. S C H W A R Z 34 F i g u r e 9 Effects o f lidocaine on current-voltage relationships (A) Application of 10 u M lidocaine (cf. Figure 8) for 8 min produced a 72% decrease in Ri, evident as reduction in amplitude of steady-state voltage responses to D C injection (pulse duration, 500 ms). Consistent with the decrease in Rj, lidocaine revcrsibly shunted rebound low threshold spike bursts (asterisk; see 1.3.8 & Figure 13). Recovery was observed after 10 min washout. (B) I-V relationships of the same neuron. Steady-state membrane potential differences (AVm) were measured at the end of 500 ms current pulses (A/ m ), injected in 10 p A steps (filled and open circle in A). Lidocaine produced a marked reduction in slope resistance over a wide voltage range (from — 8 5 m V to spike threshold). S. S C H W A R Z 35 1.3.7 Effects of lidocaine on tonic repetitive firing Lidocaine, applied at low concentrations associated with a decrease i n Ri, shunted tonic repetitive firing o f action potentials elicited by depolarizing D C pulses, producing a marked reduction in responsiveness to stimulation. Fir ing frequency (e.g., expressed as number o f spikes/500 ms pulse) and frequency accommodation decreased i n a reversible manner (Figure 10A). There were no concomitant elevations o f the threshold potential for firing or alterations i n spike configuration. The maximal rate o f rise (dV/dtmsa, determined as "greatest left slope" with Clampfit software [Axon Instruments, Inc., Foster City, C A , U.S.A.]) o f spikes remained unchanged. Fo r example, the sixth spike i n a train, very sensitive to high lidocaine concentrations i n the range known to block N a + conductance (see below and Figure 12), had a d 7 / d / m a x o f 49.0 ± 6.2 m V / m s under control conditions whereas during application o f 10 u M , it was 50.1 ± 4.1 m V / m s (mean ± S D ; P = 0.85; n — 9). For the fourth spike i n a train (the first to show a maximal magnitude o f effect for 600 p.M lidocaine; cf. Figure 12), the control value was 51.8 ± 8.7 m V / m s vs. 45.9 ± 11.8 at 10 u M (P = 0.20; 1 - (3 = 0.8 to detect a difference o f 14.68 m V / m s at a = 0.05; n — 9). In current-frequency relationships, lidocaine caused a parallel shift o f the curve to the right, indicating a relatively unimpaired distribution o f activatable N a + channels i n the area o f the spike generator (Figure 10B). Lidocaine application also diminished a slow component o f the spike-afterhyperpolarizations (AHPs) , which i n isolation would be expected to increase firing frequency (Figure 10C) (cf. Foeht ing et al. 1989). Consistent with a shunt, lidocaine markedly increased current thresholds, i.e., the amplitudes o f current pulses required for spike generation (Figure 11). S. S C H W A R Z 36 Control 10 uM Lidocaine Recovery Control Recovery 10 uM Lidocaine 0 20 40 60 80 100 120 A / M (pA) 10 uM Lidocaine 20 mV f A H P * s A H P Control 100 ms Control Spike No. 1 2 3 4 5 6 10 | J M Lidocaine 1 2 3 4 5 6 -76 mVJ 20 mVl 100pApi0° ms Control l l 10 | J M Lidocaine Figure 10 Effects o f a low concentration o f lidocaine on tonic repetitive firing (A) Lidocaine, administered at a low concentration that produced the maximum decrease in Rj (10 u M ; of. Figure 8), reversibly reduced the spike frequency and inhibited spike accommodation of neurons firing in the tonic pattern. Tonic firing in the neuron shown was evoked from a V, of—76 m V by D C injection (100 p A / 5 0 0 ms pulse; lower traces). The suppression of repetitive firing was not associated with an increase in the threshold potential for firing (arrows) or a decrease in the maximum rate of rise of the spikes (dV/dtm*x; sec below), consistent with an effect secondary to a shunt rather than N a + channel blockade. (B) The relationship between the amplitude of injected current (AJm) and the firing frequency (spikes/500 ms) was approximately linear. The suppression of repetitive firing by lidocaine was characterized by a shift of the current-frequency curve to the right, without reducing its slope. (C) Lidocaine reduced a slow component of the spikc-afterhyperpolarizations (sAHP; f A H P denotes fast aftcrhyperpolarization). The two superimposed traces arc matched for spike frequency and were obtained with 60 p A (control) and 110 p A (lidocaine) D C pulses. (D) Lidocaine increased the current required to elicit a train of 6 spikes (see also Figure 11) but produced no alterations in spike configuration, e.g., dV/dlm^. (E) Quantitative illustration of the effect of 10 u M lidocaine on dK/dAnax of spikes in a train of 6 (n = 11 neurons). Lidocaine had no effect on consecutive spikes ( A N O V A , P = 0.60; control, P = 0.99; Bonferroni's multiple comparison test, P > 0.05). Comparisons to control yielded no significant differences for any given spike number (paired / test, P > 0.05; see text for details). S. S C H W A R Z 37 Control 10 uM Lidocaine Recovery x=4 -76 mV-20 m V l 40 pA 100 ms _ F Figure 11 Effects o f a low concentration o f lidocaine on injected current In association with the decreased Rj, lidocaine shunted current injected to stimulate neurons, which manifested as a marked elevation in the threshold D C amplitude required for firing in the tonic pattern. In the neuron shown (cf. Figure 10), 10 u M lidocaine reversibly increased the current pulse amplitude required for spike generation to a level of 400% of control (control, 20 pA; 10 u M lidocaine, 80 pA). These findings illustrated the predominance o f a shunt as the primary effect at these low concentrations. In contrast, higher concentrations produced alterations i n spike configuration conventionally indicative o f a local anesthetic effect on N a + permeability. F o r example, concentrations o f lidocaine ranging from 300 u M to 1 m M decreased the dl/Vd/max o f action potentials and produced a pronounced or complete suppression o f tonic repetitive firing (Figure 12). In a concentration-dependent fashion, lidocaine application elevated the threshold potential for firing. These concentrations did not significantly shunt the current required for spike generation (cf. Figure 8 and Table 3). Consistent wi th previous observations o f others (f. Butterworth et al. 1993), recovery was significantly delayed on terminating an application at a high concentration, usually requiring washout times that exceeded 45 min. S. S C H W A R Z 38 Control Lidocaine 300 uM 600 uM 1 mM -56 mV -66 mV 20 mV 400 pA B 200 ms 30 20 E o o LO CD 10 CL CO Control Lidocaine „ „ „ . . 300 uM 6 0 0 ^ M 1 mM 100 200 300 400 500 600 A / m (pA) Control Spike No. 1 2 3 4 5 6 -66 mV • 20 mVl 600 uM Lidocaine 123 4 5 6 Control H3 600 pM Lidocaine 400 pA 200 ms 3 4 Spike No. Figure 12 Effects o f high concentrations o f lidocaine on tonic repetitive firing (A) High lidocaine concentrations produced concentration-dependent elevations in the voltage threshold for tonic firing (arrows) and alterations in spike configuration without decreasing Ri. Superfusion with 300 uM, 600 uM, or 1 mM lidocaine led to a pronounced reduction in firing produced by DC injection. At 600 uM and higher, repetitive firing was completely suppressed but could be elicited by current pulses of a markedly increased amplitude (sec C). Note the refractoriness to lidocaine of the first spike in a train of action potentials. (B) Effects of lidocaine on the relationship between the amplitude of injected current (A7m) and firing frequency (spikes/500 ms; neuron from A). Lidocaine reduced the slope of the current-frequency curve in a concentration-dependent fashion, consistent with a successive increase in the ratio of blocked versus unblocked Na + channels at the axon hillock. A saturation effect became evident at 600 uM. (C) A high lidocaine concentration (600 uM) increased the current required to elicit a train of 6 spikes (in the neuron shown, to a level of 450% of control) and successively reduced the dV/d/,mx of the spikes in the train (cf. Figure 10). (D) Effect of 600 uM lidocaine on d F / d W of 6 consecutive spikes in a train (n = 6 neurons). Lidocaine successively reduced the dF7d/ m a x (ANOVA, P = 0.01; control, P = 0.61). The asterisks denote comparisons to control for a given spike number (paired t test; *, P < 0.05; **, P < 0.01). A maximal effect was reached at the fourth spike (Bonferroni's multiple comparison test, P < 0.05). S. S C H W A R Z 39 1.3.8 Effects of lidocaine on burst firing and low threshold spikes L o w concentrations o f lidocaine associated with a decrease i n Ri exerted a depressant influence on the burst firing mode o f V P L neurons. This was observed on depolarization from prepulse-conditioned (Figure 13A) or tonically DC-maintained (Figure 13B) hyperpolarized potentials. Lidocaine (10 uM) suppressed the rebound bursts elicited by hyperpolarizing current pulses from potentials near rest (Figure 13C & Figure 9A). W h e n hyperpolarization was maintained by D C injection at potentials from which depolarizing pulses elicited L T S burst firing, a subsequent application o f lidocaine (10 uM) resulted in a marked elevation i n the amount o f current required to evoke a spike burst. This action was reversible and similar to its effect on the tonic firing mode (Figure 13D). The effects were associated with a marked decrease i n Ri , implicating a shunting o f input current as a major mechanism for the depression o f the burst activity. 1.3.9 Effects of lidocaine on high threshold spikes A s discussed in 1.3.7 and shown i n Figure 12, lidocaine, applied at high concentrations that clinically are CNS- tox ic (300 [ i M - 1 m M ) , reduced or completely suppressed tonic repetitive firing i n a concentration-dependent fashion. This effect, showing a saturation at 600 [0.M, was associated with an elevation o f firing thresholds and slowing o f the dV/d/max o f spikes, conventionally indicative o f a local anesthetic effect on N a + channels. In order to better characterize these actions, the differential effects o f 600 | i M lidocaine on tonic firing frequency, voltage threshold, and dK/d/max were examined in relation to the time o f administration (n = 2). Lidocaine slowed dV/dtmax and reduced firing S. S C H W A R Z 40 Tonic firing 20 mV 200 pA B -64 m V - ^ loo ms J -1 Burst firing LTS 1_ Tonic firing u u u Burst firing 20 mV 200 pA -74 mV-100 ms LTS, -88 mV Control 10 uM Lidocaine Recovery -66 mV 20 mV 50 pA 100 ms Control 10 uM Lidocaine Recovery LTS. LTS^ LTS -88 mV 20 mV 50 pA 100 ms Figure 13 L o w threshold spikes and the effects o f lidocaine on burst firing (A) & (B) Voltage dependent firing patterns evoked by different procedures in two V P L neurons. Injection with depolarizing current pulses from near Vt evoked repetitive tonic firing (Al , Bl) . At the same Vm, hyperpolarizing current pulses of sufficient amplitude to de-inactivate a Trtype Ca 2 + current resulted in rebound burst firing after termination of the pulse, generated by a low threshold spike (LTS). Typically, bursts of 1-7 action potentials fired on top of the LTSs (A2, arrow). When Vm was hypcrpolarized by DC injection, LTS burst firing also was evoked by depolarizing current (B2, arrow). (C) In a reversible manner, lidocaine (10 uM) shunted rebound LTS bursts evoked from potentials near rest (cf. Figure 9A). (D) In neurons that were hyperpolarizcd to elicit LTS bursts by depolarizing current pulses, lidocaine application produced a reversible elevation in the current threshold for firing. The current pulse magnitude required for burst firing was increased to a level of 233% of control (control, 30 pA; 10 uM lidocaine, 70 pA). Note the decreased Ri in C and D (cf. Figure 11). S. S C H W A R Z 41 frequency i n a time-dependent fashion to the point o f complete suppression o f firing (Figure 14A). This was accompanied by a time-dependent increase o f the voltage threshold for firing, consistent with a gradual increase o f effective lidocaine concentration until steady state is reached at the site o f action near the N a + channel. The relative effect o f lidocaine on firing frequency was significantly more pronounced than on d T / / d / m a x (Figure 14B). This implied that lidocaine at these high concentrations exerted actions on targets i n addition to N a + channels (for which slowing o f &V/dtm3* is a sensitive parameter; of. Hubbard et al. 1969) that would contribute to a suppression o f repetitive firing, well documented in the literature (cf. Discussion & Table 4 [page 77]). W h e n current pulses o f markedly increased amplitude were injected into neurons i n which lidocaine had completely suppressed tonic firing, a population o f spikes was triggered that had spike configurations and properties distinct from the "control" discharges i n the tonic mode (Figure 14A, caption labelled ">5:00 min"). These high-threshold spikes (HTSs) were broader with a lower amplitude and significantly slowed d l Z / d /max (Figure 14C). These observations raised the possibility that the tonic repetitive spikes suppressed by lidocaine and the H T S s represent distinct spike populations generated by separate mechanisms. In order to address this hypothesis, T T X (600 nM) was applied to neurons i n which H T S s were elicited during lidocaine application as described above. In all neurons tested this way, the spikes unmasked by lidocaine remained during the application o f T T X (Figure 15; n — 4). This was associated with a further small but significant elevation i n voltage threshold (P < 0.05; mean elevation, 3.1 m V [95% C I , 0.3-5.8 mV]). S. S C H W A R Z 42 Control -46 mV-20 mV 100 pAMOC 00 ms 600 uM Lidocaine 2:00 min 2:10 min 2:20 min i _r 2:30 min 3:00 min 4:00 min >5:00 min 1 J~ B a •a -o =s 2 >• c " o g> 100-, 75 50 2 £ . 25 c CM Firing frequency dV/dt, 12 S as CD h8 h4 0:00 Du 2:00 3:00 4:00 5:00 ration of lidocaine application (min) o > £ F <D i_ . c cn c o ir 600 uM Lidocaine 10 mV 20 ms Figure 14 Time-dependent effects o f a high concentration o f lidocaine on repetitive spikes (A) Tonic firing was elicited in a neuron from Vt (-46 mV) with D C injection (100 pA/500 ms pulse). Lidocaine (600 uM) inhibited repetitive spikes in a time-dependent manner (see B) and completely suppressed firing at 4:00 min of application. Note the relative lack of effect on spike frequency accommodation. A current pulse of a markedly increased amplitude (220 pA) injected after 5:00 min of lidocaine application triggered a train of high threshold spikes (HTSs [arrows]) of distinctly altered configuration/slowed dV/dtm-ax (cf. Figure 12; sec C for details & asterisks). (B) Shown are the differential effects of lidocaine on tonic firing frequency, voltage threshold, and dV/dtmrn. in relation to the duration of application. Lidocaine decreased firing frequency and dK/d/max (leftj-axis) in a time-dependent manner while increasing the voltage threshold for firing (right j-axis; control, -38 mV). Firing frequency was significantly more sensitive to lidocaine than dl>7d/max- The maximum difference between both parameters at a given time was 46% of control. (C) Magnified images of two supcrimposablc spikes from A (* & **). Compared to the control spike, the HTS had a distinctly altered spike configuration with a characteristic high voltage threshold (sec arrows). The findings raised the possibility that the repetitive spikes of the tonic firing mode suppressed by lidocaine and the HTSs represent separate spike populations with distinct underlying mechanisms (sec text). (Note: time zero [0:00] indicates the time of switching from the control perfusate [normal ACSF] to ACSF containing lidocaine. The time to overcome the dead space of the perfusion system was approx. 1:00 min.) S. S C H W A R Z 43 Control 6 0 0 | J M Lidocaine HTSs -37 mV 6 0 0 | J M Lidocaine + 6 0 0 nM TTX -48 mV 2 0 mV 1 0 0 pA 1 0 0 ms F i g u r e 15 Lidocaine unmasks high threshold spikes not blocked by T T X Lidocaine, applied at a high concentration (600 uM) that clinically is toxic to the C N S , unmasked high threshold spikes (HTSs) that were elicited by injection of a D C command with a large amplitude (140 pA; control, 40 pA; if. Figure 12 & Figure 14). Application of T T X (600 nM) did not block the HTSs. In the presence of lidocaine, T T X produced an elevation of the H T S voltage threshold of ~4 m V in the neuron shown, compared to lidocaine alone. N o other actions of T T X on H T S configuration were observed. A l l observed effects were reversible and full recovery of the neuron was observed after 45 min of washout (superfusion with normal A C S F ; not illustrated). A l l effects were reversible and the "control" (TTX-sensitive) action potentials o f the tonic firing mode exhibited recovery after washout. W h e n lidocaine was applied to neurons where T T X was present and had completely abolished tonic firing, H T S s could likewise be triggered by D C injection o f a large amplitude (n — 1 out o f 9 neurons; Figure 16). One o f these 7 neurons was excluded from further analysis due to loss o f recording prior to recovery. In the remaining neurons, lidocaine application i n the presence o f T T X effectively unmasked H T S s , i.e., current amplitudes that elicited no firing under T T X alone reversibly triggered H T S s when lidocaine was added (Figure 16A). This was associated with no consistent changes i n Ri (P > 0.05) as determined from voltage responses to hyperpolarizing D C injection (see page 24). Consistent wi th this finding, there were no significant alterations i n slope resistance or S. S C H W A R Z 44 overall I-V relationship i n the hyperpolarized range. However, lidocaine increased amplitudes o f voltage responses to depolarizing current to values up to 190% o f control i n 4 out o f 6 neurons and produced corresponding increases i n slope resistance i n the depolarized range o f the I- V relationships (Figure 16B). Concomitant with these effects, lidocaine decreased H T S voltage thresholds up to 23 m V (« = 4) and current thresholds (cf. 1.3.7, page 35) up to 50% o f control (n - 4) (Figure 16C). N o associated consistent changes i n Vt were observed. A s in the experiments with T T X application i n the presence o f lidocaine, recovery usually was observed after approx. 20—45 min o f washout. The data from this series o f experiments with T T X strongly supported the hypothesis that the H T S s unmasked by lidocaine are indeed distinct from die N a + dependent action potentials o f the tonic firing mode and generated by a different ionic mechanism. The most likely candidate for consideration other than N a + to carry such depolarizing spike potentials as the present H T S s was C a 2 + . Others have previously demonstrated that thalamocortical neurons express, in addition to the L V A C a 2 + currents (cf. 1.1.2, 1.3.4, 1.3.8), high voltage-activated ( H V A ) C a 2 + currents that generate H T S s similar to those observed here (Jahnsen and Llinas 1984b; Hernandez-Cruz and Pape 1989; Coulter et al. 1989; Pfrieger et al. 1992). In contrast to the former, which produce L T S s and are critical to the burst firing from hyperpolarized membrane potentials (cf. 1.1.2, 1.3.4), the latter have been implicated i n the regulation o f firing in the tonic mode at depolarized potentials (Kammermeier and Jones 1997; Z h o u et al. 1997; Budde et al. 2000). Overall , the modulation o f these C a 2 + currents contributes to the S. S C H W A R Z 45 Control 600nMTTX 600 nM TTX + 600 nM TTX Recovery 600 uM lidocaine (lidocaine -73 mV 20 mV J 500 pA 100 ms Control 600 nM TTX -26 mV. 600 nM TTX + 600 uM lidocaine HTSs , i -35 mV. Figure 16 Effects o f lidocaine on high threshold spikes in the presence o f T T X (A) In the neuron illustrated, repetitive tonic firing was elicited by D C injection and completely blocked by T T X (600 nM). A subsequent co-application of lidocaine (600 u.M) reversibly unmasked a high-threshold spike (HTS; cf. Figure 14 & Figure 15). Concomitantly, lidocaine produced an increase in the steady-state voltage responses to depolarizing current (see below). Close to full recovery was observed in the neuron after > 30 min washout. (B) I- V relationships of the same neuron. Whereas lidocaine had little effect on the I- V curve in the hypcrpolarizcd range, it increased slope resistance in the depolarized range by up to -25%. (C) Shown are traces from an experiment with a different neuron. Lidocaine, applied in the presence of T T X , decreased both voltage and current thresholds for the HTSs . D C injection of an amplitude that initiated no firing under T T X alone (300 pA) triggered three H T S s when lidocaine was added. Recovery was observed after 27 min of washout (not shown). S. S C H W A R Z 46 discharge patterns and synchronized oscillations o f the thalamocortical network that occur physiologically and i n association with various pathological states (Steriade and Llinas 1988; Jeanmonod et al. 1996; Shah et al. 2001; cf. Discussion, 1.4.2.1). T o test directly whether the H T S s unmasked by lidocaine in this study were mediated by C a 2 + , two sets o f experiments were conducted using Ca 2 + -depr ived A C S F and the C a 2 + channel blocker, C d 2 + , respectively. C d 2 + is a particularly useful pharmacological tool for this purpose since it allows one to differentiate H V A and L V A C a 2 + currents: i n thalamocortical neurons, 50 p M almost completely blocks H T S s while leaving L T S s relatively unaffected (Hernandez-Cruz and Pape 1989; Pfrieger et al. 1992; Tennigkeit et al. 1998a). Figure 17 summarizes the results o f these experiments. W h e n neurons i n which H T S s were triggered as described above (in the presence o f T T X and lidocaine) were perfused with extracellular solution deprived o f C a 2 + , the spikes disappeared completely (n = 4). This effect was fully reversible, wi th the H T S s reappearing instantly when the superfusing medium was changed back to the control solution. Appl ica t ion o f C d 2 + (50 pM) in the presence o f T T X and lidocaine completely blocked the H T S s (n — 4) i n a reversible manner. Neurons exhibited recovery from all effects after washout with normal A C S F . In / -^ re la t ionsh ips , C d 2 + did not block the increase i n slope resistance i n the depolarized range produced by lidocaine i n neurons superfused wi th T T X (cf. Figure 16B; see Discussion [1.4.2.1], page 85). O n the contrary, C d 2 + further increased the slope'resistance in the depolarized range in 3 out o f 4 neurons by up to ~ 2 5 % , consistent with a H V A C a 2 + conductance blockade. C d 2 + also reversibly increased slope resistance i n the hyperpolarized range by up to ~ 3 8 % (Figure 17C), S. S C H W A R Z 47 6 0 0 nM T T X + 6 0 0 | J M lidocaine -61 mV OCa 2 Recovery HTSs 1_ - J 1 _ I 200 ms 40 mV 400 pA B 6 0 0 nM T T X + 6 0 0 | J M lidocaine HTSs -61 mV 5 0 |JM Cd 2 Recovery HTSs 1_ J 200 ms 40 mV 400 pA -200 200 • 6 0 0 nM T T X • 6 0 0 nM T T X + 6 0 0 |jM lidocaine - 6 0 0 nM T T X + 6 0 0 | J M lidocaine + 5 0 ^M Cd 2 + Figure 17 Effects o f C a 2 + free extracellular solution and C d 2 + on the high threshold spikes unmasked by lidocaine (A) The H T S s that were unmasked by lidocaine and remained during the co-application of T T X revcrsibly disappeared when the extracellular solution (ACSF) contained zero C a 2 + . (B) Superfusion of neurons with 50 u M C d 2 + (a blocker of H V A C a 2 + currents; see text) completely blocked the H T S s in a reversible manner. These features implied that the spikes were carried by C a 2 + and produced by a H V A C a 2 + current, revcrsibly unmasked by lidocaine. Note that "Recovery" denotes superfusion with A C S F containing 600 n M T T X and 600 \iM lidocaine; full recovery of regular tonic and burst firing was observed after 20 min of washout with normal A C S F (not illustrated). (C) Effects of C d 2 + on the increase in slope resistance in the depolarizing range produced by lidocaine in neurons superfused with T T X . C d 2 + did not block lidocaine's effect but further increased slope resistance over a wide voltage range. In the neuron shown (cf. Figure 16B; VT = —62 mV), the increase in apparent resistance occurred in a range between —95 m V and spike threshold, amounting to maxima of ~25% in the depolarized range and ~38% in the hyperpolarized range. Recovery was observed after washout (not illustrated for enhanced clarity). S. S C H W A R Z 48 likely due to its blockade o f h (Barish and Baud 1984; Nathan 1986; Ozawa et al. 1989) (cf. page 28). In conclusion, the data obtained from these sets o f experiments confirmed the hypothesis that the H T S s unmasked by lidocaine were high threshold C a 2 + spikes, produced by a H V A C a 2 + current (Coulter et al. 1989; Hernandez-Cruz and Pape 1989; Kammermeier and Jones 1997; Tennigkeit etal. 1998a). 1.3.10 Effects of GABA.A receptor blockade by bicuculline on lidocaine actions A recent study demonstrated that local anesthetics enhance the increase i n conductance induced by G A B A in stretch receptor neurons o f crayfish (Nordmark and Rydqvist 1997). The anticonvulsants, carbamazepine and phenytoin, similarly potentiate G A B A -induced currents in cultured rat cortical neurons and in human embryonic kidney cells expressing the OC1P2Y2 subtype o f the G A B A A receptor (Granger et al. 1995). In thalamocortical neurons, application o f G A B A mediates a rapid increase i n conductance which is carried by C l (Crunelli et al. 1988; Thomson 1988). In the present study, the reversal potential for the increase i n conductance induced by low lidocaine concentrations was near the equilibrium potential for C F (calculated EQ\ at 25 °C = —53 m V ) (cf. page 31). A n increase i n C l conductance due to lidocaine application would be consistent with the observed decreases i n Rj and depolarizations. In such a case, the increased conductance produced by lidocaine would likely represent a major mechanism for inhibit ion o f firing because the driving potential (Vm — Ed) for a G A B A - i n d u c e d change in Vm would be rather small. Fo r example, despite depolarizing S. S C H W A R Z 49 cortical neurons, G A B A still produces inhibit ion o f firing due to a shunt mechanism (El-Beheiry and Pu i l 1990). In thalamic reticularis neurons, activation o f G A B A A receptors shunts burst firing (Ulrich and Huguenard 1997). Based on these findings, a series o f experiments was conducted aimed to address the possibility that the lidocaine-induced shunt observed here i n V P L neurons is mediated by G A B A A receptors. T o test this hypothesis, the effects on the lidocaine-induced changes i n membrane electrical properties and excitabilities o f the G A B A A receptor antagonist, bicuculline,* were investigated. Results on bicuculline were obtained from n — 6 neurons. One o f the neurons was excluded from the analysis due to lack o f recovery. When bicuculline (50 u,M; El-Beheiry and Pu i l 1990; v o n Kros igk et al. 1993) was applied to neurons following reduction o f D C - e v o k e d tonic firing by 10 U.M lidocaine (cf. 1.3.7, Figure 10), firing rates were increased and/or restored to control values (Figure 18) (Gao et al. 1997), consistent with previous reports on its action on G A B A A receptors i n thalamocortical neurons (Lee et al. 1994; M c C o r m i c k et al. 1995; Gao et al. 1997). Bicuculline application per se d id not elicit firing i n neurons maintained at rest, i n agreement with the absence o f significant effects on spontaneous activity i n thalamocortical neurons o f anesthetized cats and rats observed by others (Duggan and McLennan 1971; Lee et al. 1994). However, bicuculline *Bicuculline is a naturally occurring convulsant alkaloid whose sources include Dicentra cucullaria (Dutchman's breeches), Adlumiafungosa (climbing fumitory/mountain fringe/Alleghany vine), and various Cordalis spp. S. S C H W A R Z 50 -76 mV 20 mV| 50 pA J Control mMMAUMMM 10 | J M Lidocaine 10 uM Lidocaine + 50 uM bicuculline 100 ms + 50 |jM bicuculline A/m (pA) Figure 18 Effects o f bicuculline on the decrease in tonic firing due to lidocaine (A) Following reduction by lidocaine, bicuculline (50 u M ; 8 min application) restored tonic firing evoked by depolarizing D C injection to the control rate. (B) Current-frequency relationships of the same neuron. The lidocainc-induced shunt was evident as a shift of the current-frequency curve to the right (tf. Figure 10B). Bicuculline application increased tonic firing, and, at D C amplitudes > 90 pA, restored the firing rate to control values (cf. Figure 10A). A J m denotes injected current pulse amplitude. S. S C H W A R Z 51 did not influence lidocaine's actions to decrease Ri (Bonferroni's multiple comparison test following repeated measures A N O V A : lidocaine vs. lidocaine + bicuculline, P > 0.05; control vs. lidocaine, P < 0.05; control vs. bicuculline + lidocaine, P < 0.01; A N O V A overall, P < 0.0001; n — 5). Figure 19A illustrates these findings for a representative neuron. In I-V relationships, bicuculline did not antagonize the decrease i n slope resistance produced by lidocaine over a wide voltage range (Figure 19B). There also were no significant changes i n %m (Bonferroni's multiple comparison test: lidocaine vs. lidocaine + bicuculline, P > 0.05; n — 5). Likewise, bicuculline did not antagonize the shunt-associated reductions o f spike-afterhyperpolarizations (AHPs) produced by lidocaine (Figure 19C; cf. Figure 10). 1.3.11 Effects of other local anesthetic agents on membrane properties In the final part o f this section o f the thesis, a series o f experiments with a variety o f other agents was conducted to further delineate the observed effects o f low lidocaine concentrations on resting membrane properties, i.e., the lidocaine-induced shunt. In the first set o f these studies, lidocaine's effects were compared with those o f its quaternary analogue, QX-314. These experiments were aimed to test whether the lidocaine-induced decrease in Ri could be due to interaction with an intracellular, as opposed to an extracellular, target. This hypothesis was based on the findings that (1) lidocaine still produced decreases in Ri i n the presence o f T T X (1.3.5), implying a postsynaptic action; (2) the decreases i n Ri were not associated with membrane hyperpolarizations (1.3.5), S. S C H W A R Z 52 -70 mV Control 10 uM Lidocaine 10 uM Lidocaine + 50 uM bicuculline 20 m V 100 p A | 100 ms Figure 19 Effects o f bicuculline on the decrease i n input resistance due to lidocaine (A) In the neuron shown, lidocaine administration (6.5 min) produced a 20% reduction in input resistance (Rj) and shunted rebound low threshold spike bursts (cf. Figure 9 & Figure 13). Bicuculline had no effect on the decreased Ri (> 9 min of application). The shunting of low threshold spike bursts also remained unaffected during bicuculline application. (B) Corresponding current-voltage-relationships. Membrane potential differences ( A K m ) were measured at the end o f 500 ms current pulses (A7m) injected in 20 p A steps (sec arrows in A) . Bicuculline did not antagonize the reduction in slope resistance produced by lidocaine over the voltage range from —90 m V to threshold. (C) Lidocaine (dotted trace) reduced Ri and spike-afterhyperpolarizations (AHPs) while the neuron fired in the tonic firing pattern (if. Figure 10). When bicuculline was added to the perfusing media, no changes or slight further reductions in A H P s were observed (dashed trace). The labels on the right indicate the amplitudes o f the current pulses injected to obtain the respective traces matched for spike rate. S. S C H W A R Z 53 pointing to mechanisms distinct from an increase in K + channel conductance (cf. Ries and Pu i l 1999b); and (3) blockade o f the main extracellular target mediating inhibitory neurotransmission, the G A B A A receptor, had no effect on the decreases in Ri (1.3.10). In the second set o f these experiments, an effort was made to shed light on the question whether lidocaine's effects represent a novel action that is specific to this agent, or rather an effect common to local anesthetic and related drugs that has previously been unknown. Fo r this, a set o f comparative studies was carried out wi th procainamide, an aminoalkyl amide analog o f the aminoester local anesthetic, procaine, and the aminoamide local anesthetic, bupivacaine, neither o f which are known from the literature to have clinically useful systemic analgesic properties. The drugs were studied over a wide concentration range and concentration-response relationships for their effects on R i were constructed as feasible. 1.3.11.1 Q X - 3 1 4 Q X - 3 1 4 (lidocaine N-ethyl bromide; N-[2,6-dhnethylphenylcarbamoylmethyl]triethyl-ammonium bromide; M W , 343.3) is a lidocaine derivative whose sole structural difference to the mother compound is in the presence o f an additional N-ethyl group (Figure 20). This renders the amino group quaternary, i.e., permanently positively charged. A s a result, the agent cannot readily pass biological membranes. W h e n administered to central neurons intracellularly, Q X - 3 1 4 blocks both fast, Na + -dependent action potentials and voltage-dependent, noninactivating N a + conductances (Connors and Prince 1982; Mul le et al. 1985; cf Pu i l and Carlen 1984). Here, a series o f experiments S. S C H W A R Z 54 Aromatic head Amide linkage Quarternary amine tail Figure 20 Structural formula o f Q X - 3 1 4 wi th Q X - 3 1 4 applied extracellularly was conducted to compare its effects on membrane properties to those o f lidocaine and determine whether the lidocaine-induced shunt may be result o f interaction with an extracellular (as opposed to intracellular) target. The effects o f Q X - 3 1 4 were studied in n — 6 neurons. O f these, two were excluded from quantitative analyses due to loss o f recording prior to recovery. Q X - 3 1 4 , applied over a wide concentration range (1 uM—1 m M ) , produced no decreases i n Ri i n the neurons (P > 0.05) (Figure 21 A ) . Likewise, no significant reductions in T m were observed. In contrast, higher concentrations o f Q X - 3 1 4 increased Ri i n some neurons (at 1 m M , to a maximum level o f 169% o f control; mean, 127 + 18%), although this effect was short o f reaching statistical significance ( A N O V A with Dunnett 's multiple comparison test, P > 0.05). Nonlinear regression analysis with the use o f a conventional concentration-response model (cf. 1.2.5) yielded a curve with a goodness o f fit o f R 2 = 0.9994 and an E C 5 0 o f 237 u,M for the resistance increase (Figure 21B). Consistent S. S C H W A R Z 55 Control -61 mV-5 mV 20 pA 100 ms 1_ 1 uM QX-314 10 yM QX-314 100 uM QX-314 B 150' C 125-| O O o v ° 100 Of 75-1 E C W = 237 pM 10 100 1000 10000 [QX-314] (uM) Control 10 pM QX-314 100 pM QX-314 20 40 60 80 100 120 A/ m (pA) D Control 1 uM QX-314 -61 mV-f l O O ms 20 mVl 100pAp°° 10 uM QX-314 100 uM QX-314 JL JL. II w w w JL Figure 21 Effects o f Q X - 3 1 4 on membrane properties (A) Unlike lidocaine, extracellular application (~10 min per concentration) of its quaternary analogue, QX-314, did not reduce input resistance (R;) over a wide concentration range, here illustrated by the lack of decreases in amplitude o f the steady-state voltage responses to hyperpolarizing D C injection (cf. Figure 8A). Consistent with this, QX-314 did not exert significant effects on membrane time constants (in the neuron shown, T M = 25.2 ms). (B) Concentration-response relationship for the effect of QX-314 on Ri. QX-314 exerted no significant effects in the concentration range from 1 u M to 1 m M ( A N O V A , P - 0.54; for each concentration, n = 4). A t 1 m M , QX-314 produced increases in Ri that did not reach statistical significance (Dunnett's multiple comparison test, P > 0.05). However, analysis of the goodness of fit for a classic concentration-response curve (cf. 1.2.5) yielded an R 2 of 0.9994. The corresponding EC50 was 237 u M . (C) Consistent with the lack of effect on Rj, QX-314 did not shunt tonic firing like lidocaine, here illustrated in a representative current-frequency plot (see below) by the absence of a significant shift of the curve to the right (cf. Figure 10B). QX-314 did not increase current thresholds for firing (cf. Figure 11), identifiable here as the minimum current pulse amplitude (AJ m , abscissa) required for eliciting spikes (ordinate). (D) Tonic and rebound burst firing responses of the neuron in C to de- and hyperpolarizing D C injection (pulse duration, 500 ms). Increasing concentrations of QX-314 did not greatly affect spike frequency or shunt tonic and L T S burst (arrow in control) firing comparable to lidocaine (cf. Figure 10A & Figure 13C). S. S C H W A R Z 56 wi th the lack o f effect on Ri , Q X - 3 1 4 did not shunt tonic or burst firing i n the neurons (Figure 21C & D ) . O n the contrary, i n some neurons, Q X - 3 1 4 application was associated wi th small increases i n firing rate (not illustrated). N o consistent significant changes i n Vt were observed as a result o f Q X - 3 1 4 application. 1.3.11.2 Procainamide Procainamide (4-amino-N-[2-(diethylamino)ethyl]benzamide; M W , 271.8; p K a , 9.2; Figure 22) is an aminoalkyl amide that, like lidocaine, has cardiac antiarrhythmic properties. It belongs to class 1A according to the classification o f antiarrhythmic drugs by Vaughan Will iams (Bigger and Hoffman 1990). The therapeutic plasma concentration for the antiarrhythmic effects ranges between 4 and 8—10 u g / m l (approx. 14.7—36.8 uM) i n humans (Zipes 1992; Roden 2001). In contrast to lidocaine, which in the same plasma concentration range that is associated with its antiarrhythmic actions (1.5-5 u M ; Roden 2001) exerts its systemic analgesic effects (tf. 1.1), no published reports have documented systemic analgesic properties for procainamide.* O n the contrary, procainamide (73.5 nM) microinjections into the Nucleus raphe magnus block the antinociceptive effects o f nicotine (12.35 nM) injected i n the pedunculopontine tegmental nucleus (which sends ascending projections to the thalamus; tf. Hallanger et al. 1987) i n rats in vivo, as measured *An isolated exception is the anecdotal account of the use of procainamide in myotonic syndromes associated with "hyperexcitability of muscle fibres" (Mertens and Lutzenkirchen 1970) S. S C H W A R Z 57 Aromatic head Amide linkage Aminoalkyl tail F i g u r e 22 Structural formula o f procainamide by responses to tail-flick and hot-plate tests (Iwamoto 1991). Systemic toxicity due to procainamide typically occurs at plasma concentrations > 10 u g / m l (Roden 2001); its most common manifestations include gastrointestinal upset, arterial hypotension, cardiac conduction disturbances, fever, and a systemic lupus erythematosus-like syndrome (Zavisca et al. 1991; Zipes 1992). In ~0 .2% o f patients, procainamide induces bone marrow suppression and agranulocytosis, a potentially life-threatening reaction. Compared to lidocaine, symptoms o f C N S toxicity are less common; they include giddiness, psychosis, and depression. Such central actions are not unexpected because procainamide, despite its hydrophilicity, crosses the blood-brain barrier as demonstrated i n rats (Herken and Rietbrock 1969). W i t h regard to the C N S toxicity, it is noteworthy that the procainamide-induced lupus-like syndrome, unlike primary systemic lupus erythematosus, spares the brain. Experiments with procainamide were conducted i n n — 8 neurons, o f which n — 2 were excluded from statistical analyses due to lack o f recovery. Procainamide produced no significant decreases in Ri over a concentration range from 1 u M to 1 m M . In S. S C H W A R Z 58 Figure 23 Effects o f procainamide on membrane properties (A) In a concentration-dependent manner, procainamide application (1 u M - 1 mM) produced increases and no decreases in Rj, here illustrated by the amplitudes of the steady-state voltage responses to hyperpolarizing D C injection (cf. Figure 8A) in a representative neuron held at V, (-73 mV). Associated with the increases in Rj were concentration-dependent prolongations of T M . Recovery was observed after 15 min washout with A C S F (see next Figure). (B) Concentration-response relationships for the effects of procainamide on R and T M (for each concentration, n — 4—5). Fitting of the respective curves yielded EC50 values for the increases of 48 u M for Rj and 337 u.M for t m (see text for details). (D) Current-voltage relationships of the neuron in A . Procainamide produced concentration-dependent increases in slope resistance and reduced the inward rectification in die hyperpolarized voltage range, here at membrane potentials ~—15 m V negative to VT. S. S C H W A R Z 59 contrast, procainamide produced concentration-dependent increases in Ri up to 169% o f control (Figure 23A). The average increase in Ri was greatest at 1 m M (131.8 + 9.4% o f control; P — 0.04; n — 4). The fit o f a corresponding concentration-response curve (R 2 = 0.9997) yielded an ECso for the increase i n Ri o f 48 u M (Figure 23B). Concomitantly, procainamide prolonged T m to maximal values o f 217% o f control. Consistent wi th the results on Ri , the 3 .vc r9 .gc incrc3.se in Tm also was greatest at 1 m M (157.2 + 24.7% o f control; Dunnett's multiple comparison test, P < 0.05; n = 4); the EC50 was 337 u M (concentration-response curve, R 2 = 0.9985; Figure 23C). The difference in the EC50 for Ri and T m (P = 0.04; potency ratio, 7.02) likely was due to procainamide affecting active (i.e., voltage-dependent), i n addition to passive (resting, voltage-independent) membrane properties. Procainamide increased apparent resistance in excess o f what would be predicted from T m = R C (cf. 1.3.1, page 24). Three lines o f evidence provided confirmation o f this hypothesis. Firstly, the increase i n apparent resistance by 1 m M procainamide was associated with reversible depolarizations o f Vt by up to 7 m V in 3 out o f 4 neurons (not illustrated), implying blockade o f an outward (hyperpolarizing) current that contributes to Vt, i.e., a leak (voltage-independent) K + current. Secondly, analysis o f I-V relationships revealed a voltage-dependent component to procainamide's concentration-dependent action to increase slope resistance, evident as a reduction i n the inward rectification i n the hyperpolarized range (cf. 1.3.3), typically at potentials > 10 m V negative to Vm (Figure 23D). Thirdly, the best goodness o f fit o f exponential functions to, the voltage responses to hyperpolarizing D C injection (cf. 1.3.1) i n the range where procainamide reduced inward rectification was S. S C H W A R Z 60 achieved with first order exponential functions under procainamide, as opposed to second order exponential functions under control conditions. Fo r example, for the voltage responses o f the neuron shown i n Figure 23A, the S D (5) o f the fitted curve i n the control was 0.221 m V for a first order exponential function and 0.095 for a second order exponential function. In contrast, the best fit i n the presence o f 1 m M procainamide was obtained with a first order exponential function (8 = 0.116 m V ; second order exponential function, 8 = 0.119 m V ) . This implied that the voltage responses under control conditions were a result o f a combination o f passive and active membrane properties whereas i n the presence o f procainamide, the voltage responses were primarily a result o f passive membrane properties alone. In combination, these data indicated that procainamide reduced both inward rectification and resting membrane conductance, giving rise to an increase i n apparent resistance, and, on the whole, a more ohmic (linear) I - K relationship. Analysis o f procainamide's effects on tonic and burst firing showed that the agent suppressed the fast, Na + -dependent action potentials o f both firing modes, consistent with its N a + channel blocking actions well-known from the studies on the antiarrhythmic properties (for review, see Zipes 1992 and Roden 2001). In the tonic mode o f firing, this was evident as a concentration-dependent reduction i n firing rate, with 1 m M producing the greatest effect (Figure 24). In particular, procainamide at the higher concentrations preferentially increased the intervals between the initial spikes i n a train, implying a blockade o f spike accommodation. In the burst mode, procainamide similarly decreased the number o f fast spikes on top o f L T S s (of. 1.3.4 and Figure 13). However, unlike S. S C H W A R Z 61 lidocaine, procainamide, over a concentration range from 1 u.M—1 m M , did not shunt the L T S s . A Control Procainamide Recovery 10 uM 100 uM 1 mM B A/m (PA) Figure 24 Effects o f procainamide on tonic and burst firing (A) Shown are tonic and rebound burst firing responses to de- and hyperpolarizing D C injection (pulse duration, 500 ms) of a neuron manually clamped at Vt (-73 mV). Application of procainamide (1 u M - 1 m M ; - 8 - 1 2 min per concentration) reduced tonic firing frequency in a concentration-dependent fashion (accompanied by an increase in R;; see previous Figure). Whereas 1-100 u M affected spike rate comparatively little (response to 1 u M not illustrated), 1 m M produced a noticeable (38%) suppression of firing. This was associated with a reduction in spike accommodation, evident as a preferential increase in the intervals between the initial spikes in a train. Unlike lidocaine, procainamide did not shunt rebound L T S s (arrow in control; cf. Figure 9A & Figure 13C). However, procainamide reduced the frequency of the fast action potential bursts on top of the L T S s (asterisk). Full recovery of tonic firing and partial recovery of Ei were observed after 15 min washout. (B) Current-frequency relationships of the neuron in A . In a concentration-dependent fashion, procainamide shifted the current-frequency curve to the right and decreased its slope (curves for 1 & 100 u M not illustrated for enhanced clarity). Full recovery from the reduction in firing was observed after washout (sec above). S. S C H W A R Z 62 Al though neurons generally exhibited recovery from procainamide's effects, this was much more readily observed for active membrane properties (e.g., tonic firing; of. Figure 24B) than for passive ones (e.g., Ri). Partial recovery from increases i n Ri was observed i n all neurons included in the analysis, typically after washout times o f — 15 min . 1.3.11.3 Bupivacaine Bupivacaine (l-butyl-N-[2,6-dimemylphenyl]-2-piperidinecarboxamide; M W , 324.9; Figure 25) is, like lidocaine, an aminoamide local anesthetic (of. Figure 1). The agent was synthesized i n 1957 by Ekenstam as part o f a series o f N-substituted pipecolyl xylidine derivatives that also included mepivacaine (l-methyl-N-[2,6-dimethylphenyl]-2-piperidinecarboxamide) and ropivacaine (l-propyl-N-[2,6-dimethylphenyl]-2-piperidine-carboxamide; see II.1.4 later in this thesis) (Ekenstam et al. 1957). Compared to lidocaine, bupivacaine has a higher l ipid solubility, a higher p K a value (8.1 vs. 7.7), and is subject to more extensive plasma protein binding (~96% vs. ~65%). Clinically, bupivacaine is more potent, has a slower onset o f action, and produces longer lasting blockade than lidocaine. Bupivacaine is also considerably more toxic than lidocaine, particularly to the myocardium, and is not clinically used for systemic administration (Covino 1987). Bupivacaine plasma concentrations following application for regional anesthesia vary considerably depending on route, dose, concentration, and author. Whereas maximum concentrations between 0.2 and 4.95 u,g/ml have been reported wi th peak times between 5 m i n and over 1 h, typical values for most clinical procedures are below 2 u g / m l (see S. S C H W A R Z 63 Aromatic head Amide linkage Amine tail CH 3 F i g u r e 25 Structural formula o f bupivacaine Tucker and Mather 1988 for review). When present i n the systemic circulation, bupivacaine does not consistently produce the sedation and drowsiness or the E E G slowing and spindling that occur with lidocaine prior to the onset o f C N S excitation and generalized seizure activity. Fo r example, there are no distinctive preconvulsive E E G alterations associated with bupivacaine in monkeys (Covino 1987). Reported bupivacaine b lood concentrations associated with convulsive behaviour are 3.05 p g / m l i n cats, 4.5 p g / m l in monkeys, and between 5.4 and 74.0 p g / m l i n humans (Munson et al. 1975; Scott 1975; de Jong et al. 1980; Agarwal et al. 1992; McCloskey et al. 1992). On ly limited data are available on p lasma/CSF concentration ratios for bupivacaine. In one investigation on patients undergoing ophthalmic surgery who received 20 mg bupivacaine for retrobulbar or facial blockade, the CSF/p la sma ratio was in the range o f 0.56—1.33 (Le N o r m a n d et al. 1989). Fo r conversion from p g / m l into p M , 1 p g / m l corresponds to 3.08 p M ; conversely, 1 u M corresponds to 0.325 p g / m l (see M W above). Here, i n order to widely cover concentrations relevant to the low subconvulsive as well as toxic range, bupivacaine was studied between 0.1 and 100 u M . S. S C H W A R Z 64 The main conclusion from the experiments with bupivacaine was that valid interpretation o f the. results was not reliably possible due to inability to achieve recovery (before cell loss) i n the present setting o f brain slice patch-clamp experimentation, likely a result o f the high l ipid solubility o f this agent. Others have previously made similar observations i n in vitro studies (Rossner and Freese 1997). Stable recordings that allowed acquisition o f sequential concentration-response data on the effects o f bupivacaine on Ri wi th varying degrees o f recovery were obtained from n — 3 neurons. The results are presented qualitatively and no dedicated statistical analysis was performed. N o reversible decreases in Ri due to bupivacaine application were observed i n the concentration range from 0.1-100 u M . Analogous to Q X - 3 1 4 and procainamide, a high concentration o f bupivacaine (100 uM) produced increases in Ri that exhibited partial recovery. Figure 26 shows the voltage responses o f a neuron that illustrate these findings. The fast action potentials o f tonic and burst firing also were blocked by 100 u M bupivacaine (not illustrated); partial recovery was observed only after long washout times (> 30 min , similar to the report o f L i u et al. 2001) with normal A C S F . / S. S C H W A R Z 65 Control 0.1 uM Bupivacaine 1 uM Bupivacaine 5mV 40 pA Figure 26 Effects o f bupivacaine on input resistance Shown are voltage responses to hyperpolarizing D C injection (pulse duration, 500 ms; AVm < 10 mV) of a neuron held at V, (—79 mV). Application of bupivacaine (0.1—10 p.M), unlike lidocaine (Figure 8), produced no noteworthy decreases in Ri (in % of control: 0.1 u M , 106; 1 u M , 102; 10 yM, 97; ~12 min of application each). Application of 100 u M bupivacaine increased Rj to a level of 247% of control. This was associated with a prolongation of T M to 234% of control (19.8 ms; 100 u M bupivacaine, 46.3 ms). Partial recovery from these effects was observed after 33 min o f washout with normal A C S F (in % of control: Ri, 149; T M , 110). Suprathreshold de- and hyperpolarizing D C injection at this time elicited fast action potentials of tonic and burst firing (not illustrated; if. Figure 13). S. S C H W A R Z 66 1.4 D i s c u s s i o n 1.4.1 Shunting inhibition: a novel effect of low lidocaine concentrations in the CNS The results presented i n this section o f the thesis have demonstrated that lidocaine suppressed tonic and burst firing in thalamocortical relay neurons o f the V P L nucleus, known to participate in the transfer o f somatosensory information, nociceptive signals, and i n general, the generation o f conscious states. Here, novel actions o f lidocaine have been identified in vitro that may account for the central analgesic and sedative effects in vivo. These actions occurred at concentrations much lower than those known to block impulse conduction along peripheral nerve fibres (Boas et al. 1982; Tanelian and Brose 1991; Wallace et al. 1997b). The most intriguing finding was an effect that could not be attributed to N a + channel blockade: lidocaine markedly reduced neuronal responsiveness to electrical stimulation by decreasing input resistance, shunting the current required for spike generation in the tonic and burst firing mode. This effect predominated at lower concentrations (maximal amplitude at 10 uM) and not at high concentrations (> 300 pM) . Other related agents that are structurally similar but clinically not endowed with the systemic analgesic and sedative properties that lidocaine possesses (procainamide, and, under the conditions o f this study, bupivacaine) did not exhibit a similar effect. S. S C H W A R Z 67 1.4.1.1 Clinical relevance o f concentrations Fo r terms o f clinical relevance o f the lidocaine concentrations, 10 u M lidocaine H C I converts to approximately 2.7 [xg/ml (i.e., a 0.00027% solution).* Accord ing to the classic study by Usubiaga et al. (1967), cerebrospinal fluid (CSF) concentrations o f lidocaine in humans following intravenous injection correlate to arterial concentrations wi th a factor between 0.73 and 0.83. In rabbits receiving a continuous lidocaine infusion intravenously, the correlation factor (with a 10 min latency between arterial and C S F sampling) ranges between ~0.47 and 0.64 (Momota et al. 2000).t Somewhat in contrast to these observations are the results o f one single recent study which found correlation factors between —0.06 and 0.08 in humans (Tsai et al. 1998). Whereas this discrepancy remains unclear, the existing data imply that a C S F concentration o f 10 p M would correspond to arterial concentrations between ~0.16 and 2 u g / m l in vivo, which is precisely i n the range relevant to the subconvulsive C N S effects o f lidocaine (cf. 1.1). 'Based on the molecular weight of lidocaine H C I of 270.81, the 1% (i.e., 10 mg/ml) solution familiar to clinicians corresponds to a concentration of 36.93 m M . tin the same study, whole brain lidocaine concentrations were significantly higher than those in the C S F or blood, indicating that lidocaine accumulates in cerebral tissue. The fact that mean whole brain lidocaine concentrations exceeded mean cortical concentrations provides indirect evidence for a preferential accumulation in subcortical tissues, e.g., thalamic nuclei. S. S C H W A R Z 68 1.4.1.2 Previous investigations This is the first study to show that lidocaine decreases input resistance i n neurons o f the C N S . Al though previous investigations demonstrated that local anesthetics reduce neuronal excitability, most have focused on concentrations i n the high micromolar to mill imolar range. One exception is the study by Kaneda et al. (1989) on isolated C A 1 hippocampal pyramidal neurons, showing that lidocaine blocks voltage-dependent N a + currents with an IC50 around 400 u M but has no effect on the N a + currents below 30 u M , in accordance wi th the results o f the present studies. Another exception and consistent wi th the former is the report by Fried et al. (1995) that 10 u M lidocaine does not alter the configuration o f evoked population spikes i n hippocampal slices while reducing markers o f anoxic damage (e.g., A T P depletion). Finally, K u n o and Matsuura (1982) showed that lidocaine at low concentrations (< 10 uM) suppresses E P S P s i n frog spinal motoneurons by a postsynaptic mechanism and proposed a direct action on the postsynaptic membrane. N o n e o f these studies, however, have reported effects on input resistance or conductance. Butterworth et al. (1993) did investigate the effects o f extracellular lidocaine (50 uM—3 m M ) on input resistance i n hippocampal C A 1 pyramidal neurons and found no decrease or increase. In contrast, the quaternary lidocaine analogues Q X - 2 2 2 (Puil and Carlen 1984), Q X - 5 7 2 (Segal 1988), and Q X - 3 1 4 (Xie and Sastry 1992), applied intracellularly i n high (millimolar) concentrations, increase Ri i n hippocampal neurons. Outside the C N S , in cultured cardiac myocytes,' N i c k Sperelakis' group reported a "loss o f electrical excitability" associated with depolarization due to local anesthetics (i.e., tetracaine and cocaine) more than 30 years ago (Sperelakis and Lehmkuh l 1968; S. S C H W A R Z 69 H e n n and Sperelakis 1968). The millimolar concentrations studied did not change membrane resistance but produced a blockade o f N a + - K + ATPase , which was reversed by the ATPase activators, B a 2 + and S r 2 + . In rat dorsal root ganglion ( D R G ) neurons, Scholz et al. (1998) observed that lidocaine blocks TTX-sensi t ive and -resistant N a + currents with IC50S o f 42 and 210 |u.M, respectively. In sheep cardiac Purkinje fibres, Arnsdo r f & Bigger (1972) found that a low and clinically antiarrhythmic lidocaine concentration (21.4 uM)* reduces slope resistance as well as membrane time constant, and suggested that this is likely due to an increase i n K + conductance. This observation, coupled with the report that application o f 400 n M lidocaine increases conductance in isolated somata o f rat superior cervical ganglion neurons (Tabatabai and Boo th 1990), is consistent wi th the present findings that the decreased Ri occurred only wi th low concentrations o f lidocaine. 1.4.1.3 Physiological significance The shunting o f inputs and action potentials represents a powerful mechanism for inhibit ion i n the C N S . A s a result o f the reduction i n i m , the neuron's capability o f temporal summation o f synaptic inputs potentially leading to threshold responses would be diminished — effects representing a form o f "temporal shunting". The observed consequences o f the shunt on neuronal excitability were a marked increase in the current threshold for action potential generation and a suppression o f tonic repetitive firing. *It seems likely that the actual concentration was 18.5 u M , since the authors used the M W of lidocaine (234.33), and not lidocaine H C I (270.81) as used in the experiments, for the conversion of the concentration (5 ug/ml) studied. S. S C H W A R Z 70 Normal ly , thalamocortical neurons encode the intensity o f afferent somatosensory signals nearly linearly into firing frequency for "faithful" signal transmission to cortical centres (Mountcastle et al. 1963; Jahnsen and Llinas 1984a; Steriade et al. 1990). The findings that lidocaine shunts their tonic firing, and hence, disrupts the faithful transmission o f somatosensory signals, are consistent with the clinical observations o f sensory disturbances and sedation at subconvulsive concentrations. The principle o f encoding stimulus intensity into firing frequency and spike patterns also is valid for nociceptive signals, including those transmitted by the V P L neurons (Apkarian and Shi 1994), e.g., via the spinothalamic tract (Simone et al. 1991). Indeed, the vast majority o f V P L nociceptive neurons i n rats or monkeys are o f the "wide-dynamic-range" ( W D R ) type that respond in a graded fashion to stimuli ranging from innocuous to noxious, with their firing rate increasing with stimulus intensity (Guilbaud et al. 1980; Kenshalo et al. 1980; Casey and M o r r o w 1983; Chung et al. 1986; Apkar ian and Shi 1994). It is noteworthy that initial studies i n anesthetized animals had failed to reveal V P L nociceptive neurons until experiments were conducted i n awake primates, indicating that such neurons are selectively modified by analgesic and anesthetic drugs (Casey and M o r r o w 1983). G i a n Poggio and Vernon Mountcastle wrote i n their classic 1963 paper on properties o f V B neurons: "The more dynamic aspects of the system — the temporal cadence of neural activity [...], the quantitative relation of central response to peripheral stimulus — all these appeared to he most severely affected by an anesthetic agent' (Poggio and Mountcastle 1963). Several other groups have since demonstrated that analgesics from a variety o f classes, including salicylates and opioids, depress the nociceptive activity i n V B S. S C H W A R Z 71 neurons (Guilbaud et al. 1982; Braga et al. 1985; Carlsson et al. 1988). Whereas the effects o f N S A I D s on membrane properties o f thalamic neurons have not been studied systematically, Barker & Levitan (1971) showed in buccal ganglion cells o f the marine mollusc, Navanas inermis, that salicylate decreases membrane resistance and hyperpolarizes neurons. Coupled with the subsequent observations in the thalamus that \x. opioid receptor agonists decrease input resistance o f neurons i n many nuclei including V P L (Brunton and Charpak 1998), these findings are consistent with the hypothesis that a current shunt i n thalamocortical neurons is a common mode o f action for drugs to produce analgesia i n mammals. The present in vitro findings that concentrations o f lidocaine that produce clinical analgesia effectively suppressed tonic firing i n V P L neurons correspond well to the observations from the in vivo studies and represent an attractive and plausible mechanism contributing to the systemic analgesic properties o f lidocaine.* Likewise, the observed shunting o f burst firing in vitro is consistent with the in vivo efficacy o f lidocaine as a systemic analgesic in patients suffering from various chronic pain syndromes: a hallmark feature in such patients is the occurrence o f abnormal thalamic burst firing (Lenz et al. 1987, 1989; Tsoukatos et al. 1997), which is identical to the L T S burst firing seen i n intracellular and patch clamp recordings. It is conceivable that suppression by a lidocaine-induced shunt o f pathological nociceptive signals i n the form o f such burst discharges and tonic firing could contribute to the alleviation o f neuropathic pain seen with lidocaine in the clinical setting. *A reduction of firing rate in auditory fibres also has been suggested as a mechanism for lidocainc's effect to suppress tinnitus (cf. 1.1) (Huxtable 2000), and it seems possible from the present work that a shunting action in central auditory neurons plays a role. S. S C H W A R Z 72 Central analgesic properties have also been demonstrated for cocaine, both i n human and animal models (Yang et al. 1982; L i n et al. 1989). In in vivo experiments with adult rats, I V cocaine suppresses nociceptive responses o f neurons in medial thalamic nuclei (cf. 1.1.2, page 13) (Shyu et al. 1992). In contrast to lidocaine and other local anesthetics, cocaine possesses the unique property o f interacting with synaptic norepinephrine and dopamine reuptake mechanisms (for reviews, see Garfield and Gugino 1987; Leshner 1996), and the results from Shyu et al. indicate that its central analgesic effects are mediated by dopamine D i and D 2 receptors. In contrast to the medial thalamic nuclei, cocaine has no effects on neurons i n the lateral thalamus (which V P L belongs to), which may be due to the fact that these do not express either receptor subtype (reviewed in Steriade et al. 1997, page 151). Nonetheless, these results further emphasize the thalamus' role i n analgesic drug action. Suppression o f tonic repetitive firing also is likely to be a major mechanism by which a variety o f other agents exert their therapeutic effects, including the anticonvulsants, phenytoin, sodium valproate, and carbamazepine (for review, see Macdonald and Ke l ly 1995). None o f these drugs, however, are known to decrease resistance i n central neurons. Somewhat paradoxically, low concentrations o f lidocaine also are effective i n the treatment o f generalized tonic-clonic seizures and Status epilepticus (Taverner and Ba in 1958; Berry et al. 1961; Koppany i 1962; Bernhard and B o h m 1965; L e m m e n et al. 1978), and suppression o f tonic repetitive firing due to a shunt may well be a mechanism critical to these actions. The volatile general anesthetic, isoflurane, applied i n clinically relevant concentrations, likewise decreases resistance and shunts tonic and S. S C H W A R Z 73 burst firing i n V B neurons (Ries and Pui l 1993, 1999a). This observation is most striking i n view o f the clinical similarities between general and local anesthetics. L ike lidocaine, isoflurane has sedative, analgesic, and anesthetic properties, and, like other general anesthetics, also is effective as an anticonvulsant (Kofke et al. 1985). In 1963, Frank and Sanders suggested that general and local anesthetics share a common mechanism o f action in the C N S (Frank and Sanders 1963). However, it is unlikely that the receptor mechanisms o f action o f isoflurane for generating the shunt is identical to lidocaine's. Isoflurane hyperpolarizes thalamocortical neurons by increasing a leak K + conductance (Ries and Pu i l 1999b) whereas lidocaine had little effects on Vt or depolarized neurons. In addition to the reduction in repetitive firing and the shunting o f input current, low lidocaine concentrations exerted a number o f other effects that also may be interpreted as being secondary to a decrease in Rj. These include the observed reduction o f s A H P s and the suppression o f L T S bursts. W i t h regard to the former, an isolated reduction o f s A H P s , likely produced by small conductance Ca +-activated K + (SK) channels (cf. Jahnsen and Llinas 1984a,b), is not compatible with a decrease in firing frequency (cf. Foehring et al. 1989). Furthermore, lidocaine (1 m M ) blocks Ca +-acrivated K + channels in hippocampal neurons (Oda et al. 1992), bu t these channels are o f the high (or "big") conductance (BK) type, possibly similar to those expressed i n V B (Biella et al. 2001). W i t h regard to the latter, there is good evidence that the C a 2 + channels that mediate the T-type C a 2 + current (and thus, the LTSs) in V P L neurons are primarily distributed at proximal dendritic locations (Zhou et al. 1997; Destexhe et al. 1998; S. S C H W A R Z 74 Will iams and Smart 2000).* F r o m such a distribution, it would be expected that a pronounced shunting effect would result from a significantly decreased Ri. O n the other hand, the findings that lidocaine suppressed L T S bursts even after hyperpolarizing thalamocortical neurons to a voltage range where one would anticipate a maximal de-inactivation o f IT raise the possibility that lidocaine may directly decrease IT (cf Akaike and Takahashi 1992). Since the proximal dendritic regions o f thalamocortical neurons receive excitatory synaptic connections from primary afferents, L T S s likely play a role in the amplification o f sensory inputs (Williams and Stuart 2000). This is supported by experimental evidence that IT amplifies subthreshold E P S P s and IPSPs (von Kros igk et al. 1993; Turner et al. 1994; Williams et al. 1997a; K i m and M c C o r m i c k 1998). The analgesia, sedation, and sensory disturbances produced by lidocaine in vivo are consistent with an inhibit ion o f such an amplification o f afferent sensory signals. 1.4.1.4 Effects o f G A B A A receptor blockade In the literature, pharmacological correction o f a relative G A B A e r g i c hypofunction at thalamic levels has been suggested as a mechanism critical to the treatment o f central pain (Rausell et al. 1992; Canavero and Bonicalzi 1998), in which lidocaine is effective (cf. Table 1). Intracerebral injections o f lidocaine obtund the antinociceptive actions o f the G A B A A receptor antagonist, picrotoxin, in cats (Koyama et al. 1998). In addition to 'There still is some uncertainty about the precise subtype of C a 2 + channel(s) that mcdiate(s) IT in V P L neurons. Only recently have three distinct a subunits (termed alG, alH, and all) been cloned that exhibit hallmark characteristics of native T-type Ca 2 +currents and arc designated the gene subfamily, CayT (Perez-Reyes et al. 1998; Cribbs et al. 1998; Lee et al. 1999; Montcil et al. 2000). O f these, alG is expressed in the thalamus in relay (including V P L ) and ' intralaminar nuclei whereas alH and all arc found in the reticular nucleus (Talley et al. 1999). S. S C H W A R Z 75 the central analgesic effects, lidocaine's anticonvulsant properties (tf. page 72) have also been speculated to result from G A B A e r g i c stimulation (Nordmark and Rydqvist 1997). This is supported by the observation o f Smith et al. (1993) that lidocaine terminates bicuculline-induced seizures i n rats. In contrast, Stone and J avid (1988) found that lidocaine is mostly ineffective against the convulsant effects o f picrotoxin and bicuculline i n mice. It is well known from in vivo and in vitro studies that bicuculline increases evoked firing i n thalamocortical neurons (Hicks etal. 1986; Vahle -Hinz etal. 1994; Lee etal. 1994; M c C o r m i c k et al. 1995; Gao et al. 1997). This is consistent with the present observations that bicuculline reversed the decrease i n firing rate produced by lidocaine. However, the fact that bicuculline did not antagonize the lidocaine-induced shunt implies that the effects o f lidocaine and bicuculline on tonic firing result from interaction with distinct targets. Despite increasing the firing rates, bicuculline did not block the decrease in Rj and had no effect on the lidocaine-induced shunting o f tonic and burst firing or A H P s . It is possible that bicuculline may have affected a shunt i n regions distal to the recording site, but this remains speculative. In a recent report, bicuculline (5-40 pM) blocked the apamin-sensitive A H P component due to JAHP i n thalamic reticular neurons (Debarbieux et al. 1998), similar to observations i n other preparations (Johnson and Seutin 1997; Seutin et al. 1997; Johansson et al. 2001). Bicuculline methyl derivatives potently block both apamin-sensitive and -insensitive S K channels, responsible for the A H P s , in outside-out patches o f Xenopus laevis oocytes (Khawaled etal. 1999). Whereas a similar action o f bicuculline in S. S C H W A R Z 76 this study cannot be excluded with certainty (cf. Figure 19C), the observed A H P reductions produced by lidocaine are unlikely due to a predominant blockade o f JAI-IP, because, as discussed earlier, an opposite effect on tonic firing would be expected (Foehringtfa/ . 1989). In conclusion, the results o f this set o f experiments do not support the hypothesis that the effects produced by low lidocaine concentrations i n thalamocortical neurons are mediated by G A B A A receptor activation. 1.4.1.5 Molecular and cellular actions o f lidocaine Lidocaine exerted multiple and overlapping actions that affected resistance. This was evident by the distinct, non-classical concentration-response relationship (cf Figure 8), implying that the local anesthetic had at least one action that decreased Ri at lower concentrations, and at least one action that caused Ri to "return" to (and i n some cases, past) control values at high concentrations. It is well known that local anesthetics are far from being specific agents with regard to their molecular actions and have many effects i n addition to their classic blockade o f N a + channels. Lidocaine, for example, has been found to interact with a wide variety o f other membrane-associated proteins, including K + channels, C a 2 + channels, substance P receptors, and second messengers, to name but a few (for examples o f selected reviews on these topics, see Butterworth and Strichartz 1990; Arias 1999; Hol lmann and Durieux 2000; Hol lmann et al. 2001c). Table 4 gives a comprehensive overview o f the plethora o f the reported molecular and cellular effects o f local anesthetics and illustrates the dichotomy that is associated with many o f them. The S. S C H W A R Z 77 Table 4 Overview o f reported molecular and cellular actions o f local anesthetics General neuronal actions Blockade of Na+ channels (Shanes et al. 1959; Taylor 1959; Hillc 1966; Ragsdale et al. 1991) Blockade of K + channels (Taylor 1959; Oda et al. 1992; Olschcwski et al. 1998; Komai and McDowell 2001) Blockade of Ca 2 + channels (Frelin et al. 1982; Palade and Aimers 1985; Oyama et al. 1988; Sugiyama and Mutcki 1994) Increase and decrease in HVA Ca 2 + currents (Liu el al. 2001) Blockade of nicotinic ACh receptors (Stcinbach 1968; Neher and Steinbach 1978; Ruff 1982; Gentry and Lukas 2001) Blockade of muscarinic ACh receptors (Fields et al. 1978; Aguilar et al. 1980; Hollmann el al. 2000) Blockade of opioid receptors (Craviso and Musacchio 1975) Blockade of a adrenoceptors (Fairhurst et al. 1980) Inhibition of substance P binding to NK1 receptors (Li et al. 1995) Excitation of hcat-/capsaicin-sensitivc nociceptors (Vlachova et al. 1999) Increase in synaptic dopamine concentration (Graham et al. 1995) Enhancement of GABAergic neurotransmission (Granger et al. 1995; Nordmark and Rydqvist 1997) Inhibition of glutamate-induced excitation, possibly via action on glycine receptors (Biella and Sotgiu 1993) Inhibition of quisqualate-mediated excitation through a glycinc-likc action (Biclla et al. 1993) Enhancement of NMDA-mcdiatcd excitation (Biella et al. 1993) Inhibition of axonal transport (Fink et al. 1972; Anderson and Edstrom 1973; Kanai et al. 2001) Activation of calmodulin-dependcnt protein kinase II (Kanai et al. 2001) Cardiac actions Blockade of Na + channels (Weidmann 1955; Hondeghem and Katzung 1977; Grant et al. 1989) Increase in K + conductance (Arnsdorf and Bigger 1972) Blockade of K+ channels (Valcnzucla et al. 1995; Olschcwski et al. 1996) Inhibition of Ca 2 + currents (Chapman and Leoty 1981; Sanchcz-Chapula 1988; Rossncr and Frccsc 1997) Inhibition of CICR (Endo 1977; Stephenson and Wendt 1986; Zahradnikova and Palade 1993) Blockade of Na+-K+ ATPase (Henn and Sperelakis 1968) Reduction of diazoxidc-induced mitochondrial flavoprotein oxidation (Tsutsumi el al. 2001) Actions pertinent to neuro- and cardioproleclion Inhibition of cerebral oxygen and glucose consumption (Astrup et al. 1981) Depression of synaptic activity (Schurr et al. 1986) Protection against hypoxic damage and ATP depletion (Lucas et al. 1989; Fried et al. 1995) Delay and reduction of anoxic depolarization (Belousov et al. 1995; Liu et al. 1997; Chen et al. 1998) Depression of anoxic hyperpolarization (Belousov et al. 1995) Inhibition of hypoxia-induced [Ca2+]i increase (Liu et al. 1997; Chen et al. 1998) Inhibition of excitatory amino acid release/accumulation (Fujitani et al. 1994; Terada et al. 1999) Scavenging of hydroxyl radicals and singlet oxygen (Das and Misra 1992) Hematologic & miscellaneous actions Inhibition of platelet aggregation (Fcinstcin et al. 1976; Borg and Modig 1985) Inhibition of thromboxane A2 receptor-mediated signalling (Kohrs et al. 1999) Inhibition of leukocyte phagocytosis, metabolic activity, migration, and superoxide anion production (Cullcn and Haschke 1974; Stewart et al. 1980; Eriksson et al. 1992; Hollmann et al. 2001b) Inhibition of macrophages (Ogata et al. 1993) Reduction in collagen and glycosaminoglycan synthesis (Chvapil et al. 1979) Activation and inhibition of adenylyl cyclase (Gordon et al. 1980; Voeikov and Lcfkowitz 1980) Inhibition of agonist binding to P adrenoceptors (Voeikov and Lcfkowitz 1980) Inhibition of actomyosin motility (Tsuda et al. 1996) Reduction of lysophosphatidatc receptor mediated Ca2+-activated CI currents (Nietgcn et al. 1997) Inhibition and stimulation of mitochondrial phospholipasc A2 (Waitc and Sisson 1972) Inhibition of lysosomal phospholipasc At & A2 (Waite and Sisson 1972) Inhibition of leukotriene B4 & intcrleukin-loc release (Sinclair el al. 1993) Inhibition of histamine release (Yanagi et al. 1996) Inhibition of PGE2 receptor-mediated signalling (Nollet et al. 2001) Inhibition of GcCq protein function (Hollmann et al. 2001a) Enhancement of Goti protein function (Benkwitz et al. 2001) Adapted in part and modified from Hollmann and Duricux (2000). For abbreviations see appendix. S. S C H W A R Z 78 latter, i.e., the fact that local anesthetics exert concentration-/dose-dependent multiphasic effects on the nervous system has been recognized for many decades. Perhaps the most prominent example is represented by the in vivo observation discussed earlier that lidocaine induces generalized (grand mal) seizures when administered at high doses whereas it is an effective anticonvulsant at low doses (Taverner and Ba in 1958). M o r e recent examples from in vitro studies include the finding that procaine at concentrations as low as 2 )J .M produces an excitatory inward current i n rat D R G heat-/capsaicin-sensitive nociceptors while blocking N a + conductance at higher concentrations (Vlachova et al. 1999). A l s o i n D R G neurons from newborn rats, ropivacaine (II. 1.4) at 10 and 30 u M markedly increases a high voltage-activated C a 2 + current ( " H V A-Jca") but decreases it at > 50 u M (Liu et al. 2001) (cf. 1.4.2.1). The phenomenon that systemic lidocaine exerts multiphasic/dichotomous effects has similarly been documented outside the nervous system. Fo r example, whereas high concentrations are associated with vasodilatation, hypotension and cardiovascular collapse, low concentrations (between 10 and 103 n g / m l i n one study) produce vasoconstriction and increase b lood pressure both in vivo (Blair 1975; A p s and Reynolds 1976; Johns etal. 1985; Wallace etal. 1997b) and in vitro (Gherardini*/*/ . 1995). Al though it is evident from the results o f the present study that the lidocaine-induced shunt occurs in a context o f multiple overlapping effects on membrane properties, several inferences about the underlying targets and mechanisms can be made. Firstiy, the observation that lidocaine still produced decreases in resistance during T T X application implies that a postsynaptic action contributes to the shunt. However, the S. S C H W A R Z 79 possibility that lidocaine may act on nerve terminals or neurons presynaptic to the recorded electrode to produce the changes i n membrane properties cannot be excluded with absolute certainty. Secondly, as discussed in 1.4.1.4, the results obtained in the experiments with bicuculline do not support the hypothesis that the shunt produced by low lidocaine concentrations is mediated by G A B A A receptors. Thirdly, the results with Q X - 3 1 4 indicate that the decrease i n resistance due to lidocaine is mediated by interaction with an intracellular target. This would not represent a surprise, since the best-known action o f lidocaine, the blockade o f voltage-gated N a + channels through an enhancement o f channel inactivation, is mediated chiefly by its charged cation via an intracellular ("hydrophilic") pathway (reviewed by Catterall 1987, 1995; Butterworth and Strichartz 1990). However, this action is not compatible with the observed decrease in resistance, nor is the so-called "open channel block" o f N a + channels (see Butterworth and Strichartz 1990 for review). It remains a possibility, however, that lidocaine, in low concentrations, may have affected the persistent N a + current, i N a P (for review, see C r i l l 1996). In thalamocortical neurons, J N a P amplifies depolarizations in the perithreshold range (Jahnsen and Llinas 1984b; Parri and Crunelli 1998). Lidocaine (12.5-25 uM) selectively blocks this current in cardiac myocytes (Ju et al. 1992). The lower slope o f the I-V curve between Vi and — 5 0 m V (Figure 9) (if. Stafstrom et al. 1985), decreased amplitudes o f voltage responses to depolarizing current, and reduction i n tonic firing frequency during application o f 10 u M lidocaine are consistent with a blockade o f I^av i n the subthreshold range. The precise molecular basis o f 7NaP is still unclear, however, and the location o f lidocaine's binding site for its blocking effect remains speculative. Beyond S. S C H W A R Z 80 voltage-gated N a + channels, lidocaine interacts with a large number o f other intracellular targets that include ion channels, receptors, and enzymes. Whereas documented effects are summarized i n Table 4, there likely exists an abundance o f targets that are yet unidentified. The future elucidation o f the latter wi l l shed more light on the specific molecular mechanisms that mediate the lidocaine-induced decrease i n Ri and other actions o f the local anesthetic. A s i n the case o f the definition o f the structure and function o f voltage-gated ion channels, techniques o f molecular biology wi l l likely be instrumental i n this endeavour. 1.4.1.6 Lidocaine and E E G spindle waves It remains both intriguing and unclear how low lidocaine concentration could produce the transient spindle waves i n the mammalian E E G (cf. 1.1.2, page 11) by action on thalamic neurons. Whereas the mechanisms that underlie the generation o f these recurring, waxing and waning synchronized 7—14 H z oscillations by the thalamocortical system (specifically, a complex interplay between thalamic relay, reticular/perigeniculate, and neocortical neurons) have been studied i n detail both in vivo and i n slice preparations in vitro (see reviews i n Steriade and McCarley 1990; Steriade and McCarley 1990; Steriade et al. 1997), lidocaine has not been investigated in these models (see 1.4.4 later in the Discussion). Critically involved i n spindle generation are the ionic currents, IT (cf. 1.3.8) and Jh (cf. 1.3.3). Physiologically, thalamic spindling involves induction o f rebound L T S s i n relay neurons by repetitive IPSPs from reticular/perigeniculate neurons. The L T S s are associated with an increase i n [Ca 2 + ]i , which activates and upregulates K (Luthi and S. S C H W A R Z 81 M c C o r m i c k 1998). Persistent activation o f Ih i n turn depolarizes the relay neurons such that the IPSPs no longer trigger rebound L T S s , which causes the spindle waves to wane. It is possible that the disappearance o f the transiently occurring spindles associated wi th low lidocaine b lood concentrations involves a similar mechanism: in the presence o f a lidocaine-induced shunt as observed i n the present study, IPSPs would lose their ability to elicit rebound L T S s , which would cause the spindle waves to cease. It remains unclear, however, how lidocaine could induce the appearance o f the spindles. Possible hypotheses yet to be tested include excitation o f (or removal o f inhibitory influences on) reticular neurons, leading to an enhancement o f rhythmic IPSPs. Another possibility is that lidocaine acts on Ih. In thalamocortical neurons, Ih can be modulated directly or indirectly, e.g., via adenylyl cyclase (McCormick and Pape 1990a; Lee and M c C o r m i c k 1996; L u t h i et al. 1998). Whereas its enhancement abolishes spindle waves as discussed above, blockade o f Ih produces continuous spindling by blocking the refractory period after waves (Bal and M c C o r m i c k 1996; L i i t h i et al. 1998). However, a blockade o f Ih would not produce a decrease in Ri, and no consistent effect o f lidocaine on inward rectification was found in I- Vrelationships that would imply such an effect (cf. 1.3.6). 1.4.2 Effects of high lidocaine concentrations A t high concentrations (300 uM— 1 m M ) , lidocaine produced the expected signs o f N a + channel blockade (Weidmann 1955). These concentrations correspond to those i n studies on in vitro peripheral nerve preparations (for review, see Strichartz 1976) and are associated with generalized CNS/cardiovascular depression and death when present in S. S C H W A R Z 82 the systemic circulation in vivo. The refractoriness to lidocaine o f the first spike i n a train and the increasing depression o f subsequent spikes observed i n the present experiments were similar to findings by others in hippocampal C A 1 neurons (Capek and Esp l in 1994). This resilience o f the first spike most likely results from the high density o f N a + channels i n the area o f the axon hillock near the electrode, compared to more distal regions. W h e n high lidocaine concentrations were applied i n the presence o f T T X , a selective increase i n apparent resistance in the depolarized voltage became evident (Figure 16B). This was indicative o f an effect on voltage-dependent conductances and similar to the "anomalous rectification" described by Hotson et al. (1979). One possible mechanism for this observation is a blockade o f a voltage-dependent K + (outward) current. It is well known that high concentrations o f local anesthetics block voltage-gated K + channels (see reviews by Strichartz and Ritchie 1987; Butterworth and Strichartz 1990) (cf. Table 4). Al though it would seem reasonable to assume that lidocaine may exert similar actions i n thalamocortical neurons, no consistent changes i n Vt (in this case, depolarizations) occurred concomitantly when T T X was present to indicate a reduction i n K + conductance. However, the depolarizations seen i n some neurons following application o f 100 p M lidocaine alone (1.3.5) are in accord with such an effect and resemble the findings with procainamide, discussed later (1.4.3). Another possible mechanism is the activation/unmasking by lidocaine o f a subthreshold (inward) booster current that would amplify depolarizing stimuli. Whereas Ho t son et al. postulated that a noninactivating N a + / C a 2 + current may contribute to a resistance increase with depolarization, C d 2 + application i n the present study did not block the observed increase S. S C H W A R Z 83 i n apparent resistance in the depolarized range (cf. Figure 17C). Another example o f such a booster current is / N a P , discussed earlier (cf. page 79). However, / N a P activation seems unlikely since lidocaine blocks this current Qu et al. 1992). The most likely explanation thus is a mixed effect that may consist o f a combination o f K + channel blockade and activation o f an unidentified slow inward current. It is noteworthy that high concentrations o f lidocaine have been shown to be neurotoxic (Ready et al. 1985), which clinically may manifest as "transient neurologic symptoms" (TNS) or Cauda equina syndrome following subarachnoidal administration (Rigler et al. 1991; Auroy et al. 1997; Lambert and Strichartz 1998). Lidocaine 5% (~185 m M ; cf. page 67) produces irreversible conduction blockade i n bullfrog sciatic nerve preparations in vitro (Lambert et al. 1994). Similar results were obtained by others for 40 m M lidocaine (Bainton and Strichartz 1994). In rat D R G in vitro preparations, lidocaine concentrations > 30 m M depolarize neurons irreversibly and induce cell death (Go ld et al. 1998). In crayfish giant axons, 40 and 80 m M lidocaine irreversibly block action potentials (Kanai et al. 1998). A recent study demonstrated that such concentrations can damage neuronal cell membranes through the generation o f a physical leak (Kanai et al. 2000). Al though the precise mechanisms that underlie the lidocaine-induced increases i n membrane conductance in the present study remain unclear, this effect occurred at significandy lower concentrations, was fully reversible, and at the concentration that produced the greatest magnitude (10 pM) was not associated with consistent changes in Vt. Hence, lidocaine neurotoxicity does not represent a plausible explanation for the observed lidocaine-induced shunt i n V P L neurons. O n the other S. S C H W A R Z 84 hand, the results on the effects o f high lidocaine concentrations on high threshold C a 2 + spikes may indeed bear significance for its neurotoxicity. A discussion o f these data follows below. 1.4.2.1 Effects on high threshold C a 2 + spikes Lidocaine, applied at high (> 300 uM), clinically CNS- tox ic concentrations, reversibly unmasked high threshold C a 2 + spikes i n the V P L neurons. These novel findings are i n contrast to previous observations in other tissue preparations that lidocaine blocks various C a 2 + conductances (see Table 4). O n the other hand, the observations are consistent with the results o f Mul le et al. (1985), who reported an unmasking o f fast prepotentials by intracellular Q X - 3 1 4 and concluded that these represent dendritic C a 2 + spikes. In D R G neurons from newborn rats, ropivacaine (cf. II.1.4) at 10 and 30 u M markedly increases a high voltage-activated C a 2 + current ( " H V A-Jca") but decreases it at > 50 u M (Liu eta/. 2001) (cf page 78). What possible functional implications do these results have? The overall physiological role o f H T S s i n thalamocortical neurons is incompletely defined (see above). Some authors have suggested that H V A C a 2 + currents regulate tonic firing in thalamic relay neurons by triggering Ca 2 + - induced C a 2 + release from intracellular stores and subsequent activation o f Ca 2 + -dependent K + currents (Ik(Ca)) (Hernandez-Cruz and Pape 1989; G u y o n and Leresche 1995; Kammermeier and Jones 1997; Z h o u et al. 1997; Budde et al. 2000). In addition to these putative physiological functions, H V A C a 2 + channels have been implicated i n neurotoxicity. The pathogenesis o f neurotoxicity S. S C H W A R Z 85 involves several mechanisms that lead to an increase i n [Ca 2 +]i. H V A C a 2 + channels participate i n this process both directly and indirectly. They directly facilitate C a 2 + flux intracellularly, which, partially due to their slow inactivation, may produce substantial increases i n [Ca 2 +]i (Hernandez-Cruz and Pape 1989; Z h o u et al. 1997). Alternatively, H V A C a 2 + channels, particularly those o f the N-type, may increase [Ca 2 +]i indirectly by mediating excitatory amino acid ( E A A ) release (Pfrieger et al. 1992; Takahashi and Momiyama 1993) and subsequent E A A - i n d u c e d excitotoxicity (reviewed i n C h o i 1992). Hence, the present findings may have significance for the C N S toxicity o f high lidocaine concentrations seen in vivo. However, the fact that lidocaine unmasked H T S s under conditions o f presynaptic transmitter release blockade by T T X renders indirect mechanisms o f [Ca 2 +]i release less likely to be relevant for lidocaine's neurotoxicity. It is noteworthy that the H T S s in this study, although otherwise similar, had voltage thresholds that were up to ~15—20 m V higher than those reported i n rat M G B by Tennigkeit et al. (1998b). O n the other hand, Ries and Pu i l (1999a) showed i n rat V B H T S s with thresholds comparable to those observed here. Whereas these discrepancies remain unclear, it seems possible that H T S s expressed by neurons i n different thalamic nuclei have distinct properties and/or are generated by different C a 2 + channel subtypes (see below). Previous studies dedicated to isolate the specific subtypes o f H V A C a 2 + channels/ currents that produce H T S s i n thalamocortical neurons have shown that they are mediated by a composite o f N-type, L-type, and residual "R"-type currents, with the latter representing the major component (Pfrieger et al. 1992; G u y o n and Leresche 1995). S. S C H W A R Z 86 In the light o f the lack o f readily available pharmacological tools that are specific for this " R " component, no attempts were made i n this study to duplicate these findings or further characterize the H V A C a 2 + current beyond its well-documented sensitivity to C d 2 + . 1.4.3 Effects ofprocainamide on membrane properties Since there are only few reports i n the literature on procainamide action in the nervous system, its observed effects i n the present study are briefly discussed here separate from lidocaine's effects. Previously demonstrated effects o f procainamide on nervous tissue include inhibit ion o f sympathetic nerve activity (Dibner-Dunlap et al. 1992) and acoustically evoked brainstem potentials (Lenarz et al. 1984). The present work represents the first study o f procainamide's effects on membrane properties o f thalamic neurons. In cardiac tissue, procainamide's ionic mechanism o f action is well established. A t antiarrhythmic concentrations, it includes blockade o f fast N a + channel activity and (in contrast to lidocaine) blockade o f K + channels, giving rise to an increase i n cardiac action potential duration (Echt et al. 1989). Consequendy, both agents belong to different subgroups i n the Vaughan Williams classification o f antiarrhythmic drugs (procainamide, class I A ; lidocaine, class IB) (reviewed by Bigger and Hoffman 1990). A s i n the heart, the observed effects o f procainamide in thalamic neurons were in contrast to those o f lidocaine. The outstanding feature o f procainamide in the present study was that it did not share lidocaine's effect to decrease Ri and shunt tonic and L T S burst firing. In fact, procainamide's effects in the thalamus were i n harmony with the observations from S. S C H W A R Z 87 cardiac tissue. Whereas its action to decrease tonic firing rate was consistent wi th the classic N a + channel blockade, the agent also exhibited features o f K + channel blockade. These included decreases i n resting conductance associated wi th membrane depolarizations and a reduction in inward rectification in the hyperpolarized potential range. In summary, procainamide affected firing behaviour, membrane potential, and input resistance i n thalamic neurons and produced effects that implied blockade o f N a + and K + channels. Whereas the results obtained here likely have significance for the C N S effects o f procainamide observed in vivo, the absence o f a shunting action may explain why procainamide does not share the analgesic and sedative properties o f lidocaine. 1.4.4 Limitations andfuture outlook A n implici t limitation o f this study results from the fact that it is based on recordings o f single neurons in vitro. Whereas such experiments yield crucial information about drug action on membrane properties and firing rates/patterns, and hence, signalling, recent evidence indicates that information coding i n the C N S also is carried out in terms o f temporal and spatial coordination o f action potentials across groups o f many neurons (Gray et al. 1989; deCharms and Merzenich 1996). The properties o f neuronal networks i n turn impact membrane properties o f individual cells, which for the thalamo-cortical system has been studied and reviewed extensively by Mircea Steriade (2001). Thus far, the available information about the actions o f lidocaine on the dynamics and signalling patterns o f whole neuronal populations largely is indirect and comes from in vivo E E G studies {cf. 1.1.2, page 11). Hence, future research on the effects o f lidocaine (and other S. S C H W A R Z 88 CNS-act ive agents) on the (e.g., nociceptive) responses o f entire groups o f neurons recorded simultaneously has the potential to greatly add to the understanding o f its actions i n the brain. F r o m the perspective o f the present study, the recent work by Apkar ian and coworkers on the network properties o f nociceptive V P L neurons represents a step i n this direction (Apkarian et al. 2000). 1.4.5 Summary and conclusions The major implication o f this section o f the thesis is that lidocaine, at clinically relevant, subconvulsive concentrations, is capable o f inhibiting thalamocortical signal transmission by a shunting mechanism not previously described for local anesthetics in the C N S . The findings provide further support for the hypothesis that thalamocortical neurons are a crucial site o f anesthetic and analgesic drug action (Sugiyama et al. 1992; Ange l and LeBeau 1992; Ries and Pu i l 1993, 1999a,b; Tennigkeit et al. 1997; Detsch et al. 1999; Bonhomme et al. 2001). S. S C H W A R Z 89 SECTION II: CLINICAL STUDIES Analgesic properties of ropivacaine 0.2% in femoral 3-in-1 blockade for arthroscopic anterior cruciate ligament repair Results from this section o f the thesis have appeared in the following publication: Schwarz S K W , Franciosi L G , Ries C R , Regan W D , Davidson R G , N e v i n K , Escobedo S, M a c L e o d B A : Add i t ion o f femoral 3- in- l blockade to intra-articular ropivacaine 0.2% does not reduce analgesic requirements following arthroscopic knee surgery. Can J A.nesth 1999, 46: 741-747. S. S C H W A R Z 90 II.l Introduction II. 1.1 Overall aim and specific objective Whereas the previous section o f the thesis focused on laboratory studies on the possible mechanisms for the central analgesic actions o f a well-established local anesthetic agent (i.e., lidocaine), the overall aim o f this section is to explore aspects at the other end o f the spectrum o f research on analgesic properties o f local anesthetics. Here, clinical studies are directed to investigate the analgesic efficacy o f a newly introduced agent,(i.e., ropivacaine; see below) when administered peripherally. The paradigm selected for this purpose was the use o f ropivacaine 0.2 % for "femoral 3 - i n - l " lumbar plexus blockade in knee surgery. The specific objective was to test the hypothesis that the addition o f a preincisional femoral 3- in- l block with ropivacaine 0.2% to standard intra-articular local anesthetic instillation at the end o f surgery improves postoperative pain control i n patients undergoing arthroscopic anterior cruciate ligament reconstruction ( A C L R ) under general anesthesia. II. 1.2 Background A C L R is a common procedure that is frequently associated with considerable postoperative pain (Matheny et al. 1993; Reuben et al. 1998). W h e n managed with opioids, pain relief is often unsatisfactory, and associated untoward effects such as nausea, vomiting, and urinary retention delay recovery and prolong in-hospital stay (Marks and Sachar 1973; Aus t in et al. 1980; Matheny et al. 1993). Several reports indicate that postoperative pain following various lower l imb procedures including A C L R may be S. S C H W A R Z 91 reduced by regional anesthetic approaches to the lumbar plexus and femoral nerve (Coad 1991; H o o d etal. 1991; L y n c h etal. 1991; Matheny etal. 1993; Tetzlaff etal. 1997). In a recent uncontrolled study (Edkin et al. 1995), the need for administering opioids following A C L R under general anesthesia was eliminated i n 92% o f patients receiving a "femoral 3- in- l block", the inguinal paravascular approach to lumbar plexus blockade first described by Winnie et al. (1973). However, no randomized controlled trial had evaluated the efficacy o f a femoral 3- in- l block for postoperative analgesia following A C L R . II. 1.3 Femoral 3-in-1 block The sensory innervation o f the lower extremities (Figure 27) consists o f nerve fibres that originate from two principal sources: the lumbar plexus (T12/L1—L4/L5) and the sacral plexus (L4/L5—S2/S3) (Bridenbaugh 1988). These fibres are the provenance o f the four major nerves that supply the leg: the femoral (L2—L4), obturator (L2—L3), and lateral femoral cutaneous (L2—L3) nerves (AT. femoralis, N. obturatorius, and N. cutaneus femoris lateralis) from the lumbar plexus, and the sciatic nerve (N. ischiadicus; L4—S3) from the sacral plexus. S. S C H W A R Z 92 Figure 27 Sensory innervation o f the lower extremities (Adapted and modified from Bridcnbaugh 1988) In 1973, A l o n P. Winnie and colleagues described a method to block the three (i.e., the femoral, obturator, and lateral femoral cutaneous) nerves that originate from the lumbar plexus using a single injection o f local anesthetic, and hence termed the technique " 3 - i n - l b lock" (Winnie et al. 1973). This inguinal paravascular approach to the lumbar plexus involves placement o f the needle for injection just distal to the inguinal ligament into the fascial sheath o f the femoral nerve.* O w i n g to the proximal extension o f the femoral nerve sheath (situated between the iliacus muscle posteriorly and the psoas major muscle anteriorly) towards the lumbar plexus, the femoral 3- in- l block is a result o f T h i s anatomical approach to the "anterior crural nerve" had already been described in 1922 by Gaston Labat in his seminal book "Regional Anesthesia - Its Technic and Clinical Application", pp. 247-249 (Labat 1922), which was probably largely founded on the third edition of the French "LAnesthesie Regionale" published one year prior. S. S C H W A R Z 93 cephalad spread o f the distally injected local anesthetic solution. Hence, for 3- in- l blockade, the needle is angulated pointing proximally, and some authors recommend application o f pressure distal to the injection site (Btidenbaugh 1988), as did Winnie himself. In order to achieve blockade o f all three nerves, a min imum volume o f 20 m l o f local anesthetic solution is administered ("volume anesthesia"). In Winnie 's original report, this produced successful blockade o f all three nerves i n all n — 15 patients studied. In addition, reference i n the paper is made to a larger series i n which "complete anesthesia o f all three nerves" was achieved i n o f n — 69 out o f 70 patients who received > 20 m l o f local anesthetic. More recent studies have found, however, that the femoral 3- in- l block does not produce complete anesthesia o f all three nerves wi th such consistency, particularly with regard to blockade o f the obturator nerve (Lang et al. 1992, 1993; Singelyn et al. 1996; Singer et al. 1998). For the latter, success rates as low as 3.6% have been reported, which may be partially due to the fact that investigators have used motor blockade as an endpoint rather than sensory blockade alone i n cognizance o f the large motor component o f the obturator nerve (Lang et al. 1992). There are several methods to facilitate correct placement o f the needle in the femoral nerve sheath. Perhaps the oldest technique is to advance the needle until a paresthesia is elicited (Labat 1922). In order to nrinimize the inherent risk o f neuropraxia associated with this approach, newer methods have utilized short bevelled regional block needles. These allow definition o f the penetrated structures with the aid o f tactile criteria: as the needle is advanced through the Fascia lata followed by the Fascia iliaca, a distinct S. S C H W A R Z 94 "double pop" is felt, indicate positioning o f the needle tip i n the femoral nerve sheath.* The most accurate method arguably is the use o f a peripheral nerve stimulator in combination with an insulated short bevelled needle (Ford et al. 1984). Here, close proximity o f the needle tip to the femoral nerve is identified by evoking contractions o f the M. quadriceps femoris. The standard criterion for correct needle placement and injection advocated by most authorities is the presence o f patellar movement (as a result o f quadriceps muscle twitches) at an injected current magnitude < 0.5 m A (Bridenbaugh and Crews 1998) {cf. II.2.4). Clinically, the techniques o f femoral nerve and femoral 3- in- l blockade have been utilized for both analgesia and surgical anesthesia in a wide variety o f surgical settings. In addition to control o f postoperative pain following lower l imb procedures (cf. II. 1), the successful use o f these blocks has been reported for surgical anesthesia in saphenous vein stripping, knee arthroscopy, muscle biopsies o f the anterior thigh, and split thickness skin grafting o f the thigh, to name but a few (for an overview, see M o o s and Cuddeford 1998). The reports on the clinical experience with the technique o f femoral 3-in-1 blockade raised the possibility that this block is effective for postoperative analgesia following A C L R surgery. A s mentioned above, however, no controlled trial had been conducted to study the efficacy o f a femoral 3- in- l block for this purpose. 'Studying the spread of 40 ml of methylene blue injected "into femoral nerves" of six human cadavers, one isolated study (Rittcr 1995) went so far as to conclude that a femoral nerve sheath capable of conveying local anesthetic to the lumbar plexus does not exist in human cadavers. This is in sharp contrast to radiographic evidence in vivo (Winnie et al. 1973) and the large body of clinical experience. S. S C H W A R Z 95 II. 1.4 Choice of local anesthetic The recently introduced aminoamide, ropivacaine, appeared to be an attractive choice for this application. Ropivacaine (l-propyl-N-[2,6-dimethylphenyl]-2-piperidinecarboxamide; Figure 28) is a long-acting local anesthetic, chemically homologous with bupivacaine (cf. Figure 25) and mepivacaine. The sole structural difference between ropivacaine and bupivacaine is that the N-side chain o f the former is one C atom shorter (propyl- vs. butyl-group). However, whereas bupivacaine until very recently has clinically only been available as a racemate, ropivacaine is the first enantiomerically pure local anesthetic marketed commercially and is supplied as the S-isomer. Therapeutically, ropivacaine is characterized by the potential to achieve a higher sensory-motor block separation (Bader et al. 1989) at a lower level o f systemic toxicity (Scott et al. 1989) compared to racemic bupivacaine. These properties are particularly desirable i n techniques o f regional anesthesia where large volumes and doses o f a local anesthetic are injected, and analgesia rather than complete motor blockade is the desired endpoint. It is hence perhaps not surprising that epidural labour analgesia has been a focus for the clinical study o f ropivacaine (Stienstra et al. 1995; Eddleston et al. 1996; O w e n et al. 1998; Polley et al. 1999). However, ropivacaine had not been studied i n the context o f the femoral 3- in- l block. The present investigation represents the first controlled trial and the first report i n the literature (Schwarz et al. 1999) on the use o f ropivacaine i n femoral 3- in- l blockade. S. S C H W A R Z 96 Aromatic head Amide linkage Amine tail F i g u r e 28 Structural formula o f ropivacaine II. 1.5 Primary hypothesis The primary hypothesis to be tested i n this study was that the addition o f a preincisional femoral 3- in- l block with ropivacaine 0.2% (Etches et al. 1997) (augmented by peri-incisional infiltrations o f the knee) to standard intra-articular local anesthetic instillation at the end o f surgery (Chirwa et al. 1989; Karlsson et al. 1995; Tierney et al. 1995; Brandsson et al. 1996; Dent i et al. 1997; B r o w n et al. 1997; Reuben et al. 1998) reduces postoperative analgesic requirements in patients undergoing A C L R under general anesthesia. S. S C H W A R Z 97 II.2 Materials and Methods 11.2.1 Ethics A l l aspects o f the present trial were conducted in accordance with the principles stated i n the Declaration o f Hels inki (Appendix I). The study p ro toco lwas approved by the institutional human research committee (Clinical Screening Committee for Research Involving H u m a n Subjects, The University o f British Columbia; certificate number C96-0047). Writ ten informed consent was obtained from each patient prior to inclusion i n the study. E a c h patient was informed i n detail both verbally and i n writing about the nature, purpose, possible risks, and benefits o f the study before signing the consent form (Appendix II) and was given sufficient time and opportunity to ask questions. Particular emphasis was made that a patient's decision not to take part i n the study would make no difference whatsoever to the quality o f care that the patient would receive. Patients were free to discontinue their participation i n the study at any time and without prejudice to further treatment. II. 2.2 Study design The study was designed as a single centre (Vancouver Hospital & Health Sciences Centre, University o f Bri t ish Columbia Site),* prospective, randomized, placebo-controlled, double-blind, parallel-group trial. A total o f n — 44 patients were to be allocated to the treatment groups i n blocks o f four using a computer generated randomization list. 'Recently renamed to " U B C Hospital" S. S C H W A R Z 98 II. 2.3 Inclusion criteria, exclusion criteria, and patient withdrawal T o be eligible for inclusion i n this study, patients had to fulfill all o f the following criteria: Male or female scheduled for inpatient A C L R at Vancouver Hospital , U B C Site under orthopedic surgeons Drs . P. McConkey , R. Davidson, B . Day, or W . Regan Aged 19 to 45 years A S A physical status I (cf. American Society o f Anesthesiologists 1963) Writ ten informed consent Patients were excluded from the study i f they fulfilled any o f the following criteria: History o f sensitivity to local anesthetics o f the amide type, acetaminophen, or opioids Suspected inability to comply with study procedures, e.g., due to language difficulties, medical history, and/or concomitant disease Suspected alcohol, drug, or medication abuse Regular treatment with analgesics, sedatives or any other medication with C N S effects Tendency to bleed easily Inability to rule out pregnancy Previous inclusion i n the study - Participation i n clinical studies during this study or in the 14 days prior to admission to this study S. S C H W A R Z 99 Patients were free to discontinue their participation i n the study at any time as previously mentioned (II.2.1). Patients could be also be withdrawn from the study at any time at the discretion o f the investigator. Specific reasons for patient withdrawal determined a priori included technical failure defined as an inability to verify correct placement o f the needle for injection o f the femoral 3- in- l block (see below) and significant postoperative drainage from the intra-articular space o f the knee as judged by a treating physician or the investigator. II. 2.4 Treatment interventions A l l patients received a standardized general anesthetic with midazolam 0.01—0.03 m g / k g I V , fentanyl 1.5 u.g/kg I V total over the duration o f anesthesia, propofol 2-3 m g / k g I V as required, and nitrous oxide 70% with isoflurane 0.5—2% in oxygen through a laryngeal mask airway. Pr ior to surgical incision, the treatment group received a femoral 3- in- l block wi th 40 m l o f ropivacaine 0.2% (Figure 29), using the classic inguinal paravascular approach described by Winnie et al. (1973). The solution for the block was injected after correct placement o f the regional block needle (22G X 2.5" insulated short bevel needle; Preferred Medical Products, Thorold , Ontario, Canada; or 2 2 G IY2" Regional Block Needle; Becton Dick inson and Company, Franklin Lakes, N J , U.S .A. ) i n the fascial sheath o f the femoral nerve was confirmed by eliciting quadriceps muscle twitches with a peripheral nerve stimulator (Model N S - 2 C A / D X , Life-Tech, Inc., Houston, T X , U . S . A . ; or Nerve F i n d e r ® , Regional Master Corp. , Miami , F L , U.S .A. ) at < 0.5 m A . A l l patients subsequently underwent A C L R utilizing hamstring tendon (semitendinosus and gracilis S. S C H W A R Z 100 muscle) autografts with a tibial bone tunnel and "over the top" femoral placement. The surgical technique was identical for all patients. A tourniquet was used i n all cases. A t the end o f surgery, the femoral 3- in- l block was augmented by additional infiltrations o f the lateral surgical incision at the site o f staple insertion over the lateral femoral condyle and the anteromedial incision at the site o f the origin o f the semitendinosus and gracilis tendons (which receive sensory innervation by the sciatic nerve). Fo r these peri-incisional infiltrations, a total o f 20 m l (10 + 10 ml) o f ropivacaine 0.2% were administered by the surgeon. The control group received saline 0.9% instead o f ropivacaine. A l l n — 44 patients received an intra-articular instillation o f the knee with 30 m l o f ropivacaine 0.2% at the end o f surgery (cf. Figure 29); no drainage tubes were inserted. Fo l lowing completion o f the procedure, postoperative pain was assessed in the postanesthesia care unit ( P A C U ) using a 100 m m visual analog scale ( V A S ; no pain = 0 m m , worst pain imaginable = 100 m m [Biomedical Engineering, Flinders Medical Centre, Bedford Park, S.A., Australia]). A t V A S scores < 50 m m , acetaminophen 300 mg with codeine 30 mg (Carter-Homer Inc., Mississauga, O N , Canada) was given (one to two tablets orally every three to four hours as needed). A t V A S scores > 50 m m (Cepeda et al. 1995), or when pain relief was inadequate as judged by the patient, intravenous morphine (Abbott Laboratories, Limited; Saint-Laurent, Q C , Canada) was started, administered via a patient-controlled analgesia (PCA) pump (LifeCare® P C A Plus II Infuser M o d e l 4100, Abbot t Laboratories, N o r t h Chicago, I L , U . S . A . ; loading dose [given via syringe], 2—4 m g / 5 min; incremental dose, 1—3 mg; lockout time, 6-10 min ; maximal dose over 4 h, 45 mg). A l l patients received supplemental external S. S C H W A R Z 101 cryotherapy to their knee postoperatively by way o f a C r y o / C u f F M (Aircast, Inc., Summit, N J , U.S .A. ) or ice packs (Cohn et al. 1989; Brandsson et al. 1996; Edwards et al. 1996; Reuben et al. 1998). Patients were discharged home according to normal hospital procedures when they were mentally clear and cooperative, were able to void , were afebrile and had stable vital signs, tolerated oral nutrition, had satisfactory pain control on oral analgesics, and were able to ambulate with crutches. Femoral 3-in-1 block CONTROL GROUP (n = 22) 40 ml of saline 0.9% TREATMENT GROUP (n = 22) 40 ml of ropivacaine 0.2% Intra-articular instillation Surgery 30 ml of ropivacaine 0.2% Peri-incisional infiltrations 20 ml of saline 0.9% 20 ml of ropivacaine 0.2% Figure 29 Treatment interventions S. S C H W A R Z 102 11.2.5 Outcome variables The primary outcome variable was postoperative P C A morphine consumption over 24 h (Joshi et al. 1993) standardized by body weight (initial loading dose administered via syringe included). Secondary outcome variables included postoperative consumption o f acetaminophen with codeine over 24 h as well as V A S pain scores at rest and following mobilization, b lood pressure, heart rate, and the incidences o f nausea, vomiting, pruritus, urinary retention, and orthostatic hypotension at 1, 2, 4, 6, 8, 12, 16, 20,' and 24 h following completion o f surgery. The reference point (time zero) for these post-operative assessments was the time o f arrival at the P A C U . The adverse events, nausea, vomiting, pruritus, and respiratory depression, were assessed as "yes" or "no" in response to the question, "Has the patient experienced any o f the following?" Clinical signs o f orthostatic hypotension i n association with an attempt to mobilize the patient were recorded as "yes" or "no". The times to readiness for discharge from the P A C U according to the Aldrete scoring system (Aldrete and K r o u l i k 1970; Appendix III) and the times to discharge from the hospital were recorded and compared between both groups. A l l patients were followed up two to eight weeks after hospital discharge by a telephone interview that included questioning on the occurrence o f neuropraxia. 11.2.6 Study drugs and blinding Ropivacaine 0.2% (2 mg/ml) and saline 0.9% solutions were manufactured by Astra Pain Cont ro l A B , Sweden and supplied by Astra Pharma Inc., Canada. The solutions were provided i n 50 m l glass vials. Packaging and labelling o f the study drugs was carried out at S, S C H W A R Z 103 Astra Pharma Inc., Canada (Mississauga, O N , Canada). A patient-specific box containing three 50 m l glass vials was provided for each study patient: one for the femoral 3- in- l block, one for the intra-articular instillation, and one for the peri-incisional infiltration (of. Figure 29). The appearances o f the vials and solutions for the femoral 3- in- l block and peri-incisional infiltrations were identical for ropivacaine and saline. Strict blinding o f all investigators was maintained throughout the study; all data were recorded by personnel unaware o f the treatment allocation, and patients were not assessed for sensory or motor blockade following the block (Fournier et al. 1998a,b). The randomization list was held at the site o f the pharmaceutical company that supplied the study drugs (Astra Pharma Inc., Canada). The list was available only to the individuals responsible for drug packaging until all data entry, editing, and validation o f the individual case report forms had been completed. A set o f sealed individual treatment code envelopes indicating the treatment allocation for each randomized patient was kept i n a safe, accessible place at the investigational site. Another set was held by the pharmaceutical company. II. 2.7 Statistical analyses The primary outcome variable for statistical comparison was postoperative P C A morphine consumption over 24 h standardized by body weight. The primary statistical analysis o f these data (both the dose standardized by body weight in m g / k g and the total cumulative dose in mg) and acetaminophen with codeine consumption over 24 h was completed on an intention-to-treat basis using Student's / test. In order to add power to S. S C H W A R Z 104 the analysis, secondary comparisons o f P C A morphine consumption were performed following exclusion o f "zero" values (i.e., patients with no morphine consumption) and log transformation o f the data. This approach was based on the premise that measurement (unlike count or proportion) data originates from a lognormal distribution. A l l data were tested for normality prior to parametric testing. Postoperative V A S scores at rest and following mobilization were analyzed using repeated measures analysis. Categorical data were analyzed using Fisher's exact test. B l o o d pressure and heart rate were analyzed by repeated measures analysis after replacing values with the last value carried forward method. The data were analyzed using Pr i sm versions 2.01/3.02 and StatMate version 1.00 software (GraphPad, San Diego, C A , U .S .A . ) , Microsoft E x c e l 97 software (Microsoft Corporation, Redmond, W A , U.S .A. ) , and SAS version 6.12 software (see Acknowledgments) (SAS Institute Inc., Cary, N C , U.S .A. ) . A l l statistical tests were two-tailed and comparisons were declared statistically significant at P < 0.05. Based on the data from a pilot study conducted prior to the present trial, the target sample size was projected to detect a ndnimum important difference o f 20 mg in total morphine consumption over 24 h between the groups. In order to have 90% power and a type I error o f 5%, a sample o f n — 22 valid patients per group was required, assuming equal variances and approximate normal distributions o f the groups. I f the assumptions o f the / test on which this calculation was performed were shown not to hold, an equivalent non-parametric test would provide no less than 95% efficiency. S. S C H W A R Z 105 II.3 Results II. 3.1 Demographics Twenty two patients were enrolled i n each o f the two groups. A l l n — 44 patients were valid for intention-to-treat analysis. The male to female ratio was 13:9 in the control group and 17:5 i n the treatment group. Other patient demographics were statistically similar i n both groups, as were preoperative baseline vital signs and the duration o f surgery (Table 5). There were no significant differences between the groups i n the doses o f agents used for general anesthesia (data not shown). The timing o f relevant treatment interventions (i.e., the times between administration o f the femoral 3- in- l block and the start o f the procedure, between the start o f the procedure and intra-articular instillation, and between intra-articular instillation and peri-incisional infiltration) was comparable between the treatment groups (Table 6). Table 5 Patient demographics, preoperative vital signs, and surgical data Group Age Weight Height Heart Systolic Diastolic Duration n (years) (kg) (cm) rate blood blood of (min~1) pressure pressure surgery (mm Hg) (mm Hg) (min) Cont ro l 28 + 7 74 ± 1 1 174 ± 7 65 + 9 119 ± 14 75 ± 1 1 52 ± 1 3 22 Treatment 31 ± 7 78 + 11 176 ± 8 66 + 10 119 ± 1 1 76 ± 11 55 + 13 22 Data are given as mean ± SD. No statistically significant difference between the groups was seen for any of the variables. S. S C H W A R Z 106 Table 6 T i m i n g o f treatment interventions Group Mean SD Minimum Maximum n Administrat ion o f Contro l 15 4 7 28 22 femoral 3- in- l block to procedure start (min) Treatment 14 5 3 22 22 Start o f procedure to Control 46 11 17 63 22 intra-articular instillation (min) Treatment 51 13 28 80 22 Instillation to Contro l 2 2 0 7 22 peri-incisional infiltrations (min) Treatment 2 2 0 10 22 II. 3.2 Primary efficacy variable N o significant difference was found between the control group and the treatment group i n P C A morphine consumption over 24 h (standardized by body weight or expressed as total cumulative dose i n mg) or acetaminophen with codeine consumption over 24 h (intention-to-treat analysis; for each group, n — 22; Table 7). M o r e patients i n the treatment group required no P C A morphine postoperatively than i n the control group (cf. II.2.4); however, this difference was not statistically significant (Table 8). W h e n patients who required no morphine were excluded from the analysis, no. significant difference i n 24 h morphine consumption was seen (Table 9). Figure 30 gives a graphic representation o f these results showing the log-transformed data. Al though not part o f the original a priori hypothesis (cf. 11.1.5, II.2.6), post hoc analysis o f the data also revealed S. S C H W A R Z 107 Table 7 Postoperative analgesic consumption (intention-to-treat analysis) Group PCA morphine PCA morphine Acetaminophen with codeine n consumption over 24 h consumption over 24 h consumption over 24 h standardised by weight (mg/ kg) (mg) (number of tablets)* Cont ro l Treatment 0.45 ± 0.44 0.37 + 0.50 31.0 + 28.7 27.7 + 38.7 6.4 + 3.1 7.6 ± 4 . 8 22 22 Data are given as mean + SD; P C A = patient-controlled analgesia. N o statistically significant difference between the groups was seen for any of the variables. *One tablet contains 300 mg of acetaminophen and 30 mg of codeine. Table 8 Number o f patients not requiring morphine postoperatively Group No morphine required Morphine required n Cont ro l 6 16 22 Treatment 10 12 22 N o statistically significant difference between the groups was seen (Fisher's exact test, P = 0.35). Table 9 Postoperative morphine consumption (patients requiring morphine) Group PCA morphine PCA morphine n consumption over 24 h consumption over 24 h standardised by weight (mg) (mg/ kg) Contro l 0.62 ± 0.40 42.6 ± 25.0 16 Treatment 0.67 ± 0 . 5 1 50.8 + 39.8 12 Data are given as mean + SD. N o statistically significant difference between the groups was seen for either variable. S. S C H W A R Z 108 no significant differences in analgesic consumption earlier in the postoperative course, e.g., at 6 or 12 h following completion o f surgery (data not shown). a5 cn c £• E o E O) o < o n. 0.5-0.0--0.5--1.0--1.5-B E •£ "9» 8- E E o < ^ O CL 0.5 0.0 -0.5 -1.0 -1.5 Control Treatment Control Treatment Figure 30 Postoperative morphine consumption (patients with no morphine consumption excluded) (A) Presentation of the results as "box & whiskers" graph following log transformation (whiskers = range of data; box = 25 t h percentile, median, 75 t h percentile). (B) Presentation of the raw data. No statistically significant difference between the groups was seen (Student's / test, P = 0.86). II. 3.3 Secondary efficacy variables There were no significant differences between the groups in postoperative V A S pain scores at rest, b lood pressure, or heart rate at 1, 2, 4, 6, 8, 12, 16, 20, and 24 h following completion o f surgery (Figure 31—Figure 33). Median V A S scores at rest were i n the range o f 20—40 m m i n the control group and 22-42 m m in the treatment group. The majority o f patients were mobilized on postoperative day one prior to discharge according to normal hospital procedures; as a result, recording o f V A S scores following mobil ization was inapplicable i n over 80% o f the cases and this data thus excluded from analysis. The times to readiness for discharge from the P A C U according to the Aldrete S. S C H W A R Z 109 scoring system (Appendix III) were similar for both groups (control group, 19 + 11 min; treatment group, 17 + 10 min; n — 22; P = 0.44), as were the times to discharge from the hospital (control group, 21.5 ± 3.4 h; treatment group, 23.5 ± 7.9 h; n = 22; P = 0.28). -too-] o o E E o U s o co C 4 0 CC D. 30 CO ^ a o Control Treatment 1 » 1 » S O 34 Time following completion of surgery (h) F i g u r e 31 Postoperative V A S pain scores at rest over time Shown are median V A S scores; for each group, n — 22. N o statistically significant differences were seen. ISO -^ ^ ISO* X 1 4 0 -E E i a o < "•—-* 0 k_ lOO • to CO s o -CD Q . e o • loo *o-m a o -o -Control Treatment SBP DBP Time following completion of surgery (h) F i g u r e 32 Postoperative blood pressure over time Shown are median values for blood pressure; for each group, n — 22; SBP = systolic blood pressure, D B P = diastolic blood pressure. N o statistically significant differences were seen. S. S C H W A R Z 110 Control Treatment A • a i a i a Time following completion of surgery (h) F i g u r e 33 Postoperative heart rate over time Shown are median values for heart rate; for each group, « = 22. N o statistically significant differences were seen. II. 3.4 Adverse events The most common adverse events during the first 24 h following surgery were nausea, pruritus, orthostatic hypotension, vomiting, and urinary retention; their incidences are given i n Table 10. There were no significant differences between the groups in the incidences o f these adverse events at 1, 2, 4, 6, 8, 12, 16, 20, and 24 h following completion o f surgery (not shown). One patient in the treatment group reported prolonged postoperative anesthesia in the area o f distribution o f the femoral nerve on the surgical side that lasted for four days but subsided completely. There were no incidents o f persistent neuropraxia. N o signs o f systemic local anesthetic toxicity were observed. S. S C H W A R Z 111 Table 10 Incidence o f common adverse events Group Nausea Pruritus Orthostatic hypotension Vomiting Urinary retention n Cont ro l 16 8 6 7 7 22 Treatment 13 9 8 5 2 22 Shown are the total cumulative in-hospital incidences during the first 24 h following completion of surgery. Data are given as numbers of patients; each adverse event is reported only once for each patient. N o statistically significant difference between the groups was seen for any of the variables (Fisher's exact test, P > 0.05). S. S C H W A R Z 112 II.4 D i s c u s s i o n This section o f the thesis represents the first randomized controlled trial (RCT) to assess the efficacy o f a femoral 3- in- l block to improve postoperative pain control i n A C L R , and the first report on the use o f ropivacaine for this purpose (Schwarz et al. 1999). The trial found no significant effect on postoperative morphine consumption o f the addition o f a preincisional femoral 3- in- l block (augmented by peri-incisional infiltrations) with ropivacaine 0.2% to intra-articular instillation o f the knee at the end o f surgery with ropivacaine 0.2% i n patients undergoing hamstring tendon autograft A C L R under general anesthesia. There also were no differences between the groups studied i n postoperative V A S pain scores, vital signs, incidence o f adverse events, or times to readiness for discharge from P A C U and hospital discharge. The present results harmonize with those o f Tierney et al. (1987), who conducted an R C T to assess the use o f a femoral nerve block with 20 m l o f bupivacaine 0.25% i n patients undergoing open ligament reconstruction o f the knee and found no effect on the total intramuscular (IM) analgesic dose i n the first 12 h postoperatively. Likewise, Hirs t et al. (1996) saw no effect in an R C T o f a femoral 3- in- l block, either by single-injection [20 m l bupivacaine 0.5% with epinephrine 1:200,000] or as a continuous infusion, on postoperative P C A morphine requirements after total knee arthroplasty. In a recent report, Fournier et al. (1998a) similarly observed no reduction i n analgesic requirements at 24 and 48 h following prosthetic hip surgery by a preincisional femoral 3- in- l block with 40 m l o f bupivacaine 0.5% with epinephrine 1:200,000. A l s o consistent S. S C H W A R Z 113 with the results o f the present trial are the findings o f a subsequent study by Rosaeg et al. (2001), who saw no effects in A C L R patients on verbal pain scores on postoperative days 1, 3, or 7 o f a pre-emptive regimen that included femoral nerve blockade with 20 m l ropivacaine 0.25%, intra-articular ropivacaine 0.25% with epinephrine 1:200,000 (20 ml) plus morphine 2 mg, and I V ketorolac (30 mg). The present findings contrast with those o f Ringrose and Cross (1984) who reported a 40% reduction in I M opioid administration in the first 24 postoperative hours following a femoral block with 20 m l bupivacaine 0.5% in patients undergoing "knee joint (anterior cruciate) reconstruction surgery". Nonetheless, this trial was unblinded and patients likely received open knee ligament reconstructions utilizing bone-patellar tendon-bone autografts. In an uncontrolled study with patients undergoing both A C L R and A C L R combined with meniscal procedures, E d k i n et al. (1995) found the femoral 3- in- l block useful for the relief o f post-operative pain. In their report, 92% o f patients received no parenteral opioids following administration o f a femoral 3- in- l block combined with intra-articular local anesthetic injection. However, aside from the fact that these observations were from an uncontrolled study, there were other major differences to the present trial that render direct comparisons difficult. Firstly, the surgical techniques were different. In the study by E d k i n et al, nriddle-third patellar tendon autografts were used, as compared to the present trial, where the considerably less invasive technique utilizing semitendinosus and gracilis muscle tendon autografts was performed. Secondly, a different concentration, dose, and type o f local anesthetic was employed. E d k i n et al. used a dose o f 2-3 m g / k g o f bupivacaine 0.5%; in the present study, 1.3-1.5 m g / k g (80 mg) S. S C H W A R Z 114 o f ropivacaine 0.2% (Etches et al. 1997; Borgeat et al. 2000) were administered for the femoral 3- in- l block. Thirdly, E d k i n et al. administered the block postoperatively i n the P A C U , whereas it was performed prior to surgical incision in the present study. Finally, different protocols for the management o f postoperative pain were used. Al though 92% o f the patients o f E d k i n et al. were reported not to have required parenteral opioids, 75% received parenteral ketorolac and oral opioids to control postoperative pain. It is likely that the above differences contributed to differences in postoperative parenteral opioid consumption, and thus, the difference in outcome compared to our trial. In a recent hospital database and patient chart review study, a combination o f general anesthesia and femoral nerve blockade was associated with fewer total postoperative nursing interventions for treatment o f pain, nausea, vomiting, pruritus, and urinary retention compared to other anesthetic techniques (Williams et al. 1998). Similar to the present trial, no differences in discharge times were noted. Interpretation o f these data is limited, however, by major weaknesses i n study design and data analysis. Fo r example, there was no randomization or blinding, no description o f the drug or dosage used for femoral nerve blockade, no direct measure o f analgesic drug consumption or pain scales, and no report o f the actual incidences o f adverse events. Finally, the inclusion o f five different groups and utilization o f multiple / tests for determination o f differences between the individual groups limit the utility o f this report to the generation o f future hypotheses. Lastly, i n a prospective randomized study published only i n abstract form at the time o f writing (Auge and Gri f f in 2000), patients who underwent A C L R solely under 3- in- l block with local infiltration (plus a single dose o f propofol), compared to general or S. S C H W A R Z 115 i spinal anesthesia, exhibited no requirement for postoperative opioids, no nausea or urinary retention, and a "marked decrease" i n time to achieve discharge criteria. Al though no details regarding design and results were reported, it is likely that a high concentration o f local anesthetic was used (see below) and that follow-up was limited to a few hours postoperatively. In the present study, there were fewer patients i n the treatment group who required morphine than i n the control group; however, this difference was not statistically significant. It is possible that differences between the groups may have been detected had higher concentrations (e.g., 0.5% or 0.75% preparations) and higher total doses o f ropivacaine been used (Fanelli et al. 1998; Marhofer et al. 2000). A similar statement could be made about the addition o f a vasoconstrictor to the local anesthetic solution. W i t h regard to the latter, epinephrine 1:200,000 does not prolong or enhance the effects o f ropivacaine 0.5% in brachial plexus blockade for upper extremity surgery (Hickey et al. 1990). The same is the case for ropivacaine 0.2%/0.5% i n femoral 3- in- l blockade administered via catheter for analgesia after total knee replacement (Weber et al. 2001). W i t h regard to the former, bupivacaine 0.25% was used with promising results i n the pilot study at our centre prior to this trial. A recent clinical trial compared the relative analgesic potencies o f bupivacaine and ropivacaine in epidural labour analgesia (Polley et al. 1999). In this study, the analgesic potency o f ropivacaine was found to be significantly less than bupivacaine's (potency ratio, 0.6). The results have led to more general speculations whether the documented differences between ropivacaine and bupivacaine i n terms o f motor blockade and toxicity may be simply a result o f a S. S C H W A R Z 116 difference i n potency (D'Angelo and James 1999). It seems likely that these findings also bear significance for the results o f the present trial and the differences i n outcome compared to the pilot study with bupivacaine. In summary, it is evident from these observations that extensive future studies are required to establish dose-response relationships for ropivacaine's analgesic effects i n a variety o f regional anesthetic techniques, including femoral 3- in- l blockade. It has to be emphasized, however, that all patients i n this study (including those i n the control group) received an intra-articular instillation with 30 m l o f ropivacaine 0.2% at the end o f the procedure, i n compliance with our standard institutional mult imodal analgesic (Kehlet and D a h l 1993) regimen. Postoperative pain following A C L R originates from a variety o f anatomical sources (Curry et al. 1996), which include the sites o f the tendon cuts, staple insertion, and surgical incisions. The efficacy o f intra-articular local anesthetic instillation o f the knee for postoperative analgesia in A C L R is very well established (Chirwa etal. 1989; Heard etal. 1992; Karlsson etal. 1995; Tierney etal. 1995; Brandsson et al. 1996; Curry et al. 1996; B r o w n et al. 1997; Dent i et al. 1997; Reuben et al. 1998) and now standard practice at many institutions, including our centre. In the present study, no significant subsequent reduction in analgesic requirements was observed when a femoral 3- in- l block, augmented by additional local anesthetic infiltration o f the lateral and anteromedial incisions (the sites o f staple insertion and proximal cut o f the semitendinosus and gracilis tendons, whose sensory supply includes sciatic fibres), was added to the intra-articular local anesthetic instillation. Recently, Peng et al. (1999) reported on a decrease in morphine consumption i n the first S. S C H W A R Z 117 postoperative day following A C L R i n patients receiving a preoperative femoral nerve block wi th 15 m l bupivacaine 0.5% but no intra-articular local anesthetic instillation. These results provide further indirect evidence for the analgesic efficacy o f intra-articular local anesthetics i n patients undergoing knee surgery. One study on patients undergoing diagnostic knee arthroscopy, on the other hand, failed to show an effect o f intra-articular ropivacaine (20 m l o f a 0.5% solution) on postoperative V A S pain scores (Rautoma et al. 2000). However, diagnostic arthroscopy is significantly less traumatic than A C L R and easily performed under local anesthesia (Shapiro et al. 1995; Lintner et al. 1996), which may have prevented the demonstration o f a V A S pain score reduction in this particular study. It remains possible that a small statistically significant difference may have been detected had a very large sample size been used. A retrospective power analysis (performed after closure o f the database) revealed a level o f (1 — (3) = 0.8 to detect a difference i n 24 h P C A morphine consumption o f 0.41 m g / k g at a = 0.05. Nonetheless, it seems unlikely that such a statistically significant difference would be o f clinical significance. The high variability in analgesic requirements i n general and P C A requirements specifically is a phenomenon also observed by other investigators (Amanzio et al. 2001) and has been subject o f recent discussion in the literature about analgesic trial design (McQuay and Moore 2000). One possibility would be to substitute for surrogate markers as outcome variables; i n the present study, however, no differences i n secondary variables were seen. S. S C H W A R Z 118 Despite the fact that there was no difference between the groups i n postoperative adverse events, their incidence in the studied patient population was noteworthy; this was particularly the case for nausea. Al though postanesthetic nausea cannot be easily separated from nausea specifically triggered by opioids, one may reasonably assume that the high incidence o f nausea i n this study is at least partially attributable to postoperative analgesic medication. Postoperative nausea and vomiting prolong in-hospital stay and increase costs. It has recently been reported that 58% o f the cost associated with A C L R can be saved when in-hospital stay is shortened and this procedure is performed on an outpatient basis (Kao et al. 1995). These findings further illustrate the need for optimization o f perioperative care in A C L R surgery. N o persistent neurologic complications associated with femoral 3- in- l blockade and no signs or symptoms o f systemic local anesthetic toxicity were observed i n this study. The former is consistent with a review o f 882 patients who received either femoral 3- in- l or femoral nerve blocks without any persistent neurologic sequelae (Moos and Cuddeford 1998). W i t h regards to the latter, a shortcoming o f this study is the lack o f measurement o f ropivacaine plasma levels, which, although not directly addressing the primary hypothesis, would have provided valuable information. The reasons for this are related to issues involving practicality, funding, and study protocol negotiations with the supporting pharmaceutical company. In the literature, several studies have measured plasma concentrations o f bupivacaine, lidocaine, and prilocaine following femoral 3- in- l / lumbar plexus blockade (Dahl et al. 1988; Madej et al. 1989; H o o d et al. 1991). O f these, most relevant for the present trial is the report by Madej et al, S. S C H W A R Z 119 who found that peak concentrations o f both bupivacaine and lidocaine occur at a median o f 37.5 m i n following block insertion. The median peak bupivacaine concentration was 0.67 u.g/ml, wi th a range o f 0.35—0.80 u,g/ml. Al though not studied, it appears reasonable to speculate that similar values would be observed with ropivacaine. F o r lidocaine, peak plasma concentrations ranged from 1.22—4.42 ug /ml . This is particularly noteworthy in light o f the results presented in the first section o f this thesis, as these values clearly are i n the range i n which lidocaine acts as a systemic analgesic (cf. 1.1). Thus, the results by Madej et al. raise the possibility that their observed effects o f femoral 3- in- l blockade are i n part due to systemic action o f lidocaine. A similar hypothesis cannot easily be projected for the ropivacaine used i n this study's 3- in- l block, however, as no additional analgesic effect o f this intervention was observed. O n the other hand, the possibility remains that the ropivacaine injected for the intra-articular instillations (30 m l o f a 0.2% solution) exerted a systemic action, although the corresponding plasma concentrations remain unknown. II.4.1 Summary and conclusions In a randomized controlled trial, a femoral 3- in- l block with ropivacaine 0.2% had no significant effect on postoperative analgesic consumption, V A S pain scores, vital signs, or adverse events i n patients undergoing A C L R under general anesthesia, compared to intra-articular instillation with ropivacaine 0.2% alone. The data do not support the routine addition o f a preincisional femoral 3- in- l block with ropivacaine 0.2% to the standard anesthetic management o f these patients. However, this study provides further evidence S. S C H W A R Z 120 that intra-articular local anesthetic instillation o f the knee is effective for postoperative pain control and supports the routine use o f this intervention as standard o f care. Pain control and prevention o f adverse events following A C L R remain issues o f clinical and pharmacoeconomical significance, and future studies wi l l aid to further improve the management o f these patients (cf. page 122). S. S C H W A R Z 121 O v e r a l l C o n c l u s i o n a n d C l o s i n g R e m a r k s This thesis was dedicated to the study o f specific questions about the pharmacology & therapeutics o f local anesthetics. W i t h a focus on the analgesic properties o f this group o f agents, the investigations combined research on cellular pharmacological actions and clinical therapeutic efficacy, addressing diverse aspects within the wide spectrum o f this topic. In conducting the research, an attempt was made to apply the same high methodological standards to both components. In the first section o f the thesis, laboratory investigations examined cellular effects o f the prototype agent, lidocaine, taking advantage o f state-of-the-art experimental techniques. The experiments identified novel actions that potentially play a critical role i n its central analgesic and sedative actions as well as toxicity. The results may represent a first step toward the creation o f a basis for the future development o f new therapeutic agents based on precise knowledge o f the desired cellular effect, and not on empiricism or structural single-target specificity. The second section was dedicated to the study o f the analgesic efficacy o f ropivacaine, the most recendy introduced agent in clinical practice, using the "gold standard" for experimental design in clinical research — the R C T . While the trial demonstrated no additional analgesic effect o f ropivacaine administered for femoral 3- in- l blockade i n A C L R beyond that produced by standard intra-articular local anesthetic infiltration, the results emphasize the needs for and merits o f evidence-based practice i n anesthesiology. It is difficult to determine with certainty the global effect on S. S C H W A R Z 122 clinical practice o f an R C T following publication, and such an analysis for the trial presented here is beyond the scope o f this work. Fo r the purpose o f this thesis, however, it is noteworthy that the results o f the present study have had a significant local institutional impact i n several ways. Firstly, the reporting o f the data has dramatically changed clinical practice within the Department o f Anesthesia at U B C Hospital, which is the primary centre for arthroscopic knee surgery outside private practice i n Brit ish Columbia. Since 1998/1999, femoral 3- in- l blockade has no longer been utilized in the routine anesthetic management o f patients undergoing A C L R (personal communication). Secondly, the results and conclusions drawn from this study have led to the design and completion o f a subsequent R C T targeted to improve postoperative pain control following A C L R (Butterfield et al. 2001). In this trial, a combination o f specific pre- and postincisional local infiltrations o f the knee (bupivacaine 0.25% with epinephrine 1:200,000; 40 + 15 ml) reduced analgesic requirements by more than 57% (P - 0.008), compared to the standard intra-articular instillation alone. In addition, patients i n the treatment group fulfilled standard hospital discharge criteria on average 37 m i n earlier than those i n the control group (P < 0.05) and had a zero incidence o f postoperative adverse events, including P O N V . Thirdly, the present study was highlighted i n an extensive dissertation on the evaluation o f clinical trials using a novel Clinical Trial Evaluation System ( C T E S ; Franciosi 1998). In this dissertation, the C T E S was employed to compare six clinical trials with the use o f a scale consisting o f five categories that commonly define Good Clinical Practices S. S C H W A R Z 123 (i.e., "ethics", "design", "question", "statistics", and "standard operating procedures"), with a total o f 85 items. The study found that o f the trials tested, the present R C T reached the highest C T E S score (82/85) with regard to representing a "Best Possible Tr ia l " . These examples also serve to illustrate the vital importance o f communicating the findings o f clinical trials with "negative" results, which commonly remain unreported as a result o f publication bias (Easterbrook et al. 1991). The consequences o f such bias, often investigator-based (Dickersin and M i n 1993), are far-reaching. "Negative" studies, i n addition to their potential clinical and academic impact exemplified above, may affect our society, business, and governments (Miller and Moulder 1998). Preferential publication o f "positive" results may lead to overestimation o f the effects o f therapeutic interventions, l imit the validity o f meta-analyses and review articles, waste valuable resources, and unnecessarily expose patients to ineffective or intolerable treatments (Menger and Vo l lmar 2000). The Danish gastroenterologist, R C T expert, and co-ordinating editor o f the Cochrane Hepato-Biliary Group , Christian Gluud , addresses these issues i n a recent editorial, where he writes: "'Negative trials' are positive! They must be published and we should not refer to them as 'negative trials''''' (Gluud 1998).' Today, A C L R is routinely performed on an ambulatory basis at U B C Hospital , which is i n sharp contrast to the period before 1995/1996, when the planning phase for the femoral 3- in- l block trial presented in this dissertation was initiated. Al though there are multiple reasons for this development, there exists no doubt that it would not have been sustainable without improved anesthesia care and its underlying scientific basis. S. S C H W A R Z 124 Hence, above examples illustrate the potential impact on clinical anesthesia practice o f R C T s and clinical research i n general. Together with laboratory research, the latter wi l l continue to serve as the crucial basis for the creation o f the scientific evidence required to reach the ultimate goal: to provide the best possible care for our patients today and i n the future. S. S C H W A R Z 125 A p p e n d i x I World Medical Association Recommendations Guiding Physicians in Biomedical Research Involving Human Subjects [Declaration of Helsinki] Adopted by the 18 t h World Medical Assembly Helsinki, Finland, June 1964 and amended by the 29 t h World Medical Assembly, Tokyo, Japan, October 1975; 35 t h World Medical Assembly, Venice, Italy, October 1983; 41 s t World Medical Assembly, H o n g Kong , September 1989; and the 48 t h General Assembly, Somerset West, Republic of South Africa, October 1996 I N T R O D U C T I O N It is the mission of the physician to safeguard the health of the people. His or her knowledge and conscience are dedicated to the fulfillment of this mission. The Declaration of Geneva of the World Medical Association binds the physician with the words, "The Health o f my patient will be my first consideration," and the International Code of Medical Ethics declares that, "A physician shall act only in the patient's interest when providing medical care which might have the effect of weakening the physical and mental condition of the patient." The purpose of biomedical research involving human subjects must be to improve diagnostic, therapeutic and prophylactic procedures and the understanding of the aetiology and pathogenesis of disease. In current medical practice most diagnostic, therapeutic or prophylactic procedures involve hazards. This applies especially to biomedical research. Medical progress is based on research which ultimately must rest in part on experimentation involving human subjects. In the field of biomedical research a fundamental distinction must be recognized between medical research in which the aim is essentially diagnostic or therapeutic for a patient, and medical research, the essential object of which is purely scientific and without implying direct diagnostic or therapeutic value to the person subjected to the research. Special caution must be exercised in the conduct of research which may affect the environment, and the welfare of animals used for research must be respected. Because it is essential that the results of laboratory experiments be applied to human beings to further scientific knowledge and to help suffering humanity, the World Medical Association has prepared the following recommendations as a guide to every physician in biomedical research involving human subjects. They should be kept under review in the future. It must be stressed that the standards as drafted are only a guide to physicians all over the world. Physicians are not relieved from criminal, civil and ethical responsibilities under the laws o f their own countries. I. B A S I C P R I N C I P L E S 1. Biomedical research involving human subjects must conform to generally accepted scientific principles and should be based on adequately performed laboratory and animal experimentation and on a thorough knowledge of the scientific literature. 2. The design and performance of each experimental procedure involving human subjects should be clearly formulated in an experimental protocol which should be transmitted for consideration, comment and guidance to a specially appointed committee independent of the investigator and the sponsor -provided that this independent committee is in conformity with the laws and regulations of the country in which the research experiment is performed. 3. Biomedical research involving human subjects should be conducted only by scientifically qualified persons and under the supervision of a clinically competent medical person. The responsibility for the human subject must always rest with a medically qualified person and never rest on the subject of the research, even though the subject has given his or her consent. 4. Biomedical research involving human subjects cannot legitimately be carried out unless the importance of the objective is in proportion to the inherent risk to the subject. 5. Every biomedical research project involving human subjects should be preceded by careful assessment of predictable risks in comparison with foreseeable benefits to the subject or to others. Concern for the interests of the subject must always prevail over the interests of science and society. S. S C H W A R Z 126 6. The right of the research subject to safeguard his or her integrity must always be respected. Every precaution should be taken to respect the privacy of the subject and to minimize the impact of the study on the subject's physical and mental integrity and on the personality o f the subject. 7. Physicians should abstain from engaging in research projects involving human subjects unless they are satisfied that the hazards involved are believed to be predictable. Physicians should cease any investigation i f the hazards are found to outweigh the potential benefits. 8. In publication of the results of his or her research, the physician is obliged to preserve the accuracy of the results. Reports of experimentation not in accordance with the principles laid down in this Declaration should not be accepted for publication. 9. In any research on human beings, each potential subject must be adequately informed of the aims, methods, anticipated benefits and potential hazards of the study and the discomfort it may entail. He or she should be informed that he or she is at liberty to abstain from participation in the study and that he or she is free to withdraw his or her consent to participation at any time. The physician should then obtain the subject's freely-given informed consent, preferably in writing. 10. When obtaining informed consent for the research project the physician should be particularly cautious i f the subject is in a dependent relationship to him or her or may consent under duress. In that case the informed consent should be obtained by a physician who is not engaged in the investigation and who is completely independent of this official relationship. 11. In case of legal incompetence, informed consent should be obtained from the legal guardian in accordance with national legislation. Where physical or mental incapacity makes it impossible to obtain informed consent, or when the subject is a minor, permission from the responsible relative replaces that of the subject in accordance with national legislation. Whenever the minor child is in fact able to give a consent, the minor's consent must be obtained in addition to the consent of the minor's legal guardian. 12. The research protocol should always contain a statement of the ethical considerations involved and should indicate that the principles enunciated in the present Declaration are complied with. II. M E D I C A L R E S E A R C H C O M B I N E D W I T H P R O F E S S I O N A L C A R E (Clinical Research) 1. In the treatment of the sick person, the physician must be free to use a new diagnostic and therapeutic measure, if in his or her judgement it offers hope of saving life, reestablishing health or alleviating suffering. 2. The potential benefits, hazards and discomfort of a new method should be weighed against the advantages of the best current diagnostic and therapeutic methods. 3. In any medical study, every patient — including those of a control group, i f any - should be assured of the best proven diagnostic and therapeutic method. This does not exclude the use of inert placebo in studies where no proven diagnostic or therapeutic method exists. 4. The refusal of the patient to participate in a study must never interfere with the physician-patient relationship. 5. If the physician considers it essential not to obtain informed consent, the specific reasons for this proposal should be stated in the experimental protocol for transmission to the independent committee (I, 2). 6. The physician can combine medical research with professional care, the objective being the acquisition of new medical knowledge, only to the extent that medical research is justified by its potential diagnostic or therapeutic value for the patient. III. N O N - T H E R A P E U T I C B I O M E D I C A L R E S E A R C H I N V O L V I N G H U M A N S U B J E C T S (Non-Clinical Biomedical Research) 1. In the purely scientific application o f medical research carried out on a human being, it is the duty of the physician to remain the protector of the life and health of that person on whom biomedical research is being carried out. 2. The subject should be volunteers — cither healthy persons or patients for whom the experimental design is not related to the patient's illness. 3. The investigator or the investigating team should discontinue the research if in his/her or their judgement it may, if continued, be harmful to the individual. 4. In research on man, the interest of science and society should never take precedence over considerations related to the wcllbeing of the subject. S. S C H W A R Z 127 Appendix II PATIENT INFORMATION SHEET A N D CONSENT F O R M PATIENT INFORMATION Study Title: Femoral 3-in-l Block Combined with Local Infiltrations in Patients Undergoing Arthroscopic Cruciate Ligament Repair: A Double Blind Comparison Between Ropivacaine 2 mg/ml and Saline (0.9%) for Post-Operative Pain Relief Local Study Number: DC-ROA-0001 Study Site: Vancouver Hospital: U B C site Dear Patients: We would like to invite you to take part in a research study being conducted at this hospital. You will be given the opportunity to speak to one of our doctors or his staff and be able to ask questions that you feel are relevant. If you decide you do not want to take part in the study, this will make no difference whatsoever to the quality of treatment you will receive. If, however, you do decide to take part, then we ask you to do everything you can to follow all instructions given to you. Approximately 44 patients will be taking part in this study. The drug being tested Arthroscopic cruciate ligament repair (ACLR) is a procedure routinely used in the treatment of knee injuries at this hospital. Pain of varying intensity is normally experienced after A C L R surgery (postoperative pain). This postoperative pain is cornmonly treated with intravenous injections of strong analgesics (pain killers) such as morphine. Unfortunately, morphine is associated with unwanted effects such as nausea, itching, drowsiness or breathing problems. Another method of postoperative pain relief is to perform a local anaesthetic block (femoral 3-in-l block combined with local infiltrations into the area of your knee) to "freeze" the nerves that carry pain from the surgical area. Ropivacaine is the local anaesthetic to be used for this nerve block. Ropivacaine is a new long acting local anaesthetic which has been shown to be similar to other well known anaesthetics. Ropivacaine is not approved or marketed in Canada, however, it has been registered in Sweden, Finland, the Netherlands, and Australia since 1995. More than 2800 patients have received ropivacaine in clinical trials. From these trials there is sufficient information to show that ropivacaine is an effective local anaesthetic with few side effects. Consequently there should be no unusual risks brought about by the drug being tested should you decide to participate in this study. The purpose of this study is to test the ability of a ropivacaine femoral 3-in-l block combined with local infiltrations, as compared to placebo (an identical looking solution that has no active ingredients), to provide relief for pain following A C L R . S. S C H W A R Z 128 What will happen? Prior to the study: Within four weeks before surgery a physical examination including pulse rate and blood pressure will be performed. This would be performed whether or not you enter into the study. Your medical history will also be recorded and you will be asked to complete a discomfort questionnaire. Exclusion from the study You may be excluded from the study if you have had a previous reaction to amide local anaesthetics, acetaminophen or narcotics; are unable to comply with the study procedures or have significant alcohol, drug or medication abuse. You will not be included in the study if you are being treated regularly with analgesics, sedatives, or other central nervous system medications, or have a tendency to bleed. If you are a female in childbearing age and are pregnant or not practicing contraception, you may not be included in the study. Also, if you participated in another study in the last 14 days you are not eligible for this study. During the study: Surgery: Your operation will take place according to normal hospital procedures and will only differ from this routine as follows: once you have been put to sleep under general anaesthesia and before starting surgery, the anaesthetist will insert a needle into your groin region and inject the study drug into the area about the femoral nerve (femoral 3-in-l block). This injection will contain either ropivacaine or a saline solution (placebo). Neither you nor your doctor will know which treatment you are receiving. According to normal hospital routine, local anaesthetic will be injected into the knee joint space after the surgery. Following this procedure, you will receive a further injection of either ropivacaine or saline placebo in your knee area where the staples have been inserted and where the tendon has been cut. These procedures are all done under general anaesthesia. After surgery: You will be assessed according to hospital procedures, only more frequently for measurement of your pulse rate and blood pressure. We also would like to kindly ask you to verbally assess the amount of pain you are experiencing, the quality of pain management you are receiving and to tell us if you experience any side effects, e.g. nausea, itching. These assessments will be done regularly during the first 24 hours after the surgery is completed. Prior to surgery and for the first three days following surgery you will be asked to complete a discomfort questionnaire. For the first week following surgery we would like you to keep track of the pain you are experiencing and medication you are taking in a diary. We will also ask you to indicate your satisfaction with the pain treatment at 24 hours and one week after the surgery. Postoperative medication: If the pain relief is not sufficient during the first 24 hours after surgery, you will be given oral Tylenol 3 (acetaminophen with codeine). If this medication is still not sufficient, you will be given intravenous morphine through a patient controlled analgesia device. The morphine will be delivered directly into your vein when you press a button. S. S C H W A R Z 130 Study Title: CONSENT F O R M Femoral 3-in-l Block Combined with Local Infiltrations in Patients Undergoing Arthroscopic Cruciate Ligament Repair: A Double Blind Comparison Between Ropivacaine 2 mg/ml and Saline (0.9%) for Post-operative Pain Relief. Local Study Number: DC-ROA-0001 Study Site: Vancouver Hospital - U B C site I, (Name, b l o c k letters) have read the attached explanation, have discussed the study it concerns with Dr. (Name, b l o c k letters) and understand what the study involves. a) I am willing to participate in the study. Signed Date Witness Date ( S i g n a t u r e ) (Name, block letters) (Telephone number) I, (Name o f i n v e s t i g a t o r , block letters) have explained the nature of the study to: (Name, b l o c k letters) Signed ( I n v e s t i g a t o r ' s s i g n a t u r e ) Date S. S C H W A R Z 131 Appendix III Aldrete scoring system of criteria for discharge from PACU (Aldrete and K r o u l i k 1970) The following parameters were recorded every 15 minutes after arrival at the P A C U . Patients were deemed ready for discharge when a total score o f > 9 was reached. 1. Respiration 2 = A b l e to breath and cough freely 1 = Dyspnea or limited breathing 0 = Apnea 2. Circulation 2 = Systolic B l o o d Pressure + 20% o f pre-anesthetic level 1 = Systolic B l o o d Pressure ± 21 - 49% o f pre-anesthetic level 0 = Systolic B l o o d Pressure ± 50% of pre-anesthetic level 3. Skin colour 2 = P ink 1 = Pale, dusky, blotchy, other 0 = Cyanotic 4. Consciousness 2 = Fully awake 1 = Arousal on calling 0 = N o t responding 5. Nausea 2 = N o n e 1 = Present, but responding to treatment 0 = Severe, i.e., not responding to treatment 6. Pain (in surgical area) 2 = N o n e 1 = Present (adequate ongoing pain treatment) 0 = Severe (morphine on request) S. S C H W A R Z 132 Abbreviations A ampere; SI base unit for electric current (!) A C h acetylcholine A C L R arthroscopic anterior cruciate ligament reconstruction A C S F artificial cerebrospinal fluid A / D analog-to-digital A H P afterhyperpolarization A N O V A analysis o f variance A P action potential A S A American Society o f Anesthesiologists A T P adenosine-5'-triphosphate B K (channels) large ("big")-conductance Ca 2 + -activated K + (channels) C electric capacitance; unit F a input capacitance C a 2 + ionized calcium [Ca*+]i intracellular calcium concentration c A M P cyclic 3',5'-adenosine-monophosphate c G M P cyclic 3',5'-guanosine-monophosphate C I confidence interval C I C R Ca 2 + - induced C a 2 + release C I H R Canadian Institutes o f Health Research S. S C H W A R Z 133 C N S central nervous system d mathematical symbol for differential A mathematical symbol for difference D C direct current D I C - I R differential interference contrast infrared videomicroscopy D / A digital-to-analog D B P diastolic blood pressure D R G dorsal root ganglion e ~2,7182818; base o f the Eogarithmus naturalis E equilibrium potential (also reversal potential or Nernst potential) Ea equilibrium potential for CI E A A excitatory amino acid (e.g., glutamate, aspartate) EC50 concentration o f a drug that produces a half-maximal response E E G electroencephalogram E G T A ethylene glycol-bis(p-arninoethyl e the r ) -N,N,N ' ,N ' -tetraacetic acid E P S P excitatory postsynaptic potential f M R I functional magnetic resonance imaging F farad; unit for capacitance (C; m 2 • kg _ 1 • s - 4 • A 2 ) f A H P fast afterhyperpolarization g gram; SI base unit for weight ' g conductance; unit S S. S C H W A R Z 134 G giga; 109 Gi input conductance G i a (protein) inhibitory guanosine-5'-triphosphate-binding protein (a subunit) G A B A y-aminobutyric acid G T P guanosine-5'-triphosphate h hour; unit for time H E P E S N-[2-hydroxyethyl]piperazine-N'-[2-ethanesulfonic acid] H V A high voltage-activated H z hertz; unit for frequency (s - 1 ) I current; unit A IAI-IP (apamin-sensitive) afterhyperpolarization-generating current Jh hyperpolarization-activated mixed cationic current; also J q ("queer current") or If ("funny current") (of. Pape 1996) IIR inwardly rectifying ( K + ) current ik(Ca) C a 2 + dependent K + current Jm membrane current /NaP persistent N a + current; cf. (Grill 1996) /NaT transient N a + current IT l ow threshold ("transient"/"tiny") C a 2 + current; also "T-type C a 2 + current" (of. Huguenard 1996) I M intramusculardy) IPSP inhibitory postsynaptic potential I V intravenous (ly) S. S C H W A R Z 135 K+ 1 L G N L V A L T S m M M W M G B ( v ) m o l m i n M W n n N A N a + N I H N K N M D A ionized potassium liter; unit for volume lateral geniculate nucleus (visual thalamus) low voltage-activated low threshold spike mil l i ; 10~ 3; also meter; SI basis unit for length molar; m o l • 1 _ 1; unit for molarity (concentration o f a chemical substance; see mol); also: mega; 10 6 molecular weight (ventral partition o f the) medial geniculate body (auditory thalamus) mole; SI basis unit for the quantity o f a chemical substance (1 m o l = 6.02214 • 10 2 3 molecules) minute; unit for time micro; 10~ 6 molecular weight; unit g / m o l nano; 10" 9 sample size numerical aperture ionized sodium (U.S.) National Institutes o f Health neurokinin N-methyl-D-aspartate S: S C H W A R Z 136 N S A I D s non-steroidal anti-inflammatory drugs Q. ohm; unit for electric resistance (R) O s m O s m o l • l " 1 ; unit for osmolarity; quantity o f molecules i n 1 1 solution expressed i n m o l p piko; 10~ 1 2 P postnatal day (e.g., P2 = postnatal day two) P probability value; level o f statistical significance P A C U postanesthesia care unit P C A patient-controlled analgesia P E T positron emission tomography P G E 2 prostaglandin E 2 p H hydrogen ion concentration; —log [H + ] p K a dissociation constant; p H — log ([base]/[cation]) P S P postsynaptic potential R electric resistance; unit Q r 2 "r squared"; coefficient o f determination R 2 - measure o f goodness o f fit; fraction o f the total variance ofy that is explained by a model (equation) Rei electrode resistance Ri input resistance r C B F regional cerebral b lood flow R C T randomized controlled trial R E M rapid eye movement S. S C H W A R Z 137 s second; SI base unit for time S Siemens; unit for electric conductance (g); reciprocal value o f electric resistance; 1 S = 1 Q - 1 s A H P slow afterhyperpolarization; SI primary somatosensory cortex SII secondary somatosensory cortex S B P systolic blood pressure S D standard deviation S E M standard error o f the mean S K (channels) small-conductance Ca 2 + -activated K + (channels) t time; units s, min, h Xm membrane time constant; unit s; time required for AVm to reach (1 - 1/e) (~ 63.21%) o f its steady-state value as described by AVm (t) = Aim Ri (1 -T E A telraethylammonium; K + channel blocker T T X tetrodotoxin; poison o f the Japanese puffer fish, Sphaeroides rubripes; specific N a + channel blocker V volt; unit for electric potential (V) V voltage; electric potential; unit V V A S visual analog scale Vm membrane potential; unit V Vt resting membrane potential; unit V V B ventrobasal complex o f the thalamus S. S C H W A R Z 138 Nucleus ventralis posterolateralis thalami; ventral posterior lateral thalamic nucleus Nucleus ventralis posteromedialis thalami; ventral posterior medial thalamic nucleus wide-dynamic-range (neuron) S. S C H W A R Z 139 B i b l i o g r a p h y Agarwal R, Gutlove D P , Lockhart C H : Seizures occurring i n pediatric patients receiving continuous infusion o f bupivacaine. Anesth Analg 1992, 75: 284—286. Aguilar JS, Criado M , D e Robertis E : Inhibition by local anesthetics, phentolamine and propranolol o f [3H]quinuclydinyl benzylate binding to central muscarinic receptors. Eur J Pharmacol 1980, 68: 317-326. Akaike N , Takahashi K : Tetrodotoxin-sensitive calcium-conducting channels i n the rat hippocampal C A 1 region. / Physiol 1992, 450: 529-546. Al -Chaer E D , Lawland N B , Westlund K N , Will is W D : Visceral nociceptive input into the ventral posterolateral nucleus o f the thalamus: a new function for the dorsal column pathway. ] Neurophysiol 1996, 76: 2661-2674. Albe-Fessard D , Berkley K J , Kruger L , Ralston HJ I , Wil l is W D : Diencephalic mechanisms o f pain sensation (Review). Brain Res Rev 1985, 9: 217—296. Aldrete J A , K r o u l i k D : A postanesthetic recovery score. Anesth Analg 1970, 49: 924—934. A m a n z i o M , Po l io A , Maggi G , Benedetti F: Response variability to analgesics: a role for non-specific activation o f endogenous opioids. Pain 2001, 90: 205—215. American Society o f Anesthesiologists: N e w classification o f physical status. Anesthesiology 1963, 24: 111. Anderson K - E , Eds t rom A : Effects o f nerve blocking agents on fast axonal transport o f proteins i n frog sciatic nerves i n vitro. Brain Res 1973, 50: 125—134. Ange l A , LeBeau F: A comparison o f the effects o f propofol with other anaesthetic agents on the centripetal transmission o f sensory information. Gen Pharmacol 1992, 23: 945-963. Apkar ian A V , Shi T: Squirrel monkey lateral thalamus. I. Somatic nociresponsive neurons and their relation to spinothalamic terminals. / Neurosci 1994, 14: 6779-6795. Apkar ian A V , Shi T , Briiggemann J , Airapetian L R : Segregation o f nociceptive and non-nociceptive networks i n the squirrel monkey somatosensory thalamus. / Neurophysiol 2000, 84: 484-494. A p s C , Reynolds F : The effect o f concentration on vasoactivity o f bupivacaine and lignocaine. Br JAnaesth 1976, 48: 1171-1174. S. S C H W A R Z 140 Arias H R : Role o f local anesthetics on both cholinergic and serotonergic ionotropic receptors. Neurosci Biobehav Rep 1999, 23: 817-843. Arner S, L i n d b l o m U , Meyerson B A , Molander C: Prolonged relief o f neuralgia after regional anesthetic blocks. A call for further experimental and systematic clinical studies. Pain 1990, 43: 287-297. Arnsdo r f M F , Bigger JT: Effect o f lidocaine hydrochloride on membrane conductance i n mammalian cardiac Purkinje fibers. / Clin Invest 1972, 51: 2252-2263. Ashburn M A , Staats PS: Management o f chronic pain (Review). Lancet 1999, 353: 1865-1869. Astrup J , Sorensen P M , Sorensen H R : Inhibition o f cerebral oxygen and glucose consumption i n the dog by hypothermia, pentobarbital, and lidocaine. Anesthesiology 1981, 55: 263-268. Auge W K , Gr i f f in J : A C L reconstruction performed under 3- in- l nerve block: results utilizing newer generation techniques (Abstract). Arthroscopy Association of North America 19th Annual Meeting, M i a m i Beach, F L , U S A ; A p r i l 13-16, 2000. A u r o y Y , Narch i P , Messiah A , Li t t L , Rouvier B , Samii K : Serious complications related to regional anesthesia: results o f a prospective survey in France. Anesthesiology 1997, 87: 479-486. Aus t in K L , Stapleton J V , Mather L E : Multiple intramuscular injections: a major source o f variability i n analgesic response to meperidine. Pain 1980, 8: 47—62. Bach F W , Jensen T S , Kastrup J , Stigsby B , Dejgard A : The effect o f intravenous lidocaine on nociceptive processing in diabetic neuropathy. Pain 1990, 40: 29—34. Bader A M , Datta S, Flanagan H , Covino B G : Comparison o f bupivacaine- and ropivacaine-induced conduction blockade i n the isolated rabbit vagus nerve. Anesth Analg 1989, 68: 724-727. Bainton C R , Strichartz G R : Concentration dependence o f lidocaine-induced irreversible conduction loss in frog nerve. Anesthesiology 1994, 81: 657--667'. B a l T , M c C o r m i c k D A : What stops synchronized thalamocortical oscillations? Neuron 1996,17: 297-308. Barish M E , Baud C: A voltage-gated hydrogen ion current in the oocyte membrane o f the axo lo t l Ambystoma. / Physiol 1984, 352: 243-263. Barker J L , Levitan H : Salicylate: effect on membrane permeability o f molluscan neurons. Science 1971, 172: 1245-1247. S. S C H W A R Z 141 Bartlett E E , Hutaserani O : Xylocaine for the relief o f postoperative pain. Anesth Analg 1961, 40: 296-304. Belousov A B , Godfraind J M , Krnjevic K : Internal C a 2 + stores involved in anoxic responses o f rat hippocampal neurons. / Physiol 1995, 486: 547—456. Benkwitz C, Garr ison J C , Figler H , Hol lmann M W , Durieux M E : Lidocaine directly activates Goti (Abstract). Anesth Analg 2001, 92: S289. • Bernhard C G , B o h m E : Loca l Anaesthetics as Anticonvulsants: A Study on Experimental and Clinical Epilepsy. Almqvis t & Wiksell , Stockholm 1965. Berry C A , Sanner J H , Keasling H H : A comparison o f the anticonvulsant activity o f mepivacaine and lidocaine. / Pharmacol Exp Ther 1961, 133: 357—363. Biella G , Lacerenza M , Marchettini P , Sotgiu M L : Diverse modulation by systemic lidocaine o f iontophoretic N M D A and quisqualic acid induced excitations on rat dorsal horn neurons. Neurosci Lett 1993, 157: 207-210. Biella G , Meis S, Pape H C : Modulat ion o f a Ca 2 + -dependent K + - cu r ren t by intracellular c A M P i n rat thalamocortical relay neurons. Thalamus & Related Systems 2001, 1: 157—167. Biella G , Sotgiu M L : Central effects o f systemic lidocaine mediated by glycine spinal receptors: an iontophoretic study in the rat spinal cord. Brain Res 1993, 603: 201—206. Bigger J T , Hoffman B F : Antiarrhythmic drugs. In: G o o d m a n and Gilman's The Pharmacological Basis of Therapeutics, 35; Eighth Edi t ion; ed. by G o o d m a n G i l m a n A , Rai l T W , Nies A S , Taylor P ; Pergamon Press, N e w Y o r k 1990: 840-873. Blair M R : Cardiovascular pharmacology o f local anaesthetics. Br] Anaesth 1975, 47 suppl: 247-252. Blanton M G , L o Turco JJ, Kriegstein A R : Whole cell recording from neurons in slices o f reptilian and mammalian cerebral cortex. / Neurosci Methods 1989, 30: 203-210. Boas R A , Covino B G , Shahnarian A : Analgesic responses to i.v. lignocaine. Br J Anaesth 1982, 54: 501-505. Bonhomme V , Fiset P , Meuret P , Backman S, Plourde G , Paus T , Bushnell M C , Evans A C : Propofo l anesthesia and cerebral b lood flow changes elicited by vibrotactile stimulation: a positron emission tomography study. J Neurophysiol 2001, 85: 1299-1308. Bonica JJ: Pain research and therapy: Past and current status and future needs. In: Pain, Discomfor t and Humanitarian Care; ed. by N g L K W , Bonica JJ; E l sev i e r /Nor th Hol land, Amsterdam 1980: 1-46. S. S C H W A R Z 142 Bonica JJ: The Management o f Pain. 2nd Edi t ion; Lea & Febiger, Philadelphia 1990. B o r g T , M o d i g J : Potential anti-thrombotic effects o f local anaesthetics due to their inhibit ion o f platelet aggregation. Acta Anaesthesiol Scand 1985, 29: 739-742. Borgeat A , Perschak H , B i r d P , Hodler J , Gerber C: Patient-controlled interscalene analgesia with ropivacaine 0.2% versus patient-controlled intravenous analgesia after major shoulder surgery: effects on diaphragmatic and respiratory function. Anesthesiology 2000, 92: 102-108. Braga P C , Biella G , Tiengo M , Guidobono F , Pecile A , Fraschini F: Comparative study on the electrophysiological responses at thalamic level to different analgesic peptides. Int J Tissue React 1985, 7: 85-91. Brandsson S, Rydgren B , Hedner T , Eriksson B I , L u n d i n O , Sward L , Kar lsson J : Postoperative analgesic effects o f an external cooling system and intra-articular bupivacaine/morphine after arthroscopic cruciate ligament surgery. Knee Surg Sport Traumatol Arthrosc 1996, 4: 200-205. Brandt L , Brautigam K H , Goer ig M , Nemes C , Nol te H : Illustrierte Geschichte der Anasthesie. Wissenschaftliche Verlagsgesellschaft m b H Stuttgart, Stuttgart 1997. Bridenbaugh P O : The lower extremity: somatic blockade. In: Neural Blockade i n Clinical Anesthesia and Management o f Pain, Chapter 11; Second Edi t ion; ed. by Cousins M J , Bridenbaugh P O ; J . B . Lippincot t Company, Philadelphia 1988: 417-441. Bridenbaugh P O , Crews J C : Perioperative management o f patients for neural blockade. In: Neura l Blockade i n Chnical Anesthesia and Management o f Pain, Chapter 6; Th i rd Edi t ion ; ed. by Cousins M J , Bridenbaugh P O ; Lippincott-Raven, Philadelphia 1998: 179— 199. Brose W G , Cousins M J : Subcutaneous lidocaine for treatment o f neuropathic cancer pain. Pain 1991, 45: 145-148. B r o w n D W , Curry C M , Ruterbories L M , Avery F L , A n s o n PS: Evaluation o f pain after arthroscopically assisted anterior cruciate ligament reconstruction. Am J Sports Med 1997, 25: 182-186. Brunton J , Charpak S: u,-Opioid peptides inhibit thalamic neurons. / Neurosci 1998, 18: 1671-1678. Budde T , Sieg F , Braunewell K H , Gundelfinger E D , Pape H C : Ca 2 + - induced C a 2 + release supports the relay mode o f activity in thalamocortical cells. Neuron 2000, 26: 483-492. Burke M : Intravenous lignocaine for migraine headache. Aust Fam Physician 1989, 18: 1559. S. S C H W A R Z 143 Bur ton H , Jones E G : The posterior thalamic region and its cortical projection i n N e w W o r l d and O l d W o r l d monkeys. / Comp Neurol197'6, 168: 249-301. Butterfield N N , Schwarz S K W , Franciosi L G , Ries C R , Day B , M a c L e o d B A : Combined pre- and postsurgical bupivacaine wound infiltrations decrease opioid requirements after knee ligament reconstruction. Can J Anesth 2001, 48: 245-250. Butterworth J F , Strichartz G R : Molecular mechanisms o f local anesthesia: a review. Anesthesiology 1990, 72: 711-734. Butterworth J , Cole L , Mar low G : Inhibition o f brain cell excitability by lidocaine, Q X 3 1 4 , and tetrodotoxin: a mechanism for analgesia from infused local anesthetics? Acta AnaesthesiolScand 1993, 37: 516-523. Canavero S, Bonicalz i V : The neurochemistry o f central pain: evidence from clinical studies, hypothesis and therapeutic implications (Review). Pain 1998, 74: 109-114. Capek R, Esp l in B : Effects o f lidocaine on hippocampal pyramidal cells: depression o f repetitive firing. NeuroReport 1994, 5: 681-684. Carlsson K H , M o n z e l W , Jurna I: Depression by morphine and the non-opioid analgesic agents, metamizol (dipyrone), lysine acetylsalicylate, and paracetamol, o f activity i n rat thalamus neurones evoked by electrical stimulation o f nociceptive afferents. Pain 1988, 32: 313-326. Casey K L , M o r r o w TJ : Ventral posterior thalamic neurons differentially responsive to noxious stimulation o f the awake monkey. Science 1983, 221: 675-677. Cashman J N : The mechanisms o f action o f N S A I D s in analgesia (Review). Drugs 1996, 52 Suppl 5: 13-23. Cassuto J , Wal l in G , Hogstrom S, Faxen A , Rimback G : Inhibition o f postoperative pain by continuous low-dose intravenous infusion o f lidocaine. Anesth Analg 1985, 64: 971— 974. Catterall W A : C o m m o n modes o f drug action on N a + channels: local anesthetics, antiarrhythmics and anticonvulsants (Review). Trends Pharmacol Sci 1987', 8: 57-65. Catterall W A : Structure and function o f voltage gated ion channels (Review). Annu Rev Biochem 1995, 64: 493-531. C C A C : Guide to the Care and Use o f Experimental Animals . Vo lume I; ed. by Olfert E D , Cross B M , M c W i l l i a m A A ; Canadian Counci l on A n i m a l Care, Ottawa 1993. S. S C H W A R Z 144 Cepeda M S , Vargas L , Ortegon G , Sanchez M A , Carr D B : Comparative analgesic efficacy o f patient-controlled analgesia with ketorolac versus morphine after elective intraabdominal operations. Anesth Analg 1995, 80: 1150-1153. Chabal C , Jacobson L , Mariano A , Chaney E , Britell C W : The use o f oral mexiletine for the treatment o f pain after peripheral nerve injury. Anesthesiology 1992, 76: 513—517. Chapman R A , Leoty C: The effects o f tetracaine on the membrane currents and contraction o f frog atrial muscle. / Physiol 1981, 317: 475-486. Chen J , Adach i N , L i u K , Nagaro T, A r a i T: Improvement o f ischemic damage i n gerbil hippocampal neurons by procaine. Brain Res 1998, 792: 16—23. Cl i i rwa SS, M a c L e o d B A , Day B : Intraarticular bupivacaine (Marcaine) after arthroscopic meniscectomy: a randomized double-blind controlled study. Arthroscopy 1989, 5: 33—35. C h o i D W : Excitotoxic cell death. ] Neurobiol 1992, 23: 1261-1276. Chudler E H , Bonica JJ: Supraspinal mechanisms o f pain and nociception. In: Bonica's Management o f Pain, Chapter 5; Th i rd Edi t ion; ed. by Loeser J D ; Lippincot t Williams & Wilk ins , Philadelphia 2001: 153-179. Chung J M , Lee K H , Surmeier D J , Sorkin L S , K i m J , Wil l is W D : Response characteristics o f neurons in the ventral posterior lateral nucleus o f the monkey thalamus. J Neurophysiol 1986, 56: 370-390. Chvapi l M , Hameroff SR, O 'Dea K , Peacock E E : Loca l anesthetics and wound healing. / SurgRns 1979, 27: 367-371. Coad N R : Post-operative analgesia following femoral-neck surgery—a comparison between 3 i n 1 femoral nerve block and lateral cutaneous nerve block. Eur J Anaesthesiol 1991, 8: 287-290. C o h n B T , Draeger R I , Jackson D W : The effects o f cold therapy i n the postoperative management o f pain i n patients undergoing anterior cruciate ligament reconstruction. Am J Sports MedT989,17: 344-349. Connors B W , Prince D A : Effects o f local anesthetic Q X - 3 1 4 on the membrane properties o f hippocampal pyramidal neurons. / Pharmacol Exp Ther 1982, 220: 476—481. Constant! A , Galvan M : Fast inward-rectifying current accounts for anomalous rectification i n olfactory cortex neurones. / Physiol 1983, 335: 153—178. Coulter D A , Huguenard JR , Prince D A : Calcium currents in rat thalamocortical relay neurones: kinetic properties o f the transient, low-threshold current. / Physiol 1989, 414: 587-604. S. S C H W A R Z 145 Courteix C, Bardin M , Chantelauze C, Lavarenne J , Eschalier A : Study o f the sensitivity o f the diabetes-induced pain model in rats to a range o f analgesics. Pain 1994, 57: 153— 160. Cov ino B G : Toxici ty and systemic effects o f local anesthetic agents. In: Handbook o f Experimental Pharmacology, V o l . 81: Loca l Anesthetics, Chapter 6; ed. by Strichartz G R ; Springer-Verlag, Berl in 1987: 187-212. Craviso G L , Musacchio J M : Competitive inhibition o f stereospecific opiate binding by local anesthetics i n mouse brain. Life Sci 1975, 16: 1803—1808. Cribbs L L , Lee J H , Yang J , Satin J , Zhang Y , Daud A , Barclay J , Wil l iamson M P , F o x M , Rees M , Perez-Reyes E : Cloning and characterization o f a l H from human heart, a member o f the T-type C a 2 + channel gene family. CircRes 1998, 83: 103-109. C r i l l W E : Persistent sodium current in mammalian central neurons (Review). Annu Rev Physiol 1996, 58: 349-362. Crunell i V , Haby M , Jassik-Gerschenfeld D , Leresche N , Pirchio M : C F - and I n -dependent inhibitory postsynaptic potentials evoked by interneurones o f the rat lateral geniculate nucleus. ] Physiol 1988, 399: 153-176. Cul len B F , Haschke R H : Loca l anesthetic inhibition o f phagocytosis and metabolism o f human leukocytes. Anesthesiology 1974, 40: 142—146. Curry C M , B r o w n D L , Ruterbories L , Raessler K L : Localization o f pain following arthroscopic anterior cruciate ligament repair using differential local anesthetic infiltration [Abstract]. Anesth Analg 1996, 82: D 'Ange lo R, James R L : Is ropivacaine less potent than bupivacaine? Anesthesiology 1999, 90:941-943. D a h l J B , Christiansen C L , Daugaard JJ, Schultz P , Carlsson P: Continuous blockade o f the lumbar plexus after knee surgery— postoperative analgesia and bupivacaine plasma concentrations. A controlled clinical trial. Anaesthesia 1988, 43: 1015-1018. Das K C , Misra H P : Lidocaine: a hydroxyl radical scavenger and singlet oxygen quencher. Mol Cell Biochem 1992, 115: 179-185. de Jong R H : L o c a l Anesthetics. Mosby, St. Louis 1994. de Jong R H , de Rosa R, B o n i n J D , Gamble C: Cerebral and circulatory effects o f high dose bupivacaine and etidocaine. Anesthesiology 1980, 535: S224. Debarbieux F , Brunton J , Charpak S: Effect o f bicuculline on thalamic activity: a direct blockade o f IAHP i n reticularis neurons. / Neurophysiol 1998, 79: 2911-2918. S. S C H W A R Z 146 deCharms R C , Merzenich M M : Primary cortical representation o f sounds by the coordination o f action-potential timing. Nature 1996, 381: 610-613. Dejgard A , Petersen P , Kastrup J : Mexiletine for treatment o f chronic painful diabetic neuropathy. Lancet 1988, 1: 9-11. den Hartigh J , Hilders C G , Schoemaker R C , Hu l sho f J H , Cohen A F , Vermerj P: Tinnitus suppression by intravenous lidocaine in relation to its plasma concentration. Clin Pharmacol Ther 1993, 54: 415-420. Den t i M , Randelli P , Bigoni M , Vitale G , Marino M R , Fraschini N : Pre- and postoperative intra-articular analgesia for arthroscopic surgery o f the knee and arthroscopy-assisted anterior cruciate ligament reconstruction. A double-blind randomized, prospective study. Knee Surg Sport Lraumatol Arthrosc 1997', 5: 206—212. Desbois C , Villanueva L : The organization o f lateral ventromedial thalamic connections i n the rat: a l ink for the distribution o f nociceptive signals to widespread cortical regions. Neuroscience 2001, 102: 885-898. Deschenes M , Paradis M , Roy JP , Steriade M : Electrophysiology o f neurons o f lateral thalamic nuclei in cat: resting properties and burst discharges. / Neurophysiol 1984, 51: 1196-1219. i Destexhe A , Neubig M , U l r i ch D , Huguenard J : Dendritic low-threshold calcium currents i n thalamic relay cells. / Neurosci 1998, 18: 3574-3588. Detsch O , Vah le -Hinz C, Kochs E , Siemers M , B r o m m B : Isoflurane induces dose-dependent changes o f thalamic somatosensory information transfer. Brain Res 1999, 829: 77-89. Dejerine J , Roussy G : L e syndrome thalamique. Rev Neurol (Paris) 1906, 14: 521—532. D i Piero V , Jones A K , Iannotti F , Powel l M , Perani D , L e n z i G L , Frackowiak RS: Chronic pain: a P E T study o f the central effects o f percutaneous high cervical cordotomy. Pain 1991, 46: 9-12. Dibner-Dunlap M E , Cohen M D , Y u i h S N , Thames M D : Procainamide inhibits sympathetic nerve activity i n rabbits. J Lab Clin Med 1992, 119: 211-215. Dickers in K , M i n Y I : Publication bias: the problem that won't go away. Ann N Y Acad Sci 1993, 703: 135-146. Di rks J , Fabricius P , Petersen K L , Rowbotham M C , D a h l J B : The effect o f systemic lidocaine on pain and secondary hyperalgesia associated with the heat/capsaicin sensitization model i n healthy volunteers. Anesth Analg 2000, 91: 967-972. S. S C H W A R Z 147 D o d t H U , Zieglgansberger W : Infrared videomicroscopy: a new look at neuronal structure and function. Trends Neurosci 199'4, 17: 453-458. Duggan A W , McLennan H : Bicuculline and inhibition i n the thalamus. Brain Res 1971, 25: 188-191. Easterbrook PJ , Berl in J A , Gopalan R, Matthews D R : Publication bias in clinical research. Lancet 1991, 337: 867-872. E c h t D S , Black J N , Barbey JT , Coxe D R , Cato E : Evaluation o f antiarrhythmic drugs on defibrillation energy requirements i n dogs. Sodium channel block and action potential prolongation. Circulation 1989, 79: 1106-1117. Eddleston J M , Ho l l and JJ, Gr i f f in R P , Corbett A , Horsman E L , Reynolds F : A double-bl ind comparison o f 0.25% ropivacaine and 0.25% bupivacaine for extradural analgesia i n labour. Br JAnaesth 1996, 76: 66-71. E d k i n B S , Spindler K P , Flanagan J F : Femoral nerve block as an alternative to parenteral narcotics for pain control after anterior cruciate ligament reconstruction. Arthroscopy 1995, 11: 404-409. Edmondson E A , Simpson R K , Stubler D K , Beric A : Systemic lidocaine therapy for poststroke pain. South Med J 1993, 86: 1093-1096. Edwards D J , Rimmer M , Keene G C : The use o f cold therapy i n the postoperative management o f patients undergoing arthroscopic anterior cruciate ligament reconstruct ion. .^? / Sports Med 1996, 24: 193-195. Ekenstam B A F , Egner B , Pettersson G : N-a lky l p y r r o l i d i n e and N-a lky l piperidine carboxylic acid amides. Acta Chem Scand 1957, 11: 1183. El-Beheiry H , Pu i l E : Unusual features o f G A B A responses i n layers IV—V neurons o f neocortex. Neurosci Lett 1990,119: 83-85. El l io t t A M , Smith B H , Penny K I , Smith W C , Chambers W A : The epidemiology o f chronic pain i n the community. Lancet 1999, 354: 1248-1252. E n d o M : Calc ium release from the sarcoplasmic reticulum. Physiol Rev 1977, 57: 71—108. Er iksson A S , Sinclair R, Cassuto J , Thomsen P: Influence o f lidocaine on leukocyte function i n the surgical wound. Anesthesiology 1992, 77: 74—78. Er iksson E , Persson A : The effect o f intravenously administered prilocaine and lidocaine on the human electroencephalogram studied by automatic frequency analysis. Acta Chir Scand (Suppl) 1966, 358: 37-46. S. S C H W A R Z 148 Etches R C , Writer W D , Ansley D , Nydahl P A , O n g B Y , L u i A , Badner N , K a w o l s k i S, M u i r H , Shukla R, Beattie W S : Continuous epidural ropivacaine 0.2% for analgesia after lower abdominal surgery. Anesth Analg 1997, 84: 784—790. Fairhurst A S , Whittaker M L , Ehlert FJ : Interactions o f D600 (methoxyverapamil) and local anesthetics with rat brain alpha-adrenergic and muscarinic receptors. Biochem Pharmacol 1980, 29: 155-162. Fanelli G , Casati A , Beccaria P , Aldegheri G , Berti M , Tarantino F , T o r n G : A double-bl ind comparison o f ropivacaine, bupivacaine, and mepivacaine during sciatic and femoral nerve blockade. Anesth Analg 1998, 87: 597-600. Feinstein M G , Fiekers J , Fraser C: A n analysis o f the mechanism o f local anesthetic inhibit ion o f platelet aggregation and secretion. J Pharmacol Exp Ther 1976, 197: 215—228. Ferrante F M , Paggioli J , Cherukuri S, Ar thur G R : The analgesic response to intravenous lidocaine i n the treatment o f neuropathic pain. Anesth Analg 1996, 82: 91-97. Ferrington D G , Downie J W , Will is W D : Primate nucleus gracilis neurons: responses to innocuous and noxious stimuli. J Neurophysiol 1988, 59: 886—907. Fields J Z , Roeske W R , M o r k i n E , Yamamura H I : Cardiac muscarinic cholinergic receptors. Biochemical identification and characterization. / Biol Chem 1978, 253: 3251— 3258. F i n k B R , Kennedy R D , Hendrickson A E , Middaugh M E : Lidocaine inhibit ion o f rapid axonal transport. Anesthesiology 1912, 36: 422-432. Foehring R C , Schwindt P C , Cr i l l W E : Norepinephrine selectively reduces slow C a 2 + - and Na + -mediated K + currents i n cat neocortical neurons. / Neurophysiol 1989, 61: 245—256. F o r d D J , Pither C , Raj P P : Comparison o f insulated and uninsulated needles for locating peripheral nerves with a peripheral nerve stimulator. Anesth Analg 1984, 63: 925-928. Forsythe I D : Direct patch recording from identified presynaptic terminals mediating glutamatergic E P S C s i n the rat C N S , in vitro. ] Physiol 1994, 479: 381-387. Fournier R, V a n Gessel E , Gaggero G , Boccov i S, Forster A , Gamul in Z : Postoperative analgesia with " 3 - i n - l " femoral nerve block after prosthetic hip surgery. Can J Anaesth 1998a, 45: 34-38. Fournier R, V a n Gessel E , Gaggero G , Boccov i S, Forster A , Gamul in Z : " 3 - i n - l " femoral block - Reply (Letter). Can] Anaesth 1998b, 45: 1033. Franciosi L G : Evaluating the Quality o f Clinical Trials Us ing A Clinical Tr ia l Evaluation System (CTES) . M.Sc . Thesis, The University o f British Columbia, Vancouver 1998. S. S C H W A R Z 149 Frank G B , Sanders H D : A proposed common mechanism o f action for general and local anaesthetics i n the central nervous system. Br] Pharmacol 1963, 21: 1-9. Frel in C , Vigne P , Lazdunski M : Biochemical evidence for pharmacological similarities between alpha- ad renocep to r s and voltage-dependent N a + and C a + + channels. Biochem Biophys Res Commun 1982, 106: 967-973. Fr ied E , A m o r i m P , Chambers G , Cottrell J E , Kass IS: The importance o f sodium for anoxic transmission damage in rat hippocampal slices: mechanisms o f protection by Udocaine. J Physiol 1995, 489: 557-565. Fujitani T , Adach i N , Miyazaki H , L i u K , Nakamura Y , Kataoka K , A r a i T: Lidocaine protects hippocampal neurons against ischemic damage by preventing increase o f extracellular excitatory amino acids: a microdialysis study i n Mongol ian gerbils. Neurosci Lett1994, 179: 91-94. Galer B S , Harle J , Rowbotham M C : Response to intravenous lidocaine infusion predicts subsequent response to oral mexiletine: a prospective study. / Pain Symptom Manage 1996, 12: 161-167. G a o D , Benazzouz A , Bressand K , Piallat B , Benabid A L : Roles o f G A B A , glutamate, acetylcholine and S T N stimulation on thalamic V M in rats. NeuroReport 1997, 8: 2 6 0 1 -2605. Garfield J M , Gugino L : Central effects o f local anesthetic actions. In: Handbook o f Experimental Pharmacology, V o l . 81: Loca l Anesthetics, Chapter 8; ed. by Strichartz G R ; Springer-Verlag, Ber l in 1987: 253-284. Gautron M , Gui lbaud G : Somatic responses o f ventrobasal thalamic neurones in polyarthritic rats. Brain Res 1982, 237: 459-471. Gentry C L , Lukas RJ: Loca l anesthetics noncompetitively inhibit function o f four distinct nicotinic acetylcholine receptor subtypes. / Pharmacol Exp Ther 2001, 299: 1038-1048. Gherardini G , Samuelson U , Jernbeck J , Aberg B , Sjostrand N : Comparison o f vascular effects o f ropivacaine and lidocaine on isolated rings o f human arteries. Acta Anaesthesiol ScandT995, 39: 765-768. G l u u d C: "Negative trials" are positive! ] Hepatol 1999,, 28: 731-733. G o l d M S , Reichling D B , H a m p l K F , Drasner K , Levine J D : Lidocaine toxicity i n primary afferent neurons from the rat. / Pharmacol Exp Ther 1998, 285: 413-421. G o r d o n L M , Dipp le I, Sauerheber R D , Esgate J A , Houslay M D : The selective effects o f charged local anaesthetics on the glucagon- and fluoride-stimulated adenylate cyclase activity o f rat-liver plasma membranes. / Supramol Struct1980, 14: 21-32. S. S C H W A R Z 150 Graham J H , III, Maher JR , Robinson S E : The effect o f cocaine and other local anesthetics on central dopaminergic neurotransmission. / Pharmacol Exp Ther 1995, 274: 707-717. Granger P , B i ton B , Faure C , Vige X , Depoortere H , Graham D , Langer S Z , Scatton B , Avenet P: Modula t ion o f the gamma-aminobutyric acid type A receptor by the antiepileptic drugs carbamazepine and phenytoin. MolPharmacol 1995, 47: 1189-1196. Grant A O , Dietz M A , Gi l l i am F R , III, Starmer C F : Blockade o f cardiac sodium channels by lidocaine. Single-channel analysis. CircRes 1989, 65: 1247—1262. Gray C M , K o n i g P , Engel A K , Singer W : Oscillatory responses i n cat visual cortex exhibit inter-columnar synchronization which reflects global stimulus properties. Nature 1989, 338: 334-337. Gui lbaud G , Peschanski M , Gautron M , Binder D : Neurones responding to noxious stimulation i n V B complex and caudal adjacent regions i n the thalamus o f the rat. Pain 1980, 8: 303-318. Gui lbaud G , Benoist J M , Gautron M , Kayser V : Asp i r in clearly depresses responses o f ventrobasal thalamus neurons to joint stimuli in arthritic rats. Pain 1982, 13: 153—163. G u y o n A , Leresche N : Modulat ion by different G A B A B receptor types o f voltage-activated calcium currents in rat thalamocortical neurones. / Physiol 1995, 485: 29-42. Hallanger A E , Levey A l , Lee H J , Rye D B , Wainer B H : The origins o f cholinergic and other subcortical afferents to the thalamus in the rat. / Comp Neurol 1987, 262: 105-124. H a m i l l O P , Marty A , Neher E , Sakmann B , Sigworth FJ : Improved patch-clamp techniques for high-resolution current recording from cells and cell-free membrane patches. Pfliigers Arch 1981, 391: 85-100. Hamil ton G R , Baskett T F : Mandrake to morphine: anodynes o f antiquity. Annals RCPSC 1999, 32: 403-406. Hami l ton G R , Baskett T F : In the arms o f Morpheus: the development o f morphine for postoperative pain relief. Can J Anaesth 2000, 47: 367-374. H a n d PJ , Stark RJ: Intravenous lignocaine infusions for severe chronic daily headache. MedJAustlOOO, 172: 157-159. Harris R M , Hendrickson A E : Loca l circuit neurons in the rat ventrobasal thalamus—a G A B A irnmunocytochemical study. Neuroscience 1987, 21: 229—236. S. S C H W A R Z 151 Hassler R: Anatomy o f the thalamus. In: Einfuhrung i n die stereotaktischen Operationen, mit einem Adas des menschlichen Gehirns. Introduction to Stereotaxis, wi th an Adas o f the H u m a n Brain; ed. by Schaltenbrand G , Bailey P ; Thieme, Stuttgart 1959: 230-290. Head H , Holmes G : Sensory disturbances from cerebral lesions. Brain 1911, 34: 102—254. Heard S O , Edwards W T , Ferrari D , Hanna D , W o n g P D , L i land A , Wi l lock M M : Analgesic effect o f intraarticular bupivacaine or morphine after arthroscopic knee surgery: a randomized, prospective, double-blind study. Anesth Analg 1992, 74: 822-826. H e n n F A , Sperelakis N : Stimulative and protective action o f S r 2 + and B a 2 + on ( N a + - K + ) -ATPase from cultured heart cells. Biochim Biophys Acta 1968, 163: 415-417. Herken W , Rietbrock N : Organverteilung und Ausscheidung von Procainamid bei der Ratte i n Abhangigkeit v o m pH-Gradienten [Influence o f p H gradients on organ distribution and excretion o f procainamide in the rat]. Naunyn Schmiedebergs Arch Pharmakol1969, 264: 99-109. Hernandez-Cruz A , Pape H C : Identification o f two calcium currents i n acutely dissociated neurons from the rat lateral geniculate nucleus. ] Neurophysiol 1989, 61: 1270— 1283. Hickey R, Candido K D , Ramamurthy S, Winnie A P , Blanchard J , Raza S M , Hoffman J , Durran i Z , Masters R W : Brachial plexus block with a new local anaesthetic: 0.5 per cent ropivacaine. Can] Anaesth 1990, 37: 732-738. Hicks T P , Metherate R, Landry P , Dykes R W : Bicuculline-induced alterations o f response properties i n functionally identified ventroposterior thalamic neurones. Exp Brain Res 1986, 63: 248-264. Hi l l e B : C o m m o n mode o f action o f three agents that decrease the transient change in sodium permeability in nerves. Nature 1966, 210: 1220-1222. Hi ra i T , Jones E G : A new panellation o f the human thalamus on the basis o f histochemical staining. Brain Res Brain Res Rev 1989, 14: 1—34. Hirs t G C , Lang S A , Dust W N , Cassidy J D , Y i p R W : Femoral nerve block. Single injection versus continuous infusion for total knee arthroplasty. Reg Anesth 1996, 21: 2 9 2 -297. Ho l lmann M W , Durieux M E : Loca l anesthetics and the inflammatory response: a new therapeutic indication? (Review) Anesthesiology 2000, 93: 858-875. Ho l lmann M W , Fischer L G , Byford A M , Durieux M E : Loca l anesthetic inhibit ion o f m l muscarinic acetylcholine signaling. Anesthesiology 2000, 93: 497-509. S. S C H W A R Z 152 Hol lmann M W , Wieczorek K S , Betger A , Durieux M E : Loca l anesthetic inhibit ion o f G protein-coupled receptor signaling by interference with Goc q protein function. Mol Pharmacol 2001 a, 59: 294-301. Ho l lmann M W , Gross A , Jelacin N , Durieux M E : Loca l anesthetic effects on priming and activation o f human neutrophils. Anesthesiology 2001b, 95: 113—122. Ho l lmann M W , D i F a z i o C A , Durieux M E : Ca-signaling G-protein-coupled receptors: A new site o f local anesthetic action? (Review) Reg Anesth Pain Med 2001c, 26: 565-571. Holthusen H , Irsfeld S, Lipfert P: Effect o f pre- or post-traumatically applied i.v. lidocaine on primary and secondary hyperalgesia after experimental heat trauma i n humans. Pain 2000, 88: 295-302. Hondeghem L M , Katzung B G : Time- and voltage-dependent interactions o f antiarrhythmic drugs with cardiac sodium channels. Biochim Biophys Acta 1977, 472: 373— 398. H o o d G , Edbrooke D L , Gerrish SP: Postoperative analgesia after triple nerve block for fractured neck o f femur. Anaesthesia 1991, 46: 138-140. Ho t son J R , Prince D A , Schwartzkroin P A : Anomalous inward rectification i n hippocampal neurons. / Neurophysiol 1979, 42: 889-895. Hubbard J l , Llinas R, Quastel D M J : Electrophysiological Analysis o f Synaptic Transmission. Monographs o f the Physiological Society, Number 19. Edward A r n o l d (Publishers) L td . , L o n d o n 1969. Huguenard JR: Low-threshold calcium currents i n central nervous system neurons (Review). Annu Rev Physiol 1996, 58: 329-348. Hutcheon B , Miura R M , Pu i l E : Subthreshold membrane resonance in neocortical neurons. ] Neurophysiol 1996, 76: 683—697. Huxtable RJ : The deafness o f Beethoven: a paradigm o f hearing problems. Proc West Pharmacol Soc 2000, 43: 1-8. Ingram SL: Cellular and molecular mechanisms o f opioid action (Review). Prog Brain Res 2000, 129: 483-492. Israel J M , Connelly JS, McTigue ST, Brummett R E , B r o w n J : Lidocaine i n the treatment o f tinnitus aurium. A double-blind study. Arch Otolaryngol1982, 108: 471-473. Iwamoto E T : Characterization o f the antinociception induced by nicotine i n the pedunculopontine tegmental nucleus and the nucleus raphe magnus. / Pharmacol Exp Ther 1991, 257: 120-133. S. S C H W A R Z 153 Jahnsen H , Llinas R: Electrophysiological properties o f guinea-pig thalamic neurones: an i n vitro study. J Physiol 1984a, 349: 205-226. Jahnsen H , Llinas R: Ionic basis for the electro-responsiveness and oscillatory properties o f guinea-pig thalamic neurones i n vitro. / Physiol 1984b, 349: 227-247. Jeanmonod D , Magnin M , M o r e l A : Thalamus and neurogenic pain: physiological, anatomical and clinical data. NeuroReporf 1993, 4: 475-478. Jeanmonod D , Magnin M , M o r e l A : Low-threshold calcium spike bursts i n the human thalamus. C o m m o n physiopathology for sensory, motor and limbic positive symptoms. Brain 1996,119: 363-375. Johansson S, D r u z i n M , Haage D , Wang M D : The functional role o f a bicuculline-sensitive Ca 2 + -activated K + current in rat medial preoptic neurons. / Physiol 2001, 532: 625-635. Johns R A , D i F a z i o C A , Longnecker D E : Lidocaine constricts or dilates rat arterioles in a dose-dependent manner. Anesthesiology 1985, 62: 141—144. Johnson SW, Seutin V : Bicuculline methiodide potentiates N M D A - d e p e n d e n t burst firing i n rat dopamine neurons by blocking apamin-sensitive Ca 2 + -activated K + currents. Neurosci Lett 1997, 231: 13-16. Jones E G : The Thalamus. Plenum Press, N e w Y o r k 1985. Jones E G : A description o f the human thalamus. In: Thalamus. Vo lume II: Experimental and Clinical Aspects, Chapter 9; ed. by Steriade M , Jones E G , M c C o r m i c k D A ; Elsevier Science L td . , Oxfo rd 1997: 425^199. Joshi G P , M c C a r r o l l S M , McSwiney M , O'Rourke P , Hurson BJ : Effects o f intraarticular morphine on analgesic requirements after anterior cruciate ligament repair. Reg Anesth 1993, 18: 254-257. J u Y K , Saint D A , Gage P W : Effects o f lignocaine and quinidine on the persistent sodium current i n rat ventricular myocytes. Br J Pharmacol 1992, 107: 311—316. Kammermeier PJ , Jones SW: High-voltage-activated calcium currents i n neurons acutely isolated from the ventrobasal nucleus o f the rat thalamus. / Neurophysiol 1997', 77: 465— 475. Kana i Y , Katsuki H , Takasaki M : Graded, irreversible changes in crayfish giant axon as manifestations o f lidocaine neurotoxicity i n vitro. Anesth Analg 1998, 86: 569-573. K a n a i Y , Katsuk i H , Takasaki M : Lidocaine disrupts axonal membrane o f rat sciatic nerve i n vitro. Anesth Analg 2000, 91: 944-948. S. S C H W A R Z 154 Kana i A , H i ruma H , Katakura T, Sase S, Kawakami T, H o k a S: Low-concentration lidocaine rapidly inhibits axonal transport i n cultured mouse dorsal root ganglion neurons. Anesthesiology 2001, 95: 675—680. Kaneda M , Oyama Y , Ikemoto Y , Akaike N : Blockade o f the voltage-dependent sodium current i n isolated rat hippocampal neurons by tetrodotoxin and lidocaine. Brain Res 1989,484:348-351. K a o J T , Giangarra C E , Singer G , Mart in S: A comparison o f outpatient and inpatient anterior cruciate ligament reconstruction surgery. Arthroscopy 1995, 11: 151—156. Kar lsson J , Rydgren B , Eriksson B , Jarvholm U , L u n d i n O , Sward L , Hedner T: Postoperative analgesic effects o f intra-articular bupivacaine and morphine after arthroscopic cruciate ligament surgery. Knee Surg Sport Traumatol Arthrosc 1995, 3: 55—59. Kastrup J , Petersen P , Dejgard A , Angelo H R , Hilsted J : Intravenous lidocaine infusion— a new treatment o f chronic painful diabetic neuropathy? Vain 1987, 28: 69—75. K a t z J , Jackson M , Kavanagh B P , Sandler A N : Acute pain after thoracic surgery predicts long-term post-thoracotomy pain. Clin J Pain 1996, 12: 50-55. Kaube H , H o s k i n K L , Goadsby PJ: Lignocaine and headache: an electrophysiological study i n the cat with supporting clinical observations in man. / Neurol 1994, 241: 415— 420. Kehle t H , D a h l J B : The value o f "multimodal" or "balanced analgesia" i n postoperative pain treatment. Anesth Analg 1993, 77: 1048-1056. Kenshalo D R , Giesler G J , Leonard R B , Will is W D : Responses o f neurons i n primate ventral posterior lateral nucleus to noxious stimuli. / Neurophysiol 1980, 43: 1594—1614. Khawaled R, Bruening-Wright A , Adelman JP , Maylie J : Bicuculline block o f small-conductance calcium-activated potassium channels. Pflugers Arch 1999, 438: 314—321. K i m U , M c C o r m i c k D A : The functional influence o f burst and tonic firing mode on synaptic interactions i n the thalamus. / Neurosci 1998, 18: 9500-9516. K o f k e W A , Snider M T , Y o u n g RS, Ramer J C : Prolonged low flow isoflurane anesthesia for status epilepticus. Anesthesiology 1985, 62: 653—656. K o h r s R, Hoenemann C W , Feirer N , Durieux M E : Bupivacaine inhibits whole b lood coagulation i n vitro. Reg Anesth Pain Med 1999, 24: 326-330. K o m a i H , M c D o w e l l TS: Loca l anesthetic inhibition o f voltage-activated potassium currents i n rat dorsal root ganglion neurons. Anesthesiology 2001, 94: 1089—1095. S. S C H W A R Z 155 K o p p a n y i T: The sedative, central analgesic and anticonvulsant actions o f local anesthetics. Am ] Med Sci 1962, 144: 646-654. K o y a m a N , Hanai F , Yoko ta T: Does intravenous administration o f G A B A A receptor antagonists induce both descending antinociception and touch-evoked allodynia? Vain 1998, 76: 327-336. K u n o M , Matsuura S: Sites and mechanisms o f action o f lidocaine upon the isolated spinal cord o f the frog. Brain Res 1982, 249: 87-93. Labat G : Regional Anesthesia - Its Technic and Clinical Applicat ion. W . B . Saunders Company, Philadelphia 1922. Lambert D H , Strichartz G R : Every problem is an opportunity, or one person's poison is another person's remedy. Reg Anesth Vain Med 1998, 23: 3—6. Lambert L A , Lambert D H , Strichartz G R : Irreversible conduction block in isolated nerve by high concentrations o f local anesthetics. Anesthesiology 1994, 80: 1082—1093. Lang S A , Y i p R W , Chang P , Gerard M : The femoral 3- in- l block revisited. Can J Anaesth 1992, 39: A 6 6 . Lang S A , Y i p R W , Chang P C , Gerard M A : The femoral 3- in- l block revisited. / Clin Anesth 1993, 5: 292-296. L e Gros Clark W E : The thalamus o f Tarsius. J Anat 1930, 64: 371-414. L e N o r m a n d Y , de Dieuleveult C , Athouel A , Queinnec M C , de Vi l lepoix C, Larousse C: Pharmacokinetics o f lidocaine and bupivacaine i n retrobulbar and facial block. Fundam Clin Vharmacol 1989, 3: 95-102. Lee E , D o n o v a n K : Reactivation o f phantom limb pain after combined interscalene brachial plexus block and general anesthesia: successful treatment with intravenous lidocaine. Anesthesiology 1995, 82: 295-298. Lee J H , D a u d A N , Cribbs L L , Lacerda A E , Pereverzev A , Klockner U , Schneider T , Perez-Reyes E : Cloning and expression o f a novel member o f the low voltage-activated T-type calcium channel family. J Neurosci 1999, 19: 1912-1921. Lee K H , M c C o r m i c k D A : Abol i t ion o f spindle oscillations by serotonin and norepinephrine i n the ferret lateral geniculate and perigeniculate nuclei i n vitro. Neuron 1996,17: 309-321. Lee S M , Friedberg M H , Ebner F F : The role o f G A B A - m e d i a t e d inhibit ion i n the rat ventral posterior medial thalamus. II. Differential effects o f G A B A A and G A B A B receptor antagonists on responses o f V P M neurons. J Neurophysiol 1994, 71: 1716—1726. S. S C H W A R Z 156 Lemrnen L J , Klassen M , Duiser B : Intravenous lidocaine in the treatment o f convulsions. JAMA 1978, 239: 2025. Lenarz T , G u l z o w J , Honer loh H J , Hildenbrand H : D e r Einfluss membranwirksamer Medikamente (Antiarrhythmika) auf die akustisch-evozierten Hirnstammpotentiale ( B E R A ) . Laryngol RhinolOtol (Stuttg) 1984, 63: 92-97. Lenz F A , Dougherty P M : Pain processing in the human thalamus. In: Thalamus. Vo lume II: Experimental and Clinical Aspects, Chapter 13; ed. by Steriade M , Jones E G , M c C o r m i c k D A ; Elsevier Science Ltd . , Oxfo rd 1997: 617-651. Lenz F A , Tasker R R , Dostrovsky J O , K w a n H C , Gorecki J , Hirayama T, Murphy JT : A b n o r m a l single-unit activity recorded in the somatosensory thalamus o f a quadriplegic patient wi th central pain. Pain 1987, 31: 225-236. Lenz F A , K w a n H C , Dostrovsky J O , Tasker R R : Characteristics o f the bursting pattern o f action potentials that occurs i n the thalamus o f patients with central pain. Brain Res 1989, 496: 357-360. Lenz F A , Gracely R H , Rowland L H , Dougherty P M : A population o f cells i n the human thalamic principal sensory nucleus respond to painful mechanical stimuli. Neurosci Lett 1994a, 180: 46-50. Lenz F A , K w a n H C , Mart in R, Tasker R, Richardson R T , Dostrovsky J O : Characteristics o f somatotopic organization and spontaneous neuronal activity i n the region o f the thalamic principal sensory nucleus in patients with spinal cord transection. / Neurophysiol 1994b, 72: 1570-1587. Leshner A l : Molecular mechanisms o f cocaine addiction. N Engl J Med 1996, 335: 128 -129. Lewis G B H : Lignocaine suppositories for migraine (Letter). Anaesth Intensive Care 1992, 20: 533-534. L i Y M , Wingrove D E , T o o H P , Marnerakis M , Stimson E R , Strichartz G R , Maggio J E : Loca l anesthetics inhibit substance P binding and evoked increases i n intracellular C a 2 + . Anesthesiology 1995, 82: 166-173. L i n Y , M o r r o w TJ , Kir i t sy-Roy J A , Terry L C , Casey K L : Cocaine: evidence for supraspinal, dopamine-mediated, non-opiate analgesia. Brain Res 1989, 479: 306-312. Lintner S, Shawen S, Lohnes J , Levy A , Garrett W : Loca l anesthesia i n outpatient knee arthroscopy: a comparison o f efficacy and cost. Arthroscopy 1996, 12: 482—488. S. S C H W A R Z 157 L i u B G , Zhuang X L , L i ST, X u G H , Bru l l SJ, Zhang J M : Effects o f bupivacaine and ropivacaine on high-voltage—activated calcium currents o f the dorsal horn neurons i n newborn rats. Anesthesiology 2001, 95: 139-143. L i u K , Adach i N , Yanase H , Kataoka K , A r a i T: Lidocaine suppresses the anoxic depolarization and reduces the increase in the intracellular C a 2 + concentration i n gerbil hippocampal neurons. Anesthesiology 1997, 87: 1470^1478. Lucas L F , West C A , Rigor B M , Schurr A : Protection against cerebral hypoxia by local anesthetics: a study using brain slices. / Neurosci Methods 1989, 28: 47—50. Lugaresi E , M e d o r i R, Montagna P , Baruzzi A , Cortelli P , Lugaresi A , Tinuper P , Zuccon i M , Gambetti P: Fatal familial insomnia and dysautonomia with selective degeneration o f thalamic nuclei. N Engl J Med 1986, 315: 997-1003. L u t h i A , M c C o r m i c k D A : Periodicity o f thalamic synchronized oscillations: the role o f Ca 2 + -mediated upregulation o f Ih- Neuron 1998, 20: 553-563. L u t h i A , B a l T , M c C o r m i c k D A : Periodicity o f thalamic spindle waves is abolished by ZD7288 ,a blocker o f K. J Neurophysiol\99%, 79: 3284-3289. L y n c h J , Trojan S, Arhelger S, Krings-Ernst I: Intermittent femoral nerve blockade for anterior cruciate ligament repair. Use o f a catheter technique i n 208 patients. Acta Anaesthesiol Belg 1991, 42: 207-212. M a W , Peschanski M , Ralston H J , III: The differential synaptic organization o f the spinal and lemniscal projections to the ventrobasal complex o f the rat thalamus. Evidence for convergence o f the two systems upon single thalamic neurons. Neuroscience 1987, 22: 925— 934. Macdonald R L , Ke l ly K M : Antiepileptic drug mechanisms o f action (Review). Epilepsia 1995, 36 Suppl 2: S2-S12. Madej T H , El l i s F R , Halsall PJ: Evaluation o f "3 in 1" lumbar plexus block i n patients having muscle biopsy. Br J Anaesth 1989, 62: 515-517. Maizels M , Scott B , Cohen W , Chen W : Intranasal lidocaine for treatment o f migraine: a randomized, double-blind, controlled trial. JAMA 1996, 276: 319-321. M a o J , Chen L L : Systemic lidocaine for neuropathic pain relief (Review). Pain 2000, 87: 7-17. Marchettini P , Lacerenza M , Marangoni C, Pellegata G , Sotgiu M L , Smirne: Lidocaine test i n neuralgia. Pain 1992, 48: 377-382. S. S C H W A R Z 158 Marhofer P , Oismuller C , Faryniak B , Sitzwohl C, Mayer N , Kapra l S: Three-in-one blocks with ropivacaine: evaluation o f sensory onset time and quality o f sensory block. Anesth Analg 2000, 90: 125-128. Marks R M , Sachar E J : Undertreatment o f medical inpatients with narcotic analgesics. Ann IntMed 1973, 78: 173-181. Mar t in F W , Colman B H : Tinnitus: a double-blind crossover controlled trial to evaluate the use o f lignocaine. Clin Otolaryngol 1980, 5: 3—11. Matheny J M , Hanks G A , Rung G W , Blanda J B , Kalenak A : A comparison o f patient-controlled analgesia and continuous lumbar plexus block after anterior cruciate ligament reconstruction. Arthroscopy 1993, 9: 87-90. McCloskey JJ, H a u n S E , Deshpande J K : Bupivacaine toxicity secondary to continuous caudal epidural infusion i n children. Anesth Analg 1992, 75: 287-290. M c C o r m a c k K : Non-steroidal anti-inflammatory drugs and spinal nociceptive processing (Review). Vain 1994, 59: 9-43. M c C o r m i c k D A : Neurotransmitter actions i n the thalamus and cerebral cortex and their role i n neuromodulation o f thalamocortical activity. ProgNeurobiol 1992, 39: 337—388. M c C o r m i c k D A , Pape H C : Acetylcholine inhibits identified interneurons i n the cat lateral geniculate nucleus. Nature 1988, 334: 246-248. M c C o r m i c k D A , Pape H C : Noradrenergic and serotoninergic modulation o f a hyperpolarization-activated cation current i n thalamic relay neurones. / Physiol 1990a, 431: 319-342. M c C o r m i c k D A , Pape H C : Properties o f a hyperpolarization-activated cation current and its role i n rhythmic oscillation in thalamic relay neurones. / Physiol 1990b, 431: 291-318. M c C o r m i c k D A , Trent F , Ramoa A S : Postnatal development o f synchronized network oscillations i n the ferret dorsal lateral geniculate and perigeniculate nuclei. / Neurosci 1995, 15: 5739-5752. M c Q u a y H , Moore A : Reply to I .D. Conacher: Placebo by default. Pain 2000, 86: 3 2 1 -322. Meld ing PS, Goodey RJ , Thorne P R : The use o f intravenous lignocaine in the diagnosis and treatment o f tinnitus. / Laryngol Otol 1978, 92: 115-121. Melzack R, W a l l P D : Pain mechanisms: a new theory. Science 1965, 150: 971-979. S. S C H W A R Z 159 Melzack R, Casey K L : Sensory, motivational, and central control determinants o f pain: A new conceptual model. In: The Skin Senses; ed. by Kenshalo D ; Thomas, Springfield 1968: 423-443. Menger M D , Vol lmar B : Nichtveroffentlichung und Negativstudien. Bedeutung fur die Meinungsbildung und Forschung. Dtsch MedWochenschr2000, 125: 1129-1130. Mertens H G , Lii tzenkirchen H : Neuropsychopharmaka i n der Behandlung der sog. Schmerzkrankheiten. Ar%neimittelforschung 1970, 20: 928—930. M i k i K , Iwata K , Tsuboi Y , Mor imoto T, K o n d o E , D a i Y , Ren K , Noguch i K : Dorsa l column-thalamic pathway is involved i n thalamic hyperexcitability following peripheral nerve injury: a lesion study in rats with experimental mononeuropathy. Vain 2000, 85: 263-271. Mi l le r S C , Moulder J E : Publication o f negative results is an essential part o f the scientific process. RadiatRes 1998, 150: 1-2. M o m o t a Y , A r t r u A A , Powers K M , Mautz D S , Ueda Y : Concentrations o f lidocaine and monoethylglycine xylidide in brain, cerebrospinal fluid, and plasma during lidocaine-induced epileptiform electroencephalogram activity in rabbits: the effects o f epinephrine and hypocapnia. Anesth Analg 2000, 91: 362-368. Monte i l A , Chemin J , Bourinet E , Mennessier G , Lory P , Nargeot J : Molecular and functional properties o f the human CCIG subunit that forms T-type calcium channels. / Biol Chem 2000, 275: 6090-6100. M o o s D D , Cuddeford J D : A A N A Journal Course: update for nurse anesthetists—femoral nerve block and 3- in- l block in anesthesia. AANA J 1998, 66: 367-375. M o r r o w T J , Casey K L : State-related modulation o f thalamic somatosensory responses in the awake monkey. / Neurophysiol 1992, 67: 305-317. Mountcastie V B , Poggio G F , Werner G : The relation o f thalamic cell response to peripheral stimuli varied over an intensive continuum. / Neurophysiol 1963, 26: 807—834. Mul le C , Steriade M , Deschenes M : The effects o f Q X 3 1 4 on thalamic neurons. Brain Rss 1985, 333: 350-354. M u n s o n E S , Tucker W K , Ausinsch B , Malagodi M H : Etidocaine, bupivacaine, and lidocaine seizure thresholds i n monkeys. Anesthesiology 1975, 42: 471-478. Nathan R D : T w o electrophysiologically distinct types o f cultured pacemaker cells from rabbit sinoatrial node. Am J Vhysiol 1986, 250: H 3 2 5 - H 3 2 9 . S. S C H W A R Z 160 Neher E , Steinbach J H : Loca l anaesthetics transiently block currents through single acetylcholine-receptor channels. J Physiol 1978, 277: 153-176. Nietgen G W , Chan C K , Durieux M E : Inhibition o f lysophosphatidate signaling by lidocaine and bupivacaine. Anesthesiology 1997', 86: 1112—1119. N I H : Research Initiatives/Programs o f Interest 2000-2002. National Institutes o f Health, U .S . Department o f Health and H u m a n Services; Bethesda, M D 2001. Nol le t J , Sertel S, Podranski T , Berning S, van A k e n H , Mort ier E , Durieux M E , Honemann C W : Effect o f volatile and local anesthetics on P G E 2 and T X A 2 receptors o f the prostaglandin family (Abstract). MAC 2001 — Sixth International Conference on Molecular and Basic Mechanisms of Anesthesia; Bonn , Germany; June 28—30, 2001. Nordmark J , Rydqvist B : Loca l anaesthetics potentiate G A B A - m e d i a t e d C F currents by inhibiting G A B A uptake. NeuroReport 1997, 8: 465-468. O d a M , Yoshida A , Ikemoto Y : Blockade by local anaesthetics o f the single C a 2 + -activated K + channel i n rat hippocampal neurones. Br JPharmacol 1992, 105: 63—70. Ogata K , Shinohara M , Inoue H , Miyata T , Yoshioka M , Ohura K : Effects o f local anesthetics on rat macrophage phagocytosis (Japanese). Nippon Yakurigaku Zasshi 1993, 101: 53-58. Olschewski A , Brau M E , Olschewski H , Hempelmann G , Voge l W : ATP-dependent potassium channel i n rat cardiomyocytes is blocked by lidocaine. Possible impact on the antiarrhythmic action o f lidocaine. Circulation 1996, 93: 656-659. Olschewski A , Hempelmann G , Voge l W , Safronov B V : Blockade o f N a + and K + currents by local anesthetics in the dorsal horn neurons o f the spinal cord. Anesthesiology 1998, 88: 172-179. Osterweis M , Kle inman A , Mechanic D : Pain and Disability: Clinical , Behavioral and Public Pol icy Perspectives. National Academy Press; Washington, D C 1987. O w e n M D , D 'Ange lo R, Gerancher J C , Thompson J M , Foss M L , Babb J D , Eisenach J C : 0.125% ropivacaine is similar to 0.125% bupivacaine for labor analgesia using patient-controlled epidural infusion. Anesth Analg 1998, 86: 527-531. Oyama Y , Sadoshima J , Toku tomi N , Akaike N : Some properties o f inhibitory action o f lidocaine on the C a 2 + current o f single isolated frog sensory neurons. Brain Res 1988, 442: 223-228. Ozawa S, Tsuzuki K , l ino M , Ogura A , K u d o Y : Three types o f voltage-dependent calcium current i n cultured rat hippocampal neurons. Brain Res 1989, 495: 329-336. S. S C H W A R Z 161 Palade P T , Aimers W : Slow calcium and potassium currents in frog skeletal muscle: their relationship and pharmacologic properties. Pfliigers Arch 1985, 405: 91-101. Palkovits M , Brownstein M J : Maps and Guide to Microdissection o f the Rat Brain. Elsevier, N e w Y o r k 1988. Pape H C : Queer current and pacemaker: the hyperpolarization-activated cation current i n neurons (Review). Annu Rev Physiol 1996, 58: 299-327. Parri H R , Crunell i V : Sodium current in rat and cat thalamocortical neurons: role o f a non-inactivating component i n tonic and burst firing. J Neurosci 1998, 18: 854—867. Pasternak G W : Pharmacological mechanisms o f opioid analgesics (Review). Clin Neuropharmacol 1993, 16: 1—18. Peng P , Claxton A , Chung F , Chan V , Min iac i A , Krishnathas A : Femoral nerve block and ketorolac i n patients undergoing anterior cruciate ligament reconstruction. Can J Anaesth 1999, 46: 919-924. Perez-Reyes E , Cribbs L L , Daud A , Lacerda A E , Barclay J , Wil l iamson M P , F o x M , Rees M , Lee J H : Molecular characterization o f a neuronal low-voltage-activated T-type calcium channel. Nature 1998, 391: 896-900. Perez Velazquez J L , Carlen P L : Development o f firing patterns and electrical properties i n neurons o f the rat ventrobasal thalamus. Brain Res Dev Brain Res 1996, 91: 164—170. Peterson C G : Neuropharmacology o f procaine. II. Central nervous actions. Anesthesiology 1955,16: 967-993. Peyron R, Garcia-Larrea L , Gregoire M C , Convers P , Lavenne F , Veyre L , Froment J C , Mauguiere F , M i c h e l D , Laurent B : Al lodynia after lateral-medullary (Wallenberg) infarct. A P E T study. Brain 1998, 121: 345-356. Pfrieger F W , Veselovsky N S , Got tmann K , L u x H D : Pharmacological characterization o f calcium currents and synaptic transmission between thalamic neurons i n vitro. / Neurosci 1992,12: 4347-4357. Pirchio M , Turner J P , Williams SR, Asprodin i E , Crunelli V : Postnatal development o f membrane properties and delta oscillations in thalamocortical neurons o f the cat dorsal lateral geniculate nucleus. J Neurosci 1997, 17: 5428-5444. Poggio G F , Mountcasde V B : The functional properties o f ventrobasal thalamic neurons studied i n unanesthetized monkeys. / Neurophysiol 1963, 26: 775—806. S. S C H W A R Z 162 Polley L S , Columb M O , Naughton N N , Wagner D S , van de V e n C J M : Relative analgesic potencies o f ropivacaine and bupivacaine for epidural analgesia in labor: Implications for therapeutic indices. Anesthesiology 1999, 90: 944—950. Porreca F , L a i J , Bilsky E : Opioids in acute and chronic pain: lessons from the cloned receptors. In: Proceedings o f the 8 t h W o r l d Congress on Pain, Chapter 51; ed. by Jensen T S , Turner J A , Wiesenfeld-Hallin Z ; I A S P Press, Seattle 1997: 741-758. Pu i l E , Carlen P L : Attenuation o f glutamate-action, excitatory postsynaptic potentials, and spikes by intracellular Q X 222 i n hippocampal neurons. Neuroscience 1984, 11: 389— 398. P u i l E , M e i r i H , Y a r o m Y : Resonant behaviour and frequency preferences o f thalamic neurons. J Neurophysiol 1994, 71: 575-582. Ragsdale D S , Scheuer T , Catterall W A : Frequency and voltage-dependent inhibit ion o f type I I A N a + channels, expressed i n a mammalian cell line, by local anesthetic, antiarrhythmic, and anticonvulsant drugs. Mol Pharmacol 1991, 40: 756—765. Ramamurthi B , Kalyanaraman S: Stereotactic thalamotomy i n pain relief. / R Coll Surg Edinb 1966, 12: 46-48. Rausell E , Cusick C G , Taub E , Jones E G : Chronic deafferentation in monkeys differentially affects nociceptive and nonnociceptive pathways distinguished by specific calcium-binding proteins and down-regulates y-aminobutyric acid type A receptors at thalamic levels. Proc Natl Acad Sci USA 1992, 89: 2571-2575. Rautoma P , Santanen U , Avela R, Luuri la H , Perhoniemi V , E rko la O : Diclofenac premedication but not intra-articular ropivacaine alleviates pain following day-case knee arthroscopy. Can J Anaesth 2000, 47: 220-224. Ready L B , Plumer M H , Haschke R H , Aust in E , Sumi S M : Neurotoxicity o f intrathecal local anesthetics i n rabbits. Anesthesiology 1985, 63: 364—370. Reinker S, Schwarz S K W , Pu i l E : Effects o f procainamide on membrane properties o f thalamocortical neurons. Proc West Pharmacol JW2001, 44: (in press). Reuben SS, Steinberg R B , Cohen M A , K i l a r u P A , G ibson CS: Intraarticular morphine i n the mult imodal analgesic management o f postoperative pain after ambulatory anterior cruciate ligament repair. Anesth Analg 1998, 86: 374-378. Richardson D E : Recent advances in the neurosurgical control o f pain. South Med J 1967, 60: 1082-1086. Ries C R , Pu i l E : Isoflurane prevents transitions to tonic and burst firing modes i n thalamic neurons. Neurosci Lett 1993, 159: 91-94. S. S C H W A R Z 163 Ries C R , P u i l E : Mechanism o f anesthesia revealed by shunting actions o f isoflurane on thalamocortical neurons. ] Neurophysiol 1999a, 81: 1795-1801. Ries C R , P u i l E : Ionic mechanism o f isoflurane's actions on thalamocortical neurons. / Neurophysiol 1999b, 81:1802-1809. Rigler M L , Drasner K , Krejcie T C , Ye l i ch SJ, Scholnick F T , DeFontes J , Bohner D : Cauda equina syndrome after continuous spinal anesthesia. Anesth Analg 1991, 72: 275— 281. R igon A R , Takahashi R N : The effects o f systemic procaine, lidocaine and dimethocaine on nociception i n mice. Gen Pharmacol 1996, 27: 647—650. Ringrose N H , Cross M J : Femoral nerve block in knee joint surgery. Am J Sports Med 1984, 12: 398-402. Ritter J W : Femoral nerve "sheath" for inguinal paravascular lumbar plexus block is not found i n human cadavers. / Clin Anesth 1995, 7: 470—473. Roden D M : Antiarrhythmic drugs. In: Goodman & Gilman's The Pharmacological Basis of Therapeutics, 35; Tenth Edi t ion; ed. by Hardman J G , L i m b i r d L E , G o o d m a n G i l m a n A ; M c G r a w - H i l l , N e w Y o r k 2001: 933-970. Rosaeg O P , Krepsk i B , Cicutti N , Dennehy K C , L u i A C , Johnson D H : Effect o f preemptive multimodal analgesia for arthroscopic knee ligament repair. Reg Anesth Pain Med 2001, 26: 125-130. Rosen S D , Paulesu E , Fr i th C D , Frackowiak RS, Davies G J , Jones T, Camici P G : Central nervous pathways mediating angina pectoris. Lancet 1994, 344: 147—150. Rossner K L , Freese K J : Bupivacaine inhibition o f L-type calcium current in ventricular cardiomyocytes o f hamster. Anesthesiology 1997, 87: 926—934. Rowbotham M C , Reisner-Keller L A , Fields H L : B o t h intravenous lidocaine and morphine reduce the pain o f postherpetic neuralgia. Neurology 1991, 41: 1024—1028. R u f f R L : The kinetics o f local anesthetic blockade o f end-plate channels. Biophys J 1982, 37: 625-631. Sakabe T , Maekawa T , Ishikawa T , Takeshita H : The effects o f lidocaine on canine cerebral metabolism and circulation related to the electroencephalogram. Anesthesiology 1974,40:433-441. Sanchez-Chapula J : Effects o f bupivacaine on membrane currents o f guinea-pig ventricular myocytes. Eur J Pharmacol 1988, 156: 303-308. S. S C H W A R Z 164 Scholz A , Kuboyama N , Hempelmann G , Voge l W : Complex blockade o f TTX-resistant N a + currents by lidocaine and bupivacaine reduce firing frequency i n D R G neurons. / Neurophysiol 199S, 79: 1746-1754. Schurr A , Spears B , Reid K H , West C A , Edmonds H L , Rigor B M : Lidocaine depresses synaptic activity i n the rat hippocampal slice. Anesthesiology 1986, 64: 501—503. Schwarz S: Wirkungen von Lokalanasthetika i m zentralen Nervensystem: Effekte v o n Lidoca in auf Neurone des Nucleus ventralis posterolateralis thalami. Inaugural-Dissertation; Medizinische Fakultat, Georg-August-Universitat zu Gottingen, Gottingen 1998. Schwarz S K W , Pu i l E : Analgesic and sedative concentrations o f lignocaine shunt tonic and burst firing i n thalamocortical neurones. Br] Pharmacol 1998, 124: 1633-1642. Schwarz S K W , Pu i l E : Lidocaine produces a shunt in rat thalamocortical neurons, unaffected by G A B A A receptor blockade. Neurosci Lett 1999a, 269: 25-28. Schwarz S K W , Pu i l E : Lidocaine unmasks high threshold C a 2 + spikes i n thalamocortical neurons. Soc Neurosci Ahstr 1999b, 25: 723. Schwarz S K W , Franciosi L G , Ries C R , Regan W D , Davidson R G , N e v i n K , Escobedo S, M a c L e o d B A : Add i t ion o f femoral 3- in- l blockade to intra-articular ropivacaine 0.2% does not reduce analgesic requirements following arthroscopic knee surgery. Can J Anesth 1999, 46: 741-747. Scott D B : Evaluation o f the toxicity o f local anaesthetic agents i n man. Br] Anaesth 1975, 47: 56-61. Scott D B , Lee A , Fagan D , Bowler G M , Bloomfield P , L u n d h R: Acute toxicity o f ropivacaine compared with that o f bupivacaine. Anesth Analg 1989, 69: 563—569. Segal M : Effects o f a lidocaine derivative Q X - 5 7 2 on C A 1 neuronal responses to electrical and chemical stimuli i n a hippocampal slice. Neuroscience 1988, 27: 905—909. Seo N , Oshima E , Stevens J , M o r i K : The tetraphasic action o f lidocaine on C N S electrical activity and behavior i n cats. Anesthesiology 1982, 57: 451—457. Seutin V , Scuvee-Moreau J , Dresse A : Evidence for a n o n - G A B A e r g i c action o f quaternary salts o f bicuculline on dopaminergic neurones. Neuropharmacology 1997, 36: 1653-1657. Shah M J , Meis S, Munsch T, Pape H C : Modulat ion by extracellular p H o f low- and high-voltage-activated calcium currents o f rat thalamic relay neurons. J Neurophysiol 2001, 85: 1051-1058. S. S C H W A R Z 165 Shanes A M , Freygang W H , Grundfest H , Amatniek E : Anesthetic and calcium action i n the voltage clamped squid giant axon. / Gen Physiol 1959, 42: 793-802. Shapiro M S , Safran M R , Crockett H , Finerman G A : Loca l anesthesia for knee arthroscopy. Efficacy and cost benefits. Am J Sports Med 1995, 23: 50-53. Sherman S M , Guillery R W : Explor ing the Thalamus. Academic Press, San Diego, 2001. Shibata M , Shingu K , Murakawa M , Adach i T , Osawa M , Nakao S, M o r i K : Tetraphasic actions o f local anesthetics on central nervous system electrical activities in cats. Reg Anesth 1994, 19: 255-263. Shyu B C , Kir i t sy-Roy J A , M o r r o w T J , Casey K L : Neurophysiological, pharmacological and behavioral evidence for medial thalamic mediation o f cocaine-induced dopaminergic analgesia. Brain Res 1992, 572: 216-223. Simone D A , Sorkin L S , O h U , Chung J M , Owens C , LaMot te R H , Will is W D : Neurogenic hyperalgesia: central neural correlates in responses o f spinothalamic tract neurons. J Neurophysiol 1991, 66: 228-246. Simpson JJ, Davies W E : Recent advances in the pharmacological treatment o f tinnitus. Trends Pharmacol Sci 1999, 20: 12-18. Sinclair R, Er iksson A S , Gretzer C, Cassuto J , Thomsen P: Inhibitory effects o f amide local anaesthetics on stimulus-induced human leukocyte metabolic activation, LTB4 release and IL-1 secretion i n vitro. Acta AnaesthesiolScand 1993, 37: 159—165. Singelyn FJ , V a n R o y C , Goossens F , Gouverneur J M : A high position o f the catheter increases the success rate o f continuous "3 - in - l " block (CB). Anesthesiology 1996, 85: A723 . Singer T , B i r d P , Borgeat A : " 3 - i n - l " femoral block (Letter). Can J Anaesth 1998, 45: 1032-1033. Sloan P , Basta M , Storey P , von Gunten C: Mexiletine as an adjuvant analgesic for the management o f neuropathic cancer pain. Anesth Analg 1999, 89: 760—761. Smith D C , K r a h l S E , Browning R A , Barea E J : Rapid cessation o f focally induced generalized seizures i n rats through microinfusion o f lidocaine hydrochloride into the focus. Epilepsia 1993, 34: 43-53. Sorensen J , Bengtsson A , Backman E , Henriksson K G , Bengtsson M : Pain analysis in patients with fibromyalgia. Effects o f intravenous morphine, lidocaine, and ketamine. Scand J Rheumatol 1995, 24: 360-365. S. S C H W A R Z 166 Sperelakis N , Lehmkuh l D : B a 2 + A N D S r 2 + reversal o f the inhibit ion produced by ouabain and local anesthetics on membrane potentials o f cultured heart cells. Exp Cell Res 1968, 49: 396-410. Stafstrom C E , Schwindt P C , Chubb M C , Cr i l l W E : Properties o f persistent sodium conductance and calcium conductance o f layer V neurons from cat sensorimotor cortex i n vitro. J Neurophysiol 1985, 53: 153-170. Steinbach A B : Alteration by xylocaine (lidocaine) and its derivatives o f the time course o f the end plate potential. / Gen Physiol 1968, 52: 144-161. Stephenson D G , Wendt IR: Effects o f procaine on calcium accumulation by the sarcoplasmic reticulum o f mechanically disrupted rat cardiac muscle. / Physiol 1986, 373: 195-207. Steriade M : Impact o f network activities on neuronal properties i n corticothalamic systems. / Neurophysiol2001, 86: 1—39. Steriade M , Llinas R R : The functional states o f the thalamus and the associated neuronal interplay. Physiol Rev 1988, 68: 649-742. Steriade M , McCarley R W : Brainstem Control o f Wakefulness and Sleep. P lenum Press, N e w Y o r k 1990. Steriade M , Jones E G , Llinas R R : Thalamic Oscillations and Signalling. Wiley, N e w Y o r k 1990. Steriade M , Jones E G , M c C o r m i c k D A : Thalamus. Elsevier Science L t d , O x f o r d 1997. Stewart G J , Kn igh t L C , Arbogast B W , Stern H S : Inhibition o f leukocyte locomotion by tocainide, a primary amine analog o f lidocaine: at study with l l l i n d i u m - l a b e l e d leukocytes and scanning electron microscopy. Eab Invest 1980, 42: 302—309. Stienstra R, Jonker T A , Bourdrez P , Kuijpers J C , van K l e e f J W , Lundberg U : Ropivacaine 0.25% versus bupivacaine 0.25% for continuous epidural analgesia i n labor: a double-blind comparison. Anesth Analg 1995, 80: 285-289. Stone W E , Javid M J : Anticonvulsive and convulsive effects o f lidocaine: comparison with those o f phenytoin, and implications for mechanism o f action concepts. Neurol Res 1988, 10: 161-168. Strichartz G R : Molecular mechanisms o f nerve block by local anesthetics. Anesthesiology 1976,45:421-441. S. S C H W A R Z 167 Strichartz G R , Ritchie J M : The action o f local anesthetics on ion channels o f excitable tissues. In: Handbook o f Experimental Pharmacology, V o l . 81: Loca l Anesthetics, Chapter 2; ed. by Strichartz G R ; Springer-Verlag, Berl in 1987: 21-52. Stuart G J , D o d t H U , Sakmann B: Patch-clamp recordings from the soma and dendrites o f neurons i n brain slices using infrared video microscopy. Pfliigers Arch 1993, 423: 511— 518. Sug iyama r K, Mutek i T: Loca l anesthetics depress the calcium current o f rat sensory neurons i n culture. Anesthesiology 1994, 80: 1369-1378. Sugiyama K , Mutek i T , Shimoji K : Halothane-induced hyperpolarization and depression o f postsynaptic potentials o f guinea pig thalamic neurons i n vitro. Brain Res 1992, 576: 97-103. Sutor B , Habli tz JJ: Influence o f barium on rectification in rat neocortical neurons. Neurosci Lett 1993, 157: 62-66. Tabatabai M , Boo th A M : Effects o f lidocaine on the excitability and membrane properties o f the nerve cell soma. Clin Physiol Biochem 1990, 8: 289—296. Takahashi T , Momiyama A : Different types o f calcium channels mediate central synaptic transmission. Nature 1993, 366: 156-158. Talairach J , Hecaen H , D a v i d M , Monnier M , DeAguriaguerra J : Recherches sur la coagulation therapeutique des structures sous-corticales chez l 'homme. Rev Neurol (Paris) 1949, 81: 4-24. Talley E M , Cribbs L L , Lee J H , Daud A , Perez-Reyes E , Bayliss D A : Differential distribution o f three members o f a gene family encoding low voltage-activated (T-type) calcium channels. J Neurosci 1999, 19: 1895-1911. Tanelian D L , Brose W G : Neuropathic pain can be relieved by drugs that are use-dependent sodium channel blockers: lidocaine, carbamazepine, and mexiletine. Anesthesiology 1991, 74: 949-951. Taverner D , Bain B A : Intravenous lignocaine as an anticonvulsant i n status epilepticus and serial epilepsy. Lancet 1958, 2: 1145-1147. Taylor R E : Effect o f procaine on electrical properties o f squid axon membrane. Am J Physiol 1959,196:1071-1078. Tennigkeit F , Schwarz D W F , Pu i l E : Mechanisms for signal transformation i n lemniscal auditory thalamus./Neurophysiol 1996, 76: 3597-3608. S. S C H W A R Z 168 Tennigkeit F , Ries C R , Schwarz D W F , Pu i l E : Isoflurane attenuates resonant responses o f auditory thalamic neurons. / Neurophysiol 1997, 78: 591-596. Tennigkeit F , Schwarz D W F , Pu i l E : Modulat ion o f bursts and high-threshold calcium spikes i n neurons o f rat auditory thalamus. Neuroscience 1998a, 83: 1063-1073. Tennigkeit F , Schwarz D W F , Pu i l E : Postnatal development o f signal generation in auditory thalamic neurons. Dev Brain Res 1998b, 109: 255-263. Terada H , Ohta S, Nishikawa T, Mizunuma T, Iwasaki Y , Masaki Y : The effect o f intravenous or subarachnoid lidocaine on glutamate accumulation during transient forebrain ischemia in rats. Anesth Analg 1999, 89: 957-961. Tetzlaff J E , Andr i sh J , O 'Hara JJ, Dilger J , Y o o n H J : Effectiveness o f bupivacaine administered via femoral nerve catheter for pain control after anterior cruciate ligament repair. / Clin Anesth 1997, 9: 542-545. Thompson E N : Chronic pain (Editorial). Can] Anaesth 1997, 44: 243-246. T h o m s o n A M : Biphasic responses o f thalamic neurons to G A B A i n isolated rat brain slices-II. Neuroscience 1988, 25: 503-512. ^ Tierney E , Lewis G , Hur t ig J B , Johnson D : Femoral nerve block with bupivacaine 0.25 per cent for postoperative analgesia after open knee surgery. Can J Anaesth 1987, 34: 455— 458. Tierney G S , Wright R W , Smith JP , Fischer D A : Anterior cruciate ligament reconstruction as an outpatient procedure. Am ] Sports Med 1995, 23: 755—756. Travagli R A , Gi l l i s R A : Hyperpolarization-activated currents, hi and IKIR, i n rat dorsal motor nucleus o f the vagus neurons in vitro. J Neurophysiol 1994, 71: 1308—1317. Tsai PS , Buerkle H , Huang L T , Lee T C , Yang L C , Lee J H : Lidocaine concentrations i n plasma and cerebrospinal fluid after systemic bolus administration i n humans. Anesth Analg 1998, 87: 601-604. Tsoukatos J , Kiss Z H , Davis K D , Tasker R R , Dostrovsky J O : Patterns o f neuronal firing i n the human lateral thalamus during sleep and wakefulness. Exp Brain Res 1997, 113: 273-282. Tsuda Y , Mashimo T , Yoshiya I, Kaseda K , Harada Y , Yanagida T: Direct inhibit ion o f the actomyosin motility by local anesthetics in vitro. Biophys J 1996, 71: 2733-2741. Tsutsumi Y , Oshita S, Kawano T, Kitahata H , Tomiyama Y , K u r o d a Y , Nakaya Y : Lidocaine and mexiletine inhibit mitochondrial oxidation in rat ventricular myocytes. Anesthesiology 2001, 95: 766-770. S. S C H W A R Z 169 Tucker G T , Mather L E : Properties, absorption, and disposition o f local anesthetic agents. In: Neura l Blockade in Clinical Anesthesia and Management o f Pain, 3; Second Edi t ion ; ed. by Cousins M J , Bridenbaugh P O ; J . B . Lippincot t Company, Philadelphia 1988: 4 7 -110. Turner J P , Leresche N , G u y o n A , Soltesz I, Crunelli V : Sensory input and burst firing output o f rat and cat thalamocortical cells: the role o f N M D A and n o n - N M D A r e c e p t o r s . / P ^ / o / 1 9 9 4 , 480: 281-295. U l r i ch D , Huguenard JR: GABAA-receptor-mediated rebound burst firing and burst shunting i n thalamus. J Neurophysiol 1997, 78: 1748-1751. Usubiaga J E , M o y a F , Wik insk i J A , Wikinski R, Usubiaga L E : Relationship between the passage o f local anaesthetics across the blood-brain barrier and their effects on the central nervous system. Br J Anaesth 1967, 39: 943-947. Vah le -Hinz C , Hicks T P , Gottschaldt K M : A m i n o acids modify thalamo-cortical response transformation expressed by neurons o f the ventrobasal complex. Brain Res 1994,637:139-155. Valenzuela C , De lpon E , Tamkun M M , Tamargo J , Snyders D J : Stereoselective block o f a human cardiac potassium channel (Kv l .5 ) by bupivacaine enantiomers. Biophys J 1995, 69: 418-427. Velumian A A , Zhang L , Pennefather P , Carlen P L : Reversible inhibit ion o f IK, IAHP, h and Jca currents by internally applied gluconate in rat hippocampal pyramidal neurones. Pfliigers Arch 1997, 433: 343-350. Vlachova V , Vitaskova Z , Vykl icky L , Orkand R K : Procaine excites nociceptors i n cultures from dorsal root ganglion o f the rat. Neurosci Lett 1999, 263: 49—52. V o e i k o v V L , Lefkowitz RJ: Effects o f local anesthetics on guanyl nucleotide modulation o f the catecholamine-sensitive adenylate cyclase system and on beta-adrenergic receptors. Biochim Biophys Acta 1980, 629: 266-281. v o n Kros igk M , Ba l T , M c C o r m i c k D A : Cellular mechanisms o f a synchronized oscillation i n the thalamus. Science 1993, 261: 361-364. Wagman I H , de Jong R H , Prince D A : Effects o f lidocaine on spontaneous cortical and subcortical electrical activity. Production o f seizure discharges. Arch Neurol 1968, 18: 277— 290. Waite M , Sisson P: Effect o f local anesthetics on phospholipases from mitochondria and lysosomes. A probe into the role o f the calcium ion i n phospholipid hydrolysis. Biochemistry 1972, 11: 3098-3105. S. S C H W A R Z 170 Wallace M S , Lee J , Sorkin L , D u n n JS, Yaksh T, Y u A : Intravenous lidocaine: effects on controlling pain after a n t i - G D 2 antibody therapy i n children with neuroblastoma—a report o f a series. Anesth Analg 1997a, 85: 794-796. Wallace M S , Lai t in S, L ich t D , Yaksh T L : Concentration-effect relations for intravenous lidocaine infusions i n human volunteers: effects on acute sensory thresholds and capsaicin-evoked hyperpathia. Anesthesiology 1997b, 86: 1262—1272. Wallace M S , Ridgeway B M , Leung A Y , Gerayli A , Yaksh T L : Concentration-effect relationship o f intravenous lidocaine on the allodynia o f complex regional pain syndrome types I and II. Anesthesiology 2000, 92: 75-83. Weber A , Fournier R, V a n Gessel E , Riand N , Gamul in Z : Epinephrine does not prolong the analgesia o f 20 m l ropivacaine 0.5% or 0.2% in a femoral three-in-one block. Anesth Analg 2001, 93: 1327-1331. Weidmann S: The effects o f calcium ions and local anaesthetics on electrical properties o f Purkinje fibres. J Physiol 1955, 129: 568-582. Will iams B A , DeRiso B M , Figallo C M , Anders J W , Engel L B , Sproul K A , I lkin H , Harner C D , F u F H , Nagarajan N J , Evans J H , III, Watkins W D : Benchmarking the perioperative process: III. Effects o f regional anesthesia clinical pathway techniques on process efficiency and recovery profiles i n ambulatory orthopedic surgery. J Clin Anesth 1998, 10: 570-578. Will iams SR, Stuart G J : A c t i o n potential backpropagation and somato-dendritic distribution o f ion channels in thalamocortical neurons. / Neurosci 2000, 20: 1307—1317. Will iams SR, T o t h T I , Turner J P , Hughes SW, Crunelli V : The 'window' component o f the low threshold C a 2 + current produces input signal amplification and bistability i n cat and rat thalamocortical neurones. / Physiol 1997a, 505: 689—705. Will iams SR, Turner JP , Hughes SW, Crunelli V : O n the nature o f anomalous rectification i n thalamocortical neurones o f the cat ventrobasal thalamus in vitro. / Physiol 1997b, 505: 727-747. Wil l is W D : Nociceptive functions o f thalamic neurons. In: Thalamus. V o l u m e II: Experimental and Clinical Aspects, Chapter 8; ed. by Steriade M , Jones E G , M c C o r m i c k D A ; Elsevier Science L td . , Oxfo rd 1997: 373-424. Winnie A P , Ramamurthy S, Durrani Z : The inguinal paravascular technic o f lumbar plexus anesthesia: the "3 - in - l block". Anesth Analg 1973, 52: 989-996. X i e Z , Sastry B R : Actions o f somatostatin on G A B A - e r g i c synaptic transmission i n the C A 1 area o f the hippocampus. Brain Res 1992, 591: 239-247. S. S C H W A R Z 171 Yanagi H , Sankawa H , Saito H , Iikura Y : Effect o f lidocaine on histamine release and C a 2 + mobil ization from mast cells and basophils. Acta Anaesthesiol Scand 1996, 40: 1138— 1144. Y a n g J C , Clatk W C , Dooley J C , Mignogna F V : Effect o f intranasal cocaine on experimental pain i n man. Anesth Analg 1982, 61: 358-361. Zahradnikova A , Palade P: Procaine effects on single sarcoplasmic reticulum Ca 2 + release channels. Biophys J 1993, 64: 991-1003. Zavisca F G , Kyt ta J , Heavner J E , Badgwell J M : A rodent model for studying four well defined toxic endpoints during bupivacaine infusion. Reg Anesth 1991, 16: 223-227. Z h o u Q , G o d w i n D W , O'Malley D M , Adams PR: Visualization o f calcium influx through channels that shape the burst and tonic firing modes o f thalamic relay cells. / Neurophysiol 1997,77: 2816-2825. Zipes D P : Management o f cardiac arrhythmias: pharmacological, electrical, and surgical techniques. In: Heart Disease: A Textbook o f Cardiovascular Medicine, Chapter 23; Four th Edi t ion ; ed. by Braunwald E ; W . B . Saunders Company, Philadelphia 1992: 6 2 8 -666. 

Cite

Citation Scheme:

        

Citations by CSL (citeproc-js)

Usage Statistics

Share

Embed

Customize your widget with the following options, then copy and paste the code below into the HTML of your page to embed this item in your website.
                        
                            <div id="ubcOpenCollectionsWidgetDisplay">
                            <script id="ubcOpenCollectionsWidget"
                            src="{[{embed.src}]}"
                            data-item="{[{embed.item}]}"
                            data-collection="{[{embed.collection}]}"
                            data-metadata="{[{embed.showMetadata}]}"
                            data-width="{[{embed.width}]}"
                            async >
                            </script>
                            </div>
                        
                    
IIIF logo Our image viewer uses the IIIF 2.0 standard. To load this item in other compatible viewers, use this url:
https://iiif.library.ubc.ca/presentation/dsp.831.1-0090645/manifest

Comment

Related Items