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Changes in extracellular dopamine levels in the nucleus accumbens induced by low frequency stimulation… Taepavarapruk, Pornnarin 1998

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CHANGES IN EXTRACELLULARDOPAMINE LEVELS IN THE NUCLEUS A C C U M B E N S I N D U C E D BY L O W FREQUENCY S T I M U L A T I O N OF T H E V E N T R A L S U B I C U L U M / C A 1 R E G I O N OF T H E H I P P O C A M P U S : A MICRODIALYSIS STUDY I N FREELY M O V I N G RATS  by PORNNARIN B.Sc,  TAEPAVARAPRUK  S i l p a k o r n U n i v e r s i t y , T h a i l a n d , 1989  M. Sc., Chulalongkorn U n i v e r s i t y , T h a i l a n d , 1993  A THESIS SUBMITTED I N PARTIAL F U L F I L L M E N T OF THE REQUIREMENTS FOR T H E DEGREE OF M A S T E R OF SCIENCE  in T H E F A C U L T Y OF G R A D U A T E STUDIES Department of Neuroscience W e accept this thesis as conforming to the required standard  THE UNIVERSITY OF BRITISH C O L U M B I A February 1998 © P o r n n a r i n Taepavarapruk, 1998  In  presenting  degree freely  this  thesis  in partial  fulfilment  at the University  of British  Columbia, I agree that the Library  available for reference  copying  of this  department publication  or  thesis  for scholarly  by his or  of this  and study.  thesis  for financial  Department of WtVLrOSCiewce The University of British C o l u m b i a Vancouver, Canada  (2/88)  I further agree that  purposes  It  is  for an advanced  permission  may be granted  her representatives.  permission.  DE-6  of the requirements  for extensive  by the head  understood  gain shall not be allowed  shall make it  that without  of my  copying  or  my written  11  ABSTRACT The present study utilized microdialysis i n freely-moving rats to investigate 1) changes i n extracellular dopamine (DA) level i n the nucleus accumben ( N A c ) induced by electrical stimulation of the ventral s u b i c u l u m / C A l ( V s u b / C A l ) area of hippocampus, and 2) the role of metabotropic glutamate receptors (mGluRs) i n mediating  D A release  i n the N A c induced by low frequency  stimulation of  Vsub/CAl. It has been s h o w n that electrical stimulation of V s u b / C A l at 2 H z for 100 sec induces a significant decrease (p < 0.05) i n basal D A levels i n the N A c w h i c h is l o n g lasting throughout  the 2 hr m o n i t o r i n g period. Reverse dialysis of the specific  antagonist at m G l u R l / 2 , (+)-a-methyl-4-carboxyphenylglycine ( M C P G ) , at doses 10 LLM and 100 LuVL d i d not prevent the suppressive effects o n D A levels induced by low frequency stimulation of V s u b / C A l . 2 and 3 m G l u R  antagonist,  However, reverse dialysis w i t h the group  (+)-a-methyl-4-phosphonophenylglycine  (MPPG), at  dose of 100 u M and 1 m M , significantly blocked the prolonged suppressive effects of 2 H z V s u b / C A l stimulation o n D A efflux. These results suggest that presynaptic group 2 and 3 m G l u R s are likely to be i n v o l v e d i n a mechanism underlying the late phase of synaptic transmission at glutamatergic-dopaminergic synapses i n the N A c . H o w e v e r , the question w h i c h specific m G l u R  subtypes  are  responsible  for  these  suppressive mechanisms w i l l require further research.  initial  and  long  lasting  iii  TABLE OF C O N T E N T S Abstract Table of contents List of Tables List of Figures List of Abbreviations Acknowledgment I. Introduction  ii iii v vi viii xi 1  Anatomical and physiological role of the nucleus accumbens  1  Functional interaction of D A and G l u i n the N A c  5  Metabotropic glutamate receptors (mGluRs): their characteristics and anatomical distribution i n the C N S Functional roles of m G l u R s i n mediating D A release i n the N A c II. Methods  6 10 16  Subjects  16  Surgery  16  Microdialysis Procedures  17  Analysis of Dialysates  20  Electrical Stimulation Procedure  21  Pharmacological Studies  21  Histology  22  Data Analysis  22  iv  III. Results Effect of V s u b / C A l stimulation o n extracellular levels of D A i n the N A c  24 24  Pharmacological studies: Effects of selective antagonists at m G l u R s o n basal D A level i n the N A c  26  Role of m G l u R s i n regulating D A release i n the N A c induced by 2 H z stimulation of V s u b / C A l IV. Discussion Effects of V s u b / C A l stimulation on extracellular levels of D A i n the N A c  34 40 40  Effects of the selective m G l u R antagonists o n basal D A levels i n the N A c and on the suppressive effects i n N A c D A release induced by 2 H z stimulation of V s u b / C A l V . References  46 53  LIST OF T A B L E S Table 1 Dendrogram and pharmacological distinction between cloned m G l u R subtypes Table 2  A summary of potency of several agonists of m G L u R s as tested on cell lines that express m G l u R subtypes  Table 3  8  12  Summary of potency of phenylglycine compounds as antagonists of m G l u R specific agonists i n different tissue preparations  13  VI  LIST OF FIGURES Fig. 1  The general scheme of the afferent and efferent circuits of the N A c that are i n v o l v e d i n regulating locomotor activity  Fig. 2  Schematic view of the possible roles of m G l u R l at the glutamatergic synapse  Fig. 3  3  9  Diagram of proposed mechanism that regulates the release of D A i n the N A c  15  Fig. 4  Illustration of a dialysis system  18  Fig. 5  Diagram of preparation used i n the study  19  Fig. 6  Time-courses of the effects of electrical stimulation of V s u b / C A l at three different frequencies (2 H z , 5 H z and 10 H z ) o n extracellular D A levels i n the N A c  Fig. 7  Time-courses of the effects of 2 H z stimulation of V s u b / C A l on extracellular D A levels i n the N A c  Fig. 8  27  Time-courses of the effects of M C P G administration at doses of 10 u M , 100 | i M or 1 m M o n basal levels of D A i n the N A c  Fig. 9  25  28  Time-courses of the effects of M P P G administration at doses of 100 ^ . M , 1 m M or 10 m M on basal levels of D A i n the N A c  31  Fig. 10 Time-courses of the effects of administration 10 m M M P P G or its vehicle on basal levels of D A i n the N A c  33  Fig. 11 Effects of M C P G (lOuM) i n combination w i t h 2 H z stimulation of V s u b / C A l on extracellular D A levels i n the N A c  36  vu  Fig. 12 Effects of M C P G (IOOLIM) i n combination w i t h 2 H z stimulation of V s u b / C A l o n extracellular D A levels i n the N A c  37  Fig. 13 Effects of M P P G (IOOLIM) i n combination w i t h 2 H z stimulation of V s u b / C A l o n extracellular D A levels i n the N A c  38  Fig. 14 Effects of M P P G (1 m M ) i n combination w i t h 2 H z stimulation of V s u b / C A l o n extracellular D A levels i n the N A c  39  Fig. 15 D i a g r a m of proposed mechanism that involves the role m G l u R s i n regulating the release of D A i n the N A c  43  Fig. 16 Diagram of proposed mechanism that involves the effects of M P P G (100 LIM) o n the release of D A i n the N A c  49  Fig. 17 D i a g r a m of proposed mechanism that involves the effects of M P P G on the suppression of D A efflux induced by 2 H z stimulation  52  LIST OF A B B R E V I A T I O N S (1S,3R)-ACPD  =  trans (1S,3R)- l-aminocyclopentane-l,3-dicarboxylic acid  ANOVA  =  analyses of variance  AMPA  =  a-amino-3-hydroxy-5-methylisoxazole-4-propionate  AP  =  antero-posterior  AP-5  =  DL-2-amino-5-phosphopentanoic acid  BK  =  big C a  °C  =  degree celsius  =  calcium  =  calcium chloride dihydrate  =  concentration i n the m e d i u m  =  concentration i n the outflow  (S) 4 C P G  =  (S)-4-carboxy-phenylglycine  (S) 4 C 3 H P G  =  (S)-4-carboxy-3-hydroxyphenylglycine  (S)3C4HPG  =  (S)-3-carboxy-4-hydroxyphenylglycine  cyclic A M P  =  adenosine 3'5'-cyclic monophosphate  DA  =  dopamine  DCGIV  =  (2S 2'R 3'R)-2-(2,3-dicarboxycyclopropyl) glycine  DNQX  =  6,7-dinitroquinoxaline-2,3-dione  EAA  =  excitatory amino acid  ECD  =  electrochemical detector  EDTA  =  ethylenediaminetetraacetic  Ca  2+  CaCl .2H 0 2  C  2  o u t  /  2 +  activated K channel +  /  acid  ix  Glu  =  glutamate  HPLC  =  h i g h pressure l i q u i d chromatography  iGluR  =  ionotropic glutamate receptor  IK  =  i n w a r d rectifier K channel  i.p.  =  intraperitoneal  IP  =  inositol 1,4,5-triphosphate  KA  =  kainic acid  KC1  =  potassium chloride  L-AP4  =  L-2-amino-4-phosphonobutyrate  L-CCG-I  =  (2S,l'S 2'S)-2-(2'-carboxycyclopropyl) glycine  L-SOP  =  L-serine-O-phosphate  LTD  =  long term depression  L-VSCC  =  L-type voltage-sensitive calcium channel  L Y 354730  =  (±)-2-aminobicylclo [3.1.0] hexane-2,6-dicarboxylate  MCCG  =  2S lS',2S'-2-methyl-2-(2'-carboxycyclopropyl) glycine  MCPG  =  ( ± ) - a -methyl-4-carboxyphenylglycine  M3CM4HPG  =  (+)-a-methyl-3-carboxymethyl-4-hydroxyphenylglycine  MgCl .6H 0  =  magnesium chloride  mGluR  =  metabotropic glutamate receptor  ML  =  medial-lateral  MPPG  =  (+)-a-methyl-4-phosphonophenyl glycine  MSPG  =  (+)-a-methyl-4-sulphonophenylglycine  3  2  2  +  /  /  X  MTPG  (±)-a-methyl-4-tetrazolylphenylglycine  M.W  =  molecular weight  NAc  =  nucleus accumbens  NaCl  =  sodium chloride  NaOH  =  sodium hydroxide  NMDA  =  N-methyl-D-aspartate  N-VSCC  =  N-type voltage-sensitive calcium channel  6-OHDA  =  6-hydroxydopamine  PKC  =  protein kinase C  QA  =  quisqualic acid  VTA  =  ventral tegmental area  XI  ACKNOWLEDGMENT I w o u l d like to express my sincere gratitude to m y supervisor, Dr. A . G . Phillips, for his k i n d guidance and generosity. W i t h o u t his assistance, I w o u l d not have been able to complete this work. I w o u l d also like to thank Dr. C D . Blaha, Dr. A . C . C o u r y and D r . C R . Yang for their assistance and thoughtful suggestions. I w o u l d like to take the opportunity to thank m y chair and committee member of the supervisory committee, Dr. P. Finlayson and Dr. L . R a y m o n d for their invaluable insight and discussion o n this work. I w o u l d like to thank Stan Floresco, Dennis Fiorino and Soyon A h n for their kindly suggestions and Fred Lapaine for his technical assistance. Finally, I w o u l d like to express m y appreciation for all love and support I have received from m y parents and m y husband, N i w a t . This research was supported by a grant (PG-12808) from the M R C to A . G . Phillips, C D . Blaha, and C R . Yang. Pornnarin Taepavarapruk is a recipient of Royal Thai Government Scholarship.  1  INTRODUCTION Anatomical and physiological role of the nucleus accumbens. The nucleus accumbens of the ventral striatum (NAc) is a limbic structure that has been implicated i n a number of functions i n c l u d i n g learning and adaptive behavior (Mogenson et al., 1980), reward (Fibiger and Phillips, 1988; Phillips et al., 1989; Koob, 1992), motivation (Mogenson et al., 1993), locomotor activity (Yang and Mogenson, 1987; Koob and Swerdlow, 1988; G o l d et al., 1988; Dreher and Jackson, 1989; W o n g et al., 1991; W u  et al., 1992; B r u d z y n s k i et al., 1993; W u  and  Brudzynski, 1995). It is also well established that dopamine terminals w i t h i n the N A c originating from cell bodies i n the ventral tegmental area ( V T A ) are a crucial substrate for the locomotor activating properties of psychostimulant drugs such as cocaine and amphetamine  (Gold et al., 1988; P u l v i r e n t i et al., 1991; Kelley and  Throne, 1992; Steketee et al., 1992; Nestler, 1993; Smith et a l , 1995). Recently, it has been suggested that the N A c has comparatively h i g h level of a dopamine (DA) receptor subtype of D2 family, k n o w n as the D3 receptor (Sokoloff and Schwartz, 1995) w h i c h is thought to play a role i n psychiatric disease such as schizophrenia or Gilles de la Tourette's syndrome (Gilbert et al., 1995). This nucleus can be d i v i d e d into core and shell subdivisions due to the differences  i n i m m u n o l o g i c a l characterization using calcium b i n d i n g protein  calbindin-D  28kDA  (CaBP), substance P, and acetylcholinesterase  (Jongen-Reio et al., 1994) and i n their  as the  organization of afferent  and  markers efferent  projections (Groenewegen et al., 1989; Johnson et al., 1994). A n a t o m i c a l studies have s h o w n the N A c receives strong excitatory input from two major  limbic  structures; hippocampus and amygdala, and these afferents are glutamatergic i n  2 nature ( Y i m and Mogenson, 1982; Yang and Mogenson, 1984; Groenewegen et al., 1987; Robinson and Beart, 1988). A s previously observed by M o g e n s o n and colleagues (1980), the N A c has been proposed to serve as an interface between the limbic and motor systems as it appears to play an important role i n relaying limbic information to the m o t o r effector  sites.  This  hypothesis  was  later  supported  by  anatomical,  electrophysiological and behavioral findings showing that this nucleus serves as a "limbic-motor interface", by integrating signals from limbic regions and transferring them  to the  subpallidal region and then  to the  then  mesencephalic  locomotor area (Yang and Mogenson, 1987; Y i m and Mogenson, 1988; Mogenson et al, 1993). The diagram of this circuit is shown i n Fig. 1. A s noted, the N A c receives a large dopaminergic input from the V T A . Electrical stimulation of the V T A attenuates the excitatory inputs to the N A c f r o m the parafascicular nucleus of the thalamus (Sasa et al., 1991), amygdala ( Y i m and Mogenson, 1982), or from the hippocampus (Yang and Mogenson, 1984). The G A B A e r g i c m e d i u m spiny neuron, the major neuron i n the N A c , has been shown to receive both dopaminergic input from the V T A and glutamatergic input from the hippocampus and accordingly many researchers have been trying to elucidate both anatomical and functional interactions between these two major inputs. W i t h respect to the anatomical evidence, Sesack and Pickel (1990) reported that the hippocampal glutamatergic and mesolimbic catecholaminergic terminals were found to converge either o n the same spine head or o n the different part of the same dendrites of the accumbens spiny neurons. level, early w o r k revealed that the convergence  A s w e l l , at the physiological of the inputs to  accumbens  neurons from the hippocampal glutamatergic and V T A dopaminergic neurons i n  3  Fig. 1 The general scheme of the circuits showing A) the projections of the ventral subiculum, the posterior prelimbic cortex (prelimbic Cx posterior), and the posterior part of the basolateral amygdala (amygdala BL posterior) to the caudomedial accumbens (Acb), and B) the connections  of the Acb with the  mesencephalic locomotor region (MLR) via the ventral pallidum (VP). The broken line represents the ventral pallidal back-projection to the Acb (from Pennartz et al., 1994).  4 the N A c is similar i n detail to the converging inputs from amygdala and V T A (Yim and Mogenson, 1982). Mogenson  Subsequent  (1984) to investigate  the  work was conducted by Yang and  influence  of the  mesolimbic  pathway on signals reaching the N A c from the hippocampus.  dopamine  In short, results  from this study indicated that the hippocampus sends strong excitatory inputs to both the silent and spontaneously stimulation  of the  active accumbens  neurons.  Conditioning  V T A (a train of 10 H z , 300 LLA, 0.15 ms  duration),  or  iontophoretic application of D A , attenuated approximately 40-60% of the excitatory response of the accumbens neurons to hippocampal stimulation for a sustained period of time.  Iontophoretic application of trifluoperazine, or the injection of  haloperidol into the N A c could significantly block this prolonged  suppressive  effect.  mesolimbic  It is thus  feasible  that this  suppressive  action of the  dopaminergic input is functionally important i n modulating the extent to w h i c h the hippocampus  can influence  initiation of behavioral response.  motor  mechanisms,  v i a the  N A c , for  the  F r o m electrophysiological and b e h a v i o r a l  studies, there is considerable evidence that D A released from the m e s o l i m b i c terminals i n the N A c can exert a "gating" influence o n the limbic input by selecting only particular signals to be transmitted  through the N A c (Yang and  Mogenson, 1986; Mogenson et al., 1988). The gated limbic signals are subsequently relayed from the N A c to basal forebrain motor effector sites to initiate adaptive behaviors (Yang and Mogenson, 1985). Functional interaction of D A and G l u i n the N A c i n the regulation of locomotion. A n early study reported that bilateral intra-accumbens caused  a  dose-dependent  locomotor  hyperactivity  in  injection of D A  reserpine-nialamide  pretreated rats (Jackson et al., 1975). W h e n a large dose of D A was administered, a  5 suppression of exploratory locomotor activity was produced i n the first 3 m i n , and then followed by stimulation of exploratory locomotor activity (Svensson  and  A h l e n i u s , 1983). D A - i n d u c e d locomotor activity has been found to i n v o l v e both D l and D2 receptor stimulation w i t h i n the N A c (Dreher and Jackson, 1989).  On  the other hand, the neurotoxin 6-hydroxydopamine (6-OHDA) w h i c h specifically damages to dopaminergic neurons w h e n injected into the N A c , has been shown to produce motor hypoactivity w h i c h can be ameliorated by administration of the D A agonist, apomorphine (Wolterink et al., 1990). Based o n observations of the rotational behavior induced by the N M D A antagonist, DL-2-amino-5-phosphonopentanoic acid (AP-5) i n mice, it was f o u n d that glutamate  (Glu) has  a dual function  and affects behavior  in  different  directions depending o n the degree of D A D2 receptor stimulation (Svensson et al., 1992,1994a, 1995). This suggests that D A D2 receptors can modulate the behavioral effects of glutamatergic neurotransmission i n the N A c . Conversely, numerous (EAAs)  also play a role  dopaminergic mechanism.  studies have  i n regulation  s h o w n that excitatory amino of  motor  behavior  acids  by i n f l u e n c i n g  Agonists selective for different types of G l u receptors,  w h e n injected into the N A c have been shown to induce hyperactivity i n rats. For example, intra-accumbens injection of kainate ( K A ) , quisqualate ( Q A ) , an agonist at A M P A receptor, and N-methyl-D-aspartate ( N M D A ) produced a p r o n o u n c e d hypermotility response w h i c h has been shown to be antagonized by reserpine, haloperidol or fluphenazine (Donzanti and Uretsky, 1983) or antagonists of E A A receptor (Hamillton et al., 1986). Similarly, intra-accumbens injection of a - a m i n o 3-hydroxy-5-methylisoxazole-4-propionate ( A M P A ) has been s h o w n to produce a marked dose-dependent increase i n locomotor activity w h i c h is not mediated by  6 the activation of N M D A receptors (Shreve and Uretsky, 1988).  These findings  exemplify the distinctive role of separate glutamatergic ionotropic receptors i.e., N M D A vs. A M P A i n regulating motor tonic activity i n mammals. In addition, local application of the glutamatergic receptor agonists, K A and Q A , by reverse dialysis increase the efflux of D A i n the N A c (Imperato et al., 1990a) while the ionotropic glutamate receptor agonist, N M D A ,  failed to evoke D A  release (Imperato et a l , 1990b). H o w e v e r , others have reported that D A release could be evoked by G l u acting at either N M D A  or n o n - N M D A  ionotropic  receptors (Svensson et al., 1994b). Moreover, microinjection of G l u agonists, either N M D A or A M P A , into the N A c has been found to increase the locomotor activity. Prior administration of the D A D2 agonist, quinpirole, has been found to reduce this hyperkinetic effects i n dose dependent manner suggesting that D A mediated the locomotor activity induced by the G l u agonists ( W u et al., 1992). F r o m the accumulated data, it appeared that glutamatergic afferents  from  the hippocampus and dopaminergic afferents from the V T A may interact w i t h each other i n the N A c to influence a variety of behavioral responses. M e t a b o t r o p i c glutamate receptors ( m G l u R s ) : T h e i r characteristics and anatomical d i s t r i b u t i o n s i n the C N S . The  metabotropic excitatory amino acid receptor is a member  of the  glutamate receptor family that couples to G-protein to modulate m u l t i p l e second messenger systems. Presently, eight subtypes of m G l u R s have been identified and classified into three groups according to their amino acid sequence identities, signal transduction mechanisms, and agonist selectivity (Table 1 and Fig. 2) (Tanabe et al., 1992; for reviews see N a k a n i s h i , 1994; P i n and Bockaert, 1995; P i n and D u v o i s i n , 1995; C o n n and P i n , 1997).  7 The m G l u R group I ( m G l u R l and mGluR5) is coupled to phospholipase C (PLC) to stimulate phosphoinositide (PI) hydrolysis resulting i n an increase i n intracellular calcium (Ca ) as studied i n transfected C H O cells ( A r a m o n i and 2+  Nakanishi,  1992).  By using immunocytochemical-ultrastructural  approaches,  M a r t i n et al. (1992) reported the abundant presence of m G l u R l i n the olfactory bulb, hippocampus, globus pallidus, thalamus, substantia nigra, superior colliculus and cerebellum.  O n a subcellular level, m G l u R l is localized postsynaptically to  dendritic shafts, dendritic spines and also i n neuronal cell bodies.  Similarly, a  h i g h density of m G l u R 5 is located postsynaptically i n the olfactory bulb, anterior olfactory nuclei, olfactory tubercle, cerebral cortex, hippocampus, lateral septum, striatum, inferior colliculus, spinal trigeminal nuclei as w e l l as i n the nucleus accumbens (Shigemoto et al., 1993). The m G l u R  group 2 (mGluR2  and mGluR3)  and group 3 ( m G l u R 4 ,  m G l u R 6 m G l u R 7 , and m G l u R 8 ) , however, are negatively l i n k e d to adenylate cyclase activity resulting i n a reduction of adenosine 3'5'-cyclic monophosphate (cyclic A M P ) formation (Schaffhauser et al., 1997). The study of Petralia et al. (1996) has reported the location of m G l u R 2 a n d / o r m G l u R 3 i n glutamatergic presynaptic terminals, mostly at mossy fiber synapses i n the hippocampus, supporting the idea that presynaptic metabotropic m G l u R s may play a role i n plastic changes at glutamatergic synapses. Immunocytochemical evidence has s h o w n that m G l u R 2 is located both pre- and  postsynaptically  mainly i n the  cerebellar  hippocampus, neocortical and limbic cortical regions (Neki et al., 1996).  cortex, Both  m G l u R group 2 and m G l u R group 3 are also thought to act presynaptically as autoreceptor  involved  i n the induction of long term  synaptic depression  at  various brain regions, i.e., locus coeruleus (Dube' and Marshall, 1997), caudate  30 I  40 1  50 1  60 1  70 1  80 I  mGluR6  mGluR8  mGluR7  mGluR4  mGluR3  mGluR2  mGluR5  mGluRl  90 % Identity I  in  II  Group  •I cAMP  IcAMP  T PI hydrolysis  Transduction  L-AP4 > L-SOP > glutamate > ibotenate > quisqualate > (1S,3R)-ACPD  DCG-IV>L-CCG-I> L-glutamate > (1S,3R) ACPD > 4C3HPG > ibotenate > quisqualate  quisqualate > L-glutamate > ibotenate > L-homocysteine sulfinate >trans-ACPD  Rank order of agonist potency  MPPG, MSPG, MTPG M3CM4HPG, M4H3PMPG for both mGluR group 2 and group 3  MCPG for mGluR2  MCPG 4C3HPG, 4CPG for mGluRl but not mGluR5  Antagonists  Table 1 Dendrogram and pharmacological distinction between cloned mGluR subtypes, (adapted from Pin and Bockaert, 1995; Pin and Duvoisin, 1995)  00  9  Fig. 2  Schematic view of the possible roles of m G l u R s at the glutamatergic  synapse. inhibit  The m G l u R l / 5 located mainly at post-synaptic neurons or potentiate  L-Type voltage-sensitive  calcium  channel  can either (L-VSCC).  A c t i v a t i o n of m G l u R l / 5 could stimulate the release process by s t i m u l a t i n g protein kinase C (PKC) and inositol 1,4,5-triphosphate induce an increase of C a activate big C a  2+  2 +  (IP ) hydrolysis w h i c h 3  from intracellular storages.  activated K  +  channel (BK), inhibit  The m G l u R l / 5 can  the i n w a r d rectifier K  channels (IKs) and particularly modulate the activity of N M D A  and  +  AMPA  channel at postsynaptic neurons. m G l u R group 2 and 3 are located mainly at presynaptic neurons responsible for inhibiting the release process possibly v i a N type V S C C (from P i n and Bockaert, 1995).  10 nucleus (Cozzi et al., 1997), and hippocampus (Kamiya et al., 1996; M a n a h a n Vaughan, 1997). Functional roles of m G l u R s i n mediating D A release i n the N A c . A s previously mentioned, numerous  studies have addressed the role of  ionotropic glutamate receptors (iGluRs) i n mediating D A release i n the N A c as well as their effects on motor behaviors.  Recent evidence  also indicates a  functional interaction between m G l u R s and D A i n limbic striatum, particularly i n the N A c . Taber and Fibiger (1995) employing in vivo microdialysis revealed a n inhibitory effect of m G l u R s o n D A release evoked by prefrontal cortex (PFC) stimulation.  Furthermore,  a  selective  mGluR  agonist,  trans (1S,3R)-1-  aminocyclopentane-l,3-dicarboxylic acid (r-ACPD), w h e n applied locally to the N A c by reverse dialysis caused a dose-dependent effect o n D A release i n w h i c h a low dose (100 LIM) induced a decrease whereas a higher dose (1 m M ) induced a n increase i n extracellular D A levels i n the N A c .  The later effect w i t h doses i n the  m M range is consistent w i t h the finding of Ohno and Watanabe  (1995) w h o  reported a persistent increase i n D A release i n the N A c following local perfusion of A C P D (1 m M ) and this facilitatory effect could be antagonized by co-perfusion w i t h (+)-a-methy-4-carboxyphenylglycine ( M C P G ) , a specific antagonist of m G l u R 1/2. In a behavioral study, Attarian and A m a l r i c (1997) found that activation of m G l u R s by perfusion of A C P D to the N A c caused a dose-dependent increase i n locomotor activity i n rats and this effect appeared to be mediated through the D A system i n the N A c . Taken together, these studies suggest that l o w doses of m G l u R agonists may exert inhibitory effects o n D A levels i n the N A c whereas higher less specific doses may facilitate D A neurotransmission.  Table 2 and 3 show the data  11 from  the recent  studies demonstrating  the potency of several agonists a n d  antagonists at m G l u R s . A recent study by Blaha et al. (1997) using in vivo chronoamperometry w i t h stearate-graphite paste electrodes i n urethane-anaesthetized stimulation  of the  ventral  subiculum/CAl  rats has s h o w n that  (Vsub/CAl)  region  of the  hippocampus w i t h burst patterned monophasic pulses (10-100 H z / b u r s t delivered at 0.8-4 H z ) could evoke a three component change i n the D A signal i n the N A c . In brief, the first and the third component, i n w h i c h D A signals are significantly increased above baseline following antagonized  by  microfusion  burst-stimulation of V s u b / C A l  of  the  iGluR  antagonists,  dinitroquinoxaline-2,3-dione ( D N Q X ) , and kynurenate.  could be  A P - 5 , 6,7-  I n contrast, the second  component i n w h i c h the D A signal is significantly decreased below the baseline was blocked selectively by microinfusion of the m G l u R antagonist, M C P G .  These  results suggested that G l u released physiologically from V s u b / C A l inputs to the N A c selectively activates i G l u R and m G l u R w i t h i n the N A c resulting i n a n increase or an decrease i n extracellular D A levels, respectively. F r o m available data, the m G l u R s inhibiting the release of D A from  appear to play a functional role i n  the dopaminergic neurons  i n the N A c as  suggested b y several lines of evidence. Firstly, anatomical evidence from a m R N A in situ hybridization study has revealed the expression of m G l u R s mGluR5)  i n the N A c (Testa et al., 1994).  (mGluRl-  Secondly, an in vivo study has  demonstrated that reverse dialysis of A C P D at l o w concentration (100 uM) into the N A c produces a marked decrease i n extracellular D A level i n the N A c (Taber and Fibiger, 1995). Thirdly, the recent in vitro study i n the rat N A c slice preparation has s h o w n that m G l u R group 2/3 but not group 1 is implicated i n the inhibition of  12  Table 2 A summary of potency of several agonists and antagonists of m G l u R s as tested o n cell lines that express m G l u R subtype (from C o n n and P i n , 1997) mGluRla mGluRSa mGIuR2 mGluR3 mGluR4a mG!uR6 mGluR7 mGluR8 Agonists  Glutamate Quisqualate Ibotenate IS, 3R-ACPD IS, 3S-ACPD L-CCG-1 DCG-IV 2R, 4R-APDC L-AP4 L-SOP L-AP3 1-HPG 3, 5-DHPG 4C3HPG i-ADA CPAP4  9-13 0.2-3.0 10-60 10-80 >300 50  3-10 0.03-0.3 2-10 5-7 >300  n.e.  n.e.  —  — —  4-20 >1000 35-250 18 13 0.3-0.4 0.3 3*  4-5 40 10-15 8 30 1 0.2  —  n.e.  n.e.  n.e.  n.e.  n.e. Ant. 68-100 6.6 Ant. 190  Ant. 14-35 2 >300 30  —  — —  20-50 >1000  —  —  —  — — — — — — —  n.e. n.e.  3-20 100-1000 100-1000 »300 50 9-50 >1000  —  0.4-1,2 . 2-5  —  n.e. n.e. n.e. n.e.  0.6  16 >300 >300 300  — — — —  1000  0.02  — — — — —  — — — — — — —  n.e.  —  0.9 2.7  160-500 >160  — — — — — —  n.e.  — — — — — — — — — — — — — — —  n.e.  —  n.e.  — — —  0.4  — — — — — — —  ntagonists  MCPG 4C3HPG 3C4HPG 4CPG MPPG MSPG MTPG MCCG-I MAP4 L-AP3 ABHD-I AIDC PCCG-IV 7HCCMA ADPD  40-200 >200 100-1000 10-40 P. Ag. (?) Ag. 300-400 Ag— 15-65 >500 Ag. (?) >1000 n.e. 100 n.e. 250 — >1000 n.e. 450 n.e. 84 — n.e. 500 — >1000 >1000 — 300 — — 7 n.e. — n.e. n.e. 8 2 n.e. — n.e. n.e. 18,1  Noted: potency is shown in EC  5 0  , IC  5 0  >1000  — — — — — — — — — — — — — —  n.e. n.e. n.e. n.e. 54  »1000 n.e. n.e.  90-190  — —  n.e.  Ag.  — —  — — — — — — — — — — — — —  — — — — — — — — —  —  , or K values QiM); n.e., no effect; —, not determined. b  MPPG MSPG M3CM4HPG M3CMPG " M3C4HPG ' ( + )-M4CPG . E4CPG " M3CPG " M4H3PMPG M4CMPG '" ( - )M4CPG MTPG M4C3C1PG  1 2 3 4 5 6 7 8 9 10 11 12 13 8  8  a  MPPG MSPG M3CM4HPG M3CMPG * M4H3PMPG M3C4HPG " (+ VM4CPG * B4CPG M3CPG " MTPG M4C3C1PG " ( - )M4CPG M4CMPG  L-AP4 b  b  b  MTPG MPPG MSPG ( + VM4CPG a  (1S,3S)-ACPD  Neonatal spinal cord  b  b  b  MPPG MSPG MTPG (+ )-M4CPG  L-AP4  a  a  8  8  8  a  (+ VM4CPG 4C2IPG (5)-4CPG • MPPG M4C3HPG MTPG M4CMPG MSPG M3CM4HPG M4C3C1PG M3CMPG M3CPG M3C4HPG  8  8  (15,3/?)-ACPD  Neonatal cortex  Phosholipase C  (SMCPG 4C2IPG (+ )-M4CPG  L-Quisqualate  Granule cells  Abbreviations: (#S)-a-rnetriyl-4-phosprionophenylglycine (MPPG; (/?S)-a-methyl-4-sulphonophenylglycine (MSPG); (/?5)-Q-meihyl-3-carboxymethyl-4hydroxyphenylglycine (M3CM4HPG); (/?5)-a-methyl-3-carboxymethylphenylglycine (M3CMPG); (/?5)-a-methyl-3-carboxy-4-hydroxyphenylglycine (M3C4HPG); ( + )-a-methyl-4-carboxyphenylglycine (M4CPG); (/?5)-a-ethyl-4-carboxyphenylglycine (E4CPG); (/?5)-Q-methyl-3-carboxyphenylglycine (M3CPG); (/?5)-a-methyl-4-hydroxy-3-phosphonomethylphcnylglycine (M4H3PMPG); (/?5)-a-methyl-4-carboxymethylphenylglycine (( + VM4CMPG); (/?5)-Q-methyl-4-ietrazolylphenylglvcine (MTPG); (/?5)-a-methyl-4-carboxy-3-chlorophenylglycine (M4C3CIPG); (S)-4-carboxyphenylg)ycine ((5)4CPG): (A?5)-4-carboxy-2-iodophenylglycine (4C2IPG). Previously published data from (a) Bedingfield et al. (1995); (b) Jane et al. (1995).  8  L-CCG-1  Rank  a  Adult rat cortex  Tissue  a  Adenyly) cyclase  Coupling  in different tissue preparations (from Bedingfield et al., 1996).  Table 3 Summary of potency of phenylglycine compounds (in rank orders) as antagonists of mGluR specific agonists  14 transmission at the prefrontal-accumbens  synapses v i a a presynaptic m e c h a n i s m  (Manzoni et al., 1997). Finally, in vivo experiments i n urethane anaesthetized rats have s h o w n that electrical stimulation of V s u b / C A l at 2 H z frequency induces a marked decrease of D A efflux below the baseline level w h i c h c o u l d be blocked by co-application w i t h M C P G (Blaha et al., unpublished data). Therefore, it is hypothesized that 1) 2 H z stimulation of V s u b / C A l i n the freely m o v i n g rats w i l l modulate the release of G l u w h i c h subsequently induce an inhibition of D A release from the dopaminergic terminals i n the N A c , and 2) these suppressive  effects of V s u b / C A l stimulation  are mediated  by m G l u R s  located o n presyaptic G l u terminals. A diagram of the proposed role of m G l u R s i n regulating D A release i n the N A c is shown i n Fig. 3. The present study employed in vivo microdialysis techniques w i t h h i g h performance  liquid  chromatography  (HPLC) analysis of the dialysate obtained from the N A c of the unanaesthetized, freely m o v i n g rats. This procedure provided the unequivocal identification of extracellular D A and w h e n combined w i t h freely m o v i n g subjects removed  any  confounding effects of anaesthetic agents. This procedure has the added advantage that drugs can be applied locally to the N A c by reverse dialysis while collecting the dialysate for analysis from the same area. The m a i n aims of the study were: 1) to investigate the effects of low frequency electrical stimulation of V s u b / C A l o n extracellular D A levels i n the N A c , and 2) the effects of M C PG, a specific antagonist of m G l u R at m G l u R l / 2 , and M P P G , an antagonist of m G l u R group 2 and 3 , o n basal levels of D A i n the N A c , as w e l l as o n changes i n levels of D A induced by V s u b / C A l 2 H z frequency  stimulation.  In order to determine  whether  any  observed i n h i b i t i o n is of short or long duration, D A was measured for 120 m i n following 2 H z stimulation.  15  Fig. 3 Diagram of a proposed mechanism that regulates the release of D A i n the N A c .  A ) U n d e r n o r m a l condition: the spontaneous release of G l u f r o m  glutamatergic terminals of the V s u b / C A l induces the release of D A from the dopaminergic terminals i n the N A c v i a iGluRs. release  of G l u from  the  Vsub/CAl  is reduced  B) 2 H z stimulation: the by the  mechanism  of  presynaptic m G l u R group 2/3 following 2 H z stimulation w h i c h eventually attenuates the release of D A from the terminals of V T A afferents i n the N A c .  16  METHODS Subjects The subjects i n all experiments were male Long-Evans rats (Charles R i v e r ; St. Constant, Quebec, Canada), weighing between 350-400 g at the time of surgery. They were i n d i v i d u a l l y housed i n plastic cages i n a colony r o o m w i t h a n ambient temperature of 25 °C and a 12:12 hr l i g h t d a r k cycle (light o n at 7 am). Food (Purina Rat Chow) and water were available ad libitum. Surgery Prior to cannula implantation, rats were anesthetized w i t h  ketamine  hydrochloride (100 m g / k g , i.p.) and xylazine (10 m g / k g , i.p.) and placed i n a stereotaxic apparatus. drilled.  The dorsal skull surface was exposed and holes were  A microdialysis probe guide cannula (19 ga.) was implanted over the  N A c (co-ordinates: A P = +1.7 m m from bregma, M L = +1.2 m m from m i d l i n e , and D V = -1.0 m m from dura; according to the atlas of Paxinos and W a t s o n (1986)).  A bipolar stimulating electrode was implanted ipsilateral to  the  microdialysis probe guide cannula w i t h the tip centered i n the V s u b / C A l region of the hippocampus (co-ordinates from bregma: A P = -5.8 m m from bregma, M L = ±5.6 m m from midline, and D V = -6.5 m m from dura). The guide cannula and the stimulating electrode were secured chronically to the s k u l l w i t h four set screws and dental acrylic. The animals were allowed to recover fully for at least 2 days before implanting a microdialysis probe.  17  M i c r o d i a l y s i s Procedure Microdialysis probes (Fig. 4 A ) used i n all experiments were constructed i n the laboratory.  The probes were of a concentric-style consisting of  a 24-ga  stainless steel cannula (34 mm), fused silica tubing ( 75 p i i.d. x 150 u m o.d.), polyethylene (PE 50) tubing and a semipermeable hollow-fiber membrane (2 m m of exposed membrane, 340 um o.d., 65,000 M . W . cut off, Filtral 12, Hospalgambro). Epoxy glue was used to seal joints and p l u g the dialysis fiber tip. T h e inlet tubing was connected to a swivel w h i c h was mounted above the testing chamber.  A l i q u i d switch ( C M A / 1 1 0 , Carnegie Medicin), located between the  swivel and the infusion pumps, was used manually to exchange the standard perfusate solution to one containing drug.  Figure 5 shows a diagram of the  preparation used i n the study. The relative recovery for D A was obtained pre-m vivo by i m m e r s i n g the tip of the probe i n a m e d i u m containing D A at k n o w n concentration and perfusing w i t h perfusate at a constant rate of 1 | i l / m i n for at least 30 m i n before collecting samples at a fixed interval of 10 m i n .  D A concentration i n the outflow was  determined by H P L C - E C D . The relative recovery was calculated as: Recovery in vitro = C Where C  o u t  o u t  /C  i n  is the D A concentration i n the outflow and C is the m e d i u m . i n  Typical in vitro recovery for D A at ambient temperature and 1 u l / m i n was 22%. The day before conducting an experiment, the microdialysis probe was continuously perfused w i t h perfusate solution (147 m M N a C l , 3.0 m M KC1, 1.3 m M C a C l . H 0 , 1 . 0 m M M g C l . 6 H 0 , 0.01 M S o d i u m phosphate buffer; p H 7.32  2  2  2  7.4) at a constant rate of 1 u l / m i n using a syringe p u m p (Harvard model 22). T h e probe was secured i n the microdialysis probe collar (Fig. 4B) by the top screw.  18  A) Microdialysis Probe yfc  Outlet Tubing (Silica) Inlet Tubing (PE 50; Silica)  Microdialysis Probe Collar Epoxy P E 50 Tubing  Thread for Protective C o i l Attachment Setting Screws  C) Guide Cannula 15 m m  Stainless Steel Tubing (24 ga.)  Dialysis _ Membrane  Fig. 4  . Stainless Steel Tubing (19 ga.)  34 m m  -»'s  mm -Epoxy  A graphic illustration of a dialysis system. The system consists of a concentric  design microdialysis probe (A) w i t h a tip of 2 m m for collecting dialysate from the N A c , a microdialysis probe collar (B) for securing the probe and an implanted guide cannula, and a guide cannula  (C) w h i c h is used to implant  chronically  stereotaxically over the area of the N A c . (adapted from Fiorino et al., 1993)  and  Fig. 5  Diagrammatic illustration of the set up (A) w h i c h consists of a testing  chamber equipped w i t h two swivels, an electrical stimulator, an isolator unit, two syringe pumps and a l i q u i d switch. The sagittal view of the rat's brain (B) shows the placement of the stimulating electrode and the microdialysis probe.  20 After checking the v o l u m e of collected sample, the probe was inserted into the guide cannula (Fig. 4C) w h i c h had already been implanted over the N A c area of the animal.  The bottom screw of the probe collar was then secured.  The  microdialysis probe was continuously perfused overnight at a flow rate of 1 \iM/min  approximately 15-18 hr prior to experimental testing.  A n a l y s i s of Dialysates The dialysis membrane used i n these studies does not allow proteins and other large molecules above a M . W . of 65 K Daltons into the perfusate, therefore the sample is relatively cleaned up and can be injected directly into the H P L C system without further purification (Benveniste and Huttemeier, 1990). FfPLC-ECD system used i n the  experiments  consisted  of a Biorad  The pump  (Richmond, C A ) delivering 0.8 m l / m i n at a pressure of 123 K g / c m , an E C 1 0 W 2  two-position injector, an Ultrasphere c o l u m n (Beckmann, Fullerton, C A , O D S 5 u.m, 15 c m x 4.6 mm), an E S A (Bedford, M A ) , and a C o u l o c h e m II E C detector. The w o r k i n g potentials were: +450 m V (electrode 1), -300 m V (electrode 2) and +450 m V (guard cell).  The mobile phase consisted of 6 g/1 s o d i u m acetate, 70  mg/1 octyl sulfate (adjustable), 10 mg/1 ethylenediaminetetraacetic acid ( E D T A ) , 35 m l / 1 glacial acetic acid and 865 m l M i l l i Q purified water. The mobile phase was adjusted to p H 3.5 w i t h glacial acetic and filtered through 0.22 |a.m sterile n y l o n filter unit (Millipore). Filtered methanol (10% per volume) was added to the mobile phase solution and degassed prior to use. Chromatograms were registered o n a dual pen chart recorder (Kipp and Zonen, Bohemia, N Y ) . D A was quantified from each sample by comparing sample peak heights to peak heights from a calibration curve of the standard solution containing D A at three different concentrations.  21  Electrical S t i m u l a t i o n O n the day of experiment, the dialysate samples were collected every 10 min  and immediately analyzed by H P L C - E C D .  Electrical stimulation  was  performed after establishing a stable D A baseline defined as three consecutive samples w i t h less than 10% variation i n peak height. Cathodal constant current pulses were delivered to the V s u b / C A l through an isolator (Iso-flex, A.M.P.I) v i a a master stimulator  (a dual channel stimulator m o d e l 4710, Ortec, E G & G  company). Parameters for electrical stimulation were a total of 200 pulses, 300 LIA delivered at 2 H z , 5 H z or 10 H z for 100 sec, 40 sec or 20 sec, respectively. For most of the experiments reported i n this thesis, 2 H z stimulation frequency was used to produce a reliable inhibition of D A release. Pharmacological Studies After establishment of baseline D A levels, specific m G l u R  antagonists,  either M C P G (at doses of 10 u M , 100 u M or 1 m M ) or M P P G (at doses of 100 u M , 1 m M or 10 m M ) , were administered locally for 20 m i n v i a reverse dialysis (i.e., through the same microdialysis probe used to measure D A ) . Both drugs were purchased from Precision Biochemical Inc. (Vancouver, Canada).  A 10 m M  M C P G or M P P G stock solution was prepared by dissolving w i t h 50-100 Lil of 0.1 M N a O H solution w h i c h was then topped up to 1 m l w i t h n o r m a l perfusion m e d i u m and kept frozen as aliquots at  -20 ° C D r u g was diluted from frozen  aliquots w i t h n o r m a l perfusate solution immediately prior to use.  The p H of  M C P G and M P P G solutions used i n the present study are s h o w n as follows:  22  Drug  Concentration  p H value  MCPG  10 u M  7.3  100 u M  7.4  1 mM  7.6  100 u M  7.6  1 mM  7.6  10 m M  8.5-8.7  MPPG  In subsequent experiments, M C P G at dose of 10 [iM and 100 \xM or M P P G at doses of 100 ( i M and 1 m M was administered i n combination w i t h electrical stimulation of V s u b / C A l . Histology After completion of each experiment, D C current (100 u A for 10 sec) was passed through  the bipolar stimulating  electrode.  A n i m a l s were  transcardially w i t h 0.9% saline followed by 4% formaldehyde  perfused  solution.  brains were then removed and placed i n 10% sucrose i n 4%  The  formaldehyde.  Serial 50 a m coronal sections were cut o n a freezing microtome and stained for N i s s l substance w i t h cresyl violet.  Placements of the dialysis probe and the  bipolar stimulating electrode were determined under a light microscope. Data A n a l y s i s The data are presented as the percentage of the mean of three before the first electrical stimulation or before drug perfusion.  samples  Data f r o m  implanted control group, electrical stimulated group, drug-treated group or drugtreated i n combination w i t h electrical stimulation groups, were analyzed for statistical significance using two-way, b e t w e e n / w i t h i n subjects m i x e d analysis of  23 variance ( A N O V A ) design, w i t h treatment as the between subjects factor, and sample as the w i t h i n subjects factor, unless stated otherwise. significant treatment  Whenever  a  x sample interaction was observed, subsequent s i m p l e  m a i n effects analyses were conducted using one-way between subjects A N O V A w i t h Dunnet's or Tukey's post hoc tests. between groups at each sample.  These analyses assessed differences  24  RESULTS 1) Effect of V s u b / C A l stimulation on extracellular levels of D A i n the N A c . The baseline value of the extracellular D A concentration  in  dialysates  collected from the N A c was 2.42 + 0.08 n M (mean ± S.E.M., n= 67). These values were uncorrected for probe recovery w h i c h were i n the range of 20-22%. The initial experiment stimulation  of the  was designed to examine the effect of electrical  Vsub/CAl  at three different  sequential  frequencies  on  extracellular levels of D A i n the N A c . A stimulation current intensity of 300 u A and a total of 200 pulses were used as a fixed parameter for all stimulation.  A set  of three consecutive electrical stimulation of V s u b / C A l w i t h a period of seventy minutes between each stimulation at 2 H z , 5 H z , and 10 H z for 100 sec, 40 sec, and 20 sec, respectively, was found to induce changes i n extracellular level of D A i n a frequency-dependent manner  (Fig. 6).  Stimulation  of V s u b / C A l  at lowest  frequency (2 H z ) tested caused a decrease i n extracellular D A levels i n the N A c w h i c h reached statistical significant p < 0.05 at 30 m i n and p < 0.01 at 50, and 70 m i n following electrical stimulation.  In contrast, subsequent stimulation 5 H z  caused no change i n the depressed baseline  induced by 2 H z s t i m u l a t i o n .  Subsequent stimulation at 10 H z resulted i n an increase i n extracellular D A levels back to the pre-2 H z stimulation baseline. experiments  It should be noted that these  were not designed to test systematically the effects of  different  stimulation frequencies o n D A release. A l l subsequent experiments focused o n the effects of 2 H z stimulation o n D A efflux i n the N A c . In further experiments (n=9), electrical stimulation of V s u b / C A l at 2 H z for 100 sec alone was shown to produce a significant and long lasting decrease i n  25  Fig. 6 Effects of electrical stimulation of V s u b / C A l o n extracellular concentration of D A i n ipsilateral N A c . Each stimulus consisted of 200 pulses of constant current (300 uA) single pulses delivered at 2 H z (SI), 5 H z (S2), and 10 H z (S3) for 100 sec, 40 sec, and 20 sec, respectively. The data are expressed as a percentage of the mean of three basal samples before the first stimulation (SI). Each value is the mean + S E M (n=5). * significantly different from prestimulation baseline p < 0.05, ** p < 0.01, one way repeated measure A N O V A w i t h Dunnet's post hoc test.  26 extracellular D A levels i n the N A c that lasted throughout the 120 m i n period of measurement (p < 0.01) as compared to non-stimulated animals (control group) (Fig- 7). 2) Pharmacological studies. According to available data, m G l u R s i n the N A c have been s h o w n to modulate D A release from terminals of dopaminergic neurons and to i n h i b i t transmitter release i n several other brain regions (Kamiya et al., 1996; C o z z i et al., 1997; Manahan-Vaugnan, 1997). Therefore, the following experiments examined the role of m G l u R s i n modulating the basal release of D A as w e l l as i n mediating the suppressive effect o n extracellular D A levels i n the N A c observed i n the previous study following 2 H z stimulation of V s u b / C A l . 2.1 Effects of selective m G l u R s antagonists on basal D A levels i n the N A c . M C P G , a specific antagonists at m G l u R l / 2 (Sekiyama et al., 1996), and M P P G , a potent L-AP4-sensitive presynaptic m G l u R antagonists (Jane et al., 1995; Robert, 1995), were tested for their local effects o n basal extracellular D A levels i n the N A c . A s shown i n Fig. 8, reverse dialysis of M C P G at concentrations of 10 u.M (n=5) and 100 u M (n=6) for 20 m i n caused no significant change i n D A levels after drug perfusion was discontinued. Reverse dialysis of M C P G at dose 1 m M (n=6) also was without significant effect on baseline D A levels but again a trend for a delayed decrease was more marked and persisted throughout the period of sample collection. Moreover, the variability of the data at the dose of 1 m M was higher than those of 10 u M and 100 u M . The effects of M C P G o n basal levels of D A release i n the N A c are summarized i n F i g 8. In contrast, reverse dialysis of M P P G at dose of 100 u M for 20 m i n (n= 5) caused a decrease i n D A level i n the N A c w h i c h achieved significance (p < 0.05)  27  Fig. 7 Effects of electrical stimulation of V s u b / C A l o n extracellular concentration of D A i n ipsilateral N A c . The stimulus consisted of 200 pulses of constant current (300 uA) single pulses delivered at 2 H z for 100 sec. Dialysate samples were collected every 10 m i n , and stimulation was delivered after stable baselines were established. Each value is expressed as a percentage of the mean of four basal samples before stimulation (S) i n the 2 H z frequency stimulation group (n=9). Each value is the mean +. S E M . There was a significant group x sample interaction (F(14, 182) = 5.563, p < 0.001) * significantly different from the control group, p < 0.01, simple m a i n effects analysis w i t h Dunnet's post hoc test.  28  Fig.8 Time-course of the effects of local administration of M C P G at doses of 10 U.M (n=5), 100 LLM (n=6) or I m M (n=6) o n basal levels of D A i n the N A c . Dialysate samples were collected every 10 m i n and each dose of M C P G was perfused for 20 m i n as indicated by horizontal bar. Each value is expressed as a percentage of the mean  + S E M of three basal samples before drug administration.  A n overall  A N O V A analysis revealed no significant different between the drug-treated groups and the control group.  DAoutput(% baseline) DA output (% baseline)  DA output (% baseline)  30 at 80, 90, 100, and 120 m i n time points. Perfusion of M P P G at a dose of 1 m M , however,  resulted  i n no  significant changes  i n D A levels  i n the N A c .  A p p l i c a t i o n of M P P G at dose of 10 m M caused a biphasic effect i n w h i c h a significant decrease i n D A levels (p < 0.05) was observed at 20 and 40 m i n time points, followed by a return to baseline. A transient increase w i t h large variance was observed at 70 m i n .  Dose-related effects of M P P G on basal levels of D A  release i n the N A c are shown i n Fig. 9. A s previously mentioned  i n the  methods  section, a diluted  NaOH  solution was used to dissolve both drugs, and all of the 5 solutions were found to be i n the range of 7.3-7.6 p H . However, the p H of a 10 m M M P P G solution was i n the range of 8.6-8.7.  To determine whether p H may account for the biphasic  effects on D A efflux observed following the application of 10 m M M P P G , a n additional experiment was conducted consisting of perfusion w i t h a v e h i c l e solution (diluted N a O H , p H 8.7) into the N A c (n=4). A s s h o w n i n Fig. 10, a vehicle solution w i t h a p H of 8.7 induced a delayed decrease i n basal D A levels i n the N A c w h i c h reached statistical significance (p < 0.05) at 40 and 50 m i n time points as compared to the control (normal p H perfusion medium) group. W h e n the data from the control (normal perfusion medium)  group, the v e h i c l e -  d i l u t e d N a O H , p H 8.7) treated group, and the M P P G (dose 10 m M ) treated group were compared and analyzed for statistical significance, it was found that both the MPPG-treated and the vehicle-treated groups showed a significant decrease i n D A levels at 20, 30, and 40 m i n time points and at 40 and 50 m i n time points, respectively.  In addition, there was a significant increase: i n D A levels i n the  MPPG-treated group at the 70 m i n time point compared to the vehicle-treated group.  31  Fig. 9 Time courses of the effects of local administration of M P P G at doses of 100 (n=5), 1 m M (n=5) and 10 m M (n=5) o n basal levels of D A i n the N A c . Dialysate samples were collected every 10 m i n and each dose of M P P G was perfused for 20 m i n (horizontal bar) after establishing a stable baseline. Each value is expressed as a percentage  of the  administration.  mean  + S E M of three  basal  samples  before  the  drug  There was a significant group x sample interaction (F (14, 434) =  1.843, p < 0.001), * significantly different from the control group, p < 0.05, simple main effects analysis w i t h Dunnet's post hoc test.  D A output (% baseline)  DA output (% baseline)  D A output (% baseline)  33  60 H -20  1  1  1  1  1  1  1  1  1  1  1  -10  0  10  20  30  40  50  60  70  80  90  1  100  1  1  110  120  time (min)  Fig. 10 Time-course of the effects of local administration of MPPG at a dose of 10 mM (n=5) and its p H adjusted vehicle (diluted NaOH, p H 8.7, n=4) on basal levels of D A in the NAc. Dialysate samples were collected every 10 min and MPPG or its pH adjusted vehicle were perfused for 20 min (horizontal bar) after establishing a stable baseline. Each value is expressed as a percentage of the mean + SEM of three basal samples before the drug administration.  There was a significant group x sample  interaction (F (14, 168) = 2.071, p < 0.005). * significantly different from the control group (normal p H perfusion medium) p < 0.05, ** p < 0.001, # significantly different from the vehicle group  (diluted NaOH, pH 8.7) p < 0.005, simple main effects  analysis with Tukey's post hoc test.  34  2.2 Role of mGluR in the inhibition of D A release in the NAc induced by 2 Hz stimulation of V s u b / C A l . The effects of M P P G at doses of 10 u M and 100 u M and M P P G at doses of 100 u M and 1 m M o n the decrease i n D A levels i n the N A c induced by 2 H z stimulation of V s u b / C A l were investigated. It was found that M C P G at doses of 10 u.M (n=5) and 100 u M (n=6) applied 10 m i n prior to electrical stimulation d i d not antagonize the suppressive effect on D A efflux i n the N A c induced by 2 H z stimulation of V s u b / C A l as shown i n Fig. 11 and 12, respectively.  Statistical  analysis revealed no significant difference between the 2 H z stimulation (control) group and the 2 H z stimulation plus M C P G group. Local administration of M P P G at a dose of 100 u M (n=6) into the N A c 10 m i n prior to V s u b / C A l stimulation (Fig. 13) showed a trend of attenuation of the 2 H z stimulation-induced decrease i n D A levels compared to the control (2 H z stimulation) group during the first 20 m i n post-stimulation period, h o w e v e r , these values d i d not differ significantly. These D A levels i n the N A c gradually returned to basal values 80 m i n after applying electrical stimulation. There was a significant group x sample interaction and simple m a i n effects analysis w i t h Dunnet's post hoc test showed significant differences between this MPPG-treated group and the control (2 H z stimulation) group at 100 (p < 0.01), 110, and 120 (p < 0.005) m i n time points following electrical stimulation.  A t a higher dose of  M P P G ( I m M ) , the levels of D A i n the N A c returned to basal values  sooner  compared to the effects of 100 u M M P P G (Fig. 14). A s w i t h the lower dose of M P P G , the magnitude and time course of the initial phase of suppressive effects of 2 H z stimulation o n D A efflux was not altered by 1 m M M P P G . There was a significant group x sample interaction and simple m a i n effects analysis w i t h  35 Dunnet's post hoc tests showed significant differences between this group and the control (2 H z stimulation) group at 70 (p < 0.05), 80 (p < 0.001), 90 (p < 0.01), 100 (p < 0.001), 110 (p < 0.05) and 120 (p < 0.001) m i n time points following electrical stimulation of V s u b / C A l at 2 H z .  36  120  -TJ  2Hz (n=9) 2Hz+10uM-MCPG (n=5)  110-  -20  -10  0  10  20  30  40  50  60  70  80  90  100  110  120  time (min)  Fig. 11 Effects of M C P G at dose of 10 LIM (n=5) i n combination w i t h V s u b / C A l stimulation o n extracellular concentration  of D A i n the N A c .  The  stimulus  consisted of 200 pulses of constant current (300 | i A ) single pulses delivered at 2 H z for 100 sec. Dialysate samples were collected every 10 m i n and M C P G was perfused for 20 m i n (horizontal bar) after establishing a stable baseline.  Stimulation was  performed after 10 m i n of drug perfusion. Each value is expressed as a percentage of the mean + S E M of three basal samples before stimulation (S). A n overall A N O V A analysis revealed no significant different between these two groups.  37  Fig. 12 Effects of M C P G at dose of 100 u M (n=6) i n combination w i t h V s u b / C A l stimulation o n extracellular concentration  of D A  i n i:he N A c . The  stimulus  consisted of 200 pulses of constant current (300 (iA) single pulses delivered at 2 H z for 100 sec. Dialysate samples were collected every 10 m i n and M C P G was perfused for 20 m i n (horizontal bar) after establishing a stable baseline.  Stimulation was  performed after 10 m i n of drug perfusion. Each value is expressed as a percentage of the mean + S E M of three basal samples before stimulation (S). A n overall A N O V A analysis revealed no significant different between these two groups.  38  2Hz (n=10)  2Hz+100uM-MPPG (n=6)  1  ~i  -20  -10  0  10  20  i  30  r  40  50  60  70  80  90  100  110  120  time (min)  Fig. 13 Effects of M P P G at dose of lOOuM (n=6) i n combination w i t h stimulation o n extracellular concentration of D A  i n the N A c .  The  Vsub/CAl stimulus  consisted of 200 pulses of constant current (300 uA) single pulses delivered at 2 H z for 100 sec. Dialysate samples were collected every 10 m i n and M P P G was perfused for 20 m i n (horizontal bar) after establishing a stable baseline.  Stimulation was  performed after 10 m i n of drug perfusion. Each value is expressed as a percentage of the mean + S E M of three basal samples before stimulation (S).  There was a  significant group x sample interaction (F (14, 378) = 2.136, v < 0.001), * significantly different from control inhibition, p < 0.01, ** p < 0.005, simple m a i n effects analysis w i t h Dunnet's post hoc test.  39  120  2Hz  n  (n=9)  2H.z+lmM-MPPG (n=6)  110-  < D  DRUG  7060 H -20  1  -10  1  1  1  1  1  1  1  1  0  10  20  30  40  50  60  70  r 80  1  90  1  100  1  1  110  120  time (min)  Fig. 14 Effects of M P P G at dose of 1 m M (n=6) i n combination w i t h V s u b / C A l stimulation o n extracellular concentration of D A  i n the N A c .  The  stimulus  consisted of 200 pulses of constant current (300 LLA) single pulses delivered at 2 H z for 100 sec. Dialysate samples were collected every 10 m i n and M P P G was perfused for 20 m i n (horizontal bar) after establishing a stable baseline.  Stimulation was  performed after 10 m i n of drug perfusion. Each value is expressed as a percentage of the mean + S E M of three basal samples before stimulation (S).  There was a  significant group x sample interaction (F (14, 378) = 2.136, p< 0.001), * significantly different from control i n h i b i t i o n , p < 0.05, ** p < 0.01, *** p < 0.001, simple m a i n effects analysis w i t h Dunnet's post hoc test.  40  DISCUSSION Effect of V s u b / C A l stimulation on basal extracellular levels of D A i n the N A c . The results from the present study indicate that electrical stimulation of the V s u b / C A l at three consecutive frequencies (2 H z , 5 H z , and 10 H z for 100 sec, 40 sec, and 20 sec, respectively) induces frequency-dependent changes i n extracellular D A levels i n the N A c . A significant decrease i n N A c D A levels was observed w h e n the V s u b / C A l was stimulated at 2 H z frequency. 10 H z stimulation, but not 5 H z stimulation, caused a marked increase i n D A levels w h i c h reversed the inhibitory effect induced previously by 2 H z stimulation.  A s previously noted,  these experiments were not designed to test systematically the effects of each i n d i v i d u a l stimulation frequency o n D A release i n the N A c . The issue concerning the effects of each i n d i v i d u a l stimulation frequency o n N A c D A levels w i l l be the subject of further investigations. The m a i n body of experiments focused o n the effects of 2 H z stimulation o n N A c D A levels. The results from the experiment a p p l y i n g electrical stimulation at 2 H z alone confirmed that 2 H z stimulation reliably induced a suppressive effect on N A c D A levels w i t h lasted throughout the two hr m o n i t o r i n g period.  The  suppressive effect o n N A c D A levels observed i n this dialysis study is consistent w i t h previous findings of a study employing i n v i v o (unpublished  data, Blaha et al.).  The  later  chronoamperometry  study showed  that  Vsub/CAl  stimulation at 2 H z for 10 sec could induce a relatively brief decrease i n basal D A efflux i n the N A c . H o w e v e r , the suppressive effect observed i n the present study persisted throughout the 2 hr period of measurement  compared to the p r e v i o u s  chronoamperometric study i n w h i c h D A oxidation currents were decreased for  41 only 10 m i n after application of electrical stimulation.  The difference i n the  duration of suppression may be the result of several procedural  differences,  including a) type and tip size of stimulating electrode) w h i c h may have an- impact o n the area of current spread, b) the duration of stimulation (100 sec and 10 sec), and most importantly c) the condition of experimental animals  (unanaesthetized  vs. anaesthetized) w h i c h has been reported to influence the basal concentrations of extracellular D A and particularly G l u levels i n the rat striatum (Shiraishi et al., 1997). A proposed mechanism u n d e r l y i n g the suppressive effects of 2 H z s t i m u l a t i o n on N A c D A levels. A s noted, m G l u R s  have  been  classified into  three  groups  based  on  differences i n their amino acid sequences, pharmacological characteristics, and related second messenger systems (Nakanishi, 1994; P i n and Bockaert, 1995; P i n and Duvoisin, 1995; C o n n and P i n , 1997). Recently, light and electron microscopy have revealed the predominant localization of m G l u R s group 2 (mGluR2) and 3 ( m G l u R 4 a / 7 a / 7 b / 8 ) i n presynaptic elements, whereas group 1 m G l u R ( m G l u R l / 5 ) are localized i n postsynaptic elements i n the rat hippocampus (Shigemoto et al., 1997). These findings are consistent w i t h those of Bradley et al., (1996) s h o w i n g that  group  3  mGluRs  (mGluR4a/7)  are  located  presynaptically  in  the  hippocampus. In addition, m G l u R 4 a has been found to be located o n presynaptic elements i n the cerebellar cortex (Kinoshita et al., 1996). Several studies have  suggested the role of group 2 and 3 m G l u R s  in  suppressing glutamatergic excitatory transmission i n some brain regions, most likely v i a a negative feedback presyaptic G l u autoreceptor mechanism (Kamiya et  42 al., 1996; C o z z i et al., 1997; Dube' and Marshall, 1997).  In contrast, group 1  m G L u R s , appear to be responsible for stimulating the release of neurotransmitter (Pin and Bockaert, 1995) and have been reported to facilitate N M D A - i n d u c e d responses i n a striatal slice preparation v i a a G l u postsynaptic mechanism (Pisani et al., 1997b). Therefore, it is reasonable to assume that, i n the N A c , group 2 and 3 mGluRs  are located mainly o n presynaptic glutamatergic  responsible for the i n h i b i t i o n of G l u synaptic transmission autoreceptor mechanism.  terminals  and  are  by a presynaptic  Conversely, group 1 m G l u R , as w e l l as i G l u R s , may be  located m a i n l y o n postsynaptic dopaminergic terminals w h i c h may play a role i n modulating D A release. A t basal (non-electrically stimulated) conditions (Fig. 15A), it has been proposed  that presynaptic  mGluRs  are  unoccupied  by basal levels  of G l u  (Scanziani et al., 1997). Basal levels of G l u are also assumed to modulate the basal levels of D A v i a i G l u R s o n dopaminergic terminals.  This latter hypothesis is  supported by several dialysis studies showing that E A A i.e., G l u and A s p play a modulatory role i n the release of D A i n the N A c through the i G l u R s (e.g., N M D A or n o n - N M D A ) (Imperato et al., 1990a; 1009b; Youngren et a l , 1993). In addition, it has been suggested recently that m G l u R s (hypothetically group 1 mGluRs) located o n D A nerve terminals may also serve to enhance D A release i n the N A c (Ohno and Watanabe, 1995). A proposed series of mechanisms w h i c h may underlie the initial and l o n g term suppressive effects of 2 H z V s u b / C A l stimulation o n D A efflux (Fig. 15B) may be that 1) stimulation-evoked release of G l u , over and above basal values, preferentially activates particular subtypes of presynaptic m G l u R s .  A l t h o u g h we  have no direct evidence for this mechanism, activation of these presumed group 2  43  Fig. 15 A proposed mechanism i n v o l v i n g the role of m G l u R s i n regulating D A release i n the N A c . A ) A t non-stimulated basal condition, presynaptic m G l u R s are assumed to be unactivated by spontaneous basal release of G l u from presynaptic terminals. modulate  The basal level of G l u is hypothesized  the basal release of D A from  the  postsynaptic  to  dopaminergic  terminals. B) 2 H z stimulation: release of G l u from the presynaptic terminals induced by 2 H z stimulation of V s u b / C A l (1) activates presynaptic m G l u R s (2), resulting i n the inhibition of subsequent G l u release (3). Less G l u released from presynaptic terminals (4) and consequently a decrease i n D A release (5). A c t i v a t i o n of an L T D - l i k e mechanism (6) by evoked G l u release following 2 H z stimulation w o u l d result i n sustained inhibition of G l u release, w h i c h i n turn w o u l d result i n the prolonged reduction of basal D A levels.  44 and 3 presynaptic m G l u R s by this stimulation-evoked transient elevation of G l u may serve to inhibit further  G l u release from glutamatergic terminals v i a a n  m G l u R - m e d i a t e d autoreceptor inhibitory mechanism.  The decreased amount of  G l u released from glutamatergic terminals may, i n turn, lead to a decrease i n the activation of postsynapitc iGluRs, that presumably regulate the release of D A f r o m dopaminergic terminals.  Consequently, this mechanism  may account for the  observed initial decrease i n D A efflux from dopaminergic terminals i n the N A c . In addition to m G l u R autoreceptor induced-inhibition, ii: is possible that 2) the excessive and transient elevation i n G l u release following 2 H z stimulation may lead to the activation of second messenger This second messenger subsequent G l u release.  systems i n glutamatergic terminals.  mechanism may account for a long-lasting decrease i n Thus, a mechanism resembling long-term depression  (LTD) may play a role i n the long-term suppression i n D A efflux we have observed following 2 H z stimulation. The mechanism (#1) proposed above, accounting for the initial suppression i n D A efflux induced by 2 H z stimulation is supported by several lines of evidence. For example, the study of Testa et al. (1994) revealed m R N A expression of at least five subtypes of m G l u R s i n the N A c and the prominent expression of m G l u R l i n dopaminergic neurons of the substantia nigra. In addition, several studies h a v e suggested the i n v o l v e m e n t of group 2 and 3 presyaptic m G l u R s i n presynaptic inhibition mechanism of synaptic transmission i n various brain regions (Vignes et al., 1995; K a m i y a et al., 1996; C o z z i et a l , 1997; Pisani et al., 1997a).  Activation of  two pharmacologically distinct receptors by application of selective agonists of group 2 m G l u R s , (1S,1S)-ACPD and L-CCG-1, or the specific agonist of group 3 m G l u R s , L - A P 4 , have been found to induce depression of excitatory synaptic  45 transmission i n the rat N A c slice preparation ( M a n z o n i  et al., 1997).  This  proposed mechanism is also supported by studies showing that L - A P 4 can induce a reversible and dose-dependent depression of evoked EPSPs i n the locus coeruleus (Dube'  and  motoneurons  Marshall,  1997),  depression  of  monosynaptic  excitation  of  i n neonatal rat spinal cord (Jane et al., 1995), and suppression of  basal synaptic transmission i n the lateral perforant path of the rat hippocampus (Bushell et al., 1996).  In addition, application of f - A C P D i n rat striatal slice  preparation has been found to induce a synaptic depressant effect on glutamatergic transmission at corticostriate synapses (Lovinger et al., 1993). Moreover, Taber and Fibiger (1995) have reported an inhibition i n basal D A release induced by relatively low concentrations of the group 2 m G l u R agonist, ACPE>, applied locally i n the N A c by reverse dialysis i n n freely m o v i n g rats, strongly supporting a role for m G l u R s i n regulating D A release i n the N A c . Evidence suggesting a role of m G l u R s i n the expression of L T D (proposed mechanism #2) is the following.  Kobayashi et al. (1996) have demonstrated  that  low frequency (1 H z ) stimulation together w i t h activation of m G l u R s , but not of iGluRs, induced presynaptic L T D at mossy fiber-CA3 synapses i n the hippocampus. M o r e convincing evidence has been presented from a study w i t h knockout mice deficient i n m G L u R 2 .  This latter study showed an impairment of L T D at mossy  fiber-CA3 synapses normally induced by l o w frequency stimulation (Yokoi et al., 1996). In addition, application of M C C G , a specific antagonist of group 2 m G L u R s , was found to inhibit the induction of L T D i n the dentate gyrus of the  rat  hippocampus (Huang et al., 1997). A study i n freely m o v i n g rats has also suggested the critical i n v o l v e m e n t  of group 2 m G l u R s  in L T D induction (Manahan-  Vaughan, 1997). Taken together, these results strongly sugg;est a role of presynaptic  46 m G l u R i n i n d u c i n g the prolonged suppressive " L T D - l i k e " effects i n N A c D A levels induced by low frequency stimulation of V s u b / C A l . Effects of selective m G l u R antagonists suppressive  effects  on basal N A c D A levels and on the  i n N A c D A release  i n d u c e d b y 2 H z s t i m u l a t i o n of  Vsub/CAl. In the present study, two types of specific antagonists at m G l u R s , M C P G and M P P G , were reverse dialyzed into the N A c i n order to test whether m G l u R s are i n v o l v e d i n the tonic regulation of basal D A efflux, as w e l l as the suppressive " L T D - l i k e " effects i n N A c D A levels following 2 H z stimulation. M C P G and basal D A efflux. A p p l i c a t i o n of M C P G , a specific antagonist of m G l u R 1/2 (Sekiyama et al., 1996), at doses of 10 | i M , 100 u M , or 1 m M into the N A c caused a slight but n o n significant decrease i n the basal levels of N A c D A . Therefore, it is unlikely that m G l u R l a n d / o r m G l u R 2 are involved i n tonic regulation of D A release as well as i n the proposed mechanism #1. The density of m G l u R l expression i n the N A c is relatively higher than the m G l u R 2 expression (Testa et al., 1994), this fact along w i t h the ability of M C P G to block both m G l u R l and m G l u R 2 (Bond and Lodge, 1995), raises the possibility that the small decrease i n D A efflux observed f o l l o w i n g application of M C P G may have  resulted from  the blockade of m G l u R l  on  dopaminergic terminals i n the N A c . Overall, the present results are consistent w i t h the study of O h n o and Watanabe particularly m G l u R l  (1995) w h i c h suggested that m G l u R s ,  and m G l u R 2 , i n the N A c are not i n v o l v e d i n the tonic  regulation of D A since application of M C P G at a dose of 5 m M by itself d i d not  47 cause any significant change i n accumbens D A levels.  It is important to note,  however, that this dose of M C P G attenuated the ability of locally applied A C P D to evoke D A overflow i n the N A c . M C P G and stimulated D A efflux. In the present study, reverse dialysis of M C P G at doses of 10 | i M or 100 u M , 10 m i n prior to the stimulation of V s u b / C A l at 2 H z d i d not prevent the initial or long-term suppressive effect on D A release, suggesting that m G l u R l  and/or  m G l u R 2 are not likely to be the major subtypes of m G l u R s i n v o l v e d i n these suppressive mechanisms.  These results (for mechanism #2) are consistent w i t h  the study of Selig et al. (1995) showing that m G l u R l / 2 do not play a significant role i n hippocampal L T D since application of M C P G d i d not block the L T D of EPSPs i n C A 1 hippocampal neurons  induced by l o w frequency stimulation of Schaffer  collaterals. H o w e v e r , it should be noted that application of M C P G d i d inhibit tACPD  induced-LTD  of  EPSPs  at  Schaffer  collateral-CAl  synapse  in  the  hippocampal region of immature rats (Overstreets et al., 1997) and also i n h i b i t e d both the A C P D - and the l o w frequency-induced L T D i n the dentate gyrus of the adult rats (O'Mara et al., 1995). The differences i n the experimental conditions i.e., concentration of drugs used, L T D induction protocols tested, area of the brain, and ages of animals examined between these studies may account for these conflicting results. M P P G and basal D A efflux. In the present study, it was found that reverse dialysis of M P P G at a dose of 100 LiM significantly decreased D A efflux i n the N A c after a delay, whereas a dose of 1 m M produced no significant change i n N A c D A levels. The highest dose of  48 M P P G resulted i n non-specific inhibitory effects.  A s noted i n the results, the final  p H of the 10 m M solution of M P P F was i n the range of 8.5-8.7.  Therefore, the  transient decrease i n N A c D A levels observed at this dose is likely due to p H , rather than the drug itself. This was confirmed i n the additional study s h o w i n g that the drug vehicle adjusted to a p H of 8.7 was able to decrease D A levels i n a manner similar to the drug. A s previously noted, M P P G blocks the i n h i b i t i o n of forskolin-stimulated c A M P production induced by L-AP4 i n rat striatal slices (Schaffhauser et al., 1997). Jane et al. (1995) reported the ability of M P P G to block the depression of the monosynaptic  excitation of neonatal  selective agonist of group 3 m G l u R s .  rat motoneurons  induced by L-AP4, a  However, M P P G has also been reported to  block m G l u R 2 w i t h 1/2 lower potency as s h o w n i n Table 2.  One possible  explanation for the delayed suppressive effects on N A c D A release  following  washout of the blockade of m G l u R s by M P P G (100 u M ) may be that, during the application of M P P G , basal concentrations of G l u remain unaffected. under these conditions no observable change observed.  Therefore,  i n N A c D A basal levels  was  F o l l o w i n g drug washout, these group 2 and 3 m G L u R s may h a v e  become supersensitive to the resting levels of G l u . If this were the case, activation of group 2 and 3 m G l u R s by basal concentration of G l u may have resulted i n the inhibition of subsequent G l u release from glutamatergic terminals.  In turn, a  decrease i n G l u release may have lead to the observed delayed decrease i n D A efflux from dopaminergic terminals.  A diagram of this proposed mechanism is  shown i n Fig. 16. A l t h o u g h , there is no direct evidence for this mechanism, it could be tested by prolonging the perfusion of M P P G into the N A c . If the delayed decrease i n D A is mediated  by an effect of basal levels of G l u acting  on  49  Fig. 16 The proposed mechanism i n v o l v i n g the effects of M P P G (100 LIM) o n N A c D A levels. A ) A blockade of group 2 and 3 m G l u R s by M P P G failed to alter basal D A levels, suggesting that basal G l u release was unaffected by M P P G . B) After blockade, group 2 and 3 m G l u R s , w h i c h are not activated by basal levels of G l u (1), become  supersensitive  to G l u .  supersensitive m G l u R s induces the inhibition of G l u release. then cause less D A release from postsynaptic terminals.  Activation  of  Less G l u (2)  50 supersensitive receptor thereby blocking them continuously w i t h M P P G , one w o u l d expect to see no significant change i n the N A c D A levels until the drug was washed out. MPPG and stimulated D A efflux. Application of M P P G at doses of 100 u M or 1 m M 10 m i n prior to V s u b / C A l stimulation was found to block the presumed " L T D - l i k e " effects (mechanism #2) but not the autoreceptor-mediated initial suppressive effects (mechanism #1) o n D A levels, resulting i n the observed delayed return  of D A levels  to  pre-  stimulation baseline values (see figure 13 and 14). A proposed mechanism involving the effects of M P P G on the suppression of D A efflux induced by 2 Hz stimulation. A s s h o w n i n F i g . 13 and 14, after reverse dialysis of M P P G , the decrease i n NAc  D A efflux  was observed only i n the first 30-40 m i n following  2 Hz  stimulation after w h i c h D A levels returned to prestimulated values. One possible explanation for this relatively short lasting period of suppression i n D A levels may  be that M P P G applied to the N A c by reverse dialysis 10 m i n prior to  stimulation only partially blocks group 2 and 3 m G l u R s on presynaptic terminals. MPPG  is  a competitive  enhancement  receptor  antagonist,  and  therefore,  the  transient  of synaptic G l u concentrations following 2 H z stimulation may be  sufficient to displace M P P G from m G l u R s , thereby resulting i n only partial m G l u R blockade. Thus, sufficient G l u concentrations induced by 2 H z stimulation may activate some presyaptic m G l u R s resulting i n a subsequent decrease i n G l u release from presynaptic terminals by mechanism #1, an m G l u R - m e d i a t e d autoreceptor mechanism. Consequently, less G l u release from presynaptic terminals may cause  51 less activation of i G l u R s o n postsynaptic terminals resulting i n initial decrease i n D A efflux i n the N A c . Furthermore, this lower level of G l u may be insufficient to induce " L T D - l i k e " effects (mechanism #2).  A s a consequence, the G l u and the  antagonist (MPPG) competitive interactions at the presynaptic m G l u R may thus account for the observed blockade of the delayed suppression i n D A efflux.  A  diagram of this proposed mechanism is shown i n Fig. 17. General conclusion. In summary,  the present study confirmed  the  hypothesis  that 2 H z  stimulation of V s u b / C A l w o u l d result i n a rapid and prolonged suppression i n D A efflux i n the N A c . This study demonstrated that m G l u R s , presumably located on presynaptic glutamatergic terminals, may be involved i n the regulation of basal D A release at dopaminergic terminals i n the N A c v i a m o d u l a t i o n of G l u release by an autoreceptor  m G l u R - m e d i a t e d mechanism.  Secondly, the  suppressive effect o n D A efflux may be related to an L T D - l i k e Moreover, this late-phase suppression i n basal D A release  prolonged  phenomenon.  induced by 2 H z  stimulation of V s u b / C A l can be antagonized by selective blockade of group 2 and 3 m G l u R s i n the N A c . G i v e n the complexity i n the differential distribution of m G l u R subtypes i n the N A c and that only the effects of two specific m G l u R s  antagonists  were  examined, this thesis can not provide a definitive conclusion as to the subtypes of m G l u R s that are responsible for the mechanism underlying the initial and l o n g lasting suppressive effects of V s u b / C A l on extracellular D A levels i n the N A c . Future studies are needed to examine the potential mechanisms underlying these Glu-induced actions o n D A levels i n the N A c , as w e l l as to fully characterize the role and identity of i n d i v i d u a l subtypes of mGluRs.  52  2 Hz stimulation + MPPG  Fig. 17 The proposed diagram i n v o l v i n g  the  effects  of M P P G  on  the  suppression of D A efflux induced by 2 H z stimulation. 2 H z s t i m u l a t i o n causes the release of G l u over the basal levels (1) and as a consequence activate group 2 and 3 m G l u R s , w h i c h are partially blocked by M P P G .  Less  G l u (2) release, as a result of presynaptic autoreceptor activation, then cause less D A release from postsynaptic D A terminals. The amount of G l u release (2) is assumed to be insufficient to induce LTD-like effects, therefore the levels of D A i n the N A c return to prestimulated values.  53  REFERENCES Attarian S. and A m a l r i c M . (1997) Microinfusion  of the metabotropic  glutamate  receptor agonist lS,3R-l-aminocyclopentane-l,3-dicarboxylic acid into nucleus accumbens induces dopamine-dependent  the  locomotor activation i n  the rat. Eur. J. Neurosci., 9, 809-816. A r a m o r i I., and N a k a n i s h i S. (1992) Signal transduction and pharmacological characteristics of a metabotropic glutamate receptor, m G l u R l , i n transfected C H O cells. Neuron, 8, 757-765. Bedingfield J.S., Jane D.E., K e m p M . C , Toms N . J . , and Roberts P.T. (1996) N o v e l potent  selective  phenylglycine antagonists  of  metabotropic  glutamate  receptors. Eur. }. Neurosci., 309, 71-78. Benveniste H . and Huttemeier, C. (1990) Microdialysis- theory and application. Prog. Neurobiol, 35,195-215.  Blaha  C D . , Y a n g C.R., Floresco S.B., Barr  A . M . , and  Phillips  A . G . (1997)  Stimulation of the ventral subiculum of the hippocampus evokes glutamate receptor-mediated changes i n dopamine efflux i n the rat nucleus accumbens. Eur. }. Neurosci., 9, 902-911. Bond A . , and Lodge D . (1995) Pharmacology of metabotropic glutamate  receptor-  mediated enhancement of responses to excitatory and inhibitory amino acids o n rat spinal neurons in vivo. Neuropharmacol, 34, 1015-1023. Bradley S.R., Levey A.I., Hersch S.M., and C o n P.J. (1996) localization  of  group  III  metabotropic  Immunocytochemical  glutamate  receptors  in  hippocampus w i t h subtype-specific antibodies. /. Neurosci., 16, 2044-2056.  the  54 Brudzynsky S . M . , W u M . , and Mogenson G.J. (1993) Decrease i n rat locomotor activity as a result of changes i n synaptic transmission to neurons w i t h i n the mesencephalic locomotor region. Can. f. Physiol. Pharmacol, 71, 394-406. Bushell T.J., Jane D.E., Tse H - W . , Watkins J.C., Garthwaite J., and Collingridge G.L. (1996) Pharmacological antagonism of the action of group II and III m G l u R agonists i n the lateral perforant path of the rat hippocampal slices. Brit. J. Pharmacol, 117, 1475-1462. C o n n P.J., and P i n J-P.  (1997) Pharmacology and functions  of metabotropic  glutamate receptors. Annu. Rev. Pharmacol. Toxicol, 37, 205-237. C o z z i A . , Attucci S., Peruginelli F., M a r i n o z z i M . , Luneia R., Pellicciari R., and M o r o n i R. (1997) Type 2 metabotropic glutamate (mGlu) receptors tonically inhibit transmitter release i n rat caudate nucleus: In vivo studies w i t h (2S,1'S, 2'S,3'R)-2-(2'-carboxy-3'-phynylcyclopropyl)  glycine,,  a  new  potent  and  selective antagonist. Eur. J. Neurosci, 9, 1350-1355. Donzanti  B . A . and Uretsky N . J . (1983) Effects of excitatory amino  locomotor accumbens:  activity after possible  bilateral microinjection dependence  on  into  the  dopaminergic  rat  acids o n nucleus  mechanisms.  NeuropharmacoL, 22(8), 971-981. Dreher J.K. and Jackson D . M . (1989) Role of D l and D2 dopamine receptors i n mediating locomotor activity elicited from the nucleus accumbens of rats. Brain Res., 487, 267-277. Dube G.R. and Marshall K . C . (1997) M o d u l a t i o n of excitatory synaptic transmission i n locus coeruleus by multiple presynaptic metabotropic glutamate receptors. Neurosci., 80(2), 511-521. Fibiger H . C . and Phillips A . G . (1988) Mesocorticolimbic dopamine systems and reward. Ann. NY Acad. Sci., 537, 206-215.  55 Fiorino D.F., C o u r y A . , Fibiger H . C . , and Phillips A . G . (1993) Electrical s t i m u l a t i o n of  reward  sites  in  the  ventral  tegmental  area  increases  dopamine  transmission i n the nucleus accumbens of the rat. Behav. Brain Res., 55, 131141. Gilbert D.B., M i l l a r J., and Cooper S.T. (1995) The putative dopamine D3 agonist,7O H - D P A T , reduces  dopamine  release  i n the  nucleus  accumbens  and  electrical self stimulation to the ventral tegmentum. Brain Res., 681, 1-7. G o l d L . H . , Swardlow N.R., and K o o p G.F. (1988) The role of mesolimbic d o p a m i n e i n conditioned locomotion produced by amphetamine.  Behav. Neurosci.,  102(4), 544-552. Groenewegen H.J., Vermeulen-Van der Zee E . , Kortschot A . , and Witter M . P . (1987) Organization of the projections from the s u b i c u l u m to the ventral striatum in  the  rat. A study using  anterograde  transport  of Phaseolus vulgalis  leucoagglutinin. Neurosci., 23(1), 103-120. H a m i l t o n M . H . , Belleroche J.S., Gardiner I.M., and Herberg L.J. (1986) S tim u l a t o r y effect of N - m e t h y l aspartate o n locomotor activity and transmitter  release  from rat nucleus accumbens. Pharmacol. Biochem. & Behav., 25, 943-948. H u a n g L.Q., R o w a n M.J., and A n w y l R. (1997) m G l u R II agonist i n h i b i t i o n of L T P induction, and m G l u R II antagonist inhibition of L T D induction, i n the dentate gyrus in vitro. Neuroreport, 8, 687-693. Imperato A . , Honore T., and Jensen L . H . (1990a) Dopamine release i n the nucleus caudatus and i n the nucleus accumbens i n under glutamatergic control through n o n - N M D A receptors: a study i n freely-moving rats. Brain Res., 530, 223-228.  56 Imperato A . , Scrocco M . G . , Bacchi S., and Angelucci L . (1990b) N M D A receptors and i n v i v o dopamine release i n the nucleus accumbens and caudatus. Eur. }. Pharmacol, 187, 555-556. Jackson D . M . , A n d e N . , and Dahlstrom A . (1975) A functional effect of dopamine i n the nucleus accumbens and i n some other dopamine-rich parts of the rat brain. Pschopharmacologia (Berl), 45, 139-149. Jane D.E., Pittaway K . , Sunter D . C , Thomas N . K . , and W a t k i n J.C. (1995) N e w phenylglycine derivative w i t h potent and selective antagonist presynaptic  glutamate  receptors  in  neonatal  rat  activity at  spinal  cord.  Neuropharmacology, 34 851-856. Johnson L.R., A y l w a r d R . L . M . , H u s s a i n Z . , and Totterdell S. (1994) Input from the amygdala to the rat nucleus  accumbens: its relationship w i t h  tyrosine  hydroxylase immunoreactivity and identified neurons. Neuroscience, 61, 851865. Jongen-Reio A . L . , V o o r n P., and Groenewegen H.J. (1994) I m m u n o h i s t o c h e m i c a l characterization of the shell and core territories of the nucleus accumbens i n the rat. Eur. J. Neurosci. 6,1255-1264.  K a m i y a H . , S h i n o z a k i H . , and Yamamoto C. (1996) A c t i v a t i o n of metabotropic glutamate  receptor type 2/3 suppresses transmission at rat h i p p o c a m p a l  mossy fibre synapses. J. Physiol., 493,447-455. Kelley A . E . and Throne L . C . (1992) N M D A receptors mediate the behavioral effects of amphetamine infused into the nucleus accumbens. Brain Res. Bull, 20, 247254. Kinoshita A . , O h i s h i H . , N a m u r a S., Shigemoto R., N a k a n i s h i S. (1996) Presynaptic localization of a metabotropic glutamate receptor, m G l u R 4 a , i n the cerebellar  57 cortex: A light and electron microscope study i n the rat. Neurosci. Lett., 207, 199-202. Kobayashi K . , Manabe T., and Takahashi T. (1996) Presynaptic long-term depression at the hippocampal mossy fiber-CA3 synapse. Science, 273, 648-650. Koob G.F. and Swerdlow N . R . (1988) The functional output of the m e s o l i m b i c dopamine system. Ann. NY Acad. Set, 537, 216-227. Koob G.F. (1992) Drugs of abuse: anatomy, pharmacology and function of reward pathways. Trends Pharmac. Set, 13,177-184. Lovinger D . M . , Tyler E., Fidler S., and Merrit A . (1993) Properties of a synaptic metabotropic glutamate receptor i n rat neostriatal slices. /. Neurophysiol., 69, 1236-1244. Lovinger D . M . and M c C o o l B . A . (1995) Metabotropic glutamate receptor-mediated presynaptic depression at corticostriatal synapses involves m G l u R 2 or 3. / . Neurophysiol,  73,1076-1083.  Manahan-Vaughan D . (1997) G r o u p 1 and 2 metabotropic glutamate receptors play differential  roles i n hippocampal long-term depression and long  term  potentiation i n freely m o v i n g rats. /. Neurosci., 17, 3303-3311. M a n z o n i O., M i c h e l J-P., and Bockaert J. (1997) Metabotropic glutamate receptors i n the rat nucleus accumbens. Eur. J. Neurosci., 9, 1514-1523. Martin  L.J., Blackstone C . D . , H u g a n i r R . L . , and Price D . L .  (1992)  Cellular  localization of a metabotropic glutamate receptor i n rat brain. Neuron, 9, 259270. Mogenson  G.J., Jone, D . L . , and Y i m C . Y . (1980) F r o m  m o t i v a t i o n to action:  functional interface between the limbic system and motor system. Prog. Neurobiol, 14, 69-97.  58 Mogenson, G.J., Yang, C.R., and Y i m , C.Y.(1988) Influence of dopamine o n l i m b i c inputs to the nucleus accumbens. Ann. NY Acad. Sci., 537, 86-100. Mogenson G.J., B r u d z y n s k i S.M., W u M . , Yang C.R., and Y i m C . Y . (1993) F r o m motivation nucleus  to action: a review of dopaminergic regulation of limbic—>  accumbens—>  ventral  pallidum—>pedunculopontine  nucleus  circuitries i n v o l v e d i n limbic-motor integration. In: Limbic Motor Circuits and Neuropsychiatry, (Kalivas, P . W . and Barnes, C D . , Eds.), pp 193-236. Boca Raton, Florida: C R C Press. N e k i A . , O h i s h i H . , Kaneko T., Shigemoto R., N a k a n i s h i S., and M i z u n o N . (1996) Pre- and postsynaptic localization of a metabotropic glutamate mGluR2,  i n the rat brain:  an  immunohistochemical  study  receptor, with  a  monoclonal antibody. Neurosci. Lett. 202, 197-200. Nestler E.J. (1993) Molecular mechanisms of drug addiction i n the m e s o l i m b i c dopamine pathway. Sent, in Neurosci., 5, 369-376. Nakanishi  S. (1994) Metabotropic glutamate  receptors:  synaptic transmission,  modulation, and plasticity. Neuron, 13,1031-1037. Ohno M . and Watanabe S. (1995) Persistent increase i n dopamine release f o l l o w i n g activation of metabotropic glutamate receptors i n the rat nucleus accumbens. Neurosci. Lett., 200,113-116.  O ' M a r a S.M., R o w a n M.J., and A n w y l R. (1995) Metabotropic glutamate receptorinduced homosynaptic long-term depression and depotentiation  i n the  dentate gyrus of the rat hippocampus i n vitro. Neuropharmacol, 34, 983-989. Overstreet L.S., Pasternak J.F., Colley P.A., Slater N . T . , and Trommer B . L . (1997) Metabotropic  glutamate  receptor  mediated  long-term  developing hippocampus. Neuropharmacol., 36, 831-844.  depression  in  59 Paxinos G . and Watson, C . (1986) The rat brain in stereotaxic coordinates, 2nd Ed., N e w York: Academic Press. Pennartz C . M . A . , A m e e r u n R.F., Groenewegen H.J., and Lopes D a Silva F . H . (1993) Synaptic plasticity i n an in vitro slice preparation  of the rat nucleus  accumbens. Eur. f. Neurosci., 5,107-117. Pennartz C . M . A . , Groenewegen H.J., and Lopes D a Silva F . H . (1994) The nucleus accumbens as a complex of functionally distinct neuronal  ensembles: a n  integration of behavioral, electrophysiology and anatomical  data. Prog.  Neurobiol., 42, 719-761. Petralia  R.S., W a n g Y . X . , N i e d z i e l s h i  metabotropic  glutamate  A . S . , and W e n t h o l d  receptors, m G l u R 2  R.J. (1996) T h e  and m G l u R 3 ,  show  unique  postsynaptic, presynaptic and glial localizations. Neurosci. 71, 949-976. Phillips A . G . , Blaha C.D., and Fibiger H . C . (1989) Neurochemical correlates of brainstimulation  reward measured  by ex vivo and in vivo analyses. Neurosci.  Biobehav. Rev., 13, 99-104. P i n J-P. and Bockaert J. (1995) Get receptive to metabotropic glutamate receptors. Cur. Op in. in Neurobiol., 5, 342-349. Pin  J.P. and D u v o i s i n  R. (1995) Review:  Neurotransmitter  metabotropic glutamate receptors: structure and functions.  receptors  I. T h e  Neuropharmacol,  34,1-26. Pisani A . , Calabresi P., Centonze D . , and Bernardi G . (1997a) A c t i v a t i o n of group III metabotropic glutamate receptors depresses glutamatergic transmission at corticostriatal synapse. Neuropharmacology, 36, 845-851. Pisani A . , Calabresi P., Centonze D . , and Bernardi G . (1997b) Enhancement of N M D A responses by group I metabotropic glutamate receptor activation i n striatal neurones. Brit. }. Pharmacol, 120, 1007-1014.  60 P u l v i r e n t i L . , Swerdlow N . R . , and Koob G.F. (1991) Nucleus accumbens antagonist  NMDA  decreases locomotor activity produced by cocaine, heroin or  accumbens dopamine, but not caffeine. Pharmacol. Biochem. & Behav., 40, 841845. Robinson T . G . and Bert P . M . (1988) Excitant amino acid projections from  rat  amygdala and thalamus to nucleus accumbens. Brain Res. Bull, 20, 467-471. Sasa M . , H a r a M . , and Takaori S. (1991) Dopamine D - l receptor-mediated i n h i b i t i o n of nucleus accumbens neurons from the ventral tegmental area. Prog. Neuropsychopharmacol. & Biol. Psychiat., 15, 119-128.  Scanziani M . , Salin P . A . , Vogt K . E . , M a l e n k a R . C . , and N i c o l l R . A . (1997) U s e dependent  increases  in  glutamate  concentration  activate  presynaptic  metabotropic glutamate receptors. Nature, 385, 630-633. Schaffhauser  H . , Jakob-Rotne  R.,  and  Mutel  V.  (1997)  Pharmacological  characterization of metabotropic glutamate receptors linked to the i n h i b i t i o n of adenylate cyclase activity i n rat striatal slices. Neuropharmacol, 36, 933-940. Sharp T., Zetterstrom T., and Ungerstedt U . (1986) A n i n v i v o study of dopamine release and metabolism i n rat brain regions using intracerebral dialysis. / . Neurochem., 47, 113-122. Selig D.K., Lee H - K . , Bear M . F . , and M a l e n k a R . C . (1995) Reexamination of the effects  of M C P G  o n hippocampal  L T P , L T D , and  depotentiation.  /.  Neurophysiol, 74,1075-1082. Sekiyama N . , H a y a s h i Y . , N a k a n i s h i S., Jane D.E., Tse H - W . , Birse E.F., and W a t k i n s J.C. (1996) Structure-activity relationships of new agonists and antagonists of different metabotropic glutamate receptor subtypes. Brit. J. Pharmacol, 117, 1493-1503.  61 Sesack S.R., and Pickel V . M . (1990) In the rat medial accumbens, hippocampal and catecholaminergic  terminals  converge  on  spiny neurons  and  are  in  apposition to each other. Brain Res. 527, 266-278. Shigemoto R., N o m u r a S., O h i s h i H . , Sukihara H . , N a k a n i s h i S., and M i z u n o N . (1993) Immunohistochemical  localization  of a metabotropic  glutamate  receptor, m G l u R 5 , i n the rat brain. Neurosci. Lett., 163, 53-57. Shigemoto R., Kinoshita A . , W a d a E., N o m u r a S., O h i s h i H . , Takada M . , Flor P.J., N e k i A . , A b e T., N a k a n i s h i S., and M i z u n o N ; (1997) Differential presynaptic localization  of metabotropic  glutamate  receptor  subtypes  in  the  rat  hippocampus. /. Neurosci., 17, 7503-7522. Shiraishi M . , K a m i y a m a Y . , Huttemeier P.C., and Benveniste H . (1997) Extracellular glutamate and dopamine measured by microdialysis i n the rat striatum during blockade of synaptic transmission i n anesthetized and awake rats. Brain Res., 759,221-227. Shreve P.E. and Uretsky N . J . (1988) Role of quisqualic: acid receptors i n the hypermotility response produced by the injection of A M P A into the nucleus accumbens. Pharmacol. Biochem. & Behav., 30, 379-384.  Smith J. A . , M o Q., G u o H . , K u n k o P . M . , and Robinson S.E. (1995) Cocaine increases extraneuronal levels of aspartate and glutamate i n the nucleus accumbens. Brain Res., 683, 264-269. Sokoloff P., and Scwartz J. (1995) N o v e l dopamine receptors half a decade later. Trends Pharmac. Set, 16, 270-274.  Steketee J.D., Sorg B.A., and Kalivas P.W. (1992) The role of the nucleus accumbens i n sensitization to drugs abuse. Prog. Neuro-psychopkarmacol. & Biol. Psychiat.,  16,237-246.  62 Svensson L . and A h l e n i u s S. (1983) Suppression of exploratory locomotor activity by the local application of dopamine or /-noradrenaline  to the nucleus  accumbens of the rat. Pharmacol. Biochem. & Behav., 19, 693-699.  Svensson  L . , Carlsson M . L . , and  Carlsson A . (1992)  Interaction  between  glutamatergic and dopaminergic tone i n the nucleus accumbens of mice: evidence for a dual glutamatergic function w i t h respect to psychomotor control. /. Neural. Transm., 88, 235-40. Svensson L . , Carlsson M . L . , and Carlsson A . (1994a)  Glutamatergic  neurons  projecting to the nucleus accumbens can affect motor functions i n opposite directions  depending  on  the  dopaminergic  tone.  Prog.  Neuro-  Psychopharmacol. & Biol. Psychiat., 18, 1203-1218.  Svensson L . , Z h a n g J., Johannessen  K . , and Engel J. A . (1994b) Effect of local  infusion of glutamate analogues into the nucleus accumbens of rats: a n electrochemical and behavioral study. Brain Res., 643, 155-161. Svensson L . , Carlsson M . L . , and Carlsson A . (1995) Interactions between glutamate and dopamine i n the ventral striatum: evidence for dual glutamatergic function w i t h respect to motor control. In: Age-related dopamine-dependent disorders (Segawa, M . and N o m u r a , Y . , Eds.) M o n o g r . N e u r a l . Sci. Basel, Karger., 14,160-167. Taber M . T . and Fibiger H . C . (1995) Electrical stimulation of the prefrontal cortex increases dopamine release i n the nucleus accumbens of the rat: m o d u l a t i o n by metabotropic glutamate receptors. /. Neurosci., 15, 3896-3904. Tanabe Y., M a s u M . , Ishii T., Shigemoto R., and N a k a n i s h i S. (1992) A family of metabotropic glutamate receptors. Neuron, 8, 169-179.  63 Testa C M . , Standaert D . G . , Y o n g A . B . , and Penney J.R (1994) glutamate receptor m R N A  Metabotropic  expression i n the basal ganglia of the rat. / .  Neurosci. 14,3005-3018. Tombaugh G . C and Somjen G . C (1996) Effects of extracellular p H o n voltage-gated N a , K , and C a +  +  2 +  currents i n isolated rat C A 1 neurons. /. Physiol, 493, 719-732.  Vignes M . , Clarke V.R.J., Davies C . H . , Chambers A . , Jane D.E., Watkins J . C , and Collingridge G . L . (1995) Pharmacological evidence for an i n v o l v e m e n t of group II and group III m G l u R s i n the presynaptic regulation of excitatory synaptic  response  in  the  CA1  region  of  rat  hippocampal  slices.  Neuropharmacology, 34, 973-982. W o l t e r i n k G . , V a n Zanten E., Kamsteeg H . , R a d h a k i s h u n FS., and V a n Ree J M . (1990) Functional recovery after destruction of dopamine  systems i n the  nucleus accumbens of rats. I. Behavioral and biochemical studies. Brain Res., 507,92-100. W o n g L.S., Eshel G . , Dreher J., O n g J., and Jackson D . M . (1991) Role of dopamine and G A B A i n the control of motor activity elicited from the rat nucleus accumbens. Pharmacol. Biochem. & Behav., 38, 829-835.  Wu  M . , B r u d z y n s k i S . M . , and Mogenson G.J. (1992) Functional interaction of dopamine and glutamate i n the nucleus accumbens i n the regulation of locomotion. Can. J. Physiol. Pharmacol, 71, 407-413.  W u M . and Brudzyski S.M. (1995) Mesolimbic dopamine terminals and locomotor activity induced from the subiculum. Neuroreport, 6, 1601-1604. Yang C R . and Mogenson, G.J. (1984) Electrophysiological responses of neurones i n the nucleus accumbens to hippocampal stimulation and attenuation  of the  excitatory responses by the mesolimbic dopaminergic system. Brain Res., 324, 69-84.  64 Yang C R . and M o g e n s o n G.J. (1985) A n electrophysiological study of the n e u r a l projections  from  the  hippocampus  to the  ventral  pallidum  and  the  subpallidal areas by way of the nucleus accumbens. Neuroscience, 15, 10151024. Yang C R . and M o g e n s o n G.J. (1986) Dopamine enhances terminal excitability of hippocampal-accumbens neurons v i a D2 receptor: Role of dopamine i n presynaptic inhibition. /. Neurosci., 6, 2470-2478. Yang C R . and M o g e n s o n G.J. (1987) H i p p o c a m p a l signal transmission  to  the  pedunculopontine nucleus and its regulation by dopamine D2 receptors i n the  nucleus  accumbens:  an electrophysiological and  behavioral  study.  Neuroscience, 23,1041-1055. Y i m C Y . and M o g e n s o n G.J. (1982) Response of nucleus accumbens neurons to amygdala stimulation and its modulation and its modification by dopamine. Brain Res., 239, 401-415. Y i m C Y . and M o g e n s o n G.J. (1988) N e u r o m o d u l a t o r y action of dopamine i n the nucleus accumbens: A n in vivo intracellular study. Niiuroscience, 26,403-415. Y o k o i M . , Kobayashi K . , Manabe T., Takahashi T., Sakaguchi I., Katsuura G . , Shigemoto R., O h i s h i H . , N o m u r a S., N a k a m u r a K . , K a k a o K . , Katsuki M . , and N a k a n i s h i S. (1996) Impairment of hippocampal mossy fiber L T D i n mice lacking m G l u R 2 . Science, 273, 645-647. Youngren  K . D . , Daly  D . A . , and  Moghaddam  B. (1993)  Distinct  actions  of  endogenous excitatory amino acids o n the outflow of dopamine i n the nucleus accumbens. /. Phar. Exp. Ther., 264, 289-293.  

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