UBC Theses and Dissertations
Serotonin involvement in the blockade of bulbospinal and recurrent inhibition of the monosynaptic reflex Sastry, Bhagavatual Sree Rama
The monoamine uptake blocking agents, imipramine HC1 (5 mg/kg i.v.) and desipramine HC1 (4.8 mg/kg i.v.), and the monoamine oxidase inhibitor, pargyline HC1 (30 mg/kg i.v.) antagonized bulbospinal inhibition (BSI) of the monosynaptic reflex (MSR) in unanaesthetized cats decerebrated at the mid-collicular level. The effect of imipramine was quantitatively more on BSI of the quadriceps (QUAD)-MSR compared to that on BSI of the posterior biceps-semitendinosus (PBST)-MSR. Imipramine's action on this inhibition was also quantitatively greater compared to that of the equimolar dose of desipramine. Pretreatment of the animals with the tryptophan hydroxylase inhibitor, DL-p-chlorophenylalanine (p-CPA) (300 mg/kg i.p. for 3 consecutive days) completely eliminated the blocking action of imipramine. However, pretreatment of the animals with the tyrosine hydroxylase inhibitor, DL-α-methyl-p-tyrosine methyl ester HC1 (α-MPT) (126 mg/kg i.p. given 16 and 4 hours before the recording ) had no effect on imipramine's action. These findings strongly suggest that a 5-hydroxytryptamine (5-HT, serotonin) system antagonizes BSI of the MSR. They do not support the proposal of Clineschmidt and Anderson (1970) that the bulbospinal inhibitory pathway involves a 5-HT interneurone in the spinal cord. Imipramine HC1 (5 mg/kg i.v.) and pargyline HC1 (30 mg/kg i.v.) blocked recurrent inhibition (RI) of the MSR evoked by stimulation of a dorsal root. Imipramine blocked RI of the QUAD-MSR but had no effect on RI of the PBST-MSR. Pretreatment of the animals with either p-CPA or α-MPT prevented the blocking action of imipramine on RI. Application of a 'cold block' which potentiated RI of the QUAD-MSR also eliminated the blocking action of imipramine on this inhibition. These observations suggest that a supraspinal monoaminergic system which involves 5-HT and noradrenaline links has a tonic inhibitory effect on RI of the QUAD-MSR.
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