The effects of serotonergic and antiserotonergic drugs on the flexor reflex of spinal rat: a proposed model to evaluate the action on the central serotonin receptor.

The effects of serotonergic and antiserotonergic drugs on the hind limb flexor reflex (measured as a contraction of musculus tibialis anterior or as a flexion of the paw) in the spinal rat was studied. All serotonergic drugs used (L-5-hydroxytryptophan, L-tryptophan, LSD, fenfluramine, p-chloroamphetamine) stimulate the flexor reflex. Serotonin receptor blockers (cyproheptadine, WA-335, methergoline), which given alone are inactive, inhibit the stimulation induced by serotonergic drugs but do not influence that one caused by noradrenergic agents (amphetamine, clonidine). Both types of stimulation (serotonergic and noradrenergic) are antagonized by noradrenaline receptor blockers (phenoxybenzamine, clozapine). The antiserotonergic action of serotonin antagonists used was confirmed on the basis of the antagonism to the head twitches induced by L-5-hydroxytryptophan. The flexor reflex in the spinal rat may be a good model to evaluate the effect on the central (spinal cord) serotonin receptor and to differantiat this effect from that on the noradrenaline system.