Supraspinal tonic influence on spinal reflexes and involvement in the effect of chlorpromazine

Chlorpromazine (CPZ) depressed mono-(MSR) and polysynaptic reflexes in anesthetized rats. The MSR remained unaltered after spinal transection (C1). After spinal transection, the inhibitory effect of CPZ on the MSR disappeared. After CPZ injection, spinal transection enhanced the MSR to pre-drug level. Reserpine pretreatment abolished the inhibitory effect of CPZ on the MSR. Phenoxybenzamine inhibited the MSR and, when pre-injected, markedly attenuated the effect of CPZ on the MSR. These results suggest that in anesthetized rats, CPZ blocks the alpha-adrenoceptor-mediated facilitatory component of the spontaneous tonic influence on the MSR.