Involvement of noradrenergic systems in the effects of conditioning stimulation of the lower brain stem on the lumbar spinal reflex in rats.

The effects of conditioning stimulation at various positions in the pons and the medulla on the lumbar spinal monosynaptic reflex (MSR) were examined in rats. The conditioning stimulation facilitated the MSR. Facilitation with long latency was completely blocked by phenoxybenzamine, chlorpromazine or haloperidol. Phenoxybenzamine and chlorpromazine inhibited the MSR. Haloperidol, on the other hand, augmented the MSR, and this effect became more potent after the brain stem had been transected at the upper part of the medulla oblongata. These results suggest that pontine noradreneric systems have a facilitatory influence on the MSR via alpha-adrenoceptors, and that alpha-blockers exert an inhibitory effect on the MSR by blocking these receptors.