Influence of monoaminergic nuclei in lower medulla and their neurotransmitters on the activity of nociceptive units in spinal cord.

In this article, seventy nociceptive units of dorsal horn and five preganglionic sympathetic units of spinal cord in forty-four anesthetized cats immobilized with Flaxedil were studied. The results observed were: 1. Electrophoretic administration of noradrenaline (NA) induced a remarkable depression of both evoked and spontaneous discharges of nociceptive units. Similar effects could be produced by electric stimulation of noradrenergic Al nuclei or injection of amphetamine or hand pressing of "Zusanli" (one form of acupuncture) respectively. 2. The effect of 5-hydroxytryptamine (5-HT on evoked nociceptive discharge was similar to NA, but on spontaneous discharge of nociceptive units was excitement. 3. Effects of the above-mentioned factors on the nociceptive discharges of preganglionic sympathetic neurons were similar to the nociceptive units too. 4. On the contrary, the activity of inhibited neuron by noxious stimulation was augmented by administration of NA, amphetamine, the stimulation of Al nuclei and the deep muscle. It is suggested that the noradrenergic nuclei in lower brain stem may play an important role in descending inhibitory circuits of nociceptive spinal reflex.