Supraspinal loops that mediate visceral inputs to thoracic spinal cord neurones in the cat: involvement of descending pathways from raphe and reticular formation.

Single unit electrical activity has been recorded from 29 viscero-somatic neurones in the T11 spinal cord segment of chloralose anaesthetized cats. Twenty-six of these neurones showed changes in their responses to electrical stimulation of the splanchnic nerve after reversible spinalization of the animals by cold block: 14 showed increased responses whereas 12 presented reduced or abolished responses during the spinal block. The majority of neurones in the first group were located in laminae IV, V and VII and were inhibited by electrical stimulation of the nucleus raphe magnus (NRM) and the reticular formation (Ret.F). Most neurones of the second type were located in the ventral horn, and the majority were excited by electrical stimulation of the NRM and the Ret.F. This second type of neurone may play a role in the maintenance of the excitation in the central nervous system which follows visceral noxious stimulation.