Spinal neurones with long projections activated from the abdominal viscera of the cat

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Abstract
Recordings were made from 73 neurons responding to electrical stimulation of pelvic, hypogastric or lumbar colonic nerves, in decerebrate or anesthetized cats. Of the units 52 had long projections that ascended to the 1st cervical segment, and no units with visceral inputs belonged to the spino-cervical tract. Units (21) had long descending projections. Twenty percent (i.e., 11/46) responded to parasympathetic (pelvic) nerve stimulation (group 1) while 80% (35/46) responded to stimulation of hypogastric and/or lumbar colonic nerves (group 2). Of groups 2 neurons 90% also responded to pelvic nerve stimulatin. The electrical thresholds for activation of the units indicated that the largest peripheral nerve fibers responsible for the response were of the A.delta. size. Of the neurons, 31 had visceral mechanosensitive receptive fields; 21 had simple receptive fields in the bladder (7) or in the colon (14), 10 units had compound receptive fields. The response of units with simple receptive fields to mechanical stimulation were either inhibitory or excitatory, and slowly adapting or rapidly adapting. Units (42) appeared to have no visceral mechanosensitive receptive fields in spite of showing responses to visceral nerve stimulation. Of the units tested 50% responded to innocuous somatic stimuli, mostly derived from muscle or joint receptors. Some of the units responded to injections of bradykinin (10-15 .mu.g) into a hindlimb artery. Group 1 had predominantly inhibitory visceral receptive fields and somatic receptive fields in structures innervated from sacral segments of the spinal cord. Group 2 units all received inputs from visceral nerves entering the spinal cord over lumbar segments; many also received projections from sacral segmental inputs. These inputs showed an equal mixture of excitatory and inhibitory visceral receptive fields and convergence from somatic inputs arising from lumbar as well as sacral dermatomes. This group evidently represents units originating in lumbar as well as sacral segments of the cord. The possible role of these neurones as mediators of visceral sensations and visceral reflexes is discussed.