Discharge patterns of motility-regulating neurons projecting in the lumbar splanchnic nerves to visceral stimuli in spinal cats.

Reflexes in visceral preganglionic motility-regulating (MR) neurons which project in the lumbar splanchnic nerves were investigated in acutely spinalized cats. Some neurons were analyzed before and after spinalization. The stimuli used were mechanical stimulation of mucosal skin of the anus and of perianal (perigenital) hairy skin, and distension and contraction of urinary bladder and colon. Most MR neurons exhibited a reflex pattern which consists of the following components: excitation upon bladder distension, inhibition or no effect upon colon distension and excitation (or, rarely, no effect) upon anal stimulation. This is the reflex pattern of MR1 neurons. Some neurons were excited by anal stimulation but not affected from the colon and urinary bladder. Some were inhibited by anal and perianal stimulation but otherwise exhibited the reflex patterns of the MR1 neurons. Analysis of the reflexes before and after spinalization showed that, in particular, inhibition elicited by anal, perianal and bladder stimulation was abolished; inhibition elicited from the colon was enhanced after spinalization. It is concluded that the reflexes elicited in preganglionic lumbar visceral neurons by the natural stimuli probably use spinal pathways, with the afferent input occurring at the sacral spinal cord. These spinal reflex pathways are probably controlled by descending inhibitory and excitatory spinal systems from the supraspinal neuraxis.