A study of peripheral input to and its control by post‐ganglionic neurones of the inferior mesenteric ganglion.

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Abstract
Intracellular recordings were made, in vitro, from neurons of guinea pig inferior mesenteric ganglia (IMG) attached, via the lumbar colonic nerves, to segments of distal colon. Spontaneous synaptic input from colonic afferent fibers was observed in 79% of the neurons tested. In any given preparation, the level and pattern of this synaptic input to different neurones varied considerably. Superfusion of colonic segments with drugs (papaverine, isoprenaline, and ATP) which reduce colonic motility decreased colonic afferent input to IMG neurons. Superfusion of colonic segments with acetylcholine or stimulation of pelvic nerves, both of which increase colonic motility, increased colonic afferent input to IMG neurons. Superfusion of colonic segments with either atropine or tubocurarine reduced the level of spontaneous, colonic afferent input. Distension of these relaxed segments increased the colonic afferent input. Repetitive stimulation of preganglionic inputs to the IMG inhibited afferent input from drug relaxed segments of colon that were moderately distended by the injection of air into the lumen. Superfusion of the colon with phentolamine blocked this inhibition. IMG neurons apparently receive afferent input from mechanoreceptors located in the distal colon, and the mechanosensitivity of this afferent pathway may be in part controlled by efferent noradrenergic neurons of the IMG. The IMG-colon neural circuitry can be considered a feed-back control system which participates in the regulation of colonic motility.