Vagal control of lower oesophageal sphincter motility in the cat

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Abstract
The effects of vagal efferent fiber stimulation on the smooth muscle of the lower esophageal sphincter were studied on the anaesthetized animal and on the isolated and perfused organ. In both muscle layers (longitudinal and circular) vagal stimulation elicited 2 types of electromyographic (e.m.g.) potentials: excitatory junction potentials (e.j.p.s) where there is a depolarization of the smooth muscle fibers; and inhibitory junction potentials (i.j.p.s) where there is hyperpolarization of the smooth muscle fibers, often followed by a transient depolarization which may initiate spikes (post-inhibitory rebound). Pure i.j.p.s. are observed after atropine treatment which suppresses e.j.p.s. Under these conditions, a long lasting vagal stimulation induces a long duration hyperpolarization concomitant with an opening of the lower esophageal sphincter followed after the cessation of stimulation by a powerful rebound leading to a strong contraction which closes the sphincter. Preganglionic vagal fibers are apparently cholinergic and they activate intramural excitatory cholinergic neurons and intramural non-adrenergic inhibitory neurons (purinergic neurons). Preganglionic fibers leading to inhibition had a higher threshold than those leading to excitation. Both excitatory and inhibitory pathways seem to be interconnected inside the intramural network. In particular, activation of intramural inhibitory neurons, by relaxing the esophagus orally to the lower esophageal sphincter, inhibited intramural excitatory neurons and subsequently blocks vagal excitatory responses. Two functions may be attributed to the vagal extrinsic innervation: closure of the lower esophageal sphincter by maintaining the basal tone of the sphincter: this would imply, that at rest the inhibitory control is supplanted by the excitatory one; and sphincter opening during swallowing by suppressing the excitatory stimulus and reinforcing the inhibitory one (it may be recalled that after bilateral vagotomy, swallowing is no longer followed by a relaxation of the sphincter).