Effects of gut distension on Auerbach's plexus and intestinal muscle

Using a peeled longitudinal muscle strip which was attached to an intestinal segment of rabbit, the effects of gut distension upon the activities of both the neurons within Auerbach's plexus and the intestinal muscle were investigated. Spontaneous neuronal and muscular discharges were recorded by means of a micropipette electrode which was placed on a node of the exposed Auerbach's plexus. Contractions of the peeled. Longitudinal muscle strip were simultaneously recorded. Gut distension caused an excitatory or inhibitory effect on mechanosensitive neurons. The neurons whose spontaneous discharges showed a frequency increase during muscle contraction and a frequency decrease during muscle relaxation at zero intraluminal pressure responded to gut distension as well as to stretching of the longitudinal muscle with excitation. The neurons which did not show any correlation in their discharge frequency with muscle contractions responded to gut distension as well as to stretching of the longitudinal muscle with inhibition. Additional neurons were found in small numbers whose spontaneous activity did not relate in frequency to muscle contractions and did not change by gut distension. In all cases of gut distension the excitatory effect on longitudinal muscle as well as on intestinal segment, namely the peristaltic movement, were observed. Removal of mucosa did not affect the above-described effects of gut distension. It was concluded that gut distension causes an excitatory effect on specific mechanosensitive neurons in Auerbach's plexus which regulate the contractions of intestinal muscle and produce the peristaltic movements.