Effects of stimulation of Auerbach's plexus on both longitudinal and circular muscles

The effects of repetitive electrical stimulation of a node of Auerbach's plexus on both longitudinal and circular muscles were investigated by simultaneous recording of both muscle contractions. L-formed muscle strips, longitudinal and circular muscle strips, were made from a segment of rabbit small intestine. One strip was cut along, another strip was cut at 90 degrees to the oral-anal axis. The longitudinal muscle strip was peeled and Auerbach's plexus was exposed. Under a stereodissecting microscope the stimulating electrode, with tip diameter of 5--10 micron, was placed on a node of Auerbach's plexus situated at the junction of both muscle strips. Repetitive electrical stimulation of a node produced a mainly excitatory effect on spontaneous contractions of an orally-directed longitudinal muscle strip, excitatory and inhibitory effects on an anally-directed longitudinal muscle strip and a mostly excitatory effect on a circular muscle strip which always appeared with a delay after that on the longitudinal muscle. In a few instances the inhibitory effect of nodal stimulation was observed on the circular muscle. The evoked excitatory effect of longitudinal muscle was mainly due to a cholinergic mechanism, while that of circular muscle was partially due to cholinergic and partially noncholinergic activity. The evoked inhibition was nonadrenergic.