In this study, we asked whether neurons of the enteric nervous system (ENS) isolated from the central nervous system (CNS) are competent to mediate ordered autonomous gut motility (i.e. descending peristalsis, which may be functional for food propulsion down the gut) in the snail Lymnaea stagnalis. Firstly, we explored the origin of autonomous gut contraction in the esophagus and crop. Using extracellular recording, we were able to detect excitatory junctional potentials (EJPs) elicited by motor neuron activity in autonomous rhythmic bursts, showing that neurogenic autonomous contractions existed. We also determined the motor neuron as cholinergic from the antagonistic effects of d-tubocurarine (d-TC) on the EJPs. Interestingly, the “pacemaker region”, which drives the rhythm of the automaticity, was found in the crop, which is located distally to the esophagus. Thus, the burst first occurs in the crop and propagates in an ascending direction (i.e. in the opposite direction of the peristalsis) along the esophagus. From the observation of the relationship between the motor neuron activity and the driven motility, proximally decreasing time lag between the neuronal burst and the peak contraction (T-p; Time to peak) was found to be crucial in producing peristalsis. Regional T-p difference was also observed in the electrically evoked contractions in the isolated esophagus. Blocking the motor neuron activity by d-TC attenuated the regional difference. The above suggest that the processes leading up to the elicitation of EJPs by ENS activity contribute to producing the regional T-p difference.
enteric nervous system