Comparative physiology of morphology and function of the enteric nervous system.

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In a wide variety of animals, the enteric nervous system (ENS) consists of a network of neurons intrinsic to the gastrointestinal tract. In this study, we compared the structure and function of the ENS among animals beyond phylum: sea snail and pond snailfrom mollusks, shrimps and isopod from arthropods, and sea-cucumbers from echinoderms. In most of animals, ENS neurons exhibited autonomous periodic-burst activity. Simultaneous recording of neuronal activities and movements of the gastrointestinal tract revealed that only in mollusks, but not in arthropods nor echinoderms, the periodic bursts were followed by peristaltic movements. This observation shows that the ENS in mollusks contains pacemaker neurons responsible for the neurogenic rhythmicity of peristalsis. In other animals, the rhythmicity of the gut motility originated in the myogenic pacemaker. The "pacemaker region" was localized differently among related species due to the structural differences of the gastrointestinal tract. For example, Bursatella shared common characteristics with Lymnaea rather than Aplysia, even though the latter species is more closely related to Bursatella.