Enteric pathways in the stomach

This report summarises the characteristics of target specific projection an d neurochemical coding patterns of motor and interneuronal pathways in the gastric enteric nervous system (ENS) which are involved in the innervation of the mucosa, the circular and the longitudinal muscle. The pathways were identified by retrograde tracing and further characterised by optical and i ntracellular recordings of the synaptic activation of muscle motor neurones , and by recordings of pathway-specific muscle responses. All motor pathway s had polarised projections consisting of ascending cholinergic and descend ing nitrergic populations. Thus, both muscle layers were innervated by exci tatory and inhibitory motor neurones. Their projections indicated the prese nce of intrinsic circuits that mediate excitatory and inhibitory components of a peristaltic reflex and/or are involved in reflex mediated changes in gastric tone. Although polarised projections were also identified for inter neuronal pathways, a substantial proportion of descending interneurones was cholinergic. Interneurones and longitudinal muscle motor pathways had long itudinal projection preferences whereas circular muscle motor pathways had circumferential projection preferences. Target-specific coding was primaril y revealed for cholinergic populations; ChAT/ENK/+/- SP neurones projected to the muscle layers, ChAT/NPY/+/- VIP projected to the mucosa and ChAT/+/- SP/+/-5-HT/+/- Calret/+/- Calb were interneurones. Muscle strip recordings revealed the functional significance of ascending excitatory and descendin g inhibitory pathways to the circular muscle and the prominent influence of ascending and descending cholinergic interneurones which activated excitat ory and inhibitory circular muscle motor neurones through nicotinic synapse s. It is concluded that enteric pathways in the stomach have region specifi c features which reflect structural and functional adaptation of the gastri c ENS. Anat Rec 262:47-57, 2001. (C) 2001 Wiley-Liss, Inc.