Polarized enteric submucosal circuits involved in secretory responses of the guinea-pig proximal colon

1Neuronal retrograde tracing with the dye DiI (1,1′-didodecyl-3,3,3′,3′-tetramethylindocarbocyanine perchlorate), in combination with immunohistochemical detection of choline acetyltransferase (ChAT) and vasoactive intestinal peptide (VIP), were used to identify the innervation of the mucosa of the guinea-pig proximal colon by submucosal neurones. Ussing chamber experiments were performed to measure changes in short circuit current (ΔIsc) evoked by electrical stimulation of the oral or anal end of the preparation. 2The tracing studies revealed that the mucosa was primarily innervated by descending neurones (78 %); the vast majority of these were VIP positive (85 %). The numerically smaller ascending pathway (13 %) was predominantly ChAT positive (69 %). A small population (9 %) of DiI-labelled neurones projected circumferentially. 3Ussing chamber experiments revealed that oral electrical stimulation induced a significantly larger ΔIsc than anal stimulation. The VIP antagonist VIP(6–28) significantly reduced only orally induced ΔIsc. Anally induced ΔIsc were significantly more atropine sensitive that orally induced ΔIsc. Tissue incubation with carbachol or VIP significantly potentiated ΔIsc induced by VIP and carbachol, respectively, indicating cross-potentiation. 4This study provides the first functional demonstration of polarized innervation patterns from submucosal neurones to enteric mucosa. The ascending ChAT and descending VIP pathways suggest the existence of reflexes resulting in preferential release of VIP or acetylcholine. The distinct pathways might favour the observed cross-potentiation of cholinergic and VIPergic mediated secretion.