PROJECTIONS OF SUBMUCOUS NEURONS TO THE MYENTERIC PLEXUS IN THE GUINEA-PIG SMALL-INTESTINE

The distribution of submucous neurons that project to the myenteric pl exus of the guinea pig small intestine was established by retrograde t ransport of the carbocyanine dye 1,1'-didodecyl-3,3,3',3'-tetramethyl indocarbocyanine perchlorate (DiI) from myenteric ganglia in organ cul ture in combination with immunohistochemistry. Following the applicati on of DiI to the serosal surface of a single myenteric ganglion, from 2 to 15 DiI-labelled nerve cell bodies were labelled in the submucous plexus up to 7.9 mm circumferentially, 4.5 mm orally, and 3.4 mm abora lly to the DiI application site. No cells were labelled in preparation s in which connections between myenteric and submucous plexuses had be en severed prior to DiI application. Cells that were immunoreactive fo r vasoactive intestinal polypeptide (VIP) or for substance P (SP) acco unted for about 75% and 11% of DiI-labelled cells, respectively. Neith er neuropeptide Y- nor calretinin-immunoreactive submucous neurons wer e labelled by DiI, indicating that these classes of neurons do not pro ject to the myenteric plexus. Retrograde tracing from the myenteric pl exus with Neurobiotin revealed that labelled VIP-immunoreactive neuron s had several short, filamentous processes and a single long axon that could be followed through the circular muscle to myenteric ganglia wi thout branches to the mucosa. The previously described projection of s ubmucous, SP-immunoreactive putative sensory neurons to the myenteric plexus was confirmed. However, this study has identified a considerabl y larger population of presumed interneurons that are immunoreactive f or VIP that likely transmit information from the submucous plexus to t he myenteric plexus and presumably coordinate activity between the two ganglionated plexuses. J. Comp. Neurol. 399:255-265, 1998. (C) 1998 W iley-Liss, Inc.