Evidence for and significance of the projection of VIP neurons from the myenteric plexus to the taenia coli in the guinea pig.

Immunohistochemical studies of the distribution of vasoactive intestinal polypeptide were made in the cecum from normal guinea pigs and from guinea pigs after lesions of the cecal wall had been made. These experiments were designed to determine the origin of the vasoactive intestinal polypeptide axons which supply the taenia of the cecum in order to ascertain whether the projections of the vasoactive intestinal polypeptide neurons were consistent with VIP being contained in enteric inhibitory neurons. Vasoactive intestinal peptide was found in nerve cell bodies of both the myenteric and submucous taenia and the myenteric plexus the vasoactive intestinal polypeptide fibers in the taenia disappeared, but there was no effect on these fibers if the taenia was separated from the submucous plexus or surrounding muscle while leaving connections with the myenteric plexus intact. Retrograde degenerative signs were seen in VIP fibers and nerve cell bodies of the myenteric plexus after removal of the taenia. In conclusion, VIP is contained in neurons that have the same projections as the enteric inhibitory neurons from the myenteric plexus to the taenia of the cecum.