Differences in the distribution and chemical coding between neurons in theinferior mesenteric ganglion supplying the colon and rectum in the pig

The distribution and chemical coding of neurons in the porcine left and rig ht inferior mesenteric ganglion projecting to the ascending colon and rectu m have been investigated by using combined retrograde tracing and double-la belling immunohistochemistry. The ganglion contained many neurons supplying both gut regions. The colon-projecting neurons (CPN) occurred exclusively in the cranial part of the ganglia where they formed a large cluster distri buted along the dorso-lateral ganglionic border and a smaller cluster locat ed close to the caudal colonic nerve output. The rectum-projecting neurons (RPN) formed a long stripe along the entire length of the lateral ganglioni c border and, within the right ganglion only, a small cluster located close to the caudal colonic nerve output. Immunohistochemistry revealed that the vast majority of the CPN and RPN were noradrenergic (tyrosine-hydroxylase- positive). Many noradrenergic neurons supplying the colon contained somatos tatin or, less frequently, neuropeptide Y. In contrast, a significant subpo pulation of the noradrenergic RPN expressed neuropeptide Y, whereas only a small proportion contained somatostatin. A small number of the non-adrenerg ic RPN were cholinergic (choline-acetyltransferase-positive) and a much lar ger subpopulation of the nerve cells supplying both the colon and rectum we re non-adrenergic and non-cholinergic. Many cholinergic neurons contained n europeptide Y. The non-adrenergic non-cholinergic neurons expressed mostly somatostatin or neuropeptide Y and some of those projecting to the rectum c ontained nitric oxide synthase, galanin or vasoactive intestinal polypeptid e. Many of both the CPN and RPN were supplied with varicose nerve fibres ex hibiting immunoreactivity against Leu(5)-enkephalin, somatostatin, choline- acetyltransferase, vasoactive intestinal polypeptide or nitric oxide syntha se The somatotopic and neurochemical organization of this relatively large population of differently coded inferior mesenteric ganglion neurons projec ting to the large bowel indicates that these cells are probably involved in intestino-intestinal reflexes controlling peristaltic and secretory activi ties.