Projections from the prevertebral and major pelvic ganglia to the ileum and large intestine of the male rat.

The sympathetic innervation of the gut arises from the prevertebral and pelvic ganglia, and to a variable extent, from neurons located in the paravertebral ganglia, the splanchnic and intermesenteric nerves. In this study we have injected retrograde tracers into the wall of the ileum and several regions of the large intestine to determine the proportion of neurons supplying these regions from each of the ganglia and nerves. The sympathetic supply to the ileum arises primarily from neurons in the splanchnic nerves and the paravertebral ganglia T9-T11 (SPL) and the coeliaco-mesenteric ganglion complex (CG/SMG), with a small supply from the proximal intermesenteric nerves (IMN). The distribution of neurons projecting to the proximal colon is very similar, although some labelled neurons are found throughout the length of the IMN and also in the inferior mesenteric ganglion (IMG). The middle colon is primarily supplied by the IMN and the IMG, although this region receives innervation from all the ganglia and nerves investigated, including the major pelvic ganglia (MPG). Neurons located in the distal two-thirds on the IMN and more caudal structures were labelled from the distal colon. The distal colon is the only region of gut to receive a relatively large innervation from the MPG, with approximately one third of labelled neurons in each of the IMN, IMG and the MPG. These studies also compared two retrograde tracers, Fast Blue and Fluorogold. Fluorogold was found specifically to label neurons projecting to each region of intestine injected. However, when injected into the middle colon, Fast Blue labelled neurons that project to this region as well as many neurons that Fluorogold studies indicate project to other regions; Fast Blue should therefore be used only with caution.