Neurons labelled after the application of tracer to the distal stump of the transected hypogastric nerve in the rat.

Axons within the hypogastric nerve (HGN) provide sympathetic innervation to various tissues of the pelvic viscera (e.g. bladder, urethra, ureter, colon and sexual organs). Traditionally the HGN was considered to carry efferent impulses from the lumbar spinal cord to the periphery and afferent information from the periphery to the lumbar cord. In recent years however, there have been a number of reports of axons in the hypogastric nerve carrying impulses in directions opposite to these traditional ones. To further study this phenomenon fast blue dye was applied to the distal (or for comparison the proximal) stump of one transected hypogastric nerve and the locations of retrogradely labelled neurons determined in the spinal cord, the dorsal root ganglia (DRG), the sympathetic chain ganglia and the major pelvic ganglia (MPG). Labelled neurons were found in the spinal cord only for proximal stump dips. Labelled DRG neurons were mainly located in the L6-S1 ganglia when dye was applied to the distal stump, and mainly in the L1-L2 ganglia for proximal stump dips. The distribution profile of labelled sympathetic chain neurons was shifted caudally about one segment when the distal stump was dipped compared to the distribution obtained following a proximal stump dip. Labelled neurons were found contralateral to the dipped distal stump in all categories although in reduced numbers. More labelled neurons were found in male animals than in female animals. Fast blue in neurons in the DRGs and sympathetic chain labelled from the distal HGN reached these structures via the pelvic nerves. Labelled MPG neurons were found when the distal stump was dipped. Labelled MPG neurons were larger in the male than in the female. These fast blue labelled MPG neurons were also tested immunohistochemically for the presence of tyrosine hydroxylase (TH), neuropeptide Y (NPY) and vasoactive intestinal polypeptide (VIP). Labelled neurons which were TH+ were only found in the male; labelled neurons which were NPY+ or VIP+ were found in males and in females.