COLOCALIZATION OF NITRIC-OXIDE SYNTHASE AND VASOACTIVE-INTESTINAL-PEPTIDE IMMUNOREACTIVITY IN NEURONS OF THE MAJOR PELVIC GANGLION PROJECTING TO THE RAT RECTUM AND PENIS

Nitric oxide synthase (NOS)- and vasoactive intestinal peptide (VIP)-i mmunoreactive neurons projecting to the upper rectum or penis were exa mined using retrograde tracing combined with immunohistochemistry in t he major pelvic ganglion of male rats. Five days after injection of Fl uoro-Gold (FG) into the upper rectum or penis, the major pelvic gangli on was treated with colchicine. FG injected into the upper rectum labe lled many ganglion neurons in the major pelvic ganglion. Immunohistoch emistry showed that 37% of FG-labelled neurons were immunoreactive for NOS and 33% for VIP. After injection of FG into the penis, 41% of FG- labelled neurons were immunoreactive for NOS and 25% for VIP. Serial c ryostat sections stained for NOS and VIP, respectively, showed the co- localization of NOS and VIP in the ganglion cells projecting to the re ctum and penis. In the major pelvic ganglion of the colchicine-treated animals, about 17% of the ganglion cells were immunoreactive for NOS and 32% were immunoreactive for VIP. These neurons were small in diame ter (less than 30 mu m) A histogram showing cell sizes in cross-sectio nal areas of NOS-immunoreactive neurons coincided with that of VIP-imm unoreactive neurons. Most of the NOS- and VIP-immunoreactive neurons w ere less than 600 mu m(2) These results indicate that small neurons co ntaining both NOS and VIP in the major pelvic ganglion project to the rectum and penis. In the penile erectile tissues and enteric ganglia, NO and VIP may be released from the same axons and may act concomitant ly on the target tissue.