Multiple vasodilator pathways from the pelvic plexus to the penis of the rat

The main penile or cavernous nerve is usually regarded as the most important vasodilator projection in the rat. Although other descending pathways have been described, there is little detailed information on their importance. In this present report, we provide topographic and quantitative information on lateral and ventral penile branches and examine the vasodilator fibers which join the pudendal neurovascular bundle. Seventeen Sprague-Dawley rats were used. The techniques included injection of dye in the penis to label neurons in the pelvic plexus in combination with transection of the main penile nerve (MPN). NADPH diaphorase (NADPH-d) histochemistry was used to assess the effects of transection of vasodilator pathways on innervation of the penis and for in situ staining of the pelvic plexus. Distinct clusters of penile neurons are aggregated at the origin of several nerve tracts leaving the posterior margin of the major pelvic ganglion (MPG). Multiple NADPH-d+ fiber bundles coursed over the anterior surface of the prostate to reach the penis. Branches from these tracts joined the pudendal neurovascular bundle proximal to the hilum of the penis and provided innervation to the artery throughout its course in the pudendal canal. Consistent with the presence of multiple penile pathways, transection of the MPN reduced, but did not eliminate retrograde labeling of penile neurons in the MPG and only modestly decreased NADPH-d+ fibers in the penis. This study confirms that there are multiple pathways by which vasodilator fibers reach the penis. If a similar allocation of vasodilator output is present in man, preservation of finer branches of the pelvic plexus would be important in surgical procedures on the prostate.