Multiple vasodilator pathways from the pelvic plexus to the penis of the rat WG Dail 1 *, F Harji 1 , J Gonzales 1 and R Galindo 1 1 Department of Neurosciences, University of New Mexico Health Sciences Center, School of Medicine, Albuquerque, New Mexico, NM 87131-5223, USA 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 ®bers 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  ®ber 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  ®bers in the penis. This study con®rms that there are multiple pathways by which vasodilator ®bers reach the penis. If a similar allocation of vasodilator output is present in man, preservation of ®ner branches of the pelvic plexus would be important in surgical procedures on the prostate. Keywords: penis; nitric oxide synthase; pelvic plexus; prostatectomy; cavernous nerve Introduction Much of the recent interest in the neural control of penile erection have focused on intriguing questions regarding vasodilator neurotransmitters, 1,2 the cen- tral control of erection 3±6 and mechanical factors which promote ®lling of the penis. 7 A thorough knowledge of peripheral nerve pathways is also a necessary element in experiments designed to study autonomic control of erection. Information of a general nature is available on the organization of the pelvic plexus in large species such as the rabbit and cat; 8 however, size considerations and the complexity of the pelvic plexus in these species have prompted the move to a smaller animal model. Much relevant information now exists on the neuroanatomy of the pelvic portion of the auto- nomic nervous system of the rat, 8,9,10 consequently, this species is now one of the more useful models for studies of erectile physiology. 2,11 ± 14 An initial study by Langworthy 15 used methylene blue stained preparations to describe a prominent postganglionic ®ber bundle which projected to the penis (descending branch to the penis) and rectum in the rat. A cluster of nerve cell somata, presumed to be penile, were said to be related to the origin of this nerve. Purinton et al 16 con®rmed these ob- servations and identi®ed two other ®ber tracts from the rat major pelvic ganglion to the penis; lateral and ventral penile nerves. The main branch (descending branch of Langworthy) reaches the penis by cour- sing between the rectum and urethra, while the lateral and ventral branches run over the prostate gland to travel distally on the urethra. 16 Since the main penile nerve (of Purinton et al; 16 often called the cavernous nerve) is an easily located and sizable efferent nerve tract, it is often the only one stimulated or lesioned in functio- nal studies. 2,11,12,17 Indeed, some recent studies in the rat further emphasize the dominance of this pathway. For example, nitric oxide synthase immunoreactive (NOS-IR) nerve ®bers in the cavernous spaces were completely eliminated one week after bilateral lesion of the rat cavernous nerves; although some faint staining remained in *Correspondence: Dr WG Dail E-mail: Wdail@salud.unm.edu Received December 28, 1998; accepted in revised form March 23, 1999 International Journal of Impotence Research (1999) 11, 277±285 ß 1999 Stockton Press All rights reserved 0955-9930/99 $15.00 http://www.stockton-press.co.uk/ijir