THE SENSORY BRANCH OF THE PUDENDAL NERVE IS THE MAJOR ROUTE FOR ADRENERGIC-INNERVATION OF THE PENIS IN THE RAT

Background: Multiple pathways have been proposed for the course of adr energic fibers to the penis and, although it is generally recognized t hat the pudendal nerve (PudN) is the most important, there is little q uantitative information available. Methods: We used image analysis of catecholamine histofluorescence to quantify the effect of various nerv e lesions on the adrenergic innervation of the rat penis, In addition to the denervation studies and as a direct test of whether penile adre nergic fibers traversed the pelvic plexus, penile neurons in the sympa thetic chain were first labeled with a retrograde dye placed in the pe nis, The cavernous nerve of these animals was later exposed to another dye with different spectral characteristics. Results: Interruption of the sensory branch of the PudN reduced adrenergic innervation of cave rnosal smooth muscle by 86% (+/-2.5%). Vascular fibers of the deep pen ile and helicine arteries were also severely reduced but not entirely eliminated. Interruption of the motor branch of the PudN had a lesser and more variable effect on penile adrenergic innervation: a 21.2% (+/ -6,8%) decrease in cavernosal muscle innervation but no obvious affect on vasomotor fibers. Combining the nerve lesions with phenol degenera tion of perivascular fibers of the pudendal vessels further reduced bu t did not entirely eliminate adrenergic fibers in the cavernosal muscl e and penile vessels. Conclusions: The dramatic reduction of adrenergi c innervation of the penis after section of the PudN, especially the s ensory branch, and the absence of double-labeled neurons in the sympat hetic chain suggest that the PudN nerve is the major, if not the exclu sive, pathway by which adrenergic fibers reach penile erectile tissue of the rat. (C) 1997 Wiley-Liss, Inc.