Innervation of the fibro-elastic type of the penis: an immunohistochemicalstudy in the male pig

The occurrence and colocalization of several biologically active neuropepti des, catecholamine-, acetylcholine- or nitric oxide-synthesizing enzymes ty rosine hydroxylase (TH), dopamine-beta-hydroxylase (DPH), choline acetyltra nsferase (ChAT) and nitric oxide synthase (NOS I), respectively, as well as the vesicular acetylcholine transporter (VAChT) were investigated in the p enile glans (GP), corpus and crura (CP), as well as in the retractor penis muscle (RPM) of juvenile and adult boars. Immunohistochemistry revealed tha t nerves immunoreactive (IR) to TH, D beta H, vasoactive intestinal polypep tide (VIP) and somatostatin (SOM) were the most numerous, followed (in decr easing order of density) by nerves IR to NOS, neuropeptide Y (NPY), substan ce P (SP), calcitonin gene-related peptide (CGRP), galanin (GAL), Leu(5)-en kephalin (LENK) and ChAT/VAChT. The CP contained the largest number of nerv e fibres followed by the RPM, GP and corpus. Enzyme/peptide-containing nerv es were associated with both the vascular and non-vascular penile structure s. However, differences existed for their density and intrapenile distribut ion. Nerve terminals IR for different combinations of VIP, GAL or SOM were more frequent than those IR for NOS or CGRP in the non-vascular penile stru ctures while the vasculature and the RPM received a prominent TH/D beta H-, VIP-, SOM- or NOS-IR nerve input. The present data indicate that the porci ne penis receives nerve fibres that exhibit diverse chemical codes and that differences in the chemical coding of the nerve fibres may depend on their penile target-structure.