Immunohistochemical investigations of the autonomous innervation of the cervine testis

Abstract

The innervation of the cervine testis was studied in 6 roe deers, 7 red deers and 14 fallow deers. The results for the three species are rather similar. With anti-sera to neurofilament (NF) and neuron specific enolase (NSE), all small and large nerve fascicles can be demonstrated, but single fibers are incompletely stained. Immunoreactions against protein gene product-9.5 (PGP-9.5) and GAP-43 (growth-associated protein-43) are better suited to depict the complete innervation pattern. Bundles of the superior spermatic and inferior spermatic nerves reach the testis via three access routes as funicular, mesorchial and caudal nerve contributions. We found no morphological evidence that the nerves in the cervine testis are directly involved in regulating Leydig cell function or seminiferous tubular motility. The majority of the testicular nerves are associated with the testicular arteries, but the musculature in the walls of the venous plexus pampiniformis is also innervated. All vascular nerve fibers represent postjunctional sympathetic axons displaying a strong dopamine-beta-hydroxylase (DBH) activity, mostly co-expressed with neuropeptide Y (NPY). The presence of cholinergic fibers in the testis of the deer is only sporadic and probably of no functional importance. In all three species of deer, a small quantity of myelinated nerve fibers is encountered in spermatic cord and tunica albuginea and regarded as afferent. The viscerosensory quality in the testicular intrinsic innervation is very likely mediated by the CGRP (calcitonin gene-related peptide)-positive fibers that run independently from the testicular vessels and end in the connective tissue of spermatic cord and tunica albuginea. The testis of the red deer contains significantly more VIP (vasoactive intestinal polypeptide)-positive axons than that of roe and fallow deer. The nerve density in the interior of the testicular lobules shows no regional differences, but there are age- and season-related changes that correlate with the developmental and functional state of the seminiferous tubules. Small testes with solid and narrow tubules, as seen in the prepuberal phase and during seasonal reproductive quiescence, are better innervated than large testes with expanded and spermatogenetically active seminiferous tubules.