Autonomic innervation of the bovine testis.

The autonomic nerve supply of the bovine testis is investigated in animals of different ages by means of immunohistochemistry. Staining with antiserum to protein gene product 9.5 gives the most complete results for the study of the general innervation pattern. Autonomic nerves reach the testis by three different routes: with the blood vessels of the spermatic cord (funicular nervous contribution), by the mesorchium (mesorchial nervous contribution) and by the ligamentous bridge between epididymal tail and testis (caudal nervous contribution). The vessels of the spermatic cord are densely innervated. The large vessels of the vascular layer within the tunica albuginea display a discontinuous innervation pattern. In the interior of the testis, the caudal half of the gonad is completely free of any innervation. Slight differences in arrangement and fiber composition of testicular nerves in calves and bulls point to a reduction of the innervation with advancing age. The vast majority of bovine testicular nerves are dopamine-beta-hydroxylase-positive postganglionic sympathetic axons with vasomotor function. There is no evidence for a cholinergic innervation of the bovine testis. About half of the bovine testicular nerves are neuropeptide Y-immunoreactive. In the adult, solitary calcitonin gene-related peptide-immunoreactive fibers are the only ones independent of blood vessels. The absence of an innervation in the caudal half of the testis underlines the importance of local factors and blood-borne substances for the regulation of intratesticular blood flow in the bovine.