On the innervation of the donkey testis

The innervation pattern of the adult donkey testis was investigated by immu nohistochemistry and acetylcholinesterase histochemistry. Autonomous nerves reach the testis by three access-routes as funicular, mesorchial and cauda l contributions. From these, the funicular contribution accompanying the te sticular artery and pampiniform plexus is the strongest and most important one. Testicular innervation in the donkey is not uniform. The spermatic cor d as well as the epididymal region? cranial and caudal poles (tunica albugi nea and adjacent parenchyma and stroma) are well innervated, mostly by vasc ular nerves. Towards the free border of the testis, the nerve density in th e tunica albuginea decreases continuously. In the interior of the gonad, ap proximately one third of the testis, situated between the free border and t he central mediastinum, is practically devoid of any innervation. The great majority of the testicular nerves demonstrated by the present techniques a re non-myelinated vascular nerves which react positive for dopamine-beta-hy droxylase and tyrosine hydroxylase, thus representing postjunctional sympat hetic fibers. Many of these also contain neuropeptide Y. The testicular inn ervation of the donkey testis is free of cholinergic fibers. Calcitonin gen e-related peptide-containing nerves are found as solitary varicose axons in the wall of blood vessels, but also in stromal connective tissue of the sp ermatic cord, tunica albuginea and septula testis.