On the innervation of the donkey testis.

The innervation pattern of the adult donkey testis was investigated by immunohistochemistry and acetylcholinesterase histochemistry. Autonomous nerves reach the testis by three access-routes as funicular, mesorchial and caudal contributions. From these, the funicular contribution accompanying the testicular artery and pampiniform plexus is the strongest and most important one. Testicular innervation in the donkey is not uniform. The spermatic cord as well as the epididymal region, cranial and caudal poles (tunica albuginea and adjacent parenchyma and stroma) are well innervated, mostly by vascular nerves. Towards the free border of the testis, the nerve density in the tunica albuginea decreases continuously. In the interior of the gonad, approximately one third of the testis, situated between the free border and the central mediastinum, is practically devoid of any innervation. The great majority of the testicular nerves demonstrated by the present techniques are non-myelinated vascular nerves which react positive for dopamine-beta-hydroxylase and tyrosine hydroxylase, thus representing postjunctional sympathetic fibers. Many of these also contain neuropeptide Y. The testicular innervation of the donkey testis is free of cholinergic fibers. Calcitonin gene-related peptide-containing nerves are found as solitary varicose axons in the wall of blood vessels, but also in stromal connective tissue of the spermatic cord, tunica albuginea and septula testis.