Efferent Innervation of the Rat Testis1

Previous assessments of the autonomic nerve supply of the male genital tract concluded that the testis received sympathetic input primarily from paraaortic ganglia, particularly the spermatic ganglion. We challenged this consensus by using retrograde axonal tracing to examine the source and distribution of efferent fibers reaching the testis of adult rats. We also used immunohistochemical methods to assess putative neurotransmitters in testicular neurons of the abdominal and pelvic ganglia. The results indicate that the majority of retrogradely labeled cell profiles were localized within the major pelvic (38%) and pelvic accessory ganglia (37% ), and only a few labeled cell profiles were present in the paraaortic and spermatic ganglia. Injection of FluoroGold and Fast Blue dyes into the respective right and left testis demonstrated that 17% of the neurons in pelvic ganglia were labeled when tracers were microinjected beneath the capsule of the contralateral testis. About 8% of the neurons were labeled both with FluoroGold and Fast Blue, suggesting that certain neurons can provide simultaneous input to the left and right testicles. Immunohistochemical results showed that tyrosine hydroxylase, a marker for noradrenergic fibers, was present in over 33% of the cell profiles labeled with either FluoroGold or Fast Blue. Some 27% of the fluorescent-labeled cell profiles were positive for neuropeptide Y, while 22% were immunoreactive for vasoactive intestinal polypeptide. No evidence for vasoactive intestinal polypeptide immunoreactivity was detected within the testis, but neuropeptide Y-immunoreactive fibers were present in the tunica albuginea and testicular vasculature. Catecholamine fluorescent fibers were distributed sparsely throughout the periphery of the testis in association with the capsule, vasculature, and interstitium. The present findings provide new evidence showing that adrenergic and presumed noradrenergic neurons innervate the capsule, vasculature, and peripheral interstitium of the rat testis. Efferent neurons supplying the rat testis originate in the pelvic ganglia and sympathetic chain, rather than the spermatic plexus as formerly concluded on the basis of direct tracing or lesioning of nerve fibers.