TESTIS OF PREPUBERTAL RHESUS-MONKEYS RECEIVES A DUAL CATECHOLAMINERGIC INPUT PROVIDED BY THE EXTRINSIC INNERVATION AND AN INTRAGONADAL SOURCE OF CATECHOLAMINES

The mammalian testis is innervated by extrinsic catecholaminergic nerv es and responds to catecholamines with steroid secretion. Although the primate testis has also been shown to be innervated, potential differ ences in the density of this innervation between immature and sexually developed individuals have not been described. A recent study demonst rated that the primate ovary contains a network of neuron-like cells a nd that some of these cells are catecholaminergic. It is thus possible that the male gonad is also endowed with a similar intragonadal sourc e of catecholamines. The present study addresses these two issues. Cat echolaminergic nerves were identified as such by their content of immu noreactive tyrosine hydroxylase (TH; the rate-limiting step in catecho lamine biosynthesis), and in some cases by glyoxylic acid histochemist ry. Fibers containing TH were abundant in testes from juvenile animals (1-2 yr of postnatal life), but the density of this innervation was n ot maintained in adult animals, whose testis showed only a few TH-posi tive fibers scattered in the interstitial tissue. Testicular norepinep hrine (NE) concentration was much lower in adult than in juvenile anim als, suggesting that the marked increase in testicular weight that occ urs with the attainment of sexual maturity is not accompanied by corre sponding changes in NE content. At the ultrastructural level, testicul ar nerve fibers contained pleiomorphic, dense-core and clear vesicles, suggesting the presence of catecholamines and other neurotransmitters . In addition to this extrinsic catecholaminergic innervation, prepube rtal testes, but not adult gonads, contained an intrinsic population o f TH-immunopositive neuron-like elements, identified as cells by confo cal scanning laser microscopy. To determine whether the prepubertal mo nkey testis indeed expresses the TH gene, testicular RNA was subjected to reverse transcriptase polymerase chain reaction to amplify the 5' end of TH mRNA, which encodes the regulatory domain of the enzyme. The cDNA that was obtained predicts an amino acid sequence similar, but n ot identical, to that encoded by the alternatively spliced type 1 TH m RNA form present in the adrenal gland. These results indicate 1) that the primate testis receives a dual catecholaminergic input, one provid ed by the extrinsic innervation and the other by neuron-like cells loc ated within the gonad itself, and 2) that the influence exerted by bot h sources on testicular function may be more prominent during the prep ubertal period than in adulthood. The presence in the testis of a TH m RNA variant encoding amino acid substitutions in its 5' end suggests t hat regulation of testicular TH enzyme activity may include a gonad-sp ecific component.