CASTRATION, SEX HORMONES, AND TUBERO-INFUNDIBULAR DOPAMINE NEURONS

The eflects of castration and subsequent treatment with gonadal hormones and glycocorticoids were studied on the tubero-infundibular DA neurons of the adult rat, using the histochemical fluorescence method for the cellular localization of catecholamines. The turnover in the DA nerve terminals of these neurons was studied with a tyrosine-hydroxylase inhibitor, α-methyl-tyrosine-methylester. Injections of low doses of testosterone and estrogen caused marked and selective increases in turnover in the DA nerve terminals of the median eminence of both the castrated male and female rat to a rate above that found at any stage of the ovarian cycle. The amine turnover in the nigro-neostriatal DA neurons was not affected by these experimental procedures. Castration alone did not cause any definite change in the turnover in the DA nerve terminals of the male rat; in the female rat, on the other hand, castration blocked the variations in turnover observed during the ovarian cycle and set the turnover to a low and constant level similar to that found in proestrus-estrus. Injections of progesterone were considerably less effective than testosterone and estrogen in increasing DA turnover. The glyeocorticoids were practically without any action, with the exception of dexamethasone in very high doses.The changes in the DA turnover observed are probably due to changes in the nervous impulse flow in the tubero-infundibular DA neurons. The results support the view that the tubero-infundibular DA neurons participate in gonadotrophin regulation and that the negative feed-back exerted by estrogen and testosterone on the secretion of FSHRF and/or 1, HRF from the median eminence may be at least partly mediated via an increased activity of the tubero-infundibular DA neurons. © 1969 S. Karger AG, Basel.