Increased incorporation of 3H-lysine in specific hypothalamic nuclei following castration in the male rat

Abstract

The purpose of the present quantitative radioautographic investigation was to determine if castration in the adult male rat is followed by alterations in the incorporation of 3H-lysine into neurons of the preoptic and specific hypothalamic nuclei. Five adult, intact male rats and five male rats castrated for a period of 5 wk were each injected ip with 2 μCi/g body wt of l-4,5- 3H(n) lysine monohydrochloride (sp act = 7.5 Ci/mmol). Thirty minutes later the rats were perfused with a formaldehyde fixing solution and 6-μm sections cut from paraplast-embedded brains were processed for radioautography. Silver grains per neuron were determined for the medial and lateral preoptic nuclei and for eight hypothalamic nuclei, i.e., anterior, arcuate, dorsomedial, paraventricular, periventricular, suprachiasmatic, supraoptic, and ventromedial. Incorporation of 3H-lysine was significantly increased in neurons of the arcuate, periventicular, paraventricular, and supraoptic nuclei following castration. Enhancement of protein synthesis in specific hypothalamic nuclei 5 wk following removal of the major source of androgen suggests that these nuclei represent androgen sensitive, negative feedback sites.