The cellular and subcellular localization of radioactivity in the brain of 2-day-old female rats was investigated autoradiographically 2 hr after sc injection of 1.0 μg of l,2,6,7-3H-testosterone per 100 g body wt. A specific topographic pattern of nuclear concentration of testosterone or its metabolites was obtained in neurons of the basal hypothalamus, preoptic region, and amygdala. This pattern was similar, but not identical, to that seen in the adult male rat. Pretreatment with either unlabeled testosterone or estradiol-17β inhibited the nuclear concentration of radioactivity in all areas while 5α-dihydrotestosterone had little or no effect. Possible mechanisms for this interaction of exogenous steroids in the neonatal rat brain are discussed.
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