In this study we compared the binding characteristics of methyltrienolone (R1881) in pooled cytosols from the hypothalamus-preoptic area-amygdala-septum (HPAS) of adult and fetal rhesus macaques. In addition, we studied the ontogeny of cytosolic androgen receptors (AR) in fetal neural tissue. Intact adult males and fetal rhesus monkeys of known gestational age were our experimental subjects. Fetuses were delivered by cesarean section at 50, 65, 80, and 150 days gestation. HPAS cytosols from 150-day fetuses and adult males were incubated with the synthetic ligand, [3H]R1881, for determining AR characteristics and to validate the assay. A single high affinity, low capacity receptor for R1881 was found in HPAS cytosols. The apparent dissociation constant was similar between adult and fetal HPAS (1.09 × 10-10 us. 1.59 × 10-10 M, respectively). Binding specificity was determined by the addition of excess radioinert testosterone (T), 5a-dihydrotestosterone, estradiol, or progesterone to the incubation tube. R1881 binding was displaced by the addition of excess amounts of T and dihydrotestosterone, but not of estradiol or progesterone. There were no differences between fetal and adult animals. Single point analyses of AR numbers in fetal animals showed significant age and regional differences (P < 0.05). Since no sex differences were apparent, data from males and females were combined. In the hypothalamus-preoptic area there was a significant increase in AR throughout gestation [1.3 ± 0.4 (±SE) fmol/mg protein; n = 7 (50 days gestation) us. 6.2 ± 0.3 fmol/ mg protein; n = 4 (150 days of gestation); P < 0.01]. These values differed significantly from adult male hypothalamicpreoptic area (14.1 ± 0.3 fmol/mg protein; P < 0.01; n = 3). AR levels in frontal and temporal cortex were high on day 50 of gestation, but showed a significant decline by day 150 (P < 0.05). The administration of testosterone propionate (25 mg/kgday) to pregnant animals from 40-50 days gestation, which resulted in elevated levels of serum T in female, but not male, fetuses had no effect on AR in any brain region studied. These studies confirm the presence of AR in fetal monkey brain. New information is provided on the changes in AR numbers in cortical and hypothalamic tissues during the critical period for sexual differentiation of the primate brain. Since the AR must be presumed to be a cellular link in the organizational actions of T on the brain, the cortical changes that we observed may be an important cellular marker of the critical period for those actions of androgen that organize primate behavior.
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