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The Effect of Perinatal Blockade of Androgen Receptors on the Expression of Hypothalamic Estrogen Receptor‐a and Sexual Motivation in Male Rats

Male sexual differentiation of the brain occurs during the perinatal period and is dependent on testosterone (T), which is subsequently metabolized to estrogen (E) or dihydrotestosterone (DHT). E released from T results in the masculinization of the male brain by binding to hypothalamic estrogen receptor‐a (ER‐a). Whether DHT plays a role in this process is unclear. Flutamide, an anti‐androgen agent, blocks androgen receptors (AR). Whether this blockade of AR modulates the concentrations of ER‐a in mediating the effects of T through E was tested. Additionally, sexual activation of young adult male rat depends on increased levels of T but it is unknown whether its effects are dependent on ER or AR. Male Long Evans rats were administered Flutamide (20mg/kg; SC) or vehicle during the critical period of sexual dimorphism (perinatal period: prenatal day 4 to postnatal day 4). Subsequently, the rats were divided into three treatment groups, finasteride (20mg/kg, SC), a 5‐alpha reductase blocker; letrozole (2mg/kg, SC), an aromatase inhibitor; or vehicle during adulthood (postnatal day 65). Each male rat had a choice of approaching a cage containing a gonadally‐intact female or an ovariectomized (OVX) rat for 20 minutes. The movement of the male rat was video‐tracked by Any‐Maze. Animals were sacrificed after 7 weeks of drug treatment, blood sample was collected for serum estrogen measurement using ELISA and the hypothalamus was isolated to measure ER‐a concentrations using chemiluminescent western blots. Flutamide‐treated groups exhibited no preference for the gonadally‐intact or the OVX female, and their hypothalamic ER‐a and serum estrogen levels were significantly increased. These results suggest that the blockade of AR during the perinatal period causes a permanent increase in E and ER‐a expression within the hypothalamus and any further manipulation during activation period is ineffective.