Injection of an aromatase inhibitor after the critical period of sexual differentiation

We have investigated the possible role of the second week of life in the differentiation of sexually dimorphic behaviours, dependent on the androgenic aromatization, and its possible relationship with the serotonergic systems. For this purpose, 5 mg/kg of a suspension of an aromatase inhibitor, LY43578, has been intraventricularly injected to males on day 12 of life. Studies have been made in adulthood on exploratory and motor activities, anxiety, sexual motivation, and sexual performance. Indoleamine levels in the hypothalamus and corpus striatum have been measured. Sexual behaviour, exploration, and serotonergic metabolism were not affected by the treatment. Sex partner preference and anxiety in the plus-maze showed a feminized tendency in the treated group that, however, did not reach statistical significance. From these results we have confirmed the restriction of the critical period of androgenic aromatization for the organization of reproductive and exploratory behaviour.