Alteration in sex-specific behaviors in male mice lacking the aromatase gene.

Brain aromatase (P450arom) is a key enzyme in estrogen biosynthesis from testicular androgens. This local aromatization in neural tissues is thought to be an important process for sexual differentiation and activation of sexual behavior in male rodents. To determine the functional significance of the aromatase gene in development and activation of sex-specific behavior, we analyzed a series of behavioral profiles in gonadally intact male mice with targeted disruption of exons 1 and 2 of the aromatase gene (ArKO). In most cases, ArKO males were infertile and showed deficits in male sexual behavior including mount, intromission and ejaculation. Noncontact penile erection was not significantly affected by deletion of the aromatase gene. A great reduction of aggressive behavior against male intruders was also observed in ArKO males, while they tended to exhibit aggression toward estrous females during male copulatory tests. Furthermore, 73% of ArKO males showed infanticide toward pups, whereas characteristic parental behavior, but not infanticide, was observed in wild-type males. These results support the brain aromatization hypothesis and indicate that aromatase gene expression is a critical step not only for motivational and consummatory aspects of male sexual behavior, but also for aggressive and parental behaviors in male mice. Copyright 2003 S. Karger AG, Basel