Survival of reproductive behaviors in estrogen receptor β gene-deficient (βERKO) male and female mice

Previously, it was shown that the lack of a functional estrogen receptor (ER) alpha gene (ER alpha) greatly affects reproduction-related behaviors in both female and male mice. However, widespread expression of a novel second ER gene, ER beta, demanded that we examine the possible participation of ER beta in regulation of these behaviors. In dramatic contrast to our results with ER alpha knockout (alpha ERKO) males, beta ERKO males performed at least as well as wildtype controls in sexual behavior tests. Moreover, not only did beta ERKO males exhibit normal male-typical aggressive behavior, including offensive attacks, but they also showed higher levels of aggression than wild-type mice under certain conditions of social experience. These data revealed a significant interaction between genotype and social experience with respect to aggressive behavior. Finally, females racking a functional beta isoform of the ER gene showed normal lordosis and courtship behaviors, extending in some cases beyond the day of behavioral estrus. These results highlight the importance of ER alpha for the normal expression of natural reproductive behaviors in both sexes and also provide a background for future studies evaluating ER beta gene contributions to other, nonreproductive behaviors.