Aggressive behavioral phenotypes in mice

Y is there a risk to being male?

Being male or female can make a vital difference to many important biological functions and can lead to disparities in health. The Y chromosome carries the sex-determining sex reversal Y (SRY) gene and recent studies show that it might also harbor genes that have important biological functions other than sex determination. One such example is the emerging evidence from animal models and humans that supports the presence of cardiovascular genes on the Y chromosome. A significant amount of work remains to identify these genes; however, we report here observations linking the Y chromosome to hypertension, which could explain the higher incidence of cardiovascular disease in males compared with females.

In socially isolated mice, the reversal of brain allopregnanolone down-regulation mediates the anti-aggressive action of fluoxetine

Social isolation (SI) of male mice lasting >4 weeks is associated with aggression toward intruders and a down-regulation of brain allopregnanolone (Allo) content. SI of female mice fails to down-regulate brain Allo content or to induce aggressiveness. Fluoxetine (Prozac in clinical use) is an S- and R-fluoxetine (FLX) mixture, which in mammals is metabolized into S- and R-norfluoxetine (NFLX). The S isomers of FLX and NFLX are more active than their respective R isomers in normalizing brain Allo down-regulation and in reducing the aggressiveness induced by SI. Thus, FLX stereospecifically reduces brain Allo down-regulation and the aggressiveness induced by SI, whereas serotonin (5-HT) uptake inhibition lacks stereospecificity. The doses of S-FLX and S-NFLX that reduce aggressiveness and Allo brain content down-regulation induced by SI are at least one order of magnitude lower than the doses that block 5-HT reuptake. Doses of imipramine that inhibit 5-HT uptake neither reduce aggressiveness nor normalize brain Allo down-regulation. We conclude that Allo brain content normalization is a better candidate than 5-HT reuptake inhibition to explain the reduction of aggressiveness elicited by S-FLX and S-NFLX.

The Influence of Early Weaning on Aggressive Behavior in Mice

Early postnatal experiences have been shown to have a tremendous influence on behavior development. In this study, we focused on weaning time and investigated the effects of early weaning on adulthood aggressive behavior in mice with the resident-intruder test. Early weaning resulted in decreased sideways threat and tail rattle. In addition, the frequency of attack bites was more variable in the early weaned group, although the mean frequency did not differ from the normally weaned group. The results of the present study suggest that aggressive behavior is also affected by early weaning manipulation.

Altered sexual and social behaviors in trp2 mutant mice

We have used gene targeting to generate mice with a homozygous deficiency in trp2, a cation channel expressed in the vomeronasal organ (VNO). Trp2 mutant animals reveal a striking reduction in the electrophysiological response to pheromones in the VNO, suggesting that trp2 plays a central role in mediating the pheromone response. These mutants therefore afford the opportunity to examine the role of the VNO in the generation of innate sexual and social behaviors in mice. Trp2 mutant males and nursing females are docile and fail to initiate aggressive attacks on intruder males. Male-female sexual behavior appears normal, but trp2 mutant males also vigorously mount other males. These results suggest that the cation channel trp2 is required in the VNO to detect male-specific pheromones that elicit aggressive behaviors and dictate the choice of sexual partners.