Female ddY mice show a weaker diazepam-induced reduction in aggressive biting behavior toward inanimate objects and lower hypothalamic KCC2 expression than males do

Anyone may engage in aggressive behavior under the influence of stress. Animal models have been used to elucidate the mechanisms underlying aggression. Herein, we studied aggressive behavior in chronically isolation-reared male and female mice using an Aggressive Response Meter (ARM) device. The ARM device induces aggressive biting behavior (ABB) in mice toward inanimate objects, and measures its intensity and frequency, hereafter referred to as ABB intensity and ABB frequency, respectively. We characterized ABB intensity and frequency compared with open field test (OFT), social interaction test, and elevated plus maze (EPM). ABB intensity and frequency were increased and the time in the center zone in OFT was decreased in isolation-reared male and female mice compared with group-reared counterparts. No statistically significant correlation was detected between ABB intensity and other behavioral features in OFT, social interaction test, and EPM, indicating that ABB intensity reflects behavioral characteristics not fully explained by these behavioral characteristics. As the effects of GABA-targeting agents are poorly characterized, we examined the effect of diazepam on ABB. At higher doses (4 mg/kg), diazepam effectively reduced ABB levels in both males and females, with males showing higher sensitivity than females at lower doses (2 mg/kg). The number of c-Fos-expressing cells in the dmVMH and dlPAG was high in mice with high ABB. We next analyzed KCC2, a K + -Cl − co-transporter that maintains inhibitory GABA transmission. Low KCC2 expression in the hypothalamus of female was detected using qPCR and immunoblotting. Testosterone supplementation enhanced female responsiveness to diazepam at lower doses.