Intermale aggression in corticotropin-releasing factor receptor 1 deficient mice.

The anxiogenic neuropeptide, corticotropin-releasing factor (CRF), has a complex effect on intermale aggression. CRF receptor 1 (CRFR1) is the primary receptor for CRF and in this study, we examined in detail isolation-induced intermale aggression in CRFR1 deficient mice. All mice contained a mixed 50:50 inbred/outbred background to improve aggressive performance. Mice were isolated for 4 weeks prior to 2 consecutive days of aggression testing using the resident-intruder paradigm. Mice were also tested for anxiety on the elevated plus maze. Relative to littermate wild-type (WT) controls, CRFR1-mutant mice exhibited normal levels of intermale aggression over the 2 test days in terms of percentage showing aggression, number of attacks, time aggressive, and latency to first attack. In terms of sites of attacks on intruders, CRFR1-deficient mice attacked the ventral portion of the mid-section (including belly) significantly less frequently than WT males on test day 1, but these differences did not reach significance on test day 2. No other differences in sites of attacks were observed. Tail rattling also did not differ between groups. Importantly, KO males showed decreased anxiety relative to WT mice (consistent with previous reports) as evidenced by spending significantly more time on the open arms and significantly less time on the closed arms of the elevated plus maze. Plus maze performance did not correlate with any measure of levels of aggression, suggesting a dissociation between altered levels of anxiety and aggressive performance. Taken together, the results suggest that the activation CRFR1 is not necessary for the normal production of isolation-induced intermale aggression.