Effects of social defeat and of diazepam on behavior in a resident-intruder test in male DBA/2 mice

Social stress induces robust behavioral and physiological changes, some of which may alter the responsiveness to pharmacological agents, including dia zepam (DZP). We used a resident-intruder paradigm to (1) develop a comprehe nsive ethogram of behavioral changes following social defeat (SD) in the so cially reactive strain, DBA/2 male mice, (2) determine whether acute exposu re of DBA/2 mice to low-dose DZP would induce flight or aggressive behavior , both of which have been observed in other rodent models and (3) to test w hether prior social stress affects responses to DZP. Behavioral responses t o a nonaggressive intruder (NAI) mouse 24 h post-SD were measured in reside nt subject mice exposed to DZP (0, 0.5, 2.0 mg/kg, ip) either prior to the resident-intruder test (Experiment 1) or immediately post-SD (Experiment 2) ; control mice were not defeated (NOSD). In general, SD mice displayed incr eased passive and active avoidance, defense, immobility, and risk assessmen t relative to NOSD mice. In Experiment 1, mice treated acutely with 0.5 mg/ kg DZP had more approach and flight behavior, while those treated with 2.0 mg/kg DZP had more avoidance than vehicle-treated mice, independent of SD. In Experiment 2, acute DZP (2 mg/kg) induced effects 24 h later, possibly s econdary to withdrawal. In a nonsocial context (Experiment 3), DZP increase d exploratory activity. (C) 2000 Elsevier Science Inc. All rights reserved.