Diazepam enhances conditioned defeat in hamsters (Mesocricetus auratus).

Male hamsters that have been repeatedly defeated by larger, aggressive males subsequently flee from, rather than attack, nonaggressive male intruders that are introduced into their home cages. We have referred to this generalization of flight in response to nonaggressive intruders as "conditioned defeat" (CD). In an attempt to reverse CD pharmacologically, diazepam (DZP) was administered to hamsters at two different time points relative to CD acquisition and subsequent response generalization tests, which involved the exposure of subjects to nonaggressive intruders (NAIs). In Experiment 1, subjects were given a single injection of one of 4 doses of DZP (0, 2, 6, or 20 mg/kg) immediately following CD acquisition. Twenty-four hours later, contrary to expectations, subjects that had received the 6 mg/kg dose displayed elevated flight responses in the presence of an NAI. Flight responding declined over days except in subjects that received the highest dose. In the second experiment, hamsters were administered a single injection of either 0, 2, or 6 mg/kg DZP just prior to a response generalization test occurring 24 h following CD training. Flight responses to the NAIs were again exaggerated in subjects that were given the 6 mg/kg dose, an effect that persisted several days without further drug administration. The present findings suggest the possibility that benzodiazepines can potentiate fear responses under certain stressful conditions.