Desipramine enhances isolation-induced aggressive behavior in mice.

Effects of desipramine on aggressive behavior induced by long-term (6-7 weeks) isolation of mice were examined. Aggressive behavior was measured as duration of biting attack and/or wrestling during a 20-min observation period. Desipramine (5, 10 and 20 mg/kg, IP) and imipramine (10 and 20 mg/kg, IP) dose-dependently increased the duration of aggressive behavior in isolated mice, without inducing aggressive behavior in group-housed animals. Desipramine-induced increase in aggressive behavior was blocked by phentolamine (3 mg/kg, IP) and yohimbine (0.3 mg/kg, IP), but not prazosin (0.5 mg/kg, IP). Clonidine (0.001 mg/kg, IP), an alpha 2 agonist, significantly blocked desipramine-induced enhancement of aggressive behavior in isolated mice without affecting the basal aggression. These data suggest that long-term isolation may induce functional changes in the sensitivity of alpha 2 receptor in the noradrenergic system and that desipramine enhancement of aggressive behavior in isolated mice is modulated by drugs acting onto alpha 2 noradrenergic receptors.