BETA(2)-ADRENOCEPTORS BUT NOT BETA(1)-ADRENOCEPTORS ARE INVOLVED IN DESIPRAMINE ENHANCEMENT OF AGGRESSIVE-BEHAVIOR IN LONG-TERM ISOLATED MICE

The effects of several beta-adrenoceptor antagonists on the desipramine-induced increase in aggressive behavior in long-term isolated mice were examined. Desipramine HCl (10 mg/kg, IF) significantly increased the duration of aggressive behavior in isolated mice but did not significantly change the latency to the first attack consistent with our previous reports. Intraperitoneal administration of(+/-)propranolol HCl (2.5-10 mg/kg), a nonselective P-adrenoceptor antagonist, dose dependently attenuated the desipramine-induced enhancement of aggressive behavior without significantly affecting the basal aggressive responses. ICI118,551 HCl (1.25-5 mg/kg, IF), a selective beta(1)-adrenoceptor antagonist, also blocked the desipramine-induced enhancement of aggressive behavior in a dose-dependent manner, whereas metoprolol tartrate (5-20 mg/kg, IF), a selective beta(2)-adrenoceptor antagonist, did not affect it. Moreover, clenbuterol HCl (0.1-0.5 mg/kg, IF), a lipophilic P,-adrenoceptor agonist, significantly increased the duration of basal aggressive behavior. Taken together with our previous finding that the desipramine-induced enhancement of aggressive behavior can be blocked by yohimbine, an alpha(2)-adrenoceptor antagonist, the present results indicate that not only alpha(2)- but also beta(2)-adrenoceptor stimulation plays important roles in modulation of aggressive behavior in long-term isolated mice.