Effects of centrally acting beta adrenergic agonists on discrete trial conditioned avoidance behavior in rats

The acute effects of centrally acting beta adrenergic agonists on discrete trial conditioned avoidance responding in rats were examined. Clenbuterol (0.01-3.0 mg/kg), salbutamol (0.01-30 mg/kg), and prenalterol (30-300 mg/kg) suppressed avoidance responding in a dose-dependent manner at doses that did not produce escape failures. For comparative purposes, the effects of the tricyclic antidepressant desipramine (1.0-30 mg/kg) and the antipsychotic haloperidol (0.03-0.3 mg/kg) were similarly assessed. Both compounds suppressed avoidance responding in a dose-dependent manner. Only haloperidol (0.3 mg/kg) produced escape failures. Administered alone, the beta adrenergic antagonist propranolol (1.0 and 10 mg/kg) did not affect avoidance behavior. When administered prior to clenbuterol (0.1 mg/kg), salbutamol (1.0 mg/kg), or prenalterol (100 mg/kg), propranolol antagonized the beta adrenergic agonist-induced suppression of avoidance responding. The suppressive effect of desipramine (3.0 mg/kg) on avoidance performance only tended to be attenuated by propranolol. Propranolol had no effect on the ability of haloperidol (0.1 mg/kg) to reduce avoidance responding. These results suggest that the effects of the beta adrenergic agonists clenbuterol, salbutamol, and prenalterol on discrete trial avoidance behavior are mediated, in part, through agonist interactions with beta adrenergic receptors.