Propranolol-induced increases in target-biting attack

The effect of a beta-adrenoreceptor blocking agent on defensive aggression in mice was evaluated. Acute doses of d,l-propranolol (0.2, 0.4, 0.8, 1.6, 3.2, 6.4, and 12.8 mg/kg) were administered to male Rockland-Swiss mice prior to testing in a target-biting paradigm. Baseline conditions established a high target-biting rate immediately after animals received a 2 mA tail shock, an intermediate biting rate during a 2-min intershock interval, and a low biting rate during a 15-s tone stimulus preceding the next shock. Every dose of propranolol increased target-biting rates above baseline during each interval with one exception: 0.4 mg/kg decreased the biting rate immediately after delivery of the tail shock. The overall increase in aggression observed following dosing with propranolol was not expected from a review of the clinical literature. These results are discussed in reference to propranolol's known effects on the brain serotoninergic systems and the use of animal model of defensive aggression.