Psychotropic effects of adrenergic ?-blockers on agonistic behavior between resident and intruder mice

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Abstract
The present study was conducted to investigate the effect of adrenergic β-blockers on agonistic behavior in male mice, using quantitative ethological methods. Agonistic behavior was evoked using a resident-intruder paradigm. The following drugs were administered orally at four dose levels (vehicle, 5, 10 and 20 mg/kg) to either resident or intruder mice: dl-propranolol, practolol, d-propranolol, and l-propranolol. When the resident was treated with either dl-propranol or l-propranolol, aggressive episodes (offensive sideways posture, attack bite, tail rattle) were suppressed significantly in a dose-dependent manner, whereas practolol and d-propranolol were ineffective. All treatments except the high dose of l-propranolol failed to affect the resident's solitary behavior (locomotion). When the intruder was treated with β-blockers, agonistic behavior was not altered. Since practolol does not cross the blood-brain barrier, the differential suppression of agonistic behavior is due to the central action of β-blockers. d-Propranolol does cross the blood-brain barrier but is devoid of β-receptor blocking property; hence l-propranolol suppression of agonistic behavior implies inactivation of brain adrenergic β-receptors. The findings seem to indicate that β-blockers such as dl-propranolol and l-propranolol have a psychotropic action.