The effect of dl-propranolol, d-propranolol and practolol on the hyperactivity induced in rats by prolonged isolation

Exploratory behaviour in an open field situation was found to be greatly increased in rats, isolated for 6-8 weeks, when compared with grouphoused controls. Propanolol, dl- and d- and practolol, 0.2-0.5 mg/kg reduced hypermotility, sniffing and rearing in isolated rats without affecting behaviour of group-housed rats. 20 mg/kg dl-propanolol was needed to reduce exploratory behaviour of group housed rats. Chlorpromazine reduced activity of isolated rats at a dose of 0.1 mg/kg, and group housed rats at 0.5-1 mg/kg. The action of propranolol does not appear to result from central receptor blockade because of the almost equal activity of d- and dl-propranolol. Since practolol was also active in this test, the effect of these drugs also does not appear to result from general C.N.S. depression. It is suggested that these compounds may reduce hyperactivity by diminishing an excessive release of central catecholamines.