Stimulation of beta-adrenergic receptors and spontaneous motor activity in mice.

The effects of 3 beta-adrenergic agonists (clenbuterol, isoproterenol and salbutamol) on the spontaneous motor activity of mice were studied. The present research indicated that motor activity was significantly decreased 30 minutes after IP injection of either clenbuterol (0.06 mg/kg), isoproterenol (0.5 mg/kg) or salbutamol (2 mg/kg). Hypomotility induced by clenbuterol was also significantly antagonized by propranolol in doses ranging from 1 to 8 mg/kg and by penbutolol in doses from 0.03 to 0.5 mg/kg. However, practolol, which does not cross the blood brain barrier, did not antagonize the effect of clenbuterol. Therefore, it may be hypothesized that beta adrenergic agonists decrease motor activity by a central mechanism. It was also found that tachyphylaxis or resistance to treatment, observed in cardiovascular and bronchopulmonary systems with beta-adrenergic agonists, developed after 7 injections of clenbuterol (0.25 mg/kg IP, twice daily) in the behavioral model of spontaneous motor activity in mice.