Effects of propranolol on the locomotor stimulation induced by activation of postsynaptic catecholamine receptors

The present study was undertaken in order to clarify the possible involvement of a central beta-adrenoceptor mediated action on the stimulation of locomotor activity by the dopamine agonist apomorphine and the noradrenergic agonist clonidine. The effect of pretreatment with various doses of d-and dl-propranolol on apomorphine- and apomorphine plus clonidine-induced locomotor stimulation in reserpinized mice was measured in photocell activity chambers. Pretreatment with dl-propranolol prolonged the duration of apomorphine-induced locomotor stimulation without affecting the maximal level of activity. A similar tendency was seen after pretreatment with the d-form of propranolol, which has a much lower beta-receptor blocking activity. The potentiation by clonidine of the apomorphine-induced locomotor stimulation in reserpinized mice was dose-dependently reduced by pretreatment with dl-propranolol whereas d-propranolol was found to be ineffective. The results indicate that central beta-receptor mechanisms might be involved in the apomorphine plus clonidine-induced locomotor stimulation of reserpinized mice.