Effect of naloxone on apomorphine-induced changes in locomotor activity of stress-exposed rats

Acute and subacute effects of naloxone (10 mg/kg), apomorphine (0.125 mg/kg; 5 mg/kg) and stressful stimuli (immobilization, cold and sound) on locomotor activity were examined. In both acute and subacute (8 days) treatments, the lower dose of apomorphine decreased locomotor activity and the higher dose of apomorphine increased it. In the acute treatment, naloxone enhanced significantly the depressant effect of the lower dose of apomorphine on locomotor activity. Stress seemed to have no effect on apomorphine induced changes in locomotor activity of rats either in acute or in subacute treatment.