Pre- and post-synaptic actions of apomorphine: differentiation by rotatory effects in normal rats

Normal rats were tested for rotation (circling behavior) following d-amphetamine (1.0 mg/kg) and, a week later, following apomorphine (10.0 mg/kg). In most rats, d-amphetamine and apomorphine elicited rotation in opposite directions whereas, in some rats, the two drugs elicited rotation in the same direction. Subsequently, alpha-methyl-p-tyrosine was found to antagonize the rotatory effect of apomorphine in the latter but not in the former rats. The results suggest that apomorphine has both pre- and post-synaptic actions and that relative sensitivity to these actions varies among rats.