Differential sensitivity to apomorphine and clonidine following frontal cortical damage in rats.

Rats trained to bar-press on a FI 15 sec schedule for water reinforcement were administered various doses of apomorphine (0.25-10 mg/kg) and clonidine (0.002-0.1 mg/kg) both before and 6-10 weeks after bilateral ablation of frontal cortex. Both drugs monotonically depressed response rates with increasing dose. Frontal cortical lesions increased sensitivity to apomorphine without altering sensitivity to clonidine. The results suggest that the frontal cortex modulates the activity of dopaminergic but not noradrenergic neuronal pathways.