Nicardipine protects against chronic ethanol- or haloperidol-induced supersensitivity to apomorphine-induced aggression.

Affective apomorphine-induced aggression was induced in originally nonaggressive rats after withdrawal from prolonged ethanol or haloperidol treatment. If the animals were co-administered Ca(2+)-channel blockers like diltiazem or verapamil the aggressive response to apomorphine was markedly decreased. Nicardipine (2 and 5 mg/kg b.i.d.) significantly attenuated the aggression-enhancing effect of chronic ethanol or haloperidol withdrawal in nonaggressive rats. Chronic nicardipine, alone, did not enhance aggressive behavior in the nonaggressive rats. Acutely, it suppressed apomorphine-induced aggression but did not alter open field activity when injected into aggressive rats. These results demonstrate that a Ca(2+)-channel blocker of the dihydropyridine type can prevent the development of an ethanol or haloperidol-withdrawal supersensitivity to apomorphine-induced aggression. It attenuates the aggression-inducing effect of apomorphine without impairing general activity.