Strain differences in clonidine-induced aggressiveness in mice and its interaction with the dopamine system

The influence of a genotype of inbred mice on the aggressive behavior induced by clonidine and the role of dopamine D₁ and D₂ receptors in that behavior were studied. Clonidine in a dose of 10 mg/kg evoked a strong aggressiveness in BALB/c, DBA/1, and CC57Br mice and an intermediate response in C57BL/6J, Albino Swiss, and CBA mice, whereas DD, A/He, and C3HA/y mice did not show any aggressive behavior. Apomorphine significantly potentiated the clonidine-induced aggressiveness in C57BL/6J mice. In Albino Swiss mice, SK&F38393 as well as quinpirole augmented the aggressive behavior evoked by clonidine. The clonidine-induced aggressiveness was blocked by SCH23390 and cis-flupentixol but not by (-)-sulpiride. In aggressive mice, the binding of [³H]SCH23390 was decreased in the limbic forebrain, whereas the binding of [³H]spiperone was not changed. The obtained results indicate that the potency of the clonidine-induced aggressiveness depends upon genotype of mice; moreover, the presence of a physiological function of D₁ receptors is necessary for its occurrence.