[Pharmaco-ethological analysis of agonistic behavior between resident and intruder mice: effects of ethylalcohol]

The present study was conducted to investigate the effect of ethylalcohol on agonistic behavior using a resident-intruder paradigm. In this paradigm, a resident male mouse has been cohabiting with a female for 5 weeks, and an intruder male mouse is introduced into the resident's home cage. The effects of four doses of ethylalcohol (vehicle, 0.5, 1.0, and 2.0 g/kg, p.o.) were assessed in resident mice and group-housed intruder mice. Residents and intruders were drugged on alternate test days, and all animals received different sequences of drug conditions according to a random schedule. When resident mice were treated with ethylalcohol biphasic effects on resident's aggressive elements were observed: 0.5 and 1.0 g/kg of ethylalcohol increased attack bitings and sideways posture, while 2.0 g/kg of the drug suppressed aggressive elements. On the other hand, when intruder mice were drugged the resident's attack bitings were significantly increased in a dose-dependent manner. At this time, defensive upright postures of intruder mice were suppressed by the drug. Ethylalcohol at the employed doses did not affect locomotor activity in both resident and intruder mice. The results suggest that ethylalcohol enhances the hostility of resident to the intruding animal and suppresses the anxiety of an intruder to the attacking animal.