Pharmaco-ethological analysis of agonistic behavior between resident and intruder mice: effect of anticholinergic drugs.

The resident-intruder paradigm was employed in order to evoke an agonistic behavior in mice. In this situation 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. A species-specific pattern of agonistic behavior was observed in all mice. The significance of cholinergic mechanisms in the mediation of the agonistic behavior was evaluated by pharmacological manipulations. Drugs were administered to resident mice. Scopolamine hydrobromide (0.25, 0.50 and 0.75 mg/kg, i.p.) significantly suppressed the resident's aggressive episodes (offensive sideways posture, tail rattling and attack biting) in a dose-dependent manner, whereas the peripheral anticholinergic drug methylscopolamine nitrate (0.25, 0.50 and 0.75 mg/kg, i.p.) was ineffective. On the other hand, the resident's locomotor activity and rearing response were significantly increased after the administration of scopolamine hydrobromide. The evidence suggests that brain cholinoceptive mechanisms may participate in the regulation of intraspecies aggressive behavior. However, it appears that other nonspecific behavioral effects of scopolamine cannot be ruled out.