Serotonin's influence on predatory behavior of highly aggressive cba and weakly aggressive DD strains of mice

The effects of serotonin were studied on locust‐killing behavior of mice from low (DD) and high (CBA) predatory aggressive strains. 5‐HTP injected intraperitoneally (50 and 100 mg/kg) or 5‐HT administered into the lateral ventricle (10 μg) significantly reduced locust‐killing behavior in highly aggressive CBA mice. Imipramine (20, 30, and 40 mg/kg) elicited a dose‐dependent inhibitory effect on predatory behavior. Fluoxetine (10 and 20 mg/kg) alone had a slight influence on locust‐killing behavior but potentiated the action of the subthreshold dose of 5‐HTP (25 mg/kg). Pretreatment with the blocker of 5‐HT₂ type receptors methysergide (2 mg/kg) abolished the inhibitory effect of 5‐HTP. These finding indicate that serotonin of the brain exerts an inhibitory effect on predatory behavior in mice. In contrast, neither lesion of the dorsal raphe nucleus (although significantly depleting the brain serotonin) nor treatment with methysergide (2 mg/kg) induced locust‐killing behavior in weakly aggressive DD mice. Low predatory aggressiveness in DD mice is suggested to be related to the low tonus of the mechanisms activating killing behavior rather than to excessive serotonergic inhibitory influences.