Mouse-killing and motor activity: effects of chronic delta9-tetrahydrocannabinol and pilocarpine.

Chronic administration of delta9-tetrahydrocannabinol (THC) for 5--8 weeks at 4 dose levels (2, 10, 20, 50mg/kg/day) or of pilocarpine (12.5, 25 mg/kg/day) for 3 weeks induced mouse-killing in 25--70% of previously "non-killer" rats of the Sprague-Dawley strain. The maximum percent of drug-induced mouse-killing depended on the daily dose and housing conditions, 20mg/kg/day THC and 25 mg/kg/day pilocarpine in single-housed rats being the most effective treatments. Drug-induced mouse-killing appeared to be a form of behavioral pathology, differing from the species-specific predatory response, when it first appeared. Concurrent assessment of locomotor and rearing activities showed dose-dependent depressant effects of THC and pilocarpine without evidence for tolerance. Different dose-dependencies and time courses suggest that changes in motor activities are not directly linked to the appearance of the killing behavior.