Measurement of the three phases of muricidal behavior induced by delta9-tetrahydrocannabinol in isolated, fasting rats.

Delta9-Tetrahydrocannabinol (THC) has long been recognized as inducing mouse-killing behavior (muricidal behavior) in starving, isolated rats after a single injection. We showed that when the killing tendency was increased by THC, a preliminary contact with a mouse decreased the probability of muricidal behavior. By quantifying the three phases of the muricidal behavior in either nonkiller or naive THC-treated rats, we showed that the duration of each step was notably increased as compared to untreated natural killer rats, mainly the attack on the dead mouse, indicating increased aggressiveness. Finally, no significant changes were observed in the duration of the three phases in natural killer rats when the muricide assays were repeated every hour. In contrast, in THC-treated rats--either naive or nonkiller--all three phases decreased with the assay repetition to levels comparable to those of natural killer rats, suggesting that the killer behavior was progressively acquired for the six assays. These changes could be a useful model to study the central effects of THC and either its agonists or antagonists.