Differential effects of medial, central and basolateral amygdaloid lesions on four models of experimentally-induced aggression in rats

To clarify whether various nuclei of the amygdaloid complex play different roles in aggressive behavior including muricide, 4 types of aggression were experimentally induced in rats. These include olfactory bulbectomy (OB rats), midbrain raphe lesions (Raphe rats), administration of Δ⁹-tetrahydrocannabinol (THC rats) and long-term isolation (Iso rats). Rats which exhibited muricide following these treatments were subjected to bilateral lesions of either the medial (AME), central (ACE) or basolateral (ABL) amygdaloid nuclei. Both muricide and hyperemotionality in the OB rat were markedly inhibited by AME lesions. Those of the Iso and THC rats were moderately inhibited. However, in the Raphe rat, aggressive behavior was not inhibited by AME lesions. Furthermore, ACE or ABL lesions caused no significant changes in all 4 models of aggression. These results suggest that the AME plays a facilitatory role in aggression of OB, Iso and THC rats, but aggression in Raphe rat is independent of amygdaloid activity.