Aggression-associated changes in murine olfactory tubercle bioamines

The relationship between changes in regional brain bioamine levels and the expression of intraspecies aggressive behavior was evaluated in two murine models. In one study, normal male mice were maintained either in aggregate (i.e., normal, intraspecies social behavioral controls) or isolated (i.e., developed, non-social intraspecies aggressive 'fighter' behavior) housing environments, and the accompanying changes in both olfactory tubercle (OT) and hypothalamic (HYPOTH), norepinephrine (NE), dopamine (DA) and serotonin (5-HT) concentration indices quantitated by high-performance liquid chromatography (HPLC) for analysis of behavior-related alterations in localized bioamine deposition loci. Intact mice which had been housed in isolation cages and which exhibited aggressive, intraspecies reflexive-biting ('fighter') behavior when introduced to a novel (stimulus) animal, exhibited significant (P<0.05) elevations in NE levels, and depressed DA concentrations, in the OT regions relative to aggregated controls, indicating an intrinsic social influence on the maintenance of basal adrenergic indices at this neural locus. No changes in 5-HT levels were indicated between control and aggressive, isolated 'fighter' groups in either OT or HYPOTH loci. In addition, the NE and DA levels in the HYPOTH samples of both control and aggressive groups were found to be comparable. In the second study, utilizing an alternate type of aggression-induced murine model, changes in bioamine parameters were determined from samples obtained from aggregated, olfactory-bulbectomized (Obx) mice which are recognized to exhibit an overt, intraspecies, reflexive-biting behavior as compared to sham-operated (control) mice housed under identical conditions. In these studies, Obx-mice exhibited a significant increase in 5-HT levels in the OT relative to sham-operated controls, but similar NE and DA concentrations. In addition, all hypothalamic bioamine indices were found to be comparable between control and Obx groups. These data, collected for both isolation-developed, and experimentally-induced (i.e., OBX), intraspecies aggressive models, indicate that the distinctive types of aggressive behaviors displayed by these two murine models are accompanied by specific alterations in regional bioamine levels within the OT of these groups, relative to controls. These data suggest that the specific type of overt aggressive behavior demonstrated by these models may be causally related to the identified changes in bioamine concentrations in the forebrain regions of the CNS, in loci recognized to participate in environmental recognition and social processing activities.