Selection, evolution of behavior and animal models in behavioral neuroscience

We investigated whether genetic differences in various forms of intraspecif ic aggression and anxiety in four different genetic lines of mice (i.e. wil d, outbred Swiss-CD1, inbred DBA/2 and inbred C57/BL6N) may reflect modific ations in behavioral strategy. Experiments 1 and 2 used ethologically based paradigms to analyze aggressive and anxiety responses both in social (i.e. aggression) and non-social (i.e. novel environment exploration) contexts. In Experiment 3, an anxiolytic drug (chlordiazepoxide (CDP)) was used to ex amine possible differences in proximal mechanisms underlying anxiety-relate d behaviors. The data show that intrasexual aggression, infanticide and mat ernal aggressions are related and covarying. Genetic lines with the highest levels of intermale attack (i.e. Wild and Swiss-CD1) also have highest lev els of infanticide, interfemale attack and maternal aggression but, interes tingly, the lowest levels of anxiety. In fact, exploratory behavior is lowe r and risk assessment behavior markedly higher in DBA/2 and C57/BL6N mice ( i.e. the less aggressive strains) compared to Swiss and Wild genetic lines. Although reproductive status influences anxiety levels in female mice, our findings show that (contrary to previous studies) lactating mice are more anxious than virgin females in terms of risk assessment activities. These d ata demonstrate the importance of studying behavior in a more ecologically- relevant context which emphasizes 1:he function of behavior in a specific s ituation. Moreover, differential strain sensitivity to the behavioral effec ts of CDP suggests that genetic lines of mice may differ in the underlying mechanisms mediating behavior. It is therefore possible that artificial sel ection of different genotypes has resulted in differences in proximate mech anisms modulating the levels of aggression and anxiety, thereby leading to modification of social behavior. Overall, the results presented here sugges t that subtle genetic alterations in specific underlying neural mechanisms are likely to cause profound effects on behavioral responses and their adap tive significance. Implications for behavioral neuroscience research that s eeks to understand both the proximal and ultimate mechanisms of behavior ar e discussed. (C) 1999 Published by Elsevier Science Ltd. All rights reserve d.