Individual variation in aggression of feral rodent strains: a standard for the genetics of aggression and violence?

This article summarizes the broad individual differences in aggressiveness and its relationship with several other behavioral, physiological, and neurobiological characteristics that exist in an outbred laboratory strain of male feral rats. Based on the observations that the individual level of offensive aggressive behavior (i.e., the tendency to defend the home territory) is strongly related to the way they react to various other environmental challenges, it is argued that the individual's level of offensiveness is an important indicator and component of a more traitlike behavioral physiological response pattern (coping strategy) to environmental demands. The coping style of aggressive animals is principally aimed at a (pro)active prevention or manipulation of a stressor, whereas the nonaggressive individuals tend to passively accept or react to it. The (pro)active and reactive/passive behavioral coping styles are clearly associated with distinct patterns of autonomic/endocrine (re)activity and underlying neurobiological correlates and determinants. Consequently, these individual differences in aggression/coping style may not only determine the individual vulnerability to stress-related disease, and hence be an important factor in the population dynamics of the species, but may also determine responsivity to pharmacotherapeutic treatments. From an animal modeling point of view, it is argued that the aggressive extremes of this variation may, under the proper testing conditions, have an enhanced propensity to develop pathological forms of aggression and/or coping, for example, antisocial traits, violence, or impulsivity disorders. Finally, it is proposed that the use of these feral animals as base "material" for genetic association (i.e., QTL search, mRNA differential expression, nucleic acid microarray analysis) and manipulation (i.e., gene silencing or amplification by antisense ODN, siRNA, and/or viral gene-transfer methodologies) studies would most likely be the best option for dissecting successfully the genetic basis of both normal and pathological forms of aggression and/or coping.