Behavioral reactivity to social and nonsocial stimulations: A multivariate analysis of six inbred rat strains

Male rats from six inbred rat strains (Spontaneously Hypertensive Rat, Wistar Kyoto, Brown Norway, Wistar Furth, Fischer 344, and Lewis) have been compared for their behavioral reactivity when placed in several nonsocial (elevated plus-maze, open field) and social (social interaction in aversive and neutral environment, resident-intruder test, chronic social stress) settings. In addition, a factorial analysis was performed to assess how the variables measured in these different tests related to each other. Besides significant strain-related differences in all tests, the factorial analysis showed that, in nonsocial environments, the strains contrasted essentially along two independent behavioral traits, the propensity to approach or avoid an aversive stimulus and general motor activity in novel environments (two indices of emotionality). In the social settings, marked interstrain differences were observed regarding the expression of aggressive behaviors but these differences were not related to the respective levels on the two nonsocial components of reactivity. Furthermore, large genetic differences were observed in variations of body weight induced by a chronic social stressor paradigm. The factorial analysis suggested a lack of relationship between the effect of social stressors on body weight and the measures of emotionality and general activity obtained in the nonsocial tests. Conversely, these variations were influenced by the levels of aggressiveness and sociability. Taken together, these results show (i) that the behavioral variability observed in rats, in social and nonsocial environments, is influenced by genetic factors and (ii) that the behavioral reactivity to social stimulations is a specific feature, dissociable from the levels of the different components of emotionality (approach/avoidance and general activity) as evaluated by the behavioral responses to nonsocial settings.