Individual and sex differences in high and low responder phenotypes.

Individual differences in responses to a novel environment are an important tool to predict predisposition to neuropsychiatric disorders. One way to examine individual differences involves classifying animals based on locomotion in a novel context. In this study we focused on individual and sex differences by categorizing female and male mice as high (HR) or low responders (LR) on the basis of open field locomotion. We then assessed whether groups differed on behavioral measures of spontaneous alternations, anxiety, depression and contextual fear conditioning. In the Y-maze, we observed no differences across HR/LR or sex on spontaneous alternations, but HR displayed more locomotion. HR male mice showed less anxiety-like behavior in the light-dark test but not the elevated plus maze. We observed no differences in the forced swim test across HR/LR, although males exhibited greater depression-like behavior overall. HR mice exhibited less contextual fear memory compared to LR regardless of sex. Principal component analyses suggested sex-specific patterns of behaviors across tests, with female responses within individual tests tending to load together. In females anxiety- and depression-like behaviors explained a large part of the variance observed across tests in our battery, whereas male behavior was primarily explained by variables related to locomotion.