Bimodal shape of individual variation in behavior of Wistar rats: the overall outcome of a fundamentally different make-up and reactivity of the brain, the endocrinological and the immunological system.

An overview of the most important features of the two distinct types of individuals which normally co-occur in an unselected population of Wistar rats is given. It reveals that the overall make-up and reactivity of the brain, as well as the endocrinological and immunological systems differ completely between the two types of individuals. Each of these types of individuals has its own individual-specific hardware and software to cope with challenges from the internal or external environment, requires its own optimal niche, and is vulnerable for its own set of stressors.