Behavioral inhibition and glucocorticoid dynamics in a rodent model.

Behavioral inhibition (i.e. avoidance of unfamiliar) has been linked to significant differences in stress physiology and health. Developing an animal model of this common temperament provides a means to experimentally study the development and physiology of this trait as it relates to stress-related health processes. To elaborate such an animal model, we studied individual rat responses to two novel situations that mimic behavioral inhibition tests for humans (one non-social and one social). We measured individual consistency of behavioral responses across tests and time, and examined the relationship between behavior and glucocorticoid levels in outbred Sprague-Dawley male rats. Individuals were consistent in their behavioral responses to the same novel environment over time, but not in their responses across two different environments (i.e. non-social vs. social). A third of males were slow to approach novelty in both arenas (INHIBITED) and another third were fast to approach in both arenas (NON-INHIBITED). Behavioral inhibition was relatively stable across time and was associated with increased glucocorticoid production at baseline and in response to novelty but not during a post-novelty recovery period. Glucocorticoid levels were more closely related to their responses to the social novel arena than the non-social arena. Thus, behavioral inhibition is associated with acute and basal glucocorticoid over production and social inhibition is a more important predictor of adrenal activity than non-social inhibition. These preliminary observations provide strong support for an animal model of human behavioral inhibition and identify specific aspect of glucocorticoid production dynamics to examine in behaviorally inhibited children.