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. (C) 2007 Elsevier Inc. All rights reserved.