Early emergence of adult-like fear renewal in the developing rat after chronic corticosterone treatment of the dam or the pups.

Abstract

Early adversity increases the risk of nearly all mental health disorders. Although tractable animal models exist to probe the psychobiology of early adversity, the empirical research has focused largely on adult outcomes. In the current studies we examined how early exposure to the stress hormone corticosterone (CORT) affects the maturation of fear extinction in infant rats. Whereas juvenile and adult rodents exhibit extinction learning that is relapse-prone (i.e., they show renewal and reinstatement of extinguished fear), under typical rearing conditions the extinction system in infant rats appears to be relapse-resistant (i.e., extinction leads to a permanent reduction in conditioned fear). In the current studies we tested the hypothesis that chronically exposing infant rats to CORT, either indirectly (through maternal drinking water) or directly (via insertion of an osmotic pump), leads to an early transition into the adult-like extinction system (i.e., evidence of the renewal effect). Although some differences were observed between the 2 methods of CORT exposure, the data showed that infants exposed to CORT via either method exhibited premature emergence of adult-like extinction learning (i.e., they exhibited the renewal effect). The theoretical implications of these findings for typical and abnormal development of emotion learning systems, as well as their practical applications in the context of prevention and treatment of mental health disorders, are discussed.