Juvenile adversity and adult threat controllability in translational models of stress-related disorders

Juvenile variable stress modulates, in female but not in male Wistar rats, ethanol intake in adulthood

Early stress can increase vulnerability to psychopathological disorders, including substance use disorders. The effects of stress in the juvenile period of the rat, that extends between weaning and the onset of adolescence (equivalent to late human childhood), have received little attention. This study assessed short and long-term behavioral effects of juvenile stress, with a focus on effects on ethanol intake. Male and female Wistar rats were exposed to variable stress (restraint, elevated platform, forced swimming, and social instability) or to restraint stress only, between postnatal days 26 to 29 (PDs 26-29). During adolescence, patterns of anxiety (PD 31) and depression (PD 33), ethanol intake (PDs 36-45) and behavioral sensitivity to the effects of acute stress (PD 47) were evaluated. In adulthood, alcohol ingestion was assessed through two-bottle ethanol intake tests (PDs 75-85). An additional experiment measured blood ethanol levels after a limited access intake session in adolescence. Exposure to juvenile variable stress exerted very mild effects in adolescence, but reduced ethanol ingestion in adulthood, in females only. Ethanol intake during the limited access session was significantly correlated to blood alcohol levels. The results indicate that a schedule of juvenile variable stress that did not significantly alter anxiety-related behaviors induced, nonetheless, sexually dimorphic effects on ethanol intake in adulthood. Early stress exposure that reduced alcohol intake in Wistar rats has been associated with changes on brain opioid and dopamine receptors. These results highlight the impact of early stress exposure on adult female ethanol consumption and its possible underlying neurobiological changes, involving opioid and dopamine receptors.

Differences in the persistence of spatial memory deficits induced by a chronic stressor in adolescents compared to juveniles

Adolescence is thought of as a stress-sensitive developmental period. While many studies have compared adolescent responses to stress relative to that of adults, a growing body of work has examined stress responses in juveniles. Here we investigated if a chronic stressor has a differential effect on spatial memory in rats depending on whether it occurs during adolescence or the juvenile period. Male rats were exposed to the stress hormone corticosterone (Cort) in their drinking water, a vehicle control (2.5% ethanol), or water, for 7 days before being tested on a novel Object/Place task 6 days or 6 weeks later. Exposure to Cort or ethanol at either age impaired spatial memory at the 6-day test. The ethanol induced impairment was attenuated 6 weeks later. However, rats given Cort during adolescence, but not the juvenile period, were still impaired. Together, these results suggest that adolescence is indeed a stress-sensitive period.