Juvenile stress facilitates safety learning in male and female high alcohol preferring mice

Line- and sex-dependent effects of juvenile stress on contextual fear- and anxiety-related behavior in high- and low-alcohol-preferring mouse lines

Juvenile stress (JS) is a known risk factor for the development of alcohol use disorder (AUD) and post-traumatic stress disorder (PTSD), both of which are frequently co-morbid. Data suggest there may be common, genetically-influenced biological responses to stress that contribute to the development of both AUD and PTSD. The present study investigated the impact of JS on contextual fear learning and extinction, as well as corticosterone (CORT) responses before and after JS, before and after contextual fear conditioning (CFC), and after fear extinction in male and female high-alcohol-preferring (HAP2) and low-alcohol-preferring (LAP2) mouse lines. We also measured unconditioned anxiety-related behavior in the light-dark-transition test before CFC. HAP2 and LAP2 mice did not differ in fear acquisition, but HAP2 mice showed faster fear extinction compared to LAP2 mice. No effects of JS were seen in HAP2 mice, whereas in LAP2 mice, JS reduced fear acquisition in males and facilitated fear extinction in females. Females showed greater fear-related behavior relative to males, regardless of subgroup. HAP2 males demonstrated more anxiolytic-like responses than LAP2 males and LAP2 females demonstrated more anxiolytic-like responses than LAP2 males in the light-dark transition test. HAP2 and LAP2 mice did not differ in CORT during the juvenile stage; however, adult LAP2 mice showed greater CORT levels than HAP2 mice at baseline and after CFC and extinction testing. These findings build upon prior work in these unique mouse lines that differ in genetic propensity toward alcohol preference and provide new information regarding contextual fear learning and extinction mechanisms theorized to contribute to co-morbid AUD and PTSD.

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.

Environmental certainty influences the neural systems regulating responses to threat and stress

Flexible calibration of threat responding in accordance with the environment is an adaptive process that allows an animal to avoid harm while also maintaining engagement of other goal-directed actions. This calibration process, referred to as threat response regulation, requires an animal to calculate the probability that a given encounter will result in a threat so they can respond accordingly. Here we review the neural correlates of two highly studied forms of threat response suppression: extinction and safety conditioning. We focus on how relative levels of certainty or uncertainty in the surrounding environment alter the acquisition and application of these processes. We also discuss evidence indicating altered threat response regulation following stress exposure, including enhanced fear conditioning, and disrupted extinction and safety conditioning. To conclude, we discuss research using an animal model of coping that examines the impact of stressor controllability on threat responding, highlighting the potential for previous experiences with control, or other forms of coping, to protect against the effects of future adversity.