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

Behavioural profiling following acute stress uncovers associations with future stress sensitivity and past childhood abuse

Background: Individuals greatly differ in their responses to acute stress, ranging from resilience to vulnerability that may yield stress-related psychopathology. Stress-related psychopathologies involve, by definition, substantial modifications across multiple behavioural domains, including impaired cognitive, affective and social functioning. Nevertheless, and despite extensive investigation of individual variability in stress responsivity, no study to date simultaneously assessed the impact of acute stress across multiple behavioural domains within a given individual.Objective: To address this critical gap, 84 healthy female participants (mean age 24.45 ± 3.02, range 19-35) underwent an established acute stress induction procedure and completed three behavioural tasks, probing the functional domains of positive, cognitive and social processing, both before and after the acute stress procedure.Method: A novel behavioural profiling algorithm was implemented to identify individuals whose performance was substantially impacted by stress across all three functional domains.Results: Approximately 30% of participants exhibited substantial deviation in their performance from before to after stress in all three tasks, hereon defined as stress-affected. Stress-affected participants did not differ in their psychological and physiological responses to the acute stress procedure from the other stress-unaffected 70% of the sample. However, follow-up assessments in 66 of these participants revealed higher levels of stress six months following the procedure among the stress-affected compared to the stress-unaffected group. Stress-affected individuals also reported more aversive childhood experiences, such that the odds of participants who were sexually abused at an early age to be affected behaviourally by acute stress later in life increased by more than five-fold.Conclusions: Taken together, these findings suggest that being affected by acute stress across multiple functional domains is associated with future stress sensitivity and past childhood sexual abuse. Probing individual differences in the impact of acute stress across domains of functionality may better align with the multi-dimensional nature of stress responsivity, uncovering latent vulnerability.

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.

The role of hippocampal CaMKII in resilience to trauma-related psychopathology

Traumatic stress exposure can form persistent trauma-related memories. However, only a minority of individuals develop post-traumatic stress disorder (PTSD) symptoms upon exposure. We employed a rat model of PTSD, which enables differentiating between exposed-affected and exposed-unaffected individuals. Two weeks after the end of exposure, male rats were tested behaviorally, following an exposure to a trauma reminder, identifying them as trauma 'affected' or 'unaffected.' In light of the established role of hippocampal synaptic plasticity in stress and the essential role of Ca2+/calmodulin-dependent protein kinase II (CaMKII) in hippocampal based synaptic plasticity, we pharmacologically inhibited CaMKII or knocked-down (kd) αCaMKII (in two separate experiments) in the dorsal dentate gyrus of the hippocampus (dDG) following exposure to the same trauma paradigm. Both manipulations brought down the prevalence of 'affected' individuals in the trauma-exposed population. A day after the last behavioral test, long-term potentiation (LTP) was examined in the dDG as a measure of synaptic plasticity. Trauma exposure reduced the ability to induce LTP, whereas, contrary to expectation, αCaMKII-kd reversed this effect. Further examination revealed that reducing αCaMKII expression enables the formation of αCaMKII-independent LTP, which may enable increased resilience in the face of a traumatic experience. The current findings further emphasize the pivotal role dDG has in stress resilience.

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.