Juvenile exposure to acute traumatic stress leads to long-lasting alterations in grey matter myelination in adult female but not male rats

Abstract

Stress early in life can have a major impact on brain development, and there is increasing evidence that childhood stress confers vulnerability for later developing psychiatric disorders. In particular, during peri-adolescence, brain regions crucial for emotional regulation, such as the prefrontal cortex (PFC), amygdala (AMY) and hippocampus (HPC), are still developing and are highly sensitive to stress. Changes in myelin levels have been implicated in mental illnesses and stress effects on myelin and oligodendrocytes (OLs) are beginning to be explored as a novel and underappreciated mechanism underlying psychopathologies. Yet there is little research on the effects of acute stress on myelin during peri-adolescence, and even less work exploring sex-differences. Here, we used a rodent model to test the hypothesis that exposure to acute traumatic stress as a juvenile would induce changes in OLs and myelin content across limbic brain regions. Male and female juvenile rats underwent three hours of restraint stress with exposure to a predator odor on postnatal day (p) 28. Acute stress induced a physiological response, increasing corticosterone release and reducing weight gain in stress-exposed animals. Brain sections containing the PFC, AMY and HPC were taken either in adolescence (p40), or in adulthood (p95) and stained for markers of OLs and myelin. We found that acute stress induced sex-specific changes in grey matter (GM) myelination and OLs in both the short- and long-term. Exposure to a single stressor as a juvenile increased GM myelin content in the AMY and HPC in p40 males, compared to the respective control group. At p40, corticosterone release during stress exposure was also positively correlated with GM myelin content in the AMY of male rats. Single exposure to juvenile stress also led to long-term effects exclusively in female rats. Compared to controls, stress-exposed females showed reduced GM myelin content in all three brain regions. Acute stress exposure decreased PFC and HPC OL density in p40 females, perhaps contributing towards this observed long-term decrease in myelin content. Overall, our findings suggest that the juvenile brain is vulnerable to exposure to a brief severe stressor. Exposure to a single short traumatic event during peri-adolescence produces long-lasting changes in GM myelin content in the adult brain of female, but not male, rats. These findings highlight myelin plasticity as a potential contributor to sex-specific sensitivity to perturbation during a critical window of development.

Region-specific, maladaptive, gray matter myelination is associated with differential susceptibility to stress-induced behavior in rats and humans

“…1A). This is an established model with ethological validity that elicits a large corticosterone response in the rat (28,(55)(56)(57)(58). Twenty rats underwent stress, while twenty served as controls and remained minimally disturbed.…”

“…Enhancing or inhibiting this plasticity alters behaviors such as motor function, spatial memory consolidation, and motor learning (14,20,21), suggesting that adult myelin plasticity in both white and gray matter regions is necessary for proper synaptogenesis, circuit function, and learning. In addition, oligodendrocytes express glucocorticoid receptors throughout their lineage and are sensitive to various environmental stressors in a region-specific manner (22)(23)(24)(25)(26)(27)(28). For example, chronic stress decreases myelin density in the prefrontal cortex (PFC) (13,29,30), while early weaning in mice increases myelin production in the amygdala (31).…”

Hormonal Regulation of Oligodendrogenesis II: Implications for Myelin Repair

“…In our own work using animal models, we recently identified sex-, age-, and region-specific changes in OLs and myelin following exposure to acute trauma. Juvenile exposure to acute stress led to long-lasting reductions in grey matter myelin in female, but not male, adult rats [58]. In addition, male rats demonstrated short-term changes in myelin content; these changes were associated with corticosterone levels during stress exposure [58].…”

“…Juvenile exposure to acute stress led to long-lasting reductions in grey matter myelin in female, but not male, adult rats [58]. In addition, male rats demonstrated short-term changes in myelin content; these changes were associated with corticosterone levels during stress exposure [58]. Furthermore, in adult male rats exposed to the same acute stressor, hippocampal and amygdala myelin levels positively correlated with avoidance and fear scores, respectively [59].…”

Animal Models of Anxiety and Depression: Incorporating the Underlying Mechanisms of Sex Differences in Macroglia Biology

“…In addition to basal differences, sex differences in oligodendrocyte markers have been reported following acute stress with differentially altered MBP levels in male and female mice. Male mice displayedincreased levels of MBP in the amygdala and hippocampus 12 days after the stressor (Breton et al, 2020 ). Conversely, females did not have altered MBP levels until 2 months after the stressor and exhibited increases in the PFC, amygdala, and hippocampus.Thus, the temporal influence of stress on oligodendrocytes differs between the sexes and couldrepresent an important and understudied mechanism driving sex differences in neuropsychiatric diseases.…”