Early life stress induces a transient increase in hippocampal corticotropin releasing hormone in rat neonates that precedes the effects on hypothalamic neuropeptides
Early life stress (ELS) programs the hypothalamus-pituitary-adrenal (HPA) axis activity, affects synaptic plasticity, and cognitive performance in adult individuals; however, the effects of ELS during the vulnerability time window are poorly understood. This study aimed to thoroughly characterize the effects of ELS in the form of periodic maternal separation (MS180) during the time of exposure to stress. Hippocampal corticotropin releasing hormone (CRH) gene expression and baseline HPA axis activity were analyzed at postnatal (P) days 6, 12, 15, and 21, and in adulthood (P75); these factors were correlated with plasticity markers and adult behavior. Our results indicate that MS180 induces an increase in hippocampal CRH expression at P9, P12, and P15, whereas the increase in hypothalamic CRH expression was observed from P12 to P21. Increased arginine vasopressin expression and corticosterone levels were observed only at P21. Moreover, MS180 caused transient alterations in hypothalamic synaptophysin expression during early life. As adults, MS180 rats showed a passive coping strategy in the forced swimming test, cognitive impairments in the object location test, increased hypothalamic CRH expression, and decreased oxytocin (OXT) expression.