Hippocampal Dysfunction and Cognitive Impairments Provoked by Chronic Early-life Stress Involve Excessive Activation of CRH Receptors

Chronic stress impairs learning and memory in humans and rodents and disrupts long-term potentiation (LTP) in animal models. These effects are associated with structural changes in hippocampal neurons, including reduced dendritic arborization. Unlike the generally reversible effects of chronic stress on adult rat hippocampus, we have previously found that the effects of early-life stress endure and worsen during adulthood, yet the mechanisms for these clinically important sequelae are poorly understood. Stress promotes secretion of the neuropeptide corticotropin-releasing hormone (CRH) from hippocampal interneurons, activating receptors (CRF(1)) located on pyramidal cell dendrites. Additionally, chronic CRF(1) occupancy negatively affects dendritic arborization in mouse organotypic slice cultures, similar to the pattern observed in middle-aged, early-stressed (CES) rats. Here we found that CRH expression is augmented in hippocampus of middle-aged CES rats, and then tested whether the morphological defects and poor memory performance in these animals involve excessive activation of CRF(1) receptors. Central or peripheral administration of a CRF(1) blocker following the stress period improved memory performance of CES rats in novel-object recognition tests and in the Morris water maze. Consonant with these effects, the antagonist also prevented dendritic atrophy and LTP attenuation in CA1 Schaffer collateral synapses. Together, these data suggest that persistently elevated hippocampal CRH-CRF(1) interaction contributes importantly to the structural and cognitive impairments associated with early-life stress. Reducing CRF(1) occupancy post hoc normalized hippocampal function during middle age, thus offering potential mechanism-based therapeutic interventions for children affected by chronic stress.