Stress: metaplastic effects in the hippocampus.

Memory impairments, which occur regularly across species as a result of aging, disease and psychological insults (for example, stress), constitute a useful area for investigation into the neurobiological basis of learning and memory. Memory researchers have identified the hippocampus as a crucial brain structure involved in key aspects of memory formation. The most widely accepted putative mechanisms of memory storage in this structure are LTP and LTD. The hippocampus is enriched with receptors for corticosterone (a glucocorticoid hormone released in response to stress) and it plays a role in glucocorticoid negative feedback and, therefore, some hippocampal functioning might be particularly susceptible to stress. In support of this view, stress-induced modifications in learning, synaptic plasticity and endangerment of neurons have been seen in the hippocampus. Stress and glucocorticoids appear to exert a metaplastic effect through the modulation of Ca2+ levels. We propose a synaptic model that provides a conceptual scaffold to structure our understanding of the manifold actions of stress on the hippocampus. Accordingly, we suggest that stress-induced metaplasticity could disrupt Ca2+ homeostasis and thus endanger hippocampal neurons.