Glucocorticoids in hippocampal development

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The hippocampus is a part of the brain that helps with learning and memory. If it is damaged or removed, people can have trouble forming new memories, a problem famously shown in a patient called HM.

How the hippocampus develops: It forms early in brain development and, in humans, sits lower as the cortex grows around it. Many nerve cells that become hippocampal neurons originate in a nearby brain region and then move to their final places. Some cells reach their destinations quickly, while others migrate a bit later. The dentate gyrus, a part of the hippocampus, forms cells a little later and in a special growth zone that remains active into adulthood. A protein called reelin helps the layers of hippocampal neurons line up correctly; when reelin isn’t working, the layering can be disrupted.

Glucocorticoids and development: The body’s main stress hormone is cortisol. It is produced by the adrenal glands and released in response to stress. Cortisol acts through two main receptors, MR (mineralocorticoid) and GR (glucocorticoid). These receptors are found throughout the body and play roles in inflammation, development, and other processes. In the adult hippocampus, both receptor types are present, but cortisol binds more strongly to MR than to GR.

What this means for developing brains: The exact role of glucocorticoid signaling in developing the hippocampus isn’t fully understood. In animal studies, high levels of glucocorticoids before birth (from maternal stress or direct exposure) can lead to problems such as slower growth and changes in how the stress system works. These changes can affect how the hippocampus helps regulate stress and may be linked to later cognitive issues.

Clinical context: To help premature babies, doctors sometimes give dexamethasone to the mother, which acts on GRs to speed lung development. This exposure may influence the developing hippocampus. Some animal studies suggest that good postnatal care can lessen these negative effects, but more research is needed to understand the implications for humans.