Final answer:
The glucocorticoid cascade hypothesis pertains to the deleterious effects of chronic stress and elevated glucocorticoid levels on the CNS, particularly in areas like the hippocampus, leading to cellular damage and potential contributions to conditions such as major depression.
Step-by-step explanation:
The glucocorticoid cascade hypothesis is a concept in neurobiology that examines the effects of long-term stress and the increased levels of glucocorticoids (such as cortisol) culminating in cell damage within the central nervous system (CNS). Elevated glucocorticoids can enhance immune function and promote the proliferation and activation of microglia, which are immune cells of the CNS. They also lead to a reduction in the number of astrocytes, which are crucial for maintaining CNS homeostasis and neuronal support.
The CNS contains many glucocorticoid receptors, with areas like the hippocampus being particularly sensitive. These receptors, when overly activated, contribute to cellular damage via a range of mechanisms, including inhibiting the building of new tissue and stimulating the breakdown of nutrients. Interestingly, certain immune patterns observed in major depression, such as melancholic and non-melancholic types, have been linked to glucocorticoid levels and their effects on CNS function and structure.
Furthermore, stress conditions trigger the hypothalamic-pituitary-adrenal (HPA) axis, leading to the release of glucocorticoids. These hormones prepare the body for a 'fight or flight' response but chronic exposure can lead to detrimental effects on brain structure and functions, such as memory formation in the hippocampus.