Therapeutic implications of HPA axis abnormalities in Alzheimer's disease: review and update.

The adaptive and maladaptive roles of the hypothalamic-pituitary-adrenal (HPA) axis in stressful conditions and in disorders such as major depression, posttraumatic stress disorder, and Cushing's syndrome, have been the subject of substantial, ongoing study. In particular, HPA disturbances have been associated with memory impairments, and hypercortisolemic conditions with atrophy of the hippocampus, a limbic structure closely associated with declarative memory. Recent discoveries support a more complicated picture of HPA axis function and pathology in acquiring, retrieving, and consolidating new memories. These findings include: the existence of an 'inverted U-shaped relationship" between stimulation of brain glucocorticoid receptors and memory performance; that distinct areas of the hippocampus have been found to respond differently to cortisol stimulation; and that hippocampal atrophy has been found to be potentially reversible in some conditions, although whether such atrophy is a cause or effect of these pathological conditions is currently unclear. More longitudinal studies of HPA axis function in aging normal individuals, those with mild cognitive impairment,and individuals with Alzheimer' disease, examining pertinent variables such as APOEe-4 status, are needed to help clarify these new findings. Antiglucocorticoid agents appear to have therapeutic value in particular conditions. These results are relevant for understanding and treating memory dysfunction in individuals with Alzheimer's disease, a disorder prominently and invariably characterized by early hippocampal lesions and memory impairment. Given the burden of this disease, we feel it timely to encourage controlled trials of antiglucocorticoid agents in the treatment of mild cognitive impairment and Alzheimers disease.