Mood, cognition and Alzheimer's disease.

There is good evidence for sex differences in brain disease, and that oestrogen modulates brain development and ageing. For example, females are significantly more likely to suffer from Alzheimer's disease, depression and late-onset psychosis than are men. Moreover, hormone replacement therapy may reduce the rate of cognitive decline in post-menopausal women and reduce their risk of developing Alzheimer's disease (as compared to post-menopausal women who do not take hormone replacement therapy). The neurobiological basis of these differences in brain disease and ageing was unknown until relatively recently. In this chapter we discuss results of studies demonstrating that sex steroids (i) are crucial for development and ageing of brain regions affected in Alzheimer's disease; (ii) interact with neuronal networks and chemical systems at many different levels in brain, and (iii) affect mood and cognitive function in elderly women without Alzheimer's disease. The current literature supports the hypothesis that sex steroids can modulate brain ageing and provides a number of potential neurobiological explanations for the cognitive effects of hormone replacement therapy. There is only limited evidence that hormone replacement therapy is effective in women already suffering from Alzheimer's disease. Nonetheless, recent work may lead to new prevention strategies for age-related cognitive decline and brain diseases such as Alzheimer's disease.