The primary goal of the proposed research is to better understand mechanisms of brain aging. These experiments will examine the neural control of reproduction in the aging female rat as a model system. This model provides unique advantages for studying brain function during aging because the changes in the reproductive system occur early in the life-span, and occur in the absence of confounding age- related pathologies. This research will determine specifically if age-related changes in reproductive cyclicity result from a desynchronization of neural and endocrine rhythms which are driven by the circadian timing system. Many age-related pathologies including sleep-wake disturbances and depression have been linked to this neural system. These experiments will lead to new and significant information regarding the circadian timing system itself, and will help provide a foundation for possible therapeutic intervention of disorders involving the ciradian timing system.