Older animals have fragmented sleep and wakefulness, less NREM sleep, and reduced amplitude of delta waves during sleep. The mechanisms for these changes and their consequences are unknown. In this proposal, we argue that during sleep and wakefulness,there is an alteration in the cellular energy stores in brain. This alteration will affect the AMP-dependent kinase (AMPK) whose activity is sensitive to cellular ATP/AMP ratios. When the enzyme is activated under conditions of low cellular energy, it promotes the liberation of energy stores and acts to antagonizeprocesses that utilize energy such as cholesterol synthesis and protein translation. We therefore propose that the activity of this enzyme will vary between sleep and wakefulness, and that alteration in activity of AMPK will lead to alterations in cholesterol synthesis and protein translation between sleep and wakefulness. We propose that restorative molecular functions of sleep include increased cholesterol synthesis and protein translation. This hypothesis will be investigated. Since older animals have more fragmented sleep, it is likely that these molecular functions of sleep will be compromised in this age group. This will lead to decreased cholesterol synthesis in brain during sleep and thereby compromised neuronal function since cholesterol is known to play a key role in membrane signaling and synaptic plasticity. Moreover, in older animals, cellular energy charge may change more rapidly during wakefulness leading to more rapid inhibition of protein translation. Since inhibition of protein translation will have profound effects on many cellular processes, this is likely to be one variable that sets the duration of wakefulness that can be sustained. To address these hypotheses, we propose to assess the following in both old and young animals: a) changes in regulation of protein translation between sleep and wakefulness;b) changes in regulation of cholesterol synthesis between sleep and wakefulness;c) changes in AMPK phosphorylation and activity between sleep and wakefulness. Further, to show that these changes in AMPK activity cause sleep/wake changes along with concomitant cholesterol and protein synthesis changes, we will assess the effects of blocking the activity of the enzyme by local microinjection into brain of a virus expressing a dominant negative form of the enzyme. The protocols in this project develop a coordinated approach to a new study of the molecular functions of sleep and their alterations in older animals. Thus, this project will take our knowledge about sleep disturbances in the elderly to a new level of understanding, opening new approaches for interveningto enhance the functions of sleep.