The primary neurotransmitter hallmark of Alzheimer’s Disease (AD) is a loss of acetylcholine, produced by neurons of the basal forebrain cholinergic system (BFCS). Cholinergic cell loss or dysfunction is also a prominent component of Lewy Body Dementia and vascular dementia, respectively. Thus the BFCS contributes to several aspects of cognitive function that are negatively impacted in AD and related dementias, including attention, learning and memory. Regulation of the BFCS by afferent inputs, including those from the hypothalamus, is important for integration of homeostatic and cognitive functions. Because homeostatic and physiological disturbances, such as altered food intake or sleep-wake cycles, often precede and predict cognitive decline in AD, understanding these interactions may lead to novel points of intervention to treat or delay cognitive decline in conditions such as AD. An important source of this afferent regulation is the hypothalamic orexin/hypocretin neuropeptide system, which activates cholinergic neurons in response to stimuli that signal physiological valence. We have previously shown that aging, the strongest risk factor for AD, is associated with reduced orexin expression. Recently, orexin transmission has been shown to play a role in limiting neuroinflammation, suggesting that a diminished orexin system in aging may promote neuroinflammatory processes that further negatively impact cholinergic-dependent signaling and cognition. In this renewal application, we will dissect the mechanisms underlying the association between loss of orexin signaling, neuroinflammation and subsequent cholinergic dysfunction and neurodegeneration in an aged rodent model using virus-mediated gene transfer, neurochemical, pharmacological and cognitive behavioral approaches. We will further test the hypothesis that chronic restoration and maintenance of orexin function beginning in early aging will preserve the integrity of the BFCS by modulating local microglial dynamics. The proposed studies will begin to delineate the mechanisms by which age-related loss of orexin signaling drives cholinergic dysfunction and cognitive decline and suggest the potential for orexin-targeted therapies in preventing or ameliorating AD or related dementias, all of which are characterized by neuroinflammation and cholinergic dysfunction.