Disruption of neuronal calcium (Ca2+) homeostasis is associated with aging and cognitive decline in humans and animal models. However, cognitive impairment is variable in the aging population and certain neuronal cell-types are more susceptible to age-related changes than others. In humans, cholinergic neurons in the basal forebrain are preferentially affected by age-related dysfunction, including Alzheimer's disease. In rats, cholinergic dysfunction in the basal forebrain has been associated with cognitive impairment, but the cellular and molecular mechanisms that mediate cognitive dysfunction are largely unknown. Our lab has described age-related differences in gene expression and functional physiology of neurons from the rat medial septum and nucleus of the diagonal band (MS/nDB). To understand the cellular and molecular mechanisms responsible for age-related cognitive impairment, we need to define cell-type specific patterns of neuronal physiology/molecular biology relevant to cognitive decline in an aging model. We hypothesize that age-related changes in Ca2+ homeostatic function differentially affect specific subtypes of cholinergic neurons and that the initiation of these changes precipitates a cognitive decline that can be reversed or prevented by appropriate pharmacology. To investigate this, we will measure mRNA expression in acutely dissociated MS/nDB neurons from Fischer 344 rats of different ages (young, 1-4 months; middle, 12-16 months; aged, 24-26 months) using real-time fluorescent detection PCR to quantitate expression and identify cell-types. Molecular descriptions will be combined with functional assays of voltage-gated Ca2+ channels, Ca2+ homeostasis and mitochondria using patch-clamp electrophysiology, Ca2+ sensitive ratiometric microfluorimetry, laser scanning confocal microscopy and electron microscopy. Each rat will be behaviorally characterized as cognitively impaired or nonimpaired in a spatial memory test relevant to the basal forebrain cholinergic system (Morris water maze), allowing us to associate cellular results with cognitive status. We will define at least three functional and molecular properties from each animal. Finally, we will treat rats with donepezil (cholinesterase inhibitor) or nimodipine (Ca2+ channel blocker) to reverse age-related behavioral impairments and physiological changes.
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