We have made a great deal of progress over the past 4 years in identifying mechanisms through which blood flow is matched to neuronal metabolic activity. In this competitive renewal we will define at the cellular, molecular and whole animal level, the ionic and 2nd messenger systems responsible for the role of astrocytes in sensing neural activity, releasing vasoactive lipids, namely, EETs and how these mechanisms respond to hypoxia followed by re-oxygenation. We have identified two novel K+ channel types in astrocytes which are, in part, responsible for hyperpolarization in response to glutamate leading to elevation of intracellular Ca2+. This increase in intracellular Ca2+ initiates a series of signaling cascades which are responsible for the sensing of neural activity by astrocytes, leading to release of EETs and vasodilation, thereby, increasing blood flow to metabolically active neurons. The sequela of events during hypoxia/re-oxygenation result in lipid oxidation, release of ceramide and activation of cytokines which generate reactive oxygen species responsible for inhibition of functional hyperemia. We will design protocols to determine the pathological implication associated with these sequence of events. Many of the findings reported in preliminary data and published works coming from this grant are either new or poorly studied. For example, the concept of a functional neural unit composed of neuron, astrocyte and the microvasculature is a relatively new concept. To define the cellular mechanisms and physiologic consequences of activation of the individual parts of this functional unit is essential to our understanding of how the brain works, and how blood flow is coupled to neural activity. These studies will define new roles for astrocytes and how this cell type plays an integral part in functional hyperemia and other neural mechanisms.
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