Integrated Cerebral Blood Flow Regulation

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The brain requires a continuous supply of nutrients and oxygen to fuel its normal functioning. Active areas of the brain need more energy than relatively quiescent regions, so the blood supply to different areas of the brain is dynamically varied over time to meet the ongoing needs of active neurons. Significant progress has been made in understanding the essential role of localized synaptic glutamatergic signaling in regulating local cerebral blood flow (CBF) in response to increased neuronal activity, a process known as neurovascular coupling (NVC). However, little is currently known about the integration between neural (i.e., neurons and astrocytes) and vascular networks and the broader mechanisms underlying the spatiotemporal coordination of local and global vascular responses within the cortical angioarchitecture and among different brain regions. The overall goal of this proposal is to identify interactions between local and global signaling pathways that control the magnitude and distribution of blood to match metabolic demands. Our preliminary data show that the state of wakefulness and engagement of the animal that are often associated with the release of long-range modulatory neurotransmitters (e.g., serotonin [5-HT]), and that manipulations of 5-HT activity modulate vascular responses. We propose that glutamatergic and serotonergic signaling are integrated to control CBF. Our data further suggest that vascular conduction may mediate ascending vasomotor responses from the deep layer to upstream parenchyma and the surface of the cortex to coordinate blood flow. On the basis of these observations, we propose a new paradigm in which activity-dependent allocation of CBF depends on the integration of three elements: 1) local synaptic glutamatergic signaling, 2) the global serotonergic system, and 3) retrograde intercellular conduction. We will employ two-photon fluorescence imaging of the vasculature and Ca2+ dynamics in neurons and astrocytes in fully awake animals in conjunction with ex vivo preparations, knockout strategies, genetically encoded biosensors, pharmacogenetics and optogenetics to test this paradigm. These integrated approaches are novel and powerful as they give us the ability to fully explore the integration of different signaling pathways under true physiological conditions without the need for anesthetics. Aim 1 will explore the contribution of serotonergic signaling to sensory-induced increases in local CBF and to coordination of blood distribution between inactive and active regions. Aim 2 will elucidate the mechanisms underlying 5-HT–induced vasomotor responses during whisker stimulation. Aim 3 will solidify the role of the endothelium in conducting electrical signals from the subsurface microvascular network to the upstream parenchyma and surface of the cortex, a process that is proposed to complement NVC. Our investigation into this novel model may reveal new physiological processes essential to CBF regulation and ultimately provide insights that help maintain brain health.