Multi-scale mapping of 3D spatial-temporal cortical hemodynamics at the level of

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DESCRIPTION (provided by applicant): The dynamics response of individual neuronal vessels to sensory-stimuli is crucial to form a mechanistic understanding of functional imaging technologies, such as functional MRI (fMRI), as well as for understanding neurovascular dysfunction, as occurs in stroke and dementia. Toward this goal, we propose to characterize the stimulus-evoked cerebral hemodynamic response on the level of single arterioles and capillaries throughout a significant three-dimensional volume. Further, we will relate this characterization to the underlying neuronal electrical activity, the angioarchitecture, and the mitochondria density. Vibrissa sensory cortex of rat serves as our model system. Two-photon laser scanning microscopy (TPLSM), in conjunction with dyes that label the blood lumen, and all-optical histology, a related nonlinear optics technique, serve as our primary technology. As a prerequisite to the proposed measurements, we will improve the capability of TPLSM to allow rapid assessment of multiple blood vessels. This will allow us to characterize blood flow and blood vessel diameter at micrometer resolution throughout a 2 - 3 mm3 volume, along with correlations along flow in different vessels. Our analysis consists of three directions. Dynamical characterization of the diameter and flow dynamics of three classes of vessels, i.e., surface communicating arterioles, penetrating arterioles, and subsurface microvessels, in response to tactile single vibrissa stimulation. Ex vivo reconstruction of the exact angioarchitecture throughout the region of study by the in vivo vascular measurements, followed by three-dimensional mapping of the mitochondria density relative to the microvasculature. Our results will reveal, at a minimum: The characteristics, e.g., biphasic versus monophasic, of the temporal dynamics of the vessel diameter and blood flow changes of individual vessels. The dependence of the responses of a vessel on its distance from the center of the neuronal activity, its connectivity to major surface feeding arteries or penetrating arterioles, and its position relative to the local metabolic need as revealed by the mitochondria density. This work will bridge the critical gap between macroscopic functional imaging technologies such as fMRI and the microscopic understanding of single vessel responses to the neuronal activation. Stroke, vascular disease, and dementia are all dysfunctional states that relate to compromised cerebral blood flow. Our work will define the normal state of flow and bears on disruption to the normal state. It will help define optical- and MRI-based diagnostics for the detection of dysfunction and clinically appropriate interventionist therapies.