Abstract P434: A Mouse Model To Control Vessel Diameter With Light

In diseases such as stroke, hypertension, vascular cognitive impairment, and Alzheimer’s disease, defects in the cerebrovascular system lead to reduced blood flow and vasoreactivity to stimuli. Recently, there has been increased appreciation for the role of small vessels in these vascular pathologies. For example, small vessel dysfunction can cause widespread microinfarcts and capillary stalling, which may underlie cognitive impairment in cases where large scale vascular abnormalities are not readily detected. However, vascular function is difficult to dissociate from concurrent neuronal deficits cause by damage to neuronal circuitry in brain pathology. Thus the ability to directly probe smooth muscle contraction of small, individual vessels in the intact brain would be a valuable tool for increasing our understanding of vascular contributions to cognitive impairment. We developed an experimental paradigm to optically probe the contractile function of arterioles in vivo with high spatiotemporal precision. This was done by expressing the excitatory opsin ReaChR in vascular smooth muscle cells and pericytes. Using a 594 nm light-emitting diode we were able to evoke widespread vasoconstriction across the cranial window. With a 1040 nm focused, pulsed laser for two-photon stimulation, we were able to evoke highly localized constrictions targeted to individual pial artery branches or penetrating arterioles. Our dual light-path imaging system allowed the optogenetic stimulation to be performed with simultaneous two-photon imaging to monitor vessel activity. Using a spatial light modulator, we were also able to constrict vessels both above and below the imaging plane. This is a powerful tool to assay vasoconstrictive function of single arterioles across 3-dimensional vascular networks in vivo. It also presents novel opportunities to study conductance of vascular signals and to modulate dynamics of functional hyperemia.