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Jesse B. Schallek, HoanVu N. Nguyen, Christina Schwarz, David R. Williams; Non-invasive Adaptive Optics Imaging of Retinal Pericytes and Capillary Blood Velocity in Mice. Journal of Vision 2012;12(14):50. doi: 10.1167/12.14.50.
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The central nervous system locally regulates blood flow in response to modulated neural activity. However the specificity of capillary-level control is highly controversial because capillaries lack smooth muscle. Renewed interest has emerged from studies of pericytes, cells that ensheathe capillaries and demonstrate contractility, yet this has not been observed in vivo. Here, we deploy adaptive optics scanning laser ophthalmoscopy (AOSLO) to resolve the microstructure of pericytes with simultaneous measurements of capillary flow to test the capillary control hypothesis. Transgenic mice expressing NG2 DsRed fluorescent retinal pericytes were imaged in vivo with a two channel AOSLO. A reflectance channel imaged moving blood cells (789nm) while a second channel imaged fluorescent pericytes (514nm excitation, 579+22nm emission). Flashing the excitation beam served as a visual stimulus. We measured vessel diameter and the velocity of blood cells before and after stimulation. Results: 1) Fluorescently labeled pericyte somas with long distal processes showed tight colocalization with capillaries. Capillary pericytes were relatively uniform in distribution across the retina with densities 669+309 cells/mm2 (+-1SD). Immunohistochemistry validated pericyte identification using PDGFR-B and aSMA antibodies. In vivo counts showed good agreement with postmortem densities demonstrating the utility of measuring pericytes repeatedly in the same animal over time. 2) We observed dilation of the central retinal artery (~3%) when the retina was stimulated with flashing light. AOSLO has enabled the first visualization of neurovascular vasodilation in the mouse retina by providing the necessary micron-level resolution. 3) We developed automated velocity measurements that facilitate measurement of thousands of cell velocities with minimal user input. These algorithms revealed high variability of blood velocity in single capillaries including branches that became sporadically occluded. Collectively, these advances lay the foundation for investigating the role of capillary-level control of blood flow in vivo.
Meeting abstract presented at OSA Fall Vision 2012
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