SignificanceIt has been hypothesized that abnormal microcirculation in the retina might predict the risk of ischemic damages in the brain. Direct comparison between the retinal and the cerebral microcirculation using similar animal preparation and under similar experimental conditions would help test this hypothesis.AimWe investigated capillary red-blood-cell (RBC) flux changes under controlled conditions and bilateral-carotid-artery-stenosis (BCAS)-induced hypoperfusion, and then compared them with our previous measurements performed in the brain.ApproachWe measured capillary RBC flux in mouse retina with two-photon microscopy using a fluorescence-labeled RBC-passage approach. Key physiological parameters were monitored during experiments to ensure stable physiology.ResultsWe found that under the controlled conditions, capillary RBC flux in the retina was much higher than in the brain (i.e., cerebral cortical gray matter and subcortical white matter), and that BCAS induced a much larger decrease in capillary RBC flux in the retina than in the brain.ConclusionsWe demonstrated a two-photon microscopy-based technique to efficiently measure capillary RBC flux in the retina. Since cerebral subcortical white matter often exhibits early pathological developments due to global hypoperfusion, our results suggest that retinal microcirculation may be utilized as an early marker of brain diseases involving global hypoperfusion.
Although the beneficial effects of regular physical exercise on brain aging and neurodegenerative diseases are well recognized, a clear understanding of how exercise leads to such benefits remains elusive. In this work, we investigated the effects of normal aging on cortical microvascular oxygenation, perfusion, and morphology and the impact of four months of voluntary wheel running on cortical microvascular oxygenation in 20 months old mice. We used two-photon microscopy to assess age-related and exercise-induced changes in the distributions of capillary oxygen partial pressure (PO2) and red-blood-cell flux across cortical depth in awake mice. Our finding suggests the mitigating effect of exercise on the progression of age-related changes in capillary oxygenation in deeper cortical layers which may be related to health-enhancing benefits of exercise in elderly individuals.
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