Simultaneous two-photon imaging of oxygen and blood flow in deep cerebral vessels

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Abstract
Using the recently developed phosphorescent probe PtP-C343, in combination with two-photon phosphorescence lifetime microscopy, Lecoq and his colleagues offer a method for mapping oxygen levels in both microvascular and extravascular compartments with high spatial and temporal resolution. They used this set-up to make micron-scale simultaneous measurements of partial pressure of oxygen (PO2) and blood flow in the rat olfactory bulb vasculature and neuropil. Uncovering principles that regulate energy metabolism in the brain requires mapping of partial pressure of oxygen (PO2) and blood flow with high spatial and temporal resolution. Using two-photon phosphorescence lifetime microscopy (2PLM) and the oxygen probe PtP-C343, we show that PO2 can be accurately measured in the brain at depths up to 300 μm with micron-scale resolution. In addition, 2PLM allowed simultaneous measurements of blood flow and of PO2 in capillaries with less than one-second temporal resolution. Using this approach, we detected erythrocyte-associated transients (EATs) in oxygen in the rat olfactory bulb and showed the existence of diffusion-based arterio-venous shunts. Sensory stimulation evoked functional hyperemia, accompanied by an increase in PO2 in capillaries and by a biphasic PO2 response in the neuropil, consisting of an 'initial dip' and a rebound. 2PLM of PO2 opens new avenues for studies of brain metabolism and blood flow regulation.

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