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Two-photon phosphorescence lifetime microscopy (2PLM) has been used recently for depth measurements of oxygen partial pressure [(PO.sub.2]) in the rodent brain. In capillaries of olfactory bulb glomeruli, 2PLM has also allowed simultaneous measurements of [PO.sub.2] and blood flow and revealed the presence of erythrocyte-associated transients (EATs), which are [PO.sub.2] gradients that are associated with individual erythrocytes. We investigated the extent to which EAT properties in capillaries report local neuronal activity. We find that at rest, [PO.sub.2] at EAT peaks overestimates the mean [PO.sub.2] by 35 mm Hg. [PO.sub.2] between two EAT peaks is at equilibrium with, and thus reports, [PO.sub.2] in the neuropil. During odor stimulation, there is a small [PO.sub.2] decrease before functional hyperemia, showing that the initial dip in [PO.sub.2] is present at the level of capillaries. We conclude that imaging oxygen dynamics in capillaries provides a unique and noninvasive approach to map neuronal activity., Modeling studies have shown that in capillaries, as opposed to in larger vessels, blood cannot be treated as a continuum in oxygen; plasma in the vicinity of red blood cells [...]

Uncovering principles that regulate energy metabolism in the brain requires mapping of partial pressure of oxygen (P[O.sub.2]) 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 P[O.sub.2] can be accurately measured in the brain at depths up to 300 mm with micron-scale resolution. In addition, 2PLM allowed simultaneous measurements of blood flow and of P[O.sub.2] 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 P[O.sub.2] in capillaries and by a biphasic P[O.sub.2] response in the neuropil, consisting of an 'initial dip' and a rebound. 2PLM of P[O.sub.2] opens new avenues for studies of brain metabolism and blood flow regulation., Understanding the brain metabolism at rest and during periods of activity requires quantifying the amounts of oxygen entering and exiting selected volumes of neuronal tissue (1). Previous measurements of P[O.sub.2] [...]

Two-photon phosphorescence lifetime microscopy (2PLM) has been used recently for depth measurements of oxygen partial pressure (PO2) in the rodent brain. In capillaries of olfactory bulb glomeruli, 2PLM has also allowed simultaneous measurements of PO2 and blood flow and revealed the presence of erythrocyte-associated transients (EATs), which are PO2 gradients that are associated with individual erythrocytes. We investigated the extent to which EAT properties in capillaries report local neuronal activity. We find that at rest, PO2 at EAT peaks overestimates the mean PO2 by 35 mm Hg. PO2 between two EAT peaks is at equilibrium with, and thus reports, PO2 in the neuropil. During odor stimulation, there is a small PO2 decrease before functional hyperemia, showing that the initial dip in PO2 is present at the level of capillaries. We conclude that imaging oxygen dynamics in capillaries provides a unique and noninvasive approach to map neuronal activity. [ABSTRACT FROM AUTHOR]