Imaging local neuronal activity by monitoring PO2 transients in capillaries

Abstract

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.