Two-Photon Lifetime Imaging of Oxygen Dynamics in Cerebral Capillaries – TPLIODCC

The economical cost of brain diseases associated with hypoxia is extremely high. To understand the relationship between oxygenation, blood flow and brain disease, and in the long run how therapeutics can be optimised to reduce brain damage, it is important to determine how oxygen is delivered to and consumed by neurons in vivo. Recently, a two-photon phosphorescent probe PtP-C343 has been generated and two-photon phosphorescence lifetime microscopy (2PLM) has been used for depth-resolved micron-scale measurements of Po2 in the anesthetized rodent brain. In particular, we have demonstrated in olfactory bulb glomeruli, the possibility to monitor simultaneously red blood cell blood flow and the partial pressure of oxygen (Po2) in capillaries. We have also shown the presence of erythrocyte-associated transients (EATs), i.e. Po2 fluctuations associated with each individual erythrocyte flowing in capillaries2. Theoretically, EAT properties depend on several parameters, among which RBC flow and oxygen consumption in the neighbouring tissue.
We propose to use measurements of EAT properties in glomerular capillaries to investigate, i) whether capillary EATs can be used as reporters of the surrounding tissue oxygenation and ii) whether the tissue Po2 “initial dip” is associated with a capillary “Po2 dip”, observable at the level of EATs or of the mean Po2.
This short project (2 years) will allow us to determine if ETAs can be used to measure tissue Po2 non-invasively in both anesthetized and awake animals and to answer a controversial question, important in the field of functional imaging: what are the conditions of local neuronal activation required to generate a Po2 initial dip in the capillary compartment?