We utilized a novel ratiometric nano quantum dot fluorescence resonance energy transfer (NQD-FRET) optical sensor to quantitatively measure oxygen dynamics from single cell microdomains during hypoxic episodes as well as during 4-aminopyridine (4AP) induced spontaneous seizure like events in rat hippocampal slices. Coupling oxygen sensing with electrical recordings, we found the greatest reduction in [O2] in the densely packed cell body st. pyramidale layer of the CA1, and differential layer specific O2 dynamics between the st. pyramidale and st. oriens layers. These hypoxic decrements occurred up to several seconds before seizure onset could be electrically measured extracellularly. Without 4AP, we quantified a narrow range of [O2], similar to the endogenous hypoxia found prior to epileptiform activity, which permits a quiescent network to enter into a seizure-like state. We demonstrated layer specific patterns of O2 utilization accompanying layer specific neuronal interplay in seizure. None of the oxygen overshoot artifacts seen with polarographic measurement techniques were observed. We therefore conclude that endogenously generated hypoxia may be more than just a consequence of increased cellular excitability, but an influential and critical factor for orchestrating network dynamics associated with epileptiform activity.
- Copyright © 2013, Journal of Neurophysiology