Electrochemical Monitoring of Propagative Fluctuation of Ascorbate in the Live Rat Brain during Spreading Depolarization

Spreading depolarization (SD) occurs frequently in the injured brain, and its neurochemical effects are detrimental to brain function. We report the first observation that the release of ascorbate, an important neurochemical in the brain, is closely accompanied with SD. Ascorbate was monitored with carbon nanotube (CNT)-sheathed carbon fiber microelectrodes (CFEs). This system features high selectivity and temporal/spatial resolution. With our sensor, we observed a significant increase in the concentration of ascorbate in response to SD induction. Mechanistic studies show a contrasting behavior; with a SD specific inhibitor, release was completely suppressed, whereas with inhibition of commonly employed glutamate transporters, ascorbate release was increased, demonstrating a powerful means of discriminating ascorbate release between disputed pathways. Most importantly, we observed the propagative nature of ascorbate release following SD.