In this communication we review selected experiments involving the use ofcarbon paste electrodes (CPEs) to monitor and measure brain tissue O
2 levels in awakefreely-moving animals. Simultaneous measurements of rCBF were performed using the H
2clearance technique. Voltammetric techniques used include both differential pulse (O
2) andconstant potential amperometry (rCBF). Mild hypoxia and hyperoxia produced rapidchanges (decrease and increase respectively) in the in vivo O
2 signal. Neuronal activation(tail pinch and stimulated grooming) produced similar increases in both O
2 and rCBFindicating that CPE O
2 currents provide an index of increases in rCBF when such increasesexceed O
2 utilization. Saline injection produced a transient increase in the O
2 signal whilechloral hydrate produced slower more long-lasting changes that accompanied the behavioralchanges associated with anaesthesia. Acetazolamide increased O
2 levels through an increasein rCBF.
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