Extracellular glutamate: on-line monitoring using microdialysis coupled to enzyme-amperometric analysis.

An enzyme-amperometric detector cell is described for flow analysis of glutamate in dialysate emerging from an implanted microdialysis probe. Its small size allows it to be placed within a few centimetres of the animal preparation, reducing the delay for data acquisition to around 2 min. The selectivity is provided by glutamate oxidase, immobilised with glutaraldehyde on surfaces adjacent to the 3-electrode system. A film of 1,2-diaminobenzene, electropolymerized on the platinum working electrode, eliminates interference from ascorbic acid and other endogenous electroactive compounds. The high sensitivity (< 0.5 mumol/l) and fast response time of the cell (90% of maximum response in 30 s) make it particularly suitable for investigating conditions that produce rapid changes in brain extracellular glutamate. This is illustrated by monitoring changes in extracellular glutamate subsequent to cardiac arrest, and K(+)-induced local depolarization.