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Behaviorally Induced Glutamate Release Detected in Real-Time with Implanted Biosensor

Vanessa Tolosa, UCLA, Los Angeles, CA 90034, Harold G. Monbouquette, Department of Chemical Engineering, UCLA, CHemical Engineering Department, 5531 Boelter Hall, Los Angeles, CA 90095-1592, and Nigel T. Maidment, Psychiatry and Biobehavioral Sciences, University of California, Los Angeles, Los Angeles, CA 90095.

A micromachined, electroenzymatic glutamate microsensor was tested in the brain of a freely moving rat. The silicon-based probe features a 100 um tip for minimal tissue damage and three 100 x 20 um platinum electrode sites. The working electrodes are coated with an electropolymerized pyrrole film followed by a glutamate oxidase layer. The polypyrrole blocks interferents (e.g., ascorbic acid and dopamine) found in cerebral spinal fluid while allowing hydrogen peroxide, produced from the enzymatic breakdown of glutamate, to reach the platinum electrode surface. Hydrogen peroxide is electrooxidized at the surface giving rise to an amperometric signal proportional to the concentration of glutamate present. The probe is outfitted to a headstage tethered to a potentionstat, allowing the rat to move freely in a behavior box while the sensor is implanted securely in the brain. The rat exhibited normal grooming behavior and activity following probe implantation suggesting the tethered sensor has minimal effects on behavior. Tail pinch was used to behaviorally induce glutamate release and was detected in the striatum. The sensor shows rapid response to glutamate (~1 s) with good signal to noise ratio and excellent rejection of dopamine and ascorbic acid.