Multifunctional biosensors for analysis of brain functions with measurements of bioactive substances in the brain.

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The purpose of this project was to develop multifunctional biosensors which can detect local kinetics of endogenous substances influencing neuronal activity in the central nervous system. New type of biogenic amine sensors using voltammetry system was developed. We examined characteristics of the sensors in vitro and tried to apply in vivo conditions.As a working electrode of in vivo voltammetry, carbon fiber electrodes were used. These electrodes were electrochemically activated beforehand by applying a trinagular current pulses (0-2V, 70 Hz, 60 sec)in 0.1 M H SO sulution. Calibration curves (oxidation current vs. concentration) of DOPAC (metabolite of dopamine) and 5-HIAA (metabolite of serotonin) using these electodes were confirmed to be linear between 1muM and 10muM concentration.To evaluate the function of probe, serotonin release in the lateral hypothalamic area (LHA; feeding center) was measured continuously in freely moving rats. The carbon fiber electrode was combined with teflon-coated platinum-iridium wires which enabled to record the neuronal activity for long period. The results indicated that the serotonin release in the LHA began to increase at around 1800 hr and reached to the maximum level at around 2100 hr, then gradually decreased and returned to the level at around 1800 hr within 3 or 4 hours. Thirty neurons recorded simultaneously with serotonin release, 12 neurons (40%) increased their activity, 7 (23%) decreased and 11 (37%) showed no change. The results indicate that this kind of probe is useful for analysis of the brain functions with measurements of bioactive substances.