Optical recording system for monitoring neural activity in deep region of the brain.

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Optical methods for monitoring cellular transmembrane voltage activity, using voltage-sensitive dyes, offer many advantages over conventional electrophysiological techniques. However, when applying to the central nervous system, the recording has been limited to the surface of the brain. To overcome this difficulty, we developed a new system to measure the neural activity in the deep region of the central nervous system with a single fiber optics, used for both excitation and detection of the fluorescence of the voltage-sensitive dye that is previously loaded. This system consists of an excitation light source, a fiber optics, a fluorescence detector and a recording unit. The light emitted from a tungsten-halogen lamp is fed into an interference filter, and the excitation light obtained is guided to the preparation through the fiber optics. The emitted fluorescence is collected by the same fiber connected to a photodiode whose output is fed into the recording unit. The timing of the data acquisition is regulated by the recorder. The excitation and emission filters can be chosen so as to give the best fluorescence signal with the used voltage-sensitive dye.This new system has first been applied to a vagus nerve bundle to evaluate the sensitivity of the device. The preparation was stained with a membrane-impermeable voltage-sensitive styryl dye (RH795). The optical signals were evoked by a brief square-current pulse applied with a micro-suction electrode to the vagus nerve. In the evoked optical signals, action potential component was detedted with a relatively good S/N ratio. The optical signal was on the order of 10^<-3> in a fractional change. Because of the good S/N ratio as well as good temporal resolution, this new optical recording system was confirmed to be well suitable for analyzing the neural activity in the deep region of the central nervous system.