Establishment of a new method detecting neural activity using two-dimensional photon counting of ultraweak biochemiluminescence

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Using a silicon avalanche photodiode we developed a single-photon detector system which could detect ultraweak biochemiluminescence emitted from nervous systems. Within the wavelength of 400-900 nm, the total quantum efficiency was 3-5% and the noise-equivalent power was in the order of 10^<-19>W utilizing this system. Using this system we could make a device detecting ultraweak biochemiluminescence from brain slices. Under complete darkness this ultraweak biochemiluminescence light was guided to a light detector by taperfibers having an opening of 150mum in a diameter and detected. When the biochemiluminescence light emitted from cultured rat hippocampal brain slices was detected using this system, 10^<-18>W/mm^2 order of the ultraweak biochemiluminescence light was successfully detected. This biochemiluminescence light emitted from the hippocampal slices increased by depolarization using KCl and decreased by the neural suppression using tetrodotoxin. From these results, it is shown that the strength of the chemiluminescence emitted from the hippocampal slices altered in parallel with that of neural activity. Furthermore, biochemiluminescence was determined for at most 72h from the hypothalamic suprachiasmatic nuclei (SCN) of rats which is a circadian oscillator in mammals. The strength of the biochemiluminescence from the SCN had 2 peaks in their subjective day and nights, respectively. The mechanism of the generation of biochemiluminescence from these brain slices and the reason why 2 peaks existed in that in the SCN are now under investigation. In this study, it was clarified that ultraweak biochemiluminescence emitted from rat brain slices altered in parallel with neural activity. Now, we are trying to get 2 dimensional determination of these ultraweak biochemiluminescence using ARUGUS-50 (Hamamatsu Photonics, Co., Japan) .