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Keywords:L-glutamate sensor High-frequency stimulation Field excitatory postsynaptic potential Mouse hippocampal slice Long-term potentiation a b s t r a c t Real-time monitoring of L-glutamate released by high-frequency stimulation in region CA1 of mouse hippocampal slices was performed with a glass capillary-based sensor, in combination with the recoding of excitatory postsynaptic potentials (fEPSPs). A method for extracting L-glutamate currents from the recorded ones was described and applied for determining the level of extracellular L-glutamate released by 100 Hz stimulation. Recording of an L-glutamate current with a current sampling interval of 1 Hz was found to be useful for acquiring a Faradaic current that reflects L-glutamate level released by the highfrequency stimulation of 7 trains, each 20 stimuli at 100 Hz and inter-train interval of 3 s. The L-glutamate level was obtained as 15 ± 6 lM (n = 8) for the persistent enhancement of fEPSPs, i.e., the induction of longterm potentiation (LTP), and 3 ± 1 lM (n = 5) for the case of no LTP induction. Based on these observations, the level of the extracellular L-glutamate was shown to play a crucial role in the induction of LTP.

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