Simultaneous monitoring of excitatory postsynaptic potentials and extracellular l-glutamate in mouse hippocampal slices

Simultaneous monitoring of amperometric currents at a glass capillary sensor based on recombinant GluOx and field excitatory postsynaptic potentials (fEPSPs) were performed in region CA1 of mouse hippocampal slices. A transient increase in the glutamate current relative to the basal one at control stimulation (0.052 Hz) was evoked by stimulation at 2 Hz for 2 min. The magnitude of the glutamate current was dependent on the intensity (current) of a 2 Hz stimulus and reflected the slope of the fEPSP. The in situ calibration of the l-glutamate sensor revealed that the extracellular concentration of l-glutamate released by 2 Hz stimulation before tetanus is in the range from 0.8 to 2.2 μM and it is enhanced after tetanic stimulation. The l-glutamate level at a test stimulus (0.052 Hz) was estimated to be 32 nM. The recombinant GluOx-based sensor exhibited weak responses to glutamine above 300 μM and l-aspartic acid above 200 μM. The potential use of a glass capillary sensor in combination with fEPSP measurements for electrophysiological study is discussed.