Electrophysiology in vitro

Recordings of field excitatory postsynaptic potentials (fEPSP) were performed using glass electrodes (1–1.5 MΩ) placed in the stratum radiatum. The signal was amplified (Multipatch 700B) and processed using pClamp 10.2 software (Molecular Devices). To stimulate Schaffer collateral fibres, a concentric bipolar stimulating electrode was placed in the stratum radiatum ~200 μm from the stratum pyramidale. The stimulations were applied in two modes: a single pulse mode with stimuli of 3 or 32 mA in amplitude (100 μs) or burst stimulation with a train of 5 pulses of 3 or 32 mA each applied at 20 Hz.

For the whole-cell recordings of the stratum radiatum astrocytes, acute hippocampal slices were placed in a recording chamber mounted on a stage of Olympus BX51WI microscope equipped with a LUMPlanFI/IR 40 × 0.8 objective coupled to an infra-red DIC imaging system. Recordings of resting membrane potential were performed in current-clamp mode using a Multipatch 700B amplifier controlled by the pClamp 10.2 software. The recording electrodes (4.0–5.5 MΩ) were filled with a solution containing (in mM) 130 Cs-methylsulfonate, 2 KCl, 0.5 EGTA, 10 HEPES, 4 Mg-ATP, 0.5 Na-GTP; 0.2 spermine tetrahydrochloride (pH 7.2, ~290 mOsmol). Astrocytes were identified by their morphological features and electrophysiological properties (V_m < –75 mV and low membrane resistance).