2.2. Slice preparation and data acquisition
Mice were deeply anesthetized with isoflurane and decapitated. Brains were rapidly removed and placed in cold (4-8 Co) carbogenated (5% CO2 / 95% O2) artificial cerebrospinal fluid (aCSF) containing (in mM) 129 NaCl, 21 NaHCO3, 3 KCl, 1.6 CaCl2, 1.8 MgSO4, 1.25 NaH2PO4 and 10 glucose. Slices that contain ventral-to-mid hippocampal formation and entorhinal cortex were obtained by cutting horizontal brain slices at an angle of about 12° in the fronto-occipital direction. Slices were transferred to an interface-type chamber perfused with aCSF at 32 ± 0.5 °C (flow rate: 2.0 ± 0.2 ml / min, pH 7.4, osmolarity ~300 mosmol / kg). Slices were incubated at least for one hour before commencing the recordings. Signals were pre-amplified using a custom-made amplifier and low-pass filtered at 3 kHz, after which they were sampled at a frequency of 5 kHz and stored on a computer hard disc for off-line analysis (Cambridge Electronic Design, Cambridge, UK).