Acute slice preparation
Sodium pentobarbital (50 mg/kg in a 1 mL/kg volume) was used for deep anesthesia; animals were then decapitated under its effects. Once removed from the skulls, brains were placed into a frosty sucrose solution containing (in mM): 210 sucrose, 2.8 KCl, 2 MgSO4, 1.25 Na2HPO4, 25 NaHCO3, 1 MgCl2, 1 CaCl2, and 10 D-glucose. The sucrose solution was continuously bubbled with a carbogen mixture (95% O2/5% CO2). Tissue blocks of cerebral hemispheres containing the hippocampus and surrounding areas were sliced at 385 µm thickness in the transversal plane using a vibrating tissue slicer (Leica VT1000S; Nusschloc, Germany). Next, the fresh slices were stabilized at 34° C for 25 to 30 min in an artificial cerebrospinal fluid solution (ACSF; pH ≈ 7.30–7.35) containing (in mM): 125 NaCl, 2.5 KCl, 1.25 Na2HPO4, 25 NaHCO3, 4 MgCl2, 1 CaCl2, and 10 D-glucose. Next, the slices were kept at room temperature for at least 1 hour before any experimental procedure was performed. An individual slice was transferred to a submerged chamber (total volume: 400 µL). The slice was continuously perfused with modified ACSF at a rate of 2.2–2.5 mL/min, with the help of a peristaltic pump (Sci Q400, Watson-Marlow, Wilmington, MA, USA). The modified ACSF (with continuous carbogen bubbling) included the following components (in mM): 125 NaCl, 2.5 KCl, 1.25 Na2HPO4, 25 NaHCO3, 1.5 MgCl2, 2.5 CaCl2, and 10 D-glucose. The recordings were performed at 32.5 ±1 °C.