Rc 22c

The recording chamber (RC-22C; Warner Instruments) was fitted with Ag/AgCl sintered pellet electrodes (4.37 mm × L, 1.20 mm × H, separation distance 5.60 mm) insulated such that only the tissue in the camera’s field of view would be polarized as shown in Fig. 1a. Extracellular pipettes (4–6 MΩ) were pulled from thick-walled borosilicate glass capillaries with filaments (OD = 1.5 mm, ID = 0.86 mm; Sutter Instruments) and filled with 3 M KCl. The injection pipette was inserted into the middle top of layer II/III with the second pipette located directly inline ~900 µm in the deeper layers of the tissue near the bottom of the cortex. Differential voltage measurements were acquired (MultiClamp 700A; Axon Instruments) as a feedback measurement of the field inside the tissue. In order to guarantee the field strength a Labview interface was used to control a National Instruments BNC-2120 signal generator and drive voltage commands to a constant current isolated stimulator (Model 2200; AM-Systems) as in Fig. 1b. A proportional integral differential (PID) feedback control system was implemented on the differential voltage measurement measured within the cortical tissue, which allowed precise and reproducible electric field strengths to be commanded for each stimulus trial (Fig. 1c).

Acute hippocampal transversal slices were prepared from 6-month-old WT, AEP^−/−, 5XFAD and 5XFAD/AEP^−/− mice as described previously63 (link). Briefly, mice hippocampal slices were placed in a recording chamber (RC-22C, Warner Instruments) on the stage of an upright microscope (Olympus CX-31) and perfused at a rate of 3 ml min⁻¹ with a-CSF (containing 1 mM MgCl₂) at 23–24 °C. A 0.1 MΩ tungsten monopolar electrode was used to stimulate the Schaffer collaterals. The field excitatory postsynaptic potentials (fEPSPs) were recorded in CA1 stratum radiatum by a glass microelectrode filled with a-CSF with resistance of 3–4 MΩ. The stimulation output (Master-8; AMPI, Jerusalem) was controlled by the trigger function of an EPC9 amplifier (HEKA Elektronik, Lambrecht, Germany). fEPSPs were recorded under current-clamp mode. Data were filtered at 3 kHz and digitized at sampling rates of 20 kHz using Pulse software (HEKA Elektronik). The stimulus intensity (0.1 ms duration, 3–4.5 V) was set to evoke 40% of the maximum fEPSP and the test pulse was applied at a rate of 0.033 Hz. LTP of fEPSPs was induced by three theta-burst stimulation, it is four pulses at 100 Hz, repeated three times with a 200-ms interval).