Micro1401 interface

Rats were placed in a stereotaxic frame, and the plane between the bregma and lambda was adjusted to horizontal. An uninsulated tungsten wire placed in the cortex 2 mm anterior to bregma served as a reference electrode, and the stereotaxic frame was connected to the ground. A tungsten microelectrode (0.1–0.9 MΩ) for recording HPC local field potentials was placed in the right dorsal HPC in the stratum lacunosum-moleculare (3.7 mm posterior to the bregma, 2.0–2.2 mm lateral from the midline and 2.4–2.6 mm ventral to the dural surface) [94 ]. During experiments, AC amplifiers (P-511, Grass-Astromed, West Warwick, RI, USA) were used for recording HPC field potentials, with high-pass and low-pass filters set to 1 Hz and 0.3 kHz, respectively. The field activity was displayed using a digital storage oscilloscope (TDS 3014B; Tektronix, Beaverton, OR, USA). Signals were digitized by the Micro 1401 interface (Cambridge Electronic Design, Cambrige, UK) and saved onto a computer hard drive for subsequent off-line analysis (Spike 2.7 Cambridge Electronic Design, Cambridge, UK).

At the end of the recording period (typically 4–6 weeks after the implant surgery), a terminal experiment was performed in five of the animals under pentobarbitone anesthesia (60 mg/kg, i.p.). The olivary neurotoxin 3-acetylpyridine (3-AP; 75 mg/kg in 1 ml/kg saline; Aldrich) or saline was injected intraperitoneally. CFPs were evoked at ∼1.5 × T once every 3 s, and responses were recorded for up to 4 h. A single-channel data acquisition system (Neurolog) was used in conjunction with a Micro 1401 interface (Cambridge Electronic Design) and Spike 2 version 7 (Cambridge Electronic Design) software to capture evoked and spontaneous local field potential (LFP) data (30 Hz to 5 kHz, gain of 1 k Hz, sample rate of 5 kHz). The peak-to-peak amplitude of responses evoked by 20 stimulus trials were averaged every 30 min to study changes in the size of the evoked CFP over time. The same data were also sampled for 30 s at 30 min intervals to investigate changes in the power spectral density (square millivolts per Hertz) in the 200–300 Hz frequency band of the LFP signal (sampled at 0.5 Hz, frequency resolution of ∼1Hz). Spike 2 software was used to analyze both CFP and LFP data, and the results were normalized to baseline at t = −30 min. For LFP data, spectrograms were created using the mtspecgramc.m script from the chronux toolbox in MATLAB (MathWorks; Bokil et al., 2010 (link)).