Omniplex d

Mice with stable baseline spontaneous recurrent seizures were used for in vivo LFP recordings using an OmniPlex^® D neural data acquisition system (Plexon, Dallas, TX, USA) (n=10 per group). To record LFPs, two stainless steel screws into the anterior cranium and a U-shaped frame for holding the head were cemented to the skull, and a microwire array (25 μm in diameter, 16-channel, Yisikepu, China) for LFP recording was implanted into the left hippocampus. LFP activity was continuously recorded and digitized at 4 kHz and filtered (0.1–1,000 Hz) and pre-amplified (×1,000) for 30 min after the baseline was stabilized. For each recording session, we analyzed the periods of sustained epileptic discharges. The epileptiform-like discharge events were analyzed using NeuroExplorer^® v5.0 (Plexon, Dallas, TX, USA).

Stereotrodes were lowered in steps of 60 µm before each day of recording. The neuronal activity and the onset of pin prick stimulation were simultaneously recorded with acquisition equipment (OmniPlex D with Digital Headstage Processor, Plexon). Signals were monitored and recorded at a sample rate of 40 kHz. To get spike activity, the raw data were band pass filtered from 300 Hz to 7.5 kHz with subsequent offline sorting, using commercial software (Offline Sorter, Plexon). Trials were aligned to the initiation of the peripheral stimulus to compute the peri-stimulus time histograms (PSTHs) for each single unit using MATLAB (Mathworks).

At 7 days before the first recording session, rats were habituated to the OF arena and recording equipment. During habituation days, rats were allowed to freely explore the OF for 20 min and restrained lightly to connect them to the tethered and optic patch cable. On the last 2 days of habituation, the rats were familiarized to food treats (each treat: ~1/8 fruit Loops) that were thrown into the maze from above every 5 min to encourage rats to move around the arena. Neural data was acquired with a Plexon OmniplexD recording system (wide band: 40 kHz) and the PlexControl data acquisition software via implanted 50 µm Teflon-coated stainless steel electrode wires connected to an electrode interface board (Neuralynx). LFP were sampled at 1 kHz.

In vivo optostimulation of Gad2Cre⁺ cells was performed using a 40 kHz OmniPlex D (version 1.11; Plexon) neural data acquisition system and preamplified using a MiniDigi preamplifier (16 channels; Plexon). The experimental protocol used was modified from a previously described procedure (Sathyanesan et al., 2018 (link)). In summary, a 25 Hz pulse train was bilaterally applied to hippocampal CA1, each with a duration of 30 s. A total of 25 pulses was delivered per treatment at intervals of 30 s. The initial phase of the optogenetic stimulation was performed with mice placed in an empty rectangular-shaped Plexiglas box (12 × 6 cm) used for the novel object recognition test (NORT). During the last 10 min of stimulation, mice were transferred into a similar apparatus with identical objects to allow for the performance of the familiarization phase of the NORT. Control mice were not subjected to optogenetic stimulation. Chemogenetic stimulation of DREADD virus-transfected Gad2Cre mice was performed through intraperitoneal injection of CNO at a dose of 50 mg/kg body weight 45 min before the familiarization test of the NORT. Control mice were injected with saline. Learning behavior was performed 6 h postoptogenetic or chemogenic stimulation as described above.