Digital lynx sx

Anesthesia was induced with 4% isoflurane/air mixture followed by 1.3 g/kg of urethane injected i.p. to produce a long-lasting unconscious state with sleep-like brain state alterations [69 (link), 82 (link)]. The depth of anesthesia was controlled by testing the absence of peripheral reflexes of the animal, and a 0.3 g/kg bolus of urethane was given if animal showed signs of elevating level of consciousness, such as muscle movements or vocalizations. Surgery was identical to the chronic implantations except that the opening for the cortical screw was omitted, and the ground and reference electrodes were prepared from TEFLON-insulated 125 µm silver wire. Hippocampal LFP was recorded using a linear 16-channel silicon probe (Neuronexus A1 × 16-5 mm-100–177), which was slowly descended into the dorsal hippocampus to maximal (tip) depth (DV) of 2.1–2.2 mm corresponding to the DG hilus. Correct position was confirmed from the characteristic neurophysiological signals from hippocampal subfields and known anatomical distances: dentate spikes identifying the DG hilus, and SPW-ripples identifying CA1. For some animals, the probe was also dipped into Neurotracer DiI before insertion and the probe position was later histologically confirmed. LFP signals were amplified with Neuralynx HS-18 amplifier and digitized with Neuralynx Digital Lynx SX acquisition system at 30 kHz.

Multisite extracellular recordings were performed unilaterally in the mPFC of P23-25 and P38-40 mice. The adapter for head fixation was implanted at least 5 days before recordings. Under isoflurane anesthesia (5% induction, 2.5% maintenance), a metal head-post (Luigs and Neumann, Germany) was attached to the skull with dental cement and a craniotomy was performed above the mPFC (0.5–2.0 mm anterior to bregma, 0.1–0.5 mm right to the midline) and protected by a customized synthetic window. A silver wire was implanted between skull and brain tissue above the cerebellum and served as ground and reference. 0.5% bupivacaine/1% lidocaine was locally applied to cutting edges. After recovery from anesthesia, mice were returned to their home cage. After recovery from the surgery, mice were accustomed to head-fixation and trained to run on a custom-made spinning disc. For non-anesthetized recordings, craniotomies were uncovered and multi-site electrodes (NeuroNexus, MI, USA) were inserted into the mPFC (one-shank, A1 × 16 recording sites, 100 µm spacing, 2.0 mm deep).
Extracellular signals were band-pass filtered (0.1–9000 Hz) and digitized (32 kHz) with a multichannel extracellular amplifier (Digital Lynx SX; Neuralynx, Bozeman, MO, USA). Electrode position was confirmed in brain slices postmortem.

Starting two to three days after surgery, tetrodes were lowered into the brain by ∼0.25 mm daily. When spikes were observed, experiments started at least 1 h after lowering the tetrodes to stabilize tissue drift. Extracellular spikes in the left trunk somatosensory cortex of the observer animal were recorded at 32 kHz sampling rate and bandpass-filtered between 0.6 and 6 kHz using Cheetah software, and DigitalLynx SX (Neuralynx, Bozeman, MT, USA).

Concurrent home-cage recordings (n = 3 mice implanted with single shank probes in CA1) were performed using the TaiNi and tethered Digital Lynx SX (Software: Cheetah v5.6.0, Neuralynx, USA) recording systems by utilising a signal splitter placed inline between the silicon probe and headstages. For the Neuralynx recordings, data was band-pass filtered at 0.5–9000 Hz, and sampled at 20 KHz.

One-shank electrodes (NeuroNexus, MI, USA) with 16 recording sites were inserted into dorsal (depth 0.5–1.2 mm, angle 0°) or ventral OB (1.4–1.8 mm, angle 0°) as well as in LEC (depth: 2 mm, angle: 10° from the vertical plane). Two-shank optoelectrodes (Buzsaki16-OA16LP, NeuroNexus, Ann Arbor, MI, USA) with 8 recordings sites on each shank aligned with an optical fiber ending 40 μm above the top recording site were inserted into ventral OB. Extracellular signals were band-pass filtered (0.1 Hz–9 kHz) and digitized (32 kHz) by a multichannel amplifier (Digital Lynx SX; Neuralynx, Bozeman, MT, USA) and Cheetah acquisition software (Neuralynx).

Extracellular action potentials of single units were recorded at a rate of 32 kHz (Digital Lynx SX, Neuralynx, Inc). Unit activity was band-pass filtered at 600 Hz to 6 kHz. Each tetrode could be recorded differentially, being referenced by one electrode of another tetrode or the ground connected to one of the jewellers’ screws. Recordings were done with Neuralynx’ data acquisition software Cheetah v5.6.3 (https://neuralynx.com).
To sample different neurons throughout the experimental period, we lowered the position of the tetrodes along the dorsoventral axis of the mPFC. Lowering was done for 50 µm at the end of every second experimental session to allow for stabilization until the next experiment.