Dual Extracellular Recordings in the Mouse Hippocampus and Prefrontal Cortex

This study present a comprehensive protocol for performing dual, electrode LFP recordings in the mouse hippocampus and the prefrontal cortex to investigate the effects of drugs on LFP properties in these areas. This protocol provides a low cost and ultra-light, brain-signal recording device that is fully optimized for cognitive research in mice. This study provides a means to record signals with high-signal noise ratios in different brain regions, facilitating the investigation of interregional information communication within the brain.

To begin, cut polytetrafluoroethylene-coated tungsten wires to specific lengths for the prefrontal cortex, hippocampus and ground electrode. Cut the brass tube into three-millimeter segments. Using a lighter, remove two millimeters of the coating at the end of each wire, then securely solder the electrode wire to the brass tube.

For the ground electrode, solder an M1.2 stainless steel screw to the electrode and apply phosphoric acid-based flux to the screw to enhance soldering. To begin, place the anesthetized mouse on a heating pad and secure it in a stereotaxic frame. Make an eight-millimeter incision along the midline of the scalp and remove connective tissue from the area.

Align the bregma and lambda landmarks to the same level for accurate electrode placement. Then, drill holes for reference or ground electrodes, anchor screws and active electrodes as specific coordinates. Attach the custom-made electrode to the stereotaxic frame arm and ensure it is perpendicular to the brain.

Implant the electrode in the hippocampus CA1 region. Then, use a powerful adhesive and dental cement to secure the electrodes. Implant two 1.2-millimeter anchor screws to prevent movement.

Next, position the reference or ground electrode in direct contact with the dura mater, two millimeters posterior and two millimeters unilateral to the lambda landmark. Connect the brass-tube side of the electrodes to a multi-channel socket connector, placing the ground electrode in the middle. Use 0.8 millimeter heat-shrink tubing on the exterior of the middle pin for isolation.

Secure the electrodes, anchor screws and connectors with adhesive and dental cement, and allow the animal to recover. To begin, implant electrodes in the hippocampus and the prefrontal cortex of the mouse. After a one-week recovery period, place the animal in a small recording chamber within a Faraday cage to reduce external electrical interference.

Attach the custom head stage for recording. Open the recording software and select a 2.00-kilohertz sampling rate. Then, select each channel and press the space bar to disable all channels except for 13 and 20.

In the hardware bandwidth window, set the lower bandwidth to two hertz and the upper bandwidth to 100 hertz. Adjust the Low-Pass Filter to 100 hertz and the High-Pass Filter to two hertz in the software-filtering window. To choose the storage path, click on select file name, then click Record to initiate the recording.

Start each recording session with a 10-minute habituation period, followed by a 15-minute baseline electroencephalogram recording. After the baseline recording, administer the drug via intraperitoneal injection and continue recording for an additional 30 minutes without delay. The administration of saline did not affect local field potentials, power spectra or hippocampus and prefrontal cortex coherence.

Both retigabine and clozapine showed significant reductions in gamma band power in the hippocampus and prefrontal cortex, as well as the gamma band hippocampus and prefrontal cortex coherence. In contrast, four aminopyridine exhibited enhanced gamma band power in the hippocampus and prefrontal cortex, accompanied by increased coherence within the gamma band between these two regions.