Tungsten electrodes

P2 rats (mean weight: 7.78 g; n=20) were surgically implanted with two EEG electrodes, two EMG electrodes, and one reference electrode. Anesthesia was induced with 2% isoflurane and maintained with 1.5% isoflurane and 30% oxygen. After a midline vertical incision to expose the skull, forceps were used to remove any connective tissue, and the skull was cleaned and dried with 3% hydrogen peroxide for electrode placement. Two holes (0.5 mm) for EEG electrode implantation were made 2 mm before the lambda and 2 mm lateral from midline sutures using a hand-held micro-drill. In addition, a 1 mm hole was drilled 3 mm under the lambda to allow implantation of the reference electrode. Two tungsten electrodes (0.003-inch outer diameter; A-M Systems, 131 Business Park Loop Sequim, WA, USA) were implanted bilaterally in the parietal cortex with a small amount of dental cement added to secure the electrodes to the skull. Two insulated stainless-steel wire electrodes were inserted into the nuchal muscles for EMG recordings, with the wire bent to follow the curvature of the head and neck. The five electrodes were connected to a 6-pin electrode pedestal, and the weight of the entire apparatus was approximately 220–230 mg. After the procedure, the pups were allowed to recover until the return of spontaneous movements, following which they were reunited with their mothers.