Longitudinal ECoG Recording in Alzheimer's Mice

Mice were anesthetized with isoflurane and placed into a stereotaxic device where isoflurane anesthesia continued throughout surgery. A midline incision was made above the skull. Each mouse was implanted with ECoG electrodes consisting of dental screws (Pinnacle Technology, Lawrence, KS; No. 8209: 0.10-in.). Recording electrodes were screwed through cranial holes as follows: over the left frontal cortex (1.5 mm lateral and 2 mm anterior to bregma) and over the right parietal cortex (1.5 mm lateral and 2 mm posterior to bregma), a ground electrode was placed over the visual cortex (1.5 mm lateral and 4.0 mm posterior to bregma), and a reference electrode was placed over the cerebellum (1.5 mm lateral and 6.5 mm posterior to bregma). Electromyogram (EMG) signals were obtained by placing a pair of silver wires into the neck muscles. The screws were connected through silver wires to a common 6-pin connector compatible with the Pinnacle recording device. The screws and connector were fixed to the skull with dental cement. APP/PS1^± miR-155^flx/flx CX3CR1CreER^± and 5xFAD^± miR-155^flx/flx CX3CR1CreER^± mice were implanted at 7 weeks of age. Once the cap was fully dried and set (24 h) mice were fitted with a preamplifier and tether, and connected to the Pinnacle Technology recording system, where they were allowed 1 day to acclimate before recording started. The ECoG and EMG signals were sampled at 400 Hz with low-pass filters of 80 Hz and 100 Hz, respectively. Mice were connected to amplifiers where continuous recordings were made for 7 days to record a baseline reading. Mice were administered 20 mg of tamoxifen via oral gavage at 8 weeks. Continuous recordings persisted in single recording cages under a 12:12 LD cycle, with intermittent video, for 2–5 weeks until recording was stopped or when spontaneous death occurred.