Hippocampal Neural Recording in Rats

Four male and three female Long-Evans rats (300–500 grams) were used in this study. All surgeries were performed on isoflurane anesthetized animals head fixed on a stereotaxic frame. After removing hair from the head, the incision area was cleaned using alcohol and betadine. Next, an incision was made to expose the skull underneath. The skull was cleaned of tissues and blood, after which hydrogen peroxide was applied. Coordinates for probe implantation were marked above the dorsal hippocampus (AP: −3.36, ML: ±2.2) following measurement of bregma and lambda. Craniotomies were drilled at the marked location. Using a blunt needle, the dura was removed carefully to expose the brain surface. After cessation of bleeding, animals were implanted with 64 channel (8 shank “Buzsaki” probe; Neuronexus, MI; X animals) or 128 channel (8 shanks, Diagnostic Biochips, MD, 7-X animals) silicon probes. Ground and reference screws were placed over the cerebellum. Craniotomy was covered with DOWSIL silicone gel (3–4680, Dow Corning, Midland, MI) and wax. A copper mesh was built around the implant for protection and electrical shielding. All procedures involving animals were approved by the Animal Care and Use Committee at the University of Michigan.