Implant procedure

Given the size and weight of the drive it is recommended to implant adult mice, weighing at least 28-30g (approximately 14 weeks old). Mice were anaesthetized with 1.25% – 2% isoflurane and injected with analgesia (Carprofen, 5 mg/kg SC). Mice were placed in a stereotaxic frame and antibacterial ophthalmic ointment (Alcon, UK) was applied to the eyes. A circular piece of dorsal scalp (approximately 1.5 cm in diameter) was removed and the underlying skull was cleaned and dried. 3 stainless steel M0.8 screws were used to secure the drive (1 ground screw in the frontal plate, 1 screw in the parietal plate opposite to microdrive, 1 screw in the occipital plate).

For the CA1 implant, a craniotomy was made over the right cortex (top-left corner at AP: -1.20 mm; ML: 0.6 mm relative to bregma; bottom-right corner at AP: -2.30 mm; ML: 2.10 mm relative to bregma) using a 0.9 burr drill. The dura was removed and the array of the drive was slowly lowered into the brain with the silicon probe shaft out of the array and already adjusted at the final depth (≈ 2.00 mm for CA1 implant). The guide tube array was lowered right above the brain surface and the craniotomy was filled with sterile Vaseline to protect the brain and the array from cement flowing in. The drive was cemented onto the skull using dental adhesive (Superbond C&B, Sun Medical, Japan). In order to obtain a solid structure it is important to start applying the dental adhesive from the exposed skull, covering well the ground screws, and then build up to the body of the drive. Once the dental adhesive dried, and the drive was well secured tot he scalp, tetrodes were individually lowered into the brain (5 turns - ≈ 900µm) using the screw-spring mechanism.

In order to avoid damage to the implant it is recommended to single house the animals after the implant procedure. Mice igloo with a larger entrance and ceiling should be used. Enrichment (e.g. running wheel) can be introduced in the cage and safely used by the implanted animal. When implanting at an angle it is recommended to leave the silicon probe inside the guide tube and lower it at the end of the surgery. This should reduce the amount of damage to the brain and improve the precision of the implant location. Additionally, when positioning the drive over the craniotomy, pay extra attention to the position of the angled guide tube, which should be perfectly aligned with the brain surface.