2.2. Surgical Procedures

Large intact skull transcranial windows were installed on mice, as described in Ref. ¹⁵. Mice were anesthetized with 2% isoflurane and maintained with 1.5% isoflurane in air, and placed in a stereotactic frame. Body temperature was maintained at 37°C using a feedback-regulated heating pad with a rectal probe. Mice were injected under the scalp with lidocaine (0.1 mL, 0.2%) and subcutaneously with a saline solution containing buprenorphine (2mg/mL), atropine (3μg/mL), and glucose (20 mM). The fur on the top of the head was removed using scissors, and the skin was prepared with a triple scrub of 0.1% betadine in water followed by 70% ethanol. Skin on the top of the head was cut and removed, and fascia and connective tissues on the surface of the skull were removed so that the skull surface was completely clear of debris and dry. Clear dental cement, prepared by mixing 1 scoop of Metabond powder, 6 drops of C&B Metabond Quick Base, and one drop of C&B Universal catalyst (Parkell, Edgewood, New York) was used to glue a titanium head-fixing bar (22×3.25×2.8mm) to the cerebellar plate, directly posterior to the lambda.³⁷ A layer of dental adhesive was applied directly on the skull, and a precut cover glass was placed gently on top of the mixture before it solidified.^15,37 For two of the AAV-PHP.eB mice, a stainless steel setscrew¹⁵ was used for head-fixing instead of the titanium bar. Animals were monitored daily for 1 week postsurgery.