2.2. Animal experiments

Electroporation was carried out as described previously.²⁵ Briefly, ICR mouse pups (Japan SLC, Shizuoka, Japan) at postnatal day 0‐1 were anesthetized by hypothermia. 2.0 μL of a plasmid DNA mix (~5.0 μg/μL) in PBS was injected into the left lateral ventricle. Platinum Tweezertrodes (7.5 mm) were placed on each side of a mouse head with 6 pulses of 100 V (50 ms; separated by 950 ms) using the Square Wave Electropolator CUY21SC (NEPA GENE). Animals were monitored twice a week until the mice showed neurological symptoms or weight loss. For sick mice, 5‐ethynyl‐2′‐deoxyuridine (EdU) (50 mg/kg body weight) was injected ip, once per day for 4 days prior to necropsy. Intracranial injection (1 × 10⁵ cells) was done on nude mice (BALB/cSlc‐nu/nu; Japan SLC). EdU was injected once 1 day prior to necropsy. All manipulations were carried out with institutional approval (The Institute of Medical Science, The University of Tokyo).