hCS were fixed in 4% paraformaldehyde (PFA) and 8% sucrose for 30 min to 2 hrs. They were then washed in PBS, transferred to 15% sucrose solution overnight at 4°C and then to 30% sucrose for 48–72 hrs. Subsequently, they were transferred into embedding medium (Tissue-Tek OCT Compound 4583, Sakura Finetek), snap-frozen on dry ice and stored at −80°C. For immunohistochemistry, 10 to 20 μm thick sections were cut using a cryostat (Leica). Human brain tissue was fixed in 4% PFA for 48 hrs, washed in PBS and transferred to 30% sucrose for one week. Sections were then embedded in OCT and 30% sucrose (1:1) and sectioned into 30 μm sections using a Leica cryostat.
