library_construction_protocol: After perfusion with ice-cold PBS, target brain regions (right one-third cerebellum or bilateral pons) were dissected, homogenized in SET buffer (sucrose, Tris-HCl, EDTA, protease and RNase inhibitors), and centrifuged to separate nuclear (P1) and synaptosomal (S1) fractions. Nuclei were isolated from P1 by brief rinsing and resuspension in nuclear lysis buffer, followed by homogenization (cerebellum) or gentle mixing (pons), dilution, incubation on ice, filtration, centrifugation, washing, and staining with SiR-DNA in washing and staining buffer prior to flow cytometry. Synaptosomes were isolated from S1 by centrifugation to obtain synaptosomal pellet (P2), which was resuspended in washing and staining buffer, blocked with Fc receptor blocker, stained with anti-V5-Alexa Fluor 647 and anti-HA-PE antibodies, washed, and incubated with CellBrite 405 membrane dye. Nuclei were sorted by DNA content (SiR-DNA) and GFP expression, while synaptosomes were sorted based on scatter profiles, membrane integrity (CellBrite 405), and double-positivity for V5 and HA, and all sorted samples were collected into tubes containing appropriate collection buffers for downstream processing. Libraries were generated using the Chromium Next GEM Single Cell 3' GEM, Library & Gel Bead Kit v3.1, Chromium Next GEM Chip G, and 10x Chromium Controller (10x Genomics) according to manufacturer's protocol with modifications. For each experiment, approximately 20,000-30,000 individually sorted GFP-positive nuclei or double-positive synaptosomes were loaded into each channel of the chip. For nuclear libraries, cDNA was amplified, size-selected using SPRIselect beads to separate transcriptome and barcode components, and independently constructed into mRNA libraries and barcode libraries. Synaptosome libraries were constructed using barcode-specific amplification without template switching oligonucleotides.