C57BL/6 mice were purchased from Jackson Laboratories. Brains were extracted from mice and substantia nigra regions were dissected according to the Allen Brain Reference Atlas. For each sample, dissected brain tissues were pooled from 4-5 C57BL/6 mice to obtain enough nuclei for single nucleus multiome for each biological replicate, and two biological replicates were performed for each age stage. Nucleus were isolated from the directions using the protocol suggested for use with the chromium Next GEM Single Cell Multiome ATAC+Gene Expression protocol (CG000338). Libraries were performed immediately for each sample as per Chromium Next GEM Single Cell Multiome ATAC + Gene Expression User Guide (CG000338). Chromium Single Cell Multiome ATAC + Gene Expression