Determination of the molecular properties of genetically targeted cell types has led to fundamental insights into mouse brain function and dysfunction. Here, we report an efficient strategy for precise exploration of gene expression events in specific cell types in a broad range of species. We demonstrate that classically defined, homologous neuronal and glial cell types differ between rodent and human by the expression of hundreds of orthologous, cell specific genes. Confirmation that these genes are differentially active was obtained using epigenetic mapping, quantitative PCR, and immunofluorescence localization. Studies of sixteen human postmortem brains revealed cell-specific molecular responses to aging, and the induction of a shared, robust response to an unknown external event experienced by three donors. Our data establish a comprehensive approach for analysis of unique molecular events associated with specific circuits and cell types in a wide variety of human conditions. Overall design: RNA purified from nuclei or cytoplasm from mouse, rat, or human cerebellum. ATAC-seq was also performed using cerebellar nuclei from the three species.