ABSTRACT: We sought to define and compare the diversity of cells across many brain areas, including various white matter (WM) regions, the volume and complexity of which is limited in mouse brain. We employed magnetic resonance (MR) image-guided sampling and snRNA-seq to survey the transcriptome at cellular resolution. Tissue types included WM (frontal, parietal, temporal), corpus callosum (anterior, posterior), optic tract, cerebral cortex (frontal, parietal, temporal, occipital, cingulate), caudate, hippocampus, lateral geniculate nucleus, cerebellum, thalamus, midbrain, pons, and cervical spinal cord. We profiled nuclei from confined regions (cylinders of tissue 2 mm in diameter and 3 mm in height, ~10 μL), which can be consistently located and repeated based on MR images from animal to animal. We analyze and discuss the global landscape of neural cell types across brain regions, comparing compositional differences of subpopulations of glia in GM and WM, modeling intercellular communication in each milieu, and cataloging their contributions to neurological disorders.