POINTseq: Cell-type-specific barcoding reveals single-cell projection architecture of the mouse dopaminergic system

Neural circuits are shaped by the diverse axonal branching patterns of neurons across different cell types. To map these patterns, here we introduce POINTseq (projections of interest by sequencing), a barcoded connectomics method for rapid, cell-type-specific mapping of thousands of single-cell projections per animal. POINTseq leverages viral pseudotyping and cell-type-specific infection to integrate MAPseq-style high-throughput barcoded projection mapping with the established viral-genetic neural circuit analysis toolbox. We validated POINTseq by mapping genetically and projection-defined cell populations in the mouse motor cortex. We then used POINTseq to reconstruct the brain-wide projections of 5,902 individual dopaminergic neurons in the ventral tegmental area (VTA) and substantia nigra pars compacta (SNc). These neurons fall into >25 connectomic cell types, vastly exceeding the known diversity of dopaminergic cells, and form stereotyped projection motifs that may mediate parallel dopamine signaling. These data constitute the anatomical substrate on which the diverse functions of dopamine in the brain are built.