Single-neuron resolution mapping of dopaminergic connectivity across development, adulthood, and degeneration.

Individual midbrain dopamine (mDA) neurons exhibit complex morphologies, a feature that may underlie their different functions and disease vulnerability. However, the developmental programs and wiring principles underlying this morphological complexity, particularly in terms of axonal and dendritic architecture, remain largely unknown. To address this, we developed and employed a unique intersectional genetic strategy in mice (Gucy2c-iCre:Pitx3-FlpE:Ai65D [GPA]) that enables specific sparse labeling of mDA neurons across the midbrain from early developmental stages onward. Using this approach, we generated the largest dataset to date of 3D-reconstructed mDA neurons at key developmental stages, in adulthood, and in models simulating Parkinson's disease-related degeneration. Our work identifies previously uncharacterized morphological features across anatomical and molecular mDA neuron subtypes and during axonal degeneration. Moreover, we identify organizational principles-including pre-target axon sorting and subtype-specific connectivity patterns among ventral tegmental area (VTA) neurons-that offer key entry points for understanding how mDA circuitry is established and functions.