Gbx2 identifies two amacrine cell subtypes with distinct molecular, morphological, and physiological properties

Our understanding of how the nervous system works is limited by our ability to identify the neuronal subtypes that comprise functional circuits. Using a genetic approach, we show that the transcription factor Gbx2 labels two amacrine cell (AC) subtypes in the mouse retina that have distinct morphological, physiological, and molecular properties. One subtype of Gbx2+ ACs are likely the previously characterized On-type GABAergic CRH-1 AC. The other Gbx2+ AC population is a previously uncharacterized non-GABAergic, non-Glycinergic (nGnG) AC subtype. Gbx2+ nGnG ACs are On-Off type cells with asymmetric dendritic arbors. Gbx2+ nGnG ACs also exhibit tracer coupling to bipolar cells (BCs) through gap junctions that are modulated by dopamine signaling. This study genetically identifies a previously uncharacterized AC subtype and reveals an unusual AC-BC connectivity through gap junctions that may provide a novel model of synaptic communication and visual circuit function.