Genetic Single Neuron Anatomy Reveals Fine Granularity of Cortical Axo-Axonic Cells

Summary: Parsing diverse nerve cells into biological types is necessary for understanding neural circuit organization. Morphology is an intuitive criterion for neuronal classification and a proxy of connectivity, but morphological diversity and variability often preclude resolving the granularity of neuron types. Combining genetic labeling with high-resolution, large-volume light microscopy, we established a single neuron anatomy platform that resolves, registers, and quantifies complete neuron morphologies in the mouse brain. We discovered that cortical axo-axonic cells (AACs), a cardinal GABAergic interneuron type that controls pyramidal neuron (PyN) spiking at axon initial segments, consist of multiple subtypes distinguished by highly laminar-specific soma position and dendritic and axonal arborization patterns. Whereas the laminar arrangements of AAC dendrites reflect differential recruitment by input streams, the laminar distribution and local geometry of AAC axons enable differential innervation of PyN ensembles. This platform will facilitate genetically targeted, high-resolution, and scalable single neuron anatomy in the mouse brain. : Wang et al. combine mouse genetic labeling with high-resolution, large-volume light microscopy and establish a single-neuron anatomy platform. They show that cortical axo-axonic cells, a GABAergic interneuron type that innervates pyramidal neurons at axon initial segments, consist of multiple subtypes distinguished by laminar position and dendritic and axonal arborization. Keywords: GABAergic interneurons, axo-axonic cells, AACs, chandelier cells, ChCs, neuron subtypes, genetic single neuron anatomy, gSNA, fMOST