Cell Type-Specific Organization excitatory neurons in Rat Vibrissal Motor Cortex

Amina Javadova1, Rajeevan T. Narayanan1, Marcel Oberlaender1

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Vibrissal somatosensory cortex (vS1; i.e., barrel cortex) and vibrissal motor cortex (vM1) are the two key structures involved in somatosensation in rodents. Although structural and functional properties of individual neurons of vS1 are known, we know very little about vM1. We define the location and extension of vM1 using trans-synaptic rabies virus on to the intrinsic muscles of the rat whiskers. Using cell-attached recording and biocytin labeling in vivo, we recorded electrophysiological properties and reconstructed dendrite-axon morphologies of neurons of vM1. Whisker evoked electrophysiological responses were high in L5A of vM1, whereas L5B showed higher responses in vS1. The morphological classification of neurons revealed that both vS1 and vM1 are composed of similar canonical cell types. Within these cell-types, the field span of dendrites is area-specific, not cell type-specific. For instance, the basal dendrite width appeared to be larger in vM1 compared to vS1. The axonal projection pattern is both cell type-specific and area-specific. For instance, axons in L5B neurons of vM1 showed more elaborate arborization, whereas L5B axons of vS1 were sparse. We conclude that both vM1 and vS1 preserve basic structural, organizational principles; however, the morphological properties of cell types are specific to the cortical area that they are located in.