Dendritic morphology of corticospinal and crossed-corticostriatal neurons in mouse primary motor cortex

In neocortex, layer 5 is home to at least two types of pyramidal neurons, which can be distinguished by their projection targets - with roughly half projecting to subcerebral targets (pyramidal-tract, PT), including the spinal cord, and the rest extending axons only within the ipsi- and contra-lateral telencephalon (intratelencephalic, IT). These classes differ in intrinsic electrophysiology as well as local and long-range synaptic connectivity. They also differ in dendritic morphology, with PT neurons forming a ``thick tuft'' in layer 1, while IT neurons have ``thin'' tufts, or none at all. In rat frontal cortex, a quantitative analysis found additional characteristic differences between classes, and a sublaminar differentiation within ITs (Morishima & Kawaguchi, 2006). In mouse motor cortex, the quantitative dendritic differences between these classes have not been fully characterized, especially in the non-tuft regions.