Figure 6.

Pyramidal-tract but not intratelencephalic axons collateralize in the GPe. a, Single-axon reconstruction of a layer 5 (L5) cortico-pallidal neuron (neuron #AA0122) in the motor cortex. Data are adapted from the MouseLight project (http://mouselight.janelia.org). The axonal projection pattern is consistent with a pyramidal-tract (PT)-type neuron. Inset: axonal arborization of 10 different cortical neurons. GPe and axonal endpoint were used as the target location and structure queries, respectively. b, Injection site center of mass of Sim1-Cre (L5-PT) plotted and spatially clustered (n = 62, triangles). These injection sites correspond to vibrissal, forelimb, and orofacial somatosensory cortices (vS1, fS1, and orfS1); vibrissal, forelimb, and lower limb motor cortices (vM1, fM1, and llM1); and frontal areas (anterior lateral motor cortex (ALM) and secondary motor cortex (M2)). Eight clusters shown in red (M2), orange (ALM), purple (vM1), burgundy (fM1), green (llM1), yellow (fS1), teal (vS1), and gray (orfS1). Indeterminate injection sites are white. Sites are superimposed on an image of the dorsal surface of mouse cortex. Black cross marks indicate midline and bregma. For simplicity, injection sites in Tlx3-Cre (L5-IT) are not shown (see Hooks et al., 2018, for further information). c, d, Tlx3-Cre (IT-type) projections from fM1 in dStr but not GPe. Sim1-Cre (PT-type) projections from fS1 (left) and fM1 (right) in dStr and GPe (pink arrows). Inset: Coronal images of injection sites in Tlx3-Cre and Sim1-Cre showing the cell body locations and their axonal projections. e, Coronal images of the average normalized PT-type projection to GPe from eight cortical areas. Each column is a cortical projection, with rows going from anterior (top) to posterior (bottom). Each projection is normalized for comparison within the projection.