FIGURE 4.

Local excitatory inputs to CSNs in rat cerebral cortex. The dendrites of CSNs in the motor-associated areas were retrogradely labeled in a Golgi stain-like manner by the injection of tetramethylrhodamine-dextran amine (TMR-DA) into the corticospinal tract in the cervical cord with an acidic vehicle (A; Kaneko et al., 1996). In 500-μm-thick cortical slices containing labeled CSNs, pyramidal/spiny neurons were recorded and labeled intracellularly at each cortical layer (arrows in B–E). The axodendritic appositions between black-labeled axon varicosities and red-visualized dendrites (black arrowheads in F–H) were quantitatively analyzed. In some samples, the appositions were confirmed to make synaptic contacts in electron-microscopic images (I–K′), where black arrowheads and arrows indicated the postsynaptic densities and immunoreaction products for TMR-DA, respectively. Figure (K) is the image next to (K′), in which a white arrow points to the spine neck connecting the unlabeled spine to the TMR-DA-labeled dendrite. (B–K′) Modified with permission from Figures 1 and 8 of Cho et al. (2004b). AT, intracellularly labeled axon terminals; Den, TMR-DA-labeled dendritic profiles. Scale bar in (E) applies to (B–E), that in (H) to (F–H), and that in (K′) to (I–K′).