Figure 3. Microglial activation after spinal cord transection includes RGM upregulation.

A, In situ hybridization in control spinal cord wholemount revealed the presence of small RGM-expressing cells (black arrow) on the surface of the spinal cord. Scale bar, 20 μm. B, Fluorescein-labeled GSL I–isolectin B₄ histochemistry revealed several lectin-labeled cells in control spinal cord (white arrowheads) including RGM–expressing cells (black arrow). In controls, few isolectin B₄-labeled profiles were RGM-positive. C, Two weeks after spinal cord transection, increased numbers of small, rounded cells (white arrows), reminiscent of activated microglia/macrophages, were labeled with the RGM probe, and a dense accumulation of reactive macrophages/microglial cells, as evidenced by increasing IB₄ lectin reactivity, was seen (D). Most of the lectin-labeled cells co-expressed RGM mRNA (white arrows). E, Only a few RGM–expressing cells were detected in the spinal cord 1 month after injury. Some slender, elongated RGM-expressing cells (white arrows) resembled the macrophages/microglial cells seen in control spinal cord (Fig. 3A). F, At this time, numerous small, round macrophages/microglial cells (white arrowheads) could be detected by labeling with IB₄ lectin in the spinal cord, but these were never labeled by the RGM probe. On the other hand, there were some larger, elongated RGM-expressing cells that also were labeled with IB₄ lectin (white arrows). G and H, RGM-expressing cells exhibited very small rounded cell bodies (no larger than 5 μm) and possessed obvious non-neuronal morphology (black arrows). Scale bar, 20 μm(G, H).