Fig. 5.

Changes in terminal SCs correlate with the loss of nerve terminal branches from GGF2-treated muscles. Junctions were triple-labeled as in Figure 2. In the color montages (D, H, L), anti-s100 is displayed in blue, anti-neurofilament and anti-synaptophysin are displayed in green, and BTx is displayed in red. A–D, A junction from a P16 control muscle. Note in D the precise overlap of terminal SCs (A), nerve terminal branches (B), and AChRs (C).E–H, A junction from a P16 soleus muscle treated with GGF2 for 5 d. Terminal SCs at this junction (E, H) appear to have migrated off the endplate. Nerve terminal branches have been lost from most of the areas of this endplate that are no longer covered by terminal SCs. Terminal branches that remained in the absence of SC coverage (arrows, F, H) had a punctate labeling pattern and were probably in the process of being retracted. AChRs (G, H) at this endplate remained well clustered, although portions were no longer covered by either nerve terminal branches or terminal SCs. I–L, A junction from a P13 soleus muscle treated with GGF2 for 2 d. At this junction two terminal SCs have migrated off the endplate (I, L). The loss of coverage by the terminal SC at the top of the junction (apparently by movement of the upper SC) is correlated with an absence of neurofilament/synaptophysin staining in this area of the endplate, although not with a decreased staining intensity of the underlying AChRs (arrow, K, L). At the bottom of this junction a terminal SC has migrated off the endplate, leaving only a thin veil covering the underlying terminal (I, L, large arrowhead). This SC change is not associated with any change in the alignment of nerve terminal branches and AChRs (small arrowhead, J–L). Scale bar, 20 μm.