Fig. 3.

Neonatal muscles exposed to GGF2 for 10 d are characterized by robust axonal sprouting. Normally innervated (A) and GGF2-treated P14 soleus muscles (B–E). Muscles were labeled as in Figure 2.A, In normally innervated muscles, motor axons ramify shortly after branching from intramuscular nerves, establishing an endplate zone across the middle of the muscle. B, In a P14 muscle exposed to exogenous GGF2 for the previous 10 d, motor axons grew hundreds of micrometers throughout the muscle. C, SCs were closely associated with axons in these muscles and had extended processes (arrow). D, Rudimentary nerve terminals were present (arrowheads), although they lacked the arbors that characterize normal terminals. E, AChR clusters were associated with some axon terminations (arrowheads in E), although multiple, aneural AChR clusters were present as well (arrows in Dand E). Scale bar (shown in A): 100 μm; (shown in C): 50 μm.