Figure 2.

Myelin stain and ultrastructure of lesion/graft site. A, Myelin stain of the lesion site within ungrafted subject indicates occasional penetration of myelinated axons (arrows) into spontaneous cell matrix that forms in injury zone. B, In contrast, myelinated axons extensively penetrate BDNF/NT-3-secreting fibroblast graft placed in lesion site. C, Ultrastructure of lesion site in ungrafted subject demonstrates cellular influx consisting of both fibroblasts (f) and occasional ensheathing Schwann cells (s). Bundles of unmyelinated axons (a) are observed within cytoplasm of associated Schwann cell in ungrafted lesion cavity; nuclear–axonal juxtaposition is typical of Schwann cell morphology. Ungrafted subjects also exhibit abundant extracellular collagen fibrils (c), providing a substrate for axonal penetration into control lesion site. D, Subjects that received grafts of BDNF/NT-3-secreting fibroblasts into the lesion cavity generally exhibit a greater density of both cells and axons. Abundant Schwann cells are present and are associated with many myelinated axons (m). E, Higher magnification of nongrafted lesion site, demonstrating association of Schwann cell with unmyelinated axon, and extracellular collagen fibrils. F, Higher magnification of BDNF/NT-3 grafted subject within lesion site, demonstrating association of Schwann cell with myelinated axon. Scale bars: B (for A, B), 100 μm; C, D, 2 μm; E, F, 1 μm.