Figure 4.

Visualization of breakdown of the blood nerve barrier (BNB) (A,B) and inflammation in experimental nerve crush (C–F). Coronal images depict the pelvis and both thighs of a rat lying in prone position with both legs positioned in a round surface coil (CISS sequence; slice thickness 1 mm). Note that Gf accumulates in the degenerating distal stump on T1-w MRI [arrow in (A)] and binds to peripheral nerve structures as revealed by fluorescence of carbocyanine-labeled Gf (B). Gf enhancement ceases not until successful regeneration (not shown). By contrast to breakdown of the BNB, macrophage infiltration is restricted to the early phase of Wallerian degeneration. Five days after sciatic nerve crush focal signal loss is present at the lesion site and distally due to the invasion of SPIO-labeled macrophages from the blood (C). The corresponding paraffin section stained for iron confirms the infiltration of numerous iron-laden macrophages in the degenerating nerve segment (D). At day 8, macrophage infiltration is restricted again to the lesion site and ceases thereafter (E). Correspondingly, distal nerve segments no longer show iron-positive cells after application of SPIO as shown for day 10 in (F). The BNB, however, is still leaky at that time (not shown) indicating that macrophage infiltration occurs within a narrow time window and persistent BNB disturbance does not per se induce cellular infiltration. Adapted from Bendszus et al. (2005b); (A,B) and Bendszus and Stoll (2003) (C–F).