Histology verifies MR imaging findings with perineural iron-laden macrophages demonstrated only in animals injected with USPIOs without minocycline. Paraffin sections were prepared from the distal segment of the nerve, just proximal to the ligature, and stained with (A, C, E, G) hematoxylin and eosin (H&E) to provide morphological detail and with (B, D, F, H) Perl’s stain, which stains iron blue. (A, B) Control (−USPIO) longitudinal sections through the neuroma and surrounding perineural tissue harvested from the site of the neuroma show no iron staining. (C-F) Tissues harvested from SNI animals injected with USPIOs. At 200X magnification, the axial section and the longitudinal section (C, D) and an axial section (E, F) from a different animal show areas of increased iron staining in the perineural tissues. These iron containing cells demonstrate histologic characteristics of macrophages. At 200x magnification, iron and H&E stained axial sections from animals treated with minocycline and USPIOs (+MINO-USPIO) show localization of iron containing cells to the perineural tissue, albeit to a qualitatively lesser extent than the –MINO+USPIO treated sections.