Electron microscopic photomicrographs show the cross-section of the sciatic nerve fibers in the CD (A and D), HFSD (B and E) and HFSSD (C and F) groups. Dramatic pathological changes characterized by myelin breakdown or disruption and axon degeneration are mainly seen in large myelinated fibers (LMF) of rats fed HFSD (B) and HFSSD (C) when comparing with CD (A). The diets-induced LMF myelin changes are often seen as myelin lamina rarefaction, focal demyelination and vacuolization (yellow arrowheads in B-C). Axon degeneration of LMFs is characterized by abnormal high electron density and axonal plasmic shrinkage (asterisks in B-C). Ultrastructures of small myelinated fibers (SMF) and unmyelinated C fibers (UMF) in three groups are also shown (D-F). The axolemma and the Schwann cell covering are well maintained in all UMFs of rats fed CD (see red arrows in D), however, the axolemma and the Schwann cell membrane are thickened and perturbed shown as high electron density in both HFSD and HFSSD (red arrows in E-F). In addition, enlarged mitochondria and lipofuscin depositions are also seen in UMF axons of high energy/salt-treated rats (see yellow arrowheads in E-F) but not in control rats (D). The ultrastructures of SMFs in HFSD and HFSSD are well preserved when compared with CD (see yellow arrows in B-F), however, broken SMF can also be seen in the diet rats (double yellow arrows in E). My, myelin sheath; SC, the nucleus of Schwann cells; other abbreviations see . Scale bar for A-C: 5 µm, scale bar for D-F: 2 µm.