Cytochemical differentiation of the axon membrane in A- and C-fibres

Guinea pig and rat sciatic nerves were fixed with cacodylate-buffered aldehydes and OsO4, and were stained with ferric ion and ferrocyanide. Cytoplasmic surfaces of the non-myelinated nodal axon membrane of A-fibres display distinct electron-dense aggregates of stain. These aggregates were not observed in association with the paranodal or internodal axolemma. The membranes of C-fibres exhibit no staining under these conditions. Thus, the nodal axolemma of normal myelinated fibres is structurally distinct from both the myelinated internodal membrane, and from the axolemma of C-fibres. The ferric ion-ferrocyanide technique may provide a method for marking axonal membrane with normal nodal properties.