Modifications of Protein-Lipid Interactions in Nerve Fiber Myelin: Effects on Nerve Fiber Morphology

Using laser interference microscopy it was found that modifications of protein-lipid interactions in frog myelin and nerve fiber axolemma change the fiber morphology, myelin structure and the cytoplasm of axon and/or Schwann cells. Destruction of the protein extracellular sites of myelin and axolemma decreased the refractive index (RI) of the axon cytoplasm in the Ranvier nodes and increased RI in the internode regions without notable changes in the myelin. Conformation changes of myelin proteins in Ranvier nodes (but not in the internode regions) reduced the RI of axon cytoplasm and myelin. Modification of the lipid bilayer with lysolecithin lead to changes in morphology and RI of the internode axon cytoplasm. Sequestration of cholesterol with methyl-beta-cyclodextrin changed the myelin RI and the fiber morphology.