Refractive index tomography of myelinating glial cells

摘要

Refractive index tomography as an emerging technique enables the 3D morphological investigation of cells with nomarker. Here, refractive index tomographic imaging of myelinating glial cells is presented. Myelin as a signal insulationlayer around an axon is formed by the wrapping of Schwann cells or oligodendrocytes. Microscopic investigation ofmyelination traditionally requires fluorescent markers. Glial cells generally wrap the axon for more than ten layers. Thismultilayer formation has alternating and uniform layers of protein and lipid. Earlier studies on the structure of the myelinsheath have shown that the thickness period is lower than 20nm including the thickness of the extracellular medium aftereach layer. Direct observation of an individual layer is not possible (using classical microscopy techniques) due todimensions being very small compared to the wavelength of the illumination light. However, periodic nature of thelayers enables the differentiation of a myelinated axon from an unmyelinated one. Rapid change of the integratedrefractive index and the Bragg fiber like structure alters the transmission behavior as a function of wavelength andincidence angle. With the 3D sectioning capability of refractive index tomography, these features can be easilyidentified.