Intrinsic dynamical fluctuations of PNS myelin

The ultrastructure fluctuations and complex dynamics of the multi-layered membrane structure of myelin are fundamental for understanding and control its formation process and its degeneration and repair in neurological diseases such as multiple sclerosis (MS). Myelin is considered a liquid-crystal but there are no information on its multiscale fluctuations from nanoscale and mesoscale due to limitations of the available standard techniques. To overcome this limitation in this work we have used Scanning micro X-ray Diffraction (SμXRD), which is a unique non-invasive probe of both k-space and real space allowing to visualize statistical fluctuations of myelin order with high spatial resolution in real space. We have used this method to examine the myelin sheath in the sciatic nerve of Xenopus laevis. We have found first that the myelin ultrastructure period is stabilized by large anti-correlated fluctuations at nanoscale, between hydrophobic and hydrophilic layers. Our key result is that the correlated disorder of myelin spatial ultrastructural fluctuations follows a Levy distribution in the functional state, which is lost with early stage degeneration. Our results open could open new venues for understanding formation and degradation in biological ultrastructure by associating these states with dynamical structural fluctuations at nanoscale.