An X-ray diffraction study of changes in myelin structure during experimental allergic neuritis.

In order to determine whether the structure of the myelin membranes is modified during experimental allergic neuritis (EAN), we have performed X-ray diffraction studies of in vivo and of isolated sciatic nerves from Lewis rats exposed to different EAN-producing treatments. We have observed a decrease of the intensities in the X-ray reflections without changes in spatial resolution. The level of decrease correlated with the severity of the demyelinating lesions. In comparison to nerves from normal healthy rats the electron density profile of sciatic nerve myelin from animals in acute stages of EAN showed small differences at both cytoplasmic and extracellular spaces of the myelin membrane. Dynamic X-ray diffraction patterns recorded kinetically in vivo from a nerve injected intraneurally with a neuritogenic antiserum do not show additional reflections characteristic of a distinct lattice of increased periodicity, suggesting that the early stages of demyelination do not involve an intermediate ordered state.