Electron Microscope and X-ray Diffraction Studies of a Saturated Synthetic Phospholipide

The dehydration of rat optic nerve has been studied by allowing specimens to become partially or fully dried before fixation and preparation for electron microscopy. A correlation is established between electron micrographs of the myelin sheath and corresponding smallangle x-ray diffraction patterns. The modifications of the optic nerve myelin layers during drying were very similar to those described in more detail for the myelin of frog sciatic nerve. The most striking difference was that the system of fine layers characteristic of the fully dried myelin was much more extensive in the case of the optic nerve, and the layer thickness was significantly greater than the corresponding layer in the frog sciatic nerve preparation. The significance of these correlations is discussed. The small-angle x-ray diffraction characteristics of myelin of central origin have been shown to differ considerably from those of peripheral nerve myelin (1-4, 7), but the myelin lamellae revealed in electron micrographs of normal preparations of peripheral and central nerve material are virtually identical. From the diffraction data it has been suggested that different types of lipoprotein associations might be involved in the molecular organisation, but the only chemical difference so far demonstrated relates to the amount of proteolipid extracted by 2: 1 chloroform:methanol solvent (3, 6). In studying the dehydration of myelin, the comparison has been extended by doing parallel experiments with a peripheral nerve (see previous paper) and a nerve representative of the central Received for publication, January 27, 1960. nervous system. This second paper is concerned with the data obtained from the optic nerve myelin and with the comparison with data on peripheral nerve myelin presented in the previous paper.