Unraveling Myelin’s Mystery With Neutron Diffraction

Researchers have uncovered new information about myelin, a fatty substance that wraps around the axons of brain cells (neurons) allowing them to transmit information quickly from one cell to another. De-myelinating diseases in which the insulating wrap is damaged include multiple sclerosis, in which unpredictable loss of myelin causes motor, sensory and visual problems, tingling sensations and pain.

In a report published this week in the journal Acta Crystallographica D, scientists from Boston College used myelin taken from rats to examine the structure and flow of water through the fatty substance. Prof Daniel Kirschner, together with graduate student Andrew Denninger, used neutron diffraction to better understand myelin and to unravel its mysteries. Neutron deffraction is a very sensitive method that can be used to determine the structure of a material. The data was collected at the Institut Laue Langevin (ILL) in Grenoble, an international scientific center and a world leader in neutron diffraction.

The scientists measured solutions with light water (H2O) and heavy water (D2O). D2O is formed using deuterium rather than hydrogen. They compared the two types of water and how they diffused within the myelin sheath. The flow was similar to the transmission of an electrical impulse down a neuron, and could be used to make estimations about the properties of myelin.

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The study provided insights into how myelin is stacked into layers and features water-containing spaces. The investigators measured differences between the outer portion (membrane) of the cells containing myelin and the inner portion (cytoplasm). The experiments allowed for comparisons between myelin in the central nervous system (the brain and spinal cord) versus myelin in the peripheral nervous system (the nerves everywhere else in the body)–revealing new information about how myelin in these two areas of the nervous system is different. In particular, they found distinct transport of water in the two types of myelin from central nervous system versus peripheral nervous system.

Previously, myelin was investigated with microscopes, both conventional types (light) and extremely powerful (electron), and a technique called X-ray diffraction. Only neutron diffraction was able to provide a complete picture of the structure of myelin and to provide previously unknown information, particularly about how different types of myelin exist in different parts of the nervous system.

According to Bruno Demé, one of the study authors: “Neutron diffraction of the sort undertaken at ILL is ideal for determining the structure of a natural membrane such as myelin. The dense packing of layers within each sample makes the nervous system a good target for diffraction, and demonstrates the potential for further neutron diffraction studies on pathological forms of myelin.”

This study provides better understanding of myelin, which will hopefully lead to new innovative treatments for conditions such as multiple sclerosis.