Laboratory of Neuron Functional Morphology and Physiology, RAS I.P. Pavlov Institute of Physiology, St.-Petersburg.
Taking into consideration that myelin phospholipids may be partially synthesized in neuronal bodies, while neurilemma readily reacts with antibodies against gangliosides by changing the properties of membrane ionic channels, the attempt was made to test the proposed assumption of the early axonal reaction in demyelinating processes in experimental models of multiple sclerosis.
The models of chronic allergic encephalomyelitis in Lewis rats injected with homogenate of highly purified myelin or total brain gangliosides were used.
First signs of demyelination (the destruction of intermediate dense lines) were demonstrated in the inner layers of myelin close to axon and were shown to develop synchronously with the aggregation of filamentous-tubular material in the neuroplasm.
These changes are associated with significant shift of the ratio of myelin sheath thickness to axonal diameter (from 1:7-1:3 to 2:1-3:1).
This swelling of myelin seems to be caused by neuroplasmic proteins aggregation, that must be accompanied by the drop in oncotic pressure and the separation of loosely-bound water fraction that may be assimilated by myelin.
At light microscopic level the increase of myelin thickness is clearly observed that is in exact correspondence with the decrease in axonal diameter.
The process starts with the exfoliation and swelling of the nodes of Ranvier and the incisures of myelin, which fuse after elongation, that corresponds to the total disintegration of myelin with the preservation of continuity of axon which appears to be harshly shrunken.