Geada Trigo Calheiros De Figueiredo, JD; (2014) The Role Of The Periaxonal Space In Sustained Impulse Conduction. Doctoral thesis , UCL (University College London).

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Abstract

The axonal ability to sustain impulse conduction highlights the mystery regarding the return pathway of sodium ions after entering the axoplasm, as the axolemmal sodium pump must extrude these ions into the periaxonal space, rather than returning them to the nodal gap. We have explored the pathway taken by these ions using in vivo confocal microscopy to observe axons during sustained impulse activity. Mice transgenically expressing yellow fluorescent protein in some axons were stimulated electrically at physiological frequencies or pharmacologically while observing their axonal structure by confocal imaging. A series of morphological changes ensued, starting with an expansion of the periaxonal space, separating the axolemma from the Schwann cell and compressing the axoplasm. The increase in axoplasmic pressure caused an inflation of the axonal morphology at the paranodes and a herniation of the enclosed axoplasm on either side of the nodal membrane, directed back over the outside of the axon, displacing the paranodes and widening the nodal gap. Concurrently, the fluid in the expanded periaxonal space accumulated into droplets that travelled to the paranode where they escaped by apparently parting the axolemmal attachment of the paranodal loops of myelin. These alterations occurred in virtually all axons, and none occurred in axons treated with sodium channel or sodium pump inhibitors. All these changes reversed spontaneously, and impulse conduction continued throughout.

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