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The role of functional activity in myelination: an in vivo study


MacArthur Jones, Jerome Staal Ph.D., Doug Fields Ph.D.

The importance of myelin which is the principle component of white matter has long been apparent from human diseases such as multiple sclerosis. To date, most myelination research has been directed toward identifying mechanisms that promote or inhibit it during development with the goal of developing strategies to promote repair in the demyelinated CNS. Myelin may exhibit substantial plasticity throughout adult life. This has sparked renewed interest in the myelination process given that this plasticity may have profound implications for neural functioning. Previous in vitro studies published by our lab and others have found that electrical activity in nerve cells may regulate key features of the myelination process by altering the direct interactions between the neuron and the myelinating glial cell (oligodendrocyte). The role of neural activity on the regulation of myelin formation in vivo has often been difficult to study. In this study, we utilize dark rearing of mice to determine if functional activity regulates white matter formation in the optic nerve. Age matched animals were reared in either dark or light conditions until postnatal day 14 (P14) which correlates to 2-4 days after eye opening. The mice were fixed and processed for either transmission electron microscopy or immunohistochemistry. Measurements of myelin thickness, referred to as G ratio, revealed a significant increase in myelin thickness in mice reared in the dark compared to that in light conditions. The number of oligodendrocytes in the optic nerve was determined using immunhistochemistry and was found to be not significantlydifferent between the two conditions. In conclusion, our preliminary results suggest that funtional activity may play a role in myelin formation via a process that does not affect oligodendrocyte number.

Last updated December 14, 2012