Increase Of Myelinated Fibers Research Articles

Effects of an enriched environment on myelin sheaths in the white matter of rats during normal aging: A stereological study

We found that an enriched environment (EE) could delay the loss of myelinated fibers in the white matter of rats during normal aging. However, the reasons for the protective effects of EE on the myelinated fibers were unclear. In this present study, via the use of stereological methods, we quantitatively investigated the myelin sheaths and the axons of myelinated fibers in the white matter of rats reared in an EE or a standard environment (SE) during the aging process. The results showed that an EE induced significant increases in the lengths of myelinated fibers, the axon volumes and the myelin sheath volumes of aging rats when compared with SE rats and that the enrichment effects, with the exception of the axon volumes, were sex- and age-independent. The mean diameter of the myelinated fibers, the mean perimeter of the myelin sheaths and the mean thicknesses of the myelin sheaths were not significantly changed. The EE-induced increase in myelinated fibers was mostly observed in those of smaller diameter (<1μm) with thinner myelin sheaths (<0.16μm), which had an optimal axon-fiber ratio (g=0.61). Our results suggest that EE-induced an increase in myelinated fibers in the white matter of aging rats primarily due to marked remyelination and some ongoing myelination.

Transplantation strategies to promote repair of the injured spinal cord

This review describes the results of the transplantation of Schwann cells and olfactory ensheathing glia in combination with other interventions. The complete transection injury model was used to test the combination of Schwann cell bridges with methylprednisolone, neurotrophins, or olfactory ensheathing glia. The contusion injury model was used to compare Schwann cell and olfactory ensheathing glia transplantation and to examine the results of combining Schwann cell transplants with elevated levels of cyclic adenosine monophosphate. The combination strategies were more effective than cell transplantation alone. The improved regeneration response usually involved a reduction in secondary tissue loss, axonal regeneration from brainstem neurons, an increase in myelinated fibers in the transplant, the exit of regenerated fibers from the transplant into the contiguous cord, and an improvement in locomotor function.

Cutaneous overexpression of NT-3 increases sensory and sympathetic neuron number and enhances touch dome and hair follicle innervation.

Target-derived influences of nerve growth factor on neuronal survival and differentiation are well documented, though effects of other neurotrophins are less clear. To examine the influence of NT-3 neurotrophin overexpression in a target tissue of sensory and sympathetic neurons, transgenic mice were isolated that overexpress NT-3 in the epidermis. Overexpression of NT-3 led to a 42% increase in the number of dorsal root ganglia sensory neurons, a 70% increase in the number of trigeminal sensory neurons, and a 32% increase in sympathetic neurons. Elevated NT-3 also caused enlargement of touch dome mechanoreceptor units, sensory end organs innervated by slowly adapting type 1 (SA1) neurons. The enlarged touch dome units of the transgenics had an increased number of associated Merkel cells, cells at which SA1s terminate. An additional alteration of skin innervation in NT-3 transgenics was an increased density of myelinated circular endings associated with the piloneural complex. The enhancement of innervation to the skin was accompanied by a doubling in the number of sensory neurons expressing trkC. In addition, measures of nerve fibers in cross-sectional profiles of cutaneous saphenous nerves of transgenics showed a 60% increase in myelinated fibers. These results indicate that in vivo overexpression of NT-3 by the epidermis enhances the number of sensory and sympathetic neurons and the development of selected sensory endings of the skin.