Features associated with paranodal demyelination at a specialized site in the non-pathological nervous system

Experimental demyelination in the CNS and PNS have been shown in some cases to exhibit a paranodal distribution. The electric organ of the gymnotid Sternarchus is composed of specialized axons which generate external electric fields. The structure of the nodes of Ranvier changes characteristically along the course of these specialized non-pathological axons. The nodes of Ranvier in two locations along the fibers are markedly enlarged. At the enlarged nodes, but not at normal nodes from the same fibers, the paranodal myelin exhibits morphological features associated with paranodal demyelination. These features include termination of the innermost myelin lamellae at distances of up to 200 μm from the nodal gap. The results indicate that these morphological findings are not necessarily associated with pathological demyelination, and suggest that remodeling of the myelin sheath, including programmed demyelination, may play a role in the development of certain specialized neural systems.