Neurofilaments assume a less random architecture at nodes and in other regions of axonal compression

Abstract

Neurofilament distributions were mathematically characterized in four chicken somatic motor axons at each of four histologically distinct regions: compact myelinated regions, compact myelinated regions associated with Schwann cell nuclei, Schmidt-Lanterman clefts, and nodes of Ranvier. Compact myelinated regions had the largest cross-sectional areas, the lowest neurofilament densities, and the most random neurofilament organizations — nodes of Ranvier had the smallest cross-sectional areas, the highest neurofilament densities, and the most ordered architectures. In these myelinated axons, the closest natural neurofilament spacing was 25 nm. Mathematical analyses of serial sections suggested that neurofilament interactions are sufficiently weak and transient to permit a full range of variation from random to ordered cytoskeletal architectures as the neurofilaments move longitudinally through the few micron span of the paranodal-nodal region of a single axon.