Mesaxonal membrane junction of myelinated nerve in the central and peripheral nervous system.

Cell junction of the myelinated nerve mesaxon in the sciatic nerve and spinal posterior funiculus of rabbits and rats was examined by the freeze-fracture method. In replicas of fractured specimens, the cell junctions were the tight junction which was composed of parallel arrays of membrane particles. The rows of particles were straight or gently undulating along the long axis of the fibers. Occasional interconnections were formed among these rows. In the external mesaxon, the tight junctional particles in the central nerve were arranged in 3 to 6 lines and well developed more than those of the peripheral nerve consisting of 1 to 2 linear arrangement of particles. "Intramyelinic" tight junctions were well developed as well as some arrays of linear arrangement of particles in the central nerve. However, the junctions were poor and fragmental in the peripheral nerve. Functional meanings of the difference of the mesaxonal and intramyelinic tight junctions between the central and peripheral myelinated nerve are discussed.