Junctional complexes and variations in gap junctions between spinal cord ependymal cells of a teleost, Sternarchus albifrons (gymnotoidei)

Junctions between ependymal cells lining the central canal in the spinal cord of the weakly electric teleost, Sternarchus albifrons, were investigated by means of thin-section and freeze-fracture electron microscopy. Junctional complexes representing the 'terminal bar' consist of a zonula occludens, followed by intermediate junctions and desmososomes. This pattern is common in many types of epithelia but uncommon in ependyma. Three types of gap junctions were found below the leel of the terminal bar and intermixed with desmosomes: (1) gap junctions at least partially enclosed by a single strand of apparent tight junction, (2) ordinary gap junctions, partially surrounded by a particle-free halo and (3)_segmented gap junctions, in which linear arrays several particles wide are separated by fairly regular linear particle-free regions. Some of the observations may have implications for the mechanism of formation of gap junctions.