LIGHT AND ELECTRON-MICROSCOPIC STUDY OF OLIGODENDROCYTES IN THE LATERAL LINE AREA OF THE MEDULLA IN CHELON-LABROSUS (TELEOSTEI)

The oligodendrocytes of the medullary lateral line area of the teleost Chelon labrosus were studied with light and electron microscopy. oligodendrocytes are sharply differentiated from neurons or other class of glia cells from their ultrastructural characteristics. The three subtypes of oligodendrocytes (light, medium and dark) that have been recognized are not homogeneously distributed but have preferential locations related to the size of nearby myelinated fibres. No perineuronal oligodendrocytes are present in this medullary center. Oligodendrocytes show a variety of dense bodies. sometimes of bizarre shapes, in addition to characteristic mitochondria and endoplasmic reticulum. Three types of intercellular junctions were observed in these cells: gap junctions. tight junctions and puncta adhaerentia. Gap junctions and puncta adhaerentia link oligodendrocyte somata and astrocytic processes. Tight junctions were observed both between oligodendrocytes and between oligodendrocytes and astrocytic processes. The significance of these results is discussed in relation to the maturation and function of oligodendrocytes and the characteristics of fish brains.