AN IMMUNOCYTOCHEMICAL AND ULTRASTRUCTURAL-STUDY OF A SPECIALIZED GLIAL REGION OF THE MEDULLA-OBLONGATA OF THE ADULT AND JUVENILE GRAY MULLET

Electron microscopy together with glial fibrillary acidic protein (GFA P) and vimentin immunocytochemistry reveals the presence of a speciali zed glial region in the octavolateral area of the medulla oblongata of adult and juvenile grey mullets, Chelon labrosus. Glial cells, which can be characterized as ependymal and subependymal cells, originate in the walls of the lateral recess of the fourth ventricle. They contain numerous gliofilaments and are connected through frequent gap junctio ns. Electron microscopy also reveals the lack of nerve cell parikarya and processes in this region. Immunocytochemistry reveals that the gli al cells arc strongly GFAP-positive in both adults and juveniles. wher eas vimentin is only detected in this region in juveniles. The meninge s associated with this glial region contains connective fibres, formed of very thick collagen fibres, that are metachromatic and PAS-positiv e under light microscopy. These findings strongly support a structural role for this medullary specialization. Differences between adults an d juveniles in the distribution of GFAP- and vimentin-immunoreactive s tructures in other regions of the medulla oblongata are also reported.