An immunocytochemical and ultrastructural study of a specialized glial region of the medulla oblongata of the adult and juvenile grey mullet

Electron microscopy together with glial fibrillary acidic protein (GFAP) and vimentin immunocytochemistry reveals the presence of a specialized glial region in the octavolateral area of the medulla oblongata of adult and juvenile grey mullets, Chelon labrosus. Glial cells, which can he 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 junctions. Electron microscopy also reveals the lack of nerve cell parikarya and processes in this region. Immunocytochemistry reveals that the glial cells are strongly GFAP-positive in both adults and juveniles, whereas vimentin is only detected in this region in juveniles. The meninges associated with this glial region contains connective fibres, formed of very thick collagen fibres, that arc metachromatic and PAS-positive under light microscopy. These findings strongly support a structural role for this medullary specialization. Differences between adults and juveniles in the distribution of GFAP- and vimentin-immunoreactive structures in other regions of the medulla oblongata are also reported.