THE MORPHOLOGY OF TELEOST MENINGOCYTES AS REVEALED BY FREEZE-FRACTURE

We describe the morphology of the cells in the three layers of the tel eost endomeninx, as viewed by freeze-fracturing. The cells of the oute r endomeningeal layer are fusiform and closely packed, with interdigit ations that hold the cells together, gap junctions and a few strands o f particles resembling tight junctions, but no desmosomes. The interme diate layer is formed by a single layer of flattened and elongated cel ls with rectangular shape, and well developed junctional complexes (ga p junctions, tight junctions and desmosomes). These cells also show nu merous plasmalemmal vesicles (6.5 +/- 1.3/mum2) in the upper (in conta ct with the outer layer) and lower (in contact with the inner layer) m embranes. Cross fracture of these cells shows many membrane-bound and free vesicles, The inner layer is formed by spindle shaped cells with wide intercellular spaces filled with a granular matrix and collagen f ibers. The density of intramembrane particles is higher than that in t he meningocytes of the outer and intermediate layers. The morphology o f the teleost endomeninx appears similar to that of the leptomeninges of birds and mammals, but the outer endomeningeal layer of teleosts (w hich resembles the arachnoid of elasmobranchs and amphibians) appears different from any cell layer in the meninges of amniotic vertebrates.