The morphology of teleost meningocytes as revealed by freeze-fracture.

We describe the morphology of the cells in the three layers of the teleost endomeninx, as viewed by freeze-fracturing. The cells of the outer endomeningeal layer are fusiform and closely packed, with interdigitations that hold the cells together, gap junctions and a few strands of particles resembling tight junctions, but no desmosomes. The intermediate layer is formed by a single layer of flattened and elongated cells with rectangular shape, and well developed junctional complexes (gap junctions, tight junctions and desmosomes). These cells also show numerous plasmalemmal vesicles (6.5 +/- 1.3/microns 2) in the upper (in contact with the outer layer) and lower (in contact with the inner layer) membranes. 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 fibers. The density of intramembrane particles is higher than that in the meningocytes of the outer and intermediate layers. The morphology of the teleost endomeninx appears similar to that of the leptomeninges of birds and mammals, but the outer endomeningeal layer of teleosts (which resembles the arachnoid of elasmobranchs and amphibians) appears different from any cell layer in the meninges of amniotic vertebrates.