Regional differences in the ependyma of the optic tectal ventricle of adult zebrafish with structures referring to brain hydrodynamics

Abstract Classical electron microscopic morphological studies provide detailed ultrastructural information, which may lend insights into cellular functions. As a follow‐up to our morphological investigation of the adult zebrafish ( Danio rerio ) optic tectum, in this study, we have analyzed the ependymal structures lining the surfaces of the tectal ventricle: the torus, tegmental surface of the valvula cerebelli and the periventricular gray zone of the optic tectal cortex. We used toluidine blue stained plastic (semithin) sections for light microscopy and scanning electron microscopy. Our morphological findings of gated entrances and/or egresses indicate that, at least in the adult zebrafish brain, there may be a bidirectional direct flow communication between the ventricular cerebrospinal fluid and the parenchymal interstitial fluid.