LIGHT- AND ELECTRONMICROSCOPICAL OBSERVATIONS ON SACCUS VASCULOSUS OF RAINBOW TROUT

The saccus vasculosus of the rainbow trout, a sac-like outgrowing of the basis of the diencephalon consists of a strongly undulated epithelial wall, separating the cerebrospinal fluid from the endomeningeal matrix fluid. This epithelium is built up by highly specialized coronet cells, glial cells and peculiar so-called pseudo-coronet cells. The coronet cells extend from the ventricular- to the meningeal border. Morphological evidence is put forward indicating that transport of low molecular material might be the main function of these cells. Several cytochemical data support this hypothesis. A possible repulsion and renewal of globules of the coronet cells may represent steps in the functional cycle of these cells. Concerning the transport function, the observation of open connections between the lumina of the blood sinuses and the endomeningeal spaces might be important. Observations on the synaptic pattern in the epithelium suggest a possible nerve control of the functional activity of the saccus vasculosus via the glial elements. © 1969 Springer-Verlag.