Secretory phenomena at the ependyma of the IIIrd ventricle of the embryonic rat.

On the basis of previous observations of the third ventricle, the brains of rat embryos in the 17 to 21 gestation days were examined by light- and electron microscope as well as histochemically. Following results were obtained: 1. Between the 18th and 20th gestation days supraependymal secretion spherules and intraventricular secretion masses were observed in the rostral part of the third ventricular lumen. The intraventricular structures are not demonstrable with neurosecretory stains; they are PAS-negative and do not stain with periodic-acid-bisulfite-aldehydethionine. All histochemical reactions performed were negative. 2. The morphological finding in the same frontal plane is not uniform. Dorso-ventral difference exist between one ependymal region which lies caudal to the subfornical organ and an area in the same plane which is situated further ventrally near the entrance to the foramina Monroi (Fig. 1 a). In the superior portion, the supraependymal structures are spherical or bottle-shaped formations and are easily definable. In the lower ventricular portion densely situated ependymal protrusions are seen which become sperical only in the ventricular lumen. 3. In both instances (the spherical and flask-shaped protrusions of the superior portion and the strongly shaped protrusions of the lower portion of the third ventricle) cytoplasmic protuberances containing more or less dense, fine-grain ground plasma and a differentiated number of polyribosomes can be seen. Using the Richardson stain, chromophobe protrusions are seen to possess a diffuse ground plasma and only a few ribosomes, while chromophile protrusions have a dense ground plasma and numerous polyribosomes rosettes. Only rarely are single vesicles observed in the protrusions. 4. The ependyma cells contain densely packed, rough-walled endoplasmic reticulum whose cisterns are irregularly dilated and filled with electron-dense material; they also contain many ribosomes and dictyosomes. The organelles are accumulated mainly in the apical cell portions. A terminal web spans the cell surface and attaches to the zonulae adhaerentes, preventing the flow of cell organelles into the organelle-free secretory protrusions. 5. The functional implication of the ependymal secretion, which appears in the third ventricle for a few days only, during embryonic development, is still unknown and is the goal of subsequent examinations.