Morphological evidence for the presence of two cell types in the ependyma of the subcommissural organ of the snake, Natrix maura

Abstract

Two different types of ependymal cells were found in the subcommissural organ (SCO) of Natrix maura. Most secretory cells showed morphological features resembling the general structure and ultrastructure of cells in the SCO of other vertebrates. This report describes a second population of cells lining a portion of the dorsal groove of the SCO. These cells were not selectively stained by chromalum-hematoxylin and, under the electron microscope, they were characterized by scarce surface differentiations, sparse apical cytoplasm and short basal processes. Flat, parallel cisternae of the rough endoplasmic reticulum produced vesicles that appeared to be transported to the well-developed Golgi apparatus. Dense secretory granules about 200 nm in diameter were found in the Golgi region. Similar granules were seen in the vicinity of the apical plasma membrane; some of them opened toward the ventricle. All these characteristics clearly differentiate this cell group from the other secretory cells lining the SCO laterally and ventrally.

Synthesis of transthyretin by the ependymal cells of the subcommissural organ

“…This is in agreement with findings in the human fetal SCO in which all cells display secretory activity, as revealed by lectin histochemistry ), but only about half of the population of ependymocytes immunoreact with antisera raised against glycoproteins of human fetal CSF . Worth mentioning is the finding by Fernández-Llebrez et al (1984) who have described two populations of secretory ependymocytes in the SCO of the snake Natrix maura, each of them having distinct ultrastructural characteristics; the smallest cell population located in the midline does not react with anti-RF sera, whereas the largest one does (Peruzzo et al 1990). All this evidence indicates that the SCO of various species displays two populations of secretory ependymal cells, one secreting RF glycoproteins and the other secreting CSFsoluble compounds.…”

Organ culture of the bovine subcommissural organ: Evidence for synthesis and release of the secretory material

“…Indeed, based on the ultrastructural characteristics of the secretory granules, two types of secretory ependymocytes may be distinguished. Secretory ependymocytes lacking immunoreactivity with anti-RF sera have been described in other species (Ferná ndez-Llebrez et al, 1984). We have no explanation for the fact that the AFRU-negative secretory ependymocytes of the bovine SCO become more conspicuous under culture conditions.…”