The Subcommissural Organ

Abstract

We recently undertook a new study in the rat and guinea pig brain to look for the presence of cytokeratins, vimentin, and GFAP in neuroectodermally derived structures and to verify whether cytokeratins are also expressed in ependymal cells in these species. Because the available data are quite sparse (Miettinen et al. 1986; Kasper et al. 1987a), as well as the choroid plexus we also investigated another specialized ependymal tissue in the group of circum-ventricular organs (Leonhardt 1980): the subcommissural organ (SCO). Additionally, we compared immunolocalization of intermediate filament proteins in fixed (4% paraformaldehyde) versus frozen tissue to determine how dependent determination of cytokeratin expression in rat brain tissues is on appropriate fixation. Some difficulties have already been mentioned with the immunolocalization of cytokeratins in the human pineal organ after formaldehyde fixation (see Chap. 4). The rat ependyma expresses vimentin, focally GFAP, and cytokeratin (Tables 3, 5; Fig. 3) but the degree of immunoreactivity varies in the different ventricles studied. The strongest cytokeratin expression in ependymal cells was noted in the third ventricle, in the neighborhood of the SCO and the choroid plexus (Fig. 4a,b). The SCO itself was only weakly positive, showing asymmetric staining with reactivity only in the apical cytoplasm (Fig. 5a,b). Some secretory cells in the hypendyma were also cytokeratin-positive (Fig. 5b).