Light- and electron-microscopic investigation of the rat subcommissural organ grafted under the kidney capsule, with particular reference to immunocytochemistry and lectin histochemistry

Abstract

There is increasing evidence that, in the rat, a serotonin-mediated neural input may have an inhibitory influence on the secretory activity of the subcommissural organ (SCO). In the present investigation the rat SCO was studied 7, 30 and 90 days after transplantation under the kidney capsule, an area devoid of local serotonin-containing nerves. The grafted tissue was examined by use of immunocytochemistry employing a series of primary antisera, lectin histochemistry and transmission electron microscopy. The grafted SCO survived transplantation and contained, in addition to secretory ependymal and hypendymal SCO-cells, also elements immunoreactive with antisera against glial fibrillary acidic protein or S-100 protein. In transplants, SCO-cells produced a material displaying the characteristic immunocytochemical and lectin-binding properties of SCO-cells observed under in-situ conditions. The ependymal cells lined 1-3 small cavities, which contained secretory material. A fully developed structural equivalent of Reissner's fiber was, however, never found. The immunocytochemical and ultrastructural study of the grafted SCO showed an absence of nerve fibers within the graft and suggested a state of enhanced secretory activity. A network of protruding basal lamina structures connected the secretory cells to the newly formed capillaries revascularizing the SCO. One week after transplantation, long-spacing collagen started to appear in expanded areas of such laminar networks and also in the perivascular space. It is suggested (i) that the formation of long-spacing forms of collagen is triggered by factors provided by the SCO-secretory cells, and (ii) that secretory material of the ependymal and hypendymal cells may reach the reticular extensions of the basal lamina. In contrast to the SCO in situ, the grafted SCO-cells showed a positive immunoreaction for neuron-specific enolase. They became surrounded by a S-100-immunoreactive glial sheath that separated them from other transplanted cell types and the adjacent kidney tissue of the host.

The subcommissural organ

“…Furthermore, when the rat SCO was transplated under the kidney capsule, the newly formed blood capillaries that revascularized the grafted tissue became endowed after 1 week with long spacing collagen (Figs. 17,18) (Rodríguez et al, 1989). This clearly indicates that the presence of long spacing collagen in these capillaries was triggered by factors provided by the grafted SCO secretory cells.…”

“…However, many of the results obtained using these probes are confusing and difficult to interpret. Thus, whereas the SCO cells of the rat and cat do not display two typical glial markers, namely, glial fibrillary acidic protein (GFAP) and S-100 protein (S-100) (Chouaf et al, 1989;Didier et al, 1986;Rodríguez et al, 1989), the SCO of other rodents express GFAP or S-100 (Redecker, 1989). The rat SCO lacks, -enolase, a specific neuron enolase; however, when transplanted underneath the kydney capsule, the rat SCO does express the neuronal enolase (Rodríguez et al, 1989).…”

“…ϫ20,000. (From Rodríguez et al, 1989). references, see Ziegels, 1976). Several histochemical test led to the conclusion that the secretion of the SCO is a glycoprotein or a mucopolysaccharide-protein complex (Diederen, 1970;Naumann, 1968;Oksche, 1962).…”

“…Thus, whereas the SCO cells of the rat and cat do not display two typical glial markers, namely, glial fibrillary acidic protein (GFAP) and S-100 protein (S-100) (Chouaf et al, 1989;Didier et al, 1986;Rodríguez et al, 1989), the SCO of other rodents express GFAP or S-100 (Redecker, 1989). The rat SCO lacks, -enolase, a specific neuron enolase; however, when transplanted underneath the kydney capsule, the rat SCO does express the neuronal enolase (Rodríguez et al, 1989). Whereas the SCO of the rat and cat accumulates gamma-aminobutyric acid by specific uptake mechanisms, the mouse and rabbit SCO does not (Chouaf et al, 1989;Gamrani et al, 1981).…”

Tissue culture of bovine subcommissural organ

“…under the kidney capsule or into brain ventricles (Rodriguez et al 1989;Didier-Bazes et al 1991). But it has to be considered that the SCO may alter its properties as a target tissue, even though most of the morphological and immunocytochemical features persist throughout a long period under in vitro conditions.…”