Ontogenetical development of the chick and duck subcommissural organ

Summary The ontogenetical development of the subcommissural organ (SCO) was investigated in chick embryos collected daily from the 1st to the 21st day of incubation. Some duck embryos, and adult chickens and ducks were also studied. Immunocytochemistry using an anti-Reissner's fiber (RF) serum as the primary antibody was the principal method used.In the chick embryos the events occurring at different days of incubation were: day 3 morphologically undifferentiated cells in the dorsal diencephalon displayed immunoreactive material (IRM); days 4 to 6 immunoreactive cells proliferated, formed a multilayered structure and developed processes which traversed the growing posterior commissure and ended at the brain surface; day 7 i) blood vessels penetrated the SCO, ii) scarce hypendymal cells appeared, iii) the first signs of ventricular release of IRM were noticed, iv) appearance of IRM bound to cells of the floor of the Sylvius aqueduct; day 7 to 10 the number of apical granules and amount of extracellular IRM increased progressively; day 11 RF was observed along the Sylvian aqueduct; day 12 RF was present in the lumbar spinal cord; day 13 IRM on the aqueductal floor disappeared; days 10 to 21 i) hypendymal cells proliferated, developed processes and migrated dorsally, ii) ependymal processes elongated and their endings covered the external limiting membrane. In adult specimens the ependymal cells lacked basal processes and the external membrane was contacted by hypendymal cells. The duck SCO appears to follow a similar pattern of development.Supported by Grant I/60 935 from the Stiftung Volkswagenwerk, Federal Republic of Germany, and Grant RS-82-18 from the Dirección de Investigaciones, Universidad Austral de Chile. M.H. was recipient of a personal grant from JNO (29-5-54), which is gratefully acknowledged     

Ontogenetical development of the chick and duck subcommissural organ. An immunocytochemical study

The ontogenetical development of the subcommissural organ (SCO) was investigated in chick embryos collected daily from the 1st to the 21st day in incubation. Some duck embryos, and adult chickens and ducks were also studied. Immunocytochemistry using an anti-Reissner's fiber (RF) serum as the primary antibody was the principal method used. In the chick embryos the events occurring at different days of incubation were: day 3 morphologically undifferentiated cells in the dorsal diencephalon displayed immunoreactive material (IRM); days 4 to 6 immunoreactive cells proliferated, formed a multilayered structure and developed processes which traversed the growing posterior commissure and ended at the brain surface; day 7 blood vessels penetrated the SCO, scarce hypendymal cells appeared, the first signs of ventricular release of IRM were noticed, appearance of IRM bound to cells of the floor of the Sylvius aqueduct; day 7 to 10 the number of apical granules and amount of extracellular IRM increased progressively; day 11 RF was observed along the Sylvian aqueduct, day 12 RF was present in the lumbar spinal cord; day 13 IRM on the aqueductal floor disappeared; days 10 to 21 hypendymal cells proliferated, developed processes and migrated dorsally, ependymal processes elongated and their endings covered the external limiting membrane. In adult specimens the ependymal cells lacked basal processes and the external membrane was contacted by hypendymal cells. the duck SCO appears to follow a similar pattern of development.     

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

Summary 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.Supported by Grant I/63 476 from the Stiftung Volkswagenwerk, Federal Republic of Germany, Grants 187 and 0890/88 from Fondo Nacional de Desarrollo Cientifico y Tecnológico, Chile, and Grant S-85-39 from the Directión de Investigaciones, Universidad Austral de Chile. The authors wish to acknowledge the valuable help of Ms. Elizabeth Santibañez and Mr. Genaro Alvial (Valdivia) and Ms. Inge Lyncker (Giessen)     

Light- and electron-microscopic immunocytochemical investigation of the subcommissural organ using a set of monoclonal antibodies against the bovine Reissner's fiber

Ten monoclonal antibodies (Mabs) against glycoproteins of the bovine Reissner's fiber (RF) have been used in a structural and ultrastructural immunocyto-chemical investigation of the bovine subcommissural organ (SCO) and RF. The SCO of other vertebrate species has also been studied. For comparison, polyclonal antibodies against bovine RF (AFRU) were used. The SCO and RF of ox, pig and dogfish and the SCO of dog, rabbit, rat and frog were submitted to light-microscopic immunocytochemistry using AFRU and Mabs. Postembedding ultrastructural immunocytochemistry was applied to sections of bovine SCO using AFRU and Mabs. Bovine SCO consists of ependymal and hypendymal cell layers, the latter being arranged as cell strands across the posterior commissure, or as hypendymal rosette-like structures. All cytoplasmic regions of the ependymal and hypendymal cells were strongly stained with AFRU. Six Mabs showed the same staining pattern as AFRU, one Mab stained RF strongly and SCO weakly, two Mabs stained RF but not SCO, and, finally, one Mab (3B1) exclusively stained the apices of the ependymal and hypendymal cells. All Mabs recognized the SCO and RF of the pig. Two Mabs bound to the SCO of the dog. One Mab stained the SCO of the rabbit and another the SCO of the rat. The SCO of frog and dogfish were totally negative. Bovine SCO stained with AFRU, showed label in the rough endoplasmic reticulum (RER) and the secretory granules (SG) of the ependymal and hypendymal cells. The former, in the form of parallel cisternae, reticulum or concentric rings, was seen throughout all cytoplasmic regions. SG were abundant in the apical pole of the ependymal and hypendymal cells. Only one Mab showed a staining pattern similar to AFRU. Five Mabs showed strong reactions in the SG but weak labeling of the RER. Mab 3B1 showed the label confined to the SG only. Our results suggest that: (i) in the bovine tissue, some epitopes are present in both precursor and processed materials, whereas others are characteristic of mature glycoproteins present in SG and the RF; (ii) the bovine SCO secretes at least two different compounds present in ependymal and hypendymal cells: (iii) both compounds coexist in the same secretory granule; (iv) there are conserved, class-specific, and species-specific epitopes in the glycoproteins secreted by the SCO of vertebrates.     

Intercellular channels in the pars tuberalis of the rat hypophysis and their relationship to the subarachnoid space

Summary A system of intercellular channels is described in the pars tuberalis (PT) of the female rat. These spaces are lined by all types of cells found in the PT and are not sealed off by tight junctions. Ventrally and dorsally, the intercellular spaces open toward the basement membranes separating the PT from (i) the subarachnoid space, and (ii) the perivascular space of the portal capillaries, respectively. These intercellular channels differ from the follicles, which are also found in the PT, being lined by a particular type of cell.In a second group of female rats an epoxy mixture was injected into the third ventricle; 10 min thereafter horseradish peroxidase was infused into the cisterna magna. After processing the brain for the demonstration of exogenous peroxidase, it was found that the tracer had reached the subarachnoid space adjacent to the hypothalamus and entered into all ventricular cavities with the exception of the infundibular recess. Under these experimental conditions it was found that the tracer fills all intercellular channels of the PT, thus indicating that there is no barrier between the subarachnoid space and the PT. It is suggested that the subarachnoid space should be regarded as a probable route for the transport of trophic factor(s) and/or secretory product(s) of the PT.Supported by Grant S-80-13 from Directión de Investigaciones, Universidad Austral de Chile