The floor plate of the hindbrain is a highly specialized gland. Immunocytochemical and ultrastructural characteristics.

Although the participation of the floor plate (FP) in the differentiation of neurons in the ventral spinal cord is well established, the function of the FP at the level of the hindbrain is not known. The present investigation was focused on the FP of the rat hindbrain. We used an antibody specifically labeling the rat FP (FP4) and an antiserum raised against the secretory glycoproteins of the subcommissural organ that also reacts with an intracellular material in the FP. Immunocytochemical and ultrastructural evidence was obtained indicating that the rostralmost end of the FP, at the metencephalon, is a highly specialized gland which differentiates early and undergoes regression before birth. The material(s) secreted by these FP cells appear to be transported downward into their basal processes, and upward into ventricular protrusions. It is proposed that the former would participate in the differentiation of the serotonergic neurons, and the latter could be released into the ventricle and reach distant targets. Furthermore, evidence is presented supporting the occurrence of regional and temporal specializations of the FP.

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 immunocytochemical 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.

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

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.

Effects of colchicine on the hypothalamo-neurohypophysial system of chronically salt-loaded rats.

The effect of colchicine on the hypothalamo-neurohypophysial system of rats drinking 2% NaCl for 4, 6, or 90 days was investigated. Colchicine was injected at time 0 for the 4-day group and 48 h before sacrifice for the 6- and 90-day groups. Each experimental group was divided into two subgroups that were injected with 7 micrograms colchicine into either the cisterna magna or the lateral cerebral ventricle. The hypothalamo-neurohypophysial system was investigated immunocytochemically using an antiserum against both neurophysins (NPs) as primary antibody. The arginine vasopressin content of the neural lobe (NL) of rats salt loaded for 4 days and injected with colchicine on days 0 and 3 was determined by radioimmunoassay. The amount of immunoreactive NPs in the supraoptic nucleus, the paraventricular nucleus, and in the NL was decreased in salt-loaded rats. In salt-loaded rats injected with colchicine into the lateral ventricle, a substantially larger amount of immunoreactive NPs was present in these three areas. However, when colchicine was injected into the cisterna magna, only the supraoptic nucleus appeared loaded with immunoreactive NPs, while NPs were depleted from the paraventricular nucleus. In the NL of rats salt loaded for 90 days immunoreactive NPs were diminished markedly, and axon swellings (Herring bodies) had virtually disappeared. Colchicine treatment of these rats caused an increase of immunoreactive NPs in the NL approaching control values and a reappearance of a large number of axon swellings. Results similar to those obtained with immunohistochemistry for NPs were obtained when determining the arginine vasopressin content of the NL by radioimmunoassay.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

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

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 intercullular 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.