A simple method to obtain pure cultures of multiciliated ependymal cells from adult rodents

Ependymal cells form an epithelium lining the ventricular cavities of the vertebrate brain. Numerous methods to obtain primary culture ependymal cells have been developed. Most of them use foetal or neonatal rat brain and the few that utilize adult brain hardly achieve purity. Here, we describe a simple and novel method to obtain a pure non-adherent ependymal cell culture from explants of the striatal and septal walls of the lateral ventricles. The combination of a low incubation temperature followed by a gentle enzymatic digestion allows the detachment of most of the ependymal cells from the ventricular wall in a period of 6 h. Along with ependymal cells, a low percentage (less than 6 %) of non-ependymal cells also detaches. However, they do not survive under two restrictive culture conditions: (1) a simple medium (alpha-MEM with glucose) without any supplement; and (2) a low density of 1 cell/µl. This purification method strategy does not require cell labelling with antibodies and cell sorting, which makes it a simpler and cheaper procedure than other methods previously described. After a period of 48 h, only ependymal cells survive such conditions, revealing the remarkable survival capacity of ependymal cells. Ependymal cells can be maintained in culture for up to 7-10 days, with the best survival rates obtained in Neurobasal supplemented with B27 among the tested media. After 7 days in culture, ependymal cells lose most of the cilia and therefore the mobility, while acquiring radial glial cell markers (GFAP, BLBP, GLAST). This interesting fact might indicate a reprogramming of the cell identity.

Reduction of body weight, liver steatosis and expression of stearoyl-CoA desaturase 1 by the isoflavone daidzein in diet-induced obesity

BACKGROUND AND PURPOSE

The lack of safe and effective treatments for obesity has increased interest in natural products that may serve as alternative therapies. From this perspective, we have analysed the effects of daidzein, one of the main soy isoflavones, on diet-induced obesity in rats.

EXPERIMENTAL APPROACH

Rats made obese after exposure to a very (60%) high fat-content diet were treated with daidzein (50 mg·kg(-1)) for 14 days. The dose was selected on the basis of the acute effects of this isoflavone on a feeding test. After 14 days, animals were killed and plasma, white and brown adipose tissue, muscle and liver studied for the levels and expression of metabolites, proteins and genes relevant to lipid metabolism.

KEY RESULTS

A single treatment (acute) with daidzein dose-dependently reduced food intake. Chronic treatment (daily for 14 days) reduced weight gain and fat content in liver, accompanied by high leptin and low adiponectin levels in plasma. While skeletal muscle was weakly affected by treatment, both adipose tissue and liver displayed marked changes after treatment with daidzein, affecting transcription factors and lipogenic enzymes, particularly stearoyl coenzyme A desaturase 1, a pivotal enzyme in obesity. Expression of uncoupling protein 1, an important enzyme for thermogenesis, was increased in brown adipose tissue after daidzein treatment.

CONCLUSIONS AND IMPLICATIONS

These results support the use of isoflavones in diet-induced obesity, especially when hepatic steatosis is present and open a new field of use for these natural products.

Distribution of diacylglycerol lipase alpha, an endocannabinoid synthesizing enzyme, in the rat forebrain

1,2-diacylglycerol lipase alpha (DAGLα) is responsible for the biosynthesis and release of 2-arachidonoyl-glycerol (2-AG), the most abundant endocannabinoid in the brain. Although its expression has been detected in discrete regions, we showed here an integrated description of the distribution of DAGLα mRNA and protein in the rat forebrain using in situ hybridization histochemistry and immunohistochemistry. As novelty, we described the distribution of DAGLα protein expression in the olfactory system, the rostral migratory stream, neocortex, septum, thalamus, and hypothalamus. Similar DAGLα immunostaining pattern was also found in the brain of wild-type, but not of DAGLα knockout mice. Immunohistochemical data were correlated by the identification of DAGLα mRNA expression, for instance, in the somata of specific cells in olfactory structures, rostral migratory stream and neocortex, cells in some septal-basal-amygdaloid areas and the medial habenula, and magnocellular cells of the paraventricular hypothalamic nucleus. This widespread neuronal distribution of DAGLα is consistent with multiple roles for endocannabinoids in synaptic plasticity, including presynaptic inhibition of neurotransmitter release. We discuss our comparative analysis of the forebrain expression patterns of DAGLα and other components of the endocannabinoid signaling system, including the CB(1) receptor, monoacylglyceride lipase (MAGL), and fatty acid amide hydrolase (FAAH), providing some insight into the potential physiological and behavioral roles of this system.

IGF-I stimulates neurogenesis in the hypothalamus of adult rats

In the brain of adult rats neurogenesis persists in the subventricular zone of the lateral ventricles and in the dentate gyrus of the hippocampus. By contrast, low proliferative activity was observed in the hypothalamus. We report here that, after intracerebroventricular treatment with insulin-like growth factor I (IGF-I), cell proliferation significantly increased in both the periventricular and the parenchymal zones of the whole hypothalamus. Neurons, astrocytes, tanycytes, microglia and endothelial cells of the local vessels were stained with the proliferative marker 5-bromo-2'-deoxyuridine (BrdU) in response to IGF-I. Conversely, we never observed BrdU-positive ciliated cubic ependymal cells. Proliferation was intense in the subventricular area of a distinct zone of the mid third ventricle wall limited dorsally by ciliated cubic ependyma and ventrally by tanycytic ependyma. In this area, we saw a characteristic cluster of proliferating cells. This zone of the ventricular wall displayed three cell layers: ciliated ependyma, subependyma and underlying tanycytes. After IGF-I treatment, proliferating cells were seen in the subependyma and in the layer of tanycytes. In the subependyma, proliferating glial fibrillary acidic protein-positive astrocytes contacted the ventricle by an apical process bearing a single cilium and there were many labyrinthine extensions of the periventricular basement membranes. Both features are typical of neurogenic niches in other brain zones, suggesting that the central overlapping zone of the rat hypothalamic wall could be considered a neurogenic niche in response to IGF-I.

A sensitive method to analyse the effect of putative regulatory ligands on the release of glycoprotein from primary cultures of dispersed bovine subcommissural organ cells

The subcommissural organ (SCO) releases into the cerebrospinal fluid (CSF) large glycoproteins that polymerize forming the Reissner's fibre (RF), which is involved in CSF circulation and homeostasis. We obtained high purity primary cultures of bovine secretory SCO cells and measured glycoprotein release by a reliable and sensitive ELISA method. We also analysed the effect of regulatory ligands known to control the secretory activity of the SCO. Cells cultured for short time (4h) released a high amount of glycoproteins that decreased with time. In young cultures, ATP increased and serotonin inhibited secretion rate. By contrast the acetylcholine agonist carbachol and high potassium did not evoke any detectable change in SCO glycoprotein release. These results support not only the suitability of the methodological approach but an important role of both ATP and serotonin in regulating SCO secretory activity as well.

Continuous delivery of a monoclonal antibody against Reissner's fiber into CSF reveals CSF-soluble material immunorelated to the subcommissural organ in early chick embryos

The subcommissural organ (SCO) is an ependymal differentiation located in the dorsal midline of the caudal diencephalon under the posterior commissure. SCO cells synthesize and release glycoproteins into the cerebrospinal fluid (CSF) forming a threadlike structure known as Reissner's fiber (RF), which runs caudally along the ventricular cavities and the central canal of the spinal cord. Numerous monoclonal antibodies have been raised against bovine RF and the secretory material of the SCO. For this study, we selected the 4F7 monoclonal antibody based on its cross-reactivity with chick embryo SCO glycoproteins in vivo. E4 chick embryos were injected with 4F7 hybridoma cells or with the purified monoclonal antibody into the ventricular cavity of the optic tectum. The hybridoma cells survived, synthesized and released antibody into the CSF for at least 13 days after the injection. E5 embryos injected with 4F7 antibody displayed precipitates in the CSF comprising both the monoclonal antibody and anti-RF-positive material. Such aggregates were never observed in control embryos injected with other monoclonal antibodies used as controls. Western blot analysis of CSF from E4-E6 embryos revealed several immunoreactive bands to anti-RF (AFRU) antibody. We also found AFRU-positive material bound to the apical surface of the choroid plexus primordia in E5 embryos. These and other ultrastructural evidence suggest the existence of soluble SCO-related molecules in the CSF of early chick embryos.

Reissner’s fiber formation depends on developmentally regulated factors extrinsic to the subcommissural organ

Reissner's fiber (RF) is a threadlike structure present in the third and fourth ventricles and in the central canal of the spinal cord. RF develops by the assembly of glycoproteins released into the cerebrospinal fluid (CSF) by the subcommissural organ (SCO). SCO cells differentiate early during embryonic development. In chick embryos, the release into the CSF starts at embryonic day 7 (E7). However, RF does not form until E11, suggesting that a factor other than release is required for RF formation. The aim of the present investigation was to establish whether the factor(s) triggering RF formation is (are) intrinsic or extrinsic to the SCO itself. For this purpose, SCO explants from E13 chick embryos (a stage at which RF has formed) were grafted at two different developmental stages. After grafting, host embryos were allowed to survive for 6-7 days, reaching E 9 (group 1) and E13 (group 2). In experimental group 1, the secretion released by the grafted SCOs never formed a RF; instead, it aggregated as a flocculent material. In experimental group 2, grafted SCO explants were able to develop an RF-like structure, similar to a control RF. These results suggest that the factor triggering RF formation is not present in the SCO itself, since E13 SCO secretion forms an RF in E13 brains but never develops RF-like structures when placed in earlier developmental environments. Furthermore, the glycoproteins released by implanted SCOs bind specifically to several structures: the apical portion of the mesencephalic floor plate and the choroid plexus of the third and fourth ventricles.

Msx1-Deficient Mice Fail to Form Prosomere 1 Derivatives, Subcommissural Organ, and Posterior Commissure and Develop Hydrocephalus

Msx1 is a regulatory gene involved in epithelio-mesenchymal interactions in limb formation and organogenesis. In the embryonic CNS, the Msx1 gene is expressed along the dorsal midline. Msx1 mutant mice have been obtained by insertion of the nlacZ gene in the Msx1 homeodomain. The most important features of homozygous mutants that we observed were the absence or malformation of the posterior commissure (PC) and of the subcommissural organ (SCO), the collapse of the cerebral aqueduct, and the development of hydrocephalus. Heterozygous mutants developed abnormal PC and reduced SCO, as revealed by specific antibodies against SCO secretory glycoproteins. About one third of the heterozygous mutants also showed hydrocephalus. Other defects displayed by homozygous mutants were ependymal denudation, subventricular cavitations and edema, and underdevelopment of the pineal gland and subfornical organ. Some homozygous mutants developed both SCO and PC, probably as a consequence of genetic redundancy with Msx2. However, these mutants did not show SCO-immunoreactive glycoproteins and displayed obstructive hydrocephalus. This suggests that Msx1 is necessary for the synthesis of SCO glycoproteins, which would then be required for the maintenance of an open aqueduct.

Immunocytochemical characterisation of the wall of the bovine lateral ventricle

The cytoarchitecture of the walls of the bovine lateral ventricles was investigated by the use of immunocytochemistry. We defined three types of walls. Type 1 lined regions of white matter and had ciliated cuboidal ependyma, a few subependymal cells and a narrow subjacent glial layer. Type 2 lined the striatum and possessed ependymal cells with conspicuous basal processes that extended through a wide subependyma containing many subependymal cells and a wide subjacent glial network. Type 3 lined the rostral horn and displayed ependymal cells with the longest basal processes and wider subependymal and glial layers. Ependymal cells of type 2 and 3 walls were labelled with antibodies against S-100beta protein, vimentin, GFAP, BLBP and nestin. Anti-betaIII-tubulin stained small cells in the subependyma and inside the GFAP- and vimentin-positive subjacent glial network. Anti-PCNA-positive nuclei were abundant in the subependymal and glial layers of type 2 and 3 walls. DiI in vitro tracing studies revealed small bipolar cells in the glial layer at a distance from the site of the label deposit. These results suggest that neurogenesis takes place in adult bovine subependyma mostly in the walls of the striatum and the rostral horn, and that young neuroblasts may migrate in a rostro-ventral direction through the glial network.

The transcription factor Pax6 is required for development of the diencephalic dorsal midline secretory radial glia that form the subcommissural organ

During brain development, Pax6 is expressed in specific regions of the diencephalon including secretory cells of the subcommissural organ (SCO), a circumventricular organ at the forebrain-midbrain boundary that originates from the pretectal dorsal midline neuroepithelial cells beneath the posterior commissure (PC). Homozygous small eye (Sey/Sey) mice lack functional Pax6 protein and fail to develop the SCO, a normal PC and the pineal gland. Small eye heterozygotes (Sey/+) show defective development of the SCO's basal processes which normally penetrate the PC, indicating that normal development of the gland requires normal Pax6 gene-dosage. A correlation between the defects of SCO formation and altered R- and OB-cadherin expression patterns in the SCO is observed in mutants suggesting a role for cadherins in SCO development.

A programmed ependymal denudation precedes congenital hydrocephalus in the hyh mutant mouse

Hydrocephalic hyh mice are born with moderate hydrocephalus and a normal cerebral aqueduct. At about the fifth postnatal day the aqueduct becomes obliterated and severe hydrocephalus develops. The aim of the present investigation was to investigate the mechanism of this hydrocephalus, probably starting during fetal life when the cerebral aqueduct is still patent. By use of immunocytochemistry and scanning electron microscopy, mutant (n = 54) and normal (n = 61) hyh mouse embryos were studied at various developmental stages to trace the earliest microscopic changes occurring in the brains of embryos becoming hydrocephalic. The primary defect begins at an early developmental stage (E-12) and involves cells lining the brain cavities, which detach following a well-defined temporo-spatial pattern. This ependymal denudation mostly involves the ependyma of the basal plate derivatives. There is a relationship between ependymal denudation and ependymal differentiation evaluated by the expression of vimentin and glial fibrillary acidic protein. The ependymal cells had a normal appearance before and after detachment, suggesting that their separation from the ventricular wall might be due to abnormalities in cell adhesion molecules. The process of detachment of the ventral ependyma, clearly visualized under scanning electron microscope, is almost completed before the onset of hydrocephalus. Furthermore, this ependymal denudation does not lead to aqueductal stenosis during prenatal life. Thus, the rather massive ependymal denudation appears to be the trigger of hydrocephalus in this mutant mouse, raising the question about the mechanism responsible for this hydrocephalus. It seems likely that an uncontrolled bulk flow of brain fluid through the extended areas devoid of ependyma may be responsible for the hydrocephalus developed by the hyh mutant embryos. The defect in these embryos also includes loss of the hindbrain floor plate and a delayed in the expression of Reissner fiber glycoproteins by the subcommissural organ.

Immunocytochemical detection of Reissner's fiber-like glycoproteins in the subcommissural organ and the floor plate of wildtype and cyclops mutant zebrafish larvae

The subcommissural organ (SCO) and the floor plate (FP) secrete high molecular weight glycoproteins that polymerize in the form of the Reissner's fiber (RF). To study to what extent the absence of the FP affects the expression of these glycoproteins, we have investigated the brain and spinal cord of 48-h and 72-h wildtype and cyclops (cyc) mutant zebrafish larvae by using a polyclonal antiserum against bovine RF. Wildtype larvae showed immunoreactivity in the SCO at the dorsal forebrain-midbrain boundary. In the ventricle, over the SCO surface, thin immunoreactive fibers aggregated into an RF that ran along the third and fourth ventricles and the central canal of the spinal cord until, at its caudal end, the fiber disintegrated and formed a strongly immunoreactive massa caudalis that left the neural tube and invaded the surrounding tissues of the tail fin. The rostral end of the FP, lining the pontine flexure, was also strongly immunoreactive, as was the caudal third of the FP. Cyc mutants showed an immunoreactive SCO and fibrous material in the ventricle, but an RF was missing. There was no label in the ventral midline of the neural tube except in some specimens in which the caudal FP persisted and was immunoreactive. It is concluded that the product of the cyc gene is not required for the expression of SCO glycoproteins but for their polymerization into an RF in the brain ventricles.

Analysis and quantification of the secretory products of the subcommissural organ by use of monoclonal antibodies

Bovine Reissner's fiber (RF) glycoproteins were used as antigen for the production of polyclonal and monoclonal antibodies (Mabs). We also produced Mabs against intracellular secretory glycoproteins of the bovine subcommissural organ (SCO). These Mabs were used for immunodetection of secretory proteins in situ (structural and ultrastructural immunocytochemistry), in blots, and in solutions. Three different antigen-mediated ELISA were designed to evaluate the affinity of the Mabs, to study the nature of the epitopes, and for competition test among Mabs. Two double antibody sandwich ELISA were designed to detect and quantify soluble secretory materials in different samples, to study coexistence of epitopes, and to elucidate whether epitopes for Mabs are repeated or not in the RF-glycoproteins. Twenty-three Mabs recognizing the bovine RF- and SCO-glycoproteins in solutions (ELISA) as well as in tissue sections, were obtained. Nineteen of these Mabs also recognized the pig SCO, 11 the rabbit SCO, 6 the dog SCO, and 5 the rat SCO. None of the Mabs recognized the SCO of non-mammalian species. The different types of ELISA demonstrated that: (1) the epitopes reside in the proteinaceous moiety of the secretion, (2) they coexist in the same molecular forms and, with few exceptions, they did not overlap, (3) they were not repeated in the secretory molecule(s). Three Mabs were used for immunoblotting of RF; one of them revealed the same band pattern as that shown by an anti-RF serum. It is concluded that all Mabs raised in our laboratory are directed against non-repeated sequences of RF-glycoproteins that have not been conserved in vertebrate phylogeny.

Neural input and neural control of the subcommissural organ

The neural control of the subcommissural organ (SCO) has been partially characterized. The best known input is an important serotonergic innervation in the SCO of several mammals. In the rat, this innervation comes from raphe nuclei and appears to exert an inhibitory effect on the SCO activity. A GABAergic innervation has also been shown in the SCO of the rat and frog Rana perezi. In the rat, GABA and the enzyme glutamate decarboxylase are involved in the SCO innervation. GABA is taken up by some secretory ependymocytes and nerve terminals, coexisting with serotonin in a population of synaptic terminals. Dopamine, noradrenaline, and different neuropeptides such as LH-RH, vasopressin, vasotocin, oxytocin, mesotocin, substance P, alpha-neoendorphin, and galanin are also involved in SCO innervation. In the bovine SCO, an important number of fibers containing tyrosine hydroxylase are present, indicating that in this species dopamine and/or noradrenaline-containing fibers are an important neural input. In Rana perezi, a GABAergic innervation of pineal origin could explain the influence of light on the SCO secretory activity in frogs. A general conclusion is that the SCO cells receive neural inputs from different neurotransmitter systems. In addition, the possibility that neurotransmitters and neuropeptides present in the cerebrospinal fluid may also affect the SCO activity, is discussed.

Searching for specific binding sites of the secretory glycoproteins of the subcommissural organ

The molecular organization of Reissner's fiber (RF), the structure of its proteins, and the permanent turnover of these proteins are all facts supporting the possibility that RF may perform multiple functions. There is evidence that CSF-soluble RF-glycoproteins may occur under physiological conditions. The present investigation was designed to investigate the probable existence within the CNS of specific binding sites for RF-glycoproteins. Three experimental protocols were used: (1) immunocytochemistry of the CNS of bovine fetuses using anti-idiotypic antibodies, raised against monoclonal antibodies developed against bovine RF-glycoproteins; (2) in vivo binding of the RF glycoproteins, perfusing into the rat CSF 125I-labeled RF-glycoproteins, or grafting SCO into a lateral ventricle of the rat; (3) in vitro binding of unlabeled RF-glycoproteins to rat and bovine choroid plexuses maintained in culture. One of the anti-idiotypic antibody generated by a Mab raised against RF-glycoproteins binds to choroidal cells. Furthermore, binding of RF-glycoproteins to the rat choroid plexus was obtained when: (1) the choroid plexus was cultured in the presence of unlabeled RF-glycoproteins; (2) the concentration of soluble RF-glycoproteins in the CSF was increased by isografting SCOs into a lateral ventricle; (3) radiolabeled glycoproteins were perfused into the ventricular CSF. This evidence suggests that the apical plasma membrane of the ependymal cells of the choroid plexus has specific binding sites for RF-glycoproteins, of unknown functional significance. The radiolabeled RF-glycoproteins perfused into the rat CSF also bound to the paraventricular thalamic nucleus, the floor of the Sylvian aqueduct and of the rostral half of the fourth ventricle, and the meninges of the brain and spinal cord. The labeling of the paraventricular thalamic nucleus points to a functional relationship between this nucleus and the SCO. The possibility that the SCO may be a component of the circadian timing system is discussed.

Identification of Reissner's fiber-like glycoproteins in two species of freshwater planarians (Tricladida), by use of specific polyclonal and monoclonal antibodies

By using one polyclonal antiserum raised against bovine Reissner's fiber and seven monoclonal antibodies raised against bovine Reissner's fiber and against immunopurified bovine subcommissural organ glycoproteins, we have investigated two freshwater planarian species (Girardia tigrina, Schmidtea mediterranea) by light- and electron-microscopic immunocytochemistry. ELISA probes showed that the monoclonal antibodies recognized different, nonoverlapping, unrepeated, proteinaceous epitopes present in the same compounds of bovine Reissner's fiber. Cells immunoreactive to the polyclonal and monoclonal antibodies were found in the dorsal and ventral integument of both planarian species. Labeled cuboid epidermal cells bore cilia and displayed several types of secretory granules; they were covered by a film of immunoreactive material. Studies on adjacent thin and semithin sections revealed coexistence of label in the same regions and in the same cells when two different monoclonal antibodies were used. These results indicate that a secretory substance immunologically similar to the secretion of the vertebrate subcommissural organ is present in primitive tripoblasts such as planarians, suggesting that these secretions are ancient and well conserved in phylogeny.

Ependymal explants from the lateral ventricle of the adult bovine brain: a model system for morphological and functional studies of the ependyma

By gently scraping off the surface of the lateral ventricles of adult bovine brains, we obtained sheets containing the ependymal layer and some attached sub-ependymal cells. Explants were cultured in serum-free medium or in two media enriched with 20% fetal calf serum or 20% adult bovine cerebrospinal fluid, and processed for different time intervals from 4 h to 60 days. For characterization of the ependymal cells we used antisera against S-100 protein, vimentin and glial fibrillary acidic protein (GFAP). For comparison, the ependyma of adult bovines and of fetuses from days 60 to 120 post coitum was studied in situ. The adult ependyma consisted of a ciliated, cuboid cell monolayer with short basal processes; it displayed S-100 immunoreactivity but only scarce deposits of vimentin and no GFAP. The fetal ependyma had the appearance of a pseudostratified epithelium with elongated nuclei and basal processes containing S-100 and vimentin from day 80 post coitum and GFAP from day 100 post coitum. In explants, no differences were seen between the three culture media; the ependyma became pseudostratified, developed basal processes and showed increasing amounts of S-100 and vimentin first, and subsequently also GFAP. These changes were concomitant with the onset of mitotic activity in the subependymal layer leading to the production of numerous cells. The morphological and immunocytochemical features of ependymal cells in cultured explants resembled those of fetal ependyma. Our results indicate that the culture of ependymal explants from adult bovine lateral ventricles is an useful model system for morphological and functional studies of the ependyma and for the analysis of cell proliferation in the subependymal layer.

The subcommissural organ of the frog Rana perezi is innervated by nerve fibres containing GABA

The innervation of the frog subcommissural organ was studied by light-microscopic and ultrastructural immunocytochemistry using antisera against serotonin, noradrenaline, dopamine, gamma-aminobutyric acid (GABA), glutamic acid decarboxylase, different GABA receptor subunits and bovine Reissner's fibre material (AFRU). In the proximity of the organ, serotonin- and noradrenaline-containing fibres were rare whereas dopamine-immunoreactive fibres were more numerous. Many GABA- and glutamic acid decarboxylase-containing nerve fibres were found at the basal portion of the ependymal cells of the subcommissural organ. Under the electron microscope, these GABA-immunolabelled nerve endings appeared to establish axoglandular synapses with secretory ependymal cells of the subcommissural organ. In addition, the secretory ependymal cells expressed high amounts of the beta2-subunit of the GABA(A) receptor. Since GABA-immunoreactive neurons were present in the frog pineal organ proper and apparently contributed axons to the pineal tract, we suggest that at least part of the GABAergic fibres innervating the frog subcommissural organ could originate from the pineal organ.

Quantification of the secretory glycoproteins of the subcommissural organ by a sensitive sandwich ELISA with a polyclonal antibody and a set of monoclonal antibodies against the bovine Reissner's fiber

The subcommissural organ (SCO) is an ependymal brain gland that releases glycoproteins into the ventricular cerebrospinal fluid where they condense to form the Reissner's fiber (RF). We have developed a highly sensitive and specific two-antibody sandwich enzyme-linked immunosorbent assay (ELISA) for the quantification of the bovine SCO secretory material. The assay was based on the use of the IgG fraction of a polyclonal antiserum against the bovine RF as capture antibody and a pool of three peroxidase-labeled monoclonal antibodies that recognize non-overlapping epitopes of the RF glycoproteins as detection antibody. The detection limit was 1 ng/ml and the working range extended from 1 to 4000 ng/ml. The calibration curve, generated with RF glycoproteins, showed two linear segments: one of low sensitivity, ranging from 1 to 125 ng/ml, and the other of high sensitivity between 125 and 4000 ng/ml. This assay was highly reproducible (mean intra- and interassay coefficient of variation 2.2% and 5.3%, respectively) and its detectability and sensitivity were higher than those of ELISAs using exclusively either polyclonal or monoclonal antibodies against RF glycoproteins. The assay succeeded in detecting and measuring secretory material in crude extracts of bovine SCO, culture medium supernatant of SCO explants and incubation medium of bovine RF; however, soluble secretory material was not detected in bovine cerebrospinal fluid.

Neuraminidase injected into the cerebrospinal fluid impairs the assembly of the glycoproteins secreted by the subcommissural organ preventing the formation of Reissner's fiber

Neuraminidase was injected into the cerebrospinal fluid of normal rats to investigate the assembly and fate of the desialylated Reissner's fiber glycoproteins. It was established that a single injection of neuraminidase cleaved the sialic acid residues of the Reissner's fiber glycoproteins that had been assembled before the injection, and of the molecules that were released over a period of at least 4 h after the injection. These desialylated glycoproteins underwent an abnormal assembly that led to the formation of spheres instead of a fiber. The number of these spheres increased during the 4-h period following the injection, indicating that neuraminidase did not prevent the secretion of the Reissner's fiber glycoproteins into the cerebrospinal fluid. The spheres remained attached to the surface of the subcommissural organ and became intermingled with infiltrating cells, many of which were immunocytochemically identified as macrophages. The latter were seen to contain immunoreactive Reissner's fiber material. It is concluded that the desialylated Reissner's fiber glycoproteins forming the spheres underwent an in situ degradation by macrophages, thus resembling the normal process undergone by the Reissner's fiber glycoproteins reaching the massa caudalis.

Floor plate and the subcommissural organ are the source of secretory compounds of related nature: comparative immunocytochemical study

The subcommissural organ of vertebrates secretes glycoproteins into the third ventricle that condense to form Reissner's fiber (RF). Antibodies raised against the bovine RF-glycoproteins reacted with the floor plate (FP) cells of two teleost (Oncorhynchus kisutch, Sparus aurata) and two amphibian (Xenopus laevis, Batrachyla taeniata) species. At the ultrastructural level, the immunoreactivity was confined to secretory granules, mainly concentrated at the apical cell pole. In the rostro-caudal axis, a clear zonation of the FP was distinguished, with the hindbrain FP being the most, or the only (Batrachyla taeniata), immunoreactive region of the FP. In all the species studied, the caudal FP lacked immunoreactivity. Both the chemical nature of the immunoreactive material and the rostro-caudal zonation of the FP appear to be conservative features. Evidence was obtained that the FP secretes into the cerebrospinal fluid a material chemically related to the RF-glycoproteins secreted by the subcommissural organ. Thus, in addition to being the source of contact-mediated and diffusible signals, the FP might also secrete compounds into the cerebrospinal fluid that may act on distant targets.

Spontaneous congenital hydrocephalus in the mutant mouse hyh. Changes in the ventricular system and the subcommissural organ

The subcommissural organ is an ependymal gland located at the entrance of the cerebral aqueduct. It secretes glycoproteins into the cerebrospinal fluid, where they aggregate to form Reissner's fiber. This fiber grows along the aqueduct, fourth ventricle, and central canal. There is evidence that the subcommissural organ is involved in the pathogenesis of congenital hydrocephalus. This organ was investigated in the mutant mouse hyh developing a congenital hydrocephalus. The central nervous system of normal and hydrocephalic hyh mice, 1 to 40 days old, was investigated using antibodies recognizing the subcommissural organ secretory glycoproteins, and by transmission and scanning electron microscopy. At birth, the affected mice displayed open communications between all ventricles, absence of a central canal in the spinal cord, ependymal denudation of the ventricles, stenosis of the rostral end of the aqueduct, and hydrocephalus of the lateral and third ventricles and of the caudal end of the aqueduct. Around the 5th postnatal day, the communication between the caudal aqueduct and fourth ventricle sealed, and hydrocephalus became severe. It is postulated that the hyh mice carry a genetic defect affecting the ependymal cell lineage. The subcommissural organ showed signs of increased secretory activity; it released to the stenosed aqueduct a material that aggregated, but it did not form a Reissner's fiber. A large area of the third ventricular wall differentiated into a secretory ependyma synthesizing a material similar to that secreted by the subcommissural organ. It is concluded that the subcommissural organ changes during hydrocephalus; whether these changes precede hydrocephalus needs to be investigated.

Rostral floor plate (flexural organ) secretes glycoproteins immunologically similar to subcommissural organ glycoproteins in dogfish (Scyliorhinus canicula) embryos

The subcommissural organ of vertebrates secretes glycoproteins into the cerebrospinal fluid of the third cerebral ventricle. This material polymerizes in Reissner's fiber. During ontogenetic development, besides the subcommissural organ, the ependyma lining the pontine flexure constitutes an additional Reissner's fiber-secreting gland named flexural organ. We have studied the secretion of the flexural organ and the subcommissural organ in dogfish (Scyliorhinus canicula) embryos using three different antisera and the lectins concanavalin A and wheat germ agglutinin. AFRU is an antiserum against the bovine Reissner's fiber, Ab-600 is an antiserum against 600 kDa dogfish subcommissural organ glycoproteins; and APSO is an antiserum against immunoaffinity purified bovine subcommissural organ secretory glycoproteins. These three antisera immunostained the flexural organ indicating that it contains epitopes similar to those present in bovine and dogfish subcommissural organ glycoproteins. It seems highly probable that the flexural organ and the subcommissural organ of dogfish embryos secrete similar compound(s). Other ependymal regions were also immunostained with Ab-600 and APSO antisera. Then, Reissner's fiber-like glycoproteins were transiently expressed by most embryonary ependymal cells. These glycoproteins might play a role in the development of the central nervous system of vertebrates.

Identification of a high molecular weight polypeptide in the subcommissural organ of the chick embryo

The subcommissural organ is an ependymal brain gland that secretes, into the ventricular cerebrospinal fluid, high molecular weight glycoproteins that form Reissner's fiber. Precursor and processed forms of secretion have been demonstrated by immunoblotting in the subcommissural organ of mammals and fish. In the chicken only a processed form has as yet been identified. In the present report, we have studied the subcommissural organ of 13-day-old chick embryos using (1) an antiserum against bovine Reissner's fiber, and (2) the lectins, concanavalin A and Limax flavus agglutinin. Paraffin sections of the subcommissural organ and blots of subcommissural organ extracts have been analyzed. The ependymal cells of sectioned subcommissural organ are strongly stained with the antiserum. Concanavalin A binds to materials in all cytoplasmatic regions, whereas Limax flavus agglutinin identifies materials confined to the apex of the ependymal cells. In the blots, a band of 540 kDa is immunostained. This band is positive for concanavalin A positive but negative for Limax flavus agglutinin and is thereby regarded as representing a precursor form of the secretion.

Seasonal variation in the secretory activity of the subcommissural organ (SCO) of reptiles

Seasonal variations in the secretory activity of the subcommissural organ (SCO) of snakes and turtles was studied by immunocytochemistry, lectins, and electron microscopy. In animals sacrificed in summer, immunoreactive material, mostly devoid of sialic acid, occupied the whole cytoplasm. Cells showed many distended cisternae of rough endoplasmic reticulum and secretory granules. In animals sacrificed in winter, patches of immunoreactive sialic acid-rich material occupied the apical cytoplasm. Cells lacked distended cisternae and the secretory granules formed clusters. These results suggest a decreased synthesis and release of secretory material in the SCO of lethargic reptiles.

Bovine Reissner's fiber (RF) and the central canal of the spinal cord: an immunocytochemical study using a set of monoclonal antibodies against the RF-glycoproteins

The subcommissural organ secretes N-linked complex-type glycoproteins into the cerebrospinal fluid. These glycoproteins condense to form Reissner's fiber (RF), which extends along the fourth ventricle and central canal of the spinal cord. A set of three monoclonal antibodies (Mabs 3E6, 3B1, and 2A5) has been obtained using these glycoproteins as immunogens. Competitive and sandwich enzyme-linked immunoassay methods have demonstrated that the three monoclonal antibodies are directed against different epitopes, and that there is no competition among them for their binding to glycoproteins of RF. Mab 3E6 displays immunoblotting properties that are similar to those of a polyclonal antibody against the pool of glycoproteins from RF, but that are different from those of Mabs 3B1 and 2A5. All three antibodies immunostain the bovine subcommissural organ and RF. A population of ependymal cells is stained by the polyclonal antibody, and Mabs 2A5 and 3E6, but not by Mab 3B1. The material present in a population of ependymal cells of the central canal, and the glycoproteins secreted by the subcommissural organ thus probably have partial chemical identity. Some evidence suggests that the immunoreactive ependymal cells are secretory cells. The luminal surface of the central canal is coated by a thin layer of material with immunocytochemical characteristics different from those of the ependymal cells; such a coat may correspond to material released from RF.

Ependymal denudation, aqueductal obliteration and hydrocephalus after a single injection of neuraminidase into the lateral ventricle of adult rats

To investigate the role of sialic acid in the ependyma of the rat brain, we injected neuraminidase from Clostridium perfingens into the lateral ventricle of 86 adult rats that were sacrificed at various time intervals. After administration of 10 micrograms neuraminidase, ciliated cuboidal ependymal cells of the lateral ventricles, third ventricle, cerebral aqueduct, and the rostral half of the fourth ventricle died and detached. The ependymal regions sealed by tight junctions such as the choroid plexus and the subcommissural organ were not affected. Debris was removed by infiltrating neutrophils and macrophagic cells. At the same time, after ependymal disappearance, the aqueduct was obliterated. In this region, mitoses were evident and cystic ependymal cells were frequent. Hydrocephalus of the lateral and third ventricles was evident 4 days after neuraminidase injection. Gliosis was restricted to the dorsal telencephalic wall of the injected lateral ventricle. It is thought that cleavage of sialic acid from ependymal surface glycoproteins or glycolipids, likely involved in cell adhesion, led to the detaching and death of the ependymal cells. Thereafter, ependymal loss, together with edema, led to fusion of the lateral walls of the cerebral aqueduct and this in turn provoked hydrocephalus of the third and lateral ventricles. This model of experimental hydrocephalus is compared with other models, in particular those of hydrocephalus after viral invasion of the cerebral ventricles.

Distribution of galanin-like immunoreactive elements in the brain of the adult lamprey Lampetra fluviatilis

Galanin is a brain-gut peptide present in the central nervous system of vertebrates and invertebrates. The distribution of galanin-like immunoreactive perikarya and fibers in the brain of the river lamprey Lampetra fluviatilis (Agnatha) has been studied immunocytochemically by using antisera against rat and porcine galanin. Galanin-like immunoreactive perikarya were seen in the telencephalon and mediobasal diencephalon. In the telencephalon, they were present in the nucleus olfactorius anterior, nucleus basalis, and especially, in the nucleus commissurae anterioris. The diencephalon contained most of the immunoreactive neurons. They were located in the nucleus commissurae praeinfundibularis, nucleus ventralis hypothalami, nucleus commissurae postinfundibularis, nucleus ventralis thalami, and nucleus dorsalis thalami pars medius. Most of the galanin-like immunoreactive infundibular neurons showed apical processes contacting the cerebrospinal fluid. Immunoreactive fibers and terminals were widely distributed throughout the neuraxis. In the telencephalon, the richest galaninergic innervation was found in the nucleus olfactorius anterior, lobus subhippocampalis, corpus striatum, and around the nucleus septi and the nucleus praeopticus. In the diencephalon, the highest density of galanin-like immunoreactive fibers was seen in the nucleus commissurae postopticae, nucleus commissurae praeinfundibularis, nucleus ventralis hypothalami, nucleus dorsalis hypothalami, and neurohypophysis. In the mesencephalon and rhombencephalon, the distribution of immunoreactive fibers was heterogeneous, being most pronounced in a region between the nucleus nervi oculomotorii and the nucleus interpeduncularis mesencephali, in the nucleus isthmi, and in the raphe region. A subependymal plexus of immunoreactive fibers was found throughout the ventricular system. The distribution of immunoreactive neurons and fibers was similar to that of teleosts but different to those of other vertebrate groups. The possible hypophysiotropic and neuroregulatory roles of galanin are discussed.

Development of melanin-concentrating hormone-immunoreactive elements in the brain of gilthead seabream (Sparus auratus)

The development of the hypothalamic melanin-concentrating hormone (MCH) system of the teleost Sparus auratus has been studied by immunocytochemistry using an anti-salmon MCH serum. Immunoreactive perikarya and fibers are found in embryos, larvae, and juvenile specimens. In juveniles, most labeled neurons are present in the nucleus lateralis tuberis; some are dispersed in the nucleus recessus lateralis and nucleus periventricularis posterior. From the nucleus lateralis tuberis, MCH neurons project a conspicuous tract of fibers to the ventral hypothalamus; this penetrates the pituitary stalk and reaches the neurohypophysis. Most fibers end close to the cells of the pars intermedia, and some reach the adenohypophysial rostral pars distalis. Immunoreactive fibers can also be seen in extrahypophysial localizations, such as the preoptic region and the nucleus sacci vasculosi. In embryos, MCH-immunoreactive neurons first appear at 36h post-fertilization in the ventrolateral margin of the developing hypothalamus. In larvae, at 4 days post-hatching, perikarya can be observed in the ventrolateral border of the hypothalamus and in the mid-hypothalamus, near the ventricle. At 26 days post-hatching, MCH perikarya are restricted to the nucleus lateralis tuberis. The neurohypophysis possesses MCH-immunoreactive fibers from the second day post-hatching. The results indicate that MCH plays a role in larval development with respect to skin melanophores and cells that secrete melanocyte-stimulating hormone.

Antibody-mediated lysis of the bovine subcommissural organ maintained in culture

The subcommissural organ (SCO) is a brain gland that secretes glycoproteins into the cerebrospinal fluid (CSF). It is an ancient and conserved secretory structure of the brain, developing very early in ontogeny. However, the function of the SCO is unknown. The secretory cells of the SCO are arranged into a single or double, irregularly shaped layer located at the interface of the CSF and nervous tissue. This has prevented its selective surgical destruction. The present investigation was designed to destroy the secretory cells of 30-day-old explants of bovine SCO by use of an immunological approach. A membrane preparation enriched with plasma membrane of the secretory cells of the bovine SCO was obtained. This preparation was further processed to separate the structural proteins. A similar procedure was applied to obtain a fraction of integral proteins of the plasma membrane of a nonsecretory ciliated ependyma. Antisera were prepared against both preparations of integral proteins. The antiserum against the fraction obtained from the SCO cells immunostained the plasma membrane of the bovine SCO cells and in immunoblot it reacted with several proteins of the membrane preparation from SCO cells. When added to the culture medium this antibody bound to the apical plasma membrane of the secretory ependyma of the bovine SCO kept in culture; it caused the lysis of these cells when used together with complement. None of these properties were displayed by the antiserum raised against the integral proteins of the plasma membrane of the ciliated ependyma. This antiserum, however, immunostained the bovine ciliated ependyma neighboring the SCO. These results indicate that immunological surgery of the SCO in living animals may be possible to achieve.

Central projections from the goldfish pineal organ traced by HRP-immunocytochemistry

Pineal efferent projections have been traced in the brain of the goldfish (Carassius auratus) by administration of a concentrated solution of horseradish peroxidase onto the pineal organ. After different survival times, fish were sacrificed and the administered peroxidase was revealed by immunocytochemistry on paraffin sections using an anti-horseradish peroxidase antiserum. Immunoreactive fibres were seen in the anterior hypothalamus, habenula, dorsal thalamus, ventral thalamus, optic tectum, torus longitudinalis, area pretectalis, torus semicircularis and dorsal tegmentum. No immunoreactive cell bodies were visualized in the central nervous system, thus suggesting the absence of central pinealopetal innervation. Since all areas showing pineal labelled fibres are also known to receive retinal inputs, it can be suggested that an overlapping of information from retinal and extraretinal photoreceptors may be important to processes depending on photic stimulation such as entrainment of circadian rhythms or photoneuroendocrine responses.

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.

Distribution of galanin-like immunoreactivity in the brain of the turtle Mauremys caspica

Galanin is a brain-gut peptide present in the central nervous system of fish, amphibians, birds, and mammals. For comparative studies among vertebrates, the distribution of galanin in the brain of reptiles has been investigated. We studied the localization of galanin-like-immunoreactive perikarya and nerve fibers in the brain of the turtle Mauremys caspica by using an antiserum against porcine galanin. In the telencephalon, few immunoreactive perikarya were seen in the amygdaloid complex. The diencephalon contained the majority of the immunoreactive perikarya present in the lamina terminalis, nucleus periventricularis anterior, lateral preoptic area, nuclei hypothalamicus ventromedialis and posterior, nucleus basalis of the anterior commissure, and nucleus ventralis tuberis. Many immunoreactive cells, especially in the infundibulum, contacted the cerebrospinal fluid by an apical process. In the rhombencephalon, immunopositive perikarya were restricted to a few cells in the nucleus tractus solitari. In the mesencephalon, they were absent. Immunoreactive nerve fibers were present in all regions containing labeled perikarya and in 1) telencephalon: septum, nucleus fasciculi diagonalis Brocae; 2) diencephalon: nucleus paraventricularis, nucleus supraopticus, nucleus suprachiasmaticus, subventricular grey, nucleus of the paraventricular organ, nucleus mamillaris, infundibular decussation, outer layer of the median eminence, posterior commissure and subcommissural organ region, habenula, nuclei dorsomedialis anterior, and dorsolateralis anterior of the thalamus; and 3) mesencephalon and rhombencephalon: stratum griseum periventriculare, stratum fibrosum periventriculare, laminar nucleus of the torus semicircularis, periventricular grey, nucleus interpeduncularis, nucleus ruber, substantia nigra, locus coeruleus, raphe nuclei, nuclei of the reticular formation, nucleus motorius nervi trigemini, cochlear and vestibular area, and nucleus spinalis nerve trigemini. Our results suggest that galanin may have hypophysiotropic and central roles in the turtle Mauremys caspica.

Perinotochordal connective sheet of gilthead sea bream larvae (Sparus aurata, L.) affected by axial malformations: an histochemical and immunocytochemical study

BACKGROUND

Spinal malformations in adult teleosts occur under natural conditions and, more frequently, in culture exploitations. Skeletal deformities are linked with dysfunctions in collagen metabolism. We studied axial deviations appearing in early larval stages of cultured sea bream (Sparus aurata, L.).

METHODS

To evaluate connective tissue components of normal and lordotic fish we used histochemistry (alcian blue, picrosirius-polarization, clorhydric orcein, fuchsin resorcin), immunohistochemistry (anti-collagen I, II, III, and IV), and specific enzymatic digestions. The results were evaluated by semiquantitative methods.

RESULTS

Lordosis appeared before a vertebral column was developed, thus affecting the only skeletal structure present in the animal body, the notochord. At this stage the animal depends on the vitelline sac and an inflated swim-bladder is missing. The region of the curvature showed strong alterations in the arrangement of the muscle bundles and irregularities in notochord and perinotochordal collagen sheet. Histochemical and immunocytochemical analysis of the perinotochordal sheet revealed the presence of type II collagen, non-sulfated glycosaminoglycans, and elastic fibers in normal and lordotic specimens. Low collagen-proteoglycan interactions occurred in lordotic animals.

CONCLUSIONS

Lordosis in Sparus aurata originated during embryonic development and was characterized by disorganized connective tissue and muscle bundles. No major differences in connective tissue constituents were seen with respect to normal specimens.

Skeletal deformities of the gilthead sea bream (Sparus aurata, L.): study of the subcommissural organ (SCO) and Reissner's fiber (RF)

A high incidence of lordotic curvatures has been detected in commercial cultures of Sparus aurata. We have studied juvenile and adult lordotic specimens to elucidate whether the subcommissural organ and its secretion, the Reissner's fiber, play any role in the development of this syndrome. Animals were X-radiographed and then the brain and spinal cord dissected out and processed for light microscopy. Adult lordotic fishes had a well developed swim-bladder whereas juvenile did not. The central canal of the spinal cord showed dramatic alterations, and an altered Reissner's fiber was always present. Our histochemical results suggested a hyperactivity of the subcommissural organ in lordotic fishes.

Combined use of immunocytochemistry and lectin histochemistry for the study of the hypothalamic neurosecretory system of the snake Natrix maura (L.)

Natrix maura snakes were processed for immunocytochemistry and lectin histochemistry at both light- and electron-microscopic levels. Antisera against bovine neurophysins, vasotocin and mesotocin were used as well as concanavalin A, wheat germ and Limax flavus agglutinin lectins. The hypothalamic supraoptic and paraventricular nuclei were studied. Vasotocin neurons should contain a glycopeptide and displayed large colloid droplets consisting of large cisternae filled with packed secretory material. Mesotocin was located in different neurons.

Decreased cerebrospinal fluid flow through the central canal of the spinal cord of rats immunologically deprived of Reissner's fibre

The subcommissural organ is an ependymal brain gland that secretes glycoproteins to the cerebrospinal fluid (CSF) of the third ventricle. They condense to form a fibre, Reissner's fibre (RF), that runs along the aqueduct and fourth ventricle and the central canal of the spinal cord. A single injection of an antibody against the secretory glycoproteins of RF into a lateral ventricle of adult rats results in animals permanently deprived of RF in the central canal and bearing a "short" RF extending only along the aqueduct and the fourth ventricle. These animals, together with untreated control animals were used to investigate the probable influence of RF in the circulation of CSF in the central canal of the spinal cord. For this purpose, two tracers, (horseradish peroxidase and rabbit immunoglobulin) were injected into the ventricular CSF. The animals were killed 13, 20, 60, 120 and 240 min after the injection, and the amount of the tracers was estimated in tissue sections obtained at proximal, medial and distal levels of the spinal cord. In rats deprived of RF, a significant decrease in the amount of tracers present in the central canal was observed at all experimental intervals, being more evident at 20 min after the injection of the tracers. This suggests that lacking a RF in the central canal decreases the bulk flow of CSF along the central canal. Turbulences of the CSF at the entrance of the central canal of RF-deprived rats might explain the inability of the regenerating RF to progress along the central canal, as well as the reduced flow of CSF in the central canal of these animals.

Immunocytochemical localization of corticotropin-releasing factor in the brain of the turtle, Mauremys caspica

Brain sections of the turtle, Mauremys caspica were studied by means of an antiserum against rat corticotropin-releasing factor. Immunoreactive neurons were identified in telencephalic, diencephalic and mesencephalic areas such as the cortex, nucleus caudatus, nucleus accumbens, amygdala, subfornical organ, paraventricular nucleus, hypothalamic dorsolateral aggregation, nucleus of the paraventricular organ, infundibular nucleus, pretectal nucleus, periventricular grey, reticular formation and nucleus of the raphe. Many immunoreactive cells located near the ependyma were bipolar, having an apical dendrite that contacted the cerebrospinal fluid. Immunoreactive fibers were seen in these locations and in the lamina terminalis, lateral forebrain bundle, supraoptic nucleus, median eminence, neurohypophysis, tectum opticum, torus semicircularis and deep mesencephalic nucleus. Parvocellular bipolar immunoreactive neurons from the paraventricular and infundibular nuclei projected axons that joined the hypothalamo-hypophysial tract and reached the outer zone of median eminence, and the neural lobe of the hypophysis where immunoreactive fibers terminated close to intermediate lobe cells. From these results it can be concluded that, as in other vertebrates, corticotropin-releasing factor in the turtle may act as a releasing factor and, centrally, as a neurotransmitter or neuromodulator.

[Effect of environmental salinity on the melanotropic cells of the gilthead bream (Sparus aurata L.)]

The influence of the environmental salinity on the MSH cells of the pars intermedia in the euryhaline teleost Sparus aurata has been investigated. Control animals stayed in sea water (39/1000 salinity), and experimental fish in brackish water (7/1000 salinity) for two months. For light microscopy, pituitaries were fixed with Bouin fluid and embedded in paraffin. For electron microscopy they were fixed with Karvnosky and embedded in Araldite. Sections were stained with histochemical procedures and immunocytochemistry using an antiserum against human ACTH (1-24). The immunoreaction intensity was measured by microdensitometry, the nuclear area and granule size by planimetry, and the volume occupied by the ACTH cells by volumetry. Whereas the adaptation to brackish water decreased the immunoreactivity to anti-ACTH serum on the MSH cells, the volume and the nuclear area of these cells increased although without statistical significance. These results suggest that the adaptation to hypoosmotic environment elicits an increase in the synthesis and release of MSH and ACTH.

Influence of environmental salinity on prolactin and corticotropic cells in the gilthead sea bream (Sparus aurata L.)

The influence of the environmental salinity on the prolactin (PRL) and corticotropic (ACTH) cells of the rostral pars distalis of the adenohypophysis of the gilthead sea bream (Sparus aurata) adapted to sea water (SW, 980 mOsm/kg) and brackish water (BW, 200 mOsm/kg) has been studied by immunocytochemical, morphometric, and electron-microscopic techniques. Prolactin (PRL) cells of fish adapted to BW occupied a greater hypophysial volume (about 24% of the total hypophysial volume in BW, 10% in SW) and had larger nuclear areas than those of SW-adapted fish (about 21 microns 2 in BW, 12 microns 2 in SW). Conversely, immunoreactivity against PRL antiserum was lower (mean optical density 117 in BW, 157 in SW). Characteristic ultrastructural features of PRL cells of BW-adapted fishes included a distended rough endoplasmic reticulum and large granules. Together the volumetric, densitometric, and ultrastructural evidences suggest an activation of synthesis and release of PRL in S. aurata adapted to hypoosmotic environments. ACTH cells occupied similar hypophysial volumes in both SW- and BW-adapted fishes (about 6.5%), but nuclear areas were higher (16 microns 2 in BW, 13 microns 2 in SW) and immunoreactivity against ACTH antiserum was lower in BW fishes (mean optical density 117 in BW, 139 in SW). Their ultrastructure suggested cell activation in BW-adapted fishes. Plasma levels of cortisol were eventually threefold greater in BW (about 142 ng/ml) than in SW fish (54 ng/ml). These data suggest activation of ACTH cells of S. aurata adapted to BW.

The distribution of corticotropin-releasing factor--immunoreactive neurons and nerve fibers in the brain of the snake, Natrix maura. Coexistence with arginine vasotocin and mesotocin

The anatomical distribution of neurons and nerve fibers containing corticotropin-releasing factor (CRF) has been studied in the brain of the snake, Natrix maura, by means of immunocytochemistry using an antiserum against rat CRF. To test the possible coexistence of CRF with the neurohypophysial peptides arginine vasotocin (AVT) and mesotocin (MST) adjacent sections were stained with antisera against the two latter peptides. CRF-immunoreactive (CRF-IR) neurons exist in the paraventricular nucleus (PVN). In some neurons of the PVN, coexistence of CRF with MST or of CRF with AVT has been shown. Numerous CRF-IR fibers run along the hypothalamo-hypophysial tract and end in the outer layer of the median eminence. In addition, some fibers reach the neural lobe of the hypophysis. CRF-IR perikarya have also been identified in the following locations: dorsal cortex, nucleus accumbens, amygdala, subfornical organ, lamina terminalis, nucleus of the paraventricular organ, nucleus of the oculomotor nerve, nucleus of the trigeminal nerve, and reticular formation. In addition to all these locations CRF-IR fibers were also observed in the lateral septum, supraoptic nucleus, habenula, lateral forebrain bundle, paraventricular organ, hypothalamic ventromedial nucleus, raphe and interpeduncular nuclei.

Ultrastructural immunocytochemistry and lectin histochemistry of the subcommissural organ in the snake Natrix maura with particular emphasis on its vascular and leptomeningeal projections

The ependymal cells of the subcommissural organ (SCO) of the snake Natrix maura display long basal processes which terminate either on blood vessels or on the leptomeninges. The cell body and the basal processes contain a secretory material detectable immunocytochemically at the light-microscopic level using an antibody raised against bovine Reissner's fiber. The present investigation deals with the ultrastructural location in these cells of the (i) immunoreactive material; (ii) concanavalin A (Con A)- and wheat-germ agglutinin (WGA)-binding sites. In the subnuclear region the immunoreactive material was located within dilated cisternae of the rough endoplasmic reticulum and had affinity for Con A but not for WGA. In the supranuclear region the secretory material was exclusively located within numerous granules. Since all these granules showed affinity for WGA, they can be regarded as "post-Golgi" elements. Thus, at variance with the situation in the mammalian SCO, in the ophidian SCO most of the secretion is stored in secretory granules rather than in dilated cisternae of the rough endoplasmic reticulum. In the perivascular and leptomeningeal endings the immunoreactive material was located within granules which, because of their affinity for WGA, should also be regarded as true secretory granules derived from the Golgi apparatus. It is concluded that these granules are transported along the basal processes and accumulated in the perivascular and leptomeningeal endfeet. This observation favours the view of a local release of the content of these granules, since there is no evidence for a reverse transport of these granules all the way back from the distal termination to the apical pole, to be finally released into the ventricle.

[Increase in the number of colloidal droplets in the hypothalamus of Natrix maura caused by dehydration]

The influence of osmotic stress on the number of colloid droplets in the magnocellular neurosecretory nuclei of the water snake Natrix maura, has been studied. Five experimental groups of five specimens each, were submitted to dehydration by immersion in sea water for several periods of time (3 to 60 h). The number of colloid droplets, identified by histochemical procedures, was counted in serial sections of the retrochiasmatic nuclei. The study of the mean of each group revealed that the amount of colloids increased with the time of permanence in the hyperosmotic environment (48 h elicited the greatest response). As a conclusion, dehydration seems to activate the hypothalamic magnocellular neurosecretory nuclei of N. maura and, consequently, increases the production of colloid droplets.

Immunocytochemical study of the hypothalamic magnocellular neurosecretory nuclei of the snake Natrix maura and the turtle Mauremys caspica

An immunocytochemical study of the magnocellular neurosecretory nuclei was performed in the snake Natrix maura and the turtle Mauremys caspica by use of antisera against: (1) a mixture of both bovine neurophysins, (2) bovine oxytocin-neurophysin, (3) arginine vasotocin, and (4) mesotocin. Arginine vasotocin- and mesotocin-immunoreactivities were localized in individual neurons of the supraoptic and paraventricular nuclei, with a distinct pattern of distribution in both species. The same cells appeared to be stained by the anti-oxytocin-neurophysin and antimesotocin sera. The supraoptic nucleus can be subdivided into rostral medial and caudal portions. In N. maura, but not in M. caspica, neurophysin-immunoreactive neurons were found in the retrochiasmatic nucleus. No immunoreactive elements were seen in the suprachiasmatic nucleus of both species after the use of any of the antisera. A dorsolateral aggregation of neurophysin-containing cells, localized over the lateral forebrain bundle, was present in both species. Magnocellular and parvocellular neurophysin-immunoreactive neurons were present in the paraventricular nucleus of both species. In the turtle, the paraventricular neurons were arranged into four distinct layers parallel to the ependyma; these neurons were bipolar with the major axis perpendicular to the ventricle, and many of them projected processes toward the cerebrospinal-fluid compartment. In N. maura a group of large neurons of the paraventricular nucleus was found in a very lateral position. The posterior lobe of the hypophysis and the external zone of the median eminence contained arginine vasotocin- and mesotocin-immunoreactive nerve fibers. The lamina termialis of both species was supplied with a dense bundle of fibers containing immunoreactive neurophysin. Neurophysin-immunoreactive fibers were also present in the septum, some telencephalic regions, including the cortex and the olfactory tubercule, in the paraventricular organ, and the periventricular and periaqueductal gray of the brainstem.

Immunocytochemical and ultrastructural evidence for a neurophysinergic innervation of the subcommissural organ of the snake Natrix maura

The subcommissural organ (SCO) of the snake Natrix maura was studied by use of the immunoperoxidase procedure. Primary antisera against bovine neurophysins (Nps I + II, OXY-Np), oxytocin (OXY), mesotocin (MST), arginine-vasotocin (AVT), somatostatin (SOM), beta-endorphin (END) and bovine Reissner's fiber were used. A conventional ultrastructural study, with special emphasis on the nerve fibers present in the SCO, was also performed. Nerve fibers containing immunoreactive OXY-Np and MST were seen to reach the SCO. The staining of adjacent sections with the anti-Reissner's fiber serum showed that the OXY-Np- and MST-immunoreactive fibers were distributed among the cell bodies and processes of the ependymal secretory cells. No fibers containing immunoreactive OXY, AVT, SOM or END were found in the SCO. The ultrastructural analysis revealed in the SCO the presence of nerve fibers filled with electron-dense granules, 170-210 nm in diameter. Although a direct apposition between these fibers and the SCO cells was frequently seen, no synaptic differentiations were identified. Structures identical to the Herring bodies (found in the neurohypophysis) were seen in the SCO.

Vascular and leptomeningeal projections of the subcommissural organ in reptiles. Lectin-histochemical, immunocytochemical, and ultrastructural studies

In the snake, Natrix maura, and the turtle, Mauremys caspica, the basal processes of the ependymal cells of the subcommissural organ project toward the local blood vessels and the leptomeninges. These processes and their endings were studied using aldehyde-fuchsin (AF), periodic-acid Schiff (PAS), periodic-acid silver-methenamine (PA-SM), concanavalin A (ConA), wheat germ agglutinin (WGA), immunoperoxidase staining (employing an antiserum against bovine Reissner's fiber; AFRU), and conventional transmission electron microscopy. For the purposes of comparison, the ventricular cell pole was also analyzed. The secretory material located in the ventricular cell pole and that present in ependymal endings had only a few staining properties in common, i.e., affinity for AF, ConA, and AFRU at a dilution of 1:1000. On the other hand, PAS, PA-SM, WGA, and AFRU at a dilution of 1:200,000 stained the apical (ventricular) secretory material but not the secretory material of the ependymal processes. The histochemical features of the secretory material located in the terminals of ependymal processes, as well as the presence at these sites of numerous rough-endoplasmic-reticulum cisternae and secretory granules, suggest that secretory material may be synthesized in these terminals. The probable fate of this material, i.e., release to the perivascular and leptomeningeal spaces or transport to the ventricular cell pole, is discussed.