In Vivo Expression of the PTB-deleted Odin Mutant Results in Hydrocephalus

Odin has been implicated in the downstream signaling pathway of receptor tyrosine kinases, such as the epidermal growth factor and Eph receptors. However, the physiologically relevant function of Odin needs to be further determined. In this study, we used Odin heterozygous mice to analyze the Odin expression pattern; the targeted allele contained a β-geo gene trap vector inserted into the 14th intron of the Odin gene. Interestingly, we found that Odin was exclusively expressed in ependymal cells along the brain ventricles. In particular, Odin was highly expressed in the subcommissural organ, a small ependymal glandular tissue. However, we did not observe any morphological abnormalities in the brain ventricles or ependymal cells of Odin null-mutant mice. We also generated BAC transgenic mice that expressed the PTB-deleted Odin (dPTB) after a floxed GFP-STOP cassette was excised by tissue-specific Cre expression. Strikingly, Odin-dPTB expression played a causative role in the development of the hydrocephalic phenotype, primarily in the midbrain. In addition, Odin-dPTB expression disrupted proper development of the subcommissural organ and interfered with ependymal cell maturation in the cerebral aqueduct. Taken together, our findings strongly suggest that Odin plays a role in the differentiation of ependymal cells during early postnatal brain development.

Increased Reissner's fiber material in the subcommissural organ and ventricular area in bile duct ligated rats

Hepatic encephalopathy is a common neuropsychiatric complication of acute and chronic liver failure. Whether brain structures with strategic positions in the interface of blood-brain barriers such as the circumventricular organs are involved in hepatic encephalopathy is not yet established. Among the circumventricular organs, the subcommissural organ secretes a glycoprotein known as Reissner's fiber, which condenses and forms an ever-growing thread-like structure into the cerebrospinal fluid. In the present work we describe the Reissner's fiber material within the subcommissural organ and its serotoninergic innervation in an animal model of chronic hepatic encephalopathy following bile duct ligation in experimental rats. The study involved immunohistochemical techniques with antibodies against Reissner's fiber and 5-hydroxytryptamine (5-HT). Four weeks after surgical bile duct ligation, a significant rise of Reissner's fiber immunoreactivity was observed in all subcommissural organ areas compared with controls. Moreover, significant Reissner's fiber immunoreactive materials within the ependyma and inside the parenchyma close to the ventricular borders were also seen in bile duct ligated rats, but not in control rats. Increased Reissner's fiber material in bile duct ligated rats seems to be related to a reduction of 5-HT innervation of the subcommissural organ, the ventricular borders and the nucleus of origin, the dorsal raphe nucleus. Our data describe alterations of the subcommissural organ/Reissner's fiber material and the subcommissural organ 5-HT innervation probably due to a general 5-HT deficit in bile duct ligated rats.

Immunohistochemical evaluation of the effect of lead exposure on subcommissural organ innervation and secretion in Shaw's Jird (Meriones shawi)

The secretory activity of subcommissural organ cells is controlled by various extrinsic and intrinsic factors. Lead has been recognised as a neurotoxic heavy metal, since it induces morphological and functional abnormalities in the brain. In this work, we examined the effect of lead exposure on the subcommissural organ (SCO), a brain gland known by its secretion of Reissner's fiber (RF) in cerebro-spinal fluid. Glycoprotein secretion and serotonin (5HT) innervation of the SCO was examined after acute and chronic lead exposures in the sub-desert rodent Meriones shawi. Lead exposures were achieved by, respectively, intra-peritoneal injection of 25 mg/kg body weight of lead acetate for 3 days and 0.5% of lead acetate in the drinking water over 4 months until adult age. 5HT and RF immunolabeling in the SCO revealed several serotoninergic fibers reaching the SCO and abundant secretory material. An increase in both 5HT innervation and secretory material of the SCO was recorded after both acute and chronic lead exposure. These results show that lead exposure affects the serotonergic innervation of the SCO. Moreover, the enhancement of SCO secretion suggests a role of this gland in neuroprotection and lead detoxification of the brain in Meriones shawi.

The secretory ependymal cells of the subcommissural organ: which role in hydrocephalus?

Ependyma in the central nervous system gives rise to several specialized cell types, including the secretory ependymal cells located in the subcommissural organ. These elongated cells show large cisternae in their cytoplasm, which are filled with material secreted into the cerebrospinal fluid and toward the leptomeningeal spaces. A specific secretion of the subcommissural organ was named SCO-spondin, regarding its marked homology with developmental proteins of the thrombospondin superfamily (presence of thrombospondin type 1 repeats). The ependymal cells of the subcommissural organ and SCO-spondin secretion are suspected to play a crucial role in cerebrospinal fluid flow and/or homeostasis. There is a close correlation between absence of the subcommissural organ and hydrocephalus in rat and mouse strains exhibiting congenital hydrocephalus, and in a number of mice transgenic for developmental genes. The ependymal cells of the subcommissural organ are under research as a key factor in several developmental processes of the central nervous system.

Papillary neuroepithelial tumor of the pineal region. A case report

We present here an unusual case of papillary neuroepithelial tumor of the pineal region. The patient was a 29-year-old female who presented with headaches. A computed tomography scan revealed a tumorous lesion at the pineal region and hydrocephalus. The resected tumor was composed of columnar and cuboidal cells showing characteristics of papillary growth. The tumor cells exhibited diffuse and intense immunoreactivity to cytokeratins and neural cell adhesion molecule. The tumor expressed abundant levels of transthyretin (prealbumin) and appeared ependymal in nature, with numerous microlumens delineated by punctate and ring-like patterns in epithelial membrane antigen staining. Reactivity to synaptophysin and glial fibrillary acidic protein was observed only in the infiltrated non-neoplastic pineal parenchyma. These histological characteristics matched the description of the recently reported papillary tumor of the pineal region thought to originate from the specialized ependyma of the subcommissural organ (SCO). Transthyretin expression of the present case further supports the likelihood of SCO origin, as transthyretin is one of the proteins presumed to be secreted by human SCO.

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.

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.

Subcommissural organ, cerebrospinal fluid circulation, and hydrocephalus

Under normal physiological conditions the cerebrospinal fluid (CSF) is secreted continuously, although this secretion undergoes circadian variations. Mechanisms operating at the vascular side of the choroidal cells involve a sympathetic and a cholinergic innervation, with the former inhibiting and the latter stimulating CSF secretion. There are also regulatory mechanisms operating at the ventricular side of the choroidal cells, where receptors for monoamines such as dopamine, serotonin, and melatonin, and for neuropeptides such as vasopressin, atrial natriuretic hormone, and angiotensin II, have been identified. These compounds, that are normally present in the CSF, participate in the regulation of CSF secretion. Although the mechanisms responsible for the CSF circulation are not fully understood, several factors are known to play a role. There is evidence that the subcommissural organ (SCO)--Reissner's fiber (RF) complex is one of the factors involved in the CSF circulation. In mammals, the predominant route of escape of CSF into blood is through the arachnoid villi. In lower vertebrates, the dilatation of the distal end of the central canal, known as terminal ventricle or ampulla caudalis, represents the main site of CSF escape into blood. Both the function and the ultrastructural arrangement of the ampulla caudalis suggest that it may be the ancestor structure of the mammalian arachnoid villi. RF-glycoproteins reaching the ampulla caudalis might play a role in the formation and maintenance of the route communicating the CSF and blood compartments. The SCO-RF complex may participate, under physiological conditions, in the circulation and reabsorption of CSF. Under pathological conditions, the SCO appears to be involved in the pathogeneses of congenital hydrocephalus. Changes in the SCO have been described in all species developing congenital hydrocephalus. In these reports, the important question whether the changes occurring in the SCO precede hydrocephalus, or are a consequence of the hydrocephalic state, has not been clarified. Recently, evidence has been obtained indicating that a primary defect of the SCO-RF complex may lead to hydrocephalus. Thus, a primary and selective immunoneutralization of the SCO-RF complex during the fetal and early postnatal life leads to absence of RF, aqueductal stenosis, increased CSF concentration of monoamines, and a moderate but sustained hydrocephalus.

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.

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.

Dysplasia of subcommissural organ in congenital hydrocephalus spontaneously occurring in CWS/Idr rats

The subcommissural organ (SCO) of the congenital hydrocephalus spontaneously occurring in CWS/Idr rats was severely reduced in size and displaced at some distance from the anterior end of the cerebral aqueduct. The cerebral aqueduct of the hydrocephalic rats was open throughout its total length during postnatal days 1-20, though it was somewhat narrower at its middle region than in the normal brain.

Microglia in the hypendyma of the rat subcommissural organ following brain lesion with serotonin neurotoxin

The population of microglial cells in the subependymal layer of the subcommissural organ is sparse in normal adult rats. The number of microglial cells was substantially increased in this area following intraventricular injection of the serotonin neurotoxin 5,6-dihydroxytryptamine (5,6-DHT). In sections of plastic embedded material, 1 micron thick, the majority of phagocytic cells scattered in the subependymal layer had an appearance similar to that described in classical studies of microglial cells. At the electron microscopic level microglial cells exhibited the characteristic elongate nucleus with peripheral chromatin condensation. The perikaryon was scanty, containing strands of rough endoplasmic reticulum. The abundant organelles in the processes included Golgi complexes, mitochondria, rough and smooth endoplasmic reticulum as well as dense and multivesicular bodies. In addition, the processes contained phagocytosed axon terminals originating from the dense serotoninergic input to the subcommissural organ, which had degenerated on accumulating the serotonin neurotoxin. A fraction of the phagocytosed material was contained in subependymal subcommissural organ cells, astrocytes and oligodendrocytes. At the light microscopic level the phagocytosed terminals were visualized histochemically with Schmorl's reaction, which resulted in Prussian Blue precipitates. This allowed screening of microglial cells in complete series of sections through the well-defined subependymal layer of the subcommissural organ.

Morphometric changes in alcoholic mice of neurons of areas 6 and 17 and ependyma of the subcommissural organ

We have performed a karyometric study of the postnatal development of the subcommissural organ (SOC), the subjacent thalamic ependyma, and the pyramidal neurons of layer V of the motor and visual cortical areas, in alcoholic male albino mice, aged 25-100 days. Ethyl alcohol was added to the drinking water at a concentration of 20%, from birth until the day of sacrifice. Our results show that alcoholism affects the SOC ependyma and the motor cortex, and, apparently, does not affect the ventricular thalamic ependyma and the visual cortex. We suggest a neuroendocrine mechanism to explain the SOC answer, and a functional deprivation to explain the changes in the motor cortex.

Secretory activity of the subcommissural organ in Rana temporaria under osmotic stimulation

The secretory activity of the subcommissural organ (SCO) in the frog Rana temporaria was studied under conditions of dehydration. After injection of a radioactive precursor the amount and concentration of radioactively labelled material in the SCO are smaller in dehydrated than in control animals. Concomitantly, the growth rate of the CSF-fibre (Reissner's fibre) increases in dehydrated animals. It follows that water deprivation enhances the secretory activity of the SCO. To investigate whether the SCO may be responsible for the secretion of an aldosteronotropic factor as suggested in the literature, brains were incubated in vitro with a radioactive precursor and with or without aldosterone. The SCO of the aldosterone-treated brains contains more radioactively labelled material than the SCO of the control brains. It is argued that this is indicative of a lower secretory activity It means that aldosterone inhibits the secretory activity of the SCO, possibly by a process of negative feed-back regulation. The results of the present experiments can be interpreted in favour of an involvement of the SCO-Reissner's fibre complex in osmoregulation.

Comparative immunocytochemical study of the subcommissural organ

The subcommissural organs (SCO) of 76 specimens belonging to 25 vertebrate species (amphibians, reptiles, birds, mammals) were studied by use of the immunoperoxidase procedure. The primary antiserum was obtained by immunizing rabbits with bovine Reissner's fiber (RF) extracted in a medium containing EDTA, DTT and urea. Antiserum against an aqueous extract of RF was also produced. The presence of immunoreactive material in cell processes and endings was regarded as an indication of a possible route of passage. Special attention was paid to the relative development of the ventricular, leptomeningeal and vascular pathways established by immunoreactive structures. The SCO of submammalian species is characterized by (i) a conspicuous leptomeningeal connection established by ependymal cells, (ii) scarce or missing hypendymal cells, and (iii) a population of ependymal cells establishing close spatial contacts with blood vessels. The SCO of most mammalian species displays the following features: (i) ependymal cells lacking immunoreactive long basal processes, (ii) hypendymal secretory cells occurring either in a scattered arrangement or forming clusters, (iii) an occasional leptomeningeal connection provided by hypendymal cells, and (iv) in certain species numerous contacts of secretory cells with blood vessels. In the hedgehog immunoreactive material was missing in the ependymal formation of the SCO, but present in hypendymal cells and in the choroid plexuses. The SCO of several species of New and Old-World monkeys displayed immunoreactive material, whereas that of anthropoid apes (chimpanzee, orangutan) and man was completely negative with the antisera used.

Neurotoxic destruction of the serotoninergic innervation of the rat subcommissural organ is followed by reinnervation through collateral sprouting of non-monoaminergic neurons

Specific neurotoxic destruction of the serotoninergic innervation of the subcommissural organ of the rat is followed by an efficient reinnervation by collateral sprouting of non-monoaminergic axons, which normally do not innervate the SCO cells. Morphologically, the reinnervating fibres totally replace the serotoninergic synapses lost by the lesion, but, functionally, they fail to substitute for the potent inhibitory control of secretory activity normally exerted by the serotoninergic innervation. It is possible that the observed reinnervation by foreign synapses explains why the regrowing serotoninergic neurons fail to re-establish their connections with the SCO.