Uncovering the role of the subcommissural organ in early brain development through transcriptomic analysis.

BACKGROUND: The significant role of embryonic cerebrospinal fluid (eCSF) in the initial stages of brain development has been thoroughly studied. This fluid contains crucial molecules for proper brain development such as members of the Wnt and FGF families, apolipoproteins, and retinol binding protein. Nevertheless, the source of these molecules remains uncertain since they are present before the formation of the choroid plexus, which is conventionally known as the primary producer of cerebrospinal fluid. The subcommissural organ (SCO) is a highly conserved gland located in the diencephalon and is one of the earliest differentiating brain structures. The SCO secretes molecules into the eCSF, prior to the differentiation of the choroid plexus, playing a pivotal role in the homeostasis and dynamics of this fluid. One of the key molecules secreted by the SCO is SCO-spondin, a protein involved in maintenance of the normal ventricle size, straight spinal axis, neurogenesis, and axonal guidance. Furthermore, SCO secretes transthyretin and basic fibroblast growth factor 2, while other identified molecules in the eCSF could potentially be secreted by the SCO. Additionally, various transcription factors have been identified in the SCO. However, the precise mechanisms involved in the early SCO development are not fully understood. RESULTS: To uncover key molecular players and signaling pathways involved in the role of the SCO during brain development, we conducted a transcriptomic analysis comparing the embryonic chick SCO at HH23 and HH30 stages (4 and 7 days respectively). Additionally, a public transcriptomic data from HH30 entire chick brain was used to compare expression levels between SCO and whole brain transcriptome. These analyses revealed that, at both stages, the SCO differentially expresses several members of bone morphogenic proteins, Wnt and fibroblast growth factors families, diverse proteins involved in axonal guidance, neurogenic and differentiative molecules, cell receptors and transcription factors. The secretory pathway is particularly upregulated at stage HH30 while the proliferative pathway is increased at stage HH23. CONCLUSION: The results suggest that the SCO has the capacity to secrete several morphogenic molecules to the eCSF prior to the development of other structures, such as the choroid plexus.

The subcommissural organ maintains features of neuroepithelial cells in the adult mouse.

The subcommissural organ (SCO) is a part of the circumventricular organs located in the dorsocaudal region of the third ventricle at the entrance of the aqueduct of Sylvius. The SCO comprises epithelial cells and produces high molecular weight glycoproteins, which are secreted into the third ventricle and become part of Reissner's fibre in the cerebrospinal fluid. Abnormal development of the SCO has been linked with congenital hydrocephalus, a condition characterized by excessive accumulation of cerebrospinal fluid in the brain. In the present study, we characterized the SCO cells in the adult mouse brain to gain insights into the possible role of this brain region. Immunohistochemical analyses revealed that expression of Pax6, a transcription factor essential for SCO differentiation during embryogenesis, is maintained in the SCO at postnatal stages from P0 to P84. SCO cells in the adult brain expressed known neural stem/progenitor cell (NSPC) markers, Sox2 and vimentin. The adult SCO cells also expressed proliferating marker PCNA, although expression of another proliferation marker Ki67, indicating a G2 /M phase, was not detected. The SCO cells did not incorporate BrdU, a marker for DNA synthesis in the S phase. Therefore, the SCO cells have a potential for proliferation but are quiescent for cell division in the adult. The SCO cells also expressed GFAP, a marker for astrocytes or NSPCs, but not NeuN (for neurons). A few cells positive for Iba1 (microglia), Olig2 (for oligodendrocytes) and PDGFRα (oligodendrocyte progenitors) existed within or on the periphery of the SCO. These findings revealed that the SCO cells have a unique feature as secretory yet immature neuroepithelial cells in the adult mouse brain.

Hydrocephalus in mouse B3glct mutants is likely caused by defects in multiple B3GLCT substrates in ependymal cells and subcommissural organ.

Peters plus syndrome, characterized by defects in eye and skeletal development with isolated cases of ventriculomegaly/hydrocephalus, is caused by mutations in the ß3-glucosyltransferase (B3GLCT) gene. In the endoplasmic reticulum, B3GLCT adds glucose to O-linked fucose on properly folded thrombospondin type 1 repeats (TSRs). The resulting glucose-fucose disaccharide is proposed to stabilize the TSR fold and promote secretion of B3GLCT substrates, with some substrates more sensitive than others to loss of glucose. Mouse B3glct mutants develop hydrocephalus at high frequency. In this study, we demonstrated that B3glct mutant ependymal cells had fewer cilia basal bodies and altered translational polarity compared to controls. Localization of mRNA encoding A Disintegrin and Metalloproteinase with ThromboSpondin type 1 repeat 20 (ADAMTS20) and ADAMTS9 suggested that reduced function of these B3GLCT substrates contributed to ependymal cell abnormalities. In addition, we showed that multiple B3GLCT substrates (Adamts3, Adamts9 and Adamts20) are expressed by the subcommissural organ, that subcommissural organ-spondin ((SSPO) also known as SCO-spondin) TSRs were modified with O-linked glucose-fucose and that loss of B3GLCT reduced secretion of SSPO in cultured cells. In the B3glct mutant, intracellular levels of SSPO were reduced and BiP levels increased, suggesting a folding defect. Secreted SSPO colocalized with BiP, raising the possibility that abnormal extracellular assembly of SSPO into Reissner's fiber also contributed to impaired CSF flow in mutants. Combined, these studies underscore the complexity of the B3glct mutant hydrocephalus phenotype and demonstrate that impaired cerebrospinal fluid (CSF) flow likely stems from the collective effects of the mutation on multiple processes.

The subcommissural organ and the Reissner fiber: old friends revisited.

The subcommissural organ (SCO) is an ancient and conserved brain gland secreting into cerebrospinal fluid (CSF) glycoproteins that form the Reissner fiber (RF). The present investigation was designed to further investigate the dynamic of the biosynthetic process of RF glycoproteins prior and after their release into the CSF, to identify the RF proteome and N-glycome and to clarify the mechanism of assembly of RF glycoproteins. Various methodological approaches were used: biosynthetic labelling injecting 35S-cysteine and 3H-galactose into the CSF, injection of antibodies against galectin-1 into the cerebrospinal fluid, light and electron microscopical methods; isolated bovine RF was used for proteome analyses by mass spectrometry and glycome analysis by xCGE-LIF. The biosynthetic labelling study further supported that a small pool of SCO-spondin molecules rapidly enter the secretory pathways after its synthesis, while most of the SCO-spondin molecules are stored in the rough endoplasmic reticulum for hours or days before entering the secretory pathway and being released to assemble into RF. The proteomic analysis of RF revealed clusterin and galectin-1 as partners of SCO-spondin; the in vivo use of anti-galectin-1 showed that this lectin is essential for the assembly of RF. Galectin-1 is not secreted by the SCO but evidence was obtained that it would be secreted by multiciliated ependymal cells lying close to the SCO. Further, a surprising variety and complexity of glycan structures were identified in the RF N-glycome that further expands the potential functions of RF to a level not previously envisaged. A model of the macromolecular organization of Reissner fiber is proposed.

The origins of the circumventricular organs.

The circumventricular organs (CVOs) are specialised neuroepithelial structures found in the midline of the brain, grouped around the third and fourth ventricles. They mediate the communication between the brain and the periphery by performing sensory and secretory roles, facilitated by increased vascularisation and the absence of a blood-brain barrier. Surprisingly little is known about the origins of the CVOs (both developmental and evolutionary), but their functional and organisational similarities raise the question of the extent of their relationship. Here, I review our current knowledge of the embryonic development of the seven major CVOs (area postrema, median eminence, neurohypophysis, organum vasculosum of the lamina terminalis, pineal organ, subcommissural organ, subfornical organ) in embryos of different vertebrate species. Although there are conspicuous similarities between subsets of CVOs, no unifying feature characteristic of their development has been identified. Cross-species comparisons suggest that CVOs also display a high degree of evolutionary flexibility. Thus, the term 'CVO' is merely a functional definition, and features shared by multiple CVOs may be the result of homoplasy rather than ontogenetic or phylogenetic relationships.

The value of early and comprehensive diagnoses in a human fetus with hydrocephalus and progressive obliteration of the aqueduct of Sylvius: Case Report.

BACKGROUND: Mutant rodent models have highlighted the importance of the ventricular ependymal cells and the subcommissural organ (a brain gland secreting glycoproteins into the cerebrospinal fluid) in the development of fetal onset hydrocephalus. Evidence indicates that communicating and non-communicating hydrocephalus can be two sequential phases of a single pathological phenomenon triggered by ependymal disruption and/or abnormal function of the subcommissural organ. We have hypothesized that a similar phenomenon may occur in human cases with fetal onset hydrocephalus. CASE PRESENTATION: We report here on a case of human fetal communicating hydrocephalus with no central nervous system abnormalities other than stenosis of the aqueduct of Sylvius (SA) that became non-communicating hydrocephalus during the first postnatal week due to obliteration of the cerebral aqueduct. The case was followed closely by a team of basic and clinic investigators allowing an early diagnosis and prediction of the evolving pathophysiology. This information prompted neurosurgeons to perform a third ventriculostomy at postnatal day 14. The fetus was monitored by ultrasound, computerized axial tomography and magnetic resonance imaging (MRI). After birth, the follow up was by MRI, electroencephalography and neurological and neurocognitive assessments. Cerebrospinal fluid (CSF) collected at surgery showed abnormalities in the subcommissural organ proteins and the membrane proteins L1-neural cell adhesion molecule and aquaporin-4. The neurological and neurocognitive assessments at 3 and 6 years of age showed neurological impairments (epilepsy and cognitive deficits). CONCLUSIONS: (1) In a hydrocephalic fetus, a stenosed SA can become obliterated at perinatal stages. (2) In the case reported, a close follow up of a communicating hydrocephalus detected in utero allowed a prompt postnatal surgery aiming to avoid as much brain damage as possible. (3) The clinical and pathological evolution of this patient supports the possibility that the progressive stenosis of the SA initiated during the embryonic period may have resulted from ependymal disruption of the cerebral aqueduct and dysfunction of the subcommissural organ. The analysis of subcommissural organ glycoproteins present in the CSF may be a valuable diagnostic tool for the pathogenesis of congenital hydrocephalus.

Microscopic anatomy of the subcommissural organ in the brain of the adult greater cane rat (Rodentia: Thryonomyidae).

The subcommissural organ (SCO) is a well-developed gland present in the brain of vertebrates. The SCO secretes glycoproteins into the circulating cerebrospinal fluid and these assemble to form Reissner's fibre. It also plays an important function in neurogenesis and axonal guidance during embryogenesis. This study delves into the microscopic anatomy of the SCO in the adult greater cane rat (GCR), shedding light on its histoarchitectural characteristics. By utilizing histological techniques and microscopic analysis, we investigated the SCO's location and cellular composition within the brain of adult GCR. Our findings showed that the SCO in this species is located ventrally to the posterior commissure (PC) and dorsally to the third ventricle. The SCO consists of specialized ependymal or nuclear cell layer and apical processes lining the third ventricle. Moreover, the SCO's proximity to the PC and the third ventricle highlights its strategic position within the brain's ventricular system. With immunohistochemical analyses, the SCO cells expressed glial fibrillary protein when immunolabelled with Glial fibrillary acid protein (GFAP) antibody, a marker for astrocytes/astrocytic-like cells. Few microglia-like cells were immuno-positive for Ionized calcium-binding adapter molecule 1 (Iba1) antibody, that are existing within the SCO. However, the SCO in the GCR showed a negative immunostaining to NeuN antibody. This study contributes to our understanding of the microscopic anatomy of the SCO in a lesser-studied mammalian species. Further research into the SCO's functional significance especially during development in the GCR, may hold promise for more insights into neurological health and pathology.

The subcommissural organ regulates brain development via secreted peptides.

The subcommissural organ (SCO) is a gland located at the entrance of the aqueduct of Sylvius in the brain. It exists in species as distantly related as amphioxus and humans, but its function is largely unknown. Here, to explore its function, we compared transcriptomes of SCO and non-SCO brain regions and found three genes, Sspo, Car3 and Spdef, that are highly expressed in the SCO. Mouse strains expressing Cre recombinase from endogenous promoter/enhancer elements of these genes were used to genetically ablate SCO cells during embryonic development, resulting in severe hydrocephalus and defects in neuronal migration and development of neuronal axons and dendrites. Unbiased peptidomic analysis revealed enrichment of three SCO-derived peptides, namely, thymosin beta 4, thymosin beta 10 and NP24, and their reintroduction into SCO-ablated brain ventricles substantially rescued developmental defects. Together, these data identify a critical role for the SCO in brain development.

Role of the subcommissural organ in the pathogenesis of congenital hydrocephalus in the HTx rat.

The present investigation was designed to clarify the role of the subcommissural organ (SCO) in the pathogenesis of hydrocephalus occurring in the HTx rat. The brains of non-affected and hydrocephalic HTx rats from embryonic day 15 (E15) to postnatal day 10 (PN10) were processed for electron microscopy, lectin binding and immunocytochemistry by using a series of antibodies. Cerebrospinal fluid (CSF) samples of non-affected and hydrocephalic HTx rats were collected at PN1, PN7 and PN30 and analysed by one- and two-dimensional electrophoresis, immunoblotting and nanoLC-ESI-MS/MS. A distinct malformation of the SCO is present as early as E15. Since stenosis of the Sylvius aqueduct (SA) occurs at E18 and dilation of the lateral ventricles starts at E19, the malformation of the SCO clearly precedes the onset of hydrocephalus. In the affected rats, the cephalic and caudal thirds of the SCO showed high secretory activity with all methods used, whereas the middle third showed no signs of secretion. At E18, the middle non-secretory third of the SCO progressively fused with the ventral wall of SA, resulting in marked aqueduct stenosis and severe hydrocephalus. The abnormal development of the SCO resulted in the permanent absence of Reissner's fibre (RF) and led to changes in the protein composition of the CSF. Since the SCO is the source of a large mass of sialilated glycoproteins that form the RF and of those that remain CSF-soluble, we hypothesize that the absence of this large mass of negatively charged molecules from the SA domain results in SA stenosis and impairs the bulk flow of CSF through the aqueduct.

Colocalization of p450 aromatase and oxytocin immunostaining in the rat hypothalamus.

With combined immunoperoxidase and immunofluorescence, we observed colocalization of cytochrome P450 aromatase with the posterior lobe peptide oxytocin and its associated neurophysin 1 in adult male rats. P450 was most abundant in the anterior hypothalamus. Colocalization of OT with P450 was observed in the preoptic region, the periventricular nucleus of the hypothalamus, the lateral subcommissural nucleus, and in the zona incerta. Magnocellular perikarya in the supraoptic and in the paraventricular nuclei contained only occasionally both antigens. P450 immunostaining overlapped to a great extent with known estrogen target regions. Oxytocinergic functions are controlled by estradiol while androgen receptors are mostly absent in neuroendocrine hypothalamic nuclei. Our findings suggest that systemic androgens may be aromatized to estrogens in male oxytocinergic neurons linked to the limbic system.

Molecular characterization of circumventricular organs and third ventricle ependyma in the rat: potential markers for periventricular tumors.

Circumventricular organs (CVOs) are specialized ventricular structures around the third and fourth ventricles of the brain. In humans, these structures are present during the fetal period and some become vestigial after birth. Some of these organs, such as the pineal gland (PG), subcommissural organ (SCO), and organum vasculosum of the lamina terminalis, might be the sites of origin of periventricular tumors, notably pineal parenchymal tumors, papillary tumor of the pineal region and chordoid glioma. In contrast to the situation in humans, CVOs are present in the adult rat and can be dissected by laser capture microdissection (LCM). In this study, we used LCM and microarrays to analyze the transcriptomes of three CVOs, the SCO, the subfornical organ (SFO), and the PG and the third ventricle ependyma in the adult rat, in order to better characterize these organs at the molecular level. Several genes were expressed only, or mainly, in one of these structures, for example, Erbb2 and Col11a1 in the ependyma, Epcam and Claudin-3 (CLDN3) in the SCO, Ren1 and Slc22a3 in the SFO and Tph, Aanat and Asmt in the PG. The expression of these genes in periventricular tumors should be examined as evidence for a possible origin from the CVOs. Furthermore, we performed an immunohistochemical study of CLDN3, a membrane protein involved in forming cellular tight junctions and found that CLDN3 expression was restricted to the apical pole of ependymocytes in the SCO. This microarray study provides new evidence regarding the possible origin of some rare periventricular tumors.

Study of the neurochemical alterations produced by acute and subchronic Pb-exposure in Meriones shawi: Immunohistochemical study of Reissner's fiber secretion by the subcommissural organ after curcumin-III treatment.

BACKGROUND: Lead neurotoxicity is associated with numerous alterations including behavioral and neurochemical disruptions. This study evaluates the possible neurochemical disruption in the subcommissural organ (SCO) after acute (three days) and subchronic (six weeks) Pb-exposure inMeriones shawi, and the possible effect of the third active compound, curcumin-III, in mitigating the neurological alterations caused by lead exposure. METHODS: Using immunohistochemical stainings, we evaluated the Reissner's fiber (RF) secretion utilizing RF-antibody in the SCO. We compared both acute (25 mg/kg bw of Pb i.p. for 3 days) and subchronic (3 g/l of Pb in drinking water for six weeks) Pb-treatedMeriones shawi. RESULTS: The two models of lead exposure showed a significant increase in RF level in the SCO. Conversely, co-treatment with Curcumin-III at a dose of 30 mg/kg bw significantly ameliorate SCO secretory activity, as revealed by decreased RF-immunoreactivity. CONCLUSION: Together, our findings suggest the protective effects of Curcumin-III in regulating the secretory activity of the SCO after Pb-induced neuroanatomical disruptions of the SCO in Meriones.

Congenital hydrocephalus associated with abnormal subcommissural organ in mice lacking huntingtin in Wnt1 cell lineages.

Huntingtin (htt) is a 350 kDa protein of unknown function, with no homologies with other known proteins. Expansion of a polyglutamine stretch at the N-terminus of htt causes Huntington's disease (HD), a dominant neurodegenerative disorder. Although it is generally accepted that HD is caused primarily by a gain-of-function mechanism, recent studies suggest that loss-of-function may also be part of HD pathogenesis. Huntingtin is an essential protein in the mouse since inactivation of the mouse HD homolog (Hdh) gene results in early embryonic lethality. Huntingtin is widely expressed in embryogenesis, and associated with a number of interacting proteins suggesting that htt may be involved in several processes including morphogenesis, neurogenesis and neuronal survival. To further investigate the role of htt in these processes, we have inactivated the Hdh gene in Wnt1 cell lineages using the Cre-loxP system of recombination. Here we show that conditional inactivation of the Hdh gene in Wnt1 cell lineages results in congenital hydrocephalus, implicating huntingtin for the first time in the regulation of cerebral spinal fluid (CSF) homeostasis. Our results show that hydrocephalus in mice lacking htt in Wnt1 cell lineages is associated with increase in CSF production by the choroid plexus, and abnormal subcommissural organ.

Identification and morphologic assessment of mesocoelic recess by in vivo human brain imaging with 7.0-T magnetic resonance imaging.

OBJECTIVE: The mesocoelic recess (MCR) is found in the brain of human embryos and fetuses. The mesocoelic recess seems to be functionally related to the subcommissural organ that is one of neurosecretory organs involved in osmoregulation on the basis of data from other species. Subsequently, recent speculation as to the importance of the subcommissural organ in the development of congenital hydrocephalus has been raised. Yet unlike other mammals, MCR is known to be a vestigial structure in the adult human brain. Here, we performed the in vivo imaging identification of this space to investigate functional and clinical correlations. METHODS: We studied adult human brains using a 7.0-T magnetic resonance imaging (MRI). Twenty healthy individuals aged 22 to 30 years were selected, and they were all volunteers. The parasagittal images through the intercommissural line were examined. We determined the type of shape of the MCR; a triangular C shape was classified as type 1, and a trapezoidal concave shape was classified as type 2. RESULTS: In 14 brains, the recesses were radiologically demonstrated just rostral to the tectal plate of the midbrain and covered the ventral aspect of the posterior commissure and pointed the opening into the aqueduct. The average size of the circumference of the MCR measured from the end point of the C-shaped cup was 6.82 mm. CONCLUSIONS: This study on the anatomy of the MCR of adult brains in vivo is the first of its kind, thanks to the availability of 7.0-T MRI because it has been barely discernible even in autopsy specimens as well as in radiology owing to the resolution limit of the currently available imaging system. The current study raises awareness of the MCR, an important but little-known anatomic structure in adult human brain. This visualization of MCR in human in vivo with ultrahigh-field MRI will certainly provide us important clues including the functional information of MCR, a mystery of modern neurological science.

Subdivisions of chick diencephalic roof plate: implication in the formation of the posterior commissure.

The subcommissural organ (SCO) is a roof plate differentiation located in the caudal diencephalon under the posterior commissure (PC). A role for SCO and its secretory product, SCO-spondin, in the formation of the PC has been proposed. Here, we provide immunohistochemical evidence to suggest that SCO is anatomically divided in a bilateral region positive for SCO-spondin that surrounds a negative medial region. Remarkably, axons contacting the lateral region are highly fasciculated, in sharp contrast with the defasciculated axons of the medial region. In addition, lateral axon fascicles run toward the midline inside of tunnels limited by the basal prolongations of SCO cells and extracellular SCO-spondin. Our in vitro data in collagen gel matrices show that SCO-spondin induces axonal growth and fasciculation of pretectal explants. Together, our findings support the idea that SCO-spondin participates in the guidance and fasciculation of axons of the PC.

The subcommissural organ and the development of the posterior commissure in chick embryos.

The subcommissural organ (SCO) is an ependymal differentiation located in the diencephalon under the posterior commissure (PC). SCO-spondin, a glycoprotein released by the SCO, belongs to the thrombospondin superfamily and shares molecular domains with axonal pathfinding molecules. Several lines of evidence suggest a relationship between the SCO and the development of the PC in the chick: (1) their close location to each other, (2) their differentiation at the same developmental stage in the chick, (3) the abnormal PC found in null mutants lacking an SCO and (4) the release by the SCO of SCO-spondin. By application of DiI crystals in the PC of chick embryos, we have identified the neurons that give rise to the PC. Labelling is confined to the magnocellular nucleus of the PC (MNPC). To gain insight into the role of the SCO in PC development, coculture experiments of explants of the MNPC region (MNPCr) from embryos at embryonic day 4 (E4) with SCO explants from E4 or E13 embryos have been performed and the neurite outgrowth from the MNPCr explants has been analysed. In the case of coculture of E4 MNPCr with E4 SCO, the number of neurites growing from the MNPCr is higher at the side facing the SCO. However, when E4 MNPCr and E13 SCO are cocultured, the neurites grow mostly at the side opposite to the SCO. These data suggest that, at early stages of development, the SCO releases some attractive or permissive molecule(s) for the growing of the PC, whereas at later stages, the SCO has a repulsive effect over neurites arising from MNPCr.

Polarized expression of integrin beta1 in diencephalic roof plate during chick development, a possible receptor for SCO-spondin.

The roof plate of the caudal diencephalon is formed by the posterior commissure (PC) and the underlying secretory ependyma, the subcommissural organ (SCO). The SCO is composed by radial glial cells bearing processes that cross the PC and attach to the meningeal basement membrane. Since early development, the SCO synthesizes SCO-spondin, a glycoprotein that shares similarities to axonal guidance proteins. In vitro, SCO-spondin promotes neuritic outgrowth through a mechanism mediated by integrin beta1. However, the secretion of SCO-spondin toward the extracellular matrix that surrounds the PC axons and the expression of integrins throughout PC development have not been addressed. Here we provide immunohistochemical evidence to suggest that during chick development SCO cells secrete SCO-spondin through their basal domain, where it is deposited into the extracellular matrix in close contact with axons of the PC that express integrin beta1. Our results suggest that SCO-spondin has a role in the development of the PC through its interaction with integrin beta1.

The neuroactive neurosteroid Dehydroepiandrosterone Sulfate (DHEAS) modulates the serotonergic system within the dorsal Raphe nucleus and the cerebrospinal fluid release of Reissner's fiber in rat.

Dehydroepiandrosterone sulfate (DHEAS) exerts important functions in the nervous system, such as modulation of neuronal death, brain development, cognition and behavior. However, little is known about the possible interactions of this steroid with the glial cells, in particular those forming circumventricular organs (CVOs). The present study, on the one hand, was focused on the assessment of the possible effect of DHEAS on the subcommissural organ in rats. Known as one of the CVOs, the SCO can release a glycoprotein of high molecular weight named Reissner's fiber (RF) into the cerebrospinal fluid (CSF), a remarkable secretory activity. On the other hand, we examined the serotonergic innervation in the Dorsal Raphe nucleus (DRN) and the subsequent SCO. Our finding has revealed a significant increase in RF immunoreactivity within the SCO following a single i.p injection of DHEAS at a dose of 5 mg/kg B.W. A loss of serotonin (5-HT) within the DRN and fibers reaching the SCO was also observed. The present findings have brought evidence of a possible modulator potential of neurosteroids, in particular DHEAS, upon the secretory activity of the SCO. This study will open a new window for a better understanding of the main role and interaction of neurosteroids with one of the relevant circumventricular organs in the mammalian brain.

La Dehydroépiandrostérone sulfate (DHEAS) exerce des fonctions importantes dans le système nerveux central comme la modulation de la mort neuronale, le développement du cerveau, la cognition et le comportement. Cependant, très peu est connu concernant l'interaction de cette stéroïde avec les cellules gliales, en particulier celles formant les organes circumventriculaires (CVOs). La présente étude, d'une part, s'est focalisée sur l'évaluation du possible effet de la DHEAS sur l'organe sous commissural (SCO) chez le rat connu en tant qu'un des CVOs. L'organe sous commissural peut libérer une glycoprotéine de grand poids moléculaire nommée fibre de Reissner (RF) dans le liquide céphalorachidien (CSF) ; une activité sécrétoire remarquable. D'autre part, nous avons examiné l'innervation sérotoninérgique du noyau de Raphé dorsal (DRN) et l'éventuelle innervation du SCO. Nos données ont révélé une élévation significative de l'immunoréactivité à la RF dans le SCO après une seule injection i.p de la DHEAS à une dose de 5mg/kg B.W. une réduction de sérotonine (5-HT) dans le DRN et les fibres atteignant le SCO a été aussi observée. Les présentes données ont apporté une évidence d'un possible potentiel modulateur des neurostéroïdes, en particulier la DHEAS sur l'activité sécrétoire du SCO. Cette étude pourra ouvrir une nouvelle fenêtre pour une meilleure compréhension du rôle et de l'interaction des neurostéroïdes avec un des organes circumventriculaires les plus importants du cerveau des mammifères.

Neuropeptide signaling and hydrocephalus: SCO with the flow.

Congenital hydrocephalus affects 0.1-0.3% of live births, with a high mortality rate (approximately 50%) in the absence of surgical intervention. Although the insertion of shunts alleviates the symptoms of the majority of congenital cases, the molecular basis of hydrocephalus and the mechanisms of cerebrospinal fluid (CSF) circulation remain largely unknown. Two important players are the subcommissural organ/Reissner's fiber (SCO/RF) complex and the ventricular ependymal (vel) cells that together facilitate the flow of the CSF through the narrow canals of the ventricular system. In this issue of the JCI, Lang et al. demonstrate that overexpression of the pituitary adenylate cyclase-activating polypeptide (PACAP) type I (PAC1) receptor gene results in abnormal development of the SCO and vel cells, leading to congenital hydrocephalus (see the related article beginning on page 1924). The ligand for the PAC1 receptor is the neuropeptide PACAP, which uncovers what the authors believe to be a novel role for this signaling cascade in the regulation of CSF circulation.

Physiological response of bovine subcommissural organ to endothelin 1 and bradykinin.

The circumventricular organs (CVOs) regulate certain vegetative functions. Receptors for bradykinin (BDK) and endothelin (ET) have been found in some CVOs. The subcommissural organ (SCO) is a CVO expressing BDK-B2 receptors and secreting Reissner's fiber (RF) glycoproteins into the cerebrospinal fluid. This investigation was designed to search for ET receptors in the bovine SCO and, if found, to study the functional properties of this ET receptor and the BDK-B2 receptor. Cryostat sections exposed to (125)I ET1 showed dense labeling of secretory SCO cells, whereas the adjacent ciliated ependyma was devoid of radiolabel. The binding of (125)I ET1 was abolished by antagonists of ETA and ETB receptors. The intracellular calcium concentration ([Ca(2+)](i)) was measured in individual SCO cells prior to and after exposure to ET1, BDK, or RF glycoproteins. ET1 (100 nM) or BDK (100 nM) caused an increase in [Ca(2+)](i) in 48% or 53% of the analyzed SCO-cells, respectively. RF glycoproteins had no effect on [Ca(2+)](i) in SCO cells. ET and BDK evoked two types of calcium responses: prolonged and short responses. Prolonged responses included those with a constant slow decline of [Ca(2+)](i), biphasic responses, and responses with a plateau phase at the peak level of [Ca(2+)](i). ET1-treated SCO explants contained a reduced amount of intracytoplasmic AFRU (antiserum to RF glycoproteins)-immunoreactive material compared with sham-treated control explants. Our data suggest that ET1 and BDK regulate [Ca(2+)](i) in bovine SCO cells, and that the changes in [Ca(2+)](i) influence the secretory activity of these cells.