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.

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.

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 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.

Subcommissural organ-Reissner's fiber complex plasticity in two animal models of copper intoxication and modulatory effect of curcumin: Involvement of serotonin.

Metal neurotoxicity is a universal health preoccupation. Previous data revealed an obvious neurochemical impairment induced by metal elements as copper. This investigation was conducted to study the subcommissural organ (SCO) response to acute and subchronic Cu exposure as well as its serotoninergic innervation in Wistar rats, and the probable protective potential of curcumin in these toxicological circumstances. By mean of immunohistochemistry using antibodies against Reissner's fiber (RF) and serotonin (5-HT) in acute model (10 mg/kg i.p. for 3 days) and subchronic model (0.125% in drinking water for six weeks), we noted a significant decrease of RF-immunoreactivity and a whole amplified 5-HT innervation of SCO and ventricular borders in intoxicated rats. Co-treatment with curcumin-I (30 mg/kg B.W) has shown a beneficial effect, reinstating both SCO secretory activity and serotoninergic innervation damaged by Cu exposure. This data revealed for the first time an obvious response of SCO-RF complex to Cu intoxication as well as the neuroprotective effect of curcumin-I. Thus, SCO could play a fundamental role in the strategies of brain resistance to neurotoxicity induced by metal elements in rats, and may be used as biomarker to assist in the diagnosis of this neurotoxicological conditions in rodents.

Evidence of a subcommissural organ involvement in the brain response to lead exposure and a modulatory potential of curcumin.

Substantial evidence supports the neurochemical vulnerability to lead (Pb) as one of the most potent neurotoxic heavy metals. In the present study, we aimed to assess: (i) The subcommissural organ (SCO) responsiveness as a secretory circumventricular organ to chronic and acute Pb intoxication together with its serotoninergic innervation. (ii) The possible restorative effect of curcumin against Pb intoxication under the same pathological conditions. We used immunohistochemistry with antibodies against Reissner's fiber and serotonin [5-hydroxytryptophan (5-HT)] in Wistar rats following chronic as well as acute Pb administration, respectively, at 25 mg/kg intraperitoneally for 3 days and 0.3% in drinking water from the intrauterine stage until 2 months of adult age. Our data showed a significant decrease in Reissner's fiber material immunoreactivity concomitant with an overall increased 5-HT innervation of the SCO and the ventricular borders. Coadministration of curcumin (50 mg/kg body weight) restores this impairment by reversing the effect of chronic and acute Pb on the secretory activity and the 5-HTergic innervation of the SCO. The investigation showed, on the one hand, the involvement of the SCO in the response to heavy metals, especially Pb, and on the other, the beneficial corrector role of curcumin. As a part of the circumventricular organ, known as a privileged area of brain-blood exchanges, the SCO may play a key role in the mechanism of brain defense against heavy metal neurotoxicity in rats.

Camk2a-Cre-mediated conditional deletion of chromatin remodeler Brg1 causes perinatal hydrocephalus.

Mammalian SWI/SNF-like BAF chromatin remodeling complexes are essential for many aspects of neural development. Mutations in the genes encoding the core subunit Brg1/SmarcA4 or other complex components cause neurodevelopmental diseases and are associated with autism. Congenital hydrocephalus is a serious brain disorder often experienced by these patients. We report a role of Brg1 in the pathogenesis of hydrocephalus disorder. We discovered an unexpected early activity of mouse Camk2a-Cre transgene, which mediates Brg1 deletion in a subset of forebrain neurons beginning in the late embryonic stage. Brg1 deletion in these neurons led to severe congenital hydrocephalus with enlargement of the lateral ventricles and attenuation of the cerebral cortex. The Brg1-deficient mice had significantly smaller subcommissural organs and narrower Sylvian aqueducts than mice that express normal levels of Brg1. Effects were non-cell autonomous and may be responsible for the development of the congenital hydrocephalus phenotype. Our study provides evidence indicating that abnormalities in Brg1 function result in defects associated with neurodevelopmental disorders and autism.

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 ß-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.

Chronic aluminum intoxication in rat induced both serotonin changes in the dorsal raphe nucleus and alteration of glycoprotein secretion in the subcommissural organ: Immunohistochemical study.

Aluminum (Al) causes multiple impairments in several body systems including the central nervous system. In fact, Al exposure has been mostly associated with neurological dysfunctions that occur in some brain diseases. The effect of Al neurotoxicity on the dopaminergic system is well documented, but this effect on the serotoninergic system is poorly studied. The aim of this work is to evaluate the effect of chronic Al intoxication (0.3% of aluminum chloride exposure from the intra-uterine age until 4 months of adult age) on dorsal raphe nucleus (DRN) which is the main source of serotonin, and also on the glycoprotein secretion of subcomissural organ (SCO), receiving important serotoninergic innervation. This will be executed using immunohistochemistry procedure, with both the anti serotonin and the anti Reissner's fiber antibodies in the rat. Our results showed a significant increase of serotonin immunoreactivity in the DRN, accompanied by a noticeable decrease of RF immunoreactivity in the SCO ependymocytes. This study provides further evidence confirming the toxic effect of Al exposure on serotonin neurotransmission in the brain likely through increased synthesis or decreased release. Al exposure was also shown to decrease RF glycoprotein which is involved in the detoxification of cerebrospinal fluid.

Extracellular matrix components mark the territories of circumventricular organs.

In the central nervous system the extracellular matrix has important roles, e.g. supporting the extracellular space, controlling the tissue hydration, binding soluble factors and influencing their diffusion. The distribution of the extracellular matrix components in the brain has been mapped but data on the circumventricular organs (CVOs) is not available yet. The CVOs lack the blood-brain barrier and have relatively large perivascular spaces. The present study investigates tenascin-R and the lecticans: aggrecan, brevican, neurocan, and versican in the median eminence, the area postrema, the vascular organ of the lamina terminalis, the subfornical organ, the pineal body and the subcommissural organ of the rat applying immunohistochemical methods, and lectin histochemistry, using Wisteria floribunda agglutinin (WFA). The extracellular matrix components were found intensely expressed in the CVOs with two exceptions: aggrecan immunoreactivity visualized only neurons in the arcuate nucleus, and the subcommissural organ was not labeled with either WFA, or lecticans, or tenascin-R. The different labelings usually overlapped each other. The distribution of the extracellular matrix components marked the territories of the CVOs. Considering these we suppose that the extracellular matrix is essential in the maintenance of CVO functions providing the large extracellular space which is required for diffusion and other processes important in their chemosensitive and neurosecretory activities. The decrease of extracellular matrix beyond the border of the organs may contribute to the control of the diffusion of molecules from the CVOs into the surrounding brain substance.

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.

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.

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.

The rat SCO responsiveness to prolonged water deprivation: implication of Reissner's fiber and serotonin system.

The osmotic stress is a potent stimulus that can trigger several peripheral as well as central impairments. The brain is a vulnerable target of the osmotic stress and particularly circumventricular organs (CVOs) regarding their strategic localization as sensory organs of biochemical changes in the blood and cerebrospinal fluid circulations. The subcommissural organ (SCO) is a CVO which releases doubly in the CSF and blood circulation a glycoprotein called Reissner's fiber (RF) that has been associated to several functions including electrolyte and water balances. The present work was aimed on the assessment of the secretory activity of the SCO and its serotoninergic innervation following 2 weeks of total water restriction in Wistar rat. Using the immunohistochemistry of RF and serotonin (5HT), our data showed a significant overall reduction of RF immunoreactivity within both ependymal and hypendymal cells of the SCO of dehydrated rats compared to their corresponding controls, this decrease was concomitant with an enhancement of fibers 5HT immunoreactivity in the SCO as well as in the classical ependyma and in the dorsal raphe nucleus (DRN), constituting the origin of this innervation. The present findings support the possible involvement of the SCO in the response to prolonged water deprivation by decreasing its secretory materials which may result from either a direct peripheral hormonal control and/or the consequence of the enhanced 5HT innervation of the SCO.

The subcommissural organ and the development of the posterior commissure.

Growing axons navigate through the developing brain by means of axon guidance molecules. Intermediate targets producing such signal molecules are used as guideposts to find distal targets. Glial, and sometimes neuronal, midline structures represent intermediate targets when axons cross the midline to reach the contralateral hemisphere. The subcommissural organ (SCO), a specialized neuroepithelium located at the dorsal midline underneath the posterior commissure, releases SCO-spondin, a large glycoprotein belonging to the thrombospondin superfamily that shares molecular domains with axonal pathfinding molecules. Several evidences suggest that the SCO could be involved in the development of the PC. First, both structures display a close spatiotemporal relationship. Second, certain mutants lacking an SCO present an abnormal PC. Third, some axonal guidance molecules are expressed by SCO cells. Finally, SCO cells, the Reissner's fiber (the aggregated form of SCO-spondin), or synthetic peptides from SCO-spondin affect the neurite outgrowth or neuronal aggregation in vitro.

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.

Calcitonin-like immunoreactivity in the subcommissural organ-Reissner's fiber complex of some freshwater and marine teleosts.

The subcommissural organ (SCO) is a highly specialised circumventricular ependymal organ covering and penetrating the posterior commissure. The secretory products of the SCO condense to form Reissner's fiber (RF). Because of its extensive secretory activity and the chemical properties of its secretion, the organ functions as similar to the neurosecretory cells. Teleosts comprised of more than 20,000 extant species that show great diversity in terms of the form, habit and habitat. Affinity of calcitonin antibodies for the SCO-RF complex was used as a histochemical tool to study the morphology of some freshwater and seawater teleosts and its potential correlate to their osmotic environment. While intense to moderate calcitonin-like immunoreactivity was seen in the cells of the SCO of majority of the freshwater species viz., common carp, catfish, eel and perch; the SCO of goldfish revealed limited immunoreactivity. Like the SCO, the RF in all species was also immunostained with antibodies against calcitonin. It appeared as a single, continuous fiber that ran from SCO into the third ventricle and extended through the aqueduct, fourth ventricle and central canal of the spinal cord. In contrast to that in the freshwater fishes, the SCO-RF complex in majority of the seawater fishes, showed no calcitonin-like immunoreactivity. The data presented in this study described the comparative histomorphology of the SCO-RF complex and suggest a possibility that the calcitonin-like immunoreactivity in the SCO-RF complex might be a feature correlated to the osmotic environment of the fish.

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.

Water deprivation affects serotoninergic system and glycoprotein secretion in the sub-commissural organ of a desert rodent Meriones shawi.

Water deprivation is a stress that has been associated with activation of several endocrine systems, including circumventricular organs of the central nervous system. The sub-comissural organ (SCO), characterized by its glycoprotein secretion called Reissner's fiber has been suggested to play a role in the regulation of body water balance. Meriones shawi, a semi-desertic rodent characterized by its resistance to long periods of thirst was subjected to water deprivation for 1 and 3 months. Effect of water deprivation was evaluated immunohistochemically on 5-hydroxytryptamine (5-HT; serotonin) system and glycoprotein secretion of the SCO. Our findings demonstrate significant reduction of anti-Reissner's fiber immunoreactive materials within basal and apical parts of the SCO ependymocytes. These changes seem to be the consequence of reduced control by 5-HT fibers reaching the SCO as a concomitant and significant reduction of anti-5-HT immunoreactive fibers are also observed following water deprivation. 5-HT immunoreactive reduction is seen in several regions in the brain including the neurons of origin within the dorsal raphe nucleus and the projecting supra and sub-ependymal fibers reaching the classical ependyma of the third ventricle. The extent of Reissner's fiber and 5-HT immunoreactive changes significantly correlates with the severity of water restriction. We suggest that water deprivation causes changes of the classical ependyma and the specialized ependyma that differentiates into the SCO as well as other cirumventricular organs such as the subfornical organ and the organum vasculosum laminae terminalis known to control drinking behaviors.

A monoclonal antibody as a tool to study the subcommissural organ and Reissner's fibre of the sea lamprey: an immunofluorescence study before and after a spinal cord transection.

Lampreys are vertebrate animal models in spinal cord regeneration studies. In order to gain knowledge on the mechanisms that provide to the lamprey spinal cord its capacity of regeneration we decided to compare the expression patterns of the growth-associated protein 43 (GAP-43) in the CNS of the sea lamprey before and after a complete spinal transection by immunocytochemical methods using an anti-GAP-43 antibody. Surprisingly, in the brain/spinal cord of both normal and injured animals, anti-GAP-43-like labeling was only observed in the subcommissural organ (SCO) and Reissner's fibre (RF). In injured larvae, a dotted labeling was also observed in the meninges and in the blood the vessels of the neighbouring tissues at the site of lesion. The experiments in injured animals showed that after complete spinal cord transection the SCO seems to continue to produce the Reissner's substance (RS), which is accumulated at the proximal site of spinal transection. The dotted labeling observed in the neighbouring tissues could correspond to RS that was released from the site of injury. In Western blot experiments done using protein extracts of the lamprey brain, the anti-GAP-43 antibody did not recognize any protein band of the expected GAP-43 molecular weight, indicating that the secreted material is not this protein. An anti-serotonin antibody was also used as a marker of some brain structures. Serotonergic afferent fibres innervated the SCO. Here we show a new tool that can be used as a highly specific marker in further studies of the SCO/RF system of lampreys.