Planar polarity of ependymal cilia.

Ependymal cells, epithelial cells that line the cerebral ventricles of the adult brain in various animals, extend multiple motile cilia from their apical surface into the ventricles. These cilia move rapidly, beating in a direction determined by the ependymal planar cell polarity (PCP). Ciliary dysfunction interferes with cerebrospinal fluid circulation and alters neuronal migration. In this review, we summarize recent studies on the cellular and molecular mechanisms underlying two distinct types of ependymal PCP. Ciliary beating in the direction of fluid flow is established by a combination of hydrodynamic forces and intracellular planar polarity signaling. The ciliary basal bodies' anterior position on the apical surface of the cell is determined in the embryonic radial glial cells, inherited by ependymal cells, and established by non-muscle myosin II in early postnatal development.

[Extraependymal ependymocytes in the rat brain].

The aim of the study was to test the hypothesis on the presence, in intact rat brain, of the cells located outside the ependymal layer, but possessing the structural organization and cytochemical characteristics similar to those of ependymocytes. The study was carried out on Wistar rats (n=10). Ependymocytes were identified using immunocytochemical reactions to ezrin and vimentin and were visualized with light and confocal microscopy. Cells, structurally and cytochemically similar to typical ependymocytes, were found outside the layer of ependymocytes in the nervous tissue of intact rat brain. It is suggested that extraependymal ependymocytes may have a function of reserve population of the neural stem cells in the brain.

Iron accumulation in the choroid plexus, ependymal cells and CNS parenchyma in a rat strain with low-grade haemolysis of fragile macrocytic red blood cells.

Iron accumulation in the CNS is associated with many neurological diseases via amplification of inflammation and neurodegeneration. However, experimental studies on iron overload are challenging, since rodents hardly accumulate brain iron in contrast to humans. Here, we studied LEWzizi rats, which present with elevated CNS iron loads, aiming to characterise choroid plexus, ependymal, CSF and CNS parenchymal iron loads in conjunction with altered blood iron parameters and, thus, signifying non-classical entry sites for iron into the CNS. Non-haem iron in formalin-fixed paraffin-embedded tissue was detected via DAB-enhanced Turnbull Blue stainings. CSF iron levels were determined via atomic absorption spectroscopy. Ferroportin and aquaporin-1 expression was visualised using immunohistochemistry. The analysis of red blood cell indices and serum/plasma parameters was based on automated measurements; the fragility of red blood cells was manually determined by the osmotic challenge. Compared with wild-type animals, LEWzizi rats showed strongly increased iron accumulation in choroid plexus epithelial cells as well as in ependymal cells of the ventricle lining. Concurrently, red blood cell macrocytosis, low-grade haemolysis and significant haemoglobin liberation from red blood cells were apparent in the peripheral blood of LEWzizi rats. Interestingly, elevated iron accumulation was also evident in kidney proximal tubules, which share similarities with the blood-CSF barrier. Our data underscore the importance of iron gateways into the CNS other than the classical route across microvessels in the CNS parenchyma. Our findings of pronounced choroid plexus iron overload in conjunction with peripheral iron overload and increased RBC fragility in LEWzizi rats may be seminal for future studies of human diseases, in which similar constellations are found.

Intramedullary subependymoma of the cervical spinal cord: a case report with immunohistochemical study.

Spinal subependymomas, which have a relatively benign nature, are very rare tumors. It is difficult to distinguish spinal subependymomas from other intramedullary spinal tumors based on neuroradiological findings. A case of cervical intramedullary subependymoma in a 63-year-old female is reported. The diffused enlargement of the spinal cord at C2 level involved the lesion with isointensity on a T1-weighted MRI and relatively high intensity on a T2-weighted MRI. Enhancement in the small part of the tumor was observed on a T1-weighted MRI with gadolinium administration. The tumor occupied the left side of the spinal cord, and was totally removed through a laminoplasty of C2. Immunohistochemistry was useful for pathological diagnosis. The clinical feature of this patient is described with the review of literatures.

Neuronal and ependymal expression of selenoprotein P in the human brain.

Selenoprotein P (SePP) is central to selenium (Se) metabolism in the mammalian organism. Human SePP contains 10 Se atoms that are covalent constituents of the polypeptide chain incorporated as the rare amino acid selenocysteine (Sec). Since hepatocytes secrete SePP into plasma, SePP is commonly regarded as a Se transport protein, although SePP mRNA is expressed in many organs. Gene targeting of SePP in mice leads to neurological dysfunction resulting from Se deficiency and associated reduction of selenoenzyme activities in the brain. However, more recent data revealed that isolated hepatic SePP deficiency does not alter brain Se levels, suggesting a role for SePP locally expressed in the brain. Some of the best characterized and most abundant selenoenzymes, glutathione peroxidases, thioredoxin reductases, and methionine sulfoxide reductase B, play major roles in the cellular defense against reactive oxygen species. Therefore, it was hypothesized that reduced brain Se bioavailability may be involved in the pathogenesis of neurodegenerative disease and normal ageing. We present evidence that human CSF contains SePP and that the human brain expresses SePP mRNA. Moreover, SePP-like immunoreactivity localizes to neurons and ependymal cells and thus appears strategically situated for maintenance and control of Se-dependent anti-oxidative defense systems.

The mouse Jhy gene regulates ependymal cell differentiation and ciliogenesis.

During the first postnatal week of mouse development, radial glial cells lining the ventricles of the brain differentiate into ependymal cells, undergoing a morphological change from pseudostratified cuboidal cells to a flattened monolayer. Concomitant with this change, multiple motile cilia are generated and aligned on each nascent ependymal cell. Proper ependymal cell development is crucial to forming the brain tissue:CSF barrier, and to the establishment of ciliary CSF flow, but the mechanisms that regulate this differentiation event are poorly understood. The JhylacZ mouse line carries an insertional mutation in the Jhy gene (formerly 4931429I11Rik), and homozygous JhylacZ/lacZ mice develop a rapidly progressive juvenile hydrocephalus, with defects in ependymal cilia morphology and ultrastructure. Here we show that beyond just defective motile cilia, JhylacZ/lacZ mice display abnormal ependymal cell differentiation. Ventricular ependyma in JhylacZ/lacZ mice retain an unorganized and multi-layered morphology, representative of undifferentiated ependymal (radial glial) cells, and they show altered expression of differentiation markers. Most JhylacZ/lacZ ependymal cells do eventually acquire some differentiated ependymal characteristics, suggesting a delay, rather than a block, in the differentiation process, but ciliogenesis remains perturbed. JhylacZ/lacZ ependymal cells also manifest disruptions in adherens junction formation, with altered N-cadherin localization, and have defects in the polarized organization of the apical motile cilia that do form. Functional studies showed that cilia of JhylacZ/lacZ mice have severely reduced motility, a potential cause for the development of hydrocephalus. This work shows that JHY does not only control ciliogenesis, but is a crucial component of the ependymal differentiation process, with ciliary defects likely a consequence of altered ependymal differentiation.

Immunohistochemical expression of prion protein (PrPC) in the human forebrain during development.

The cellular prion protein (PrPC) is a ubiquitous protein whose expression in the adult brain occurs mainly in synapses. We used monoclonal antibodies to study fetal and perinatal PrPC expression in the human forebrain. Double immunofluorescence and confocal microscopy with GFAP, Iba1, MAP2, doublecortin, synaptophysin, and GAP-43 were used to localize PrPC. PrPC immunoreactivity was observed in axonal tracts and fascicles from the 11th week to the end of gestation. Synapses expressed PrPC at increasing levels throughout synaptogenesis. At midgestation, a few PrPC-labeled neurons were detected in the cortical anlage and numerous ameboid and intermediate microglial cells were PrPC-positive. In contrast, at the end of gestation, microglial PrPC expression decreased to almost nothing, whereas neuronal PrPC expression increased, most notably in ischemic areas. In adults, PrPC immunoreactivity was restricted to the synaptic neuropil of the gray matter. At all ages, choroid plexus, ependymal, and endothelial cells were labeled, whereas astrocytes were only occasionally immunoreactive. In conclusion, the early expression of PrPC in the axonal field may suggest a specific role for this molecule in axonal growth during development. Moreover, PrPC may play a role in early microglial cell development.

Hypothalamic tanycytes: a key component of brain-endocrine interaction.

Tanycytes are bipolar cells bridging the cerebrospinal fluid (CSF) to the portal capillaries and may link the CSF to neuroendocrine events. During the perinatal period a subpopulation of radial glial cells differentiates into tanycytes, a cell lineage sharing some properties with astrocytes and the radial glia, but displaying unique and distinct morphological, molecular, and functional characteristics. Four populations of tanycytes, alpha(1,2) and beta(1,2), can be distinguished. These subtypes express differentially important functional molecules, such as glucose and glutamate transporters; a series of receptors for neuropeptide and peripheral hormones; secretory molecules such as transforming growth factors, prostaglandin E(2), and the specific protein P85; and proteins of the endocytic pathways. This results in functional differences between the four subtypes of tanycytes. Thus, alpha(1,2) tanycytes do not have barrier properties, whereas beta(1,2) tanycytes do. Different types of tanycytes use different mechanisms to internalize and transport cargo molecules; compounds internalized via a clathrin-dependent endocytosis would only enter tanycytes from the CSF. There are also differences in the neuron-tanycyte relationships; beta(1,2) tanycytes are innervated by peptidergic and aminergic neurons, but alpha(1,2) tanycytes are not. Important aspects of the neuron-beta(1) tanycyte relationships have been elucidated. Tanycytes can participate in the release of gonadotropin-releasing hormone (GnRH) to the portal blood by expressing estrogen receptors, absorbing molecules from the CSF, and providing signal(s) to the GnRH neurons. Removal of tanycytes prevents the pulse of GnRH release into the portal blood, the peak of luteinizing hormone, and ovulation. The discovery in tanycytes of new functional molecules is opening a new field of research. Thus, thyroxine deiodinase type II, an enzyme generating triiodothyronine (T(3)) from thyroxine, appears to be exclusively expressed by tanycytes, suggesting that these cells are the main source of brain T(3). Glucose transporter-2 (GLUT-2), a low-affinity transporter of glucose and fructose, and ATP-sensitive K(+) channels are expressed by tanycytes, suggesting that they may sense CSF glucose concentrations.

Apoptosis in the subependyma of young adult rats after single and fractionated doses of X-rays.

Ionizing radiation is commonly used in the treatment of brain tumors but can cause significant damage to surrounding normal brain. The pathogenesis of this damage is uncertain, and understanding the response of potential target cell populations may provide information useful for developing strategies to optimize therapeutic irradiation. In the mammalian forebrain, the subependyma is a mitotically active area that is a source of oligodendrocytes and astrocytes, and it has been hypothesized that depletion of cells from this region could play a role in radiation-induced white matter injury. Using a distinct morphological pattern of nuclear fragmentation and an immunohistochemical method to specifically label the 3'-hydroxyl termini of DNA strand breaks (terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling), we quantified apoptosis in the subependyma in the young adult rat brain after single and fractionated doses of X-rays. Significant increases in apoptotic index (percentage of cells showing apoptosis) were detected 3 h after irradiation, and the peak apoptotic index was detected at 6 h. Six h after irradiation, the dose response for apoptosis was characterized by a steep increase in apoptotic index between 0.5 and 2.0 Gy and a plateau from 2-30 Gy. The fraction of cells susceptible to apoptosis was estimated to be about 40%, and treatment of rats with cycloheximide inhibited apoptosis. When daily 1.5-Gy fractions of X-rays were administered, the first three fractions were equally effective at decreasing the cell population via apoptosis. There was no additional apoptosis or decrease in cellularity in spite of one to four additional doses of X-rays. Those data suggested some input of cells into the subependymal population during fractionated treatment, and subsequent studies showed that there was a significant rise in 5-bromo-2' deoxyuridine labeling index 2-3 days after irradiation, indicating increased cellular proliferation. The proliferative response after depletion of cells via apoptosis may represent the recruitment of a relatively quiescent stem cell population. It is possible that the radiation response of subependymal stem cells and not the apoptotic-sensitive population per se are critical elements in the response of the brain to radiation injury.

Discovery of a letter from Rokitansky to Virchow about subependymal corpora amylacea.

Until recently, Rokitansky and Virchow were thought to have never exchanged letters. Recently, however, a letter from Rokitansky to Virchow dated 1853 was discovered. In this letter, Rokitansky commented on Virchow's discovery of subependymal corpora amylacea. This report comprises an English translation of this letter together with a historical appraisal and a short comment on the importance of corpora amylacea in the brain.

Cell proliferation and nestin expression in the ependyma of the adult rat spinal cord after injury.

A population of precursor cells is known to exist in the subependyma of the lateral ventricles in adult rodents. However, the source of the precursor cells in the adult mammalian spinal cord has not been identified in vivo, although the adult spinal cord was recently reported to contain neural stem cells in vitro. In this study we found active cell proliferation and nestin expression in the adult ependyma of the central canal after spinal cord injury. The normal ependyma showed limited proliferative activity indicated by a low Ki-67 labeling index (1.5% at T1 level) and no immunoreactivity to nestin, a marker for neural precursor cells. In contrast, the spinal cord injured by clip compression demonstrated a dramatic increase in ependymal proliferation indicated by a high Ki-67 labeling index (maximum of 26% at 3 days [d] after injury) and concomitant strong nestin expression in the ependyma. These responses were downregulated by 7 d after injury. The increased cell proliferation in the ependyma was observed only at sites immediately adjacent to the lesion. After injury, nestin positive, GFAP negative cell populations were found in areas surrounding the ependymal layer, which suggests migration of the ependymal cells. These results indicate the precursor cell qualities of the adult ependyma after injury. Thus, we propose the ependyma of the central canal, which is normally latent but activates locally and temporally in response to spinal cord injury, as the in vivo source for precursor cells in the adult mammalian spinal cord.

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.

Estrogen receptor-immunoreactive glia, endothelia, and ependyma in guinea pig preoptic area and median eminence: electron microscopy.

The presence of estrogen receptors (ERs) in nonneural cells in brain, including glia, ependyma, and endothelia, has not previously been documented with electron microscopy. This study employed immunocytochemistry to investigate whether ER immunoreactivity (ER-ir) is present in glial, ependymal, or endothelial cells in the medial preoptic area (POA) and median eminence (ME) in the brain of gonadally intact female guinea pigs. Tissue sections through these regions were immunostained with monoclonal antibody H222 for ER localization using 3,3',5,5'-tetramethylbenzidine (TMB) as the chromogen. ER-ir cells were identified ultrastructurally by the presence of distinct spicule-like TMB crystals in nuclei. While neurons constituted the clear majority of ER-immunopositive cells, labeled astrocytes, ependyma, and endothelia were also present. Distinct intranuclear TMB crystals were present in astrocytes at the anterior pole of the POA within the preventricular periventricular nucleus, anterior compact subnucleus of the medial preoptic nucleus (MPNa), and organum vasculosum of the lamina terminalis, indicating ER-ir. In the MPNa, cell counts performed at the ultrastructural level revealed that 9.6% (15 of 156) of the astrocytes were ER-ir. To further explore the relationship of ERs with astrocytes, ER/glial fibrillary acidic protein (GFAP) double labeling experiments were performed using TMB and diaminobenzidine tetrahydrochloride for ER and GFAP localization, respectively. These studies verified the presence of ERs in astrocytes at the anterior pole of the POA and demonstrated the presence of ERs in GFAP-ir cells in the ME. Cell counts at the ME showed that 23 of 50 (46%) GFAP-ir cells were ER-ir. ER-ir was also present in scattered ependymal cells lining the third ventricle at the POA and overlying the ME. Typically, approximately four to eight ER-ir ependymal cells were present around the perimeter of the third ventricle, although occasionally small aggregations of greater numbers of labeled cells were observed. Both common ependyma and cells morphologically identified as tanycytes were ER-ir. Some endothelial cells and vascular smooth muscle cells also contained ERs. While approximately 11% of the vessels were lined by ER-ir cells in sections through the MPNa and preventricular periventricular nucleus, approximately 15% of the vessels were labeled in the organum vasculosum of the lamina terminalis. In the ME a greater percentage (59%) of the vessels contained ER-ir endothelial cells. Collectively, these results indicate that in addition to regulating the activity of neurons, estrogen may affect brain function through effects exerted on astrocytes, ependymal cells, and endothelial cells.

In vitro increase in intracellular calcium concentrations induced by low or high extracellular glucose levels in ependymocytes and serotonergic neurons of the rat lower brainstem.

Pancreatic glucokinase (GK)-like immunoreactivities are located in ependymocytes and serotonergic neurons of the rat brain. The present study investigated in vitro changes in intracellular calcium concentrations ([Ca(2+)](i)) in response to low (2 mm) or high (20 mm) extracellular glucose concentrations in isolated cells from the wall of the central canal (CC), raphe obscurus nucleus (ROb), ventromedial hypothalamus (VMH), and lateral hypothalamic area (LHA) in male rats. An increase in [Ca(2+)](i) was found in cells from the CC (21.1% or 9.8% of ependymocytes), ROb (10.9% or 14.5% of serotonergic neurons), VMH (7.8% and 25.2% of neurons), and LHA (20% or 15.7% of neurons), when extracellular glucose levels were changed from 10 to either 2 or 20 mm, respectively. Most of the ependymocytes and serotonergic neurons responding to the glucose changes were immunoreactive to the anti-GK in the CC (96.8% for low glucose and 100% for high glucose) and ROb (100% for low and high glucose). The [Ca(2+)](i) increase was blocked with calcium-free medium or L-type calcium channel blocker. Cells with an increase in [Ca(2+)](i) in response to low glucose did not respond to high glucose and vice versa. Inhibition of GK activity with acute alloxan treatment blocked low or high glucose-induced [Ca(2+)](i) increases in most GK-immunoreactive cells from the CC or ROb. The glucose-sensitive [Ca(2+)](i) increase in neurons of the VMH and LHA was also alloxan-sensitive, but no cells taken from the VMH and LHA were immunoreactive to the antibody used. The present study further indicates that ependymocytes of the CC and serotonergic neurons in the ROb are also sensitive to the changes in extracellular glucose in a GK-dependent manner, but that the subtype of GK in these cells could be different from that in the VMH and LHA.

Tanycytes in the sunfish brain: NADPH-diaphorase histochemistry and regional distribution.

NADPH-diaphorase histochemistry has been shown to be a useful method for identifying cells that synthesize and release nitric oxide, which is implicated in the modulation of a variety of neural functions, including synaptic transmission, cerebral blood flow, and excitotoxicity. In the sunfish brain, NADPH-diaphorase histochemistry stains tanycytes specifically and almost exclusively, allowing for a thorough examination of the morphology and distribution of this type of cell. Tanycytes are nonciliated, process-bearing ependymal and extraependymal cells that contact the ventricular surface via apical processes, and the pial surface via basal processes. Ependymal tanycytes are located at the ventricular surface, and project basal processes into the parenchyma of the brain. Extraependymal tanycytes are found away from the ventricular matrix. Some extraependymal tanycytes are small, bipolar, and tend to be associated with bundles of basal processes. Isolated extraependymal tanycytes are larger, darkly stained, and multipolar. Their basal processes terminate in specialized endfeet on blood vessels, neuronal somata, or the pial surface. Specialized types of tanycytes are found in the optic tectum, the epineurial septum between axonal bundles along the midline in the medulla, and in restricted regions on the pial surface in the medulla. The only NADPH-diaphorase-positive neurons are found in the commissural nucleus of area ventralis telencephali. Injection of horseradish peroxidase into the ventricles shows that tanycytes lining the third and fourth ventricles are capable of taking up the tracer and transporting it into their basal processes. Tanycytes are unevenly distributed in the brain. There is a rough rostrocaudal gradient of cell density: tanycytes are sparse in the telencephalon and dense in the isthmus and medulla, although cell density is low in the spinal cord. Not all ventricular linings contain tanycytes: cell density is low in the medial ventricle of the telencephalon and in the infundibular recess, and high along the fourth ventricle. The function of tanycytes in the sunfish is not known. The association of tanycytes with both the ventricles and blood vessels raises the possibility that they play some role in sampling the biochemical constituents of both compartments and communicating the information to neural elements. It is proposed that tanycytes react to the biochemical composition in the ventricle and plasma by increasing or decreasing nitric oxide synthesis and release, which in turn influence neuronal activity or cerebral blood flow.

Projection patterns from the raphe nuclear complex to the ependymal wall of the ventricular system in the rat.

The goal of the present study was to characterize the anatomical and neurochemical relationships that the raphe nuclear complex maintains with respect to lateralized and centralized components of the ventricular system. From this investigation, we 1) determined the ipsilateral vs. contralateral distribution of raphe efferents to the ependymal wall of the lateral ventricle, 2) assessed the degree of collateralization of individual ependymal projection neurons to other sites along the ventricular path, 3) compared the topography of raphe neurons that project to the ventricular lining as well as the lumen of the fourth and lateral ventricles, and 4) evaluated the neurochemical identity of raphe neurons that innervate the ventricular system. After tracer injections into the lateral ventricle, labeled cells were distributed evenly on both sides of the midline in the dorsomedial subregion of the intermediate dorsal raphe nucleus. Further rostrally, labeled cells were clustered bilaterally above the medial longitudinal fasciculi and extended into the median raphe nucleus. Injections that involved the ependymal wall of the lateral ventricle resulted in prominent ipsilateral labeling within the dorsal raphe nucleus, just ventral to the cerebral aqueduct. Most of the labeled cells in this latter group had collateral projections to other sites along the ventricular path. Most of the ventricle projection cells contained serotonin but not nicotinamide adenine dinucleotide phosphate diaphorase. These findings indicate that the raphe nuclear complex is topographically organized with respect to the ventricular system. Selected subsets of serotoninergic dorsal raphe neurons may influence discrete segments of the ventricular system independently as well as coordinate functions throughout the system through axon collaterals to other sites along the ventricular neuraxis.

Distribution of alpha 2A-adrenergic receptor-like immunoreactivity in the rat central nervous system.

In this study, we analyzed immunohistochemically the distribution of the A subtype of alpha 2-adrenergic receptor (alpha 2A-AR) in the rat central nervous system using light level immunohistochemistry. By using affinity-purified antisera, we found perikaryal labeling was diffuse and/or punctate; immunoreactive puncta were heterogeneous in size and number in a region-specific manner. Dense deposits of immunoreaction product were found associated with neuropil also, particularly in the lateral parabrachial nucleus, locus coeruleus, lateral septum, diagonal band, stratum lacunosum-moleculare of CA1, and various nuclei of the amygdala and extended amygdala. Prominently immunoreactive olfactory structures include the anterior olfactory nucleus and the granular layer of the olfactory bulb. The cortex was generally light to moderately labeled with greater immunoreactivity in the cingulate and insular cortices. alpha 2A-AR-like immunoreactivity was intense in the basal forebrain and continuous from the nucleus accumbens through the substantia innominata and fundus of the striatum. Most immunoreactivity in the diencephalon was restricted to the hypothalamus with light to moderate labeling in the thalamus. Generally light immunoreactivity was observed in midbrain structures. In the pons and medulla, both perikaryal and neuropil labeling were observed. Together with the accompanying paper describing the neural distribution of alpha 2C-AR-like immunoreactivity, our results provide an extensive immunohistochemical cartography of alpha 2-ARs in the adult rat central nervous system.

Differential distribution of the glutamate transporters GLT-1 and GLAST in tanycytes of the third ventricle.

The ventral one-third of the ventricular lining in the hypothalamus is formed by specialized ependymal cells called the tanycytes. These cells may serve a neuroendocrine transport function because of their structural specializations, which include apical microvili on the ventricular surface and long basal processes that terminate on blood vessels or on the glia limitans. Here, we describe the expression of mRNA and protein for the glutamate transporters GLT-1 and GLAST in unique tanycyte populations of the third ventricle in rat brain. Using nonisotopic in situ hybridization, we demonstrate GLAST mRNA labeling in tanycytes of the ventral floor and lateral walls in the tuberal and mammillary recess portions of the third ventricle. This GLAST mRNA labeling had a higher intensity than the labeling intensity observed in regular ependymal cells throughout the ventricular system. Furthermore, we have identified strong GLT-1 mRNA labeling in a population of tanycytes situated in the dorsolateral walls of caudal tuberal and mammillary recess portions. Immunocytochemical staining indicates that both GLT-1 and GLAST protein are expressed in the tanycyte populations as well. These data corroborate previous findings that third ventricle tanycytes are functionally heterogeneous. Furthermore, the GLT-1-expressing tanycytes represent a population of tanycytes that, to date, has not been recognized as functionally distinct. The strong GLAST expression by the ventral tanycytes in the hypophysiotropic area suggests a role of tanycyte-mediated glutamate transport in neuroendocrine activity. The functional role of GLT-1 in dorsal wall tanycytes remains to be explored.

Localization of epidermal growth factor receptors and putative neuroblasts in human subependymal zone.

Studies in rodents and monkeys suggest that neuronal precursor cells continue to exist and differentiate well into adulthood in these species. These results challenge the long held assumption that neurogenesis does not occur in the postnatal human brain. We examined the rostral subependymal zone (SEZ) of postnatal human brain for expression of cell phenotypic markers that have been associated with neuronal precursors and neuroblasts in rodent brain. We found epidermal growth factor receptor (EGF-R) mRNA and protein to be expressed in infant, teen, young adult, and adult human SEZ. Some SEZ cells expressed the polysialic acid form of neural cell adhesion molecule (PSA-NCAM), characteristic of migrating neuroblasts, as well as class III beta-tubulin and Hu protein, characteristic of neuroblasts and early neurons. These neuroblast-like cells were negative for glial fibrillary acidic protein (GFAP), 2;,3;-cyclic nucleotide 3;-phosphohydrolase (CNPase), and vimentin, suggesting that they were not differentiating as glia. Our results show that neuroblast-like cells exist in the human SEZ and support the theory that SEZ of postnatal human brain has neurogenic potential.

ATP-binding cassette transporter ABCA2 (ABC2) expression in the developing spinal cord and PNS during myelination.

We examined developmental characteristics of the ATP-binding cassette transporter ABCA2 (or ABC2) -expressing cells in rat spinal cord and peripheral nerves. In adult spinal cord, ABCA2 immunoreactivity was detected in lysosome-like organelles of mature oligodendrocyte cell bodies, and a single specific band was detected by Western blot analysis. In postnatal developing spinal cord, ABCA2 immunolabeling was first detected in a small number of cells restricted to the ventral marginal area and the dorsal funiculus at birth (P0). ABCA2-positive cells were co-immunolabeled by O4, a marker for late progenitor and immature oligodendrocytes. At the same time, myelin basic protein was apparent in the same restricted regions. The number of ABCA2 and O4 co-immunolabeled cells increased quickly in both dorsal and ventral regions from P2 and reached a peak at P8. After transient expression from P0 to P8, O4 labeling in white matter tracts decreased and disappeared. In contrast, ABCA2-positive oligodendrocytes persisted in gray and white matter throughout the spinal cord into adulthood. These data suggest a role for the ABCA2 transporter in maturation of oligodendrocyte lineage cells and the onset of myelination in the central nervous system. In addition, ABCA2 immunoreactivity was detected in the ciliated region of the ependyma in the central canal from early postnatal development. ABCA2 immunoreactivity was also detected in the Schwann cell lineage in developing spinal nerves and in adult trigeminal and sciatic nerves. ABCA2 was also expressed in numerous undetermined cells distributed in para-nerve connective tissues and nerve sheaths throughout early postnatal development. These data indicate multiple levels of involvement for ABCA2 in nervous system development especially with strong evidence for a role in myelination.