Ependymal Tanycytes Research Articles

The tissue-specific transcription factor Pit-1 is expressed in the spinal cord of the lancelet, Branchiostoma lanceolatum

The spinal cord of the lancelet Branchiostoma lanceolatum was studied by using a monoclonal antibody to the rat tissue-specific transcription factor, Pit-1. Our previous studies have demonstrated Pit-1 immunoreactivity in different nervous and endocrine structures of the head region of adults and in the rostral central nervous system (CNS) of larval lancelet. Our present results show the presence of Pit-1-like protein in dorso-lateral nerve cells and ependymocytes of the adult spinal cord. Using double immunofluorescence techniques, we have revealed the coexistence of the glial fibrillary acidic protein (GFAP) with Pit-1 in groups of laterally located ependymocytes. The occurrence of GFAP, a specific marker of mammalian astrocytes and radial glia, in some lancelet ependymocytes confirms that glial elements are also present in protochordates. Furthermore, other ependymocytes, located in the roof of the central canal and containing Pit-1-like protein exclusively, could be considered as ependymal tanycytes.

Distribution of immunoreactive multiple forms of gonadotropin-releasing hormone in the brain of the antarctic fish, Notothenia coriiceps

Previous studies have shown that different gonadotropin-releasing hormone (GnRH) molecular forms are present in different groups of bony fish. In the present study, we have investigated the possible influence of the antarctic environmental contributions upon the distribution and biochemical patterns of GnRH- related molecules. The immunocytochemical distribution of GnRH-like peptides has been studied in the brain of the antarctic fish, Notothenia coriiceps, using antisera raised against three variants of GnRH: mammalian (m-GnRH), chicken (cII-GnRH) and salmon (s-GnRH). cII-GnRH immunoreactivity appears confined to cell bodies located in the lateral hypothalamus, the ventral thalamus and the midbrain rostral tegmentum; immunoreactive nerve fibers densely innervated the hypothalamic periventricular region. By contrast, m-GnRH-like immunoreactive neurons are present exclusively in the torus semicircularis of the mesencephalon and in the outer plexiphorm layers of the optic tectum. These findings suggest that cII-GnRH-like peptides appear to function as hypophysiotropic factors, as demonstrated in other species of bony fish, whereas m-GnRH-like peptides could be involved in modulatory pathways of vestibular and visual functions of N. coriiceps. Incubation with s-GnRH antiserum failed to prove the occurrence of immunoreactive elements; consequently, at least two molecular forms related to cII-GnRH and m-GnRH seem to act as hypophysiotropic and neuromodulatory factors in the brain of Notothenia coriiceps. Moreover, m-GnRH immunoreactivity in ependymal tanycytes suggests the involvement of such specialized glial cells in neuroendocrine function by linking the cerebrospinal fluid and the median eminence, as demonstrated in mammals.

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.

Adenosine triphosphate-lead histochemical reactions in ependymal epithelia of murine brains do not represent calcium transport adenosine triphosphatase.

The strong enzyme histochemical reactions for adenosine triphosphatase (ATPase) seen in ependymal tanycytes after incubation in calcium-containing media have previously been reported as calcium transport ATPase. Investigation of these reactions showed that: (1) any nucleoside triphosphate can serve as a substrate; (2) diphosphates and monophosphates cannot replace triphosphates; this includes p-nitrophenyl phosphate which is readily hydrolysed by plasma membrane transport ATPases; (3) strong localization occurs in the presence of millimolar concentrations of either calcium or magnesium ions; there is no absolute requirement for calcium ions; (4) they are not inhibited by sulphydryl inhibitors or calmodulin antagonists; (5) lead phosphate precipitates are localized almost entirely on the external face of tanycyte plasma membranes. In addition, the technique gives strong localization to vessels in the choroid plexus but not to the choroidal epithelium. Immunohistochemistry with a primary antibody raised against Ca2+, Mg2(+)-ATPase stains the choroidal epithelium but not the vessels or the ependymal tanycytes. These results are inconsistent with identification of the reaction as calcium transport ATPase but support characterization as an ecto-ATPase.

Astrocytes immunoreactive for glial fibrillary acidic protein (GFAP) are increased in the mediobasal hypothalamus in hypogonadal ( hpg) mice

The actions of gonadal steroids on neuronal activity in the hypothalamus are well documented, but the effects on glial cells are less clear. Here we have investigated glial cell activity in normal and hypogonadal ( hpg) mice, in which gonadal development is arrested postnatally. Astrocytes immunoreactive for filial fibrillary acidic protein (GFAP) were examined throughout the hypothalamus, using immunohistochemical techniques. The number of GFAP immunoreactive (GFAP-IR) cells was 25-fold higher in the mediobasal hypothalamus of hpg compared with normal mice, but there was no evidence of a sex difference in either hpg or normal mice. Castration of normal mice on the fifth postnatal day did not result in any hypothalamic astrocytosis. Treatment of adult hpg mice with estradiol-17β, testosterone, or 5α-dihydrotestosterone significantly reduced the number of GFAP-positive cells in the periventricular area, but they were still 10–20 times higher in number than in normal mice. In hpg mice treated from birth with testosterone propionate, the staining pattern was still markedly abnormal. Ependymal tanycytes, which also express GFAP-IR, were significantly shorter in male hpg compared with normal male mice. These results suggest that the GFAP-IR cells in the hypothalamus are partially affected by sex steroids, but that other factors, possibly related to the congenital defect in hpg mice, are also involved.

Immunohistochemical Localization of Basic Fibroblast Growth Factor in Ependymal Cells of the Rat Lateral and Third Ventricles

The presence of basic fibroblast growth factor (bFGF) in the third and the lateral ventricular ependyma of the rat has been investigated under the light microscope using a polyclonal antibody against bFGF, through the unlabelled peroxidase-antiperoxidase procedure; bFGF-immunoreactivity (bFGF-IR) is observed in the entire ependymal cell layer of ventricles. Also ependymal tanycytes within the inferior portion of the wall and floor of the third ventricle show bFGF-IR. Tanycytic processes are in close contact with hypothalamic capillaries. The present study strongly suggests that brain ependymal bFGF plays unidentified roles unrelated to its angiogenic or mitogenic capacities.

Ependymoma: Ultrastructural Studies of Two Cases

Several unusual ultrastructural findings in two ependymomas are reported. In case 1, a grade I ependymoma of the fourth ventricle, there were rosettes, perivascular pseudorosettes, and tumor cells having unusual intracytoplasmic vacuoles by light microscopy. Ultrastructurally, these vacuoles were frequently microrosettes as well as scattered, degenerated cytoplasmic processes of tumor cells. The lumina of some of the microrosettes were bordered by abnormally long and malformed zonulae adherentiae. In case 2, a recurrent grade III ependymoma of the third ventricle, there were rosettes and perivascular pseudorosettes as well as more cellular and anaplastic areas by light microscopy. Ultrastructurally, the cytoplasmic processes of tumor cells in perivascular pseudorosettes contained frequent dense-core vesicles and occasional parallel arrays of microtubules. These structures do not occur in normal mammalian ependymal cells but do occur in the ependymal tanycyte, a related cell that is plentiful in the walls of the third ventricle. Thus some of the tumor cells of this third ventricle ependymoma appear to have differentiated as tanycytes.

Postnatal development of glial fibrillary acidic protein (GFAP) immunoreactivity in pituicytes and tanycytes of the Mongolian gerbil (Meriones unguiculatus).

The postnatal development (day of birth up to the end of the third month) of neurohypophyseal pituicytes and tanycytes of the median eminence (ME) and the medial basal hypothalamus (MBH) was studied immunohistochemically in the Mongolian gerbil (Meriones unguiculatus) with antibodies directed against glial fibrillary acidic protein (GFAP; the major protein subunit of glial filaments). Weak GFAP-immunoreactivity (IR) was scattered in the neural lobe (NL), the ME and the lining of the ventral 3rd ventricle at the first postnatal days. By the end of the second postnatal week, the intensity of the IR had reached a level comparable to that of adult animals. Generally, in the whole neurohypophysis a cytoarchitectonic pattern, which essentially corresponded to adult conditions, was reached around the beginning of the second month. During the first week postnatum, solely perinuclear stainings, mostly unipolar pituicytes with short processes and isolated fibers were discernible in the NL. In the course of the second and third postnatal week, a growing number of the densely arranged pituicytes appeared in form of bi- and multipolar cells. Thickness and length of pituicyte processes, as well as their degree of branching, increased progressively in the first month. The number of GFAP-positive tanycytes in the ventral 3rd ventricle and in the ME most markedly augmented in the first week postnatum. In the MBH, long tanycyte processes emerged from the ventricular lining to cross the arcuate nucleus in large bows, delimiting groups of neurons. Ependymal and subependymal tanycytes in the ME gave rise to radial processes extending to the external zone.(ABSTRACT TRUNCATED AT 250 WORDS)

DARPP-32, a dopamine- and cyclic AMP-regulated phosphoprotein in tanycytes of the mediobasal hypothalamus: Distribution and relation to dopamine and luteinizing hormone-releasing hormone neurons and other glial elements

The distribution of a dopamine- and cyclic adenosine-3':5'-monophosphate (cAMP)-regulated phosphoprotein with an apparent molecular weight of 32,000 (DARPP-32) was investigated in the rat diencephalon and monkey hypothalamus by use of immunohistochemical techniques. In addition to single cells located peri- and paraventricularly in hypothalamus and thalamus in the rat and ependymal cells, DARPP-32-immunoreactivity was found to be present in a subpopulation of ependymal tanycytes. These DARPP-32-positive tanycytes lined the walls and floor of the third ventricle, sending processes towards the arcuate nucleus, surrounding blood vessels in this nucleus and continuing towards the median eminence, where they abutted on portal vessels. A second group of DARPP-32-positive tanycytes with cell bodies within the median eminence was also observed. Simultaneous labeling with antiserum against tyrosine hydroxylase, a presumptive marker for tuberoinfundibular dopamine neurons, revealed a close relation to DARPP-32-containing tanycytes in several anatomical locations. Thus, in the periventricular area DARPP-32-positive tanycytes ensheathed tyrosine hydroxylase-positive processes. These processes, presumably representing dopaminergic dendrites, virtually penetrated between the ependymal cells to the ventricular space and thus perhaps established direct contact with the cerebrospinal fluid. Tyrosine hydroxylase-terminals were also observed in close association with DARPP-32-immunoreactive tanycytes in the rat median eminence. However, in view of the density of DARPP-32-positive processes in the external layer of the median eminence, the DARPP-32 processes may be related to a number of other types of nerve endings, including luteinizing hormone-releasing hormone, as shown in this study. The close association of DARPP-32-immunoreactive processes with tyrosine hydroxylase- and luteinizing hormone-releasing hormone-immunoreactive nerve endings in the rat was directly visualized at the ultrastructural level using triple-labeling immunocytochemistry. Both the ultrastructural analysis and immuno-histochemistry at the light microscopic level, comparing the distribution of DARPP-32 and glial fibrillary acidic protein, indicated the presence of two types of glial processes in the median eminence. The electron microscopic studies also suggested the presence of both DARPP-32-positive and DARPP-32-negative glial processes in the external layer of the median eminence. In agreement, double-staining experiments with glial fibrillary acidic protein antiserum and DARPP-32-antibodies demonstrated a population of glial fibrillary acidic protein-positive/DARPP-32-negative fibers in this area. Thus, dopamine may not influence all glial elements in the median eminence. The possible neuro-endocrine role of DARPP-32-containing tanycytes is discussed.

The hypothalamic arcuate nucleus-median eminence complex: immunohistochemistry of transmitters, peptides and DARPP-32 with special reference to coexistence in dopamine neurons.

In this paper, we describe the results of a series of experiments which have examined the distribution within the arcuate nucleus of the hypothalamus of neurons containing the following immunoreactivities: TH-LI, GAD-LI, NT-LI, GAL-LI, GRF-LI, Met-ENK-LI, Leu-ENK-LI, Met-ENK-7-LI, Met-ENK-8-LI, metorphamide-LI, DYN-LI, NPY-LI, SOM-LI, FMRFamide-LI, and CLIP-LI and ependymal tanycytes containing DARPP-32-LI. Using elution-restaining and double antibody staining techniques we have established numerous patterns of coexistence of these various neurotransmitters and neuropeptides. Thus, neurons containing TH-LI were, in some instances, also found to contain GAD-LI, NT-LI, GAL-LI, GRF-LI, Met-ENK-8-LI, Leu-ENK-LI, or DYN-LI or combinations of these compounds. For example, some TH-IR neurons also contained GAL-LI and GRF-LI, while other TH-IR. neurons were also seen to contain GRF- and NT-LI. These neurons may, in fact, contain even more compounds. NPY-IR neurons and those containing SOM-LI and CLIP-LI were distinct and separate from those containing TH-LI. The distribution of these different neurochemical types of neurons and their patterns of coexistence are summarized in Fig. 34, while the relative distribution patterns of immunoreactive fibres in the median eminence are summarized in Fig. 35.

Light microscopy of the medial wall of the cerebral cortex of the lizard Psammodromus algirus.

The telencephalic medial wall of the lizard Psammodromus algirus was studied using Golgi and conventional light microscopic techniques. The area is formed by two different cytological fields-medial cortex and dorsomedial cortex. These two cortices possess three layers dorsoventrally: a superficial plexiform layer, a cellular layer, and a deep plexiform layer. The alveus, a deep fiber system, runs adjacent to the ependyma. Four classes of neurons are found in the cellular layer of the medial cortex on the basis of soma shape, dendritic pattern, and position in the layer: horizontal, double pyramidal, and candelabra cells. Solitary cells are present in the superficial and deep plexiform layers of the medial cortex. Those of the superficial plexiform layer are stellate cells. Horizontal and vertical cells are found in the deep plexiform layer. Double pyramidal cells are the most frequently impregnated in the cellular layer of the dorsomedial cortex. In addition, candelabra cells are present at the lateral end of the layer. Two cell types are found in the deep plexiform layer of the dorsomedial cortex: solitary pyramidal cells and, among the fibers of the alveus, horizontal cells. Ependymal tanycytes line the ventricular surface, and protoplasmic astrocytes are found in the plexiform layers of both medial and dorsomedial cortices.

The structure of the mediodorsal cerebral cortex in the lizard Agama agama: a Golgi study.

A Golgi analysis was made of the cell types present in the mediodorsal cerebral cortex of the lizard Agama agama. Mediodorsal cortex can be divided into two areas, small-celled mediodorsal cortex (sMDC) and large-celled mediodorsal cortex (lMDC). Both sMDC and lMDC are four-layered cortices: superficial plexiform layer, cellular layer, deep plexiform layer and fiber layer, lMDC partially overlaps dorsal cortex (medial superposition). Using characteristics of the dendrites and criteria of location, dendritic field shape and soma size, two classes of neurons can be distinguished in sMDC. The first class consists of two types of solitary cells present in the superficial and deep plexiform layers and in the fiber layer. The second class consists of six types of pyramidal-like candelabra cells, composing the cellular layer. In lMDC solitary cells are also present in the superficial and deep plexiform layers and in the fiber layer. Large pyramidal cells of one type lie in the cellular layer. In addition, neurons of the dorsal cortex and of the ventral cell plate of Unger lie in the medial superposition area of lMDC. Throughout the entire mediodorsal cortex, protoplasmic and fibrous astrocytes and ependymal tanycytes are found.

Ependymal tanycytes projecting to the ventromedial hypothalamic nucleus as demonstrated by retrograde and anterograde transport of HRP

Ependymal tanycytes projecting to the ventromedial hypothalamic nucleus as demonstrated by retrograde and anterograde transport of HRP

Changes in the fine structure of tanycytes during the annual reproductive cycle of the male little brown bat Myotis lucifugus lucifugus

The hypothalamic arcuate nucleus in the male little brown bat Myotis lucifugus lucifugus was studied with the electron microscope. Animals were killed by intracardial perfusion at each season throughout the year so that the arcuate nucleus could be examined for seasonal variations in morphology. Striking seasonal changes in the fine structure of ependymal tanycytes lining the arcuate nucleus were observed. Tanycytes in animals collected in the fall and early winter exhibited pale processes characterized by a scant internal framework of microtubules and fine filaments. These processes, which were found throughout the arcuate nucleus, exhibited simple irregular shapes. In animals collected between January and June, tanycyte processes contained dense accumulations of fine filaments intermingled with microtubules, and projected long attenuated extensions that often formed multilamellar sheets around axodendritic terminals or other neuronal elements. Tanycyte processes of animals collected in July and August were densely packed with microtubules and fine filaments. The processes radiated elaborate multilamellar extensions that encapsulated axons, dendrites and even entire neuronal perikarya. Multilamellar sheets consisted of as many as 10 or 12 closely spaced gyres. The seasonal variations in tanycyte structure are suggestive of astrocyte-like behaviour. These changes are discussed with respect to seasonal changes in hypothalamic neuroendocrine activity.

Ultrastructure of Homografts of the Rat Median Eminence into the Anterior Chamber of the Eye

Median eminences (MEs) were transplanted into the anterior chamber of the eye and collected at times varying between 10 and 72 days. At 10 days, all axons had degenerated leaving behind a well-vascularized epitheloid glial organ. With increasing age of the grafts, the characteristic lipid inclusions in the glial cells diminished and even disappeared, and the clear ultrastructural distinction between ependymal (tanycytes) and other glial cells became difficult or even impossible. In both the perikarya and perivascular terminals, an increased number of membrane-bounded, pleomorphic, electron-dense granulated vesicles occurred, the significance of which is unknown. Regrafting of these transplants into various hypothalamic and hypophysial sites is expected to yield information on the function of the glial cells of the ME.

Immunohistochemical and electron microscopic study of the rat hypothalamic nuclei and cell clusters under various experimental conditions. Possible sites of hormone release.

In untreated, pregnant and thirsting rats the neurosecretory hypothalamic areas were investigated by means of the immunoperoxidase technique in order to demonstrate vasopressin- and oxytocin containing elements at the light- and electron microscopic level. In addition, chromalum-hematoxylinphloxin (CHP) staining and conventional double staining of ultrathin sections were used. The areas investigated included the anterior and posterior supraoptic nuclei, the numerous accessory cell clusters in the region between the tractus opticus and the third ventricle as well as the median eminence. In all nuclei and in the accessory cell clusters, the number of vasopressin-reactive neurons exceeds that of oxytocin-reactive neurons. Compared with the anterior supraoptic nucleus, the posterior supraoptic nucleus and the accessory cell clusters react more heavily to prolonged thirst. In the median eminence the neurosecretory axons display close contacts with the portal vessels not only in its lateral portion but in thirsting animals also around the mid-line. There the internal layer is broadened and vasopressin-positive tanycytic processes reach the external zone. Parasagittally, fine vasopressin-positive material can be traced from the internal layer to small deposits at the portal vessels. In long term thirsting animals the typical feature of swollen axons exhibits a characteristic distribution in the median eminence and renders a distinct positive reaction to anti-vasopressin. The release of peptide hormones from the perikarya and from the axons within the nuclei as well as the mode of release within the the median eminence are discussed. The significance of the positive immunostaining of the ependymal tanycytes and of some perikarya of the suprachiasmatic nucleus must be reconsidered by further studies.

Fine structure of neurons of the arcuate nucleus and median eminence of the hypothalamus of the golden hamster following immobilization.

The fine structure of arcuate neurons of the arcuate nucleus, the ependymal tanycytes and the contact zone of the median eminence was examined following immobilization, an acute stress which significantly activated the hypothalamo-pituitary-adrenal (HPA) axis. Arcuate neurons of immobilized adult male hamsters displayed morphological indications of heightened activity; the number of lysosomes and dense core vesicles (80-120nm) was increased. A markedly greater number of dense core vesicles was present in axon terminals of the contact zone of the mid-central median eminence and the ventral proximal stalk. Tanycytes of the median eminence exhibited an augmented number of electron dense bodies in both perikarya and end processes. These results indicate that the arcuate neurons, the axons of the contact zone, and the ependymal tanycytes of the hamster medial basal hypothalamus (MBH) may be involved in the response to immobilization.

A Golgi study on tanycytes liquor-contacting cells in the posterior hypothalamus of the newt.

Golgi methods were employed to study neurons and ependymal tanycytes in the posterior hypothalamus of the newt. The tanycytes send a few coarse, spiny or barbed processes towards the pia mater. In the periventricular grey, the neurohistological methods show common neurons, ranging from a multipolar to a plumed organization, and abundant liquor-contacting cells. These cells, possibly neurons, give rise to a process that reaches the cerebro-spinal fluid, and terminates in a spindle-shaped swelling, with a thin thread at its tip. In other cells, the intraventricular endings are bulbous or finger-like. The occurrence of: (1) branches of the liquor-contacting process, running parallel to the infundibular surface; (2) infundibular processes which end at the base or between the ependymal cell bodies; and (3) axons coursing in the same position, all indicates that the subependymal layer is a site for complex intercellular relationships. The significance of liquor-contacting cells and tanycytes is discussed, in view of the possibility that they may represent part of a system for hypothalamic regulation in response to changes in the CSF.

Morphological plasticity in the wall of the third ventricle during the estrous cycle in the rat: a scanning electron microscopic study.

AbstractThe ependymal tanycytes lining the ventral basal region of the third ventricle were studied in female rats during different stages of the estrous cycle. At mid‐diestrus, the apical membranes of tanycytes were shown to be devoid of microvilli and of other surface irregularities. During proestrus, a multitude of microvilli and small bulbous protrusions characterize this region of the ventricular wall. These surface disruptions persist through estrus and disappear during diestrus. In addition, so‐called supraependymal cells were observed and counted. Their numbers also vary with respect to the estrous cycle. The significance of these changes is discussed with respect to a possible mechanism for transporting substances from the cerebrospinal fluid (CSF) to the parenchyma of the hypothalamus and to the circulation.

Ependymal tanycytes of the rabbit third ventricle: a scanning electron microscopic study

Ependymal tanycytes of the rabbit third ventricle: a scanning electron microscopic study