Developmental genes controlling neural circuit formation are expressed in the early postnatal hypothalamus and cellular lining of the third ventricle

The arcuate nucleus of the hypothalamus is central in the regulation of body weight homeostasis through its ability to sense peripheral metabolic signals and relay them, through neural circuits, to other brain areas, ultimately affecting physiological and behavioural changes. The early postnatal development of these neural circuits is critical for normal body weight homeostasis, such that perturbations during this critical period can lead to obesity. The role for peripheral regulators of body weight homeostasis, including leptin, insulin and ghrelin, in this postnatal development is well described, yet some of the fundamental processes underpinning axonal and dendritic growth remain unclear. Here, we hypothesised that molecules known to regulate axonal and dendritic growth processes in other areas of the developing brain would be expressed in the postnatal arcuate nucleus and/or target nuclei where they would function to mediate the development of this circuitry. Using state-of-the-art RNAscope^® technology, we have revealed the expression patterns of genes encoding Dcc/Netrin-1, Robo1/Slit1 and Fzd5/Wnt5a receptor/ligand pairs in the early postnatal mouse hypothalamus. We found that individual genes had unique expression patterns across developmental time in the arcuate nucleus, paraventricular nucleus of the hypothalamus, ventromedial nucleus of the hypothalamus, dorsomedial nucleus of the hypothalamus, median eminence and, somewhat unexpectedly, the third ventricle epithelium. These observations indicate a number of new molecular players in the development of neural circuits regulating body weight homeostasis, as well as novel molecular markers of tanycyte heterogeneity.

The Lactate Receptor HCA1 Is Present in the Choroid Plexus, the Tela Choroidea, and the Neuroepithelial Lining of the Dorsal Part of the Third Ventricle

The volume, composition, and movement of the cerebrospinal fluid (CSF) are important for brain physiology, pathology, and diagnostics. Nevertheless, few studies have focused on the main structure that produces CSF, the choroid plexus (CP). Due to the presence of monocarboxylate transporters (MCTs) in the CP, changes in blood and brain lactate levels are reflected in the CSF. A lactate receptor, the hydroxycarboxylic acid receptor 1 (HCA1), is present in the brain, but whether it is located in the CP or in other periventricular structures has not been studied. Here, we investigated the distribution of HCA1 in the cerebral ventricular system using monomeric red fluorescent protein (mRFP)-HCA1 reporter mice. The reporter signal was only detected in the dorsal part of the third ventricle, where strong mRFP-HCA1 labeling was present in cells of the CP, the tela choroidea, and the neuroepithelial ventricular lining. Co-labeling experiments identified these cells as fibroblasts (in the CP, the tela choroidea, and the ventricle lining) and ependymal cells (in the tela choroidea and the ventricle lining). Our data suggest that the HCA1-containing fibroblasts and ependymal cells have the ability to respond to alterations in CSF lactate in body-brain signaling, but also as a sign of neuropathology (e.g., stroke and Alzheimer's disease biomarker).

Third Ventricular Injection of CCL2 in Rat Embryo Stimulates CCL2/CCR2 Neuroimmune System in Neuroepithelial Radial Glia Progenitor Cells: Relation to Sexually Dimorphic, Stimulatory Effects on Peptide Neurons in Lateral Hypothalamus

Clinical and animal studies show maternal alcohol consumption during pregnancy causes in offspring persistent alterations in neuroimmune and neurochemical systems known to increase alcohol drinking and related behaviors. Studies in lateral hypothalamus (LH) demonstrate in adolescent offspring that maternal oral administration of ethanol stimulates the neuropeptide, melanin-concentrating hormone (MCH), together with the inflammatory chemokine C-C motif ligand 2 (CCL2) and its receptor CCR2 which are increased in most MCH neurons. These effects, consistently stronger in females than males, are detected in embryos, not only in LH but hypothalamic neuroepithelium (NEP) along the third ventricle where neurons are born and CCL2 is stimulated within radial glia progenitor cells and their laterally projecting processes that facilitate MCH neuronal migration toward LH. With ethanol's effects similarly produced by maternal peripheral CCL2 administration and blocked by CCR2 antagonist, we tested here using in utero intracerebroventricular (ICV) injections whether CCL2 acts locally within the embryonic NEP. After ICV injection of CCL2 (0.1 µg/µl) on embryonic day 14 (E14) when neurogenesis peaks, we observed in embryos just before birth (E19) a significant increase in endogenous CCL2 within radial glia cells and their processes in NEP. These auto-regulatory effects, evident only in female embryos, were accompanied by increased density of CCL2 and MCH neurons in LH, more strongly in females than males. These results support involvement of embryonic CCL2/CCR2 neuroimmune system in radial glia progenitor cells in mediating sexually dimorphic effects of maternal challenges such as ethanol on LH MCH neurons that colocalize CCL2 and CCR2.

Isolation and characterization of cluster of differentiation 9-positive ependymal cells as potential adult neural stem/progenitor cells in the third ventricle of adult rats

Ependymal cells located above the ventricular zone of the lateral, third, and fourth ventricles and the spinal cord are thought to form part of the adult neurogenic niche. Many studies have focused on ependymal cells as potential adult neural stem/progenitor cells. To investigate the functions of ependymal cells, a simple method to isolate subtypes is needed. Accordingly, in this study, we evaluated the expression of cluster of differentiation (CD) 9 in ependymal cells by in situ hybridization and immunohistochemistry. Our results showed that CD9-positive ependymal cells were also immunopositive for SRY-box 2, a stem/progenitor cell marker. We then isolated CD9-positive ependymal cells from the third ventricle using the pluriBead-cascade cell isolation system based on antibody-mediated binding of cells to beads of different sizes and their isolation with sieves of different mesh sizes. As a result, we succeeded in isolating CD9-positive populations with 86% purity of ependymal cells from the third ventricle. We next assayed whether isolated CD9-positive ependymal cells had neurospherogenic potential. Neurospheres were generated from CD9-positive ependymal cells of adult rats and were immunopositve for neuron, astrocyte, and oligodendrocyte markers after cultivation. Thus, based on these findings, we suggest that the isolated CD9-positive ependymal cells from the third ventricle included tanycytes, which are special ependymal cells in the ventricular zone of the third ventricle that form part of the adult neurogenic and gliogenic niche. These current findings improve our understanding of tanycytes in the adult third ventricle in vitro.

Three-plane description of astroglial populations of OVLT subdivisions in rat: Tanycyte connections to distant parts of third ventricle

This study demonstrates glial and gliovascular markers of organon vasculosum laminae terminalis (OVLT) in three planes. The distribution of glial markers displayed similarities to the subfornical organ. There was an inner part with vimentin- and nestin-immunopositive glia whereas GFAP and the water-channel aquaporin 4 were found at the periphery. This separation indicates different functions of the two regions. The presence of nestin may indicate stem cell-capabilities whereas aquaporin 4 has been reported to promote the osmoreceptor function. Glutamine synthetase immunoreactivity was sparse like in the area postrema and subfornical organ. The laminin and β-dystroglycan immunolabelings altered along the vessels such as in the subfornical organ indicating altering gliovascular relations. The different subdivisions of OVLT received glial processes of different origins. The posterior periventricular zone contained short vimentin-immunopositive processes from the ependyma of the adjacent surface of the third ventricle. The lateral periventricular zone received forceps-like process systems from the anterolateral part of the third ventricle. Most interestingly, the "dorsal cap" received a mixed group of long GFAP- and vimentin-immunopositive processes from a distant part of the third ventricle. The processes may have two functions: a guidance for newly produced cells like radial glia in immature brain and/or a connection between distant parts of the third ventricle and OVLT.

Low-dose infusions of leptin into the nucleus of the solitary tract increase sensitivity to third ventricle leptin

Previous studies suggest that weight loss occurs when leptin receptors in both the forebrain and hindbrain are activated. Experiments described here tested whether this integration is mediated through a neural connection or by leptin diffusion through the subarachanoid space. If the hypothalamus and hindbrain communicated through a neural pathway, then a very low dose of leptin infused directly into the nucleus of the solitary tract (NTS) would enhance the response to third ventricle (3V) leptin but would have no effect if infused into the fourth ventricle (4V). A 12-day infusion of 10 ng/24 h into the 4V or the NTS reduced body fat. Leptin at 5 ng/24 h into the 4V or NTS had no effect on food intake or body composition, but infusion of 5 ng of leptin/24 h into the NTS combined with a 3V injection of 0.1 μg of leptin inhibited food intake between 6 and 12 h after injection. Cumulative intake was inhibited for up to 36 h. 3V leptin had no effect on food intake of rats receiving the 4V leptin infusion. Similar results were found using infusions of 5 ng leptin/24 h and a 3V injection of 0.025 μg leptin. These data suggest that activation of leptin receptors in the NTS lowers the threshold for response to leptin in the forebrain through a neural network.

Low-dose leptin infusion in the fourth ventricle of rats enhances the response to third-ventricle leptin injection

We previously reported that low-dose leptin infusions into the third or fourth ventricle that do not affect energy balance when given independently cause rapid weight loss when given simultaneously. Therefore, we tested whether hindbrain leptin enhances the response to forebrain leptin or whether forebrain leptin enhances the response to hindbrain leptin. Rats received fourth-ventricle infusions of saline or 0.01, 0.1, 0.3, or 0.6 μg leptin/day for 13 days. On days 9 and 13, 0.1 μg leptin was injected into the third ventricle. The injection inhibited food intake for 36 h in saline-infused rats but for 60 h in those infused with 0.6 μg leptin/day. Leptin injection increased intrascapular brown fat temperature in leptin-infused, but not saline-infused, rats. In a separate experiment, rats received third-ventricle infusions of saline or 0.005, 0.01, 0.05, or 0.1 μg leptin/day and fourth-ventricle injections of 1.0 μg leptin on days 9 and 13 Leptin injection inhibited food intake, respiratory exchange ratio, and 14-h food intake in rats infused with saline or the two lowest doses of leptin. There was no effect with higher-dose leptin infusions because food intake, body fat, and lean mass were already inhibited. These data suggest that activation of leptin receptors in the hindbrain enhances the response to third-ventricle leptin, whereas activation of forebrain leptin receptors does not enhance the response to fourth-ventricle leptin, consistent with our previous finding that weight loss in rats treated with fourth-ventricle leptin is associated with indirect activation of hypothalamic STAT3.

Prolactin regulation of kisspeptin neurones in the mouse brain and its role in the lactation-induced suppression of kisspeptin expression

Hyperprolactinaemia is a major cause of infertility in both males and females, although the mechanism by which prolactin inhibits the reproductive axis is not clear. The aim of the present study was to test the hypothesis that elevated prolactin causes suppression of kisspeptin expression in the hypothalamus, resulting in reduced release of gonadotrophin-releasing hormone (GnRH) and consequent infertility. In oestrogen-treated ovariectomised mice, chronic prolactin-treatment prevented the rise in luteinising hormone (LH) seen in vehicle-treated mice. Kiss1 mRNA was significantly suppressed in both the rostral periventricular region of the third ventricle (RP3V) and arcuate nucleus after prolactin treatment. Exogenous prolactin treatment induced phosphorylated signal transducer and activator of transcription 5 (pSTAT5) in kisspeptin neurones, and suppression of endogenous prolactin using bromocriptine reduced levels of pSTAT5 in kisspeptin neurones, suggesting that prolactin acts directly on kisspeptin neurones. By contrast, fewer than 1% of GnRH neurones expressed pSTAT5 in either dioestrous or lactating mice. As reported previously, there was significant suppression of kisspeptin mRNA and protein in the RP3V on day 7 of lactation, although not in the arcuate nucleus. Bromocriptine treatment significantly increased Kiss1 mRNA expression in the RP3V, although not to dioestrous levels. Unilateral thelectomy, aiming to eliminate sensory inputs from nipples on one side of the body, failed to alter the reduction in the number of kisspeptin neurones observed in the RP3V. These data demonstrate that chronic prolactin administration suppressed serum LH, and reduced Kiss1 mRNA levels in both the RP3V and arcuate nucleus, consistent with the hypothesis that prolactin-induced suppression of kisspeptin secretion might mediate the inhibitory effects of prolactin on GnRH secretion. During lactation, however, the suppression of Kiss1 mRNA in the RP3V was only partially reversed by the administration of bromocriptine to block elevated levels of prolactin, suggesting that, although elevated prolactin contributes to lactational anovulation, additional non-neural factors must also contribute to the lactation-induced suppression of kisspeptin neurones.

Sustained alterations of hypothalamic tanycytes during posttraumatic hypopituitarism in male mice

Traumatic brain injury is a leading cause of hypopituitarism, which compromises patients' recovery, quality of life, and life span. To date, there are no means other than standardized animal studies to provide insights into the mechanisms of posttraumatic hypopituitarism. We have found that GH levels were impaired after inducing a controlled cortical impact (CCI) in mice. Furthermore, GHRH stimulation enhanced GH to lower level in injured than in control or sham mice. Because many characteristics were unchanged in the pituitary glands of CCI mice, we looked for changes at the hypothalamic level. Hypertrophied astrocytes were seen both within the arcuate nucleus and the median eminence, two pivotal structures of the GH axis, spatially remote to the injury site. In the arcuate nucleus, GHRH neurons were unaltered. In the median eminence, injured mice exhibited unexpected alterations. First, the distributions of claudin-1 and zonula occludens-1 between tanycytes were disorganized, suggesting tight junction disruptions. Second, endogenous IgG was increased in the vicinity of the third ventricle, suggesting abnormal barrier properties after CCI. Third, intracerebroventricular injection of a fluorescent-dextran derivative highly stained the hypothalamic parenchyma only after CCI, demonstrating an increased permeability of the third ventricle edges. This alteration of the third ventricle might jeopardize the communication between the hypothalamus and the pituitary gland. In conclusion, the phenotype of CCI mice had similarities to the posttraumatic hypopituitarism seen in humans with intact pituitary gland and pituitary stalk. It is the first report of a pathological status in which tanycyte dysfunctions appear as a major acquired syndrome.

Blockade of the cerebral aqueduct in rats provides evidence of antagonistic leptin responses in the forebrain and hindbrain

Previously, we reported that low-dose leptin infusions into the fourth ventricle produced a small but significant increase in body fat. These data contrast with reports that injections of higher doses of leptin into the fourth ventricle inhibit food intake and weight gain. In this study, we tested whether exogenous leptin in the fourth ventricle opposed or contributed to weight loss caused by third ventricle leptin infusion by blocking diffusion of CSF from the third to the fourth ventricle. Male Sprague-Dawley rats received third ventricle infusions of PBS or 0.3 μg leptin/24 h from miniosmotic pumps. After 4 days, rats received a 3-μl cerebral aqueduct injection of saline or of thermogelling nanoparticles (hydrogel) that solidified at body temperature. Third ventricle leptin infusion inhibited food intake and caused weight loss. Blocking the aqueduct exaggerated the effect of leptin on food intake and weight loss but had no effect on the weight of PBS-infused rats. Leptin reduced both body fat and lean body mass but did not change energy expenditure. Blocking the aqueduct decreased expenditure of rats infused with PBS or leptin. Infusion of leptin into the third ventricle increased phosphorylated STAT3 in the VMHDM of the hypothalamus and the medial NTS in the hindbrain. Blocking the aqueduct did not change hypothalamic p-STAT3 but decreased p-STAT3 in the medial NTS. These results support previous observations that low-level activation of hindbrain leptin receptors has the potential to blunt the catabolic effects of leptin in the third ventricle.

Lactational anovulation in mice results from a selective loss of kisspeptin input to GnRH neurons

In mammals, lactation is associated with a period of infertility characterized by the loss of pulsatile secretion of GnRH and cessation of ovulatory cycles. Despite the importance of lactational infertility in determining overall fecundity of a species, the mechanisms by which the suckling stimulus suppresses GnRH secretion remain unclear. Because kisspeptin neurons are critical for fertility, the aim of this study was to test the hypothesis that reduced kisspeptin expression might mediate the lactation-induced suppression of fertility, using mouse models. In the rostral periventricular area of the third ventricle (RP3V), a progressive decrease in RP3V Kiss1 mRNA levels was observed during pregnancy culminating in a 10-fold reduction during lactation compared with diestrous controls. This was associated with approximately 60% reduction in the numbers of kisspeptin-immunoreactive neurons in the RP3V detected during lactation. Similarly, in the arcuate nucleus there was also a significant decrease in Kiss1 mRNA levels during late pregnancy and midlactation, and a notable decrease in kisspeptin fiber density during lactation. The functional characteristics of the RP3V kisspeptin input to GnRH neurons were assessed using electrophysiological approaches in an acute brain slice preparation. Although endogenous RP3V kisspeptin neurons were found to activate GnRH neurons in diestrous mice, this was never observed during lactation. This did not result from an absence of kisspeptin receptors because GnRH neurons responded normally to 100 nM exogenous kisspeptin during lactation. The kisspeptin deficit in lactating mice was selective, because GnRH neurons responded normally to RP3V gamma aminobutryic acid inputs during lactation. These data demonstrate that a selective loss of RP3V kisspeptin inputs to GnRH neurons during lactation is the likely mechanism causing lactational anovulation in the mouse.

Molecular mechanisms that drive estradiol-dependent burst firing of Kiss1 neurons in the rostral periventricular preoptic area

Kisspeptin (Kiss1) neurons in the rostral periventricular area of the third ventricle (RP3V) provide excitatory drive to gonadotropin-releasing hormone (GnRH) neurons to control fertility. Using whole cell patch clamp recording and single-cell (sc)RT-PCR techniques targeting Kiss1-CreGFP or tyrosine hydroxylase (TH)-EGFP neurons, we characterized the biophysical properties of these neurons and identified the critical intrinsic properties required for burst firing in 17β-estradiol (E2)-treated, ovariectomized female mice. One-fourth of the RP3V Kiss1 neurons exhibited spontaneous burst firing. RP3V Kiss1 neurons expressed a hyperpolarization-activated h-current (Ih) and a T-type calcium current (IT), which supported hyperpolarization-induced rebound burst firing. Under voltage clamp conditions, all Kiss1 neurons expressed a kinetically fast Ih that was augmented 3.4-fold by high (LH surge-producing)-E2 treatment. scPCR analysis of Kiss1 neurons revealed abundant expression of the HCN1 channel transcripts. Kiss1 neurons also expressed a Ni(2+)- and TTA-P2-sensitive IT that was augmented sixfold with high-E2 treatment. CaV3.1 mRNA was also highly expressed in these cells. Current clamp analysis revealed that rebound burst firing was induced in RP3V Kiss1 neurons in high-E2-treated animals, and the majority of Kiss1 neurons had a hyperpolarization threshold of -84.7 mV, which corresponded to the V½ for IT de-inactivation. Finally, Kiss1 neurons in the RP3V were hyperpolarized by μ- and κ-opioid and GABAB receptor agonists, suggesting that these pathways also contribute to rebound burst firing. Therefore, Kiss1 neurons in the RP3V express the critical channels and receptors that permit E2-dependent rebound burst firing and provide the biophysical substrate that drives the preovulatory surge of GnRH.

Genetic deletion of afadin causes hydrocephalus by destruction of adherens junctions in radial glial and ependymal cells in the midbrain

Adherens junctions (AJs) play a role in mechanically connecting adjacent cells to maintain tissue structure, particularly in epithelial cells. The major cell–cell adhesion molecules at AJs are cadherins and nectins. Afadin binds to both nectins and α-catenin and recruits the cadherin-β-catenin complex to the nectin-based cell–cell adhesion site to form AJs. To explore the role of afadin in radial glial and ependymal cells in the brain, we generated mice carrying a nestin-Cre-mediated conditional knockout (cKO) of the afadin gene. Newborn afadin-cKO mice developed hydrocephalus and died neonatally. The afadin-cKO brain displayed enlarged lateral ventricles and cerebral aqueduct, resulting from stenosis of the caudal end of the cerebral aqueduct and obliteration of the ventral part of the third ventricle. Afadin deficiency further caused the loss of ependymal cells from the ventricular and aqueductal surfaces. During development, radial glial cells, which terminally differentiate into ependymal cells, scattered from the ventricular zone and were replaced by neurons that eventually covered the ventricular and aqueductal surfaces of the afadin-cKO midbrain. Moreover, the denuded ependymal cells were only occasionally observed in the third ventricle and the cerebral aqueduct of the afadin-cKO midbrain. Afadin was co-localized with nectin-1 and N-cadherin at AJs of radial glial and ependymal cells in the control midbrain, but these proteins were not concentrated at AJs in the afadin-cKO midbrain. Thus, the defects in the afadin-cKO midbrain most likely resulted from the destruction of AJs, because AJs in the midbrain were already established before afadin was genetically deleted. These results indicate that afadin is essential for the maintenance of AJs in radial glial and ependymal cells in the midbrain and is required for normal morphogenesis of the cerebral aqueduct and ventral third ventricle in the midbrain.

Galanin-like peptide (GALP) facilitates thermogenesis via synthesis of prostaglandin E2 by astrocytes in the periventricular zone of the third ventricle

Administration of galanin-like peptide (GALP) leads to a decrease in both total food intake and body weight 24 h after injection, compared to controls. Moreover, GALP induces an increase in core body temperature. To elucidate the mechanism by which GALP exerts its effect on energy homeostasis, urethane-anesthetized rats were intracerebroventricularly injected with GALP or saline, after which oxygen consumption, heart rate, and body temperature were monitored for 4 h. In some cases, animals were also pretreated with the cyclooxygenase (COX) inhibitor, diclofenac, via intracerebroventricular (i.c.v.) or intravenous (i.v.) injection. c-Fos expression in the brain was also examined after injection of GALP, and the levels of COX and prostaglandin E(2) synthetase (PGES) mRNA in primary cultured astrocytes treated with GALP were analyzed by using qPCR. The i.c.v. injection of GALP caused biphasic thermogenesis, an effect which could be blocked by pretreatment with centrally (i.c.v.), but not peripherally (i.v.) administered diclofenac. c-Fos immunoreactivity was observed in astrocytes in the periventricular zone of the third ventricle. GALP treatment also increased COX-2 and cytosolic PGES, but not COX-1, microsomal PGES-1, or microsomal PGES-2 mRNA levels in cultured astrocytes. We, therefore, suggest that GALP elicits thermogenesis via a prostaglandin E(2)-mediated pathway in astrocytes of the central nervous system.

Photoperiodic expression of two RALDH enzymes and the regulation of cell proliferation by retinoic acid in the rat hypothalamus

Retinoic acid (RA) has been found to regulate hypothalamic function, but precisely where it acts is unknown. This study shows expression of retinaldehyde dehydrogenase (RALDH) enzymes in tanycytes that line the third ventricle in an area overlapping with the site of hypothalamic neural stem cells. The influence of RA was examined on the proliferation of progenitors lining the third ventricle using organotypic slice cultures. As has been shown in other regions of neurogenesis, RA was found to inhibit proliferation. Investigations of the dynamics of RALDH1 expression in the rat hypothalamus have shown that this enzyme is in tanycytes under photoperiodic control with highest levels during long versus short days. In parallel to this shift in RA synthesis, cell proliferation in the third ventricle was found to be lowest during long days when RA was highest, implying that RALDH1 synthesized RA may regulate neural stem cell proliferation. A second RA synthesizing enzyme, RALDH2 was also present in tanycytes lining the third ventricle. In contrast to RALDH1, RALDH2 showed little change with photoperiodicity, but surprisingly the protein was present in the apparent absence of mRNA transcript and it is hypothesized that the endocytic tanycytes may take this enzyme up from the cerebrospinal fluid (CSF).

Gonadal steroid induction of kisspeptin peptide expression in the rostral periventricular area of the third ventricle during postnatal development in the male mouse

Kisspeptin and its G-protein coupled receptor Gpr54 are essential for the pubertal activation of gonadotrophin-releasing hormone (GnRH) neurones, with Gpr54 mutation or deletion resulting in failed puberty and infertility in humans and mice. The number of kisspeptin-immunoreactive neurones in the rostral periventricular area of the third ventricle (RP3V) increases during pubertal development in concert with the appearance of kisspeptin appositions with GnRH neurones in the mouse rostral preoptic area. We recently demonstrated that the pubertal increase in RP3V kisspeptin neuronal number in females is dependent upon circulating oestradiol levels. The present experiments investigated the potential role of gonadal steroids in the induction of kisspeptin expression in the RP3V during pubertal development in the male mouse. Using immunocytochemistry (ICC), we show that gonadectomy of male pups at postnatal day (P) 20 resulted in a 60-70% reduction in the number of kisspeptin immunoreactive (IR) neurones within the RP3V of P45 mice (P<0.05) compared to sham-treated littermates. We established a profile of circulating testosterone levels during postnatal development in male mice and found that circulating testosterone was low throughout early postnatal development and increased from P35-40 to reach adult levels. Treatment of P20-gonadectomised male mice with 17β-oestradiol or testosterone from P38-45 restored kisspeptin-IR neurone number in the RP3V to intact control levels (P>0.05). Using double-label ICC, we demonstrate that the majority of RP3V kisspeptin neurones express androgen receptors and oestrogen receptor α, indicating that RP3V kisspeptin neurones in the male mouse are equipped to respond to both androgen and oestrogen signals. These results indicate that, as in females, gonadal steroids are essential for the increase in kisspeptin immunoreactive cell number that occurs in the RP3V during pubertal development in the male mouse.

Immunocytochemical localization of kisspeptin neurons in the rat forebrain with special reference to sexual dimorphism and interaction with GnRH neurons

Kisspeptin/metastin has been implicated as a critical regulator in luteinizing hormone (LH) secretion and the reproductive system mediating the effect of estrogen on GnRH neurons. In the present study we examined the sex differences in the effects of estrogen on Kiss1/kisspeptin expression in the forebrain by using gonadectomized rats to assess the interaction of kisspeptin and GnRH neurons. Kiss1/kisspeptin cell bodies were abundant in the rostral periventricular area of the third ventricle (RV3P) and the arcuate nucleus (ARC). A few cell bodies were also observed in other portions of the forebrain, i.e. the bed nucleus of the stria terminalis (BST), the paraventricular hypothalamic nucleus (PaAP), the ventromedial hypothalamic nucleus (VMH), and the medial amygdaloid nucleus (MeA). Kisspeptin-immunoreactive fibers were found mainly in the median eminence (ME), the ARC, and the RV3P, but were scarce in the preoptic area (POA), where GnRH neurons are localized. We also found that estrogen triggers expression of the Kiss1 gene and peptide within all the regions except the ARC, and that the effects in the RV3P, BST, PaAP, and VMH are greater in estrogen treated ovariectomized female rat. It is noteworthy that kisspeptin and GnRH neurons were densely associated in the ME but were rarely in contact in the POA. Thus, our results suggest that kisspeptin-positive neurons, except for the ones in the ARC, are related not only to estrogen-positive feedback, but also sex dimorphism, and that kisspeptin regulates GnRH release in the ME rather than the POA.

Ambient temperature and 17β-estradiol modify Fos immunoreactivity in the median preoptic nucleus, a putative regulator of skin vasomotion

Estrogen has pronounced effects on thermoregulation, but the anatomic sites of integration between the reproductive and thermoregulatory axes are unknown. In this study, we tested whether estradiol-17β (E(2)) treatment would alter the activity of thermoregulatory brain regions responding to mild changes in ambient temperature (T(AMBIENT)). Core and tail skin temperatures were recorded at the ambient temperatures of 20, 24, or 31 C in ovariectomized (OVX) rats with and without E(2). Neuronal activity was evaluated by counting the number of Fos-immunoreactive cells in the brains of rats killed 90 min after exposure to one of the three ambient temperatures. Of 14 brain areas examined, the median preoptic nucleus (MnPO) was the only site that exhibited increased Fos immunoreactivity at the high T(AMBIENT) of 31 C. At 24 C, OVX rats exhibited increased numbers of MnPO Fos-immunoreactive cells, compared with OVX + E(2) rats. Interestingly, tail skin vasomotion and MnPO Fos expression were affected in a similar manner by T(AMBIENT) and E(2) treatment. In the arcuate nucleus and anteroventral periventricular nucleus (AVPV), Fos immunoreactivity was highest at the low T(AMBIENT) of 20 C, with inhibitory (arcuate nucleus) and stimulatory (AVPV) effects of E(2). No other areas responded to both T(AMBIENT) and E(2) treatment. These results implicate the MnPO, the arcuate nucleus, and the AVPV as sites of integration between the reproductive and thermoregulatory axes. Combined with studies showing the importance of MnPO neurons in heat-defense pathways, the MnPO emerges as a likely site for E(2) modulation of thermoregulatory vasomotion.

Projections of arcuate nucleus and rostral periventricular kisspeptin neurons in the adult female mouse brain

The important role of kisspeptin neurons in the regulation of GnRH neuron activity is now well accepted. However, the ways in which kisspeptin neurons located in the arcuate nucleus (ARN) and rostral periventricular area of the third ventricle (RP3V) control GnRH neurons are poorly understood. The present study used anterograde and retrograde tracing techniques to establish the neuronal projection patterns of kisspeptin cell populations in the female mouse brain. Anterograde tracing studies revealed that kisspeptin neurons in the ARN innervated a wide number of hypothalamic and associated limbic region nuclei, whereas RP3V kisspeptin neurons projected to a smaller number of mostly medially located hypothalamic nuclei. Retrograde tracing confirmed a major projection of RP3V kisspeptin neurons to the ARN and showed that kisspeptin neurons located in the rostral half of the ARN projected to the rostral preoptic area. Peripheral administration of Fluorogold was found to label the majority of GnRH neurons but no kisspeptin neurons. Together, these studies highlight the complexity of the brain kisspeptin neuronal system and indicate that both ARN and RP3V kisspeptin neurons participate in a variety of limbic functions. In relation to the GnRH neuronal network, these investigations demonstrate that, alongside the RP3V kisspeptin cells, rostral ARN kisspeptin neurons may also project to GnRH neuron cell bodies. However, no kisspeptin neurons innervate GnRH nerve terminals in the external layer of the median eminence. These studies provide a neuroanatomical framework for the further elucidation of the functions of the ARN and RP3V kisspeptin neuron populations.

Changes in vasopressin release and autonomic function induced by manipulating forebrain GABAergic signaling under euvolemia and hypovolemia in conscious rats

The anteroventral third ventricular region (AV3V) is a pivotal area for osmotic responses and integration of autonomic functions. The purpose of this study was to investigate whether the gamma-aminobutyric acid (GABA)-ergic activity in the AV3V may be involved in the regulation of arginine vasopressin (AVP) secretion and related phenomena under the conditions with or without hypovolemia. Experiments were performed in conscious rats. We found that AV3V infusion with the GABA(A) receptor antagonist bicuculline in euvolemic rats caused prompt increases in plasma AVP, osmolality, glucose, arterial pressure and heart rate. The effects of the bicuculline infusion were abolished by prior infusion of a GABA(A) receptor agonist, muscimol. When repeated twice with a 10-min interval, removal of systemic blood (10 mL/kg body weight) lowered arterial pressure and enhanced plasma AVP, osmolality, glucose and angiotensin II. Muscimol infusion in the AV3V, but not in the cerebral ventricle, inhibited the responses of plasma AVP and glucose, despite having no effect in a sham hemorrhagic state. The inhibition of the AVP response by the muscimol infusion was also verified in rats given a combined stimulus of bleeding plus an osmotic load. In contrast, AV3V infusion with the GABA(B) receptor agonist baclofen tended to intensify the hemorrhagic responses of plasma AVP and glucose, despite its potency to prevent the hemorrhagic fall in arterial pressure. These results, taken together with our previous data, suggest that hypovolemic stimuli, like hyperosmotic stimuli, may promote AVP secretion by causing the inhibition of AV3V GABA(A)-ergic activity responsible for potentiation of glutamatergic activity.

[Using MR PC cine to evaluate CSF dynamics in neuroendoscopic third ventriculostomy:an analysis of 146 cases]

OBJECTIVE

To evaluate the change of CSF dynamics using MR PC Cine for neuroendoscopic third ventriculostomy.

METHODS

146 cases of hydrocephalus were treated by neuroendoscopic third ventriculostomy including 36 cases checked with MR PC Cine study randomly. The successful result was assessed by clinical symptom and imaging study. All the patients were given 3 months to 1 year follow-up.

RESULTS

The symptoms of 121 (83%) patients were recovered soon. CT, MRI and MR PC Cine demonstrated the CSF velocity, flow rate and dynamics change to the normal level compared with preoperative check. The effective rate of this group was 75.3% with one year follow-up.

CONCLUSION

The method of MR PC Cine to evaluate the CSF dynamics result for neuroendoscopic third ventriculostomy is simple, fast and safe. It is worth the clinical application.

Electrical and morphological characteristics of anteroventral periventricular nucleus kisspeptin and other neurons in the female mouse

Neurons in the rodent anteroventral periventricular nucleus (AVPV) play a key role in integrating circadian and gonadal steroid hormone information in the control of fertility. In particular, estradiol-sensitive kisspeptin neurons located in the AVPV, and adjacent structures [together termed the rostral periventricular area of the third ventricle (RP3V)], are critical for puberty onset and the preovulatory LH surge. The present study aimed to establish the morphological and electrical firing characteristics of RP3V neurons, including kisspeptin neurons, in the adult female mouse. Cell-attached electrical recordings, followed by juxtacellular dye filling, of 129 RP3V neurons in the acute brain slice preparation revealed these cells to exhibit multipolar (53%), bipolar (43%), or unipolar (4%) dendritic morphologies along with silent (16%), irregular (41%), bursting (25%), or tonic (34%) firing patterns. Postrecording immunocytochemistry identified 17 of 100 filled RP3V cells as being kisspeptin neurons, all of which exhibited complex multipolar dendritic trees and significantly (P < 0.05) higher bursting or high tonic firing rates compared with nonkisspeptin neurons. The firing pattern of RP3V neurons fluctuated across the estrous cycle with a significant (P < 0.05) switch from irregular to tonic firing patterns found on proestrus. A similar nonsignificant trend was found for kisspeptin neurons. All RP3V neurons responded to gamma-aminobutyric acid and glutamate, about 10% to RFamide-related peptide-3, about 5% to vasopressin, 0% to vasoactive intestinal peptide, and 0% to kisspeptin. These studies provide a morphological and electrical description of AVPV/RP3V neurons and demonstrate their cycle-dependent firing patterns along with an unexpected lack of acute response to the circadian neuropeptides.

Acute food deprivation reduces expression of diazepam-binding inhibitor, the precursor of the anorexigenic octadecaneuropeptide ODN, in mouse glial cells

In the central nervous system of mammals, the gene encoding diazepam-binding inhibitor (DBI) is exclusively expressed in glial cells. Previous studies have shown that central administration of a DBI processing product, the octadecaneuropeptide ODN, causes a marked inhibition of food consumption in rodents. Paradoxically, however, the effect of food restriction on DBI gene expression has never been investigated. Here, we show that in mice, acute fasting dramatically reduces DBI mRNA levels in the hypothalamus and the ependyma bordering the third and lateral ventricles. I.p. injection of insulin, but not of leptin, selectively stimulated DBI expression in the lateral ventricle area. These data support the notion that glial cells, through the production of endozepines, may relay peripheral signals to neurons involved in the central regulation of energy homeostasis.

Ghrelin decreases food intake in juvenile rainbow trout (Oncorhynchus mykiss) through the central anorexigenic corticotropin-releasing factor system

Ghrelin stimulates pituitary growth hormone (GH) release, and has a key role in the regulation of food intake and adiposity in vertebrates. To investigate the central effect of native rainbow trout ghrelin (rtghrelin) on food intake in rainbow trout, as well as its possible mode of action, four groups of fish received a single injection into the third brain ventricle (i.c.v. injection): (1) control group (physiological saline) (2) ghrelin-treated group (2.0 ng rtghrelin g bwt(-1)), (3) group given the corticotropin-releasing hormone receptor antagonist alpha-helical CRF 9-41 (ahCRF) (4.0 ng g bwt(-1)) and (4) group receiving the same dose of both ghrelin and ahCRF. Food intake was assessed 1h after treatment. In addition, the presence of the GHS-R (the ghrelin receptor) in the rainbow trout CNS was examined with Western blot. To investigate peripheral effects of ghrelin, rainbow trout received an intraperitoneal cholesterol-based implant with or without rtghrelin, and daily food intake was measured during 14 days. Weight and length were measured at the start and termination of the experiment and specific growth rates were calculated. Mesenteric fat stores, muscle and liver lipid content were analysed after the treatment period. Central ghrelin injections decreased food intake compared with controls, and treatment with ahCRF abolished the ghrelin-effect. Western blot analysis of the GHS-R revealed a single band at around 60 kDa in pituitary, hypothalamus, brain and stomach. Long-term peripheral ghrelin treatment decreased daily food intake compared with controls. This was reflected in a ghrelin-induced decrease in weight growth rate (p<0.06). There was no effect of ghrelin on plasma GH levels or tissue fat stores. The conclusion from this study is that the GHS-R is indicated in the CNS in rainbow trout and that ghrelin may act there as an anorexigenic hormone, through a CRF-mediated pathway. Elevated peripheral ghrelin levels also seem to lead to decreased feed intake in the longer term.

Photoperiodic control of TSH-beta expression in the mammalian pars tuberalis has different impacts on the induction and suppression of the hypothalamo-hypopysial gonadal axis

Seasonal reproduction depends on photoperiod-regulated activation or suppression of the gonadal axis. Recent studies in quail have identified long-day induced TSH-beta expression in the pars tuberalis (PT) as a rapid trigger of gonadal activation. Thyroid-stimulating hormone (TSH) induces type 2 deiodinase (Dio2) in the ependymal cell layer (EC) of the infundibular recess to stimulate the gonadal axis. A similar mechanism is proposed in sheep and mice, but the experimental data on the temporal patterns of induction and suppression of TSH-beta and Dio2 expression are incomplete. In the present study, we examined the expression of TSH-beta and Dio2 in hamsters transferred from short- to long-day conditions for 9 days, and demonstrate the induction of TSH-beta and Dio2 on day 8 after transition. These data demonstrate the close relationship between TSH-beta and Dio2 expression in the inductive pathway. The temporal expression of TSH-beta and Dio2 in the suppressive pathway was also examined by s.c. melatonin injection, which mimics the transition from long to short days. Importantly, Dio2 expression in the EC is suppressed on day 1 after the onset of injection, whereas TSH-beta expression in the PT was not suppressed until day 10. These data suggest that regulated transcription of TSH-beta is involved in the induction of the gonadal axis in mammals, whereas the suppression of this axis is mediated by different mechanisms.

Effect of photoperiod on the thyroid-stimulating hormone neuroendocrine system in the European hamster (Cricetus cricetus)

Recent studies have characterised a retrograde mechanism whereby the pineal hormone melatonin acts in the pars tuberalis (PT) of the pituitary gland to control thyroid hormone action in the hypothalamus, leading to changes in seasonal reproductive function. This involves the release of thyroid-stimulating hormone (TSH) from PT that activates type II deiodinase (DIO2) gene expression in hypothalamic ependymal cells, locally generating biologically active T3, and thus triggering a neuroendocrine cascade. In the present study, we investigated whether a similar regulatory mechanism operates in the European hamster. This species utilises both melatonin signalling and a circannual timer to time the seasonal reproductive cycle. We found that expression of betaTSH RNA in the PT was markedly increased under long compared to short photoperiod, whereas TSH receptor expression was localised in the ependymal cells lining the third ventricle, and in the PT, where its expression varied with time and photoperiod. In the ependymal cells at the base of the third ventricle, DIO2 and type III deiodinase (DIO3) expression was reciprocally regulated, with DIO2 activated under long and repressed under short photoperiod, and the reverse case for DIO3. These data are consistent with recent observations in sheep, and suggest that the PT TSH third ventricle-ependymal cell relay plays a conserved role in initiating the photoperiodic response in both long- and short-day breeding mammals.

Negative correlation between neuropeptide Y profile in the cerebrospinal fluid and growth hormone pulses in the peripheral circulation in goats

BACKGROUND/AIMS

Growth hormone (GH) is secreted in pulsatile fashion, but the involvement of neuropeptides in the generation of GH pulses is not fully understood. The present study was conducted to elucidate the relationship between GH pulses and neuropeptide levels in the cerebrospinal fluid (CSF) of the third ventricle in ovariectomized goats.

METHODS

CSF and plasma samples were collected every 15 min. Levels of plasma GH and profiles of GH-releasing hormone (GHRH), somatostatin (SRIH) and neuropeptide Y (NPY) in the CSF were measured by radioimmunoassay. Pulse/trough characteristics and correlations were assessed by the ULTRA algorithm, cross-correlation analysis and approximate entropy test.

RESULTS

The periodicity of GH pulses was 2.20 h. Although most GH pulses were associated with GHRH peaks, there was no correlation between GH and GHRH or GH and SRIH. NPY levels in the CSF fluctuated episodically at 2.03-hour intervals. GH pulse peaks occurred 0-30 min after NPY troughs, and there was a significant negative cross-correlation and negative synchronicity between GH and NPY profiles. In addition, intracerobroventricular infusion of NPY suppressed GH secretagogue (KP102)-induced GH release.

CONCLUSION

The periodic decrease in NPY may be involved in the generation of GH pulsatility in goats.

Gonadotropin-releasing hormone in third ventricular cerebrospinal fluid: endogenous distribution and exogenous uptake

GnRH is detectable in the cerebrospinal fluid (CSF), but its source remains unidentified. Previous studies have harvested CSF for GnRH analysis from the median eminence region, but it is unknown whether GnRH in CSF is restricted to this region. If CSF-GnRH plays a physiological role, through volume transmission, to communicate with brain regions that express GnRH receptors but are not evidently innervated by GnRH neurons, then it is essential to establish whether GnRH is more pervasive throughout the cerebroventricular system. Three cannulae were placed in the supraoptic, infundibular, and pineal recesses of the third ventricle. GnRH was undetectable in lateral ventricle CSF. GnRH pulses were detected in all ewes in infundibular recess CSF, but at sites more rostral (supraoptic) and caudal (pineal), GnRH pulse frequency and amplitude significantly (P<0.05) decreased. A GnRH surge was evident in CSF collected simultaneously from all cannulae, but the amplitude was greatest (P<0.05) at the infundibular recess. A final study established whether iv administered GnRH enters the CSF. A 250-ng GnRH dose did not affect CSF-GnRH concentrations (1.6+/-0.3 pg/ml), but 2.5 microg (2.7+/-0.2 pg/ml; P<0.001) and 1 mg (38.5+/-10.6 pg/ml; P<0.05) significantly increased CSF-GnRH concentrations. The present study shows: 1) the median eminence region is likely to be the major, if not only, source of GnRH entering the cerebroventricular system; and 2) exogenous GnRH crosses the blood-brain barrier, but extremely high doses are required to elevate CSF concentrations to physiological levels. Thus, CSF-GnRH may affect sites that are closer in proximity to the infundibular recess region than previously thought.

[Protein 70 kDa in control of sleep and thermoregulation]

Studies of expression of molecular chaperones of the family of Heat Shock Proteins 70 kDa (HSP70) in the mouse and rat brain during sleep deprivation do not answer the question whether the HSP70 produce somnogenic effect. In the present work there are studied effects of exogenous Hsp70 that is known to be able to penetrate into living cells in vitro and to acquire properties of endogenous chaperone. Hsp70 was microinjected into the third brain ventricle of rats and pigeons at the beginning of the inactive period of the day when under natural conditions the sleep duration increases and the somato-visceral parameters decrease. Hsp70 was found to enhance this natural process and to produce an additional increase in the total time of slow-wave sleep, a more pronounced inhibition of the muscle contractive activity, and a deeper decrease in the brain temperature. A similarity in effects of Hsp70 in rats and pigeons was revealed. In both species the somnogenic effect of Hsp70 in is realized by activation of mechanisms of maintenance of in longer episodes of in slow-wave sleep. The hypothermic Hsp70 effect seems to be associated with a decrease in the muscle contractive activity level, rather than with an enhancement in peripheral vasodilation and with an increase of heat loss. A hypothesis is put forward that the neuroleptic effect of Hsp70 that includes the somnogenic, myorelaxing, and hypothermic effects is mediated by activation of GABAA receptors of the main inhibitory brain system.

Developmental expression of FMRP in the astrocyte lineage: implications for fragile X syndrome

One of the most common causes of mental retardation in humans, Fragile X syndrome, results from the absence of FMRP, the protein product of the FMR1 gene. In the nervous system, expression of FMRP has been thought to be confined mainly to neurons as little research has examined FMRP expression in non-neuronal lineages. We present evidence that, in addition to neuronal expression, FMRP is expressed in developing CNS glial cells in vitro and in vivo. The neurosphere assay was used to establish cultures of stem and progenitor cells from the brains of wildtype and FMRP knockout (B6.129.FMR1/FvBn) mouse pups. When the neurospheres were differentiated in vitro, approximately 50% of the FMRP positive cells also expressed GFAP. Immunocytochemical studies of the embryonic and postnatal mouse brain revealed coexpression of FMRP and GFAP in the developing hippocampus. Prominent coexpression was also observed in ependymal cells surrounding the third ventricle and astrocytes of the glia limitans. No double-labeled cells were evident in the brains of young adult mice. Cells coexpressing FMRP and the oligodendrocyte precursor marker NG2 were also identified in the hippocampus and corpus callosum of the early postnatal brain. Our results suggest that FMRP is expressed in cells of non-neuronal lineage(s) during development. This represents potential involvement of glial cells in the neural development of fragile X syndrome.

Hypothalamic activity during altered salt and water balance in the snake Bothrops jararaca

The effects of water and salt overload on the activities of the supraoptic and paraventricular nuclei and the adjacent periventricular zone of the hypothalamus of the snake Bothrops jararaca were investigated by measurements of Fos-like immunoreactivity (Fos-ir). Both water and salt overload resulted in changes in body mass, plasma osmolality, and plasma concentrations of sodium, potassium, and chloride. Hyper-osmolality increased Fos immunoreactivity in the rostral supraoptic nucleus (SON), the paraventricular nucleus (PVN), and adjacent periventricular areas. Both hyper- and hypo-osmolality increased Fos immunoreactivity in the intermediate SON, but not in other areas of the hypothalamus. Immunostaining was abundant in cerebrospinal fluid (CSF)-contacting tanycyte-like cells in the ependymal layer of the third ventricle. These data highlight some features of regional distribution of Fos immunoreactivity that are consistent with vasotocin functioning as a hormone, and support the role of hypothalamic structures in the response to disruption of salt and water balance in this snake.

Ultrastructure of ependyma in brain third ventricle of the rats exposed to repeated tail-suspension. Scanning electron microscopical study

By means of scanning electron microscopy the ultrastructure of ependyma was studied in the brain third ventricle of the rats repeatedly exposed to 14-day tail-suspension (TS). Animals were subjected to TS for 30 days, then readapted to horizontal position during 30 days and again, repeatedly subjected to TS for 14 days simultaneously with the rats which were in TS for the first time during 14 days. Repeated TS of rats, inspite of repeated redistribution of body liquid mediums in cranial direction, results in considerably less expressed destructive changes in ultrastructure of ependymocyte cilia, then after primary 14- and 30-day TS, showing much greater cerebrospinal fluid (CSF) outflow from brain ventricles into sagittal venous sinus at postponed for a long time, repeated simulation of weightlessness effects in comparison with CSF outflow at primery one.

New insights on Saccus vasculosus evolution: a developmental and immunohistochemical study in elasmobranchs

The saccus vasculosus (SV) is a circumventricular organ of the hypothalamus of many jawed fishes whose functions have not yet been clarified. It is a vascularized neuroepithelium that consists of coronet cells, cerebrospinal fluid-contacting (CSF-c) neurons and supporting cells. To assess the organization, development and evolution of the SV, the expression of glial fibrillary acidic protein (GFAP) and the neuronal markers gamma-aminobutyric acid (GABA), glutamic acid decarboxylase (GAD; the GABA synthesizing enzyme), neuropeptide Y (NPY), neurophysin II (NPH), tyrosine hydroxylase (TH; the rate-limiting catecholamine-synthesizing enzyme) and serotonin (5-HT), were investigated by immunohistochemistry in developing and adult sharks. Coronet cells showed GFAP immunoreactivity from embryos at stage 31 to adults, indicating a glial nature. GABAergic CSF-c neurons were evidenced just when the primordium of the SV becomes detectable (at stage 29). Double immunolabeling revealed colocalization of NPY and GAD in these cells. Some CSF-c cells showed TH immunoreactivity in postembryonic stages. Saccofugal GABAergic fibers formed a defined SV tract from the stage 30 and scattered neurosecretory (NPH-immunoreactive) and monoaminergic (5-HT- and TH-immunoreactive) saccopetal fibers were first detected at stages 31 and 32, respectively. The early differentiation of GABAergic neurons and the presence of a conspicuous GABAergic saccofugal system are shared by elasmobranch and teleosts (trout), suggesting that GABA plays a key function in the SV circuitry. Monoaminergic structures have not been reported in the SV of bony fishes, and were probably acquired secondarily in sharks. The existence of saccopetal monoaminergic and neurosecretory fibers reveals reciprocal connections between the SV and hypothalamic structures which have not been previously detected in teleosts.

[Pilomyxoid astrocytoma: a clinicopathologic study of three cases]

OBJECTIVE

To study the clinicopathologic features of pilomyxoid astrocytoma (PmA).

METHODS

The clinical and pathologic features in 3 cases of PmA were analyzed. Immunohistochemical study for glial fibrillary acidic protein (GFAP), CD34 and Ki-67 was performed on paraffin-embedded sections by standard EnVision method.

RESULTS

All the 3 cases occurred in female patients at the age of 10 months, 10 years and 19 years respectively. Two cases were located in the third ventricle, while the remaining case was located at the optic pathway. Histologically, the tumor was composed of bipolar spindle cells setting in a strikingly mucinous background. There was a marked proliferation of vessels within the tumor. In some areas, the tumor cells exhibited an angiocentric growth pattern. The biphasic pattern noted in a classic pilocytic astrocytoma was not found in PmA. Rosenthal fibers and eosinophilic granular bodies were also not identified. Immunohistochemcal study showed that the tumor cells were diffusely positive for GFAP. The Ki-67 labeling index measured less than 1%. CD34 highlighted mainly the vascular networks.

CONCLUSIONS

PmA is a distinctive variant of pilocytic astrocytoma with subtle histologic differences. Compared with conventional pilocytic astrocytoma, PmA behaves more aggressively. Some cases tend to occur in older children and adolescents. Immunohistochemical study for GFAP is helpful in differential diagnosis.

Anteroventral third ventricular N-methyl-d-aspartate receptors, but not metabotropic glutamate receptors are involved in hemorrhagic AVP secretion

This study aimed to investigate the roles of glutamate (Glu) receptors in the anteroventral third ventricular region (AV3V), a pivotal area for water, cardiovascular and neuroendocrine regulations, in causing vasopressin (AVP) secretion and other phenomena in response to bleeding. The effects of intracerebral infusions of MK-801 [a N-methyl-D-aspartate (NMDA) receptor antagonist] or a metabotropic Glu receptor antagonist (MCPG) on plasma levels of AVP, electrolytes, osmolality and glucose, heart rate and arterial pressure following AV3V administration with NMDA or bleeding stimuli were analyzed in conscious rats. NMDA provoked prominent rises of plasma AVP, osmolality, glucose and arterial pressure, without changing plasma electrolytes or heart rate significantly. All the effects of NMDA were blocked by pre-administration of MK-801 into the same loci. Removal through a femoral arterial line of 10 ml blood per kg body weight did not affect arterial pressure or other variables significantly, although plasma AVP and angiotensin II (ANG II) tended to increase. When bleeding was repeated after 10 min (B2), arterial pressure dropped promptly, and plasma AVP, ANG II, osmolality and glucose augmented remarkably. MK-801 applied 35 min preceding B2, to loci such as the median preoptic nucleus, periventricular nucleus and medial preoptic area inhibited the response of plasma AVP significantly, without exerting any effects on other variables. When MK-801 was administered intracerebroventricularly, or when MCPG was infused into the AV3V, significant alterations did not occur in B2-evoked responses of plasma AVP nor in those of the other variables. In rats given sham bleeding after AV3V infusions of MK-801 or MCPG or intracerebroventricular applications of MK-801, all monitored variables roughly remained at stable levels throughout the experiments. We conclude that NMDA receptors in AV3V, but not metabotropic Glu receptors, may facilitate AVP secretion in hypotensive hypovolemia.

Central neuropeptide Y receptors are involved in 3rd ventricular ghrelin induced alteration of colonic transit time in conscious fed rats

Background

Feeding related peptides have been shown to be additionally involved in the central autonomic control of gastrointestinal functions. Recent studies have shown that ghrelin, a stomach-derived orexigenic peptide, is involved in the autonomic regulation of GI function besides feeding behavior. Pharmacological evidence indicates that ghrelin effects on food intake are mediated by neuropeptide Y in the central nervous system.

Methods

In the present study we examine the role of ghrelin in the central autonomic control of GI motility using intracerobroventricular and IP microinjections in a freely moving conscious rat model. Further the hypothesis that a functional relationship between NPY and ghrelin within the CNS exists was addressed.

Results

ICV injections of ghrelin (0.03 nmol, 0.3 nmol and 3.0 nmol/5 μl and saline controls) decreased the colonic transit time up to 43%. IP injections of ghrelin (0.3 nmol – 3.0 nmol kg^-1 BW and saline controls) decreased colonic transit time dose related. Central administration of the NPY₁ receptor antagonist, BIBP-3226, prior to centrally or peripherally administration of ghrelin antagonized the ghrelin induced stimulation of colonic transit. On the contrary ICV-pretreatment with the NPY₂ receptor antagonist, BIIE-0246, failed to modulate the ghrelin induced stimulation of colonic motility.

Conclusion

The results suggest that ghrelin acts in the central nervous system to modulate gastrointestinal motor function utilizing NPY₁ receptor dependent mechanisms.

HistoGreen: a new alternative to 3,3′-diaminobenzidine-tetrahydrochloride-dihydrate (DAB) as a peroxidase substrate in immunohistochemistry?

Abide its toxicity, 3,3'-diaminobenzidine-tetrahydrochloride-dihydrate (DAB) was the most potent marker for immunochemistry at the light and electron microscopic level in the last decades. Recently, a sensitive substrate for immunohistochemical staining methods and in-situ hybridization, HistoGreen, was developed for the use with peroxidase. In peroxidase reactions, HistoGreen delivers a green staining product which is suitable for permanent embedding without water. In contrast to DAB, HistoGreen is not toxic. To evaluate its usefulness, we performed comparative immunohistochemistry on angiotensin II (AT1)-receptors with DAB- and HistoGreen-staining on paraffin embedded slices of the rat brain at the light microscopic level. This also included counterstaining with Mayer's Hemalum and Nuclear Fast Red, respectively. We could demonstrate that HistoGreen delivers a coarsely grained label which is fast detectable in light microscopy. HistoGreen equals DAB in the exact localization of the immunoreaction to a large degree but its reaction product is considerably less stable in alcohol and water than DAB. In combination with Nuclear Fast Red, HistoGreen provides excellent imaging properties for the visualization and documentation of immunoreactive structures paired with an adequate demonstration of cellular details. Its tendency towards rapid over-staining as well as its low stability will restrict the use of HistoGreen in some areas of immunohistochemical research, yet the new chromogen represents an interesting alternative to DAB at the light microscopic level.

Sodium vitamin C cotransporter SVCT2 is expressed in hypothalamic glial cells

Kinetic analysis of vitamin C uptake demonstrated that different specialized cells take up ascorbic acid through sodium-vitamin C cotransporters. Recently, two different isoforms of sodium-vitamin C cotransporters (SVCT1/SLC23A1 and SVCT2/SLC23A2) have been cloned. SVCT2 was detected mainly in choroidal plexus cells and neurons; however, there is no evidence of SVCT2 expression in glial and endothelial cells of the brain. Certain brain locations, including the hippocampus and hypothalamus, consistently show higher ascorbic acid values compared with other structures within the central nervous system. However, molecular and kinetic analysis addressing the expression of SVCT transporters in cells isolated from these specific areas of the brain had not been done. The hypothalamic glial cells, or tanycytes, are specialized ependymal cells that bridge the cerebrospinal fluid with different neurons of the region. Our hypothesis postulates that SVCT2 is expressed selectively in tanycytes, where it is involved in the uptake of the reduced form of vitamin C (ascorbic acid), thereby concentrating this vitamin in the hypothalamic area. In situ hybridization and optic and ultrastructural immunocytochemistry showed that the transporter SVCT2 is highly expressed in the apical membranes of mouse hypothalamic tanycytes. A newly developed primary culture of mouse hypothalamic tanycytes was used to confirm the expression and function of the SVCT2 isoform in these cells. The results demonstrate that tanycytes express a high-affinity transporter for vitamin C. Thus, the vitamin C uptake mechanisms present in the hypothalamic glial cells may perform a neuroprotective role concentrating vitamin C in this specific area of the brain.

Regional expression of the radial glial marker vimentin at different stages of the kindling process

The classical view of the function of radial glia in brain development is a supporting function guiding radial neural migration. However, recent evidence indicates that they may play key roles in neurogenesis and gliogenesis, as ubiquitous precursors that generate neurons and glia. Although we previously reported the emergence of radial glia after spinal cord injury in adult rats, their precise function in this process is still unknown. In the present study, we examined emergence of radial glia in rat brain during progression of kindling, by performing immunohistochemical staining for vimentin which is a specific marker of radial glia. Vimentin immunoreactivity was found to be highest at clonus 3 and then decreased at clonus 5 in the hippocampal formation, regions around the third ventricle, caudate putamen and lateral habenular nucleus. Contrast, vimentin immunoreactivity consistently increased with progression of kindling in the cingulum and parietal cortex. These findings indicate dynamic changes in vimentin expression dependent on the kindling stage of seizure-prone state, and suggest that these changes play roles in formation of new circuits following kindling.

Serotonin innervation of the primate suprachiasmatic nucleus

The suprachiasmatic nucleus (SCN) in rodents receives a dense innervation from serotonin neurons of the midbrain raphe. This projection overlaps the terminal field of the retinohypothalamic tract in the SCN core, the central part of the nucleus characterized by a population of vasoactive intestinal polypeptide (VIP)-containing neurons. To determine whether a similar pathway is present in primates, we carried out an immnunocytochemical investigation of the primate SCN using antisera against either serotonin (monkey) or the serotonin transporter (human). This demonstrated a dense serotonergic plexus over the SCN core in both species. As in rodents, the distribution of the serotonin innervation of the primate SCN overlaps that of the retinohypothalamic input and the VIP neuronal population. We also find a supraependymal plexus of serotonin axons in the third and lateral ventricles of the human and monkey brains that is similar in distribution, but less dense, than the one reported in rodents.

Estrogen receptor-α expression in osmosensitive elements of the lamina terminalis: regulation by hypertonicity

The subfornical organ (SFO), median preoptic nucleus (MnPO), and organum vasculosum lamina terminalis (OVLT), which are associated with the lamina terminalis, are important in the control of body fluid balance. Neurons in these regions express estrogen receptor (ER)-α, but whether the ER-α neurons are activated by hypertonicity and whether hypertonicity regulates ER-α expression are not known. Using fluorescent, double-label immunocytochemistry, we examined the expression of ER-α-immunoreactivity (ir) and Fos-ir in control and water-deprived male rats. In control animals, numerous ER-α-positive neurons were expressed in the periphery of the SFO, in both the dorsal and ventral MnPO, and in the dorsal cap of the OVLT. Fos-positive neurons were sparse in euhydrated rats but were numerous in the SFO, MnPO, and the dorsal cap of the OVLT after 48-h water deprivation. Most ER-α-ir neurons in these areas were positive for Fos, indicating a significant degree of colocalization. To examine the effect of dehydration on ER-α expression, animals with and without lesions surrounding the anterior and ventral portion of the 3rd ventricle (AV3V) were water deprived for 48 h. Water deprivation resulted in a moderate increase in ER-α-ir in the SFO of sham-lesioned rats ( P = 0.03) and a dramatic elevation in AV3V-lesioned animals ( P < 0.05). This was probably induced by the significant increase in plasma osmolality in both dehydrated groups ( P < 0.001) rather than a decrease in blood volume, because hematocrit was significantly increased only in the dehydrated sham-lesioned animals. Thus these studies implicate the osmosensitive regions of the lamina terminalis as possible targets for sex steroid effects on body fluid homeostasis.

Alterations in the central vasopressin and oxytocin axis after lesion of a brain osmotic sensory region

The anteroventral region of the third ventricle (AV3V) is critical in mediating osmotic sensitivity. AV3V lesions increase plasma osmolality and block osmotic-induced vasopressin (VP) and oxytocin (OT) secretion. The aim was to evaluate the effects of AV3V lesions on neurosecretion under control/water replete conditions and after 48 h dehydration. The focus was on central peptidergic changes with measurement of OT and VP content in the hypothalamic paraventricular (PVN) and supraoptic (OT) regions and the posterior pituitary. AV3V-lesioned rats exhibited an elevated plasma osmolality and higher OT content in SON and PVN. There was an increase in VP content in PVN, but no change in SON. As predicted, the plasma peptide response to dehydration was absent in lesioned animals. However, dehydration produced depletion in posterior pituitary VP in lesioned animals with no change in OT. No changes in nuclear VP and OT levels were seen after dehydration. These results demonstrate that AV3V lesions alter the VP and OT neurosecretory system, seen as a blockade of osmotic-induced release and an increase in basal nuclear peptide content. The data indicate that interruption of the osmotic sensory system affects the central neurosecretory axis, resulting in a backup in content and likely changes in synthesis and processing.

Pursuit of roles for metabotropic glutamate receptors in the anteroventral third ventricular region in regulating vasopressin secretion and cardiovascular function in conscious rats

This study aimed to evaluate the roles of metabotropic glutamate receptors (mGluRs) in the anteroventral third ventricular region (AV3V; a pivotal area for osmotic responses and PGE2 actions) in regulating AVP secretion and cardiovascular function. In conscious and unrestrained rats, we examined the effects of AV3V infusion of t-ACPD (an agonist for mGluRs) and 8-bromo (Br)-cAMP (an agonist for cAMP associated with mGluR action) on plasma and cardiovascular variables, and the effects of MCPG (an antagonist for mGluRs) on the responses to t-ACPD, PGE2, and hyperosmolality. AV3V infusion of t-ACPD or 8-Br-cAMP produced dose-dependent rises in plasma AVP, arterial pressure and heart rate after 5 or 15 min, without altering plasma osmolality, sodium, potassium or chloride. t-ACPD administration into the cerebral ventricle had no effects on the variables. The plasma AVP and arterial pressure responses to AV3V t-ACPD infusion were blocked by preadministration of MCPG 15 min before the infusion. MCPG treatment was also potent at inhibiting the augmentation of plasma AVP elicited by AV3V infusion of PGE2, although its pressor and tachycardiac actions were not influenced. MCPG application, however, had no effect on either the increases in plasma AVP or arterial pressure in response to the enhanced plasma osmolality induced by i.v. infusion of hypertonic saline or their stable levels during isotonic saline infusion. Histological analysis showed that the AV3V drug infusion sites were located in structures such as the median or medial preoptic nucleus and periventricular nucleus. These results suggest that AV3V mGluRs may act to potentiate AVP release and cardiovascular function when stimulated in the basal state, and may participate in the hormone secretion prompted by AV3V PGE2, despite probable negligible contributions to the mechanisms responsible for the PGE2 cardiovascular effects or the phenomenon provoked by osmotic load.

Cellular mechanisms involved in the stenosis and obliteration of the cerebral aqueduct of hyh mutant mice developing congenital hydrocephalus

Two phases may be recognized in the development of congenital hydrocephalus in the hyh mutant mouse. During embryonic life the detachment of the ventral ependyma is followed by a moderate hydrocephalus. During the first postnatal week the cerebral aqueduct becomes obliterated and a severe hydrocephalus develops. The aim of the present investigation was to elucidate the cellular phenomena occurring at the site of aqueduct obliteration and the probable participation of the subcommissural organ in this process. Electron microscopy, immunocytochemistry, and lectin histochemistry were used to investigate the aqueduct of normal and hydrocephalic hyh mice from embryonic day 14 (E-14) to postnatal day 7 (PN-7). In the normal hyh mouse, the aqueduct is an irregularly shaped cavity with 3 distinct regions (rostral, middle, and caudal) lined by various types of ependyma. In the hydrocephalic mouse, these 3 regions behave differently; the rostral end becomes stenosed, the middle third dilates, and the caudal end obliterates. The findings indicate that the following sequence of events lead to hydrocephalus: 1) denudation of the ventral ependyma (embryonic life); 2) denudation of dorsal ependyma and failure of the subcommissural organ to form Reissner fiber (first postnatal week); 3) obliteration of distal end of aqueduct; and 4) severe hydrocephalus. No evidence was obtained that NCAM is involved in the detachment of ependymal cells. The process of ependymal denudation would involve alterations of the surface sialoglycoproteins of the ependymal cells and the interaction of the latter with macrophages.

Drinking behavior elicited by central injection of angiotensin II: roles for protein kinase C and Ca2+/calmodulin-dependent protein kinase II

Prior studies utilizing neurons cultured from the hypothalamus and brain stem of newborn rats have demonstrated that ANG II-induced modulation of neuronal firing involves activation of both protein kinase C (PKC) and Ca2+/calmodulin-dependent protein kinase II (CaMKII). The present studies were performed to determine whether these signaling molecules are also involved in physiological responses elicited by ANG II in the brain in vivo. Central injection of ANG II (10 ng/2 microl) into the lateral cerebroventricle (icv) of Sprague-Dawley rats increased water intake in a time-dependent manner. This ANG II-mediated dipsogenic response was attenuated by central injection of the PKC inhibitors chelerythrine chloride (0.5-50 microM, 2 microl) and Go-6976 (2.3 nM, 2 microl) and by the CaMKII inhibitor KN-93 (10 microM, 2 microl). Conversely, icv injection of chelerythrine chloride (50 microM, 2 microl) and KN-93 (10 microM, 2 microl) had no effect on the dipsogenic response elicited by central injection of carbachol (200 ng/2 microl). Furthermore, injection of ANG II (10 ng/2 microl) icv increases the activity of both PKC-alpha and CaMKII in rat septum and hypothalamus. These data suggest that signaling molecules involved in ANG II-induced responses in vitro are also relevant in physiological responses elicited by ANG II in the whole animal model.

Immunocytochemical evidence for growth hormone-releasing hormone in the tanycytes of the median eminence of the rat

The current study was performed to analyse the potential existence and structure of a GHRH-transporting tuberoinfundibular system in the rat median eminence. The immunocytochemical analysis using anti-GHRH revealed an intense immunoreaction in the ependimary cells, tanycytes, at the level of the floor of the infundibular recess forming part of the median eminence. The basal processes of these cells course towards the external layer of the median eminence and reach the growth hormone-releasing hormone (GHRH) fibres of the tuberoinfundibular tract and this reaction was increased after intraventricular treatment with colchicine. Thus, these observations suggest the existence of a second or alternative cerebrospinal fluid-mediated route of GHRH transport to the median eminence and implicate the involvement of tanycytes in the regulation of this novel transport system.

A study on the mechanism by which sodium nitroprusside, a nitric oxide donor, applied to the anteroventral third ventricular region provokes facilitation of vasopressin secretion in conscious rats

We reported previously that sodium nitroprusside (SNP) applied to the anteroventral third ventricular region (AV3V), a pivotal area for autonomic functions, facilitates vasopressin (AVP) secretion in conscious rats. The aim of this study was to pursue the problems of whether nitric oxide (NO) generated from the agent may be responsible for the phenomenon, and whether it may be mediated by cyclic guanosine monophosphate (cGMP), the biosynthesis of which could reportedly be activated by NO. The infusion of SNP into the AV3V of conscious rats produced dose-related increases in plasma AVP, the maximal responses of which appeared at 5 min. Blood pressure and heart rate tended to rise at 15 min. The plasma osmolality, sodium, potassium or chloride did not show marked alteration following the SNP administration. Although the SNP solution was hypertonic and hypernatremic, AV3V application of hypertonic saline with a relatively higher osmolality and an equal sodium level was significantly less effective in augmenting plasma AVP. When injected into the lateral ventricle, SNP did not change plasma AVP and reduced arterial pressure, different from the results provoked by the AV3V application. The rise in plasma AVP in response to the AV3V application of SNP was diminished by preadministration of hemoglobin, a scavenger of NO, that did not affect the responses of the other variables. In contrast, pretreatment with methylene blue, an agent capable of antagonizing the potency of NO to activate guanylate cyclase, did not attenuate but potentiated the responses of both plasma AVP and arterial pressure to the AV3V infusion of SNP. Hemoglobin or methylene blue given alone into the AV3V did not affect any of the variables monitored. On the other hand, the AV3V injection of 8-bromo cGMP, a stable analogue of cGMP, was not potent for causing a significant rise in plasma AVP, in contrast to the notable AVP-enhancing effect of 8-bromo cAMP. Arterial pressure and heart rate were elevated by both of these agents, whereas the remaining variables were not altered. Histological inspection indicated that the infusion sites of the drugs in the AV3V had included areas such as the organum vasculosum of the lamina terminalis, median preoptic nucleus, medial preoptic nucleus and periventricular nucleus. On the basis of these results, we concluded that the AVP secretion prompted by the AV3V application of SNP may be attributable to NO, whereas its well-known ability to stimulate guanylate cyclase activity may hardly contribute to this phenomenon.

Neurons of the superior nucleus of the medial habenula and ependymal cells express IL-18 in rat CNS

The habenular-interpeduncular pathway is involved in the modulation of several functions including neuroendocrine and stress responses. Interleukin-18 (IL-18) is a pro-inflammatory cytokine predominantly studied as a modulator of immune functions and also produced in the adrenal cortex following activation of the hypothalamic-pituitary-adrenal axis. In the central nervous system, IL-18 was demonstrated to induce sleep and to influence long-term potentiation and was proposed to mediate local inflammatory reactions. The present study investigated the localization of IL-18 and its expression following either acute or chronic restraint stress in the brain of adult male Wistar rats. Using immunocytochemistry and in situ hybridization we report the unprecedented localization of IL-18 in the neurons of the superior part of the medial habenula (MHbS), their projections to the interpenducular nucleus and its expression in the ependymal cells surrounding the third and the lateral ventricles. In addition, acute (2 h) or chronic (6 h/day for 3 weeks) restraint stress induced a strong elevation of IL-18 immunostaining in the MHbS but not in ependymal cells. The present data suggest that IL-18 may participate in the modulation of stress responses in the MHbS. They also suggest that ependymal cells may be the source of IL-18 previously reported in the cerebrospinal fluid (CSF). The role of IL-18 in the ependyma and the CSF remains to be elucidated.

Contribution of N-methyl-d-aspartate receptors in the anteroventral third ventricular region to vasopressin secretion, but not to cardiovascular responses provoked by hyperosmolality and prostaglandin E2 in conscious rats

The aim of this study is to pursue roles of N-methyl-d-aspartate (NMDA) receptors in the anteroventral third ventricular region (AV3V; a pivotal area for autonomic functions) in controlling vasopressin (AVP) release and cardiovascular system. In conscious rats, we examined effects of AV3V infusion of MK-801 (a selective antagonist for NMDA receptor) on plasma AVP, osmolality, electrolytes, arterial pressure and heart rate, in the absence or presence of NMDA, hyperosmotic or prostaglandin (PG) E2 stimulus. The AV3V infusion of NMDA caused significant increases in plasma AVP, osmolality and sodium, hematocrit, arterial pressure and heart rate after 5 or 15min. When NMDA was administered into the cerebral ventricle, relatively smaller elevations were observed only in plasma AVP and arterial pressure. The effects of AV3V infusion of NMDA were nearly completely prevented by MK-801 applied to the same region before 15min. The application of MK-801 was also potent to block rises of plasma AVP elicited by AV3V injection of PGE2 or i.v. infusion of hypertonic saline. However, it inhibited neither increases of arterial pressure and heart rate due to the PGE2 treatment nor those of arterial pressure, plasma osmolality and sodium in response to the osmotic load. Histological analysis on the AV3V infusion sites of NMDA, MK-801 and PGE2 indicated that they had been located in the structures such as the median and medial preoptic nuclei, periventricular nucleus and medial preoptic area. These results suggest that stimulation of AV3V NMDA receptors in the basal state may facilitate AVP secretion and cause pressor and tachycardiac actions, and that these receptors may be involved in both the hyperosmolality- and PGE2-induced hormone release, but not in the cardiovascular responses to these stimuli.

Bcl-2 expression in thalamus, brainstem, cerebellum and visual cortex of adult primate

Due to the functional importance of Bcl-2, which acts as an anti-apoptotic protein that also affects neural differentiation and adult neurogenesis, we undertook a detailed immunohistochemical study of the distribution of this protein in the brain of squirrel monkeys. The present study describes findings obtained at thalamic, brainstem, cerebellum and visual cortex levels, and the data are compared with our previous results gathered in the same species. At thalamic level, Bcl-2-positive neurons occur in anterior, rostral intralaminar, midline and lateral habenular nuclei. The protein is also expressed in several structures associated with the ventricular system, including the subventricular zone (SVZ), the subcommissural organ, and the periventricular grey at rostral and caudal tips of the fourth ventricle. At brainstem and cerebellar levels, Bcl-2-positive neurons occur in the dorsal raphe nucleus, inferior olivary complex, and in molecular and granular layers of the cerebellum. Finally, neurons of layer IV of the striate cortex display a very strong Bcl-2 immunoreactivity that contrasts with the poor labeling of neurons in adjacent parastriate and peristriate cortices. These finding suggests that Bcl-2 plays a role in the plasticity and structural maintenance of various structures in the primate brain and indicate that the mitotically active SVZ might be more extended along the rostrocaudal axis in primates than in rodents.