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.

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.

Functional interleukin-6 receptor-α is located in tanycytes at the base of the third ventricle

Interleukin (IL)-6^- /^- mice develop mature onset obesity, whereas i.c.v. injection of IL-6 decreases obesity in rodents. Moreover, levels of IL-6 in cerebrospinal fluid (CSF) were reported to be inversely correlated with obesity in humans. Tanycytes lining the base of the third ventricle (3V) in the hypothalamus have recently been reported to be of importance for metabolism. In the present study, we investigated whether tanycytes could respond to IL-6 in the CSF. With immunohistochemistry using a well characterised antibody directed against the ligand binding receptor for IL-6, IL-6 receptor α (IL-6Rα), it was found that tanycytes, identified by the two markers, vimentin and dopamine- and cAMP-regulated phosphoprotein of 32 kDa, contained IL-6Rα. There were fewer IL-6Rα on another type of ventricle-lining cells, ependymal cells, as identified by the marker glucose transporter-1. To demonstrate that the immunoreactive IL-6Rα were responsive to IL-6, we injected IL-6 i.c.v. This treatment increased immunoreactive phosphorylated signal transducer and activator of transcription-3 (pSTAT3) in tanycytes after 5 minutes and in cells in the medial part of the arcuate nucleus after 5 and 15 minutes. Intracerebroventricular injection of leptin exerted similar effects. As expected, i.p. injection of leptin also induced pSTAT3 staining in the hypothalamus, whereas i.p. IL-6 injection had little effect on this parameter. Intracerebroventricular or i.p. injection of vehicle only had no effect on pSTAT3-immunoreactivity. In summary, there are functional IL-6Rα on tanycytes at the bottom of the 3V, in agreement with the possibility that ventricular administration of IL-6 decreases obesity in mice via an effect on this cell type.

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).

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.

Melatonin controls photoperiodic changes in tanycyte vimentin and neural cell adhesion molecule expression in the Djungarian hamster (Phodopus sungorus)

The Djungarian hamster displays photoperiodic variations in gonadal size synchronized to the seasons by the nightly secretion of the pineal hormone melatonin. In short photoperiod (SP), the gonads regress in size, and circulating sex steroids levels decline. Thus, the brain is subject to seasonal variations of both melatonin and sex steroids. Tanycytes are specialized glial cells located in the ependymal lining of the third ventricle. They send processes either to the meninges or to blood vessels of the medio-basal hypothalamus. Furthermore, they are known to locally modulate GnRH release in the median eminence and to display seasonal structural changes. Seasonal changes in tanycyte morphology might be mediated either through melatonin or sex steroids. Therefore, we analyzed the effects of photoperiod, melatonin, and sex steroids 1) on tanycyte vimentin expression by immunohistochemistry and 2) on the expression of the neural cell adhesion molecule (NCAM) and polysialic acid as markers of brain plasticity. Vimentin immunostaining was reduced in tanycyte cell bodies and processes in SP. Similarly, tanycytes and their processes contained lower amounts of NCAM in SP. These changes induced by SP exposure could not be restored to long photoperiod (LP) levels by testosterone supplementation. Likewise, castration in LP did not affect tanycyte vimentin or NCAM expression. By contrast, late afternoon melatonin injections mimicking a SP-like melatonin peak in LP hamsters reduced vimentin and NCAM expression. Thus, the seasonal changes in vimentin and NCAM expression in tanycytes are regulated by melatonin independently of seasonal sex steroid changes.

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.

New ependymal cells are born postnatally in two discrete regions of the mouse brain and support ventricular enlargement in hydrocephalus

A heterogeneous population of ependymal cells lines the brain ventricles. The evidence about the origin and birth dates of these cell populations is scarce. Furthermore, the possibility that mature ependymal cells are born (ependymogenesis) or self-renewed (ependymal proliferation) postnatally is controversial. The present study was designed to investigate both phenomena in wild-type (wt) and hydrocephalic α-SNAP mutant (hyh) mice at different postnatal stages. In wt mice, proliferating cells in the ventricular zone (VZ) were only found in two distinct regions: the dorsal walls of the third ventricle and Sylvian aqueduct (SA). Most proliferating cells were monociliated and nestin+, likely corresponding to radial glial cells. Postnatal cumulative BrdU-labeling showed that most daughter cells remained in the VZ of both regions and they lost nestin-immunoreactivity. Furthermore, some labeled cells became multiciliated and GLUT-1+, indicating they were ependymal cells born postnatally. Postnatal pulse BrdU-labeling and Ki-67 immunostaining further demonstrated the presence of cycling multiciliated ependymal cells. In hydrocephalic mutants, the dorsal walls of the third ventricle and SA expanded enormously and showed neither ependymal disruption nor ventriculostomies. This phenomenon was sustained by an increased ependymogenesis. Consequently, in addition to the physical and geometrical mechanisms traditionally explaining ventricular enlargement in fetal-onset hydrocephalus, we propose that postnatal ependymogenesis could also play a role. Furthermore, as generation of new ependymal cells during postnatal stages was observed in distinct regions of the ventricular walls, such as the roof of the third ventricle, it may be a key mechanism involved in the development of human type 1 interhemispheric cysts.

Dual phenotype kisspeptin-dopamine neurones of the rostral periventricular area of the third ventricle project to gonadotrophin-releasing hormone neurones

The neuropeptide kisspeptin and its G-protein-coupled receptor, Gpr54, are critical regulators of fertility. Two major populations of kisspeptin neurones exist in the rodent: one in the rostral periventricular area of the third ventricle (RP3V) and another in the arcuate nucleus. The RP3V population of kisspeptin neurones is crucial for the generation of the luteinising hormone surge that drives ovulation in females. The RP3V kisspeptin neurones are sexually dimorphic, with many more neurones in females than males, and they project to gonadotrophin-releasing hormone (GnRH) neurones. Tyrosine hydroxylase (TH) expressing neurones in the RP3V are also sexually dimorphic and are assumed to project to GnRH neurones. In the present study, we examined the coexpression of kisspeptin and TH peptides in the RP3V of dioestrous and pro-oestrous female mice. We also investigated whether kisspeptin and TH peptides colocalised in terminal appositions with GnRH neurones in the rostral preoptic area (rPOA). Approximately half of the kisspeptin neurones in the RP3V were found to also express TH and vice versa, although there was no difference between mice in dioestrus or pro-oestrus. The majority (95%) of GnRH neurones in the rPOA exhibited a close apposition from a kisspeptin fibre, whereas only one quarter exhibited a close apposition from a TH fibre. Many of the TH close appositions with GnRH neurones coexpressed kisspeptin (62-86%), although these dual-labelled appositions comprised <20% of all kisspeptin appositions on GnRH neurones. The percentage of GnRH neurones with kisspeptin, TH and double-labelled appositions did not differ between dioestrous and pro-oestrous mice. These findings indicate that a subpopulation of kisspeptin neurones expressing dopamine innervate GnRH neurones in the rPOA.

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.

Rhythmic expression of clock genes in the ependymal cell layer of the third ventricle of rodents is independent of melatonin signaling

Reproductive physiology is regulated by the photoperiod in many mammals. Decoding of the photoperiod involves circadian clock mechanisms, although the molecular basis remains unclear. Recent studies have shown that the ependymal cell layer lining the infundibular recess of the third ventricle (EC) is a key structure for the photoperiodic gonadal response. The EC exhibits daylength-dependent changes in the expression of photoperiodic output genes, including the type 2 deiodinase gene (Dio2 ). Here we investigated whether clock genes (Per1 and Bmal1) and the albumin D-binding protein gene (Dbp) are expressed in the EC of Syrian hamsters, and whether their expression differs under long-day and short-day conditions. Expression of all three genes followed a diurnal rhythm; expression of Per1 and Dbp in the EC peaked around lights-off, and expression of Bmal1 peaked in the early light phase. The amplitude of Per1 and Dbp expression was higher in hamsters kept under long-day conditions than in those kept under short-day conditions. Notably, the expression of these genes was not modified by exogenous melatonin within 25 h after injection, whereas Dio2 expression was inhibited 19 h after injection. Targeted melatonin receptor (MT1, MT2, and both MT1 and MT2) disruption in melatonin-proficient C3H mice did not affect the rhythmic expression of Per1 in the EC. These data show the existence of a molecular clock in the rodent EC. In the hamster, this clock responds to long-term changes in the photoperiod, but is independent of acute melatonin signals. In mice, the EC clock is not affected by deletion of melatonin receptors.

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.

Mu opioid receptors are expressed on radial glia but not migrating neuroblasts in the late embryonic mouse brain

Mu opioid receptor ligands such as morphine and met-enkephalin are known to modulate normal brain development by perturbing gliogenesis and inhibiting neuronal proliferation. Surprisingly, the distribution of the mu opioid receptor (MOR) in the embryonic brain, especially in proliferative regions, is poorly defined and subject to conflicting reports. Using an immunohistochemical approach, we found that MOR protein was expressed in the neuroepithelia of the lateral ventricles, third ventricle, and aqueduct within the late embryonic (E15.5 and E18.5) mouse brain. In contrast to the ventricular neuroepithelia, the proliferative external granule layer of the embryonic cerebellum did not express MOR protein, although the Purkinje cell layer did. Within the ventricular neuroepithelium, GLAST-positive radial glia that incorporate BrdU expressed MOR, while migrating neuroblasts (doublecortin-positive) do not. BrdU labeling of proliferating cells showed an anterior to posterior gradient of proliferation (P<0.05), while an opposing posterior to anterior gradient of MOR expression (P<0.05) was found. The localization of MOR immunoreactivity within the embryonic ventricular neuroepithelia is consistent with a role for opioids in modulating neurogenesis.

Infundibular tanycytes as modulators of neuroendocrine function: hypothetical role in the regulation of the thyroid and gonadal axis

Tanycytes comprise a heterogeneous population of specialized cells of glial origin that line the floor and ventrolateral walls of the third ventricle between the rostral and caudal limits of the hypothalamic median eminence. While morphologic and ultrastructural features suggest a role as barrier cells, creating separate compartments between the cerebrospinal fluid, median eminence and hypothalamus, tanycytes likely have multiple other important functions that have yet to be fully elucidated. Possibilities to consider are a role in neuroendocrine regulation including modulation of the hypothalamic-pituitary-thyroid axis during fasting and infection, regulation of reproductive function, particularly in seasonal breeders, and in feeding.

Specification of optic nerve oligodendrocyte precursors by retinal ganglion cell axons

Cell fate commitment in the developing CNS frequently depends on localized cell-cell interactions. In the avian visual system the optic nerve oligodendrocytes are derived from founder cells located at the floor of the third ventricle. Here we show that the induction of these founder cells is directly dependent on signaling from the retinal ganglion cell (RGC) axons. The appearance of oligodendrocyte precursor cells (OPCs) correlates with the projection of RGC axons, and early eye removal dramatically reduces the number of OPCs. In vitro signaling from retinal neurites induces OPCs in responsive tissue. Retinal axon induction of OPCs is dependent on sonic hedgehog (Shh) and neuregulin signaling, and the inhibition of either signal reduces OPC induction in vivo and in vitro. The dependence of OPCs on retinal axonal cues appears to be a common phenomenon, because ocular retardation (or(J)) mice lacking optic nerve have dramatically reduced OPCs in the midline of the third ventricle.

Neurogenesis in the ependymal layer of the adult rat 3rd ventricle

Neurogenesis has been described in limited regions of the adult mammalian brain. In this study, we showed that the ependymal layer of the 3rd ventricle is a neurogenic region in the adult rat brain. DiI labeling of the 3rd ventricle revealed that neural progenitor cells were derived from cells at the ependymal layer of the adult 3rd ventricle. The mitosis of these progenitor cells at the ependymal layer was promoted by bFGF administration. Combination of BrdU administration, nestin/GFAP immunohistochemistry, and labeling by GFP-recombinant adenoviral infection (vGFP) indicated that at least some tanycytes might be neural progenitor cells in the ependymal layer of the 3rd ventricle. Tracing by vGFP indicated that neural progenitor cells may have migrated from the 3rd ventricle to the hypothalamic parenchyma, where they were integrated into neural networks by forming synapses. In addition, some BrdU(+) neurons had immunoreactivity for orexin A in the hypothalamus. These results indicate that neural progenitor cells exist in the ependymal layer of the adult rat 3rd ventricle and that they may differentiate into neurons functioning in the hypothalamus.

The distribution of neural nitric oxide synthase-positive cerebrospinal fluid-contacting neurons in the third ventricular wall of male rats and coexistence with vasopressin or oxytocin

The detailed distribution of neural nitric oxide synthase (nNOS)-positive cerebrospinal fluid-contacting neurons (CSF-CN) was studied in the wall of the third ventricle of rats by anti-nNOS immunohistochemistry. The coexistence of nNOS and 8-arginine vasopressin (AVP) or oxytocin (OT) was also investigated in the CSF-CN using double labeling immunohistochemistry. The results demonstrated a widespread occurrence of nNOS-CSF-CN throughout the wall of the hypothalamic third ventricle. The vast majority of nNOS-CSF-CN cell bodies were of magnocellular type, commonly classified as oval, fusiform, multipolar, and inverted pear shape. These cell bodies were located in the ependyma, the subependyma, or the parenchyma, and their processes inserted in the ependymal layer or directly contacted with the CSF space. Electron microscopy demonstrated many nNOS-immunoreactive somas, dendrites, and/or axons that were situated at the subependyma, the ependyma, or the supraependyma. Generally, the distribution of OT-CSF-CN in the third ventricular wall was similar to the nNOS-CSF-CN and the ratio of NOS/OT co-expression was approximately 88%. In comparison, the distribution of AVP-CSF-CN was mainly restricted to the rostral part of the third ventricle and the ratio of nNOS/AVP co-expression was only about 6%. The widespread presence of nNOS-CSF-CN-expressing OT in the third ventricular region suggests that NO is an important messenger in the CSF-hypothalamo-hypophyseal neuroendocrine regulation that may in part act in concert with OT.

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.

Reactive gliosis in areas around third ventricle in association with epileptogenesis in amygdaloid-kindled rat

Repeated focal electrical stimulation of the brain is known to produce epileptogenesis, and this phenomenon is recognized as kindling. It is also considered to be a model of temporal lobe epilepsy. In the present study, morphological changes in areas around third ventricle in rat brain were examined according to the progression of kindling stage. Very few Glial Fibrillary Acidic Protein (GFAP)-positive astrocytes were present in ependymal cell layer at C0 stage. However, there was a specific increase in GFAP-positive cells in ependymal cell layer at stage C3 as compared to stage C0. Furthermore, GFAP-positive cells showed migration to subependymal zone (SEZ). By stage C5, almost all GFAP-positive cells had migrated to SEZ. While the precise mechanism of this cell migration is not clear, the results suggest a relationship between progression of kindling stage and astrogliosis.

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.

Photoperiodic regulation of type 2 deiodinase gene in Djungarian hamster: possible homologies between avian and mammalian photoperiodic regulation of reproduction

The molecular mechanisms responsible for seasonal time measurement have yet to be fully described. Recently, we used differential analysis to identify that the type 2 iodothyronine deiodinase (Dio2) gene is responsible for the photoperiodic response of gonads in Japanese quail. It was found that expression of Dio2 in the mediobasal hypothalamus is induced by light and that T(3) content in the mediobasal hypothalamus increased under long day conditions. In addition, we showed that intracerebroventricular infusion of T(3) mimics photoperiodically induced testicular growth. Because it is well known that thyroid hormone is also essential for the maintenance of the seasonal reproductive changes in a number of mammals, we examined expression of Dio2 in Djungarian hamsters and found expression in the ependymal cell layer lining the infralateral walls of the third ventricle and the cell-clear zone overlying the tuberoinfundibular sulcus. Signal intensity was high under long days and weak under short days. Although light pulse did not affect Dio2 expression, melatonin injections decreased Dio2 expression under long days. These results indicate that Dio2 may be involved in the regulation of seasonal reproduction in mammals in the same way as observed in birds.

Directional cues for arcuate NPY projections are present in the adult brain

Arcuate nucleus neuropeptide Y (NPY) neurons project within the hypothalamus and to several extrahypothalamic brain areas. Plasticity in the formation of arcuate NPY projections established postnatally may underlie the phenotypic characteristics of food intake and body weight. In this work we determined if directional cues for axonal outgrowth of NPY arcuate neurons exist in the adult brain. For this purpose, an embryonic (E15) arcuate nucleus of WT mice was grafted into the third ventricle of 2-week- and 2-month-old NPY knockout (KO) mice. One month after the transplantation, the distribution of NPY-positive terminals in the brains of NPY-KO mice was studied using immunohistochemistry. NPY-positive terminals were found inside of the grafted tissue as well as in the host hypothalamus, including the arcuate nucleus, the paraventricular and periventricular nuclei, the lateral hypothalamic and preoptic areas, and in extrahypothalamic areas such as the amygdala and the thalamic paraventricular nucleus. This pattern of distribution of NPY fibers was found in both groups of grafted mice. The brain areas reinnervated by NPY-positive terminals in the NPY-KO mice closely corresponded to the normal targets for the arcuate NPY neurons as revealed by the distribution of agouti gene-related protein immunoreactivity. Our data show that directional cues for NPY arcuate nucleus projections are present in the adult brain, suggesting their involvement in the formation of normal arcuate NPY connections and a possibility for their functional reconstruction.

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.

Structural characterization of a hypothalamic visceromotor pattern generator network

A high resolution PHAL analysis of axonal connections suggests the existence of a visceromotor pattern generator network in the periventricular region of the rat hypothalamus (HVPG), and a preliminary account of its structure is provided here. Six nodes identified thus far include the dorsomedial nucleus and five small nuclei in the preoptic region (anteroventral and anterodorsal preoptic, parastrial, median preoptic, and anteroventral periventricular). Aside from its location between the neuroendocrine motor zone and the medial hypothalamic nuclei (behavior control column), three other primary features characterize the HVPG network. First, each HVPG nucleus generates a pattern of terminal fields that differentially targets a unique set of hypothalamic neuroendocrine motoneuron pools, and of preautonomic parts of the paraventricular nucleus. Second, the six HVPG nuclei are massively interconnected themselves. And third, the majority of projections from the HVPG nuclei remain within the medial half of the hypothalamus; additional outputs reach the septum, other parts of the diencephalon, and the brainstem central gray. Possible control of activity in the HVPG by neural inputs from the cerebral hemispheres, sensory systems, behavioral state-related cell groups, and the hypothalamic behavior or motivation control column is discussed, along with certain key functional data related to HVPG nuclei. Finally, the HVPG is incorporated into a working model of hypothalamic organization.

Fractones and other basal laminae in the hypothalamus

The physiological role of basal laminae (BL) and connective tissue (meninges and their projections) in the adult brain is unknown. We recently described novel forms of BL, termed fractones, in the most neurogenic zone of the adult brain, the subependymal layer (SEL) of the lateral ventricle. Here, we investigated the organization of BL throughout the hypothalamus, using confocal and electron microscopy. New types of BL were identified. First, fractones, similar to those found in the lateral ventricle wall, were regularly arranged along the walls of the third ventricle. Fractones consisted of labyrinthine BL projecting from SEL blood vessels to terminate immediately beneath the ependyma. Numerous processes of astrocytes and of microglial cells directly contacted fractones. Second, another form of BL projection, termed anastomotic BL, was found between capillaries in dense capillary beds. The anastomotic BL enclosed extraparenchymal cells that networked with the perivascular cells coursing in the sheaths of adjacent blood vessels. Vimentin immunoreactivity was often detected in the anastomotic BL. In addition, the anastomotic BL overlying macrophages contained numerous fibrils of collagen. We also found that the BL located at the pial surface formed labyrinthine tube-like structures enclosing numerous fibroblast and astrocyte endfeet, with pouches of collagen fibrils at the interface between the two cell types. We suggest that cytokines and growth factors produced by connective tissue cells might concentrate in BL, where their interactions with extracellular matrix proteins might contribute to their effects on the overlying neural tissue, promoting cytogenesis and morphological changes and participating in neuroendocrine regulation.

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.

Functional relationship between subfornical organ cholinergic stimulation and cellular activation in the hypothalamus and AV3V region

The subfornical organ (SFO) has been suggested to be important for water intake and secretion of vasopressin (AVP). However, the role of the SFO cholinergic mechanism in the control of body fluid regulation is not clear. This study determined the effects of local cholinergic stimulation in the SFO produced by administration of physostigmine on drinking and cellular excitation in the anterior third ventricle (AV3V) region and in the supraoptic and paraventricular nuclei (SON and PVN). The results showed that injection of physostigmine into the SFO induced water intake and c-fos expression in the AV3V area as well as in the AVP containing neurons in the hypothalamus. Pretreatment of the SFO with mecamylamine, a nicotinic receptor antagonist, had no effect on physostigmine induced behavioral and c-fos responses. The muscarinic receptor blocker atropine, however, abolished both drinking and cellular activation after injection of physostigmine into the SFO. Immunostaining experiments demonstrated positive acetyltransferase (ChAT) in the SFO. Intensive ChAT immunoreactivity was located in the cholinergic fibers in the SFO. Together, the results indicate that SFO cholinergic mechanisms are important in co-operation with the AV3V and hypothalamic neurons in the control of thirst and AVP-mediated body fluid homeostasis.

Orexin (hypocretin) gene expression in rat ependymal cells

The expression of prepro-orexin (PPO) mRNA in the rat brain was investigated by in situ hybridization histochemistry. In the lateral and posterior hypothalamic areas, which are considered to produce exclusively PPO mRNA, we found high levels of PPO mRNA expressions. We also localized PPO mRNA hybridization signals at lower levels around the lateral ventricles, the third and fourth ventricle. Cellular analysis by emulsion autoradiography revealed the expression of PPO mRNA in the ependymal cell layer. Our results demonstrate that beside the lateral and posterior hypothalamus PPO mRNA is expressed in ependymal cells.

Presence of sst2(a) receptor immunoreactivity in rat ependyma and tanycytes

Somatostatin sst2(a) receptor was observed, by immunofluorescence, in ependymal cells and in tanycytes of the wall of the ventricle and the hypothalamic recess of the male rat median eminence. Strong immunoreactivity for the receptor protein was observed in lateral tanycytes (alpha-type) while a moderate signal was seen in medial tanycytes (beta-type). In high magnification the immunoreactive material, of moderate intensity, had a coarse granular appearance. Only few of the alpha-tanycytes also displayed immunoreactive GFAP. The apical portion of the ependymal cells as well as of tanycytes contained immunoreactive S-100 (alphabeta). Since rather high levels of somatostatin are demonstrated to occur in the cerebrospinal fluid of the third ventricle, it is suggested that somatostatin via the sst2(a) receptor may regulate the physiology of tanycytes.

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

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

Fos immunoreactivity in the lamina terminalis of adrenalectomized rats and effects of angiotension II type 1 receptor blockade or deoxycorticosterone

Neural activity, as measured immunohistochemically by the presence of Fos protein, was determined in the lamina terminalis, a thin strip of tissue forming the anterior wall of the third brain ventricle, after adrenalectomy. Several weeks after surgery, the adrenalectomized rats were maintained with access to water and a low sodium diet for five days. In addition, hypertonic (0.5M) NaCl solution was available for the entire five-day period (sodium available) or only during the first four days (sodium unavailable). The number of neurons expressing Fos, determined at the end of the fifth day, was increased in the adrenalectomized rats with or without NaCl solution to drink. Fos activity in the median preoptic nucleus was increased only in adrenalectomized rats without access to NaCl solution. Treatment of adrenalectomized rats with the sodium-retaining mineralocorticoid hormone, deoxycorticosterone, at the end of the fourth day, decreased Fos expression in the subfornical organ and the organum vasculosum of the lamina terminalis when NaCl solution was available but not when the NaCl solution was unavailable. In the adrenalectomized rats with NaCl solution available, mineralocorticoid treatment decreased both urinary sodium excretion and daily sodium intake. Brain nuclei in the lamina terminalis also became activated in intact rats made sodium deplete by treatment with the diuretic, furosemide. Relative to sodium-deplete intact rats, however, sodium-deplete adrenalectomized rats had a greater number of neurons expressing Fos in the organum vasculosum. Treatment of sodium-deplete rats, adrenalectomized or intact, with the angiotensin II-type 1 receptor antagonist, ZD7155, decreased sodium intake and Fos expression in the subfornical organ but not in the organum vasculosum of the lamina terminalis or median preoptic nucleus. In conclusion, the results demonstrated that activation of the brain nuclei located in the lamina terminalis of adrenalectomized rats was primarily related to sodium deficit and not to the absence of the mineralocorticoid hormones, although the adrenal hormones may have a role in limiting the activation of organum vasculosum of the lamina terminalis during sodium depletion. Furthermore, the results obtained with the administration of the angiotensin receptor antagonist are consistent with the proposal that sodium appetite of the sodium-deplete rat, adrenalectomized or intact, is mediated by circulating angiotensin II acting in the subfornical organ.

Detailed localization of aquaporin-4 messenger RNA in the CNS: preferential expression in periventricular organs

We have performed a detailed in situ hybridization study of the distribution of aquaporin-4 messenger RNA in the CNS. Contrary to expectation, we demonstrate that aquaporin-4 is ubiquitously expressed in the CNS. Strong hybridization labeling was detected in multiple olfactory areas, cortical cells, medial habenular nucleus, bed nucleus of the stria terminalis, tenia tecta, pial surface, pontine nucleus, hippocampal formation and multiple thalamic and hypothalamic areas. A low but significant hybridization signal was found, among others, in the choroid plexus of the lateral ventricles, ependymal cells, dorsal raphe and cerebellum. Overall, a preferential distribution of aquaporin-4 messenger RNA-expressing cells was evident in numerous periventricular organs. From the distribution study, the presence of aquaporin-4 messenger RNA-expressing cells in neuronal layers was evident in neuronal layers including the CA1 -CA3 hippocampal pyramidal cells, granular dentate cells and cortical cells. Further evidence of neuronal expression comes from the semicircular arrangement of aquaporin-4 messenger RNA-expressing cells in the bed nucleus of the stria terminalis and medial habenular nucleus exhibiting Nissl-stained morphological features typical of neurons. Combined glial fibrillary acidic protein immunohistochemistry and aquaporin-4 messenger RNA in situ hybridization demonstrated that aquaporin-4 messenger RNA is expressed by glial fibrillary acidic protein-lacking cells. We conclude that aquaporin-4 messenger RNA is present in a collection of structures typically involved in the regulation of water and sodium intake and that aquaporin-4 water channels could be the osmosensor mechanism responsible for detecting changes in cell volume by these cells.

Comparative analysis of FMRFamide-like immunoreactivity in caiman (Caiman crocodilus) and turtle (Trachemys scripta elegans) brains

The distribution of FMRFamide (FMRFa)-like peptides in caiman (Caiman crocodilus) and turtle (Trachemys scripta elegans) brains was studied by immunohistochemistry. In both species, distinct groups of FMRFa-like immunoreactive (ir) perikarya were present in the medial septal nucleus, accumbens nucleus, nucleus of the diagonal band of Broca, suprachiasmatic area, lateral hypothalamic area, and periventricular hypothalamic nucleus. A few FMRFa-ir neurons in the hypothalamic area were located in the neuroepithelial cell lining of the third ventricle. FMRFa-ir fibers were scattered in all major areas of the brain, from the olfactory bulbs to the rhombencephalon. They formed dense aggregates in the medial septal area, basal telencephalon, median eminence, and infundibulum, and adjacent to the fourth ventricle. The most obvious difference between the FMRFa-ir systems in caimans and turtles concerned the number of nuclei that contained neurons with this immunoreactivity. Eight such clusters were present in the caiman brain, whereas thirteen clusters were found in the turtle brain. The turtle also displayed scattered FMRFa-ir somata in the anterior olfactory nucleus, striatum, lateral septal nucleus, medial and lateral cortex, medial forebrain bundle, lateral preoptic area, and lateral geniculate nucleus. In the caiman brain, a few FMRFa-ir neurons were noted in the ventrolateral area of the pallial commissure and an even smaller number of ir neurons was found dispersed in the optic tracts. Neither formed nuclear aggregates. The results are compared with those described for other vertebrates.

Neuronal progenitor-like cells expressing polysialylated neural cell adhesion molecule are present on the ventricular surface of the adult rat brain and spinal cord

In the adult rodent brain, it is now well established that neurons are continuously generated from proliferating neuronal progenitor cells located in the subventricular zone of the lateral ventricle (SVZ) and the dentate gyrus of the hippocampus. Recently, it has been shown that neurons can also be generated in vitro from various regions of the adult brain and spinal cord ventricular neuroaxis. As the highly polysialylated neural cell adhesion molecule (PSA-NCAM) has been shown to be specifically expressed by neuronal progenitor cells of the SVZ and the hippocampus, the present study was designed to determine whether cells expressing this molecule could be detected in the vicinity of the ventricular system of the adult rat brain and spinal cord. After double or triple immunostaining for different neuronal and glial markers, confocal microscopy was used to examine the surface of the ventricular neuroaxis in either 40- to 50-microm-thick transverse vibratome sections cut through different brain regions, or in 200- to 300-microm-thick tissue slices including the intact surface of the brain ventricles or of the spinal cord central canal. In untreated rats, PSA-NCAM, microtubule associated protein 2 (MAP2) and class III-beta-tubulin were found to be associated with a number of neuron-like cells located on the surface of the third and fourth ventricles and of the spinal cord central canal. The proliferation of the PSA-NCAM-immunoreactive (IR) neuron-like cells detected on the surface of the third and fourth ventricles was not affected by injection of epidermal growth factor (EGF) or basic fibroblast growth factor (bFGF) into these ventricles, but was stimulated by the combined injection of EGF + bFGF. These data indicate that cells exhibiting features of neuronal progenitors are present on the ependymal surface of the adult rat brain and spinal cord ventricular axis.

Post-traumatic migration and emergence of a novel cell line upon the ependymal surface of the third cerebral ventricle in the adult mammalian brain

This investigation describes the migration and emergence of significant numbers of what appear to be neuron-like cells upon the surface of the median eminence of the adult rodent neurohypophyseal system of the endocrine hypothalamus following the trauma of hypophysectomy. These cells appear to migrate through the neuropil of the underlying median eminence and emerge in large numbers upon the surface of the third cerebral ventricle within 7 days following hypophysectomy (axotomy) of supraoptic (SON) and paraventricular neurites (PVN) of the adult neurohypophyseal system. Previous investigations have demonstrated regeneration of the neural stem and neural lobe in a variety of mammalian species (Adams et al., J Comp Neurol, 1969;135:121-144; Beck et al., Neuroendocrinology, 1969;5:161-182; Scott et al., Exp Neurol, 1995;131-1:23-39; Scott and Hansen, Vir Med 1997;124:249-261). It also has been demonstrated that the process of regeneration is invariably accompanied by the up-regulation of nitric oxide synthase (NOS), the enzyme that catalyzes arginine to nitric oxide (NO) and that both neurohypophyseal regeneration, as well as migration and emergence of neuron-like cells upon the surface of the adjacent third cerebral ventricle, is associated with the up-regulation of NOS and increased expression of NO. It also has been amply demonstrated that this entire process of neurohypophyseal regeneration and cell migration is completely inhibited by the introduction of the antagonist of nitric oxide, namely, nitroarginine (Scott et al., Exp Neurol, 1995;131-1:23-39; Scott and Hansen, Vir Med, 1997;124:249-261). The emergence and migratory dynamics of this novel cell line upon the floor of the rodent third cerebral ventricle are discussed with respect to the role of the ubiquitous free radical NO and the implications and potential clinical applications of neuronal migration following trauma in the human central nervous system (CNS).