GFAP-expressing cells in the adult hypothalamus can generate multiple neural cell lineages in vitro.

Adult neural stem cells (NSCs) located in the two canonical neurogenic niches, the subventricular zone (SVZ) and the subgranular zone (SGZ), express the glial fibrillary acidic protein (GFAP). Recently, proliferative activity has been described in the hypothalamus although the characterization of hypothalamic neural stem/progenitor cells (NSPCs) is still uncertain. We therefore investigated whether hypothalamic GFAP-positive cells, as in the SVZ and SGZ, also have neurogenic potential.

Multiparametric MR Evaluation of the Photoperiodic Regulation of Hypothalamic Structures in Sheep.

Most organisms on earth, humans included, have developed strategies to cope with environmental day-night and seasonal cycles to survive. For most of them, their physiological and behavioral functions, including the reproductive function, are synchronized with the annual changes of day length, to ensure winter survival and subsequent reproductive success in the following spring. Sheep are sensitive to photoperiod, which also regulates natural adult neurogenesis in their hypothalamus.

Seasonal remodeling of the progenitor pool and its distribution in the ewe mediobasal hypothalamus.

Recent studies have reported the presence of adult neurogenesis in the arcuate nucleus periventricular space (pvARH) and in the median eminence (ME), two structures involved in reproductive function. In sheep, a seasonal mammal, decreasing daylight in autumn induces a higher neurogenic activity in these two structures. However, the different types of neural stem and progenitor cells (NSCs/NPCs) that populate the arcuate nucleus and median eminence, as well as their location, have not been evaluated.

Selective Depletion of Adult GFAP-Expressing Tanycytes Leads to Hypogonadotropic Hypogonadism in Males.

In adult mammals, neural stem cells are localized in three neurogenic regions, the subventricular zone of the lateral ventricle (SVZ), the subgranular zone of the dentate gyrus of the hippocampus (SGZ) and the hypothalamus. In the SVZ and the SGZ, neural stem/progenitor cells (NSPCs) express the glial fibrillary acidic protein (GFAP) and selective depletion of these NSPCs drastically decreases cell proliferation and . In the hypothalamus, GFAP is expressed by α-tanycytes, which are specialized radial glia-like cells in the wall of the third ventricle also recognized as NSPCs.

Seasonal vascular plasticity in the mediobasal hypothalamus of the adult ewe.

Sheep, like most seasonal mammals, exhibit a cyclic adaptive reproductive physiology that allows ewes to give birth to their progeny during the spring when environmental conditions are favorable to their survival. This process relies on the detection of day length (or photoperiod) and is associated with profound changes in cellular plasticity and gene expression in the hypothalamic-pituitary-gonadal axis, mechanisms that are suggested to participate in the seasonal adaptation of neuroendocrine circuits. Recently, pituitary vascular growth has been proposed as a seasonally regulated process in which the vascular endothelial growth factor A (VEGFA), a well-known angiogenic cytokine, is suspected to play a crucial role.

Two repeated motifs enriched within some enhancers and origins of replication are bound by SETMAR isoforms in human colon cells.

Setmar is a gene specific to simian genomes. The function(s) of its isoforms are poorly understood and their existence in healthy tissues remains to be validated. Here we profiled SETMAR expression and its genome-wide binding landscape in colon tissue.

Blood oxygen level dependent fMRI and perfusion MRI in the sheep brain.

The ovine model could be an effective translational model but remains underexplored. Here, Blood Oxygen Level dependent functional MRI during visual stimulation and resting-state perfusion MRI were explored. We aimed at investigating the impact of isoflurane anesthesia during visual stimulation and evaluate resting cerebral blood flow and cerebral blood volume parameters in the lamb and adult sheep brain.

Chemerin impairs food intake and body weight in chicken: Focus on hypothalamic neuropeptides gene expression and AMPK signaling pathway.

Unlike mammals, the role of adipokines and more particularly of chemerin in the regulation of food intake is totally unknown in avian species. Here we investigated the effect of chemerin on the food and water consumption and on the body weight in chicken. We studied the effects on the plasma glucose and insulin concentrations and the hypothalamic neuropeptides and AMPK signaling pathway.

Differential effects of oxytocin on olfactory, hippocampal and hypothalamic neurogenesis in adult sheep.

New neurons are continuously added in the dentate gyrus of the hippocampus, the olfactory bulb and the hypothalamus of mammalian brain. In sheep, while the control of adult neurogenesis by the social environment or the photoperiod has been the subject of several studies, its regulation by intrinsic factors, like hormones or neurotransmitters is less documented. We addressed this question by investigating the effects of central oxytocin administration on hippocampal, olfactory and hypothalamic neurogenesis.

Pineal-dependent increase of hypothalamic neurogenesis contributes to the timing of seasonal reproduction in sheep.

To survive in temperate latitudes, species rely on the photoperiod to synchronize their physiological functions, including reproduction, with the predictable changes in the environment. In sheep, exposure to decreasing day length reactivates the hypothalamo-pituitary-gonadal axis, while during increasing day length, animals enter a period of sexual rest. Neural stem cells have been detected in the sheep hypothalamus and hypothalamic neurogenesis was found to respond to the photoperiod.

Adult Neurogenesis in Sheep: Characterization and Contribution to Reproduction and Behavior.

Sheep have many advantages to study neurogenesis in comparison to the well-known rodent models. Their development and life expectancy are relatively long and they possess a gyrencephalic brain. Sheep are also seasonal breeders, a characteristic that allows studying the involvement of hypothalamic neurogenesis in the control of seasonal reproduction.

Seasonal reorganization of hypothalamic neurogenic niche in adult sheep.

Neurogenesis is the process by which new neurons are generated. This process, well established during development, persists in adulthood owing to the presence of neural stem cells (NSCs) localized in specific brain areas called neurogenic niches. Adult neurogenesis has recently been shown to occur in the hypothalamus, a structure involved in the neuroendocrine regulation of reproduction and metabolism, among others.

Adult neurogenesis and reproductive functions in mammals.

During adulthood, the mammalian brain retains the capacity to generate new cells and new neurons in particular. It is now well established that the birth of these new neurons occurs in well-described sites: the hippocampus and the subventricular zone of the lateral ventricle, as well as in other brain regions including the hypothalamus. In this review, we describe the canonical neurogenic niches and illustrate the functional relevance of adult-born neurons of each neurogenic niche in the reproductive physiology.

Sensitivity to the photoperiod and potential migratory features of neuroblasts in the adult sheep hypothalamus.

Adult neurogenesis, a process that consists in the generation of new neurons from adult neural stem cells, represents a remarkable illustration of the brain structural plasticity abilities. The hypothalamus, a brain region that plays a key role in the neuroendocrine regulations including reproduction, metabolism or food intake, houses neural stem cells located within a hypothalamic neurogenic niche. In adult sheep, a seasonal mammalian species, previous recent studies have revealed photoperiod-dependent changes in the hypothalamic cell proliferation rate.

Seasonal regulation of structural plasticity and neurogenesis in the adult mammalian brain: focus on the sheep hypothalamus.

To cope with variations in the environment, most mammalian species exhibit seasonal cycles in physiology and behaviour. Seasonal plasticity during the lifetime contributes to seasonal physiology. Over the years, our ideas regarding adult brain plasticity and, more specifically, hypothalamic plasticity have greatly evolved.

Evidence that histaminergic neurons are devoid of estrogen receptor alpha in the ewe diencephalon during the breeding season.

In sheep as in rat, it has been highly suggested that neuronal histamine (HA) participates to the estradiol (E2)-induced GnRH and LH surges, through H1 receptor. With the aim of determining if E2 could act directly on HA neurons, we examined here whether HA neurons express estrogen receptor alpha (ERα) in the ewe diencephalon during the breeding season. We first produced a specific polyclonal antibody directed against recombinant ovine histidine decarboxylase (oHDC), the HA synthesizing enzyme.

DCX-expressing cells in the vicinity of the hypothalamic neurogenic niche: a comparative study between mouse, sheep, and human tissues.

Neural stem and precursor cells persist postnatally throughout adulthood and are capable of responding to numerous endogenous and exogenous signals by modifying their proliferation and differentiation. Whereas adult neurogenesis has been extensively studied in the dentate gyrus of the hippocampal formation and in the subventricular zone adjacent to the wall of the lateral ventricles, we and others have recently reported constitutive adult neurogenesis in other brain structures, including the hypothalamus. In this study, we used immunohistochemistry to study the expression of the neuroblast marker doublecortin (DCX), and compared its expression pattern in adult ovine, mouse, and human hypothalamic tissues.

Neuroanatomical distribution of the orphan GPR50 receptor in adult sheep and rodent brains.

GPR50, formerly known as melatonin-related receptor, is one of three subtypes of the melatonin receptor subfamily, together with the MT(1) and MT(2) receptors. By contrast to these two high-affinity receptor subtypes and despite its high identity with the melatonin receptor family, GPR50 does not bind melatonin or any other known ligand. Specific and reliable immunological tools are therefore needed to be able to elucidate the physiological functions of this orphan receptor that are still largely unknown.

Seasonal changes in cell proliferation in the adult sheep brain and pars tuberalis.

To adapt to seasonal variations in the environment, most mammalian species exhibit seasonal cycles in their physiology and behavior. Seasonal plasticity in the structure and function of the central nervous system contributes to the adaptation of this physiology in seasonal mammals. As part of these plasticity mechanisms, seasonal variations in proliferation rate and neuron production have been extensively studied in songbirds.

Emerging new sites for adult neurogenesis in the mammalian brain: a comparative study between the hypothalamus and the classical neurogenic zones.

In adult mammalian brain, two main germinative regions located in the subventricular zone of the lateral ventricle and in the subgranular cell layer of the hippocampal dentate gyrus have been considerably documented and are still under intense scrutiny. However, new neuron formation has recently been reported in various other brain areas including the hypothalamus. This central structure, responsible for the control of many major neuroendocrine functions such as reproduction, expresses high levels of PSA-NCAM and nestin, both proteins being involved in structural and morphological plasticity mechanisms.

Functional characterization of polymorphic variants for ovine MT1 melatonin receptors: possible implication for seasonal reproduction in sheep.

In seasonal breeding species, the gene encoding for the melatonin MT(1) receptor (oMT(1)) is highly polymorphic and numerous data have reported the existence of an association between an allele of the receptor and a marked expression of the seasonality of reproduction in ewes. This allele called "m" (previously named "-" allele) carries a mutation leading to the absence of a MnlI restriction site as opposed to the "M" allele (previously named "+" allele) carrying the MnlI restriction site (previously "+" allele). This allows the determination of the three genotypes "M/M" (+/+), "M/m" (+/-) and "m/m" (-/-).

Modulation of estrogen receptors during development inhibits neurogenesis of precursors to GnRH-1 neurones: in vitro studies with explants of ovine olfactory placode.

The aim of the present study was to explore the putative effects of agonists and antagonists of the estradiol receptor on the early phase of GnRH-1 neuron development. To address this question we used an in vitro model of GnRH-1 neurons using cultured olfactory placode from sheep embryos on day 26 of gestation. Previous studies on this model have shown that in vitro the development of GnRH-1 neurons mimics in vivo development up to the start of pulsatile GnRH-1 secretion, To address the effects of modulating the estrogen receptor, cultures were treated with the endogenous and synthetic ligands of estradiol receptors: 17beta-estradiol, 17alpha-estradiol and tamoxifen.

Neuroanatomical organization of gonadotropin-releasing hormone neurons during the oestrus cycle in the ewe.

Background: During the preovulatory surge of gonadotropin-releasing hormone (GnRH), a very large amount of the peptide is released in the hypothalamo-hypophyseal portal blood for 24-36H00. To study whether this release is linked to a modification of the morphological organization of the GnRH-containing neurons, i.e.

Pulsatile GnRH secretion from primary cultures of sheep olfactory placode explants.

The aim of this study was to investigate the development of pulsatile GnRH secretion by GnRH neurones in primary cultures of olfactory placodes from ovine embryos. Culture medium was collected every 10 min for 8 h to detect pulsatile secretion. In the first experiment, pulsatile secretion was studied in two different sets of cultures after 17 and 24 days in vitro.

Neuronal projections to the lateral retrochiasmatic area of sheep with special reference to catecholaminergic afferents: immunohistochemical and retrograde tract-tracing studies.

The retrochiasmatic area contains the A15 catecholaminergic group and numerous monoaminergic afferents whose discrete cell origins are unknown in sheep. Using tract-tracing methods with a specific retrograde fluorescent tracer, fluorogold, we examined the cells of origin of afferents to the retrochiasmatic area in sheep. The retrogradely labeled cells were seen by observation of the tracer by direct fluorescence or by immunohistochemistry with specific antibodies raised in rabbits or horses.