scispace - formally typeset
Search or ask a question
Author

Valérie Simonneaux

Bio: Valérie Simonneaux is an academic researcher from Centre national de la recherche scientifique. The author has contributed to research in topics: Melatonin & Pineal gland. The author has an hindex of 40, co-authored 133 publications receiving 6077 citations. Previous affiliations of Valérie Simonneaux include University of Strasbourg & University of Nebraska Medical Center.


Papers
More filters
Journal ArticleDOI
TL;DR: The aim of this review is to gather together early and recent data on the effects of the nonadrenergic transmitters on modulation of melatonin synthesis, which reveals the variety of inputs that can be integrated by the pineal gland; what elements are crucial to deliver the very precise timing information to the organism.
Abstract: Melatonin, the major hormone produced by the pineal gland, displays characteristic daily and seasonal patterns of secretion. These robust and predictable rhythms in circulating melatonin are strong synchronizers for the expression of numerous physiological processes in photoperiodic species. In mammals, the nighttime production of melatonin is mainly driven by the circadian clock, situated in the suprachiasmatic nucleus of the hypothalamus, which controls the release of norepinephrine from the dense pineal sympathetic afferents. The pivotal role of norepinephrine in the nocturnal stimulation of melatonin synthesis has been extensively dissected at the cellular and molecular levels. Besides the noradrenergic input, the presence of numerous other transmitters originating from various sources has been reported in the pineal gland. Many of these are neuropeptides and appear to contribute to the regulation of melatonin synthesis by modulating the effects of norepinephrine on pineal biochemistry. The aim of this review is firstly to update our knowledge of the cellular and molecular events underlying the noradrenergic control of melatonin synthesis; and secondly to gather together early and recent data on the effects of the nonadrenergic transmitters on modulation of melatonin synthesis. This information reveals the variety of inputs that can be integrated by the pineal gland; what elements are crucial to deliver the very precise timing information to the organism. This also clarifies the role of these various inputs in the seasonal variation of melatonin synthesis and their subsequent physiological function.

672 citations

Journal ArticleDOI
23 Sep 1993-Nature
TL;DR: Rhythmic adrenergic signals originated by the clock direct ICER expression by stimulation of the cAMP signal transduction pathway are derived.
Abstract: Transcription factor CREM appears to play a key physiological and developmental role within the hypothalamic-pituitary-gonadal axis This axis is modulated by the pineal hormone melatonin, whose production is in turn driven by the endogenous clock There is striking circadian fluctuation of a novel CREM isoform, ICER, which is expressed at high levels during the night ICER is generated from an alternative, intronic promoter and functions as a powerful repressor of cyclic AMP-induced transcription Rhythmic adrenergic signals originated by the clock direct ICER expression by stimulation of the cAMP signal transduction pathway

410 citations

Journal ArticleDOI
TL;DR: It is proposed that photoperiod, via melatonin, modulates KiSS-1 signaling to drive the reproductive axis, consistent with a role of Ki SS1/GPR54 in the seasonal control of reproduction.

261 citations

Journal ArticleDOI
TL;DR: Evidence is presented that the gene orthologous to GnIH, the RFamide-related peptide (RFRP) gene, expressed in the mediobasal hypothalamus, is strongly regulated by the length of the photoperiod, via melatonin, which raises questions on the role of RFRP as a general inhibitor of reproduction and evoke new perspectives for understanding how melatonin controls seasonal processes via hypothalamic targets.
Abstract: In seasonal species, various physiological processes including reproduction are organized by photoperiod via melatonin, but the mechanisms of melatonin action are still unknown. In birds, the peptide gonadotropin-inhibiting hormone (GnIH) has been shown to have inhibitory effects on reproductive activity and displays seasonal changes of expression. Here we present evidence in mammals that the gene orthologous to GnIH, the RFamide-related peptide (RFRP) gene, expressed in the mediobasal hypothalamus, is strongly regulated by the length of the photoperiod, via melatonin. The level of RFRP mRNA and the number of RFRP-immunoreactive cell bodies were reduced in sexually quiescent Syrian and Siberian hamsters acclimated to short-day photoperiod (SD) compared with sexually active animals maintained under long-day photoperiod (LD). This was contrasted in the laboratory Wistar rat, a non-photoperiodic breeder, in which no evidence for RFRP photoperiodic modulation was seen. In Syrian hamsters, the reduction of RFRP expression in SD was independent from secondary changes in gonadal steroids. By contrast, the photoperiodic variation of RFRP expression was abolished in pinealectomized hamsters, and injections of LD hamsters with melatonin for 60 d provoked inhibition of RFRP expression down to SD levels, indicating that the regulation is dependent on melatonin. Altogether, these results demonstrate that in these hamster species, the RFRP neurons are photoperiodically modulated via a melatonin-dependent process. These observations raise questions on the role of RFRP as a general inhibitor of reproduction and evoke new perspectives for understanding how melatonin controls seasonal processes via hypothalamic targets.

190 citations

Journal ArticleDOI
TL;DR: In this article, a time series of eight high-resolution Landsat TM images, ranging over the crop season, has been acquired over an irrigated area in central Morocco and a Normalized Difference Vegetation Index (NDVI) profile was generated for each pixel.
Abstract: A time series of eight high-resolution Landsat TM images, ranging over the crop season, has been acquired over an irrigated area in central Morocco. From this time series, a Normalized Difference Vegetation Index (NDVI) profile was generated for each pixel. In order to get significant profiles, the images were radiometrically corrected, first, using invariant objects located on the scene, based on visual observation of the images, and second, using the reflectance of these objects, estimated from a previously corrected image. In the following step, these NDVI profiles were used to identify four main crop types-bare soil, annual crops, trees on bare soil and trees on annual understory-using a decision tree algorithm. The resulting land cover map and the associated NDVI profiles were then used for an evapotranspiration estimate over the whole area, using the Food and Agriculture Organization (FAO) model. Daily outputs of the Moroccan meteorological model Aire Limitee Adaptation Dynamique developpement International (ALADIN) were used to generate reference evapotranspiration (ET0) maps and K c estimates were determined using the NDVI profiles.

187 citations


Cited by
More filters
Journal ArticleDOI
TL;DR: The molecular mechanisms by which Ser133-phosphorylated CREB activates transcription, intracellular signaling pathways that lead to phosphorylation ofCREB at Ser133, and features of each signaling pathway that impart specificity at the level of CREB activation are discussed.
Abstract: Extracellular stimuli elicit changes in gene expression in target cells by activating intracellular protein kinase cascades that phosphorylate transcription factors within the nucleus. One of the best characterized stimulus-induced transcription factors, cyclic AMP response element (CRE)-binding protein (CREB), activates transcription of target genes in response to a diverse array of stimuli, including peptide hormones, growth factors, and neuronal activity, that activate a variety of protein kinases including protein kinase A (PKA), pp90 ribosomal S6 kinase (pp90RSK), and Ca2+/calmodulin-dependent protein kinases (CaMKs)[corrected]. These kinases all phosphorylate CREB at a particular residue, serine 133 (Ser133), and phosphorylation of Ser133 is required for CREB-mediated transcription. Despite this common feature, the mechanism by which CREB activates transcription varies depending on the stimulus. In some cases, signaling pathways target additional sites on CREB or proteins associated with CREB, permitting CREB to regulate distinct programs of gene expression under different conditions of stimulation. This review discusses the molecular mechanisms by which Ser133-phosphorylated CREB activates transcription, intracellular signaling pathways that lead to phosphorylation of CREB at Ser133, and features of each signaling pathway that impart specificity at the level of CREB activation.

2,078 citations

Journal ArticleDOI
15 Aug 2002-Neuron
TL;DR: This review focuses on the current level of understanding of where, when, and how CREB family members function in the nervous system.

1,984 citations

Journal ArticleDOI
TL;DR: This review focuses on melatonin metabolism which includes the synthetic rate‐limiting enzymes, synthetic sites, potential regulatory mechanisms, bioavailability in humans, mechanisms of breakdown and functions of its metabolites.
Abstract: Melatonin is a highly conserved molecule. Its presence can be traced back to ancient photosynthetic prokaryotes. A primitive and primary function of melatonin is that it acts as a receptor-independent free radical scavenger and a broad-spectrum antioxidant. The receptor-dependent functions of melatonin were subsequently acquired during evolution. In the current review, we focus on melatonin metabolism which includes the synthetic rate-limiting enzymes, synthetic sites, potential regulatory mechanisms, bioavailability in humans, mechanisms of breakdown and functions of its metabolites. Recent evidence indicates that the original melatonin metabolite may be N 1 -acetyl-N 2 -formyl-5-methoxykynuramine (AFMK) rather than its commonly measured urinary excretory product 6-hydroxymelatonin sulfate. Numerous pathways for AFMK formation have been identified both in vitro and in vivo. These include enzymatic and pseudo-enzymatic pathways, interactions with reactive oxygen species (ROS)/reactive nitrogen species (RNS) and with ultraviolet irradiation. AFMK is present in mammals including humans, and is the only detectable melatonin metabolite in unicellular organisms and metazoans. 6-Hydroxymelatonin sulfate has not been observed in these low evolutionary-ranked organisms. This implies that AFMK evolved earlier in evolution than 6-hydroxymelatonin sulfate as a melatonin metabolite. Via the AFMK pathway, a single melatonin molecule is reported to scavenge up to 10 ROS/RNS. That the free radical scavenging capacity of melatonin extends to its secondary, tertiary and quaternary metabolites is now documented. It appears that melatonin's interaction with ROS/RNS is a prolonged process that involves many of its derivatives. The process by which melatonin and its metabolites successively scavenge ROS/RNS is referred as the free radical scavenging cascade. This cascade reaction is a novel property of melatonin and explains how it differs from other conventional antioxidants. This cascade reaction makes melatonin highly effective, even at low concentrations, in protecting organisms from oxidative stress. In accordance with its protective function, substantial amounts of melatonin are found in tissues and organs which are frequently exposed to the hostile environmental insults such as the gut and skin or organs which have high oxygen consumption such as the brain. In addition, melatonin production may be upregulated by low intensity stressors such as dietary restriction in rats and exercise in humans. Intensive oxidative stress results in a rapid drop of circulating melatonin levels. This melatonin decline is not related to its reduced synthesis but to its rapid consumption, i.e. circulating melatonin is rapidly metabolized by interaction with ROS/RNS induced by stress. Rapid melatonin consumption during elevated stress may serve as a protective mechanism of organisms in which melatonin is used as a first-line defensive molecule against oxidative damage. The oxidative status of organisms modifies melatonin metabolism. It has been reported that the higher the oxidative state, the more AFMK is produced. The ratio of AFMK and another melatonin metabolite, cyclic 3-hydroxymelatonin, may serve as an indicator of the level of oxidative stress in organisms.

1,454 citations

Journal ArticleDOI
TL;DR: This article reviews findings up to the end of 1997 about the inducible transcription factors c-Jun, JunB, JunD, c-Fos, FosB, Fra,1, Fra-2, Krox-20 (Egr-2) and Krox -24 (NGFI-A, Egr-1, Zif268) as they pertain to gene expression in the mammalian nervous system and describes their expression and possible roles in glial cells.

1,361 citations