Publications by authors named "Paul Klosen"

Article Synopsis
  • Identifying melatonin receptors is crucial for understanding the hormone's function, and various techniques have been used to localize these receptors, each with its own challenges.
  • The initial tool for this localization was radioligand 2-[I] iodomelatonin, followed by in situ hybridization and antibody generation for the MT1 and MT2 receptors once their sequences were known.
  • Despite advancements, issues like low receptor expression levels and antibody specificity continue to complicate identification, necessitating more rigorous validation methods for future studies.
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Genetic technology allows inserting transgenic reporters such as beta-galactosidase (LacZ) into the loci of the Mtnr1a (MT) and Mtnr1b (MT) receptor genes to track MT and MT melatonin receptor expression. Given the limited sensitivity of nonradioactive in situ hybridization and the problematic specificity of existing melatonin receptor antibodies for immunohistochemistry, this new technology is a key tool to study the localization and the phenotypes of cells expressing melatonin receptors. Here we describe two protocols to detect transgenic LacZ expression driven by the MT or MT promoters either by the enzymatic activity of the transgenic LacZ enzyme or by using specific antibodies against LacZ with immunohistochemistry.

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Identifying and phenotyping the target cells of a neuroendocrine messenger is one of the key steps to understand neuroendocrine networks and the physiological action of such messengers. In the absence of reliable antibodies directed against the receptor of a neuroendocrine messenger, detecting the expression of the messenger RNA of this receptor is an important tool to identify the target cells of a neuroendocrine messenger such as melatonin. While radioactive in situ hybridization has a higher sensitivity, nonradioactive in situ hybridization has a much better cellular resolution than radioactive in situ hybridization and is therefore better suited for phenotyping the target cells of melatonin.

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Female reproductive success relies on proper integration of circadian- and ovarian- signals to the hypothalamic-pituitary-gonadal axis in order to synchronize the preovulatory LH surge at the end of the ovarian follicular stage with the onset of the main active period. In this study, we used a combination of neuroanatomical and electrophysiological approaches to assess whether the hypothalamic neurons expressing Arg-Phe amide-related peptide (RFRP-3), a gonadotropin inhibitory peptide, exhibit daily and estrous stage dependent variations in female mice. Furthermore, we investigated whether arginine vasopressin (AVP), a circadian peptide produced by the suprachiamatic nucleus regulates RFRP-3 neurons.

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In addition to its regulatory role in luteinising hormone secretion, Rfamide-related peptide 3 (RFRP3) has also been reported to modulate food intake in several mammalian species. Djungarian hamsters (Phodopus sungorus), similar to other seasonal mammals, display a remarkable inhibition of RFRP3 expression in winter short-day conditions, associated with decreased food intake and bodyweight. This species is therefore a valuable model for assessing whether RFRP3 might be involved in the seasonal control of feeding behaviour and investigating its possible brain targets.

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The dromedary camel (Camelus dromedarius) is a desert mammal whose cycles in reproductive activity ensure that the offspring's birth and weaning coincide with periods of abundant food resources and favorable climate conditions. In this study, we assessed whether kisspeptin (Kp) and arginine-phenylalanine (RF)-amide related peptide-3 (RFRP-3), two hypothalamic peptides known to regulate the mammalian hypothalamo-pituitary gonadal axis, may be involved in the seasonal control of camel's reproduction. Using specific antibodies and riboprobes, we found that Kp neurons are present in the preoptic area (POA), suprachiasmatic (SCN), and arcuate (ARC) nuclei, and that RFRP-3 neurons are present in the paraventricular (PVN), dorsomedial (DMH), and ventromedial (VMH) hypothalamic nuclei.

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Melatonin (MLT) exerts its physiological effects principally through two high-affinity membrane receptors MT1 and MT2. Understanding the exact mechanism of MLT action necessitates the use of highly selective agonists/antagonists to stimulate/inhibit a given MLT receptor. The respective distribution of MT1 and MT2 within the CNS and elsewhere is controversial, and here we used a "knock-in" strategy replacing MT1 or MT2 coding sequences with a LacZ reporter.

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Many animals exhibit remarkable metabolic and reproductive adaptations to seasonal changes in their environment. When day length shortens, Djungarian hamsters (Phodopus sungorus) reduce their body weight and inhibit their reproductive activity, whereas the opposite occurs in springtime. These physiological adaptations are considered to depend on photoperiodic changes in hypothalamic genes encoding the peptides kisspeptin (Kp) and RFamide-related peptide 3 (RFRP3) for the control of reproduction, as well as pro-opiomelanocortin and somatostatin for metabolic regulation.

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In seasonal rodents, reproduction is activated by a long photoperiod. Furthermore, maintaining an inhibitory short photoperiod for over 20 weeks triggers a spontaneous reactivation of the gonadotropic axis called photorefractoriness. Photoactivation is proposed to involve melatonin, hypothalamic thyroid hormones (TH) and (Arg) (Phe)-amide peptides.

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Obesity triggers changes in protein expression in various organs that might participate in the pathogenesis of obesity. Melatonin has been reported to prevent or attenuate such pathological protein changes in several chronic diseases. However, such melatonin effects on plasma proteins have not yet been studied in an obesity model.

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Jerboa (Jaculus orientalis) is a semi-desert rodent displaying strong seasonal variations in biological functions in order to survive harsh conditions. When environmental conditions become unfavorable in early autumn, it shuts down its reproductive axis, increases its body weight, and finally hibernates. In spring, the jerboa displays opposite regulations, with a reactivation of reproduction and reduction in body weight.

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In mammals, melatonin is the pivotal messenger synchronizing biological functions, notably reproductive activity, with annual daylength changes. Recently, two major findings clarified melatonin's mode of action. First, melatonin controls the production of thyroid stimulating hormone (TSH) by the pars tuberalis of the adenohypophysis.

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Reproduction is a fundamental biological function ensuring individual descendant survival and species perpetuity. It is an energy-consuming process, and therefore, all underlying mechanisms have to work in synchrony to ensure reproductive success. Synchronization of reproductive activity with the best time of the day or the year is part of such adaptive processes.

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Mutations of clock genes can lead to diabetes and obesity. REV-ERBα, a nuclear receptor involved in the circadian clockwork, has been shown to control lipid metabolism. To gain insight into the role of REV-ERBα in energy homeostasis in vivo, we explored daily metabolism of carbohydrates and lipids in chow-fed, unfed, or high-fat-fed Rev-erbα(-/-) mice and their wild-type littermates.

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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.

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G protein-coupled receptor (GPCR) associated sorting protein 1 (GASP-1) interacts with GPCRs and is implicated in their postendocytic sorting. Recently, GASP-1 has been shown to regulate dopamine (D(2)) and cannabinoid (CB1) receptor signalling, suggesting that preventing GASP-1 interaction with GPCRs might provide a means to limit the decrease in receptor signalling upon sustained agonist treatment. In order to test this hypothesis, we have generated and behaviourally characterized GASP-1 knockout (KO) mice and have examined the consequences of the absence of GASP-1 on chronic cocaine treatments.

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Reproduction is a complex and energy demanding function. When internal and external conditions might impair reproductive success (negative energy balance, stress, harsh season) reproductive activity has to be repressed. Recent evidence suggests that these inhibitory mechanisms operate on Kiss1-expressing neurons, which were recently shown to be implicated in the regulation of GnRH release.

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In seasonal species, photoperiod (i.e. daylength) tightly regulates reproduction to ensure that birth occurs at the most favorable time of year.

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Species differences have been reported for the nighttime regulation of arylalkylamine N-acetyltransferase (AA-NAT), the melatonin rhythm-generating enzyme. In particular, de novo synthesis of stimulatory transcription factors is required for Aa-nat transcription in the Syrian hamster but not in the rat pineal gland. The present work investigated the contribution of phosphorylated cAMP-responsive element-binding protein, c-FOS, c-JUN, and JUN-B in the regulation of Aa-nat transcription in Syrian hamsters compared with rats.

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The suprachiasmatic nuclei of the hypothalamus (SCN) are the site of the master circadian clock in mammals. The SCN clock is mainly entrained by the light-dark cycle. Light information is conveyed from the retina to the SCN through direct, retinohypothalamic fibres.

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In mammals, interacting transcriptional/post-translational feedback loops involving 'clock genes' and their protein products control circadian organisation. These genes are not only expressed in the master circadian clock of the suprachiasmatic nuclei (SCN) but also in many peripheral tissues where they exhibit similar but not identical dynamic to that seen in the SCN. Among these peripheral tissues, the pars tuberalis (PT) of the pituitary expresses clock genes.

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The pars tuberalis (PT) of the pituitary represents an important target site for the time-pacing pineal hormone melatonin because it expresses a large number of mt1 receptors. Functional studies suggest that the PT mediates the seasonal effects of melatonin on prolactin (PRL) secretion. The aim of this study was the characterization of the phenotype of melatonin-responsive cells.

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Per1 and Per2, two clock genes rhythmically expressed in the suprachiasmatic nucleus (SCN), are implicated in the molecular mechanism of the circadian pacemaker and play a major role in its entrainment by light. To date, it is not known if every cell of the SCN, a heterogeneous structure in respect of neuropeptide content, expresses clock genes equally. The aim of this study was to identify, by single and double non-radioactive and/or radioactive hybridizations, the cell types (AVP, VIP and GRP) expressing Per1 or Per2 in the SCN of rats, (1) when Per are highly expressed during the daytime, and (2) after induction of Per expression by a light pulse at night.

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In mammals, the suprachiasmatic nuclei (SCN) are the site of the master circadian pacemaker whose molecular core mechanism is based on interlocking transcriptional/translational feedback loops involving clock genes. Among clock genes, Per1 and Per2 are important for both the maintenance of circadian rhythmicity and entrainment to light cues. Several circadian rhythms (e.

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