Phase shift of the circannual reproductive rhythm in European hamsters by 2 days of long photoperiod.

Objectives And Design: In European hamsters a circannual clock drives the seasonal changes in the reproductive state. Its resetting by photoperiod is clearly phase dependent. In mid subjective winter a 1-month pulse of long photoperiod (LP) advances the onset of the reproductive phase of animals maintained in constant short photoperiod (SP) by up to 1.

Circannual phase response curves to short and long photoperiod in the European hamster.

This study investigated in male European hamsters (Cricetus cricetus ) whether entrainment of circannual rhythms follows the principles of the nonparametric entrainment model. In 2 experiments the times of the year when long (LP) or short photoperiod (SP) are able to synchronize the reproductive cycle were determined, by recording phase response curves (PRCs). A total of 28 groups of 10 hamsters were synchronized by SP, before being subjected to 2 converse experiments: a) 14 groups were transferred to constant LP, only interrupted by SP for 1 month (SP-pulse), the pulse being increasingly delayed between groups by 2 weeks or 1 month steps; and b) the remaining 14 groups stayed in constant SP interrupted by LP for 1 month (LP-pulse) at different phases of the cycle.

Opposite actions of hypothalamic vasopressin on circadian corticosterone rhythm in nocturnal versus diurnal species.

Relatively little is known about the function of the biological clock and its efferent pathways in diurnal species, despite the fact that its major transmitters and neuronal connections are also conserved in humans. The mammalian biological clock is located in the hypothalamic suprachiasmatic nuclei (SCN). Several lines of evidence suggest that the activity cycle of the SCN itself is similar in nocturnal and diurnal mammals.

RFamide-related peptide gene is a melatonin-driven photoperiodic gene.

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.

Daily torpor affects the molecular machinery of the circadian clock in Djungarian hamsters (Phodopus sungorus).

Daily torpor in the Djungarian hamster (Phodopus sungorus) is a precisely timed event gated by the circadian clock situated in the suprachiasmatic nuclei (SCN) of the hypothalamus. Timing-controlled hypothermia during which body temperature (Tb) decreases to approximately 15 degrees C implies temperature compensation of the circadian system. Nevertheless, it remains controversial how the molecular clockwork functions at those low Tb values and whether the torpor bout affects the circadian system.

The circadian clock stops ticking during deep hibernation in the European hamster.

Hibernation is a fascinating, yet enigmatic, physiological phenomenon during which body temperature and metabolism are reduced to save energy. During the harsh season, this strategy allows substantial energy saving by reducing body temperature and metabolism. Accordingly, biological processes are considerably slowed down and reduced to a minimum.

Kisspeptin: a key link to seasonal breeding.

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

Rapid and reversible changes in intrahippocampal connectivity during the course of hibernation in European hamsters.

The hippocampal formation is a highly plastic brain structure that undergoes structural remodeling in response to internal and external challenges such as metabolic imbalance and repeated stress. We investigated whether the extreme alterations in metabolic status that occur during the course of hibernation in European hamsters cause structural changes in the dendritic arborizations of the CA3 pyramidal neurons and their main excitatory afferents, the mossy fiber terminals (MFT), that originate in the dentate gyrus. We report that apical, but not basal, dendritic trees of Golgi-impregnated CA3 principal neurons are significantly shorter, less branched, and less spiny in hypothermic hamsters compared with active animals.

Kisspeptin mediates the photoperiodic control of reproduction in hamsters.

The KiSS-1 gene encodes kisspeptin, the endogenous ligand of the G-protein-coupled receptor GPR54. Recent data indicate that the KiSS-1/GPR54 system is critical for the regulation of reproduction and is required for puberty onset. In seasonal breeders, reproduction is tightly controlled by photoperiod (i.

Melatonin regulates type 2 deiodinase gene expression in the Syrian hamster.

In seasonal species, photoperiod organizes various physiological processes, including reproduction. Recent data indicate that the expression of type 2 iodothyronine deiodinase (Dio2) is modulated by photoperiod in the mediobasal hypothalamus of some seasonal species. Dio2 is believed to control the local synthesis of bioactive T(3) to regulate gonadal response.

KiSS-1: a likely candidate for the photoperiodic control of reproduction in seasonal breeders.

In seasonal species, photoperiod exerts tight regulation of reproduction to ensure that birth occurs at the most favorable time of yr. A distinct photoneuroendocrine circuit composed of the retina, suprachiasmatic nucleus (SCN) of the hypothalamus, and pineal gland transduces daylength into a rhythmic secretion of melatonin. The duration of the night-time rise of this hormone conveys daylength information to the organism.

Daily torpor alters multiple gene expression in the suprachiasmatic nucleus and pineal gland of the Djungarian hamster (Phodopus sungorus).

Circadian rhythms are still expressed in animals that display daily torpor, implying a temperature compensation of the pacemaker. Nevertheless, it remains unclear how the clock works in hypothermic states and whether torpor itself, as a temperature pulse, affects the circadian system. To reveal changes in the clockwork during torpor, we compared clock gene and neuropeptide expression by in situ hybridization in the suprachiasmatic nucleus (SCN) and pineal gland of normothermic and torpid Djungarian hamsters (Phodopus sungorus).

Trans-pineal microdialysis in the Djungarian hamster (Phodopus sungorus): a tool to study seasonal changes of circadian clock activities.

The Djungarian hamster is a highly seasonal small mammal. The rhythmic secretion of melatonin by the pineal gland is under control of the circadian clock, conveying the photoperiodic message to the organism. Trans-pineal microdialysis permits the in vivo study of this well-defined and precise clock output by measuring melatonin release directly in the pineal gland.

A functional subdivision of the circadian clock is revealed by differential effects of melatonin administration.

The biological clock of the suprachiasmatic nuclei drives numerous physiological and behavioural circadian rhythms. In this study, we addressed the question as to whether different components of the clock may control separately various circadian functions. Using the rat transpineal microdialysis tool, we analysed the effect of clock perturbation by exogenous melatonin injection on two hormonal clock outputs: pineal melatonin and adrenal corticosterone secretions.

Impaired cognitive performance in rats after complete epithalamus lesions, but not after pinealectomy alone.

In the midbrain, the epithalamus comprises the habenular nuclei and the pineal gland. Based on evidence including imaging studies in schizophrenia patients, several investigators have postulated that dysfunction of this structure is causally involved in symptoms of schizophrenia. Recently, we showed that bilateral habenula lesions in the rat induced some schizophrenia-like behavioural changes, namely memory and attention impairments, but unaltered social interaction in a brief encounter and prepulse inhibition (PPI) of the startle reflex.

Light and melatonin inhibit in vivo serotonergic phase advances without altering serotonergic-induced decrease of per expression in the hamster suprachiasmatic nucleus.

In the Syrian hamster a serotonergic (5-HTergic) stimulation during daytime acts on the circadian timing system by inducing behavioral phase advances and by decreasing Per1 and Per2 (Period) mRNA levels in the suprachiasmatic nuclei, containing the main circadian clock in mammals. The present study was conducted in Syrian hamsters, housed in constant darkness, to investigate the interactions between light or melatonin with serotonergic stimulation in terms of phase resetting and clock gene expression. Both light exposure and systemic administration of melatonin prior to the injection of a 5-HT(1A/7) receptor agonist, 8-OH-DPAT, in the middle of the day blocked behavioral phase advances.

Temporal organization of the 24-h corticosterone rhythm in the diurnal murid rodent Arvicanthis ansorgei Thomas 1910.

Arvicanthis ansorgei is a diurnal murid rodent from sub-Saharan Africa. The present study reports on the temporal organization of one of the major hormonal rhythms, i.e.

Inhibition of hibernation by exercise is not affected by intergeniculate leaflets lesion in hamsters.

The circadian clock of mammals, located in the suprachiasmatic nuclei (SCN) of the hypothalamus, has been demonstrated to integrate day length change from long (LP) to short photoperiod (SP). This photoperiodic change induces in Syrian hamsters a testicular regression through melatonin action, a phenomenon that is inhibited when hamsters have free access to a wheel. The intergeniculate leaflets (IGL), which modulate the integration of photoperiod by the SCN, are a key structure in the circadian system, conveying nonphotic information such as those induced by novelty-induced wheel running activity.

Pineal melatonin synthesis and release are not altered throughout the estrous cycle in female rats.

Melatonin times reproduction with seasons in many photoperiodic mammalian species. Whether sexual hormones reflect on melatonin synthesis is still debated. The aim of this work was to study, using a large panel of technical approaches, whether the daily profile of pineal melatonin synthesis and release varies with the estrous cycle in the female rat.

In the rat, exogenous melatonin increases the amplitude of pineal melatonin secretion by a direct action on the circadian clock.

The effect of exogenous melatonin on pineal melatonin synthesis was studied in the rat in vivo. Daily melatonin profiles were measured by transpineal microdialysis over 4 consecutive days in rats maintained on a 12-h light : 12-h dark schedule (LD 12 : 12). Curve-fitting was used to determine the amplitude of the peak of melatonin production, and the times of its onset (IT50) and offset (DT50).

Circadian tryptophan hydroxylase levels and serotonin release in the suprachiasmatic nucleus of the rat.

Serotonin (5-HT) plays an important role in the regulation of the time-keeping system in rodents. In the present study, we have investigated the interplay between the rhythms of 5-HT synthesis and release in the suprachiasmatic nuclei (SCN) of the rat. The quantitative distribution of tryptophan hydroxylase (TpH) protein was used as an index of 5-HT synthesis, in perikarya and terminals areas.