Melatonin-independent Photoperiodic Entrainment of the Circannual TSH Rhythm in the Pars Tuberalis of the European Hamster

Adaptation of biological rhythms to a seasonal environment in circannual mammals is achieved via the synchronization of intrinsic circannual rhythms to the external year by photoperiod. In mammals, the photoperiodic information is integrated to seasonal physiology via the pineal hormone melatonin regulation of pars tuberalis (PT) TSH expression and its downstream control of hypothalamic dio2 gene expression. In the circannual European hamster, however, photoperiodic entrainment of the circannual clock is possible in pinealectomized animals. The present study explores whether the TSH expression in the PT and the downstream hypothalamic pathways are regulated by photoperiod in European hamsters in the absence of melatonin. All animals were kept on an accelerated photoperiodic regime, which compressed the natural year to a 6-month cycle. Sham-operated European hamsters and half of the pinealectomized European hamsters entrained their annual cycle in reproduction, body weight, and activity pattern to this cycle, whereas the other half of the pinealectomized animals followed only each second cycle. In all animals, PT TSH and hypothalamic dio2 expressions were higher in hamsters displaying a summer physiological state than in those in winter state. Moreover, in agreement with their seasonal state, reproductive animals (summer state) showed higher expression of rfrp and lower expression of kiss1-genes encoding central regulators of the reproductive axis-than those animals in reproductive quiescence (winter state), indicating the hypothalamic integration of the photoperiodic signal even in pinealectomized animals. The appropriate occurrence of a well-characterized activity pattern indicative of a so-called sensitive phase to short photoperiod suggested that the SCN constructs the melatonin-independent photoperiodic message. This message is sufficient to entrain the circannual rhythm in TSH expression in the PT and the downstream hypothalamic neuroendocrine pathway through a yet unknown pathway. These results reinforce the hypothesis that the PT is the site for the integration of circannual and photoperiodic information

Standards of evidence in chronobiology: critical review of a report that restoration of Bmal1 expression in the dorsomedial hypothalamus is sufficient to restore circadian food anticipatory rhythms in Bmal1-/- mice

Daily feeding schedules generate food anticipatory rhythms of behavior and physiology that exhibit canonical properties of circadian clock control. The molecular mechanisms and location of food-entrainable circadian oscillators hypothesized to control food anticipatory rhythms are unknown. In 2008, Fuller et al reported that food-entrainable circadian rhythms are absent in mice bearing a null mutation of the circadian clock gene Bmal1 and that these rhythms can be rescued by virally-mediated restoration of Bmal1 expression in the dorsomedial nucleus of the hypothalamus (DMH) but not in the suprachiasmatic nucleus (site of the master light-entrainable circadian pacemaker). These results, taken together with controversial DMH lesion results published by the same laboratory, appear to establish the DMH as the site of a Bmal1-dependent circadian mechanism necessary and sufficient for food anticipatory rhythms. However, careful examination of the manuscript reveals numerous weaknesses in the evidence as presented. These problems are grouped as follows and elaborated in detail: 1. data management issues (apparent misalignments of plotted data), 2. failure of evidence to support the major conclusions, and 3. missing data and methodological details. The Fuller et al results are therefore considered inconclusive, and fail to clarify the role of either the DMH or Bmal1 in the expression of food-entrainable circadian rhythms in rodents

Road mortality of the algerian hedgehog (Atelerix algirus) in the Soummam valley (Algeria)

There are several reasons for mortality in a population of wild animals, but the most important in small animals is the mortality due to the road traffic. Because of the dense road network the hedgehog is in Western Europe one of the species most affected by road kills. In North-African countries and particularly in Algeria, both the road network and the number of cars have considerably increased in the last decades. Thus, the number of Algerian Hedgehogs (Atelerix algirus) victims of the traffic is high and regular. Along a road of ca 100 km with high traffic volume, localized in the Soummam valley (from Béjaia to Bouira), we recorded during 5 years (from 2002 to 2006) the number, places and dates of hedgehogs found killed. The road was surveyed from a car, three times a week, and the overall number of hedgehogs found killed was 459. The distribution of animals respective to their location showed a very high density in suburban areas with their diverse environmental structures such as forests, agricultural areas, hedges, and the woodlands around the wadi El Soummam tributaries. In the course of the year, the hedgehog road kills were maximal in spring and summer (42.92 and 34.64 % respectively), decreasing in autumn and reaching a minimum in winter (5.66 %). It was possible to determine the age and sex of 404 animals. Every year males were observed first in spring from March onwards. During this period more males than females were found dead (45.30 % and 31.19 % respectively). The strong locomotor activity of males in spring (maximum in May) and summer coincides with the period of reproduction. Additionally, their home range is larger than that of females. Juveniles were found mostly at the end of summer and the beginning of autumn (23.51 %). This period corresponds to dispersion and foraging for winter. At the end of autumn, the activity started to decrease and was further reduced in winter in order to save energy during the adverse times of the year. In this period it is likely that the animals reduce their metabolism and hibernate. These road kill data in Algerian hedgehogs reflect precisely the seasonal variations of locomotor activity, and physiological variations such as reproduction (in spring and summer) and hibernation (autumn, winter)Les causes de mortalité des populations d'animaux sauvages sont variées mais une des plus importantes chez les espèces de taille moyenne est due à la circulation routière. En Europe de l'Ouest, en relation avec l'existence d'un réseau routier dense, le Hérisson est une des espèces communes les plus touchées par le trafic routier. Dans les pays d'Afrique du Nord, et en particulier en Algérie, le parc automobile et les réseaux routiers se sont développés considérablement ces dernières décennies. Le Hérisson d'Algérie (Atelerix algirus) est une des principales espèces victimes du trafic routier dans la vallée de la Soummam (entre Béjaia et Bouira). Le long de cet axe routier d'environ 100 km à très fort trafic, nous avons pu relever pendant 5 ans (de 2002 à 2006) le nombre de hérissons trouvés morts. Les relevés effectués régulièrement, chaque semaine, ont permis de dénombrer 459 animaux écrasés. La répartition des animaux par localité a montré que le Hérisson est très fréquent à la périphérie des agglomérations présentant des milieux diversifiés: zones forestières, parcelles cultivées, haies, bocages bordés par les affluents de l'Oued El Soummam. Au cours de l'année, chez le Hérisson, la mortalité routière est maximale au printemps et en été (42,92 et 34,64 % respectivement), décroît en automne et est minimale en hiver (5,66 %). Chez 404 animaux, il a été possible de déterminer le sexe et l'âge. Ainsi, nous avons pu préciser que les mâles sont observés régulièrement les premiers, au printemps à partir de mars et que, pendant cette période, plus de mâles que de femelles sont trouvés morts (45,30 % et 31,19 % respectivement). Chez les mâles, cette forte activité locomotrice printanière (maximum en mai) et estivale est à relier à la période de reproduction et au fait que leur domaine vital est plus grand que celui des femelles. Les jeunes sont surtout trouvés en fin d'été et en début d'automne (23,51 %), période qui correspond à la dispersion et à la recherche de nourriture avant l'hiver. L'activité moindre en fin d'automne, puis réduite en hiver, est à relier aux conditions défavorables du milieu et à des stratégies de conservation d'énergie incluant des épisodes de vie ralentie. Ces résultats montrent des variations saisonnières nettes de l'activité locomotrice du Hérisson d'Algérie et reflètent des variations physiologiques précises comme la reproduction (au printemps et en été) et des épisodes de torpeur (en automne et en hiver)

Intrinsic photosensitive retinal ganglion cells in the diurnal rodent, Arvicanthis ansorgei.

Intrinsically photosensitive retinal ganglion cells (ipRGCs) represent a new class of photoreceptors which support a variety of non-image forming physiological functions, such as circadian photoentrainment, pupillary light reflex and masking responses to light. In view of the recently proposed role of retinal inputs for the regulation of diurnal and nocturnal behavior, we performed the first deep analysis of the ipRGC system in a diurnal rodent model, Arvicanthisansorgei, and compared the anatomical and physiological properties of ipRGCs with those of nocturnal mice. Based on somata location, stratification pattern and melanopsin expression, we identified two main ipRGC types in the retina of Arvicanthis: M1, constituting 74% of all ipRGCs and non-M1 (consisting mainly of the M2 type) constituting the following 25%. The displaced ipRGCs were rarely encountered. Phenotypical staining patterns of ganglion cell markers showed a preferential expression of Brn3 and neurofilaments in non-M1 ipRGCs. In general, the anatomical properties and molecular phenotyping of ipRGCs in Arvicanthis resemble ipRGCs of the mouse retina, however the percentage of M1 cells is considerably higher in the diurnal animal. Multi-electrode array recordings (MEA) identified in newborn retinas of Arvicanthis three response types of ipRGCs (type I, II and III) which are distinguished by their light sensitivity, response strength, latency and duration. Type I ipRGCs exhibited a high sensitivity to short light flashes and showed, contrary to mouse type I ipRGCs, robust light responses to 10 ms flashes. The morphological, molecular and physiological analysis reveals very few differences between mouse and Arvicanthis ipRGCs. These data imply that the influence of retinal inputs in defining the temporal niche could be related to a stronger cone input into ipRGCs in the cone-rich Arvicanthis retina, and to the higher sensitivity of type I ipRGCs and elevated proportion of M1 cells.journal articleresearch support, non-u.s. gov't20132013 08 09importedFunding: Research was carried out within the scope of the Associated European Laboratory “European Laboratory for Circadian Research”, LEA CNRS-UdS-MPG (LEA No. 367) funded by the Max Planck Society, München, and CNRS, Paris. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript

Rev-erbα in the brain is essential for circadian food entrainment.

Foraging is costly in terms of time and energy. An endogenous food-entrainable system allows anticipation of predictable changes of food resources in nature. Yet the molecular mechanism that controls food anticipation in mammals remains elusive. Here we report that deletion of the clock component Rev-erbα impairs food entrainment in mice. Rev-erbα global knockout (GKO) mice subjected to restricted feeding showed reduced elevations of locomotor activity and body temperature prior to mealtime, regardless of the lighting conditions. The failure to properly anticipate food arrival was accompanied by a lack of phase-adjustment to mealtime of the clock protein PERIOD2 in the cerebellum, and by diminished expression of phosphorylated ERK 1/2 (p-ERK) during mealtime in the mediobasal hypothalamus and cerebellum. Furthermore, brain-specific knockout (BKO) mice for Rev-erbα display a defective suprachiasmatic clock, as evidenced by blunted daily activity under a light-dark cycle, altered free-running rhythm in constant darkness and impaired clock gene expression. Notably, brain deletion of Rev-erbα totally prevented food-anticipatory behaviour and thermogenesis. In response to restricted feeding, brain deletion of Rev-erbα impaired changes in clock gene expression in the hippocampus and cerebellum, but not in the liver. Our findings indicate that Rev-erbα is required for neural network-based prediction of food availability.journal article2016 Jul 062016 07 06importe

Food-anticipatory activity in Syrian hamsters: behavioral and molecular responses in the hypothalamus according to photoperiodic conditions.

When food availability is restricted, animals adjust their behavior according to the timing of food access. Most rodents, such as rats and mice, and a wide number of other animals express before timed food access a bout of activity, defined as food-anticipatory activity (FAA). One notable exception amongst rodents is the Syrian hamster, a photoperiodic species that is not prone to express FAA. The present study was designed to understand the reasons for the low FAA in that species. First, we used both wheel-running activity and general cage activity to assess locomotor behavior. Second, the possible effects of photoperiod was tested by challenging hamsters with restricted feeding under long (LP) or short (SP) photoperiods. Third, because daytime light may inhibit voluntary activity, hamsters were also exposed to successive steps of full and skeleton photoperiods (two 1-h light pulses simulating dawn and dusk). When hamsters were exposed to skeleton photoperiods, not full photoperiod, they expressed FAA in the wheel independently of daylength, indicating that FAA in the wheel is masked by daytime light under full photoperiods. During FAA under skeleton photoperiods, c-Fos expression was increased in the arcuate nuclei independently of the photoperiod, but differentially increased in the ventromedial and dorsomedial hypothalamic nuclei according to the photoperiod. FAA in general activity was hardly modulated by daytime light, but was reduced under SP. Together, these findings show that food-restricted Syrian hamsters are not prone to display FAA under common laboratory conditions, because of the presence of light during daytime that suppresses FAA expression in the wheel.journal articleresearch support, non-u.s. gov't20152015 05 13importedFunding: This work was supported by doctoral scholarship from Fundação de Amparo à Pesquisa do Estado do São Paulo (São Paulo State, Brazil) to RFDF, and by Centre National de la Recherche Scientifique and University of Strasbourg (France) to EC, VS and PP

Daily regulation of body temperature rhythm in the camel (Camelus dromedarius) exposed to experimental desert conditions.

In the present work, we have studied daily rhythmicity of body temperature (Tb) in Arabian camels challenged with daily heat, combined or not with dehydration. We confirm that Arabian camels use heterothermy to reduce heat gain coupled with evaporative heat loss during the day. Here, we also demonstrate that this mechanism is more complex than previously reported, because it is characterized by a daily alternation (probably of circadian origin) of two periods of poikilothermy and homeothermy. We also show that dehydration induced a decrease in food intake plays a role in this process. Together, these findings highlight that adaptive heterothermy in the Arabian camel varies across the diurnal light-dark cycle and is modulated by timing of daily heat and degrees of water restriction and associated reduction of food intake. The changed phase relationship between the light-dark cycle and the Tb rhythm observed during the dehydration process points to a possible mechanism of internal desynchronization during the process of adaptation to desert environment. During these experimental conditions mimicking the desert environment, it will be possible in the future to determine if induced high-amplitude ambient temperature (Ta) rhythms are able to compete with the zeitgeber effect of the light-dark cycle.journal article2014 Sep 012014 09 28importe

Attenuated Food Anticipatory Activity and Abnormal Circadian Locomotor Rhythms in Rgs16 Knockdown Mice

Regulators of G protein signaling (RGS) are a multi-functional protein family, which functions in part as GTPase-activating proteins (GAPs) of G protein α-subunits to terminate G protein signaling. Previous studies have demonstrated that the Rgs16 transcripts exhibit robust circadian rhythms both in the suprachiasmatic nucleus (SCN), the master circadian light-entrainable oscillator (LEO) of the hypothalamus, and in the liver. To investigate the role of RGS16 in the circadian clock in vivo, we generated two independent transgenic mouse lines using lentiviral vectors expressing short hairpin RNA (shRNA) targeting the Rgs16 mRNA. The knockdown mice demonstrated significantly shorter free-running period of locomotor activity rhythms and reduced total activity as compared to the wild-type siblings. In addition, when feeding was restricted during the daytime, food-entrainable oscillator (FEO)-driven elevated food-anticipatory activity (FAA) observed prior to the scheduled feeding time was significantly attenuated in the knockdown mice. Whereas the restricted feeding phase-advanced the rhythmic expression of the Per2 clock gene in liver and thalamus in the wild-type animals, the above phase shift was not observed in the knockdown mice. This is the first in vivo demonstration that a common regulator of G protein signaling is involved in the two separate, but interactive circadian timing systems, LEO and FEO. The present study also suggests that liver and/or thalamus regulate the food-entrained circadian behavior through G protein-mediated signal transduction pathway(s)

Régulation photopériodique du fonctionnement journalier des neurones sérotoninergiques du raphé dorsal et médian chez le hamster doré

Chez les mammifères, la sérotonine (5-HT) intervient dans la régulation de paramètres physiologiques et comportementaux contrôlés par l horloge circadienne et variant avec les saisons. Nous avons cherché à déterminer si la longueur du jour/24h (photopériode) influence le fonctionnement des neurones 5-HT du raphé chez une espèce photopériodique, le hamster doré. Une étude sur 24h de plusieurs paramètres sérotoninergiques chez deux groupes de hamsters placés en photopériode longue et courte a montré que la photopériode modifie la régulation journalière de la synthèse de 5-HT. Dans une deuxième partie, nous avons montré que le message photopériodique est délivré aux cellules 5-HT depuis l horloge par voie hormonale, par l intermédiaire des glucocorticoïdes (cortisol et corticostérone) et de la testostérone. Ces résultats montrent pour la première fois que le message photopériodique peut être transmis par l intermédiaire des glucocorticoïdes, hormones ubiquitaires.In mammals, serotonin (5-HT) is implicated in the regulation of circadian clock-controlled physiological and behavioral parameters which vary with seasons. We sought to determine whether daylength (photoperiod) could influence the functioning of 5-HT neurons in the raphé of a seasonal species, the Syrian hamster. A 24h-hour study of two groups of hamsters, in long and short photoperiod, has shown that photoperiod modifies the daily regulation of 5-HT synthesis. In a second part, we have shown that the photoperiodic message is delivered to 5-HT cells from the clock by hormonal route, via glucocorticoids (corticosterone and cortisol) and testosterone. These results show for the first time that the photoperiodic message can be delivered by the ubiquitous hormones glucocorticoids.STRASBOURG-Sc. et Techniques (674822102) / SudocSudocFranceF

Régulation circadienne de la tryptophane hydroxylase dans les neurones sérotoninergiques du Raphé dorsal et médian chez le Rat

Chez les mammifères, les rythmes biologiques sont générés par une horloge circadienne située dans les noyaux suprachiasmatiques (SCN). Cette horloge reçoit une innervation sérotoninergique (5-HT) issue des noyaux du Raphé médian (RM) et dorsal (RD). Si l implication de la 5-HT dans la synchronisation photique et non photique des rythmes biologiques est bien établie, la régulation de sa synthèse sur une échelle circadienne demeure peu documentée. La tryptophane hydroxylase (TPH) qui catalyse l étape limitante de la synthèse de 5-HT est un paramètre clé dans la régulation de la synthèse de ce neurotransmetteur. L ARNm de la TPH2 et la protéine TPH présentent des variations nycthémérales de leurs niveaux d expression et leurs profils rythmiques sont maintenus en obscurité constante, permettant de suggérer l existence d une régulation circadienne de la synthèse de 5-HT au sein des neurones du RM et du RD. Cette synthèse circadienne est sous le contrôle de l horloge principale via un ou plusieurs médiateurs. Parmi les nombreuses sorties des SCN, nous avons considéré le rôle joué par deux messagers rythmiques: la sécrétion de corticostérone et l activité locomotrice. L expression rythmique du gène tph2 est directement contrôlée par la sécrétion journalière de corticostérone; l ablation des glandes surrénales induit une suppression de la rythmicité de l ARNm de la TPH2 et la restauration artificielle du pic nocturne de corticostérone après surrénalectomie rétablit un profil rythmique de cet ARNm. D autre part, l activité locomotrice induite par un accès à une roue modifie les niveaux d expression du gène tph2, aussi bien chez des Rats témoins que des Rats surrénalectomisés.En conclusion, le fonctionnement circadien des neurones sérotoninergiques est contrôlé par l horloge principale via au moins deux sorties rythmiques, l une endocrine et l autre comportementale. La rétroaction de ces deux messagers sur les SCN pourrait s effectuer via les neurones sérotoninergiques du RD et du RM.Biological rhythms are generated by the endogenous pacemaker located within the hypothalamic suprachiasmatic nuclei (SCN). The serotonergic (5-HT) input to the SCN originates from two distinct serotonergic pathways: the first arising from the median raphe nucleus (MR) and the second from the dorsal raphe nucleus (DR). Tryptophan hydroxylase (TPH), the first and rate-limiting enzyme in the biosynthesis pathway of 5-HT, is expressed in the serotonergic neurons and thereby considered as a marker of 5-HT synthesis as its amount and activity reflect the intraneuronal levels of the neurotransmitter. We have demonstrated that TPH protein and TPH2 mRNA levels display circadian variations in both MR and DR. These patterns suggest a circadian synthesis of serotonin which is under the control of the master clock. The SCN are known to distribute circadian messages via neural, endocrine and behavioral outputs. Among these outputs, we examined the involvement of corticosterone daily surge and locomotor activity upon TPH2 mRNA rhythmicity. In the absence of adrenals, a complete suppression of TPH2 mRNA rhythm was observed in MR and DR. The restoration of corticosterone daily variations in adrenalectomized rats induced a TPH2 mRNA rhythmic pattern de novo, indicating that TPH2 mRNA rhythm is dependent upon daily fluctuations of glucocorticoids. Enhanced voluntary locomotor activity increased the level of TPH2 mRNA in both Raphe nuclei of control rats and was able to restore significant variation of TPH2 mRNA in adrenalectomized rats.In conclusion, both endocrine and behavioral cues can modulate tph2 expression: corticosterone surge acts as a rhythmic cue that induces the rhythmic expression of tph2 in the Raphe neurons and long-term exercise modulates the expression levels of this gene. Thus, the 5-HT neurons are a target for both endocrine and behavioral circadian cues and the 5-HT input to the SCN might feedback and influence the functioning of the clock itself.STRASBOURG-Sc. et Techniques (674822102) / SudocSudocFranceF