Predictability of individual circadian phase during daily routine for medical applications of circadian clocks

Background: Circadian timing of treatments can largely improve tolerability and efficacy in patients. Thus, drug metabolism and cell cycle are controlled by molecular clocks in each cell, and coordinated by the core body temperature 24-hour rhythm, which is generated by the hypothalamic pacemaker. Individual circadian phase is currently estimated with questionnaire-based chronotype, center-of-rest time, dim light melatonin onset (DLMO), or timing of CBT maximum (acrophase) or minimum (bathyphase). Methods: We aimed at circadian phase determination and read-out during daily routine in volunteers stratified by sex and age. We measured (i) chronotype; (ii) q1min CBT using two electronic pills swallowed 24-hours apart; (iii) DLMO through hourly salivary samples from 18:00 to bedtime; (iv) q1min accelerations and surface temperature at anterior chest level for seven days, using a tele-transmitting sensor. Circadian phases were computed using cosinor and Hidden-Markov modelling. Multivariate regression identified the combination of biomarkers that best predicted core temperature circadian bathyphase. Results: Amongst the 33 participants, individual circadian phases were spread over 5h10min (DLMO), 7h (CBT bathyphase) and 9h10 min (surface temperature acrophase). CBT bathyphase was accurately predicted, i.e. with an error <1h for 78.8% of the subjects, using a new digital health algorithm (INTime), combining time-invariant sex and chronotype score, with computed center-of-rest time and surface temperature bathyphase (adjusted R-squared = 0.637). Conclusion: INTime provided a continuous and reliable circadian phase estimate in real time. This model helps integrate circadian clocks into precision medicine and will enable treatment timing personalisation following further validation

Hypothalamic tanycytes generate acute hyperphagia through activation of the arcuate neuronal network

Hypothalamic tanycytes are chemosensitive glial cells that contact the cerebrospinal fluid in the third ventricle and send processes into the hypothalamic parenchyma. To test whether they can activate neurons of the arcuate nucleus, we targeted expression of a Ca2+-permeable channelrhodopsin (CatCh) specifically to tanycytes. Activation of tanycytes ex vivo depolarized orexigenic (neuropeptide Y/agouti-related protein; NPY/AgRP) and anorexigenic (proopiomelanocortin; POMC) neurons via an ATP-dependent mechanism. In vivo, activation of tanycytes triggered acute hyperphagia only in the fed state during the inactive phase of the light–dark cycle

Hypothalamic ventricular ependymal thyroid hormone deiodinases are an important element of circannual timing in the siberian hamster (Phodopus sungorus)

Exposure to short days (SD) induces profound changes in the physiology and behaviour of Siberian hamsters, including gonadal regression and up to 30% loss in body weight. In a continuous SD environment after approximately 20 weeks, Siberian hamsters spontaneously revert to a long day (LD) phenotype, a phenomenon referred to as the photorefractory response. Previously we have identified a number of genes that are regulated by short photoperiod in the neuropil and ventricular ependymal (VE) cells of the hypothalamus, although their importance and contribution to photoperiod induced physiology is unclear. In this refractory model we hypothesised that the return to LD physiology involves reversal of SD expression levels of key hypothalamic genes to their LD values and thereby implicate genes required for LD physiology. Male Siberian hamsters were kept in either LD or SD for up to 39 weeks during which time SD hamster body weight decreased before increasing, after more than 20 weeks, back to LD values. Brain tissue was collected between 14 and 39 weeks for in situ hybridization to determine hypothalamic gene expression. In VE cells lining the third ventricle, expression of nestin, vimentin, Crbp1 and Gpr50 were down-regulated at 18 weeks in SD photoperiod, but expression was not restored to the LD level in photorefractory hamsters. Dio2, Mct8 and Tsh-r expression were altered by SD photoperiod and were fully restored, or even exceeded values found in LD hamsters in the refractory state. In hypothalamic nuclei, expression of Srif and Mc3r mRNAs was altered at 18 weeks in SD, but were similar to LD expression values in photorefractory hamsters. We conclude that in refractory hamsters not all VE cell functions are required to establish LD physiology. However, thyroid hormone signalling from ependymal cells and reversal of neuronal gene expression appear to be essential for the SD refractory response

Tele-monitoring of cancer patients’ rhythms during daily life identifies actionable determinants of circadian and sleep disruption

The dichotomy index (I < O), a quantitative estimate of the circadian regulation of daytime activity and sleep, predicted overall cancer survival and emergency hospitalization, supporting its integration in a mHealth platform. Modifiable causes of I < O deterioration below 97.5%—(I < O)low—were sought in 25 gastrointestinal cancer patients and 33 age- and sex-stratified controls. Rest-activity and temperature were tele-monitored with a wireless chest sensor, while daily activities, meals, and sleep were self-reported for one week. Salivary cortisol rhythm and dim light melatonin onset (DLMO) were determined. Circadian parameters were estimated using Hidden Markov modelling, and spectral analysis. Actionable predictors of (I < O)low were identified through correlation and regression analyses. Median compliance with protocol exceeded 95%. Circadian disruption—(I < O)low—was identified in 13 (52%) patients and four (12%) controls (p = 0.002). Cancer patients with (I < O)low had lower median activity counts, worse fragmented sleep, and an abnormal or no circadian temperature rhythm compared to patients with I < O exceeding 97.5%—(I < O)high—(p < 0.012). Six (I < O)low patients had newly-diagnosed sleep conditions. Altered circadian coordination of rest-activity and chest surface temperature, physical inactivity, and irregular sleep were identified as modifiable determinants of (I < O)low. Circadian rhythm and sleep tele-monitoring results support the design of specific interventions to improve outcomes within a patient-centered systems approach to health care

Dual signal transduction pathways activated by TSH receptors in rat primary tanycyte cultures

Tanycytes play multiple roles in hypothalamic functions, including sensing peripheral nutrients and metabolic hormones, regulating neurosecretion and mediating seasonal cycles of reproduction and metabolic physiology. This last function reflects the expression of TSH receptors in tanycytes, which detect photoperiod-regulated changes in TSH secretion from the neighbouring pars tuberalis. The present overall aim was to determine the signal transduction pathway by which TSH signals in tanycytes. Expression of the TSH receptor in tanycytes of 10-day-old Sprague Dawley rats was observed by in situ hybridisation. Primary ependymal cell cultures prepared from 10-day-old rats were found by immunohistochemistry to express vimentin but not GFAP and by PCR to express mRNA for Dio2, Gpr50, Darpp-32 and Tsh receptors that are characteristic of tanycytes. Treatment of primary tanycyte/ependymal cultures with TSH (100 IU/l) increased cAMP as assessed by ELISA and induced a cAMP-independent increase in the phosphorylation of ERK1/2 as assessed by western blot analysis. Furthermore, TSH (100 IU/l) stimulated a 2.17-fold increase in Dio2 mRNA expression. We conclude that TSH signal transduction in cultured tanycytes signals via Gαs to increase cAMP and via an alternative G protein to increase phosphorylation of ERK1/2

Calcium imaging in hypothalamic cells

International audienceCalcium imaging is a powerful tool to explore communication in neural networks. The hypothalamus is the region of the brain that regulates functions such as reproduction, appetite, lactation, stress or hydration. Understanding the orchestration of neural networks in this region is a fundamental question of neuroscience. Calcium imaging can be used and performed not only on dissociated cells and acute brain slices but also on living animals. To date, the ideal experimental setup to explore nutrient sensing in the hypothalamus is acute brain calcium imaging. The technique readily incorporates pharmacological tools, as it uses bath applications or patch puffing. The technique can also be coupled with electrophysiological recordings. Here is presented the technical protocol for calcium imaging on acute brain slices of mice hypothalami

Plasticité saisonnière cérébrale chez deux espèces de hamsters : le hamster djoungarien (Phodopus sungorus) et le hamster syrien (Mesocricetus auratus)

L'alternance des saisons est un phénomène astronomique et périodique qui a pour effet de changer les paramètres environnementaux. Par conséquent, les animaux, doivent s'adapter à ces variations en modifiant, par exemple leur poids, leur pelage, ou la période de reproduction. Les animaux utilisent la longueur du jour (la photopériode) pour synchroniser ces fonctions avec les saisons. Les variations jour/nuit sont perçues par le cerveau et transmises à la glande pinéale qui va sécréter la mélatonine uniquement pendant la nuit. Le signal mélatoninergique va diffuser dans l'ensemble de l'organisme dont le cerveau et l'axe hypothalamo-hypophysaire. Les neurones de l'hypothalamus sécrètent le GnRH (gonadotropin-releasing hormone) qui va activer les cellules gonadotropes de l'hypophyse permettant ainsi la libération de la FSH (follicle-stimulating hormone) et de la LH (luteinizing hormone). Ces deux hormones vont réguler la gamétogenèse et la synthèse des hormones sexuelles au niveau des gonades. Les changements saisonniers de la sécrétion de la mélatonine aboutissent donc au repos sexuel de l'animal en hiver. Ces changements saisonniers de l'activité reproductrice affectent donc les niveaux des stéroïdes sexuels circulants. Les stéroïdes sexuels vont rétroagir sur les structures hypothalamiques et extrahypothalamiques. Dans ce contexte, nous avons étudié les effets de ces deux hormones, régulées de façon saisonnière, sur le cerveau, chez deux espèces d'hamsters. Ces travaux ont permis de mettre en évidence des phénomènes de plasticité neuronale et gliale structurale ou neurochimique contrôlés par les deux principaux médiateurs des saisons, la mélatonine et les stéroïdes sexuels.The alternation of seasons is an astronomical and periodical phenomenon which induces changes in environmental parameters. As a consequence, animals have to adapt to these variations and for that different strategies have been developed to save energy in winter, such as variations in body weight, fur or reproductive period. Animals use photoperiod (i.e. day length) to synchronise these functions to the seasons. To decode photoperiod and adapt their physiology and behaviour, mammals rely on their photoneuroendocrine system, which includes the pineal gland and its rhythmic release of melatonin. Melatonin secretion occurs exclusively at night, and transmits the photoperiodic information to the rest of the body including the brain, and the hypothalamo-hypophyseal axis. Neurones in the hypothalamus secrete GnRH (gonadotropin-releasing hormone) which will activate the gonadotropes in the pituitary gland to produce and release FSH (follicle-stimulating hormone) and LH (luteinizing hormone). These hormones will stimulate gametogenesis and the synthesis of sex steroids at the level of the gonads. We know that the lenghtening melatonin signal towards winter leads to reproductive quiescence. Also sex steroids can feedback on the hypothalamic and extrahypothalamic structures. Accordingly, the general goal of this work was to study the effects of these two photoperiodically regulated hormones, on the brain, in two hamster species. Our results showed evidences of neuronal and glial structural or neurochemical plasticity controlled by the principal mediators of seasons, melatonin and sex steroids

Plasticité saisonnière cérébrale chez deux espèces de hamsters : le hamster djoungarien (Phodopus sungorus) et le hamster syrien (Mesocricetus auratus)

L'alternance des saisons est un phénomène astronomique et périodique qui a pour effet de changer les paramètres environnementaux. Par conséquent, les animaux, doivent s'adapter à ces variations en modifiant, par exemple leur poids, leur pelage, ou la pérThe alternation of seasons is an astronomical and periodical phenomenon which induces changes in environmental parameters. As a consequence, animals have to adapt to these variations and for that different strategies have been developed to save energy i

Seasonal cerebral plasticity in two hamster species: the Djungarian hamster (Phodopus sungorus) and the Syrian hamster (Mesocricetus auratus)

L’alternance des saisons est un phénomène astronomique et périodique qui a pour effet de changer les paramètres environnementaux. Par conséquent, les animaux, doivent s’adapter à ces variations en modifiant, par exemple leur poids, leur pelage, ou la période de reproduction. Les animaux utilisent la longueur du jour (la photopériode) pour synchroniser ces fonctions avec les saisons. Les variations jour/nuit sont perçues par le cerveau et transmises à la glande pinéale qui va sécréter la mélatonine uniquement pendant la nuit. Le signal mélatoninergique va diffuser dans l’ensemble de l’organisme dont le cerveau et l’axe hypothalamo-hypophysaire. Les neurones de l’hypothalamus sécrètent le GnRH (gonadotropin-releasing hormone) qui va activer les cellules gonadotropes de l’hypophyse permettant ainsi la libération de la FSH (follicle-stimulating hormone) et de la LH (luteinizing hormone). Ces deux hormones vont réguler la gamétogenèse et la synthèse des hormones sexuelles au niveau des gonades. Les changements saisonniers de la sécrétion de la mélatonine aboutissent donc au repos sexuel de l’animal en hiver. Ces changements saisonniers de l’activité reproductrice affectent donc les niveaux des stéroïdes sexuels circulants. Les stéroïdes sexuels vont rétroagir sur les structures hypothalamiques et extrahypothalamiques. Dans ce contexte, nous avons étudié les effets de ces deux hormones, régulées de façon saisonnière, sur le cerveau, chez deux espèces d’hamsters. Ces travaux ont permis de mettre en évidence des phénomènes de plasticité neuronale et gliale structurale ou neurochimique contrôlés par les deux principaux médiateurs des saisons, la mélatonine et les stéroïdes sexuels.The alternation of seasons is an astronomical and periodical phenomenon which induces changes in environmental parameters. As a consequence, animals have to adapt to these variations and for that different strategies have been developed to save energy in winter, such as variations in body weight, fur or reproductive period. Animals use photoperiod (i.e. day length) to synchronise these functions to the seasons. To decode photoperiod and adapt their physiology and behaviour, mammals rely on their photoneuroendocrine system, which includes the pineal gland and its rhythmic release of melatonin. Melatonin secretion occurs exclusively at night, and transmits the photoperiodic information to the rest of the body including the brain, and the hypothalamo-hypophyseal axis. Neurones in the hypothalamus secrete GnRH (gonadotropin-releasing hormone) which will activate the gonadotropes in the pituitary gland to produce and release FSH (follicle-stimulating hormone) and LH (luteinizing hormone). These hormones will stimulate gametogenesis and the synthesis of sex steroids at the level of the gonads. We know that the lenghtening melatonin signal towards winter leads to reproductive quiescence. Also sex steroids can feedback on the hypothalamic and extrahypothalamic structures. Accordingly, the general goal of this work was to study the effects of these two photoperiodically regulated hormones, on the brain, in two hamster species. Our results showed evidences of neuronal and glial structural or neurochemical plasticity controlled by the principal mediators of seasons, melatonin and sex steroids

Molecular pathways involved in seasonal body weight and reproductive responses governed by melatonin

Seasonal mammals typically of temperate or boreal habitats use the predictable annual cycle of daylength to initiate a suite of physiological and behavioural changes in anticipation of adverse environmental winter conditions, unfavourable for survival and reproduction. Daylength is encoded as the duration of production of the pineal hormone melatonin, but how the melatonin signal is decoded has been elusive. From the studies carried out in birds and mammals together with the advent of technologies such as microarray analysis of gene expression, progress has been achieved to demystify how seasonal physiology is regulated in response to the duration of melatonin signalling. The critical tissue for the action of melatonin is the pars tuberalis (PT) where melatonin receptors are located. At the molecular level, regulation of cyclic adenosine monophosphate (cAMP) signalling in this tissue is likely to be a key event for melatonin action, either an acute inhibitory action or sensitization of this pathway by prolonged stimulation of melatonin receptors reflecting durational melatonin presence. Melatonin action at the PT has been shown to have both positive and negative effects on gene transcription, incorporating components of the circadian clock as part of the mechanism of decoding the melatonin signal and regulating thyrotrophin-stimulating hormone (TSH) expression, a key output hormone of the PT. Microarray analysis of gene expression of PT tissue exposed to long and short photoperiods has identified important new genes that may be regulated by melatonin and contributing to the seasonal regulation of TSH production by this tissue. In the brain, tanycytes lining the third ventricle of the hypothalamus and regulation of thyroid hormone synthesis by PT-derived TSH in these cells are now established as an important component of the pathway leading to seasonal changes in physiology. Beyond the tanycyte, identified changes in gene expression for neuropeptides, receptors and other signalling molecules pinpoint some of the areas of the brain, the hypothalamus in particular, that are likely to be involved in the regulation of seasonal physiology