Zeitgeber Research Articles

Circadian patterns of behaviour change during pregnancy in mice.

Food intake and activity adapt during pregnancy to meet the increased energy demands. In comparison to non-pregnant females, pregnant mice consume more food, eating larger meals during the light phase, and reduce physical activity. How pregnancy changes the circadian timing of behaviour was less clear. We therefore randomised female C57BL/6J mice to mating for study until early (n=10), mid- (n=10) or late pregnancy (n=11) or as age-matched, non-pregnant controls (n=12). Mice were housed individually in Promethion cages with a 12h light-12h dark cycle [lights on at 07.00h, Zeitgeber (ZT)0] for behavioural analysis.Food intake between ZT10 and ZT11 was greater in pregnant than non-pregnant mice on days 6.5-12.5 and 12.5-17.5. In mice that exhibited a peak in the last 4h of the light phase (ZT8-ZT12), peaks were delayed by 1.6h in the pregnant compared with the non-pregnant group. Food intake immediately after dark-phase onset (ZT13-ZT14) was greater in the pregnant than non-pregnant group during days 12.5-17.5. Water intake patterns corresponded to food intake. From days 0.5-6.5 onwards, the pregnant group moved less during the dark phase, with decreased probability of being awake, in comparison to the non-pregnant group. The onset of dark-phase activity, peaks in activity, and wakefulness were all delayed during pregnancy. In conclusion, increased food intake during pregnancy reflects increased amplitude of eating behaviour, without longer duration. Decreases in activity also contribute to positive energy balance in pregnancy, with delays to all measured behaviours evident from mid-pregnancy onwards. KEY POINTS: Circadian rhythms synchronise daily behaviours including eating, drinking and sleep, but how these change in pregnancy is unclear. Food intake increased, with delays in peaks of food intake behaviour late in the light phase from days 6.5 to 12.5 of pregnancy, in comparison to the non-pregnant group. The onset of activity after lights off (dark phase) was delayed in pregnant compared with non-pregnant mice. Activity decreased by ∼70% in the pregnant group, particularly in the dark (active) phase, with delays in peaks of wakefulness evident from days 0.5-6.5 of pregnancy onwards. These behavioural changes contribute to positive energy balance during pregnancy. Delays in circadian behaviours during mouse pregnancy were time period and pregnancy stage specific, implying different regulatory mechanisms.

Circadian dependency of microglial heme oxygenase-1 expression and inflammation determine neuronal injury in hemorrhagic stroke

BackgroundThe heme oxygenase-1 (HO-1) enzyme pathway is of crucial importance in the removal of toxic blood components and regulation of neuroinflammation following hemorrhagic stroke. Although a circadian pattern dependency in the incidence and severity of hemorrhagic stroke exists, it is unknown whether the activity of the HO-1 system in the context of hemorrhagic injury also exhibits circadian dependency. We hypothesized that the circadian regulation of microglial HO-1 would determine the extent of neuroinflammation and neuronal injury in a murine model of subarachnoid hemorrhage (SAH).MethodsIn vitro expression patterns of HO-1 and circadian rhythm genes were analyzed in the microglial BV-2 cell line and primary microglia (PMG) using Western blot and qPCR. PMG isolated from Hmox1fl/fl and LyzM-Cre-Hmox1fl/fl mice were used to evaluate the role of microglial HO-1. We further investigated the in vivo relevance in a murine subarachnoid hemorrhage (SAH) model using Hmox1fl/fl and LyzM-Cre-Hmox1fl/fl mice with myeloid cell HO-1 deficiency, inducing SAH at different zeitgeber (ZT) times and analyzing the expression of HO-1 and the circadian control gene Period-2 (Per-2), respectively. Furthermore, we measured the inflammatory cytokine Monocyte Chemoattractant Protein-1 (MCP-1) in the cerebrospinal fluid of SAH patients in correlation with clinical outcome.ResultsHO-1 baseline expression and response to CO with blood exposure depended on ZT. In vitro expression of circadian control genes was de-synchronized in LyzM-Cre-Hmox1fl/fl PMG and did not respond to exogenous CO exposure. We found that circadian rhythm plays a crucial role in brain damage after SAH. At ZT2, we observed less phagocytic function, more vasospasm and increased microglial activation. CO reduced mortality at ZT12 in HO-1 deficient mice and reduced the difference between ZT2 and ZT12 in the inflammatory response. Induction of MCP-1 in the CSF from SAH patients was time-dependent and correlated with the expression of circadian control genes, SAH severity, functional impairment and delirium.ConclusionsOur data point towards a crucial role for the HO-1 enzyme system and circadian control in neuronal injury after a hemorrhagic stroke.

Circadian variation in hematotoxicity of the antineoplastic agent “5 Fluorouracil (5 FU)” in female rats and its relevance to chronotherapy

ABSTRACT 5-Fluorouracil (5-FU) is an antineoplastic drug. Although 5-FU is effective in targeting cancer cells, it also affects healthy cells, which can lead to clear haematological toxicity. The present study aimed to determine whether the haematological toxicity of 5-FU varies over a 24-hour period. Female rats were synchronised to a 12/12 light-dark (L/D) cycle. Rats were injected with 300 mg/kg 5-FU at six different circadian stages (1, 5, 9, 13, 17, 21 Zeitgebers (ZT)). The maximum rhythmic alteration was observed when 5-FU was administered at 5-ZT, while the minimum was observed at 21-ZT. These results suggest that the haematological toxicity of 5-FU is maximal when administered in the middle of the light-rest phase, while the haematological tolerance is optimal when 5-FU is administered at the end of the dark phase in rats, which corresponds to the end of the daytime activity phase in human patients.

Dysbiosis of the Saliva Microbiome in Patients With Polycystic Ovary Syndrome.

Significant differences in salivary microbiota communities between polycystic ovary syndrome (PCOS) patients and healthy controls have been reported, and interestingly, some salivary microbiota exhibit diurnal oscillation in healthy people. However, whether the diurnal oscillation of salivary microbiota is present in PCOS patients is unknown. In this study, we describe the differences in the saliva microbiome between the PCOS group and the control group at different time points over 24 h. 16S rRNA gene amplicon sequencing was performed on salivary and fecal samples from 10 PCOS patients and 10 healthy controls, and salivary samples were collected at 6-h intervals over 24 h (Zeitgeber (ZT)0, ZT6, ZT12, and ZT18). Among the salivary samples, those from the PCOS group showed significant differences from those of the control group at each time point. Differences were evident in taxa level and metabolic pathways. Interestingly, we found that PCOS disrupted the diurnal rhythm of the salivary microbiota abundance, as determined in the group of healthy women. In addition, no similar changes were found in PCOS patients and controls between the oral and fecal microbiota, including differential microbiota at the phylum level. In this study, significant differences in the composition of the salivary microbiota between PCOS and healthy women were detected at different time points. We also showed that the diurnal rhythm of relative abundance of the salivary microbiota was disrupted in patients with PCOS, which might be related to development of oral-related diseases and systematic metabolic disorders.

Pregnancy, but not dietary octanoic acid supplementation, stimulates the ghrelin-pituitary growth hormone axis in mice.

Circulating growth hormone (GH) concentrations increase during pregnancy in mice and remain pituitary-derived. Whether abundance or activation of the GH secretagogue ghrelin increase during pregnancy, or in response to dietary octanoic acid supplementation, is unclear. We therefore measured circulating GH profiles in late pregnant C57BL/6J mice and in aged-matched non-pregnant females fed with standard laboratory chow supplemented with 5% octanoic or palmitic (control) acid (n = 4-13/group). Serum total and acyl-ghrelin concentrations, stomach and placenta ghrelin mRNA and protein expression, Pcsk1 (encoding prohormone convertase 1/3) and Mboat4 (membrane bound O-acyl transferase 4) mRNA were determined at zeitgeber (ZT) 13 and ZT23. Total and basal GH secretion were higher in late pregnant than non-pregnant mice (P < 0.001), regardless of diet. At ZT13, serum concentrations of total ghrelin (P = 0.004), but not acyl-ghrelin, and the density of ghrelin-positive cells in the gastric antrum (P = 0.019) were higher, and gastric Mboat4 and Pcsk1 mRNA expression were lower in pregnant than non-pregnant mice at ZT23. In the placenta, ghrelin protein was localised mostly to labyrinthine trophoblast cells. Serum acyl-, but not total, ghrelin was lower at mid-pregnancy than in non-pregnant mice, but not different at early or late pregnancy. In conclusion, dietary supplementation with 5% octanoic acid did not increase activation of ghrelin in female mice. Our results further suggest that increases in maternal GH secretion throughout murine pregnancy are not due to circulating acyl-ghrelin acting at the pituitary. Nevertheless, time-dependent increased circulating total ghrelin could potentially increase ghrelin action in tissues that express the acylating enzyme and receptor.

Roles of HDAC3-Orchestrated Circadian Clock Gene Oscillations in Diabetic Rats Following Myocardial Ischemia / Reperfusion Injury

Background: Circadian clock has been closely related to the development of diabetes mellitus and cardiovascular disease; the disruption of circadian clock exacerbates myocardial ischemia/reperfusion injury (MI/RI). HDAC3 is a key component of the circadian negative feedback loop by recruitmenting the expression pattern of circadian nuclear receptor Rev-erbα, then to maintain the stability of circadian gene such as BMAL1. In this research, we explored the mechanism of HDAC3-orchestrated Rev-erbα/BMAL1 pathway in increasing MI/RI vulnerability of diabetes, and its relationship with mitophagy. Methods: Streptozocin (STZ) was used to establish type 1 diabetes by intraperitoneal injection. After 8 weeks, the diabetic and non-diabetic rats were exposed to MI/RI by ligating the left anterior descending coronary artery (LDA) for 30 minutes and reperfusion for 120 minutes at four time points of zeitgeber (ZT) 0, 6, 12 and 18. In vitro experiments, primary cardiomyocytes with or without HDAC3 siRNA and Rev-erbα siRNA exposed to hypoxia/reoxygenation (H/R). Findings: Circadian clock gene oscillations were rapidly attenuated in diabetic I/RI hearts, versus sham and/or the non-diabetic I/RI hearts, in accord with circadian mitophagy. By utilizing AAV-HDAC3 to knockdown HDAC3 expression, HDAC3 deficiency significantly attenuated diabetic MI/RI associated with increased autophagy activation. The expression of HDAC3 and Rev-erbα in cardiomyocytes was increased under high glucose condition with decreased BMAL1 expression and autophagy level. After H/R stimulation, the cell injury was obviously increased with upregulated HDAC3 and Rev-erbα expression and decreased BMAL1 level. Moreover, high glucose aggravated H/R injury compared with low glucose by reducing autophagy level, increasing the levels of HDAC3 and Rev-erbα and down-regulating BMAL1 expression. HDAC3 and Rev-erbα siRNA can alleviate high glucose and H/R-induced injury by up-regulating BMAL1 expression and mitophagy levels. Interpretation: These findings suggest that in the MI/RI of diabetic rat, the circadian clocks were rapidly impaired then to inhibit mitophagy; cardiac-targeted manipulation of HDAC3-orchestrated Rev-erbα/BMAL1 pathway may be the mechanism of the decreased toleration to ischemia with a circadian dependent variability. Funding Statement: This study was supported by grants from the National Natural Science Foundation of China 81970722, 81671891 and 81701891. Declaration of Interests: The authors declare that there is no conflict of interests regarding the publication of this paper. Ethics Approval Statement: Experimental protocols were implemented after being reviewed and approved by the Laboratory Animal Welfare & Ethics Committee (IACUC) of Renmin Hospital of Wuhan University. All researchers have obtained the certificate of professional laboratory animal technology in Hubei Province.

VGLUT1 Binding to Endophilin or Intersectin1 and Dynamin Phosphorylation in a Diurnal Context

Glutamate is concentrated into synaptic vesicles (SV) by the vesicular glutamate transporters (VGLUT) 1 and 2. VGLUTs also harbor a Na+/Pi-transport activity when residing at the plasma membrane. Here we aimed to identify whether the diurnal switches of VGLUT1 parallels interactions with or modification of endocytic proteins.VGLUT1 and dynamin bind to SH3 domains of either endophilin (Enph) or intersectin 1 (ITSN1) harboring one or five SH3 domains A–E, respectively. We followed diurnal variations by pull down experiments using SH3 fusion protein and brains from mice entrained in a strict 24-h light–dark cycle (12-h light Zeitgeber (ZT) 0, 6; 12-h dark ZT 12 and 18). In pull downs with EnphSH3 interaction with VGLUT1 is high during the resting light and reduced during the active dark period while dynamin binding does not vary. This diurnal light/dark pattern depends on a functional period 2 gene and changes when animals are kept in complete darkness. Pull downs using ITSN1SH3 A reveal diurnally varying binding of VGLUT1 with slightly reduced VGLUT1/dynamin ratios at the beginning of the light (ZT 0) or the dark (ZT 12) period. Phosphorylation increases binding of VGLUT1 but not of dynamin to EnphSH3. In contrast binding of dynamin to ITSN1SH3 A decreases under phosphorylating conditions with no changes in VGLUT1 binding. Phosphorylation of dynamin at Ser 774 is high at ZT 6 and ZT 18 when more VGLUT1 is at the plasma membrane but low at ZT 0 and ZT 12 the diurnal peaks of VGLUT1 endocytosis. In conclusion the diurnally varying endocytosis of VGLUT1 involves differential interactions with the SH3 domains of Enph and ITSN1 and correlates with the de-phosphorylation of dynamin1.

β-carotene ameliorates CUS-induced circadian alternations of locomotor activity and melatonin patterns in rats

Circadian and stress systems have a crucial role in adaptation of organisms to environmental challenges. This study investigates the ability of Oscillatoria brevis (O. brevis) β-carotene extract (βC) in modulating the circadian alternations of locomotor activity (LA) and serum melatonin (M) rhythms under chronic unpredictable stress (CUS) in rats. Twenty rats (5 rats/group) were used in monitoring LA using running wheels. Eighty rats (20 rats/group) were used in observing circadian serum M profile. Rats were randomly divided into four groups, viz. control, βC-treated, CUS-exposed, and “βC-treated&CUS-exposed” groups. CUS-exposure was applied for 21 days. One hour before exposure, βC was daily administered (10 mg/kg), intraperitoneally (IP). Blood was sampled at 6-h intervals for 5 rats/time point at Zeitgeber (ZT) 3, 9, 15, and 21. Results demonstrated that unstressed rats exhibited circadian M pattern and nocturnal LA rhythm with acrophase around ZT 21 and ZT 15, respectively. CUS-exposure revealed a disturbance in these patterns. Phase shifting of M and LA profiles was recorded. A decrease M acrophase and a significant decrease in LA (p < 0.05) were recorded at ZT 9. Daily βC administration in stressed rats modulates the CRs alternation induced by CUS. It may be concluded that βC ameliorated the induced alternations in circadian rhythms.

Can Watching TV at Night Affect Your Mood

As light is the most potent zeitgeber, could nighttime exposure to light alter circadian rhythms and mood that are entrained to environmental

Progress in studies of the reciprocal interaction between sleep disorders and Alzheimer's disease

Alzheimer's disease (AD) is a common neurodegenerative disease in the elderly, and is the most common cause of dementia. Epidemiological studies have discovered that, 44% of patients with AD are associated with sleep disorders and (or) circadian rhythm disorders. Now there are growing evidences indicating that interstitial fluid amyloid-β protein (A β) levels exhibit circadian rhythm fluctuation, and sleep disorders will accelerate the process of Aβ deposition, which may act as a risk factor of AD, suggesting the possible reciprocal interaction between sleep disorders and AD. The mechanism is not yet completely clear. Sleep disorders may be related with the impairments of both sleep-wake regulating system, circadian rhythm regulating system and the change of zeitgeber in AD. Sleep disorders would affect neuronal activity, neurotransmitter secretion, and as a stressor affecting A β processing and metabolism, thus accelerate the pathological process of AD. This paper reviewed the progress in the studies of reciprocal interaction between sleep disorders and Alzheimer's disease and the possible mechanisms.

Effects of 1800-MHz Radiofrequency Fields on Circadian Rhythm of Plasma Melatonin and Testosterone in Male Rats

Radiofrequency fields (RF) at 1800 MHz are known to affect melatonin (MEL) and testosterone in male rats, but it remains to be determined whether RF affected circadian rhythm of these plasma hormones. Male Sprague-Dawley rats were exposed to 1800-MHz RF at 208 μw/cm2 power density (SAR: 0.5762 W/kg) at different zeitgeber (ZT) periods of the day, including 0 (ZT0), 4 (ZT4), 8 (ZT8), 12 (ZT12), 16 (ZT16), and 20 (ZT20) h. RF exposure was 2 h/d for 32 d. From each rat, the concentrations of plasma MEL and testosterone were determined in plasma after RF exposure and compared with controls. The results confirmed the existence of circadian rhythms in the synthesis of MEL and testosterone, but revealed an inverse relationship in peak phase of these rhythms. These rhythms were disturbed after exposure to RF, with the effect being more pronounced on MEL than testosterone. The most pronounced effect of RF exposure on MEL and testosterone appears to be in rats exposed to RF at ZT 16 and ZT0 h, respectively. Data suggest that regulation of testosterone is controlled by MEL and that MEL is more sensitive to RF exposure.

Scheduled exercise modulates daily rhythms of behavior, physiology, and gene expression in mice

Light is the primary environmental signal that synchronizes the circadian system coordinating the temporal patterning of behavior and underlying biological processes. Other cues such as activity may be able to influence the output of this system. In our studies, we used scheduled wheel access to manipulate magnitude and phasing of locomotor activity and explored subsequent effects on daily rhythms of heart rate (HR) and body temperature in WT mice. Mice were subject to 5 wheel access conditions: no access, free access, Zeitgeber (ZT) 12–18, ZT 18–24 and ZT 0–6 access. We found that giving the mice the opportunity to run on a wheel can significantly increase activity levels and therefore considered as exercise. Furthermore, shifting the phase of exercise with wheel access altered the temporal patterning of rhythms in HR and body temperature. We also examined the effects of wheel access induced exercise on the molecular clock underlying the generation of circadian rhythms. Using the Per2:LUC knockin mouse, we found that exercise at ZT 0–6 shifted the phase of PER2:LUC expression in the SCN and peripheral tissues. We conclude that wheel access induced exercise can be used to shape daily rhythms of activity in mice and influence the rhythms of other biological outputs such as HR and body temperature. Activity can also influence the phasing of PER2:LUC expression in the SCN and peripheral tissues.

Coordination of the transcriptome and metabolome by the circadian clock

The circadian clock governs a large array of physiological functions through the transcriptional control of a significant fraction of the genome. Disruption of the clock leads to metabolic disorders, including obesity and diabetes. As food is a potent zeitgeber (ZT) for peripheral clocks, metabolites are implicated as cellular transducers of circadian time for tissues such as the liver. From a comprehensive dataset of over 500 metabolites identified by mass spectrometry, we reveal the coordinate clock-controlled oscillation of many metabolites, including those within the amino acid and carbohydrate metabolic pathways as well as the lipid, nucleotide, and xenobiotic metabolic pathways. Using computational modeling, we present evidence of synergistic nodes between the circadian transcriptome and specific metabolic pathways. Validation of these nodes reveals that diverse metabolic pathways, including the uracil salvage pathway, oscillate in a circadian fashion and in a CLOCK-dependent manner. This integrated map illustrates the coherence within the circadian metabolome, transcriptome, and proteome and how these are connected through specific nodes that operate in concert to achieve metabolic homeostasis.

Timeless is a critical gene in the diapause of silkworm, Bombyx mori

The diapause is a specific physiological phenomenon induced by circadian zeitgebers of temperature and photoperiod at the stage of maternal embryonic development. In this research, the authors investigated the linkage of diapause and the regulation of circadian rhythm by inspecting the expression profiles of a circadian clock gene timeless (tim) under diapause-inducing temperature and photoperiod inBombyx mori. The results show that the level of tim mRNA was higher in 25LL than in 20LD or in 15DD during the late embryonic stages (EAT 2520-3240°C·h), which is the most effective inducing period of temperature and photoperiod on diapause in the progeny. The tim transcription level was significantly higher in darkness than in light during postembryonic development, which contradicted the results found in the pupa and adult stages at 25°C. Exposure of maternal embryos to a high temperature (25°C) resulted in up-regulated levels of tim mRNA in egg stage of progeny. However, this up-regulation only occurred before egg-age at 72 h, which was a pivot for diapause and diapause termination. In conclusion, diapause-inducing temperature and photoperiod of incubation directly affect tim gene expression throughout the life cycle of B. mori. Key words: Circadian clock gene, timless gene, diapause, temperature, photoperiod, Bombyx mori.

Ketogenic diet treatment abolishes seizure periodicity and improves diurnal rhythmicity in epileptic Kcna1‐null mice

Seizures are known to perturb circadian rhythms in humans as well as in animal models of epilepsy. However, it is unknown whether treatment of the underlying epilepsy restores normal biologic rhythms. We asked whether: (1) seizure activity is characterized by diurnal rhythmicity, (2) chronically epileptic mice exhibit impaired rest-activity rhythms, and (3) treatment with the anticonvulsant ketogenic diet (KD) improves such perturbations. Chronically epileptic Kcna1-null mice were fed either a standard diet (SD) or KD for 4 weeks and subjected to continuous video-EEG (electroencephalography) and actigraphy monitoring for 3-5 days to assess seizure activity and rest-activity cycles. Seizure activity in Kcna1-null mice demonstrated diurnal rhythmicity, peaking at zeitgeber (ZT)2.30 +/- 1.52. Rest-activity rhythms of epileptic mice were significantly disrupted. Whereas locomotor activity for wild-type mice peaked at ZT15.45 +/- 0.28 (ZT14:26-ZT16:51), peak activity of epileptic mice was more unpredictable, occurring over a 12.4 h range (ZT06:33-ZT18:57). In six of nine epileptic mice, peak activity was delayed to ZT17.42 +/- 0.38, whereas peak activity was advanced to ZT10.00 +/- 1.26 in the remaining mice. Treatment with the KD abolished seizure periodicity and restored the rest-activity rhythm to values resembling those of wild-type mice (i.e., activity peaking at ZT16.73 +/- 0.67). Kcna1-null mice experience seizures with 24-h periodicity and impaired circadian behavior. KD reduces the number and periodicity of seizures and restores normal behavioral rhythms, suggesting that this nonpharmacologic therapy may benefit biologic rhythm disturbances in epileptic patients.

I’ve Got Rhythm, Who Could Ask for Anything More (to Avoid Relapse)?

Light, as a natural zeitgeber, is well known to affect mood. Social cues (e.g., meals, meetings, or exercise) also may entrain circadian rhythm. Does lack of social rhythms or their disruption result in mood instability that precipitates the onset of affective episodes? These researchers examined social rhythm regularity and its effect on vulnerability …

Anticipation of a daily meal: a process of learning due to entrainment

SUMMARY In many animals, single daily meals are anticipated in physiological and behavioral activities as especially documented by the ‘anticipatory activity’ (AA) of rats prior to the meals, and the early arrivals of bees at a food dish offered daily at a certain time of day. Both phenomena have been described as a process of ‘learning’ but can as well be explained as resulting from the entrainment of a circadian rhythm, provided it can be shown that periodic meal timing has the capacity of a Zeitgeber. The paper demonstrates the effects of restricted daily feeding (RF) on bees, rats, and monkeys, with an introductory reference to preliminary studies with mice. Colonies of bees (Apis mellifera capensis Eschscholtz) kept in constant illumination (LL) were either fed ad libitum or trained to forage at a sugar dish presented for 2 hr in intervals? of 23, 24, or 25 hr. The activity rhythm of each colony was freerunning in LL during ad libitum feeding, and well entrained by the feeding cycle during RF; the du...