Wheel-running Activity Rhythms Research Articles

Circadian and sleep phenotypes in a mouse model of Alzheimer's disease characterized by intracellular accumulation of amyloid β oligomers.

Disturbances in sleep-wake and circadian rhythms may reportedly precede the onset of cognitive symptoms in the early stages of Alzheimer's disease (AD); however, the underlying mechanisms of these AD-induced sleep disturbances remain unelucidated. To specifically evaluate the involvement of amyloid beta (Aβ) oligomers in AD-induced sleep disturbances, we examined circadian and sleep phenotypes using an Aβ-GFP transgenic (Aβ-GFP Tg) mouse characterized by intracellular accumulation of Aβ oligomers. The circadian rhythm and free-running period of wheel running activity were identical between Aβ-GFP Tg and littermate wild-type mice. The durations of rapid eye movement (REM) sleep were elongated in Aβ-GFP Tg mice; however, the durations of non-REM sleep and wakefulness were unaffected. The Aβ-GFP Tg mice exhibited shifts in the electroencephalogram (EEG) power spectra toward higher frequencies in the inactive light phase. These findings suggest that the intracellular accumulation of Aβ oligomers might be associated with sleep quality; however, its impact on circadian systems is limited.

Gut microbiota depletion minimally affects the daily voluntary wheel running activity and food anticipatory activity in female and male C57BL/6J mice.

Emerging evidence has highlighted that the gut microbiota plays a critical role in the regulation of various aspects of mammalian physiology and behavior, including circadian rhythms. Circadian rhythms are fundamental behavioral and physiological processes that are governed by circadian pacemakers in the brain. Since mice are nocturnal, voluntary wheel running activity mostly occurs at night. This nocturnal wheel-running activity is driven by the primary circadian pacemaker located in the suprachiasmatic nucleus (SCN). Food anticipatory activity (FAA) is the increased bout of locomotor activity that precedes the scheduled short duration of a daily meal. FAA is controlled by the food-entrainable oscillator (FEO) located outside of the SCN. Several studies have shown that germ-free mice and mice with gut microbiota depletion altered those circadian behavioral rhythms. Therefore, this study was designed to test if the gut microbiota is involved in voluntary wheel running activity and FAA expression. To deplete gut microbiota, C57BL/6J wildtype mice were administered an antibiotic cocktail via their drinking water throughout the experiment. The effect of antibiotic cocktail treatment on wheel running activity rhythm in both female and male mice was not detectable with the sample size in our current study. Then mice were exposed to timed restricted feeding during the day. Both female and male mice treated with antibiotics exhibited normal FAA which was comparable with the FAA observed in the control group. Those results suggest that gut microbiota depletion has minimum effect on both circadian behavioral rhythms controlled by the SCN and FEO respectively. Our result contradicts recently published studies that reported significantly higher FAA levels in germ-free mice compared to their control counterparts and gut microbiota depletion significantly reduced voluntary activity by 50%.

A ketogenic diet containing medium-chain triglycerides reduces REM sleep duration without significant influence on mouse circadian phenotypes

Ketogenic diets (KDs) affect the circadian rhythms of behavior and clock gene expression in experimental animals. However, these diets were designed to simulate a fasting state; thus, whether these effects are caused by diet-induced ketogenesis or persistent starvation is difficult to distinguish. The present study aimed to define the effects of a KD containing medium-chain triglycerides (MCT-KD) that increase blood ketone levels without inducing carbohydrate starvation, on circadian rhythms and sleep regulation. Mice were fed with a normal diet (CTRL) or MCT-KD for 2 weeks. Blood β-hydroxybutyrate levels were significantly increased up to 2 mM by the MCT-KD, whereas body weight gain and blood glucose levels were identical between the groups, suggesting that ketosis accumulated without carbohydrate starvation in the MCT-KD mice. Circadian rhythms of wheel-running activity and core body temperature were almost identical, although wheel-running was slightly reduced in the MCT-KD mice. The circadian expression of the core clock genes, Per1, Per2, Bmal1, and Dbp in the hypothalamus, heart, liver, epididymal adipose tissues, and skeletal muscle were almost identical between the CTRL and MCT-KD mice, whereas the amplitude of hepatic Per2 and adipose Per1 expression was increased in MCT-KD mice. The MCT-KD reduced the duration of rapid-eye-movement (REM) sleep without affecting the duration of non-REM sleep and the duration of wakefulness. These findings suggested that the impact of ketone bodies on circadian systems are limited, although they might reduce locomotor activity and REM sleep duration.

Circadian disruption of hippocampus in an early senescence male mouse model

Age-related cognitive decline and disruptions in circadian rhythms are growing problems as the average human life span increases. Multiple strains of the senescence-accelerated mouse (SAM) show reduced life span, and the SAMP8 strain in particular has been well documented to show cognitive deficits in behavior as well as a bimodal pattern of circadian locomotor activity. However, little is known about circadian regulation within the hippocampus of these strains of mice. Here we test the hypothesis that in this early senescence model, disruption of the molecular circadian clock in SAMP8 animals drives disrupted behavior and physiology. We found normal rhythms in PER2 protein expression in the SCN of SAMP8 animals at 4 months, despite the presence of disrupted wheel-running activity rhythms at this age. Interestingly, a significant rhythm in PER2 expression was not observed in the hippocampus of SAMP8 animals, despite a significant 24-h rhythm in SAMR1 controls. We also examined time-restricted feeding as a potential strategy to rescue disrupted hippocampal plasticity. Time-restricted feeding increased long-term potentiation at Schaffer collateral-CA1 synapses in SAMP8 mice (compared to SAMR1 controls). Overall, we confirm disrupted circadian locomotor rhythms in this early senescence model (as early as 4 months) and discovered that this disruption is not due to arrhythmic PER2 levels in the SCN; however, other extra-SCN circadian oscillators (i.e., hippocampus) are likely impaired with accelerated aging.

Deletion of Six3 in post-proliferative neurons produces weakened SCN circadian output, improved metabolic function, and dwarfism in male mice

ObjectiveThe increasing prevalence of obesity makes it important to increase the understanding of the maturation and function of the neuronal integrators and regulators of metabolic function. MethodsBehavioral, molecular, and physiological analyses of transgenic mice with Sine oculis 3 (Six3) deleted in mature neurons using the Synapsincreallele. ResultsConditional deletion of the homeodomain transcription factor Six3 in mature neurons causes dwarfism and weakens circadian wheel-running activity rhythms but increases general activity at night, and improves metabolic function, without impacting pubertal onset or fertility in males. The reduced growth in 6-week-old Six3fl/fl:Synapsincre (Six3syn) males correlates with increased somatostatin (SS) expression in the hypothalamus and reduced growth hormone (GH) in the pituitary. In contrast, 12-week-old Six3syn males have increased GH release, despite an increased number of the inhibitory SS neurons in the periventricular nucleus. GH is important in glucose metabolism, muscle function, and bone health. Interestingly, Six3syn males have improved glucose tolerance at 7, 12, and 18 weeks of age, which, in adulthood, is associated with increased % lean mass and increased metabolic rates. Further, 12-week-old Six3syn males have reduced bone mineralization and a lower bone mineral density, indicating that reduced GH levels during early life cause a long-term reduction in bone mineralization. ConclusionOur study points to the novel role of Six3 in post-proliferative neurons to regulate metabolic function through SS neuron control of GH release.

Role of heterozygous and homozygous alleles in cryptochrome-deficient mice

The circadian rhythms of physiology and behavior are based on molecular systems at the cellular level, which are regulated by clock genes, including cryptochrome genes, Cry1 and Cry2. In mammals, the circadian pacemaker in the suprachiasmatic nucleus (SCN) of the hypothalamus maintains the circadian rhythms throughout the body. Cry1 and Cry2 play distinct roles in regulating the circadian rhythm. However, the different effects of manipulating clock genes in heterozygous and homozygous alleles, Cry1 and Cry2, remain unclear. Therefore, this study aimed to understand the haplosufficiency of cryptochrome genes in regulating the circadian system. We examined wheel-running activity rhythms and PER2::LUC expression rhythms in SCN slices and pituitary explants in mice. Compared with wild-type mice, Cry1−/− or Cry2−/− mice had shortened or lengthened periods in free-running behavioral rhythms and PER2::LUC expression in the SCN and pituitary gland. Cry1+/− mice had similar circadian rhythms as wild-type mice, although Cry2+/− mice had lengthened periods. The amplitude of PER2::LUC expression exhibited faster damping in Cry1−/− mice. Therefore, Cry1 deficiency affects the circadian period length and stability of the circadian system. A single allele of Cry2 deficiency affects the circadian rhythm, whereas that of Cry1 deficit is compensated.

Altered circadian activity and sleep/wake rhythms in the stable tubule only polypeptide (STOP) null mouse model of schizophrenia.

Sleep and circadian rhythm disruptions commonly occur in individuals with schizophrenia. Stable tubule only polypeptide (STOP) knockout (KO) mice show behavioral impairments resembling symptoms of schizophrenia. We previously reported that STOP KO mice slept less and had more fragmented sleep and waking than wild-type littermates under a light/dark (LD) cycle. Here, we assessed the circadian phenotype of male STOP KO mice by examining wheel-running activity rhythms and EEG/EMG-defined sleep/wake states under both LD and constant darkness (DD) conditions. Wheel-running activity rhythms in KO and wild-type mice were similarly entrained in LD, and had similar free-running periods in DD. The phase delay shift in response to a light pulse given early in the active phase under DD was preserved in KO mice. KO mice had markedly lower activity levels, lower amplitude activity rhythms, less stable activity onsets, and more fragmented activity than wild-type mice in both lighting conditions. KO mice also spent more time awake and less time in rapid eye movement sleep (REMS) and non-REMS (NREMS) in both LD and DD conditions, with the decrease in NREMS concentrated in the active phase. KO mice also showed altered EEG features and higher amplitude rhythms in wake and NREMS (but not REMS) amounts in both lighting conditions, with a longer free-running period in DD, compared to wild-type mice. These results indicate that the STOP null mutation in mice altered the regulation of sleep/wake physiology and activity rhythm expression, but did not grossly disrupt circadian mechanisms.

Memory dysfunction and anxiety-like behavior in a mouse model of chronic sleep disorders

Sleep disturbances can contribute to cognitive decline and neuropsychiatric disorders. However, the underlying mechanisms of these processes are poorly understood. The present study evaluated the effects of a chronic sleep disorder (CSD) on long-term memory formation and anxiety-like behavior in our originally established mouse model of psychophysiological stress-induced CSD characterized by disrupted circadian rhythms of wheel-running activity and sleep-wake cycles. Model mice are continuously exposed to mild stress imposed by perpetually staying on a running-wheel to avoid water. The findings of novel object recognition (NORT) and open field (OFT) tests showed that CSD impaired recognition memory and elicited anxiety-like behavior, respectively. These results suggested that the CSD impaired cognitive function and emotional status. Thus, this CSD model could be useful for studying the underlying mechanisms of neurobehavioral difficulties caused by sleep disorders. We then examined the hippocampal mRNA expression of genes associated with learning and memory, and anxiety and depression. The CSD increased the mRNA expression of Crhr1, Ngf and Phlpp1, and suppressed that of Ace, Egr2 and Slc6a4. Based on the functions of these genes, we inferred that the increase in Crhr1 mRNA was associated with the pathogenesis of psychiatric conditions, whereas mRNA levels of the other five genes were directed towards symptom relief. Upregulating hippocampal Crhr1 expression might contribute in part to the activation of corticotropin-releasing hormone (CRH)-CRH receptor1 signaling that mediates CSD-evoked mental disorders.

Dietary natural cocoa ameliorates disrupted circadian rhythms in locomotor activity and sleep-wake cycles in mice with chronic sleep disorders caused by psychophysiological stress.

Cocoa contains many chemical compounds that affect the physiological functions of experimental animals and humans. The present study used a mouse model characterized by disrupted circadian rhythms of locomotor activity and sleep-wake cycles to determine whether natural cocoa improves chronic sleep disorders (CSDs) induced by psychophysiological stress. Mice were fed a high-fat, high-sucrose diet supplemented with 2.0% natural cocoa and stressed for 30 d to induce CSDs. Dietary cocoa restored the amplitude reduction of day-night activity rhythms by improving reduced nocturnal wheel-running activities during CSDs. Electroencephalography revealed that dietary cocoa significantly ameliorated CSD-induced increases in wakefulness during the first half of the inactive phase and in nonrapid eye movement sleep during the first half of the active phase. The attenuation of circadian rapid eye movement sleep rhythms and increased electroencephalography slow-wave activity (a marker of nonrapid eye movement sleep intensity) induced by CSDs improved in mice supplemented with cocoa. Dietary cocoa notably did not affect wheel-running activity rhythms or sleep-wake cycles under normal conditions. Dietary cocoa significantly increased the hypothalamic mRNA expression of Hspa1 a that encodes HSP70 and is associated with sleep regulation. Furthermore, Hspa1 a expression was not induced by CSDs in mice supplemented with cocoa. These findings suggest that dietary cocoa exerts beneficial effects on insomnia and circadian sleep disorders induced by psychophysiological stress.

RNA Splicing Factor Mutations That Cause Retinitis Pigmentosa Result in Circadian Dysregulation.

Circadian clocks regulate multiple physiological processes in the eye, but their requirement for retinal health remains unclear. We previously showed that Drosophila homologs of spliceosome proteins implicated in human retinitis pigmentosa (RP), the most common genetically inherited cause of blindness, have a role in the brain circadian clock. In this study, we report circadian phenotypes in murine models of RP. We found that mice carrying a homozygous H2309P mutation in Pre-mRNA splicing factor 8 (Prpf8) display a lengthened period of the circadian wheel-running activity rhythm. We show also that the daily cycling of circadian gene expression is dampened in the retina of Prpf8-H2309P mice. Surprisingly, molecular rhythms are intact in the eye cup, which includes the retinal pigment epithelium (RPE), even though the RPE is thought to be the primary tissue affected in this form of RP. Downregulation of Prp31, another RNA splicing factor implicated in RP, leads to period lengthening in a human cell culture model. The period of circadian bioluminescence in primary fibroblasts of human RP patients is not significantly altered. Together, these studies link a prominent retinal disorder to circadian deficits, which could contribute to disease pathology.

Effects of testosterone on circadian rhythmicity in old mice.

Serum testosterone concentration decreases with age in humans and rodents. Accordingly, old male mice show changes in locomotor activity rhythms: a lengthened free-running period and decreased activity levels among others. To investigate whether testosterone replacement improves the age-related decline in circadian rhythmicity, we examined the effects of testosterone on the circadian rhythms of wheel running activity in old male mice. Intact male C57BL/6J mice (18-22months old) were subcutaneously implanted with silicone tubes packed with testosterone propionate (TP) or cholesterol. TP treatment significantly decreased the daily wheel running revolutions in a normal light/dark (LD) cycle and in constant darkness (DD), but did not affect the free-running period. The same experiment performed on young male gonadectomized mice (3-5months old) demonstrated that TP treatment significantly increased activity levels in both LD and DD. These results suggest that testosterone replacement exacerbates the age-related decline in circadian rhythmicity.

Dietary Heat-Killed Lactobacillus brevis SBC8803 Attenuates Chronic Sleep Disorders Induced by Psychophysiological Stress in Mice.

We previously reported that dietary heat-killed Lactobacillus brevis SBC8803 affects sleep in mice and humans. The present study examined whether SBC8803 improves psychophysiological stress-induced chronic sleep disorders (CSD) using a mouse model characterized by disrupted circadian rhythms of wheel-running activity and sleep-wake cycles. Mice were fed with a diet supplemented with 0.5% heat-killed SBC8803 for 6 wk and imposed stress-induced CSD for last 2 wk. Dietary SBC8803 suppressed the reduction in wheel-running activity induced by CSD. Electroencephalography (EEG) revealed that SBC8803 significantly restored wakefulness and increased non-rapid eye movement (NREM) sleep during the second half of the active phase during CSD. The CSD-induced reduction in EEG slow wave activity, a marker of NREM sleep intensity, during the beginning of the inactive phase was significantly improved by SBC8803 supplementation. These findings suggest that dietary heat-killed SBC8803 confers beneficial effects on insomnia and circadian sleep disorders induced by psychophysiological stress.

Electroacupuncture Intervention Regulates Circadian Rhythms by Down-regulating Per Gene Expression in Hypothalamic Suprachiasmatic Nucleus of Hepatocellular Carcinoma Mice

To observe the effect of electroacupuncture (EA) on the rhythm of running-wheel activity of hepatocellular carcinoma (HCC) mice and the expression of Per 1 and Per 2 (circadian rhythm genes) in the hypothalamic suprachiasmatic nucleus (SCN), so as to investigate its mechanism underlying regulating circadian rhythm. A total of 108 male C 57 BL / 6 J mice were randomly divided into control, HCC model and EA groups which were further assigned to six zeitbeger (environmental light-dark cycle) time (ZT) point (ZT 0, ZT 4, ZT 8, ZT 12, ZT 16 and ZT 20) subgroups. The HCC model was established by injection of H 22 cancer cell (abdominal 3rd generation, 10 µL) suspension into the larger live lobe. Mice of the control group received saline injection of the liver lobe. EA (2 Hz/15 Hz, 0.2 mA) was applied to bilateral "Ganshu" (BL 18) and "Zhiyang" (GV 9) for 15 min, once daily for 10 days. Mice of the control and model groups received the same binding-fixing to those of the EA group. Circadian running-wheel activity of 12 h∶12 h light darkness (LD) cycle (activity onset and acrophase of actogram, amplitude or peak of periodogram) was recorded by using ClockLab (ACT-500) software and analyzed by MATLAB (R 2007 b) before and after EA treatment. The pathological changes of liver cells were observed under light microscope after sectioning and H．E. staining. The expression levels of Per 1 mRNA and Per 2 mRNA in the liver tissues were determined by fluorogenic quantitative real time-PCR. (1) Following modeling, the amplitude of periodogram of running-wheel activity was significantly lowered at ZT 0, ZT 4, ZT 8, ZT 12, ZT 16, and ZT 20 relevant to the control group (P<0.05). After EA intervention, the amplitude of periodogram at ZT 8 (15：00) was considerably increased relevant to the model group (P<0.05), and the acrophase at ZT 8 was remarkably advanced (P<0.05). No significant changes were found in the onset time and periods of periodogram at the 6 time-points after modeling and EA intervention (P>0.05). (2) The expression levels of Per 1 mRNA and Per 2 mRNA in the SCN were significantly up-regulated at the 6 time-points in the model group relevant to the control group (P<0.05), and obviously down-regulated at ZT 8 after EA intervention relevant to the model group (P<0.05)．. EA can benignly regulate the rhythm of running-wheel activity of HCC mice, which may be closely related to its effect in down-regulating the expression of circadian rhythm genes Per 1 and Per 2 in the SCN.

Photic phase-response curves for cycling female mice

The photic entrainment system is critical for the internal circadian clock to be synchronized by external time cues. In nocturnal rodents, exposure to light during the early subjective night causes a phase delay, whereas it causes a phase advance during the late subjective night. This is represented by a phase-response curve (PRC). The PRC of females has not been well studied due to their estrous cycles. Our aim in this study was to understand the characteristics of photic entrainment in female cycling rodents and identify differences in photic entrainment among the stages of the estrous cycle. To establish two types of PRC, immediate PRC (iPRC) and steady state PRC (ssPRC), in each stage of the estrous cycle, we recorded circadian rhythms of wheel running activity, applying a 15-min light pulse to cycling female mice in constant darkness. In the iPRC, which was evaluated on the next day of the light pulse, the amount of phase shift in the diestrus was larger than that in the metestrus stage at circadian time (CT) 2. Similarly, the amount of phase shift in metestrus was larger than that in proestrus at CT 10. In the ssPRC, which was evaluated after completion of a new steady state, no significant estrous variations in the amount of photic phase shifts were detected for any CTs. Although these results indicate that the intrinsic photic entrainment system is not influenced by the estrous cycle, it may affect photoreception and cause sudden behavioral changes.

Parameters of photic resetting of the circadian system of a durnal rodent, the nile grass rat

Research on circadian rhythms has been hampered by the lack of a suitable rodent model with diurnal habits. The goal of this study was to characterize the parameters of photic entrainment of the circadian system of the Nile grass rat, a small rodent that can potentially serve as a model for the study of circadian rhythms in diurnal animals. The state of the circadian system was accessed through the rhythm of running-wheel activity and manipulated by photic stimulation (white light). The results indicated that the grass rat exhibits a robust rhythm of running-wheel activity with a mean free-running period of 23.9 hours (range: 23.6 to 24.3 hours). The animal is clearly diurnal and starts activity daily approximately 50 minutes before lights-on under an L12:D12 light-dark cycle. Its photic phase-response curve shows a dead zone during most of subjective day, a phase delay region during early subjective night (maximal delay: 1.5 hours), and a phase advance region during late subjective night (maximal advance: 2.2 hours). When exposed to constant illumination, the grass rat exhibits longer circadian periods as the intensity of illumination increases, with a ceiling between 100 and 1,000 lux. Finally, its range of entrainment extends from at least 23.0 to 25.0 hours (from 22.0 to 25.5 in some animals).

Chronic sleep disorder induced by psychophysiological stress induces glucose intolerance without adipose inflammation in mice

Sleep disturbances are associated with various metabolic diseases such as hypertension and diabetes. We had previously established a mouse model of a psychophysiological stress-induced chronic sleep disorder (CSD) characterized by disrupted circadian rhythms of wheel-running activity, core body temperature, and sleep-wake cycles. To evaluate the underlying mechanisms of metabolic disorders induced by CSD, we created mice with CSD for six weeks and fed them with a high-fat diet. Glucose intolerance with hyperglycemia resulted, although plasma insulin levels and body weight increases were identical between control and CSD mice. Gluconeogenesis and glycolysis were enhanced and suppressed, respectively, in the livers of CSD mice, because the mRNA expression of Pck1 was significantly increased, whereas that of Gck and Pklr were significantly decreased in the CSD mice. Adipose inflammation induced by the high-fat diet seemed suppressed by the CSD, because the mRNA expression levels of Adgre1, Ccl2, and Tnf were significantly downregulated in the adipose tissues of CSD mice. These findings suggest that CSD impair glucose tolerance by inducing gluconeogenesis and suppressing glycolysis. Hyperphasia with hypoleptinemia, hypercorticosteronemia, and increased plasma free fatty acids might be involved in the impaired glucose metabolism under a CSD. Further studies are needed to elucidate the endocrine and molecular mechanisms underlying the associations between sleep disorders and impaired glucose homeostasis that consequently causes diabetes.

Circadian wheel-running activity rhythms are unaltered by acute cage enrichment with nests and shelters

C57BL/6J inbred male mice were assessed for the effects of cotton nesting material on circadian running-wheel assays at 60, 157 and 222 days of age. The oldest mice were also tested for effects of access to plastic igloo shelters and the combination of cotton plus igloos. All mice were assayed for mean activity level, acrophase and entrained circadian period in 12:12 LD, and mean activity level and free-running period in DD for circadian wheel-running activity. There were no significant effects, at any age, of either nesting material or shelters, or the combination of both, on any measures of circadian running-wheel activity. We conclude that circadian rhythm assessment is unlikely to be significantly altered by the inclusion of enrichment materials in running wheel cages.

Disrupted reproduction, estrous cycle, and circadian rhythms in female mice deficient in vasoactive intestinal peptide.

The female reproductive cycle is gated by the circadian timing system and may be vulnerable to disruptions in the circadian system. Prior work suggests that vasoactive intestinal peptide (VIP)-expressing neurons in the suprachiasmatic nucleus (SCN) are one pathway by which the circadian clock can influence the estrous cycle, but the impact of the loss of this peptide on reproduction has not been assessed. In the present study, we first examine the impact of the genetic loss of the neuropeptide VIP on the reproductive success of female mice. Significantly, mutant females produce about half the offspring of their wild-type sisters even when mated to the same males. We also find that VIP-deficient females exhibit a disrupted estrous cycle; that is, ovulation occurs less frequently and results in the release of fewer oocytes compared with controls. Circadian rhythms of wheel-running activity are disrupted in the female mutant mice, as is the spontaneous electrical activity of dorsal SCN neurons. On a molecular level, the VIP-deficient SCN tissue exhibits lower amplitude oscillations with altered phase relationships between the SCN and peripheral oscillators as measured by PER2-driven bioluminescence. The simplest explanation of our data is that the loss of VIP results in a weakened SCN oscillator, which reduces the synchronization of the female circadian system. These results clarify one of the mechanisms by which disruption of the circadian system reduces female reproductive success.

Acute inhibition of casein kinase 1δ/ε rapidly delays peripheral clock gene rhythms.

Circadian rhythms are generated through a transcription-translation feedback loop involving clock genes and the casein kinases CSNK1D and CSNK1E. In this study, we investigated the effects of the casein kinase inhibitor PF-670462 (50 mg/kg) on rhythmic expression of clock genes in the liver, pancreas and suprachiasmatic nucleus (SCN) as well as plasma corticosterone, melatonin and running behaviour in rats and compared them to the responses to a 4 h extension of the light phase. PF-670462 acutely phase delayed the rhythmic transcription of Bmal1, Per1, Per2 and Nr1d1 in both liver and pancreas by 4.5 ± 1.3 and 4.5 ± 1.2 h, respectively, 1 day after administration. In the SCN, the rhythm of Nr1d1 and Dbp mRNA expression was delayed by 4.2 and 4 h, respectively. Despite these changes, the time of peak plasma melatonin secretion was not delayed, although the plasma corticosterone rhythm and onset of wheel-running activity were delayed by 2.1 and 1.1 h, respectively. These changes are in contrast to the effects of the 4 h light extension, which resulted in delays in peak expression of the clock genes of less than 1 h and no change in the melatonin or corticosterone rhythms. The ability of the casein kinase inhibitor to bring about large phase shifts in the rhythms of major metabolic target tissues may lead to new drugs being developed to rapidly phase adjust circadian rhythms to alleviate the metabolic impact of shift work.

Disruption of behavioral circadian rhythms induced by psychophysiological stress affects plasma free amino acid profiles without affecting peripheral clock gene expression in mice

Disordered circadian rhythms are associated with various psychiatric conditions and metabolic diseases. We recently established a mouse model of a psychophysiological stress-induced chronic sleep disorder (CSD) characterized by reduced amplitude of circadian wheel-running activity and sleep–wake cycles, sleep fragmentation and hyperphagia. Here, we evaluate day–night fluctuations in plasma concentrations of free amino acids (FAA), appetite hormones and prolactin as well as the hepatic expression of circadian clock-related genes in mice with CSD (CSD mice). Nocturnal increases in wheel-running activity and circadian rhythms of plasma prolactin concentrations were significantly disrupted in CSD mice. Hyperphagia with a decreased leptin/ghrelin ratio was found in CSD mice. Day–night fluctuations in plasma FAA contents were severely disrupted without affecting total FAA levels in CSD mice. Nocturnal increases in branched-chain amino acids such as Ile, Leu, and Val were further augmented in CSD mice, while daytime increases in Gly, Ala, Ser, Thr, Lys, Arg, His, Tyr, Met, Cys, Glu, and Asn were significantly attenuated. Importantly, the circadian expression of hepatic clock genes was completely unaffected in CSD mice. These findings suggest that circadian clock gene expression does not always reflect disordered behavior and sleep rhythms and that plasma FFA profiles could serve as a potential biomarker of circadian rhythm disorders.