12-hour Rhythm Research Articles

Temporal dynamics and composition of ocular surface microbiota in C57BL/6J mice: uncovering a 12h ultradian rhythm.

This study aimed to investigate the presence of rhythmic fluctuations in the composition, abundance, and functions of commensal core bacteria on the ocular surface of C57BL/6J mice. Male C57BL/6J mice, aged 12 weeks, were subjected to a 12-hour light/12-hour dark cycle. Ocular surface tissue samples were collected at four time points (ZT) over a 24-hour period at six-hour intervals. The core ocular surface microbiota's oscillation cycles and frequencies were assessed using 16S rRNA gene sequencing targeting the V3-V4 region, along with the JTK_CYCLE algorithm. Functional predictions of these bacteria were conducted using PICRUSt2. Deep sequencing of the ocular surface microbiota highlighted the high abundance of commensal bacteria, with Proteobacteria, Actinobacteriota, and Firmicutes collectively constituting over 90% of the total sample abundance. Among the 22 core bacterial genera, 11 exhibited robust 12-hour rhythms, including Halomonas, Pelagibacterium, Pseudomonas, Nesterenkonia, norank_f_Hyphomonadaceae, Stenotrophomonas, Anoxybacillus, Acinetobacter, Zoogloea, Brevibacillus, and Ralstonia. Further taxonomic analysis indicated significant intra-cluster similarities and inter-cluster differences at the order, family, and genus levels during ZT0/12 and ZT6/18. Community interaction networks and functional prediction analyses revealed synchronized 12-hour rhythmic oscillations in neural, immune, metabolic, and other pathways associated with symbiotic bacteria. This study demonstrates the presence of ultradian rhythmic oscillations in commensal bacteria on the ocular surface of normal C57BL/6J mice, with a 12-hour cycle. These findings suggest a crucial role for ultradian rhythms in maintaining ocular surface homeostasis in the host.

Two-meal caloric restriction induces 12-hour rhythms and improves glucose homeostasis.

Glucose metabolism is tightly regulated and disrupting glucose homeostasis is a hallmark of many diseases. Caloric restriction (CR), periodic fasting, and circadian rhythms are interlinked with glucose metabolism. Here, we directly investigated if CR depends on periodic fasting and circadian rhythms to improve glucose metabolism. CR was implemented as two‐meals per day (2M‐CR), provided at 12‐hour intervals, and compared with one meal per day CR, mealtime (MT), and ad libitum (AL) feeding. The 2M‐CR impacted the circadian rhythms in blood glucose, metabolic signaling, circadian clock, and glucose metabolism gene expression. 2M‐CR significantly reduced around the clock blood glucose and improved glucose tolerance. Twenty‐four‐hour rhythms in mTOR signaling and gene expression observed under AL, MT, and CR, became 12‐hour rhythms in 2M‐CR. The 12‐hour rhythms in behavior, gene expression, and signaling persisted in fasted mice, implicating some internal regulation. The study highlights that the reduction in caloric intake rather than meal frequency and duration of fasting is essential for metabolic reprograming and improvement in glucose metabolism and provides evidence on food‐entrained molecular pacemaker, which can be uncoupled from the light‐entrained circadian clock and rhythms.

Brain-Specific Rescue of Clock Reveals System-Driven Transcriptional Rhythms in Peripheral Tissue

The circadian regulatory network is organized in a hierarchical fashion, with a central oscillator in the suprachiasmatic nuclei (SCN) orchestrating circadian oscillations in peripheral tissues. The nature of the relationship between central and peripheral oscillators, however, is poorly understood. We used the tetOFF expression system to specifically restore Clock function in the brains of ClockΔ19 mice, which have compromised circadian clocks. Rescued mice showed normal locomotor rhythms in constant darkness, with activity period lengths approximating wildtype controls. We used microarray analysis to assess whether brain-specific rescue of circadian rhythmicity was sufficient to restore circadian transcriptional output in the liver. Compared to Clock mutants, Clock-rescue mice showed significantly larger numbers of cycling transcripts with appropriate phase and period lengths, including many components of the core circadian oscillator. This indicates that the SCN oscillator overcomes local circadian defects and signals directly to the molecular clock. Interestingly, the vast majority of core clock genes in liver were responsive to Clock expression in the SCN, suggesting that core clock genes in peripheral tissues are intrinsically sensitive to SCN cues. Nevertheless, most circadian output in the liver was absent or severely low-amplitude in Clock-rescue animals, demonstrating that the majority of peripheral transcriptional rhythms depend on a fully functional local circadian oscillator. We identified several new system-driven rhythmic genes in the liver, including Alas1 and Mfsd2. Finally, we show that 12-hour transcriptional rhythms (i.e., circadian “harmonics") are disrupted by Clock loss-of-function. Brain-specific rescue of Clock converted 12-hour rhythms into 24-hour rhythms, suggesting that signaling via the central circadian oscillator is required to generate one of the two daily peaks of expression. Based on these data, we conclude that 12-hour rhythms are driven by interactions between central and peripheral circadian oscillators.

Amplified amplitudes of circadian rhythms and nighttime hypotension in patients with chronic fatigue syndrome: improvement by inopamil but not by melatonin.

Fatigue is an important symptom of a disturbed circadian rhythm. To date, no studies of circadian rhythms in patients with chronic fatigue syndrome (CFS) have been published. The objectives of the study were to study rhythms of heart rate and systolic and diastolic blood pressure in patients with chronic fatigue syndrome compared with age-matched normotensive controls and to study the effects of melatonin and inopamil on such rhythms. Ambulatory blood pressure (ABP) measurements (Space Lab, Inc, validated) of 18 patients with CFS were made according to the 1987 U.S. Center for Disease Control Criteria, and measurements of 12 age-matched normotensive controls were used in a cosinor analysis of the two groups. The effects of melatonin and inopamil on ABP were studied subsequently in four patients in an 8-week open-label evaluation. One patient was hypertensive (diastolic blood pressure > 90 mm Hg at least once every 4 hours), and was, therefore, excluded. The data of the remaining 17 patients (15 women, 2 men) revealed a significant 12-hour rhythm in heart rate and 24-hour rhythm in systolic and diastolic blood pressure with 95% confidence intervals not significantly different from sinusoidal patterns. Although these rhythms were synchronous with the control group rhythms, their amplitudes were not and showed, respectively, 2.8, 2.8, and 9.0 times the size of the control group rhythms (p < 0.001, p < 0.001, and p < 0.0001, respectively). Systolic blood pressures in the patients with CFS were consistently below 100 mm Hg during the nighttime. In a subsequent pilot study of four patients from the study population treated with melatonin 4 mg daily and inopamil 200 mg daily for 4 weeks, inopamil reduced nighttime hypotension (p < 0.05), whereas melatonin increased nighttime hypotension (p < 0.02). Patients with CFS have increased amplitudes of circadian rhythms and systolic blood pressures consistently below 100 mm Hg during the nighttime. Positive inotropic compounds may be beneficial in such patients, but melatonin may not be.

Analysis of cocaine chronotoxicology in an urban ED

To describe the chronotoxicology of cocaine and its potential impact on emergency department (ED) staffing and services, Drug Abuse Warning Network (DAWN) data from a single urban university ED were retrospectively reviewed. The DAWN data reviewed spanned an 11-year period (1/1/83 through 12/31/93), and 3,762 patients were enrolled. Patients were included if the ED records included documentation of recent cocaine abuse prior to presentation to the ED. Of the 3,762 study patients, 1,609 (43%) had documentation of recent cocaine use: 506 (32%) had used cocaine alone, 614 (38%) had used cocaine and ethanol in combination, and 489 (30%) had used cocaine in combination with other drugs. For all patients using cocaine, there were two significant rhythms ( P < .05) identified: a circadian rhythm that peaked at 1800 and a 12-hour rhythm that peaked at approximately noon and midnight. A significant rhythmicity was found among cocaine-using patients who presented during the study period. Increased or shift-adjusted staffing focusing specifically on psychosocial services, detoxification, and security during these peak hours may provide more efficient emergent care for this subpopulation of patients.

Chronobiological parameters of pain sensitivity of rats and mice

Circadian and 12-hour rhythms of pain sensitivity to stimuli of different origin were detected in male rats and mice by cosinor analysis in chronobiological experiments. The minimal pain sensitivity to thermal and electric stimulation was observed in rats during the first half of the light phase of 24 h, while in the case of mechanical stimulation it was observed during the dark phase. Biorhythms of sensitivity of mice and rats to thermal pain exposure were similar. Hence, the chronobiological organization of pain sensitivity depends mainly on the type of nociceptive stimulation.

Circadian rhythms of circulating NK cells in healthy and human immunodeficiency virus-infected men.

Antiviral immunity involves NK cells, which circulate rhythmically every 24 hours. We have investigated circadian and 12-hour rhythms in the peripheral count of circulating NK cells in 15 men infected with human immunodeficiency virus (HIV) and 13 healthy controls. We analyzed three phenotypes using double-labeling with monoclonal antibodies and flow cytometry assessment: CD3- CD16+, CD3-CD57+, and CD2+CD3-. A statistical validation of time-dependent differences was achieved if significance (p < 0.05) was validated both with analysis of variance and cosinor. The circadian rhythm had a similar asymmetric waveform for the three phenotypes and is homogeneous on an individual basis. The circulating NK cell count peaked in the early morning and was low at night. A circadian rhythm and a circahemidian harmonic characterized all phenotypes in healthy subjects. We considered two groups of HIV-infected men: those who were asymptomatic (eight) and those with acquired immune deficiency syndrome (AIDS) (seven). Circadian changes in NK cell count were similar in both subgroups and in healthy controls. The circadian pattern was also consistent among individual patients. Asymptomatic HIV-infected men (early-stage disease) exhibited more pronounced 12-hour rhythmicity than did patients with AIDS or controls. The circulation of NK cells does not appear to share the same synchronizer(s) as other circulating T- or B-lymphocyte subsets. Thus, HIV infection gradually abolished circadian rhythmicity in circulating T and B cells, whereas it did not disturb that in NK cells.

Rhythms in Glutamine Synthetase Activity, Energy Charge, and Glutamine in Sunflower Roots

Roots of sunflower plants (Helianthus annuus L. var. Mammoth Russian) subjected to L12:D12, L18:D6, and L12:D12 followed by continuous light all display rhythms of about 12 hours for glutamine synthetase (GS) activity (transferase reaction) with one peak in the ;light phase' and one in the ;dark phase.' Root energy charge (EC = ATP+(1/2)ADP/ATP+ADP+AMP) is directly correlated with GS, but the GS rhythm is better explained as the result of a rhythmic adenine nucleotide ratio (ATP/ADP+AMP) that regulates enzyme activity through allosteric modification. When L12:D12 plants are subjected to free-running conditions in continuous darkness, only diurnal rhythms for GS and EC, with peaks in the dark phase, remain. The 12-hour root rhythms for GS and EC appear to be composed of two alternating rhythms, one a diurnal, light-dependent, incompletely circadian light phase rhythm and the other a light-independent, circadian dark phase rhythm.Only glutamine, of the root amino acids, displays cyclical changes in concentration, maintaining under all conditions a 12-hour rhythm that is consistently synchronized with, but nearly always inversely correlated with, GS and EC rhythms.

Change in diurnal temperature rhythm in manic-depressive illness.

The temperatures of six manic-depressive patients were taken every three hours consecutively for many weeks, covering at least one depressive and one manic episode in each patient. While the daily temperature curve was essentially normal in manic phases, with pronounced 24-hour rhythm, during depression the daytime temperatures appeared disorganised, often falling during the morning instead of rising, and with suggestions of a 12-hour rhythm. It may be useful to look on manic-depressive illness as resulting from a desynchronisation of circadian rhythms and to compare the pharmacologies of temperature regulation and mood regulation in psychosis.