Significant Circadian Changes Research Articles

Circadian metabolites for evaluating the timing of bloodstain deposition: A preliminary study

Metabolites, as products of cellular metabolism, can provide a wealth of biological information and are less susceptible to degradation than other biomarkers due to their low molecular weight. Due to these properties, metabolites can be used as valuable biomarkers for forensic investigations. Knowing the timing of deposition of bloodstain could help to reconstruct crime scenes, draw conclusions about the time of the crime, and narrow down the circle of possible suspects. Previous studies have indicated that the concentration of some metabolites in blood is subject to circadian changes. However, the circadian metabolites of bloodstains have been still unclear. A total of sixty-four bloodstain samples were prepared under real conditions in three time categories (morning/noon (09:00 h ∼ 17:00 h), afternoon/evening (18:00 h ∼ 23:00 h) and night/early morning (24:00 h ∼ 08:00 h)). Fifty metabolites of bloodstains with significant differences were identified in the three time categories. Twenty-eight of these metabolites exhibited significant circadian changes. Finally, three independently contributing circadian metabolites were selected to build the logistic regression model, with an area under the curve of 0.91, 0.84 and 0.87 for the prediction of bloodstain deposition time in the morning/noon, afternoon/evening and night/early morning, respectively. The study indicated that circadian metabolites can be used for evaluating the timing of bloodstain deposition. This would provide a valuable perspective for analyzing the deposition time of biological traces in forensic investigations.

The role of the SIRT1-BMAL1 pathway in regulating oxidative stress in the early development of ischaemic stroke

Oxidative stress is the primary cause of ischaemic stroke and is closely related to circadian rhythm. However, the mechanism by which circadian rhythm regulates oxidative stress in ischaemic stroke remains elusive. The Silent Information Regulator 1 (SIRT1) controls circadian rhythm by activating the transcription of the circadian clock core protein Basic Helix-Loop-Helix ARNT Like 1 (BMAL1) through deacetylation. Studies have shown that the SIRT1-BMAL1 pathway can regulate oxidative stress. To investigate its correlation with oxidative stress, we examined the expression levels and influencing factors of SIRT1-BMAL1 at different times in ischaemic stroke patients and analyzed their clinical indexes, oxidative stress, and inflammatory factor indicators. The expression levels of oxidative stress and inflammatory factor indicators, including malondialdehyde (MDA), superoxide dismutase (SOD), interleukin-6 (IL-6), and tumor necrosis factor-a (TNF-α), SIRT1, and BMAL1, were detected in ischaemic stroke patients within 4.5 h of onset and in non-stroke patients. Patients were divided into four subgroups based on onset time: subgroup 1 (0:00–05:59); subgroup 2 (06:00–11:59); subgroup 3 (12:00–17: 59); and subgroup 4 (18:00–23:59). Our results showed higher MDA, IL-6, and TNF-α levels, and lower SOD, SIRT1, and BMAL1 levels in ischaemic stroke patients compared to control patients (P < 0.05). Among the four subgroups, the content of MDA, IL-6, and TNF-α was highest in patients with ischaemic stroke onset from subgroup 2 (06:00–11:59), while the expression levels of SOD, BMAL1, and SIRT1 were lowest in patients with ischaemic stroke in subgroup 2. Additionally, myeloperoxidase (MPO) reached the highest value showing the same trends consistent with MDA, IL-6, and TNF-ɑ and opposite trends consistent with SOD, BMAL1, and SIRT1. However, triglycerides (TGs), total cholesterol (TC), low-density lipoprotein (LDL), high-density lipoprotein (HDL), immediate blood glucose, immediate diastolic blood pressure, immediate systolic blood pressure, and homocysteine (HCY) did not show any statistically significant circadian rhythm changes (P > 0.05). Our findings suggest that the SIRT1-BMAL1 pathway may be involved in early oxidative stress in ischaemic stroke, which may be related to MPO.

Effect of Constant Illumination on the Function of the Hypothalamic-Pituitary-Adrenal Axis in Nonhuman Primates.

We studied the effect of constant illumination on the effects of administration of arginine vasopressin (AVP), one of the most important regulators of the key adaptive hypothalamic-pituitary-adrenal (HPA) axis under basal conditions and during stress, as well as on the circadian rhythm of activity of HPA axis and the pineal gland in laboratory primates. In young adult female rhesus monkeys exposed to constant illumination for 7 weeks, the rise in the concentration of ACTH and cortisol in response to administration of AVP was markedly reduced in comparison with both the basal period and with the control group of animals. In addition, a destructive effect of constant lighting on circadian rhythm of cortisol secretion was observed in the absence of significant circadian changes in melatonin secretion. The inhibitory effect of constant illumination on the function of the HPA axis under basal conditions and under conditions of its activation can reduce the body's adaptive abilities.

Light-induced and circadian expressions of melanopsin genes opn4xa and opn4xb in the eyes of juvenile grass puffer Takifugu alboplumbeus.

Animals regulate a variety of aspects of physiology according to environmental light conditions via nonvisual opsins such as melanopsin. In order to study photic regulation of fish physiology, expression changes of the genes for melanopsin (opn4xa and opn4xb) and effects of light on them were examined in juvenile grass puffer Takifugu alboplumbeus using quantitative real-time PCR. In the brain of juvenile fish, no significant diurnal nor circadian changes were observed in opn4x mRNA levels. On the other hand, in the eyes, the mRNA level of opn4xa showed a significant diurnal rhythm with a peak at Zeitgeber time (ZT) 4, while no apparent circadian changes were observed. The mRNA level of opn4xb in the eyes showed a diurnal change similar to that of opn4xa, while it showed a significant circadian change. Furthermore, continuous exposure to light during a subjective night significantly increased the mRNA levels of opn4xa in the eyes at ZT24, suggesting that light induces gene expression of opn4xa in the eyes and that the induction occurs only during the night-day transition period. These results suggest that Opn4xa and Opn4xb play differential roles in the eyes of juvenile grass puffer to mediate the physiological effects of environmental light information.

Circadian clock regulates the shape and content of dendritic spines in mouse barrel cortex.

Circadian rhythmicity affects neuronal activity induced changes in the density of synaptic contacts and dendritic spines, the most common location of synapses, in mouse somatosensory cortex. In the present study we analyzed morphology of single- and double-synapse spines under light/dark (12:12) and constant darkness conditions. Using serial electron micrographs we examined the shape of spines (stubby, thin, mushroom) and their content (smooth endoplasmic reticulum, spine apparatus), because these features are related to the maturation and stabilization of spines. We observed significant diurnal and circadian changes in the shape of spines that are differentially regulated: single-synapse spines remain under circadian clock regulation, while changes of double-synapse spines are driven by light. The thin and mushroom single-synapse spines, regardless of their content, are more stable comparing with the stubby single-synapse spines that show the greatest diversity. All types of double-synapse spines demonstrate a similar level of stability. In light/dark regime, formation of new mushroom single-synapse spines occurs, while under constant darkness new stubby single-synapse spines are formed. There are no shape preferences for new double-synapse spines. Diurnal and circadian alterations also concern spine content: both light exposure and the clock influence translocation of smooth endoplasmic reticulum from dendritic shaft to the spine. The increasing number of mushroom single-synapse spines and the presence of only those mushroom double-synapse spines that contain spine apparatus in the light phase indicates that the exposure to light, a stress factor for nocturnal animals, promotes enlargement and maturation of spines to increase synaptic strength and to enhance the effectiveness of neurotransmission.

Glycyrrhizin treatment ameliorates post-traumatic stress disorder-like behaviours and restores circadian oscillation of intracranial serotonin.

Post-traumatic stress disorder (PTSD) has become a major disease that threatens human health. Neurotransmitters and the amygdala are found to be critical in the development and maintenance of PTSD. We aim to investigate the role of glycyrrhizin in treating PTSD. Contextual fear extinction and elevated plus maze test were applied to evaluate the anxiety and fear memory. Microdialysis and high-performance liquid chromatography were used to analyze the expression of amygdala neurotransmitters in PTSD animal models and to verify the effects of glycyrrhizin on major neurotransmitters. The protein levels of tryptophan hydroxylase 2 (TPH2) were examined by western bolt. Glycyrrhizin treatment significantly reduced anxiety and fear memory after 1 and 7days of PTSD modelling. In addition, glycyrrhizin treatment restored the circadian rhythm changes of serotonin and TPH2. The present study found a significant circadian rhythm change of serotonin in the amygdala in PTSD rats. Besides, glycyrrhizin treatment restored the altered serotonin diurnal fluctuations, which raises important implications for PTSD treatment.

Abstract 13027: Risk of Sudden Cardiac Arrest According to the Time of STEMI Occurrence: the e-MUST Study

Introduction: STEMI mortality decreased drastically during the last decades, and out-of-hospital sudden cardiac arrest (SCA) has become its main mode of death. The risk of out-of-hospital SCA according to the timing of STEMI occurrence has not been assessed. Hypothesis: The risk of SCA, prior to hospital admission, differs according to the timing of STEMI occurrence. Methods: Data were taken from a prospective pre-hospital study (e-MUST study) on all STEMI patients managed by emergency medical services in Paris and its suburbs between January 2006 and December 2010. In this area, emergency calls are routed to the closest dispatch center and regulated by physicians who send, in the field, an ambulance with a physician on board in case of suspected acute myocardial infarction. Pre-hospital EKGs are obtained for all patients and those presenting STEMI are included in the study. We assessed the rate of SCA, prior to hospital admission, according to the timing of STEMI occurrence (4 hours-time intervals starting at midnight). Results: Among the 8,112 STEMI patients enrolled (mean age (SD) 61.6 (14.3) years, 78% males), 452 patients (5.6%) developed out-of-hospital SCA. We observed significant circadian change in the rate of SCA per STEMI, with a progressive increase between 4am and 8pm, followed by a decrease between 8pm and 4am (P=0.0009). The peak rate of SCA per STEMI occurred in the 4pm-8pm time interval (7.7%), while the lowest rate was seen between 4am and 8am (4.2%) (Figure). Conclusions: The risk of STEMI-related SCA is almost 2-fold higher in STEMI occurring in the late afternoon hours. A better understanding of patients’ characteristics, circumstances of occurrence, and pre-hospital care is needed to eventually reduce the risk of SCA promptly after STEMI diagnosis in the field.

Dynamic approachs for system identification applied to deformation study of the dams

To dynamical study of the dams, the prediction of occurred deformation caused by hydrostatic and hydrodynamic pressures during the operation phase as well as the designing phase is necessary. The reservoir water changes also the permanent variations of atmospheric temperature especially in the areas where there are significant seasonal and circadian changes in conditions are important factors to “dynamic system” of the dams. The aim of this paper is to present an applied dynamic method to identify the body of the dam as a dynamic system and to predict its behavior in the variable environmental conditions based on the monitoring observations. Non-parametric methods such as cross-covariance and coherence method are applied for system identification of the dam based on time series of input signal of measured forces and output signal of deformation measurements. The main feature of this paper is using the weighting function method which enables “System Identification” of the dam as a dynamic system, to model the deformation of the dam. The applied weighting function method benefits from measurements of effective factors on system of the dam also the deformation monitoring measurements from different sensors. For practical applicability of the method for a dam, Masjed–Soleiman “earth–dam” in Iran has been chosen. A wide range of instruments has been installed inside the dam to control the deformation; therefore multiple measurements are available for analysis. Since changing atmospheric temperature has not an important role in geotechnical study of an earth-dam singly, the authors decided to investigate the environmental condition such as atmospheric temperature and reservoir water-level changes as input signal to the “dam-sensors-combination” system. Here the authors carried out their investigation using seven epochs of geodetic measurements between 2000 and 2008, moreover the measurements of four anchors inside an installed rod-extensometer between 2007 and 2013, settlement observations on settlement-plates in different levels between 2008 and 2013, and a long-time series of the daily observations of three installed soil-extensometers between 2005 and 2013. A significant correlation between temperature changes and soil-extensometer observations has been determined, besides the coherence method leads to common periods of 351 days between input and output time series. The weighting function method is applied to model the deformation of the dam using deformation measurements of installed soil-extensometer with temperature and water-level changes as effective sources. The RMS of difference between the estimated dam deformations from weighting function model compared to original measurements was calculated at 0.039 mm also from the point of correlation the original deformation measurements and modeled deformations are correlated at 95 %. The RMS of the difference between measurements and the predicted dam deformations using the weighting function model was calculated at 0.057 mm leading to a correlation value of 91 %. If the absolute values are transformed in percentage of the deformation, the maximum error of prediction is 10 %. The results show the success of weighting function method to model the deformation observations of the dam affected by input factors. One of the most important achievements of this paper is to draw a distinction between temperature as a systematic error sources and the other effective factors on the settlement observations of the earth-dam via comparison of the results of non-parametric methods on different sensors.

Performance of blue- and green-sensitive photoreceptors of the cricket Gryllus bimaculatus

The compound eye of the cricket Gryllus bimaculatus contains a specialized dorsal rim area (DRA) populated by distinct blue-sensitive photoreceptors responsible for perception of polarized light. The rest of the eye is dominated by green-sensitive photoreceptors. Using patch clamp we studied dissociated ommatidia of nocturnal adults and diurnal eight-instar nymphs with the goals (1) of characterizing the biophysical properties of cricket photoreceptors in general and (2) describing the functionally dissimilar blue- and green-sensitive photoreceptors in terms of voltage-gated channel composition and signal coding. Despite different lifestyles, adult and nymph photoreceptors were indistinguishable. No significant circadian changes were observed in K⁺ currents. In contrast, prominent differences were seen between blue- and green-sensitive photoreceptors. The former were characterized by relatively low absolute sensitivity, high input resistance, slow quantum bumps with long latencies, small light-induced and K⁺ currents and low steady-state depolarization. Information rate, a measure of photoreceptor performance calculated from voltage responses to bandwidth-limited white noise-modulated light contrast, was 87 ± 8 bits s⁻¹ in green-sensitive photoreceptors vs. 59 ± 14 bits s⁻¹ in blue-sensitive photoreceptors, implying a limited role of DRA in the perception of visual contrasts. In addition, evidence of electrical coupling between photoreceptors is presented.

Pigment-dispersing hormone in Daphnia interneurons, one type homologous to insect clock neurons displaying circadian rhythmicity.

We report identification of a beta-type pigment-dispersing hormone (PDH) identical in two water flea species, Daphnia magna and Daphnia pulex. It has been identified by cloning of precursors, chromatographic isolation from tissue extracts followed by immunoassays and de novo-mass spectrometric sequencing. The peptide is restricted to a complex system of distinct interneurons in the brain and visual ganglia, but does not occur in neurosecretory cells projecting to neurohemal organs as in decapod crustaceans. Thirteen neuron types individually identified and reconstructed by immunohistochemistry were almost identical in terms of positions and projection patterns in both species. Several neurons invade and form plexuses in visual ganglia and major brain neuropils including the central body. Five neuron types show contralateral pathways and form plexuses in the lateral, dorsal, or postlateral brain neuropils. Others are local interneurons, and a tritocerebral neuron connects the protocerebrum with the neuropil of the locomotory second antenna. Two visual ganglia neuron types lateral to the medulla closely resemble insect medulla lateral circadian clock neurons containing pigment-dispersing factor based upon positional and projectional criteria. Experiments under 12:12h light/dark cycles and constant light or darkness conditions showed significant circadian changes in numbers and activities of one type of medulla lateral PDH neuron with an acrophase in the evening. This simple PDH system shows striking homologies to PDH systems in decapod crustaceans and well-known clock neurons in several insects, which suggests evolutionary conservation of an ancient peptidergic interneuronal system that is part of biological clocks.

Effects of dosing time and schedule on cisplatin-induced nephrotoxicity in rats.

Renal dysfunction induced by a single injection of cisplatin depends on the timing of the dose. However, the effects of repeated administration of cisplatin on time-dependent toxicity have not been evaluated despite the fact that in clinical practice high doses are repeatedly injected at intervals or low doses are administered daily. We studied chrononephrotoxicity in rats after weekly or daily cisplatin injections. Weekly high doses (5 mg kg(-1)) or daily low doses (1.2 mg kg(-1)) of cisplatin were injected at four time points (3, 9, 15 and 21 h after the light was turned on (HALO)) for 3 weeks. Changes in body weight after weekly cisplatin administration were independent of the timing of the doses. In the group that received daily cisplatin, the loss in body weight in the 3 HALO group was smaller than in animals receiving injections at 15 and 21 HALO (P < 0.05 and 0.001, respectively). The blood urea nitrogen and serum creatinine levels in the control rats showed a significant circadian change (peak at 15 HALO and trough at 9 HALO), but these parameters were markedly elevated in both trials and their circadian variations were disturbed. In conclusion, cisplatin-induced nephrotoxicity was the lowest at 3HALO compared with other time points of both dose regimens.

Changes of Isoflavone Profile in the Hypocotyls and Cotyledons of Soybeans during Dry Heating and Germination

A gradient reversed-phase high-performance liquid chromatography (HPLC) method has been developed to be suitable for the separation and determination of 12 isoflavones in soybeans. Profiles of daidzein, genistein, glycitein, and their malonyl-, acetyl-, and nonconjugated beta-glycosides were determined in cotyledons and hypocotyls of soybeans as affected by dry heating and germination. The results showed that the compositions and concentrations of isoflavones were remarkably different in the two parts of soybeans, and hypocotyls contained a much higher content of isoflavones than cotyledons (e.g., 7.8-fold higher). In hypocotyls, daidzein and its glycoside conjugates (59.6%) were the most abundant isoflavones, being followed by glycitein (26.6%) and genistein series (13.8%). In cotyledons, genistein and its glycoside conjugates (61.9%) were the main isoflavones, being followed by daidzein series (38.1%), and no glycitein series was found. Both hypocotyls and cotyledons contained remarkably high amounts of malonylglycosides (69.1 and 69.4%, respectively) and beta-glycosides (27.1 and 25.4%), and only a very small quantity of aglycones (3.8 and 5.2%) and no acetylglycosides were detected. Acetylglycosides and beta-glycosides were the thermal decarboxylation and deesterification products, respectively, of malonylglycosides, which were thermally unstable. The relative rates of decarboxylation and deesterification reactions were different in cotyledons and hypocotyls at different temperatures. During the process of germination, beta-glycosides decreased, and malonylglycosides and aglycones increased, and then, malonylglycosides were the major fractions in germinating soybeans. Interestingly, the present study occasionally found a significant circadian change between malonylglycosides and aglycones with a nocturnal increase of aglycones and decrease of malonylglycosides during germination, and even aglycones became the most abundant forms at night. However, this mechanism is yet to be investigated.

Key clinical considerations for demonstrating the utility of preclinical models to predict clinical drug‐induced torsades de pointes

While the QT/QTc interval is currently the best available clinical surrogate for the development of drug-induced torsades de pointes, it is overall an imperfect biomarker. In addition to low specificity for predicting arrhythmias, other issues relevant to using QT as a biomarker include (1) an apparent dissociation, for some drugs (for example, amiodarone, sodium pentobarbital, ranolazine) between QT/QTc interval prolongation and TdP risk, (2) Lack of clarity regarding what determines the relationship between QTc prolongation and TdP risk for an individual drug, (3) QT measurement issues, including effects of heart rate and autonomic perturbations, (4) the significant circadian changes to the QT/QTc interval and (5) concerns that the development, regulatory and commercial implications of finding even a mild QT prolongation effect during clinical development has significant impact the pharmaceutical discovery pipeline. These issues would be significantly reduced, clinical development simplified and marketing approval for some drugs might be accelerated if there were a battery of preclinical tests that could reliably predict a drug's propensity to cause TdP in humans, even in the presence of QTc interval prolongation. This approach is challenging and for it to be acceptable to pharmaceutical developers, the scientific community and regulators, it would need to be scientifically well validated. A very high-negative predictive value demonstrated in a wide range of drugs with different ionic effects would be critical. This manuscript explores the issues surrounding the use of QT as a clinical biomarker and potential approaches for validating preclinical assays for this purpose against clinical data sets.

Lack of circadian change of concentration of C-type natriuretic peptide in rabbit aqueous humor

To determine whether there is a circadian change of the concentration of C-type natriuretic peptide (CNP) in rabbit aqueous humor. Forty-one male white New Zealand rabbits were submitted to a 12 h light and 12 dark lighting schedule; lights on was at 0 h, lights off at 12 h. C-type natriuretic peptide was assayed at 3 light (2 h, 6 h and 10 h) and 3 dark (14,18 and 22 h) times. All groups consisted of four animals but two had more animals to increase the power of tests (6 h, n = 12; 22 h, n = 13). Dependence between the two eyes was tested by Pearson's correlation. The mean of two eyes was considered for analysis. Differences in concentration in pg/200 ml were evaluated by one-way ANOVA, t test and COSINOR analysis. There were no significant differences between the 6 analyzed groups (one-way ANOVA p = 0.157). Pooled into two groups (light and dark), the C-type natriuretic peptide concentration of the light group was lower, 2.626 +/- 0.92 pg/200 ml compared with the dark group 3.02 +/- 1.16 pg/200 ml but did not reach a significant difference (t test; p = 0.23). COSINOR analysis was not statistically significant (R% = 7.72 p = 0.209). These data demonstrate that the concentration of CNP in aqueous humor did not show a statistically significant circadian change in rabbits entrained to a 12 h light: 12 h dark lighting schedule.

Circadian Intraocular Pressure Rhythm Is Generated by Clock Genes

The present study in a mouse model was undertaken to reveal the role of the circadian clock genes Cry1 and Cry2 in generation of 24-hour intraocular pressure (IOP) rhythm. IOP was measured at eight time points daily (circadian time [CT] 0, 3, 6, 9, 12, 15, 18, and 21 hours), using a microneedle method in four groups of C57BL/6J mice (groups 1 and 3, wild-type; groups 2 and 4, Cry-deficient [Cry1-/-Cry2-/-]). During the IOP measurements, mice in groups 1 and 2 were maintained in a 12-hour light-dark cycle (LD), whereas mice in groups 3 and 4 were kept in a constant darkness (DD) that started 24 to 48 hours before the measurements. Circadian IOP variations in each group were evaluated by one-way analysis of variance (ANOVA) and Scheffé tests. In wild-type mice living in LD conditions, pressures measured in the light phase were significantly lower than those in the dark phase. This daily rhythm was maintained under DD conditions with low pressure in the subjective day and high pressure in the subjective night. In contrast, Cry-deficient mice did not show significant circadian changes in IOP, regardless of environmental light conditions. These findings demonstrate that clock oscillatory mechanisms requiring the activity of core clock genes are essential for the generation of a circadian rhythm of intraocular pressure.

Circadian variations of histamine binding to lymphocytes and neutrophils and skin reactivity to histamine in atopic and healthy subjects

Numerous pathophysiological conditions change during 24-hour periods. Histamine, the main mediator in allergic reactions, exerts a multiplicity of pathophysiological actions through binding to specific receptors on effector cells. Nocturnal exacerbation of symptoms occurs in many atopic diseases in which histamine is an important mediator. Nocturnal wheezing is a very common symptom of asthma. The aim of this study was to determine whether the binding of (fluorescein-labeled) histamine to cells participating in allergic-inflammatory processes (lymphocytes, neutrophils) and skin reactivity to histamine undergo circadian changes and to compare these phenomena in atopic asthmatic and healthy subjects. Blood samples were collected at 8 am, 2 pm, 8 pm, 2 am, and 8 am the next day. Histamine skin-prick tests were performed at the same times. It was found that skin reactivity to histamine (wheal, erythema) in healthy subjects underwent significant circadian changes with acrophase at 8 am (wheal) or 8 pm (erythema), the lowest values being at night (2 am, p = 0.017), in contrast to atopics, in whom the highest reactivity was found at night (2 am, p = 0.002). Significant differences in the binding of fluorescein-labeled histamine between day (8 am-2 pm) and night (2 am) were observed for lymphocytes (p = 0.006) and neutrophils (p = 0.018). In the asthmatic group these changes were not significant. Circadian changes in both the binding of histamine by effector cells and skin reactivity to histamine were different in healthy and asthmatic subjects, and this may play a role in the pathomechanism, course, and chronopharmacotherapy of atopic diseases.

Correlation between activity of antioxidant enzymes and circadian rhythms of corticosteroids in Macaca mulatta monkeys of different age

Young rhesus monkey females ( Macaca mulatta) demonstrate the well-defined circadian rhythm in activity of erythrocyte SOD with maximum at 10.00 h and minimum at 22.00 h. However, neither GSH-Px nor GR demonstrated any significant circadian changes, contrastingly to SOD. The diurnal changes in the SOD activity tightly correlate with the diurnal changes in the levels of cortisol and DHEAS in the animals’ blood plasma. With aging, these circadian rhythms of SOD, cortisol and DHEAS are smoothed out although the correlation between the diurnal changes in cortisol and SOD still maintains even for old animals. These results suggest that corticosteroids play an essential role in regulation of the SOD activity and that the reliability of the hormonal regulation decreases with aging.

The Treatment of Early-Morning Awakening Insomnia With 2 Evenings of Bright Light

To assess the effectiveness of brief bright-light therapy for the treatment of early-morning awakening insomnia. Twenty-four healthy adults with early-morning awakening insomnia were assigned to either the bright-light condition (2,500-lux white light) or the control (dim red light) condition. The circadian phase of rectal temperature and urinary melatonin rhythms were assessed with 26-hour constant routines before and after 2 evenings of light therapy. Sleep and daytime functioning were monitored using sleep diaries, activity monitors, and mood scales before light therapy and for 4 weeks during the follow-up period. While there were no significant circadian phase changes in the dim-light control group, the bright-light group had significant 2-hour phase delays of circadian temperature and melatonin rhythm. Compared to pretreatment measures, over the 4-week follow-up period, the bright-light group had a greater reduction of time awake after sleep onset, showed a trend toward waking later, and had a greater increase of total sleep time. Participants in the bright-light condition also tended to report greater reductions of negative daytime symptoms, including significantly fewer days of feeling depressed at the 4-week follow-up, as compared with the control group. Two evenings of bright-light exposure phase delayed the circadian rhythms of early-morning awakening insomniacs. It also improved diary and actigraphy sleep measures and improved some indexes of daytime functioning for up to 1 month after light exposure. The study suggests that a brief course of evening bright-light therapy can be an effective treatment for early-morning awakening insomniacs who have relatively phase advanced circadian rhythms.

Circadian expression of clock genes and clock-controlled genes in the rat retina

The circadian expression patterns of genes encoding for proteins that make up the core of the circadian clock were measured in rat retina using real-time quantitative PCR (qPCR). Transcript levels of several genes previously used for normalization of qPCR assays were determined and the effect of ischemia–reperfusion on the expression of clock genes was studied. Statistically significant circadian changes in transcript levels were found for: Per2, Per3, Cry2, Bmal1, Rora, Rorb, and Rorc with changes ranging between 1.6- and 2.6-fold. No changes were found for Per1, Cry1, Clock, Rev-erb α, and Rev-erb β. Significant differences in transcript levels were observed for several candidate reference genes: HPRT, GAPDH, rhodopsin, and Thy1 and, consequently, the use of these genes for normalization purposes in qPCR or Northern blots may lead to erroneous conclusions. Ischemia–reperfusion leads to a persistent decrease of Per1 and Cry2, which may be related to the selective degeneration of amacrine and ganglion cells. We conclude that while all clock genes are expressed in the retina, only a few show a clear circadian pattern.

Chronobiology and anesthesia.

CHRONOBIOLOGY investigates biologic rhythms that are involved in the organization of living organisms. Biologic rhythms consist of variations of biologic phenomena that are periodic and foreseeable in time. They are genetically determined as indicated by their persistence during constant conditions such as continuous light or darkness. Temporal variations in cycles of light– dark, rest–activity, fasting–eating, and other environmental conditions, defined as synchronizers, give the organism temporal markers and thus impose their period on these biologic rhythms. These rhythms can therefore be characterized by different periods, leading to the division of circadian (a period of approximately 24 h), ultradian (a cycle that is shorter than 1 day), and infradian (a cycle that may last weeks, months, or seasons). These clocks influence how our bodies change throughout the day, affecting blood pressure, activity of the immune system, blood coagulation, and gastric and renal functions. Almost all hormones are regulated by circadian rhythms. For example, cortisol naturally decreases to its lowest concentrations at bedtime and reaches its highest concentrations during the early waking hours. This variation may be fit to a sinusoidal function by the cosinor method, a linear method of least squares (fig. 1). This function is characterized by parameters such as the midline-estimating statistic of rhythm (MESOR), i.e., the mean level that is equal to the 24-h average), amplitude (half of the peak-to-trough difference of the fitted cosinus function), and acrophase (the crest time of rhythm given in degrees, where 360° corresponds to a 24-h cycle, or in hours and minutes). Other methods, such as Fourier transformation, may be used to detect the periodicity of the rhythm. Biologic rhythms are influenced by socioecologic factors, such as jet lag and shiftwork, as well as by illness and drugs. Available clinical data have shown that signs and symptoms are not constant over time and often have cyclic patterns. More strokes and heart attacks occur in the morning compared with any other time of day, and people with osteoarthritis tend to feel less pain in the morning than at night. Studies also suggest that chemotherapy and treatments for asthma and arthritis may be more effective and less toxic if drugs are administered at carefully selected times. Taking into account the circadian rhythms for medical treatment by choosing the time of day for drug administration is called chronotherapy. Drug effects can be optimized and side effects can be reduced by basing drug administration on the circadian patterns of a disease. Chronopharmacology is the study of the influence of the moment of administration of a drug (hour, month, and year) on its response according to the temporal structure of the organism receiving it. Chronopharmacology also studies the drug-induced alterations of biologic rhythms. Two aspects of chronopharmacology must be distinguished: the time of administration of a drug may determine a different response from a qualitative or a quantitative point of view (chronopharmacodynamics) and/or a different effective drug concentration (chronopharmacokinetics). Pharmacokinetic parameters are influenced by different physiologic functions displaying circadian rhythm. Temporal changes of drug kinetics have been reported in animals and humans for more than a hundred drugs, including anesthetics. It has been shown, for example, that despite a constant infusion rate of heparin, the risk of bleeding and the activated partial thromboplastin are higher at night. Chronopharmacokinetic data may partly explain chronopharmacodynamic phenomena. Knowledge of the influence of the time of administration on the drug kinetics could therefore have implications for its prescription by modulating the distribution of the total daily dose over a 24-h period. The aim of this review is to provide an update on the chronobiologic and chronopharmacologic findings that could have an impact on the daily practice of anesthesiology and/or research in this area.