Circadian rhythm disruption and retinal dysfunction:a bidirectional link in Alzheimer’s disease?

Dysfunction in circadian rhythms is a common occurrence in patients with Alzheimer’s disease.A predominant function of the retina is circadian synchronization,carrying information to the brain through the retinohypothalamic tract,which projects to the suprachiasmatic nucleus.Notably,Alzheimer’s disease hallmarks,including amyloid-β,are present in the retinas of Alzheimer’s disease patients,followed/associated by structural and functional disturbances.However,the mechanistic link between circadian dysfunction and the pathological changes affecting the retina in Alzheimer’s disease is not fully understood,although some studies point to the possibility that retinal dysfunction could be considered an early pathological process that directly modulates the circadian rhythm.

Probiotics administration alleviates cognitive impairment and circadian rhythm disturbance induced by sleep deprivation

Gut microbiome is indispensable for maintaining normal brain function.Specifically,gut microbiota plays a causal role in sleep deprivation(SD)-induced cognitive impairment.In this study,neurobehavioral effects of the Bifidobacterium breve strain(CCFM1025)were assessed in sleep-deprived mice.CCFM1025 improved the body weight and food and water intake of the mice.It also alleviated SD-induced cognitive behavioural abnormalities(in the novel object recognition test),but did not show beneficial effects on mood-and spatial memory-related behaviours.CCFM1025 significantly altered the gut microbial composition and genome function.Key microbial metabolites that may regulate sleep function were also identified,such as isovaleric acid andγ-aminobutyric acid in the gut and purine metabolites in the serum.Those metabolites may participate in gutbrain communication by acting on the striatal melatonin system,for example to increase melatonin levels,and by regulating the expression of circadian clock genes such as those encoding the adenosine A2A receptor and period circadian regulator 1.Collectively,administration of probiotics alleviated cognitive impairment and circadian rhythm disturbance induced by SD via modulation of gut microbiome and its metabolites.These findings may help guide the treatment of insomnia or other sleep disorders via dietary strategies.

The modulatory effect of oolong tea polyphenols on intestinal flora and hypothalamus gene expression in a circadian rhythm disturbance mouse model

The interaction between host circadian rhythm and gut microbes through the gut-brain axis provides new clues for tea polyphenols to improve host health.Our present research showed that oolong tea polyphenols(OTP)improved the structural disorder of the intestinal flora caused by continuous darkness,thereby modulating the production of metabolites related to pyruvate metabolism,glycolysis/gluconeogenesis,and tryptophan metabolism to alleviate the steady-state imbalance.After fecal microbiota transplantation from the OTP group,the single-cell transcriptomic analysis revealed that OTP significantly increased the number of hypothalamus cell clusters,up-regulated the number of astrocytes and fibroblasts,and enhanced the expression of circadian rhythm genes Cry2,Per3,Bhlhe41,Nr1d1,Nr1d2,Dbp and Rorb in hypothalamic cells.Our results confirmed that OTP can actively improve the intestinal environmental state as well as internal/peripheral circadian rhythm disorders and cognitive impairment,with potential prebiotic functional characteristics to notably contribute to host health.

Autophagy and circadian rhythms:interactions and clinical implications

Autophagy is a widespread biological process that controls cellular growth,survival,development,and death.Circadian rhythm is a recurring reaction of living organisms and behaviors to variations in surrounding brightness and obscurity.Most of the fundamental physiological processes in mammals,such as the sleep-wake pattern and the rhythm of nutrition and energy metabolism,are governed by circadian rhythms.Research has indicated that autophagy exhibits a specific circadian pattern in both normal and abnormal conditions.Autophagy can modulate circadian rhythms by breaking down proteins that regulate the circadian clock.The potential regulatory connection between the two has been a popular subject of clinical and fundamental research.Understanding the interaction between circadian rhythm and autophagy could potentially lead to the development of novel approaches for disease treatment in the future.The present analysis presented a summary of the molecular processes implicated in the interplay between autophagy and circadian rhythm,as well as the pathological importance of the disrupted regulatory association between these two phenomena.

Potential Power of the Pyramidal Structure VII: Effects of Pyramid Power and Bio-Entanglement on the Circadian Rhythm of Biosensors

We have demonstrated the existence of a pyramid power and have revealed its characteristics by strictly scientific experiments using biosensors. We also revealed the existence of a Bio-Entanglement, an entangled relationship between biosensors. A parallel study of biosensors (edible cucumber slices) had also been conducted, and we found that the circadian rhythm of gas concentrations emitted from biosensors changes seasonally. The pyramid power and Bio-Entanglement did not change the number of cycles in the periodic approximation curve representing circadian rhythm. Therefore, in this paper we analyzed the influence of the pyramid power and Bio-Entanglement, i.e., their influence on the phase, amplitude, and correlation coefficient of the periodic approximation curve representing the circadian rhythm of emitted gas concentrations. The main results are as follows. 1) The pyramid power shifted the phase of the periodic approximation curve representing the circadian rhythm by 43 minutes. 2) The amplitude of the periodic approximation curve changed with the pyramid power and the Bio-Entanglement. The effect on the lower and upper sections of the biosensors stacked in two layers was different, with a tendency to increase the amplitude of the lower layer and decrease the amplitude of the upper layer. 3) The pyramid power and the Bio-Entanglement affected the correlation coefficient between gas concentration and the periodic approximation curve representing the circadian rhythm of gas concentration. The effect on the lower and upper layers of the biosensors was different, with a tendency for the lower layer correlation coefficient to be larger and the upper layer correlation coefficient to be smaller. Previously we demonstrated that the pyramid power and the Bio-Entanglement affect the ratio of gas concentration, i.e., psi index Ψ. In this paper we demonstrate for the first time that the pyramid power and the Bio-Entanglement affect time, i.e., phase difference.

Circadian Rhythm of Childbirths and Maternal and Neonatal Prognosis at the YaoundéCentral Hospital

Background: The circadian variation of childbirths has been described by several authors around the globe. De Graaf showed that hospital childbirths at night were associated with increased perinatal mortality and adverse perinatal outcome. To improve obstetric care, we carried out this study to evaluate the circadian rhythm of childbirths and to assess the outcome following variations in the time of childbirths during the day. Methods: It was a cross-sectional descriptive study at the Yaoundé Central Hospital (YCH), over a two years period. We collected data from files of women who delivered from the 1st of January 2017 to 31st December 2018. We included files of women who delivered at least at 28 weeks of pregnancy. We excluded files of those who delivered by elective caesarean section, those whose hour of delivery was not noted and those who delivered before reaching the hospital. Sociodemographic, obstetrical characteristics, and immediate prognosis were recorded. Data were entered into excel, then analysed with SPSS v23 software. Tools used to appreciate our results were means, median, number, percentage, P, and OR with its 95% confidence interval. The difference in p is significant if p is less than 5%. Results: We analyzed 6041 files bearing the time of birth. Childbirths took place at all hours of the day, but the times of the day where the highest numbers of births were recorded were 10, 11, 12, 13 (that’s 1pm), 14 (that’s 2 pm), 15 (that’s 3 pm), 16 (that’s 4 pm), 17 (that’s 5 pm) and 23 (that’s 11 pm) hours, with respectively 224 (3.7%), 277 (4.6%), 256 (4.2%), 265 (4.4%), 207 (3.4%), 255 (4.2%), 228 (3.8%), 216 (3.6%) and 226 (3.7%) births. The peak of births was at 11 am while the time of day where the lowest number of births was recorded was 6 pm, with 175 (2.9%) births. The mean age of participants was 27.34 ± 6.03 years with extremes of 13 and 49, with 87.6% between 20 to 39 years. Sociodemographic characteristics of participants, prematurity and bleeding during delivery, had no dependence on the time of delivery. Perineal tear, duration of observation, Apgar score of the newborn, birthweight, delivery mode, health personnel who performed the delivery, and episiotomyseemed to be influenced by the time of delivery. Daily shifts were not independently associated with the poor Apgar score (0 - 6) at 5 mins, when adjusted for all other factors (p = 0.109). Conclusion: Childbirths were more frequent between 10 am and 5 pm. The period where episiotomy was most performed is the same as when there was macrosomia childbirth. Tears of the perineum are more frequent between 2 pm and 10 pm. There was no independent association between Daily shifts and poor Apgar score. The poor APGAR score would be more related to low birth weight.

Circadian rhythms in the growth and reproduction of the brown alga Undaria pinnatifida and gametogenesis under different photoperiods

Circadian growth rhythm of the juvenile sporophyte of the brown alga Undaria pinnatifida was measured with the computer-aided image analysis system in constant florescent white light under constant temperature （ 10 ℃ ）. The growth rhythm persisted for 4 d in constant light with a free-running period of 25.6 h. Egg release from filamentous gametophytes pre-cultured in the light - dark regime was evaluated for six consecutive days at fixed time intervals in constant white light and 12 h light per day. Egg release rhythm persisted for 3 d in both regimes, indicating the endogenous nature. Temporal scale of egg release and gametogenesis in 18, 16, 12 and 8 h light per day were evaluated respectively using vegetatively propagated filamentous gametophytes. Egg release occurred 2 h after the onset of dark phase and peaked at midnight. Evaluation of the rates of oogonium formation, egg release or fertilization revealed no significant differences in four light-dark regimes, indicating the great plasticity of sexual reproduction. No photoperiodic effect in gametogenesis in terms of oogonium formation and egg release was found, but fertilization in short days was significantly higher than in long days. Results of this investigation further confirmed the general occurrence of circadian rhythms in intertidal seaweed species.

The role of pineal microRNA-325 in regulating circadian rhythms after neonatal hypoxic-ischemic brain damage

Circadian rhythm disorder is a common,but often neglected,consequence of neonatal hypoxic-ischemic brain damage(HIBD).However,the underlying molecular mechanisms remain largely unknown.We previously showed that,in a rat model of HIBD,up-regulation of microRNA-325(miR-325)in the pineal gland is responsible for the suppression of Aanat,a key enzyme involved in melatonin synthesis and circadian rhythm regulation.To better understand the mechanism by which miR-325 affects circadian rhythms in neonates with HIBD,we compared clinical samples from neonates with HIBD and samples from healthy neonates recruited from the First Affiliated Hospital of Soochow University(Dushuhu Branch)in 2019.We found that circulating miR-325 levels correlated positively with the severity of sleep and circadian rhythm disorders in neonates with HIBD.Furthermore,a luciferase reporter gene assay revealed that LIM homeobox 3(LHX3)is a novel downstream target of miR-325.In addition,in miR-325 knock-down mice,the transcription factor LHX3 exhibited an miR-325-dependent circadian pattern of expression in the pineal gland.We established a neonatal mouse model of HIBD by performing doublelayer ligation of the left common carotid artery and exposing the pups to a low-oxygen environment for 2 hours.Lhx3 mRNA expression was significantly down-regulated in these mice and partially rescued in miR-325 knockout mice subjected to the same conditions.Finally,we showed that improvement in circadian rhythm-related behaviors in animals with HIBD was dependent on both miR-325 and LHX3.Taken together,our findings suggest that the miR-325-LHX3 axis is responsible for regulating circadian rhythms and provide novel insights into the identification of potential therapeutic targets for circadian rhythm disorders in patients with neonatal HIBD.The clinical trial was approved by Institutional Review Board of Children’s Hospital of Soochow University(approval No.2015028)on July 20,2015.Animal experiments were approved by Animal Care and Use Committee,School of Medicine,Soochow University,China(approval No.XD-2016-1)on January 15,2016.

Effects of Exposure to Extremely Low Frequency Electro-magnetic Fields on Circadian Rhythms and Distribution of Some Leukocyte Differentiation Antigens in Dairy Cows

Objective To investigate the effects of extremely low frequency magnetic and electric fields （ELFEMFs） emitted from 380 kV transmission lines on some leukocyte differentiation antigens in dairy cows. Methods The study was carded out in 5 cows exposed to 1.98-3.28 μT of ELFEMFs and in 5 control cows exposed to 0.2-0.7 μT of ELFEMFs. Following haematological and immunologic parameters were measured in both groups： WBC, CD45R, CD6, CD4, CD8, CD21, and CD11B leukocyte antigen expression. Results Some of the haematological and immunologic parameters under investigation were similar in both groups. However, CD8 （T lymphocyte surface antigen） was higher in the exposed group （1.35 ±0.120 vs 0.50 ±0.14×10^3/mL）. Furthermore, the CD4/CD8 ratio （0.84 ±0.05 and 2.19±0.16 for exposed and not exposed cows respectively） and circadian rhythm were different between the two groups. Conclusion Exposure to ELFEMFs is responsible of the abnormal temporal variations and distribution of some haematological and immunological parameters in dairy cows.

Hepatitis B and circadian rhythm of the liver

The circadian rhythm in humans is determined by the central clock located in the hypothalamus’s suprachiasmatic nucleus,and it synchronizes the peripheral clocks in other tissues.Circadian clock genes and clock-controlled genes exist in almost all cell types.They have an essential role in many physiological processes,including lipid metabolism in the liver,regulation of the immune system,and the severity of infections.In addition,circadian rhythm genes can stimulate the immune response of host cells to virus infection.Hepatitis B virus(HBV)infection is the leading cause of liver disease and liver cancer globally.HBV infection depends on the host cell,and hepatocyte circadian rhythm genes are associated with HBV replication,survival,and spread.The core circadian rhythm proteins,REV-ERB and brain and muscle ARNTL-like protein 1,have a crucial role in HBV replication in hepatocytes.In addition to influencing the virus’s life cycle,the circadian rhythm also affects the pharmacokinetics and efficacy of antiviral vaccines.Therefore,it is vital to apply antiviral therapy at the appropriate time of day to reduce toxicity and improve the effectiveness of antiviral treatment.For these reasons,understanding the role of the circadian rhythm in the regulation of HBV infection and host responses to the virus provides us with a new perspective of the interplay of the circadian rhythm and anti-HBV therapy.Therefore,this review emphasizes the importance of the circadian rhythm in HBV infection and the optimization of antiviral treatment based on the circadian rhythm-dependent immune response.

The role of circadian rhythm in breast cancer

The circadian rhythm is an endogenous time keeping system shared by most organisms. The circadian clock is comprised of both peripheral oscillators in most organ tissues of the body and a central pacemaker located in the suprachiasmatic nucleus （SCN） of the central nervous system. The circadian rhythm is crucial in maintaining the normal physiology of the organism including, but not limited to, cell proliferation, cell cycle progression, and cellular metabolism; whereas disruption of the circadian rhythm is closely related to multi-tumorigenesis. In the past several years, studies from different fields have revealed that the genetic or functional disruption of the molecular circadian rhythm has been found in various cancers, such as breast, prostate, and ovarian. In this review, we will investigate and present an overview of the current research on the influence of circadian rhythm regulating proteins on breast cancer.

Genes related to circadian rhythm are involved in regulating tuberization time in potato

Early tuberization,a short period from stolon occurrence to tuber formation,is one of the major characteristics of a good early-maturing potato cultivar,while the regulatory mechanism of tuberization time(TT)is still unclear.In this study,two tetraploid cultivars,Zhongshu 3(Z3)and Zhongshu 18(Z18),with short and long TT respectively,were examined to reveal regulatory genes related to TT using RNA sequencing of tissue samples taken during stolon occurrence,stolon swelling and tuber formation.Cluster analysis showed that the gene expression patterns at the stolon swelling and tuber formation stages were significantly different from those at stolon occurrence in both Z3 and Z18.Therefore,we screened the differentially expressed genes(DEGs)at stolon swelling and tuber formation and compared them to those at stolon occurrence.A total of 3085 DEGs were specifically identified and analyzed according to Gene Ontology and Kyoto Encyclopedia of Genes and Genomes enrichment,and DEGs involved in starch and sucrose metabolism,plant hormone signal transduction and plant circadian clock were significantly enriched.The circadian clock genes were significantly differentially expressed between Z3 and Z18,revealing an important role for the plant circadian pathway in regulating TT.Furthermore,three candidate genes,StGI,StPRR and StEFM involved in circadian regulation and significantly differentially expressed between Z3 and Z18,were discovered and confirmed by qRT-PCR.The results provide valuable information for understanding the regulatory mechanisms of potato TT and represent a step toward breeding early-maturing potato cultivars.

Seasonal Changes in the Circadian Rhythm of Gas Released from Harvested Cucumbers

Vegetables and fruits are known to have long-lasting biological reactions even after harvesting. Volatile components may be released as a biological response to stimulation or injury. We measured the concentrations of volatiles released from the cut surfaces of cucumbers after their harvest and analyzed the relationship between the time the cucumbers were cut and gas concentrations. The results showed that gas concentrations indicate a circadian rhythm. We previously reported that the circadian rhythm of gas concentrations was 6 hours per cycle in the summer, i.e., from the vernal equinox to the autumnal equinox, and 24 hours per cycle in the winter, i.e., from the autumn equinox to the vernal equinox. We analyzed the gas concentrations emitted from cucumber sections in more detail in this paper and found that the circadian rhythms differ among winter, spring, summer, and autumn seasons. We found that one cycle of the circadian rhythm was 8 hours in winter, 6 hours in spring, 24 hours in summer, and a mixed cycle of 24 and 12 hours in autumn.

The effect of lens aging and cataract surgery on circadian rhythm

Many organisms have evolved an approximately 24-hour circadian rhythm that allows them to achieve internal physiological homeostasis with external environment.Suprachiasmatic nucleus（SCN） is the central pacemaker of circadian rhythm,and its activity is entrained to the external light-dark cycle.The SCN controls circadian rhythm through regulating the synthesis of melatonin by pineal gland via a multisynaptic pathway.Light,especially shortwavelength blue light,is the most potent environmental time cue in circadian photoentrainment.Recently,the discovery of a novel type of retinal photoreceptors,intrinsically photosensitive retinal ganglion cells,sheds light on the mechanism of circadian photoentrainment and raises concerns about the effect of ocular diseases on circadian system.With age,light transmittance is significantly decreased due to the aging of crystalline lens,thus possibly resulting in progressive loss of circadian photoreception.In the current review,we summarize the circadian physiology,highlight the important role of light in circadian rhythm regulation,discuss about the correlation between age-related cataract and sleep disorders,and compare the effect of blue light-filtering intraocular lenses（lOLs） and ultraviolet only filtering lOLs on circadian rhythm.

Effects of Different Electromagnetic Fields on Circadian Rhythms of Some Haematochemical Parameters in Rats

Objective To investigate the effects of different electromagnetic fields on some haematochemical parameters of circadian rhythms in Sprague-Dawley rats. Methods The study was carried out in 18 male and 18 female rats in good health conditions exposed to 50 Hz magnetic sinusoid fields at the intensity of 1000 μT, 100 μT, and 0 μT （control group） respectively, and in 18 male and 18 female rats in good health conditions exposed to 1.8 GHz electromagnetic fields at the intensity of 50 V/m, 25 V/m and 0 V/m （control group）, respectively. Following haematochemical parameters for glucose, triglycerides, and total cholesterol were measured. Results Different effects of electromagnetic fields on circadian rhythms of both male and female rats were observed. Different changes occurred in some haematochemical parameters for glucose, triglycerides, and total cholesterol （P〈0.05）. Conclusion Exposure to different electromagnetic fields is responsible for the variations of some haematochemical parameters in rats.

Nobiletin protects against metabolic syndrome by enhancing circadian rhythms

OBJECTIVE Dysregulation of circadian rhythms is associated with metabolic dysfunction,yet it is unclear whether enhancing clock function by small molecules can ameliorate metabolic disorders.METHODS We used an unbiased chemical screen in fibroblasts expressing PER2::Luc to identify the Clock amplitude-Enhancing Small Mole⁃cule.In diet-induced obese mice and DB/DB mutant mice,we evaluated the effects of the Clock amplitude-Enhancing small Molecule on metabolic syndrome and locomotor activity.RESULTS We identified Nobiletin(NOB),a natural poly⁃methoxylated flavone,as a Clock amplitude-Enhancing Small Molecule by an unbiased chemical screen.In diet-induced obese mice,NOB strongly improved metabolic syndrome and enhanced locomotor activity in a Clock gene-dependent manner.Moreover,the clock is also required for the beneficial effects of NOB on metabolic disorders in DB/DB mutant mice.Notably,NOB enhanced clock protein levels and reprogramed metabolic gene expressions in the liver.Finally,we revealed retinoid acid receptor-related orphan receptors(RORα/γ)as direct targets of NOB.CONCLUSION Altogether,our results demonstrate that a pharmacological intervention that enhances circadian rhythms by small molecule may be as a novel strategy for combating metabolic disease.

WNT/β-catenin pathway and circadian rhythms in obsessive-compulsive disorder

The neuropsychiatric disease named obsessive-compulsive disorder is composed by obsessions and/or compulsions.Obsessive-compulsive disorder etiologies are undefined.However,numerous mechanisms in several localizations are implicated.Some studies showed that both glutamate,inflammatory factors and oxidative stress could have main functions in obsessive-compulsive disorder.Glycogen synthase kinase-3β,the major negative controller of the WNT/β-catenin pathway is upregulated in obsessive-compulsive disorder.In obsessive-compulsive disorder,some studies presented the actions of the different circadian clock genes.WNT/β-catenin pathway and circadian clock genes appear to be intricate.Thus,this review focuses on the interaction between circadian clock genes and the WNT/β-catenin pathway in obsessive-compulsive disorder.

Chronic corticosterone disrupts the circadian rhythm of CRH expression and m^(6)A RNA methylation in the chicken hypothalamus

Background:Corticotropin-releasing hormone(CRH),the major secretagogue of the hypothalamic-pituitary-adrenal(HPA)axis,is intricately intertwined with the clock genes to regulate the circadian rhythm of various body functions.N6-methyladenosine(m^(6)A)RNA methylation is involved in the regulation of circadian rhythm,yet it remains unknown whether CRH expression and m^(6)A modification oscillate with the clock genes in chicken hypothalamus and how the circadian rhythms change under chronic stress.Results:Chronic exposure to corticosterone(CORT)eliminated the diurnal patterns of plasma CORT and melatonin levels in the chicken.The circadian rhythms of clock genes in hippocampus,hypothalamus and pituitary are all disturbed to different extent in CORT-treated chickens.The most striking changes occur in hypothalamus in which the diurnal fluctuation of CRH mRNA is flattened,together with mRNA of other feeding-related neuropeptides.Interestingly,hypothalamic m^(6)A level oscillates in an opposite pattern to CRH mRNA,with lowestm^(6)A level after midnight(ZT18)corresponding to the peak of CRH mRNA before dawn(ZT22).CORT diminished the circadian rhythm of m^(6)A methylation with significantly increased level at night.Further site-specific m^(6)A analysis on 3’UTR of CRH mRNA indicates that higher m^(6)A on 3’UTR of CRH mRNA coincides with lower CRH mRNA at night(ZT18 and ZT22).Conclusions:Our results indicate that chronic stress disrupts the circadian rhythms of CRH expression in hypothalamus,leading to dysfunction of HPA axis in the chicken.RNA m^(6)A modification is involved in the regulation of circadian rhythms in chicken hypothalamus under both basal and chronic stress conditions.

Body-temperature circadian rhythm in 67 patients after heart valve replacement surgery secondary to valvular heart disease

Purpose:Patient body temperature was monitored after cardiac valve replacement,in order to explore the characteristics of body-temperature circadian rhythm and the factors influencing that rhythm.Methods:A cohort of 67 patients who received cardiac valve replacement in a Fuzhou,Fujian province,China,general hospital underwent temperature measurements and analysis(by cosine curve)of their body-temperature circadian rhythm.A biological rhythm model was established through principal component analysis and evaluation of biological rhythm features.Multiple circadian parameters were included through linear regression analysis.Results:Patients’temperature after cardiac valve replacement exhibited circadian characteristics(p<0.05),among which the scores of temperature mesor,amplitude,and acrophase were respectively(37.61
0.08),(0.10
0.09),and33(e355,e119).Body-temperature rhythms were influenced by both gender and cardiopulmonary bypass time(p<0.05).Conclusion:Although some patients’circadian characteristics disappeared after cardiac valve replacement,circadian rhythms remained intact for most patients.Measures that were found to mitigate body-temperature circadian rhythm disruption included building a natural rhythm of light/darkness and decreasing cardiopulmonary bypass time.

Biomarkers of Aging: Changes in Circadian Rhythms Related to the Modulation of Metabolic Output

Twenty-four hour (circadian) rhythmicity is an important component of biological variability associated with studies relating to biomarkers of aging. Chronobiological testing techniques must be utilized because (1) many variables that are related to the modulation of metabolic output vary dramatically at different times of the day; (2) various experimental variable and treatment groups must be synchronized with environmental cues that control circadian rhythms; and (3) multiple circadian variables may interact together to modulate the rate of aging. The rhythm for physiological factors such as whole animal metabolic output, body temperature, heart rate, urine flow, potassium, etc. were found to be dissociated or altered by the senescence process; behavioral variables such as spontaneous activity, wheel running, feeding and drinking, verbal performance, as well as sleep-wakefulness rhythms, seem to be accurate predictors of biological age. Circadian rhythms for a variety of enzymes of intermediary metabolism which are directly associated with energy metabolism have been well documented. These well-defined rhythms of enzyme activity have also been shown to degenerate with aging. Rhythms tend to lose amplitude as activity falls with age and as a general loss of regulation (especially time of day where maximal activity might be found) of activity across the 24-h span occurs. As with behavioral variables, changes in enzyme rhythms appear to accurately predict aging. Generally speaking, the loss of temporal organization with age, characterized by decreased circadian amplitude, loose internal synchronization, and poor response to external environmental time queues, is associated with poor health states and decreased longevity. Temporal rhythms for whole animal parameters are highly correlated with molecular events, such as regulation of cellular metabolism. DNA repair, and gene expression. Automated data acquisition and process control systems will be required for future Chronobiological studies to develop biomarkers of aging.