Chronobiology and aging

Validation of the Internal Coherence Scale (ICS) in Healthy Geriatric Individuals and Patients Suffering from Diabetes Mellitus Type 2 and Cancer

BACKGROUND

With increased life expectancy, the coexistence of functional impairment and multimorbidity can negatively impact life quality and coherence in geriatric individuals. The self-report 10-item Internal Coherence (ICS) measures how individuals cope with and make sense of disease-specific life challenges. The aim of this study was to validate the ICS in a sample of geriatric individuals.

METHODS AND PROCEDURE

In a cross-sectional study, geriatric individuals with and without chronic diseases were recruited. A factor analysis with principal component extraction (PCA) and a structural equation model (SEM) was conducted to assess the ICS factor structure in a geriatric sample. To measure convergent validity, the following scales were used: Short Health Survey (SF-12), Karnofsky Performance Index (KPI), Trait autonomic regulation (Trait aR), Sense of Coherence Scale (SOC), and Geriatric Depression Scale (GDS).

RESULTS

A sample of n = 104 (70-96 years of age) patients with Diabetes Mellitus Type 2 (n = 22), cancer diseases (n = 31) and healthy controls (n = 51) completed the ICS. PCA and SEM yielded the original two-factor solution: 1. Inner resilience and coherence and 2. Thermo coherence. Overall internal consistency for this cohort was satisfying (Cronbach's α with rα = 0.72), and test-retest reliability was moderate (rrt = 0.53). ICS scores were significantly correlated to all convergent criteria ranging between r = 0.22 * and 0.49 ** (p < 0.05 *; p < 0.01 **).

CONCLUSION

Study results suggest that the ICS appears to be a reliable and valid tool to measure internal coherence in a geriatric cohort (70-96 years). However, moderate test-retest reliability prompts the consideration of potential age-effects that may bias the reliability for this specific cohort.

Aging affects circadian clock and metabolism and modulates timing of medication

Aging is associated with impairments in the circadian rhythms, and with energy deregulation that affects multiple metabolic pathways. The goal of this study is to unravel the complex interactions among aging, metabolism, and the circadian clock. We seek to identify key factors that inform the liver circadian clock of cellular energy status and to reveal the mechanisms by which variations in food intake may disrupt the clock. To address these questions, we develop a comprehensive mathematical model that represents the circadian pathway in the mouse liver, together with the insulin/IGF-1 pathway, mTORC1, AMPK, NAD+, and the NAD+ -consuming factor SIRT1. The model is age-specific and can simulate the liver of a young mouse or an aged mouse. Simulation results suggest that the reduced NAD+ and SIRT1 bioavailability may explain the shortened circadian period in aged rodents. Importantly, the model identifies the dosing schedules for maximizing the efficacy of anti-aging medications.

Sleep in older adults and in subjects with dementia

The neuronal structures for the regulation of sleep and wakefulness are located in the brain. This complex network is vulnerable to numerous factors, most importantly neurodegenerative diseases and drugs. The macrostructure and microstructure of sleep change with age. These changes are more pronounced in subjects with dementia. Sleep disorders in subjects with dementia may be independent of dementia or caused by dementia. Furthermore, epidemiological studies reveal that sleep disorders per se may induce dementia by reduction of cerebral clearance of beta-amyloids. The population attributable risk (PAR) of sleep disturbances to the incidence of dementia is estimated to be about 15%; therefore, management of sleep disturbances in older adults and subjects with dementia gives the opportunity of an impact on incidence and course of dementia. Sleep history should be taken from each individual and obvious sleep disturbances, especially sleep apnea, should be managed according to current guidelines. Future studies that concern the incidence and the management of dementia must take into account sleep and sleep disturbances.

How do Fetal Grafts of the Suprachiasmatic Nucleus Communicate with the Host Brain?

Fetal grafts containing the hypothalamic suprachiasmatic nucleus (SCN), the site of an endogenous circadian pacemaker, can reinstate behavioral rhythms in lesioned recipients but the precise routes of communication between the graft and the host brain remain unknown. Grafts containing the SCN may convey temporal information to the host brain via neural efferents, diffusible factors, or a combination of both. We examined graft-host connections in anterior hypothalamic homografts (hamster-to hamster) and heterografts (rat-to hamster) implanted in the third ventricle by: (a) applying the carbocyanine dye, dil, directly onto homo- and heterografts in fixed tissue sections; and (b) using a donor-specific neurofilament (NF) antibody to immuno-cytochemically visualize heterograft efferents. Dil applied onto either homografts or heterografts labeled relatively few graft efferents which could be followed only short distances into the host brain. In contrast, NF-labeled heterograft efferents were both more numerous and extended for longer distances into the host brain than anticipated on the basis of dil tract tracing. The results suggest that anterior hypothalamic grafts implanted in the third ventricle provide substantial input to the adjacent host hypothalamus although it is not known whether these projections arise from SCN cells or from other extra-SCN hypothalamic tissue within these grafts. Nor is it known whether these projections are functional. To determine if neural efferents are required for the restoration of rhythmicity after grafting, we have encapsulated fetal anterior hypothalamus in a permselective polymer which prevents neurite outgrowth but allows diffusible signals to reach the host brain. Polymer-encapsulated grafts of fetal anterior hypothalamus from wild-type hamster fetuses have been implanted into the third ventricle of heterozygote tau mutant, SCN-lesioned hamsters. Because the free-running period of tau mutant hamsters is significantly shorter than that of wild-type hamsters, restored rhythms when they occur can be unambiguously attributed to the presence of donor tissue. Encapsulated grafts that survive contain neuropeptide cell markers characteristic of the intact SCN, but the survival rate of encapsulated neural tissue is low. Nevertheless, if we find that even a few encapsulated grafts restore donor-specific rhythms, this would suggest that diffusible signals emitted from SCN grafts may be sufficient to support circadian function. It may be that the SCN in the intact animal communicates with the rest of the brain by redundant signals, either efferent fibers or diffusible signals. Alternatively, different circadian rhythms may be mediated by distinct output signals from the SCN.

Comparison of sleep quality based on direction of shift rotation in electronics workers

Background

Previous studies have reported the effects of direction of shift rotation on sleep, however, the findings are inconsistent. In this study, we investigated sleep quality related to direction of shift rotation using large-scale data from shiftwork-specific health examinations of electronics workers.

Methods

This study included 4750 electronics workers working in a rotating 3-shift system who completed a medical examination for shift workers survey from January 1 to December 31, 2014, at a general hospital. The subjects were categorized into one of two groups according to direction of shift rotation. We compared sleep quality index between the subjects who worked in forward rotation and backward rotation systems.

Results

Backward rotation was positively associated with prevalence of poor sleep quality. In the multivariable-adjusted model, when comparing backward rotation to forward rotation, the odds ratio (OR) with 95 % confidence interval (95 % CI) for poor sleep quality was 1.95 (1.58–2.41). After stratifying by gender, the ORs (95 % CIs) for poor sleep quality in male and female was 1.92 (1.47–2.49) and 2.13 (1.47–3.08), respectively. In subgroup analyses, backward rotation was significantly associated with poor sleep quality in workers ≥30 years of age compared with workers <30 years of age (adjusted OR 2.60 vs. 1.89, respectively; P for interaction <0.001).

Conclusions

Our study supports that a backward rotation system is associated with poor sleep quality. Forward rotation systems should be considered to reduce sleep problems.

Some clinical consequences of the rest and activity disturbance in Alzheimer's disease

Recently, the use of activity monitoring has led to several interesting findings related to activity/rest issues in the care and management of Alzheimer patients. Evidence suggests that the “sleep” disturbances commonly reported in Alzheimer patients are actually a disturbance of the normal circadian cycle. This seems to be a normal progression of the disease and as such is not likely treatable with behavioral or pharmacological methods. These altered activity/rest patterns have direct implications for such areas as physical and pharmacological restraint use, supervision and injury risk, access and mobility issues, hospital ward design, and staffing policies.

Circadian rhythms of body temperature and locomotor activity in aging BALB/c mice: early and late life span predictors

Impairment of one or more parameters of circadian rhythms (CR) of body temperature (BT) and locomotor activity (LMA) are considered among the hallmarks of mammalian aging. These alterations are frequently used as markers for imminent death in laboratory mice. However, there are still contradictory data for particular strains and it is also uncertain which changes might predict senescence changes later in life, including the force of mortality. In the present paper we use telemetry to study LMA and CR of BT during aging of BALB/c mice. At our knowledge this is the first time that CR of BT and LMA are investigated in this strain in a range of age covering the whole lifespan, from young adult up to very old age. CR of BT was analyzed with a cosine model using a cross sectional approach and follow-up measurements. The results show that BT, LMA, amplitude, goodness-of-fit (GoF) to circadian cycle of temperature decrease with different shapes during chronological age. Moreover, we found that the % change of amplitude and BT in early life (5-19 months) can predict the remaining lifespan of the mice. Later in life (22-32 months), best predictors are single measurements of LMA and GoF. The results of this study also offer potential measures to rapidly identifying freely unrestrained mice with the worst longitudinal outcome and against which existing or novel biomarkers and treatments may be assessed.

Effects of resveratrol on daily rhythms of locomotor activity and body temperature in young and aged grey mouse lemurs

In several species, resveratrol, a polyphenolic compound, activates sirtuin proteins implicated in the regulation of energy balance and biological clock processes. To demonstrate the effect of resveratrol on clock function in an aged primate, young and aged mouse lemurs (Microcebus murinus) were studied over a 4-week dietary supplementation with resveratrol. Spontaneous locomotor activity and daily variations in body temperature were continuously recorded. Reduction in locomotor activity onset and changes in body temperature rhythm in resveratrol-supplemented aged animals suggest an improved synchronisation on the light-dark cycle. Resveratrol could be a good candidate to restore the circadian rhythms in the elderly.

Sex and age related changes in the locomotor activity and phototactic behaviors of two closely related species of Camponotus ants

A virgin ant queen has only one opportunity in her lifetime to realize her reproductive fitness when she leaves her nest for a mating flight. After successful mating she sheds her wings, excavates a nest and starts laying eggs to initiate her own colony. Here we report the results of our study on two related species of Camponotus ants - day active Camponotus paria and night active Camponotus compressus - aimed at investigating (i) if there exist inter-species differences in the activity and phototactic behaviors of males and queens, (ii) whether these behaviors in the queen change after mating, and (iii) whether the activity rhythm of queens changes with age. We find that while activity profiles differ between C. paria and C. compressus virgin males and queens, such differences in queens disappear after mating. Once mated, the activity rhythm of queens shows little change with age; the rhythm in virgin queens, on the other hand, changes considerably. As virgins, C. paria queens are positively phototactic, while C. compressus queens are negatively phototactic. After mating, C. paria queens become less phototactic, particularly during the subjective night, while C. compressus queens remain negatively phototactic. These results indicate that there are considerable differences in the activity and phototactic behaviors of virgin queens of the two related species of Camponotus ants. Most of these differences disappear after mating, which suggests that these behaviors may have evolved primarily for the proper execution of pre-mating events.

The grey mouse lemur: a non-human primate model for ageing studies

The use of non-human primate models is required to understand the ageing process and evaluate new therapies against age-associated pathologies. The present article summarizes all the contributions of the grey mouse lemur Microcebus murinus, a small nocturnal prosimian primate, to the understanding of the mechanisms of ageing. Results from studies of both healthy and pathological ageing research on the grey mouse lemur demonstrated that this animal is a unique model to study age-dependent changes in endocrine systems, biological rhythms, thermoregulation, sensorial, cerebral and cognitive functions.

Occupational sleep medicine: practice and promise

Occupational sleep medicine is a new field within sleep medicine. Occupational sleep medicine applies (1) the science of sleep, frequently as instantiated into mathematical modeling; (2) the tactics, techniques, and procedures of sleep and performance measurement in the operational environment; and (3) the clinical practice of sleep medicine to reduce the risks of poor performance, lost productivity, and error, incident, and accident in the workplace. As envisioned here, occupational sleep medicine will play a crucial role in fatigue risk management to, in the short term, improve performance, productivity, and safety and in the longer term improve worker health and well-being.

Hormone levels in centenarians

The serum profiles of total triiodothyronine (T(3)), free thyroxin (fT(4)), thyroid stimulating hormone (TSH), cortisol, prolactin (HPRL), parathormone (PTH), osteocalcin and growth hormone (GH) were measured in a group of 12 centenarians and compared to the values of a control group of twenty-nine subjects, aged 67-98 years. The study was aimed at revealing whether there are appreciable differences or age-related modifications in the hormone status of healthy control elderly and the centenarian population. In this series, the modifications in hormone levels were unremarkable, and the serum levels of the studied hormones in centenarians often fell within a range considered to be normal for the younger age classes.

Sleep disturbance in midlife women

Emphasizing midlife women, this review describes sleep and compares self-report sleep data with objective findings from laboratory studies of women. Sleep disturbance is a more prevalent complaint for women than men. Not due to chronologic age per se, it is associated with menopausal symptoms and most importantly with comorbidities and stress. Sleep problems in midlife women should not be attributed only to the menopausal symptom experience and should trigger a clinical evaluation. Assessment guidelines are included.

Age‐Related Effects on the Biological Clock and its Behavioral Output in a Primate

In humans, activity rhythms become fragmented and attenuated in the elderly. This suggests an alteration of the circadian system per se that could in turn affect the expression of biological rhythms. In primates, very few studies have analyzed the effect of aging on the circadian system. The mouse lemur provides a unique model of aging in non-human primates. To assess the effect of aging on the circadian system of this primate, we recorded the circadian and daily rhythms of locomotor activity of mouse lemurs of various ages. We also examined age-related changes in the daily rhythm of immunoreactivities for vasoactive intestinal polypeptide (VIP) and arginine-vasopressin (AVP) in suprachiasmatic nucleus neurons (SCN), two major peptides of the biological clock. Compared to adult animals, aged mouse lemurs showed a significant increase in daytime activity and an advanced activity onset. Moreover, when maintained in constant dim red light, aged animals exhibited a shortening of the free-running period compared to adult animals. In adults, AVP immunoreactivity (ir) peaked during the second part of the day, and VIP ir peaked during the night. In aged mouse lemurs, the peaks of AVP ir and VIP ir were significantly shifted with no change in amplitude. AVP ir was most intense at the beginning of the night; whereas, VIP ir peaked at the beginning of the daytime. A weakened oscillator could account for the rhythmic disorders often observed in the elderly. Changes in the daily rhythms of AVP ir and VIP ir may affect the ability of the SCN to transmit rhythmic information to other neural target sites, and thereby modify the expression of some biological rhythms.

Time of day affects episodic memory in older adults

The neuropsychological test scores of 2030 cognitively normal older adults were examined to evaluate performance patterns as they related to time of day (TOD) at which testing was initiated. Multiple regression analyses were used to examine the association of TOD with scores on seven neuropsychological tests used in the clinical evaluation of dementia. Episodic memory performance was significantly related to TOD, while memory span and verbal fluency were not. Best performance occurred during early morning hours and late afternoon; worst performance occurred mid-day (i.e., noon). These findings may have implications for clinical assessment, the design of research on dementia, and the daily functioning of older adults.

Expression profiles of PERIOD1, 2, and 3 in peripheral blood mononuclear cells from older subjects

AIMS

Circadian clocks regulate daily rhythms of behavior and physiology such as the sleep-wake cycle and hormonal secretion. Numerous characteristics of the behavioral and physiological processes change with age. In this study, we evaluated the circadian clockwork in older people by measuring daily profiles of PERIOD (PER) gene expression in peripheral blood mononuclear cells (PBMCs).

MAIN METHODS

Blood samples were collected from 6 healthy older subjects (mean age 62 years) at 2-h intervals over a 24-h period under a semi-constant routine condition where masking effects are minimized. PBMCs were isolated from whole blood and temporal mRNA expression profiles of PER1, PER2, and PER3 were determined by RT-PCR. Phases of the PER rhythms, and times of sleep onset and offset were determined using data from those subjects who showed significant 24-h rhythms. The values for the parameters were compared between the older subjects and 8 young control subjects (mean age 21 years).

KEY FINDINGS

Prominent daily rhythms of PER1, PER2, and PER3 mRNA levels, advanced sleep-wake timing and advanced phases of PER rhythms were observed in the older subjects compared to the young controls. There was no significant age-related phase difference in PER1 or PER2 rhythm with respect to sleep timing; however, PER3 expression pattern was altered in the older subjects.

SIGNIFICANCE

This preliminary study shows that human circadian clockwork in PBMCs remains intact at least until the presenile stage and suggests that the altered PER3 expression pattern may reflect decreased homeostatic sleep drive in older people.

Alterations in the circadian system in advanced age

In addition to light, a variety of non-photic stimuli can induce phase shifts in the circadian clock of rodents. We have examined the effects of advanced age on the response of the circadian clock to both photic and non-photic stimuli in old hamsters (i.e., over 16 months of age). Among the age-related changes in the circadian rhythm of locomotor activity are: (1) alterations in the phase angle of entrainment to the light-dark cycle; (2) an altered response to the phase-shifting effects of light pulses; (3) changes in the time it takes to re-entrain to a new light-dark cycle; and (4) a loss of responsiveness to the phase-shifting or entraining effects of stimuli which induce an acute increase of activity. Many of the effects of ageing on the circadian clock system can be simulated in young animals by depleting brain monoamine levels, suggesting that ageing alters monoaminergic inputs to the clock. Some of the age-related changes in the response of the clock to an activity-inducing stimulus can be reversed by implanting old animals with fetal suprachiasmatic nuclear tissue. Determining the physiological basis of age-related changes in the responsiveness of the clock to both internal and external stimuli, and the mechanisms by which normal circadian functioning can be restored, should lead to new insight into the functioning of the circadian clock and may suggest new approaches to the normalization of disturbed circadian rhythms.

Sleep habits and circadian preference in Italian children and adolescents

Sleep habits and circadian preference (morningness/eveningness, M/E) have been extensively analyzed in adolescents and young adults, while few studies were conducted on children and early adolescents. Aim of the present study was to investigate the developmental changes of circadian preference and to analyze its relationship with sleep habits, sleep problems and circadian preference in a large sample by means of a school-based survey. One thousand seventy-three participants (50.8% boys and 49.2% girls; mean age = 10.6; range = 8-14 years), recruited from four schools randomly extracted within the district of Rome, completed a modified version of School Sleep Habits Survey developed by Carskadon et al. The questionnaire included items about sleep habits during schooldays and weekends; a Sleepiness Scale; a Sleep-Wake Problems Behaviour Scale; a Morningness/Eveningness scale. The results show a consistent age-related change in sleep habits, particularly in the weekends. The difference in sleep duration between schooldays and weekends increases linearly with age. No gender difference was observed in morningness/eveningness, while a significant linear increase in evening preference was found with increasing ages. M/E total scores correlated significantly with both self-reported sleep/wake problems and daytime sleepiness indicating a higher prevalence of sleep complaints in evening-type subjects. Overall, the present results support the existence of consistent age-related changes in sleep habits and M/E dimension in the 8- to 14-year age range.

Age-related disruptions of circadian rhythm and memory in the senescence-accelerated mouse (SAMP8)

Common complaints of the elderly involve impaired cognitive abilities, such as loss of memory and inability to attend. Although much research has been devoted to these cognitive impairments, other factors such as disrupted sleep patterns and increased daytime drowsiness may contribute indirectly to impaired cognitive abilities. Disrupted sleep-wake cycles may be the result of age-related changes to the internal (circadian) clock. In this article, we review recent research on aging and circadian rhythms with a focus on the senescence-accelerated mouse (SAM) as a model of aging. We explore some of the neurobiological mechanisms that appear to be responsible for our aging clock, and consider implications of this work for age-related changes in cognition.

Vieillissement et rythmes biologiques chez les primates

All living organisms exhibit rhythmic activities in a wide variety of endocrine and behavioural parameters. These biological rhythms are endogenously generated by a circadian clock, and they are entrained by cyclic variations of environmental factors called synchronizers. Aging is associated with changes in amplitude and temporal organization of many daily and seasonal rhythms. In humans, daily rhythms of sleep, thermoregulation and hormonal secretion are severely altered with aging. Except in humans, studies on primates are scarce. However, age-related effects on biological rhythms are relatively consistent among primate species studied to date, including humans. Therefore, non human primates are of valuable use for such investigations. Most studies have been performed on the Rhesus macaque (longevity 35-40 years) and on the gray mouse lemur (longevity 10-12 years). Like in humans, the rest-activity rhythm becomes fragmented in aged primates, and shows an increased activity during the resting period. Aging induces a decrease in amplitude of the body temperature rhythm and an increase in energy consumption. Various hormonal secretions exhibit a decrease with aging, but the rhythmic components of these declines have not always been depicted. Moreover, changes (amplitude or phase) in daily variations depended of the hormonal secretion tested. Taken together, these results suggest that the biological clock in the brain would be a primary target of aging. The main central clock is located in the suprachiasmatic nucleus of the hypothalamus whose endogenous oscillations are entrained by light. In this brain structure, cellular function and sensitivity to light show drastic changes with age in the mouse lemur. The precise knowledge of age-related alterations of biological rhythms in primates can have important consequences on the development of new treatments to maintain or restore biological rhythmicity in the elderly.

Shortened seasonal photoperiodic cycles accelerate aging of the diurnal and circadian locomotor activity rhythms in a primate

The gray mouse lemur (Microcebus murinus), a prosimian primate, exhibits seasonal rhythms strictly controlled by photoperiodic variations. Previous studies indicated that longevity can be altered by long-term acceleration of seasonal rhythms, providing a model for assessing various aspects of aging. To assess the effect of aging and accelerated aging on the circadian system of this primate, we compared the circadian rhythm of the locomotor activity in adult mouse lemurs (2-4.5 years, n = 9), aged mouse lemurs (5-9 years, n = 10), and adult mouse lemurs that had been exposed from birth to a shortened seasonal photoperiodic cycle (2-4.5 years, n = 7). Compared to adult animals, aged mouse lemurs showed a significant increase in intradaily variability and an advanced activity onset. Aging was characterized by a decrease in amplitude, with both a decrease in nocturnal activity and an increase in daytime activity. When maintained in constant dim red light, aged animals exhibited a shortening of the free-running period (22.8 +/- 0.1 h) compared to adult animals (23.5 +/- 0.1 h). A 3- to 5-year exposure to an accelerated seasonal photoperiodic rhythm ("annual" duration of 5 months) in accelerated mouse lemurs produced disturbances of the locomotor activity rhythm that resembled those of aged mouse lemurs, whether animals were studied in entrained or in free-running conditions. The present study demonstrated a weakened and fragmented locomotor activity rhythm during normal aging in this primate. Increasing the number of expressed seasonal cycles accelerated aging of parameters related to circadian rhythmicity in adult animals.

Shiftwork locus of control, situational and behavioural effects on sleepiness and fatigue in shiftworkers

A number of situational and behavioural individual differences moderate the impact of shift and night work. The aims of this study were to identify individual differences correlates of sleep and fatigue-related shiftwork outcomes and examine their potential relative causal impact. Power company shiftworkers completed a questionnaire that measured age/experience, number of dependents, shiftwork locus of control, morningness-eveningness, workload and sleep/health-related behaviours. Shiftwork sleep and fatigue outcome variables were also measured. Hierarchical multiple regression was used to examine predictive contributions of the individual difference variables and to generate path coefficients from situational and psychological predictors through behavioural variables to the outcome variables. Shiftwork-specific internality showed the most systematic significant causal relationships with sleep and fatigue outcomes. While not having as strong a direct causal influence on sleep and fatigue outcomes as internality, the other predictors did show more significant causal effects upon sleep-related behaviours than did internality. Behavioural variables made little contribution to the total causal effects of the predictors on the outcome variables. The results suggest control beliefs to be a moderating factor in shiftwork exposure and the potential utility of this construct in aiding more effective targeting of interventions.

Relativistic parameters of senescence

The laws of biochemistry and biology are governed by parameters whose description in mathematical formulas is based on the three-dimensional space. It is a fact, however, that the life span of a cell and its specific functions, though limited, can be extended or diminished depending on the genetic code but also, on the natural pressure of the environment. The plasticity exhibited by a cellular system has been attributed to the change of the three-dimensional structure of the cell, with time being a simple measure of this change. The model of biological relativity proposed here, considers time as a flexible fourth dimension that corresponds directly to the inertial status of the cells. Two types of clocks are defined: the relativistic biological clock (RBC) and the mechanical clock (MC). In contrast to the MCs that show the astrological reference time, the time shown by the RBCs delay because it depends on cellular activity. The maximum and the expected life span of the cells and/or the organisms can be therefore relied on time transformation. One of the most important factors that can affect time flow is the energy that is produced during metabolic work. Based on this observation, RBCs can be constructed following series of theoretical experiments in order to assess biological time and life span changes.

The timing of activity rhythms in patients with dementia is related to survival

BACKGROUND

Older adults with dementia often have disruptions in circadian rhythms, including disruptions of the rest-activity rhythm. These disruptions are a product of internal neuronal activity and external environmental influences, both of which are deficient in dementia. However, the consequences of disturbed rhythms are unknown. This study examined the relationship between rest-activity rhythms and death in patients with dementia.

METHODS

The authors recruited 149 older adults with dementia (104 women; mean age, 84.1 years) from nursing homes. Activity was recorded with wrist actigraphs from each participant for 3 days. Survival was determined by examining public death records. Cox proportional hazards models were used to determine which aspects of rest-activity rhythms were related to survival.

RESULTS

The timing of each participant's rest-activity rhythm compared with a sample of persons without dementia was related to survival, such that those who more closely resembled the persons without dementia lived longer.

CONCLUSIONS

Although rest-activity rhythms as a whole were not related to survival, the timing of the rhythm was. Patients with dementia appear to develop an abnormal timing of their rhythms, which is predictive of shorter survival. It may be possible to intervene with these patients to correct the timing of their rhythms and possibly prolong their lives.

Spontaneous fos expression in the suprachiasmatic nucleus of young and old mice

The senescence-accelerated mouse (SAMP8) is an animal model of aging that displays an array of circadian rhythm disruptions as early as 7 months of age. The present study explored the physiological basis for age-related changes in circadian rhythms by measuring c-Fos immunostaining. Cellular activity in the SCN "core" and "shell" was examined for 2-, 7-, and 12-month-old SAMP8 at circadian times (CTs) 2 and 14. Consistent with previous studies in rats, we observed higher levels of cellular activity at CT2 than at CT14, and higher levels of activity in the "shell" than in the "core" of the SCN. However, there was no effect of age on the pattern of cellular activity in either the "core" or the "shell" of the SCN. These results are discussed in the context of current research on spontaneous and light-induced c-Fos expression in the SCN of rodents.

Are age-related deficits in balance performance mediated by time of day in a prosimian primate (Microcebus murinus)?

We examined the effects of age and time of day on balance performance in the gray mouse lemur (Microcebus murinus) in relation to body temperature variations. Groups of young, adult and aged animals were entrained to either short (SP, L/D 10/14) or long photoperiod (LP, L/D 14/10) and tested in the accelerating Rotarod at three phases of their light/dark cycle (beginning and end of the light phase, beginning of the dark phase). In addition, for each test, rectal temperature (Tr) was measured. Under LP, whatever the test phase, this primate showed a clear age-related decrease in balance performance. Under SP, no significant age-related decline in balance could be detected. Whatever the photoperiod, an effect of time of day on balance performance could only be seen in adults, with better performances at the beginning of the dark phase when Tr values were higher. Under LP, daily variations of both balance performance and Tr disappeared with advancing age. Consequently, age differences were substantially greater when testing was conducted during the dark phase of the light/dark cycle. The time of day effect on balance performance and the loss of daily variations with age suggest the influence of age-related changes within the biological clock.

Age and time-of-day effects on learning and memory in a non-matching-to-sample test

This study provides further evidence that the time-of-day (TOD) when testing is conducted affects cognitive performance in old rats and, for the first time in an animal model, in young adult rats as well. Groups of young and old rats were entrained to a 12-h light-dark schedule and administered tests of learning and memory in a non-matching-to-sample (NMTS) task in a water maze. Testing was conducted at the beginning of the rats' activity cycle (AM) or at the end of the cycle (PM). In addition to age differences in performing the task, there were major findings with respect to time of testing: (1) young rats tested in the PM were better than young rats tested in the AM at learning the NMTS rule and in the delayed-NMTS (DNMTS) task; (2) old rats tested in the AM were better than PM-tested old rats on the DNMTS task, with the former attaining performance levels that approximated those of young rats; (3) the TOD effect in old rats extended to a DNMTS reversal (DNMTS-R) condition in which rats, originally tested in the AM, subsequently were administered the test in the PM, and vice versa; (4) the TOD effects in young and old rats in the DNMTS and DNMTS-R tests were strongest at relatively long delays, suggesting that hippocampal function may be particularly vulnerable to such effects; (5) there was evidence in the old rats of a relationship between diurnal drinking patterns and performance at the longest delay in the DNMTS test. These results, which parallel similar findings with human subjects, emphasize a linkage between circadian rhythmicity and cognitive performance throughout adulthood, and indicate the importance of circadian disruption in old age as a contributing factor to age differences in learning and memory performance.

Period responses to Zeitgeber signals stabilize circadian clocks during entrainment

Circadian clocks with characteristic period (tau) can be entrained to light/dark (LD) cycles by means of(i) phase shifts which are due to D/L "dawn" and/or L/D "dusk" transitions, (ii) period changes associated with long-term light exposure, or (iii) by combinations of the above possibilities. Based on stability analysis of a model circadian clock it was predicted that nocturnal burrowing mammals would benefit less from period responses than their diurnal counterparts. The model further predicted that maximal stability of circadian clock is reached when the clock slightly changes both its phase and period in response to light stimuli. Analyses of empirical phase response curve (PRC) and period response curve (tauRC) of some diurnal and nocturnal mammals revealed that PRCs of both diurnal and nocturnal mammals have similar waveform while tauRCs of nocturnal mammals are of smaller amplitude than those of diurnal mammals. The shape of the tauRC also changes with age and with increasing strength of light stimuli. During erratic fluctuations in light intensity under different weather conditions, the stability of phase of entrainment of circadian clocks appears to be achieved by an interplay between phase and period responses and the strength of light stimuli.

Age-related disruptions in circadian timing: evidence for "split" activity rhythms in the SAMP8

In the senescence-accelerated mouse of the P8 line (SAMP8), age-related changes in circadian timing include a decrease in amplitude of the rhythm, a slower rate of re-entrainment following a phase advance, and a longer free-running period (tau). The present study extends previous research by investigating possible split activity rhythms in the SAMP8. Running wheel activity was examined in 2-, 7-, and 12-month SAMP8. Consistent with previous research, rhythms of older SAMP8 were decreased in amplitude and showed high levels of activity during the light phase of the light-dark cycle. Contrary to previous reports, lengthening of tau in constant darkness was not observed. Additionally, activity rhythms were "split" in older SAMP8, demonstrated by 1) the appearance of a secondary peak in the periodogram at approximately half the value of tau and 2) the perceptual classification of actograms by naïve observers. This result differs from previous studies in hamsters demonstrating an age-related decrease in the incidence of rhythm splitting. Overall, the present findings provide further evidence for age-related disruption of circadian timing in SAMP8.

Senescence, sleep, and circadian rhythms

The goal of this review article is to summarize our knowledge and understanding of the overlapping (interdisciplinary) areas of senescence, sleep, and circadian rhythms. Our overview comprehensively (and visually wherever possible), emphasizes the organizational, dynamic, and plastic nature of both sleep and circadian timing system (CTS) during senescent processes in animals and in humans. In this review, we focus on the studies that deal with sleep and circadian rhythms in aged animals and how these studies have closely correlated to and advanced our understanding of similar processes in ageing humans. Our comprehensive summary of various aspects of the existing research on animal and human ageing, both normal and pathological, presented in this review underscores the invaluable advantage of close collaboration between clinicians and basic research scientists and the future challenges inherent in this collaboration. First, our review addresses the common age-related changes that occur in sleep and temporal organization of both animals and humans. Second, we examine the specific modifications that often accompany sleep and CTS during aging. Third, we discuss the clinical epidemiology of sleep dysfunctions during ageing and their current clinical management, both pharmacological and non-pharmacological. Finally, we predict the possible future promises for complementary and alternative medicine (CAM) that pave the way to the emergence of a "Holistic Sleep Medicine" approach to the treatment of sleep disorders in the ageing population. Further studies will provide additional valuable insights into the understanding of both sleep and circadian rhythms during senescence.

Aged men display blunted biorhythmic variation of muscle performance and physiological responses

Aging is known to disrupt the "biological clock" that governs physiological variables at rest. This study sought to determine whether aged men demonstrated biorhythmic variation in muscle performance during resistance exercise and physiological responses to that stimulus. Ten aged (75.6 +/- 1.6 yr; mean +/- SE) men completed an isokinetic testing protocol of knee extensors and flexors at 0800, 1200, 1600, and 2000 h. Although time of day variation in peak torque was detectable, significant (P < or = 0.05) oscillation was established only in the knee flexors at 3.14 rad/s. Heart rate, blood pressure, and rectal temperature displayed no significant variation, but trends (P < 0.10) in oscillation of postexercise blood pressure and rectal temperature were noted. Temporal patterns in biorhythmic variation of muscle performance, as well as thermal and cardiovascular measures, emulated those observed in a previous study involving young men where the magnitude of variation was sufficient to achieve statistical significance. Similar to our earlier findings in young men, however, pre- and postexercise testosterone and cortisol concentrations demonstrated significant variation among aged men. These data confirm the blunting of biorhythmic variation in muscle performance and physiological variables, except for circulating hormones, in aged men.

Effect of light treatment on sleep and circadian rhythms in demented nursing home patients

OBJECTIVES

To determine whether fragmented sleep in nursing home patients would improve with increased exposure to bright light.

DESIGN

Randomized controlled trial.

SETTING

Two San Diego-area nursing homes.

PARTICIPANTS

Seventy-seven (58 women, 19 men) nursing home residents participated. Mean age +/- standard deviation was 85.7 +/- 7.3 (range 60-100) and mean Mini-Mental State Examination was 12.8 +/- 8.8 (range 0-30).

INTERVENTIONS

Participants were assigned to one of four treatments: evening bright light, morning bright light, daytime sleep restriction, or evening dim red light.

MEASUREMENTS

Improvement in nighttime sleep quality, daytime alertness, and circadian activity rhythm parameters.

RESULTS

There were no improvements in nighttime sleep or daytime alertness in any of the treatment groups. Morning bright light delayed the peak of the activity rhythm (acrophase) and increased the mean activity level (mesor). In addition, subjects in the morning bright light group had improved activity rhythmicity during the 10 days of treatment.

CONCLUSION

Increasing exposure to morning bright light delayed the acrophase of the activity rhythm and made the circadian rhythm more robust. These changes have the potential to be clinically beneficial because it may be easier to provide nursing care to patients whose circadian activity patterns are more socially acceptable.

Artificially accelerated aging by shortened photoperiod alters early gene expression (Fos) in the suprachiasmatic nucleus and sulfatoxymelatonin excretion in a small primate, Microcebus murinus

In mammals, a number of anatomical and functional changes occur in the circadian timing system with aging. In certain species, aging can be modified by various factors which induce a number of pathological changes. In a small primate, the gray mouse lemur (Microcebus murinus), long-term acceleration of seasonal rhythms by exposing the animals to a shortened photoperiodic regime (up to 2.5 times the natural photoperiodic regime) alters longevity, based on survival curves and morphological changes. This provides a model for challenging the idea that modifications of the circadian pacemaker are related to chronological (years) versus biological (photoperiodic cycles) age. To assess the effect of aging and accelerated aging on the circadian pacemaker of this primate, we measured body weight variations, the daily rhythm in urine 6-sulfatoxymelatonin and the light-induced expression of the immediate early gene (Fos) in the suprachiasmatic nucleus of mouse lemurs that had been exposed to different photoperiodic cycles. Urine samples were collected throughout the day and urine 6-sulfatoxymelatonin levels were measured by radioimmunoassay. Light-induced Fos expression in the suprachiasmatic nucleus was studied by exposing the animals to a 15-min monochromatic pulse of light (500 nm) at saturating or sub-saturating levels of irradiance (10(11) or 10(14) photons/cm(2)/s) during the dark phase. The classical pattern of 6-sulfatoxymelatonin excretion was significantly altered in aged mouse lemurs which failed to show a nocturnal peak. Fos expression following exposure to low levels of irradiance was reduced by 88% in the suprachiasmatic nucleus of aged mouse lemurs. Exposure to higher irradiance levels showed similar results, with a reduction of 66% in Fos expression in the aged animals. Animals subjected to artificially accelerated aging demonstrated the same alterations in melatonin production and Fos response to light as animals that had been maintained in a routine photoperiodic cycle. Our data indicate that there are dramatic changes in melatonin production and in the cellular response to photic input in the suprachiasmatic nucleus of aged mouse lemurs, and that these alterations depend on the number of expressed seasonal cycles rather than on a fixed chronological age. These results provide new insights into the mechanisms underlying artificial accelerated aging at the level of the molecular mechanisms of the biological clock.

Circadian profile of Per gene mRNA expression in the suprachiasmatic nucleus, paraventricular nucleus, and pineal body of aged rats

Aging alters circadian components such as the free-running period, the day-to-night activity ratio and photic entrainment in behavioral rhythms, and 2-deoxyglucose uptakes and neuronal firing in the suprachiasmatic nucleus (SCN). A core clock mechanism in the mouse SCN appears to involve a transcriptional feedback loop in which Period (Per) and Cryptochrome (Cry) genes play a role in negative feedback. The circadian rhythm systems include photic entrainment, clock oscillation, and outputs of clock information such as melatonin production. In this experiment, we examined clock gene expression to determine whether circadian input, oscillation, and output are disrupted with aging. Circadian expression profiles of rPer1, rPer2, or rCry1 mRNA were very similar in the SCN, the paraventricular nucleus of the hypothalamus (PVN), and the pineal body of young and aged (22-26 months) rats. On the other hand, the photic stimulation-induced rapid expression of Per1 and Per2 in the SCN was reduced with aging. The present results suggest that the molecular mechanism of clock oscillation in the SCN, PVN, and pineal body is preserved against aging, whereas the impairment of Per1 induction in the SCN after light stimulation may result in impaired behavioral photic entrainment in aged rats.

Effects of aging on the intrinsic circadian period of totally blind humans

Age-related changes in the intrinsic circadian period (tau) have been hypothesized to account for sleep symptoms in the elderly such as early morning awakening. The authors sought to determine whether the aging process produced quantifiable differences in the tau of totally blind men who had free-running circadian rhythms. The melatonin onset was used as the indicator of circadian phase. Melatonin rhythms had been characterized about a decade previously when the participants were 38 +/- 6 (SD) years old. Both previous and current assessments of tau were derived from at least 3 serial measurements of the 24-h melatonin profile from which the melatonin onset was determined. All 6 participants exhibited a longer tau in the 2nd assessment (mean increase +/- SD of 0.13 +/- 0.08 h; p < 0.01). Four participants exhibited differences in tau with nonoverlapping 95% confidence intervals. The results do not support the commonly held view that tau shortens during human aging. On the contrary, tau appears to slightly, but significantly, lengthen during at least 1 decade in midlife.

A melatonin agonist facilitates circadian resynchronization in old hamsters after abrupt shifts in the light-dark cycle

Age-related changes in the mammalian circadian system may be associated with a decline in circulating melatonin levels. Using 'jet lag' paradigms involving abrupt shifts in the light-dark cycle, we showed that a melatonin agonist, S-20098, accelerated by approximately 25% resynchronization of the circadian activity rhythm in old hamsters to the new light-dark cycle. It suggests the usefulness of melatonin-related compounds to treat circadian disorders associated with aging.

The suprachiasmatic nucleus and the circadian time-keeping system revisited

Many physiological and behavioral processes show circadian rhythms which are generated by an internal time-keeping system, the biological clock. In rodents, evidence from a variety of studies has shown the suprachiasmatic nucleus (SCN) to be the site of the master pacemaker controlling circadian rhythms. The clock of the SCN oscillates with a near 24-h period but is entrained to solar day/night rhythm by light. Much progress has been made recently in understanding the mechanisms of the circadian system of the SCN, its inputs for entrainment and its outputs for transfer of the rhythm to the rest of the brain. The present review summarizes these new developments concerning the properties of the SCN and the mechanisms of circadian time-keeping. First, we will summarize data concerning the anatomical and physiological organization of the SCN, including the roles of SCN neuropeptide/neurotransmitter systems, and our current knowledge of SCN input and output pathways. Second, we will discuss SCN transplantation studies and how they have contributed to knowledge of the intrinsic properties of the SCN, communication between the SCN and its targets, and age-related changes in the circadian system. Third, recent findings concerning the genes and molecules involved in the intrinsic pacemaker mechanisms of insect and mammalian clocks will be reviewed. Finally, we will discuss exciting new possibilities concerning the use of viral vector-mediated gene transfer as an approach to investigate mechanisms of circadian time-keeping.

Effects of the 5HT1A agonist/antagonist BMY 7378 on light-induced phase advances in hamster circadian activity rhythms during aging

The entrainment of some circadian rhythms in rodents and humans to the environmental light-dark cycle deteriorates during aging. Recent evidence suggests that the time-keeping ability of the circadian pacemaker maintains its endogenous period in both hamsters and humans. This suggests that any changes in the coupling between environmental cues and the circadian pacemaker are not due to changes in "clock speed," but rather due to a weakened coupling between the afferent systems relaying environmental information and the circadian pacemaker located in the suprachiasmatic nucleus. The suprachiasmatic nucleus receives serotonergic input from the raphe nuclei, and serotonergic 5HT1A,7 agonists have been reported to lose their circadian phase-adjusting efficacy during aging in hamsters. In the present study, the authors report the effects of a novel serotonergic agonist BMY 7378 on light-induced phase advances during aging in the hamster. The present report demonstrates that BMY 7378 is a highly efficacious chronobiotic that more than doubles the magnitude of light-induced phase shifts in hamster wheel-running activity rhythms. Light-induced phase advances in hamster wheel-running activity of at least 6 h following a single systemic dose of BMY 7378 are routinely observed. Furthermore, BMY 7378 potentiation of phase shifts is maintained in old hamsters, suggesting that BMY 7378 has a different site of activity than previously reported 5HT1A,7 agonists that have a diminished effect on circadian phase during aging.