Changes in circadian rhythms and sleep quality with aging: mechanisms and interventions

The effect of bright light on sleep and behavior in dementia

The purpose of this study was to examine bright light as a means of intervention in sleep-wakefulness and behavior disorder among patients with dementia through a review of the relevant literature. Fourteen articles were reviewed in depth for study design, intervention protocols, concurrent control groups, subject characteristics, and outcome measures of behavior and sleep. Previous studies found that behavior disorders improved, although not all the studies reviewed reported a quantitative measure of improvement. The effects on sleep disorders were controversial. As a result of limitations in past studies, the effect of bright light on dementia patients is inconclusive. The current review has revealed areas of weakness in previous research that might profitably be explored in the future.

Imaging of the 5-HT2A system: age-, gender-, and Alzheimer's disease-related findings

Serotonin (5-HT) and more specifically the 5-HT(2A) receptor is involved in cognitive and non-cognitive behavior and plays an important role in Alzheimer's disease (AD). The objective was to assess the 5-HT(2A) binding potential (BP) in healthy volunteers and AD with SPECT and 123I-5-I-R91150, a selective radio-iodinated 5-HT(2A) receptor antagonist. Twenty-six controls and nine AD patients were included. A semiquantitive analysis with normalization on cerebellar uptake provided estimates of BP for 26 cortical regions of interest. An age-related decline of neocortical BP was found (11.6% per decade). Compared to age-matched controls, a generally decreased neocortical BP in AD was found with a significant regional reduction in the orbitofrontal, prefrontal, lateral frontal, cingulate, sensorimotor, parietal inferior, and occipital region. These results are in line with previous postmortem, in vitro, and PET findings. The age-related decline highlights the necessity for matched advanced age study samples. The fact that the 5-HT(2A) receptor is differentially affected in AD patients has implications for both the etiological basis and therapeutic management of AD.

Caffeine raises the serum melatonin level in healthy subjects: an indication of melatonin metabolism by cytochrome P450(CYP)1A2

Caffeine is metabolized in the liver by cytochrome P450(CYP)1A2. Recent findings imply that this enzyme may also be of importance for the metabolism of human melatonin (MT). If caffeine and MT are metabolized by the same enzyme, one may expect to find different serum MT levels after ingestion of coffee compared with placebo. Although coffee is consumed by people all over the world, few studies have focused on whether caffeine actually affects serum MT levels in normal subjects. We decided to study that particular topic. For that purpose 12 healthy individuals were tested on two occasions, one week apart. On one of these occasions they were given a capsule containing 200 mg caffeine in the evening. On the other, they received placebo. The experimental order was randomized. Serum MT levels were determined every second hour between 22:00 h and 08:00 h, and the melatonin areas under the curve (MT-AUCs) were calculated. After caffeine the serum MT level rose from 0.09 +/- 0.03 nmol/l at 22:00 h to 0.48 +/- 0.07 nmol/l at 04:00 h. The corresponding rise after placebo was less prominent (from 0.06 +/- 0.01 to 0.35 +/- 0.06 nmol/l). This was reflected by the MT-AUC which was 32% larger after ingestion of caffeine compared with placebo (MT-AUC(caffeine) 3.16 +/- 0.44 nmol/l x h vs MT-AUC(placebo) 2.39 +/- 0.40 nmol/l x h; p < 0.02). These findings imply that caffeine, ingested in the evening at a dose corresponding to two ordinary cups of coffee, augments the nocturnal serum MT level, which in turn supports the notion that cytochrome P450(CYP)1A2 is involved in the hepatic metabolism of human MT.

Decline in long-term circadian rest-activity cycle organization in a patient with dementia

Continuous measurement of the circadian rest-activity cycle for 598 days in a demented patient with probable Alzheimer's disease revealed slow progressive changes in temporal organization until death. Circadian and sleep analysis of the actigraphic data provided objective documentation of the gradual insertion of wakefulness into rest and rest into wake periods. Pacing, a nonphotic zeitgeber strengthening, led to improved synchronization of the rest-activity cycle.

Age-associated difference in circadian sleep-wake and rest-activity rhythms

Using actigraphic monitoring of wrist activity, we investigated the sleep and rest-activity patterns of 65 young, middle-aged, old and the oldest subjects in their natural environmental conditions. To assess the effects of age and gender on sleep and circadian rhythms in activity, multivariate analyses were performed. Age significantly affected circadian sleep and rest-activity rhythms. In the old and oldest groups, the actigraphic estimates of "actual sleep time" and "sleep efficiency" decreased significantly. The estimates of "sleep latency," the number of "nighttime awakening," sleep fragmentation and daytime naps significantly increased in the old and oldest groups. Concerning the circadian patterning of rest and activity, the interdaily stability (IS) was similar in the four age groups, while the old and oldest subjects showed significant increases in intradaily variability (IV) and nighttime activity and a decrease in amplitude (AMP). The present study demonstrated weakened and fragmented circadian sleep and rest-activity rhythms during aging. However, no gender-related difference was found.

Awakening from sleep

Awakening is a crucial event for the organism. The transition from sleep to waking implies physiological processes which lead to a new behavioural state. Spontaneous awakenings have varying features which may change as a function of several factors. The latter include intrasleep architecture, circadian phase, time awake, age, or disordered sleep. Despite its clear theoretical and clinical importance, the topic of awakening (in humans) has received little attention so far. This contribution focuses on major issues which relate to awakening from both basic (experimental) and clinical research. Recent knowledge on neurophysiological mechanisms is reported. The experimental data which provide in the human suggestions on the regulation of awakening are discussed, mainly those concerning sleep architecture and homeostatic/circadian factors also in a life-span perspective, since age is a powerful factor which may influence awakening. Clinical contributions will examine two main sleep disorders: insomnia and hypersomnia. Daytime functioning is shown in insomniac patients and compared to other pathologies like sleep apnea. A final section evokes links between some types of night waking and psychological factors.

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.

Peak of circadian melatonin rhythm occurs later within the sleep of older subjects

We investigated the relationship between sleep timing and the timing of the circadian rhythm of plasma melatonin secretion in a group of healthy young and older subjects without sleep complaints. The timing of sleep and the phase of the circadian melatonin rhythm were earlier in the older subjects. The relationship between the plasma melatonin rhythm and the timing of sleep was such that the older subjects were sleeping and waking earlier relative to their nightly melatonin secretory episode. Consequently, the older subjects were waking at a time when they had higher relative melatonin levels, in contrast with younger subjects, whose melatonin levels were relatively lower by wake time. Our findings indicate that aging is associated not only with an advance of sleep timing and the timing of circadian rhythms but also with a change in the internal phase relationship between the sleep-wake cycle and the output of the circadian pacemaker. In healthy older subjects, the relative timing of the melatonin rhythm with respect to sleep may not play a causal role in sleep disruption.

Sleep disturbances in patients with Alzheimer's disease: epidemiology, pathophysiology and treatment

Older adults represent an ever-growing proportion of the population of the industrialised nations, with a corresponding increase in the numbers of patients with dementing disorders. A common complaint in both normal aging and the dementias is that of significant sleep disturbance. The major causes of sleep disruption in aging and dementia include: (i) physiological changes that arise as part of normal, 'nonpathological' aging; (ii) sleep problems due to one of many physical or mental health conditions and their treatments; (iii) primary sleep disorders; (iv) poor 'sleep hygiene', that is, sleep-related practices and habits; and (v) some combination of these factors. Disrupted sleep in patients with dementia is a significant cause of stress for caregivers and frequently leads to institutionalisation of patients. It should be a target of clinical management when the goal is sustained home care, and when it is associated with disturbances of mood or behaviour. While the neuropathology of dementia can directly disrupt sleep, sleep disturbances in patients with dementia often have multiple causes that require systematic evaluation. Thorough assessment of associated psychopathology, day-time behaviour, medical disorders, medications, pain and environmental conditions is needed for optimal management. Differential diagnosis of a sleep problem in dementia is the basis of rational pharmacotherapy. However, patients with dementia are likely to be more sensitive than elderly persons without dementia to adverse cognitive and motor effects of drugs prescribed for sleep. Clinicians need to: (i) evaluate sleep outcomes when treating medical, psychiatric and behavioural disorders in older adults; (ii) be alert to emerging behavioural and environmental approaches to treatment; (iii) combine nonpharmacological strategies with drug therapies, when required, for added value; and (iv) avoid use of multiple psychotropic medications unless they prove essential to the adequate management of sleep disturbances.

Sleep Complaints of Postmenopausal Women

OBJECTIVE: To study correlates of sleep problems in postmenopausal women. METHODS: Baseline questionnaire items related to sleep patterns and problems were administered to 98,705 postmenopausal women as part of the Clinical Trial and the Observational Study of the Women's Health Initiative. RESULTS: Less than 27% of the sample reported sleeping 8 hours or more. Many women reported that at least once a week they awoke several times at night (61%), fell asleep during quiet activities (52%), or reported other symptoms suggestive of insomnia or excessive daytime sleepiness. More frequent insomnia problems were reported among women who reported nocturnal sleep longer than the mode of 7 hours, as well as among women who reported very short sleep. Age, ethnicity, hormone replacement therapy, employment, marital status, diet, and season explained remarkably little of the variance in sleep duration or insomnia complaints; however, black women reported sleeping 0.45 hours on average less than whites, with the other minorities being intermediate between these groups. CONCLUSIONS: The results suggest that simple abbreviation of sleep and demographic factors may be less important in the sleep complaints of postmenopausal women than other possible factors. Cognitive-behavioral processes, depression, and obesity with apnea may be among the causes.

Age differences in sleep-wake behavior under natural conditions

Differences in lifestyle may account for a considerable portion of the reported age-related changes in overt circadian rhythmicity. By instructing a group of healthy, noninstitutionalized, elderly subjects and a group of young adults to keep a sleep-wake log for a period of two weeks, and to wear an activity monitor for an overlapping period of 11 days, we attempted to assess age-related differences in the habitual sleep-wake behavior, in particular its day-to-day variability. Four clusters of coherent variables were constructed, reflecting (1) circadian phase, (2) variability of sleep-wake behavior, (3) sleep-wake continuity and (4) subjective sleep-wake quality. The results showed that, in comparison with the young subjects, the elderly had a relatively advanced and more regular sleep-wake pattern, reported more midnight awakening and did not differ in their subjective sleep evaluation. In spite of a greater regularity in their lifestyle (which would favor a larger amplitude of the overt circadian rhythmicity) oral temperature measurements showed some evidence of a weakened 24-h periodicity in the elderly.

Melatonin or a melatonin agonist corrects age-related changes in circadian response to environmental stimulus

The effects of a melatonin agonist, S-20098, included in the diet were tested on a specific effect of aging in hamsters: the marked decline in the phase shifting effects of a 6-h pulse of darkness on a background of constant light. In contrast to young hamsters, old hamsters fed with the control diet showed little or no phase shifts in response to a dark pulse presented in the middle of their inactive or active period. Old hamsters fed with S-20098 showed phase shifts that were ~70% of the ones in young animals and significantly greater than those in old controls. The phase advancing response to a dark pulse presented during the inactive period was dose dependent and reversed after S-20098 discontinuation. Melatonin included in the diet showed comparable restorative effects on the phase shifting response to a dark pulse in old hamsters. Replacement therapy with melatonin or melatonin-related compounds could prove useful in treating, preventing, or delaying disturbances of circadian rhythmicity and/or sleep in older people.

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.

Aging-induced changes in 24-h rhythms of mitogenic responses, lymphocyte subset populations and neurotransmitter and amino acid content in rat submaxillary lymph nodes during Freund's adjuvant arthritis

In young (two months) and aged (18 months) male rats injected s.c. with Freund's adjuvant or adjuvant's vehicle 18 days earlier, 24-h variations in mitogenic responses, lymphocyte subsets and monoamine and amino acid content were examined in submaxillary lymph nodes. Mitogenic responses to concanavalin A (Con A) and lipopolysaccharide (LPS) were higher during the light phase of daily photoperiod. Old rats exhibited a suppressed or impaired mitogenic response to Con A but not to LPS. Acrophases of 24-h rhythm in lymphocyte subset populations in submaxillary lymph nodes were: 18:37-19:44h (B cells), 09:00-10:08h (T and CD4(+) cells) and 12:19-15:58h (CD8(+) cells). Aging augmented B cells and decreased T, CD4(+) and CD8(+) cells. Significant correlations were found between Con A activity and T cells, between lymph node 5HT content and B, T and CD8(+) lymphocytes, and between lymph node 5HT and taurine and GABA content. Aging increased lymph node 5HT content but did not modify NE content. Lymph node concentration of aspartate, glutamate and taurine was higher at night while that of GABA attained peak values at late afternoon. Old rats injected with Freund's adjuvant showed a higher mean value (glutamate) and smaller amplitude (glutamate, taurine) than their respective young controls. The results further document the effects of aging on the chronobiology of the immune system.

Circadian phase resetting in older people by ocular bright light exposure

BACKGROUND

Aging is associated with frequent complaints about earlier bedtimes and waketimes. These changes in sleep timing are associated with an earlier timing of multiple endogenous rhythms, including core body temperature (CBT) and plasma melatonin, driven by the circadian pacemaker. One possible cause of the age-related shift of endogenous circadian rhythms and the timing of sleep relative to clock time is a change in the phase-shifting capacity of the circadian pacemaker in response to the environmental light-dark cycle, the principal synchronizer of the human circadian system.

METHODS

We studied the response of the circadian system of 24 older men and women and 23 young men to scheduled exposure to ocular bright light stimuli. Light stimuli were 5 hours in duration, administered for 3 consecutive days at an illuminance of approximately 10,000 lux. Light stimuli were scheduled 1.5 or 3.5 hours after the CBT nadir to induce shifts of endogenous circadian pacemaker to an earlier hour (phase advances) or were scheduled 1.5 hours before the CBT nadir to induce shifts to a later hour (phase delays). The rhythms of CBT and plasma melatonin assessed under constant conditions served as markers of circadian phase.

RESULTS

Bright light stimuli elicited robust responses of the circadian timing system in older people; both phase advances and phase delays were induced. The magnitude of the phase delays did not differ significantly between older and younger individuals, but the phase advances were significantly attenuated in older people.

CONCLUSIONS

The attenuated response to light stimuli that induce phase advances does not explain the advanced phase of the circadian pacemaker in older people. The maintained responsiveness of the circadian pacemaker to light implies that scheduled bright light exposure can be used to treat circadian phase disturbances in older people.

Treatment of sleep disturbance in Alzheimer's disease

The prevalence of Alzheimer's disease (AD) is rapidly increasing as growing numbers of people around the world are living to old age. Sleep disturbances are a common, and often highly disruptive, behavioral symptom associated with AD. Nevertheless, the study of sleep in AD is relatively new. Little is known about the moderating factors that may alter a given patient's risk for developing sleep problems, or that may influence severity of presentation and persistence. Current treatments for improving sleep in AD fall into three broad categories: (i) pharmacological; (ii) cognitive-behavioral or psycho-educational strategies; and (iii) biological/circadian therapies. There are few studies demonstrating the efficacy of these treatments with community-dwelling AD patients, although studies with persons in institutional settings are promising. In this review, it is suggested that sleep problems in AD are multi-factorial, and influenced by a variety of demographic, physical, psychiatric and situational factors. These factors vary in how readily they can be modified and in how relevant they are to any individual case. Thus, when developing a treatment plan for sleep problems in a dementia patient, it is important to evaluate the underlying causes as well as the context in which the problems are occurring, and to target the intervention accordingly.

Sleep and circadian phase characteristics of adolescent and young adult males in a naturalistic summertime condition

Our aim was to compare the circadian phase characteristics of healthy adolescent and young adult males in a naturalistic summertime condition. A total of 19 adolescents (mean age 15.7 years) and 18 young adults (mean age 24.5 years) with no sleep problems took part in this study. Two-night polysomnographic (PSG) sleep recordings and 24h secretion patterns of urinary 6-sulfatoxymelatonin were monitored in all 37 subjects. Sleep-wake patterns were initially assessed at home using a standard sleep diary. Circadian assessment included the measure of dim light melatonin offset (DLMOff) and the morningness-eveningness (M/E) questionnaire. As expected, compared to young adults, adolescents habitually spent more nocturnal time in bed and spent more time (and percentage) in delta sleep. No difference was found between adolescents and young adults on multiple sleep latency test (MSLT) sleep onset latencies, M/E, melatonin secretion measures (24h total, nighttime, daytime, and night ratio), and DLMOff. For the subjects as a whole, correlational analyses revealed a significant association between the DLMOff and M/E and between both these phase markers and habitual bedtimes, habitual rising times, and melatonin secretion measures (daytime levels and the night ratio). No association was found between phase markers and daytime sleepiness or sleep consolidation parameters such as sleep efficiency or number of microarousals. These results together indicate that adolescents and young adults investigated during summertime showed similar circadian phase characteristics, and that, in these age groups, an evening phase preference is associated with a delayed melatonin secretion pattern and delayed habitual sleep patterns without a decrease in sleep consolidation or vigilance.

Contribution of circadian physiology and sleep homeostasis to age-related changes in human sleep

The circadian pacemaker and sleep homeostasis play pivotal roles in vigilance state control. It has been hypothesized that age-related changes in the human circadian pacemaker, as well as sleep homeostatic mechanisms, contribute to the hallmarks of age-related changes in sleep, that is, earlier wake time and reduced sleep consolidation. Assessments of circadian parameters in healthy young (approximately 20-30 years old) and older people (approximately 65-75 years old)--in the absence of the confounding effects of sleep, changes in posture, and light exposure--have demonstrated that an earlier wake time in older people is accompanied by about a 1 h advance of the rhythms of core body temperature and melatonin. In addition, older people wake up at an earlier circadian phase of the body temperature and plasma melatonin rhythm. The amplitude of the endogenous circadian component of the core body temperature rhythm assessed during constant routine and forced desynchrony protocols is reduced by 20-30% in older people. Recent assessments of the intrinsic period of the human circadian pacemaker in the absence of the confounding effects of light revealed no age-related reduction of this parameter in both sighted and blind individuals. Wake maintenance and sleep initiation are not markedly affected by age except that sleep latencies are longer in older people when sleep initiation is attempted in the early morning. In contrast, major age-related reductions in the consolidation and duration of sleep occur at all circadian phases. Sleep of older people is particularly disrupted when scheduled on the rising limb of the temperature rhythm, indicating that the sleep of older people is more susceptible to arousal signals generated by the circadian pacemaker. Sleep-homeostatic mechanisms, as assayed by the sleep-deprivation-induced increase of EEG slow-wave activity (SWA), are operative in older people, although during both baseline sleep and recovery sleep SWA in older people remains at lower levels. The internal circadian phase advance of awakening, as well as the age-related reduction in sleep consolidation, appears related to an age-related reduction in the promotion of sleep by the circadian pacemaker during the biological night in combination with a reduced homeostatic pressure for sleep. Early morning light exposure associated with this advance of awakening in older people could reinforce the advanced circadian phase. Quantification of the interaction between sleep homeostasis and circadian rhythmicity contributes to understanding age-related changes in sleep timing and quality.

The human circadian clock and aging

The suprachiasmatic nucleus (SCN) of the hypothalamus is implicated in the timing of a wide variety of circadian processes. Since the environmental light-dark cycle is the main zeitgeber for many of the rhythms, photic information may have a synchronizing effect on the endogenous clock of the SCN by inducing periodic changes in the biological activity of certain groups of neurons. By studying the brains obtained at autopsy of human subjects, marked diurnal oscillations were observed in the neuropeptide content of the SCN. Vasopressin, for example, one of the most abundant peptides in the human SCN, exhibited a diurnal rhythm, with low values at night and peak values during the early morning. However, with advancing age, these diurnal fluctuations deteriorated, leading to a disrupted cycle with a reduced amplitude in elderly people. These findings suggest that the synthesis of some peptides in the human SCN exhibits an endogenous circadian rhythmicity, and that the temporal organization of these rhythms becomes progressively disturbed in senescence.

Age-dependent effect of Freund's adjuvant on 24-hour rhythms in plasma prolactin, growth hormone, thyrotropin, insulin, follicle-stimulating hormone, luteinizing hormone and testosterone in rats

The effect of Freund's adjuvant administration on 24-hour changes of plasma prolactin, growth hormone (GH), thyrotropin (TSH), insulin, follicle-stimulating hormone (FSH), luteinizing hormone (LH) and testosterone were studied in young (2 months) and aged (18 months) male Wistar rats. Rats were injected s.c. with Freund's adjuvant or adjuvant's vehicle and, 18 days later, they were killed at 6 different time intervals throughout a 24-hour cycle to measure circulating hormone levels by specific RIAs. Young rats receiving adjuvant's vehicle exhibited significant time-of-day-dependent variations in plasma TSH, LH and testosterone, with maximal levels at 1300 h, 0100 h and 1700 h, respectively. Prolactin and insulin levels, analyzed globally in a factorial ANOVA, showed significant time-of-day changes with maximal levels at 1300 - 1700 h and 2100 h, respectively. The daily rhythms in plasma LH and testosterone found in young rats were not longer observed in Freund's adjuvant-injected rats, while as far as TSH, a second peak was observed at 0100 h after Freund's adjuvant administration. Twenty-four hour rhythms in circulating TSH, LH and testosterone were blunted in old rats receiving either Freund's adjuvant or its vehicle. Aged rats exhibited significantly higher circulating levels of prolactin, and lower levels of GH, TSH, FSH and testosterone. The results indicate that secretion of prolactin, GH, TSH, FSH and testosterone are age-dependent, as are the responses of TSH, LH and testosterone to Freund's adjuvant administration.

Sleep-wake cycle, sleep-related disturbances, and sleep disorders: a chronobiological approach

There is convincing evidence that the functions of sleep include restoration of brain energy storage and memory consolidation. The circadian timing system (CTS) is involved in the daily variation of almost any physiological and psychological variable evaluated thus far. Disturbances of the CTS can be clinically observed by their influence on the sleep-wake cycle, hormones, body temperature, and locomotor activity. This article reviews the basic mechanisms of circadian rhythm sleep disturbances, names the applicable diagnostic tools and specific therapeutic strategies, and thereby hints at the impact of circadian rhythm sleep disturbance on psychiatric disorders, especially disorders of affect and cognition. In light of the preventive, diagnostic, and therapeutic tools now available, a new round of chronobiological studies in psychiatry seems justified, promising, and necessary.

Circadian heart rate rhythms in Japanese centenarians

OBJECTIVE

To investigate age-associated changes in the circadian rhythm of the heart rate.

DESIGN

The circadian rhythm was extracted from diurnal heart rate (HR) variations, and patterns of HR rhythm were compared in centenarians and controls.

SETTING

Centenarians living in the metropolitan area of Tokyo and in Aichi prefecture in 1992.

PARTICIPANTS

Fifty centenarians underwent 24-hour ambulatory electrocardiogram (Holter) monitoring. The control group, comprised of 100 clinically healthy subjects who underwent similar Holter monitoring, was subdivided, by age, into two groups: the younger controls (age range 23 to 54 years, mean age 41) and the older controls (age range 55 to 82 years, mean age 69).

MEASUREMENTS

Harmonic analysis was used to approximate the 24-hour RR interval (the interval between two neighboring R waves on the electrocardiogram) data obtained by Holter monitoring to a summation of three cosine waves with 24-hour, 12-hour, and 8-hour periods. The power of the period was adjusted for the goodness of curve-fit. The power of each period and the circadian acrophase (the timing of the peak in a 24-hour rhythm) were compared among the centenarians, older controls, and younger controls. HR rhythms were classified by k-means cluster analysis based on the power of the period. The prevalence of each pattern was compared among the three age groups. In the centenarians, the relationship between clinical parameters (activities of daily living, cognitive function, nutritional status, and present illness) and patterns of HR rhythm was investigated.

RESULTS

The power of the 24-hour period in the centenarians was significantly smaller than that in the older (P < .05) and younger (P < .001) controls. The power of the 8-hour period in the centenarians was significantly larger than that in the younger controls (P < .05). Advances or delays in the circadian acrophase were frequently observed in the centenarians compared with the younger controls. The power of each period did not differ between centenarians with (n = 11) and without (n = 39) overt diseases capable of altering HR rhythms. Five patterns of HR rhythm were identified: 24-hour period dominant (n = 84), 24-hour+12-hour period (n = 18), 12-hour period dominant (n = 11), 8-hour period dominant (n = 7), and low goodness of curve-fit (n = 30). The 8-hour period dominant pattern and the low goodness of curve-fit pattern were observed commonly in the centenarians, whereas the 24-hour period dominant pattern and the 24-hour+12-hour period pattern were observed frequently in the younger controls. Patterns of HR rhythm were not related to clinical parameters in the centenarians.

CONCLUSIONS

The circadian rhythm of HR changed with aging: there was reduction in the power of the 24-hour period, augmentation in the power of the 8-hour period, and a shift in the circadian acrophase.

Free-running circadian period does not shorten with age in female Syrian hamsters

It has been reported that the free-running period of circadian rhythms shortens with age in mammals, including humans, and this shortening has been suggested to be the underlying cause of early morning awakening and difficulty maintaining sleep in older people. A recent study found that the free-running period of male hamsters does not change with age. The present study extends those findings to female hamsters. We studied the locomotor activity rhythm of 22 female hamsters kept in constant conditions from early adulthood until their death, and compared their data to those from male hamsters. We found no shortening of free-running period with age in the female hamsters, and no difference in free-running period between females and males. In contrast, mean activity level and amount of time per cycle spent running declined with age in females and males. These findings demonstrate that the free-running period in hamsters does not systematically shorten with age, and suggest that alternative explanations for the observed age-related advance of sleep-wake times in humans should be explored.

Stability, precision, and near-24-hour period of the human circadian pacemaker

Regulation of circadian period in humans was thought to differ from that of other species, with the period of the activity rhythm reported to range from 13 to 65 hours (median 25.2 hours) and the period of the body temperature rhythm reported to average 25 hours in adulthood, and to shorten with age. However, those observations were based on studies of humans exposed to light levels sufficient to confound circadian period estimation. Precise estimation of the periods of the endogenous circadian rhythms of melatonin, core body temperature, and cortisol in healthy young and older individuals living in carefully controlled lighting conditions has now revealed that the intrinsic period of the human circadian pacemaker averages 24.18 hours in both age groups, with a tight distribution consistent with other species. These findings have important implications for understanding the pathophysiology of disrupted sleep in older people.

Ageing and the circadian and homeostatic regulation of human sleep during forced desynchrony of rest, melatonin and temperature rhythms

1. The circadian timing system has been implicated in age-related changes in sleep structure, timing and consolidation in humans. 2. We investigated the circadian regulation of sleep in 13 older men and women and 11 young men by forced desynchrony of polysomnographically recorded sleep episodes (total, 482; 9 h 20 min each) and the circadian rhythms of plasma melatonin and core body temperature. 3. Stage 4 sleep was reduced in older people. Overall levels of rapid eye movement (REM) sleep were not significantly affected by age. The latencies to REM sleep were shorter in older people when sleep coincided with the melatonin rhythm. REM sleep was increased in the first quarter of the sleep episode and the increase of REM sleep in the course of sleep was diminished in older people. 4. Sleep propensity co-varied with the circadian rhythms of body temperature and plasma melatonin in both age groups. Sleep latencies were longest just before the onset of melatonin secretion and short sleep latencies were observed close to the temperature nadir. In older people sleep latencies were longer close to the crest of the melatonin rhythm. 5. In older people sleep duration was reduced at all circadian phases and sleep consolidation deteriorated more rapidly during the course of sleep, especially when the second half of the sleep episode occurred after the crest of the melatonin rhythm. 6. The data demonstrate age-related decrements in sleep consolidation and increased susceptibility to circadian phase misalignment in older people. These changes, and the associated internal phase advance of the propensity to awaken from sleep, appear to be related to the interaction between a reduction in the homeostatic drive for sleep and a reduced strength of the circadian signal promoting sleep in the early morning.

Polysomnographic study of the effect of melatonin on sleep in elderly patients with chronic primary insomnia

The effect of 3-mg melatonin capsules p.o. on sleep in ten elderly patients suffering from chronic primary insomnia was assessed by polysomnographic recordings. In general, melatonin significantly reduced wake time after sleep onset and increased total sleep time and sleep efficiency during the 2-week treatment period. In five of the ten patients treated with melatonin, the increase in total sleep time was clinically significant. Side effects were absent during the period of drug administration. A slight increase of power density in the delta and the theta regions was found during the early phase (i.e. nights 4-5) of melatonin administration, whereas the opposite changes were observed at a late phase of treatment (i.e. nights 15-16). No strict correlation was found between prior 6-sulphatoxymelatonin levels in urine and subsequent sleep improvement after receiving melatonin. Our results further support the proposal that melatonin is beneficial for sleep disturbances in elderly insomniacs.

Circadian regulation of human sleep and age-related changes in its timing, consolidation and EEG characteristics

The light-entrainable circadian pacemaker located in the suprachiasmatic nucleus of the hypothalamus regulates the timing and consolidation of sleep by generating a paradoxical rhythm of sleep propensity; the circadian drive for wakefulness peaks at the end of the day spent awake, ie close to the onset of melatonin secretion at 21.00-22.00 h and the circadian drive for sleep crests shortly before habitual waking-up time. With advancing age, ie after early adulthood, sleep consolidation declines, and time of awakening and the rhythms of body temperature, plasma melatonin and cortisol shift to an earlier clock hour. The variability of the phase relationship between the sleep-wake cycle and circadian rhythms increases, and in old age sleep is more susceptible to internal arousing stimuli associated with circadian misalignment. The propensity to awaken from sleep advances relative to the body temperature nadir in older people, a change that is opposite to the phase delay of awakening relative to internal circadian rhythms associated with morningness in young people. Age-related changes do not appear to be associated with a shortening of the circadian period or a reduction of the circadian drive for wake maintenance. These changes may be related to changes in the sleep process itself, such as reductions in slow-wave sleep and sleep spindles as well as a reduced strength of the circadian signal promoting sleep in the early morning hours. Putative mediators and modulators of circadian sleep regulation are discussed.

Peripheral heat loss: a predictor of the hypothermic response to melatonin administration in young and older women

Core hypothermia following daytime melatonin administration typically displays significant interindividual variability. As this hypothermia has been associated with significant increases in skin temperature, the mechanism by which melatonin decreases core temperature may involve increasing peripheral heat loss. If so, the interindividual variability in this effect may reflect concomitant interindividual variability in heat loss capacity at the distal periphery. For six younger (mean +/- SEM: 23.4 +/- 0.3 years) and 10 older women (mean +/- SEM: 65.6 +/- 0.7 years), the maximum decrease in core body temperature following a 5-mg (p.o.) dose of melatonin was correlated with the capacity to lose heat. This was determined by the maximum increase in contralateral hand temperature following a mild positive thermal challenge (PTC). The regression analysis yielded a significant (p < 0.01) correlation of 0.80, suggesting that the individual magnitude of hypothermia following melatonin administration may reflect the capacity of an individual to dissipate heat at the distal periphery.

The relationship between 6-sulphatoxymelatonin and polysomnographic sleep in good sleeping controls and wake maintenance insomniacs, aged 55-80 years

The pineal hormone, melatonin, is reported to possess hypnotic properties. This has led to an investigation of the relationship between the endogenous melatonin rhythm and sleep. However, this relationship has yet to be fully examined in aged insomniacs and controls. From media advertisements, 16 good sleeping controls (11F, 5M) and 16 sleep maintenance insomniacs (11F, 5M), aged over 55 years, were recruited to participate in a study involving four nights of polysomnographically (PSG) measured sleep followed by a 26 h constant routine. During the constant routine, 2 h urine samples were collected and analysed for the melatonin metabolite, 6-sulphatoxymelatonin (aMT.6S). This was used to determine total melatonin excretion. As well, the following circadian melatonin parameters were calculated from fifth order polynomial curve fitting analyses, the goodness of the polynomial curve fit, peak melatonin concentration, the phase of the melatonin rhythm, and melatonin and sleep rhythm synchrony. Apart for one control, all subjects showed significant circadian melatonin rhythms. Although insomniacs showed a greater amount of wakefulness, less sleep in total, and lower sleep efficiency, no significant group differences were observed in any of the melatonin parameters. In addition, while subjects with more reliable melatonin curve fits showed shorter sleep latencies and higher sleep efficiencies, correlational analyses revealed no other significant relationships between any melatonin and PSG sleep parameters. Overall, the present results suggest that neither melatonin amplitude nor phase are related to sleep quality in the aged.

Attenuated amplitude of circadian and sleep-dependent modulation of electroencephalographic sleep spindle characteristics in elderly human subjects

Sleep spindles are 12-15 Hz electroencephalographic (EEG) oscillations characteristic of non-rapid eye movement (non-REM) sleep. Sleep EEG recordings (total 252 episodes; duration, 9 h 20 min each) distributed across the circadian cycle were analyzed in eight young and eight elderly human subjects. In the young subjects, sleep spindle amplitude, frequency, duration and incidence displayed significant circadian modulation, with the highest spindle incidence and amplitude and the lowest spindle frequency coincident with circadian phases associated with times of habitual sleep. In the elderly subjects, overall amplitude, duration, and incidence were reduced, and only spindle frequency exhibited a detectable circadian modulation. The results demonstrate that a circadian process modulates sleep spindle characteristics and that the strength of this circadian modulation is reduced with age.

Are age differences in sleep due to phase differences in the output of the circadian timing system?

Our aim was to evaluate whether age-related changes in the phase of the output of the circadian timing system (CTS) can explain age differences in habitual bedtime/wake time and in sleep consolidation parameters. Analyses focused on a group of healthy elderly people (older than 70 years) with no sleep problems and with similar subjective sleep quality as a young control group. The 2-week sleep diary data and 24h laboratory temperature recordings were examined for 70 subjects (22 young men [YM], 19 old men [OM], 29 old women [OW]). Polysomnographic (PSG) sleep data recorded during temperature data acquisition were also available for 62 subjects. These analyses made use of our recently developed technique to demask temperature rhythm data. As expected, compared to the young subjects, older subjects showed earlier habitual bedtime and wake time, more disturbed sleep, and a tendency for an earlier minimum of the circadian temperature rhythm. Despite sleep consolidation differences, the groups showed very similar habitual phase-angle differences (interval between the time occurrence of the fitted temperature minimum and habitual wake time). Both elderly and young subjects woke up on average 3 h after the temperature minimum. After controlling for the effects of age group, habitual bedtime and wake time were related to clock time phase of the circadian temperature rhythm, with an earlier phase associated with earlier habitual bedtime and wake time. None of the sleep consolidation parameters were linked to the temperature phase angle. In conclusion, sleep consolidation changes associated with healthy aging do not appear to be related to changes in the phase-angle difference between the output signal from the CTS and sleep.

Effect of sustained nocturnal transbuccal melatonin administration on sleep and temperature in elderly insomniacs

Previous research has suggested a role for the pineal hormone melatonin in the control of the body's sleep-wake and thermoregulatory systems. In the elderly population, there have been reports of decreased nighttime secretion of melatonin and suggestions that this may, in turn, be responsible for the increased incidence of sleep disorders reported by this age group. On this basis, it has been suggested that augmented nocturnal melatonin levels may improve sleep quality in age-related sleep disorders. Following screening assessments, 12 elderly (> 55 years) subjects with sleep maintenance insomnia were treated with either 0.5 mg transbuccal melatonin or a placebo for two sessions of 4 consecutive nights, at least 3 days apart. Subjects self-selected lights-out times, and sleep was assessed using standard polysomnographic (PSG) measures. Body temperature was measured continually from 2100 to 0700 h, and sleep quality was assessed from PSG variables measured. Nightly urine samples were assayed for the melatonin metabolite 6-sulfatoxy-melatonin (aMT.6S). Compared to the placebo, transbuccal melatonin administration significantly increased mean nocturnal aMT.6S excretion (mean +/- SEM: 194.2 +/- 16.5 vs. 42.5 +/- 7.7 nmol). In addition, there was a significant reduction in core body temperature relative to the placebo condition (p < .05). However, sustained transbuccal melatonin treatment had no positive significant effect on any PSG measure of sleep quality. The results from the present study suggest that sustained nocturnal administration of melatonin, in the low pharmacological range, might be of limited clinical benefit in this subject population.

Diurnal rhythms in norepinephrine and acetylcholine synthesis of sympathetic ganglia, heart and adrenals of aging rats: effect of melatonin

The effect of aging and melatonin on 24-h rhythms in tyrosine hydroxylase activity and 3H - choline conversion into 3H - acetylcholine were examined in cervical, stellate, coeliac-mesenteric and hypogastric ganglia, and in the adrenal medulla and heart of rats. Young (50 days old) and old (18 months old) rats received evening injections of 10 or 100 microg of melatonin or its vehicle for 17 days. In superior cervical, stellate and coeliac-superior mesenteric ganglia, as well as in the adrenal medulla, norepinephrine and acetylcholine synthesis attained maximal values at night (c.a. 2030-0100 h). In the hypogastric ganglion, maximal tyrosine hydroxylase activity occurred at night at both studied ages. Two maxima in acetylcholine synthesis were detected in hypogastric ganglion of young rats (c.a. 1300 h and 0100 h, respectively) while in old rats a single maximum was observed at noon. Cardiac tyrosine hydroxylase activity peaked at early night (c.a. 2200-2300 h) while cardiac acetylcholine synthesis peaked at the afternoon (c.a. 1700-1900 h). Old rats exhibited a significant decrease of rhythm amplitude and increase of mean values in tyrosine hydroxylase activity in autonomic ganglia and adrenal medulla, and abolition of tyrosine hydroxylase rhythm in the heart. Twenty-four hour rhythmicity in acetylcholine synthesis was impaired or abolished in aged rats. Treatment of old rats with 10 or 100 microg melatonin generally augmented amplitude of rhythms and reinduced the nocturnal peak of acetylcholine synthesis in the hypogastric ganglion. Only the high melatonin dose significantly augmented rhythm amplitude of tyrosine hydroxylase activity (superior cervical and coeliac-superior mesenteric ganglia) and acetylcholine synthesis (superior cervical, stellate and coeliac-superior mesenteric ganglia) in young rats. The results indicate that the activity of the central oscillator, driven to the organs in part via the autonomic nervous system, deteriorates significantly with aging and that melatonin may restore partially such a deterioration.

Later endogenous circadian temperature nadir relative to an earlier wake time in older people

The contribution of the circadian timing system to the age-related advance of sleep-wake timing was investigated in two experiments. In a constant routine protocol, we found that the average wake time and endogenous circadian phase of 44 older subjects were earlier than that of 101 young men. However, the earlier circadian phase of the older subjects actually occurred later relative to their habitual wake time than it did in young men. These results indicate that an age-related advance of circadian phase cannot fully account for the high prevalence of early morning awakening in healthy older people. In a second study, 13 older subjects and 10 young men were scheduled to a 28-h day, such that they were scheduled to sleep at many circadian phases. Self-reported awakening from scheduled sleep episodes and cognitive throughput during the second half of the wake episode varied markedly as a function of circadian phase in both groups. The rising phase of both rhythms was advanced in the older subjects, suggesting an age-related change in the circadian regulation of sleep-wake propensity. We hypothesize that under entrained conditions, these age-related changes in the relationship between circadian phase and wake time are likely associated with self-selected light exposure at an earlier circadian phase. This earlier exposure to light could account for the earlier clock hour to which the endogenous circadian pacemaker is entrained in older people and thereby further increase their propensity to awaken at an even earlier time.

Effects of melatonin in two individuals with Alzheimer's disease

Dementia has been associated with circadian rhythm disturbances expressed in several dimensions including body temperature, hormonal concentrations, sleep and wakefulness patterns, and rest-activity cycles. These disturbances may be the result of a dampening in the amplitude of the circadian rhythm. One of the symptoms associated with the aging process has been a decline in the amplitude of the melatonin rhythm. Here, the results of melatonin administration to two patients with Alzheimer's disease are presented. Melatonin administration enhanced and stabilized the circadian rest-activity rhythm in one of the patients along with some reduction of daytime sleepiness and an improvement in mood. The other patient, who was characterized by less cognitive impairment, showed no significant changes associated with melatonin ingestion. Interestingly, the acrophase of rest-activity was delayed for about one hour in both patients. These results suggest that melatonin may have beneficial effects in some patients with Alzheimer's disease.

Influence of neonatal focal cerebral hypoxia-ischemia on cardiovascular and neurobehavioral functions in adult Wistar rats

No experimental studies looked at the disturbances appearing after a neonatal focal cerebral hypoxia-ischemia (HI) when animals become adults. Using radiotelemetry, we examined the effects of neonatal focal cerebral HI on blood pressure (BP), heart rate (HR), locomotor activity (LA), body temperature (BT) levels and circadian rhythm parameters of unrestrained adult Wistar rats. At 15 weeks of age, we continuously recorded the cardiovascular and neurobehavioral parameters of HI (n = 6) and sham-operated (n = 6) rats. In adult rats, HI induced persistent hypertensive effects associated with alteration in BP circadian rhythms and pronounced decreases in mesor and percent rhythm of LA. HR and BT parameters were not significantly modified. Therefore, our results suggest that the rat cardiovascular and behavioural circadian control systems may involve several structures which present selective vulnerability to early cerebral HI.

Diurnal rhythms in ornithine decarboxylase activity and norepinephrine and acetylcholine synthesis in submaxillary lymph nodes and spleen of young and aged rats during Freund's adjuvant-induced arthritis

Aging has been associated with attenuation of amplitude and changes in period of many circadian rhythms. The present study was carried out to examine, in young (50 days old) and old (18 months old) rats, whether 24-h rhythms of cell proliferation (as assessed by measuring ornithine decarboxylase activity) and of presynaptic adrenergic and cholinergic markers change in lymph nodes and spleen during Freund's adjuvant-induced arthritis. Groups of young and old Sprague-Dawley rats were studied the day before, and on days 6, 12 and 18 after Freund's adjuvant injection. On day 16 after adjuvant injection, inflammation of hind paws, mainly in the ankle joints, was less marked in old than in young rats. Lymph node and splenic ornithine decarboxylase activity exhibited significant 24-h variations with maximal activity during daily hours. Before treatment, enzyme activity values were significantly lower in old rats in both tissues examined. During the immune reaction, lymph node and splenic ornithine decarboxylase augmented 8-10-fold, with progressively smaller amplitude of daily variations as arthritis developed. In every case, mesor and amplitude of ornithine decarboxylase activity were lowest in old rats. Submaxillary lymph node and splenic tyrosine hydroxylase activity attained maximal values at night. At every time interval after mycobacterium adjuvant injection, amplitude and mesor of tyrosine hydroxylase activity rhythm were lowest in old rats. A maximum in submaxillary lymph node 3H-acetylcholine synthesis occurred at the afternoon. On day 6 and 12 after Freund's adjuvant injection, lymph node 3H-acetylcholine synthesis was significantly smaller in old rats. Day-night differences in submaxillary lymph node or splenic ornithine decarboxylase and tyrosine hydroxylase activities, or in submaxillary lymph node 3H-acetylcholine synthesis, of rats treated with the adjuvant's vehicle, did not differ significantly from those seen in untreated controls. The results are compatible with an age-dependent decline of immune-mediated inflammatory responses. The activity of the central circadian oscillator, driven to the organs in part via the autonomic nervous system, seems also to deteriorate during aging.

Melatonin excretion is not related to sleep in the elderly

We examined the association between 6-sulphatoxymelatonin (6-SMT) excretion and sleep in 68 volunteers 60-79 years of age who complained of insomnia or depression. An Actillume wrist monitor was worn for 5-7 consecutive days and nights in home-living conditions. Activity was used to estimate total sleep time (TST) and wake after sleep onset (WASO). Throughout two 24 hr periods, urine was collected approximately every 2 hr during the day and after any voidings during the sleep period. During the next week, subjects spent 5 nights and 4 days in the laboratory. Sleep was measured and scored with standard polysomnographic techniques. Urine was collected, as for home recording, on days 1 and 4. Urinary concentrations of 6-SMT were assayed. Cosine-fitting of urine data across both days at home and both laboratory collections established the mesors and amplitudes of 24 hr 6-SMT excretion rhythms, but neither was significantly correlated with sleep. Mean and peak 6-SMT excretion during the sleep period was also determined. Significant correlations were found between mean 6-SMT during the laboratory sleep period and TST and WASO. However, these associations were not independent of circadian timing: sleep was better when sleep occurred near the circadian acrophase of 6-SMT excretion. These data indicate that low melatonin production may not be an important factor in insomnia among the elderly.

Sleep and morningness-eveningness in the 'middle' years of life (20-59 y)

The following four issues were assessed in a group of 110 adults between the age of 20 and 59y: (1) the effect of age (regarded as a continuous variable) on polysomnographic sleep characteristics, habitual sleep-diary patterns, and subjective sleep quality; (2) the effects of age on morningness-eveningness; (3) the effects of morningness-eveningness on sleep, after controlling for the effects of age; and (4) the role of morningness-eveningness as a mediator of the age and sleep relationship. Increasing age was related to earlier habitual waketime, earlier bedtime, less time in bed and better mood and alertness at waketime. In the laboratory, increasing age was associated with less time asleep, increased number of awakenings, decreased sleep efficiency, lower percentages of slow-wave sleep (SWS) and rapid eye movement (REM) sleep, higher percentages of Stage 1 and 2, shorter REM latency and reduced REM activity and density. Increasing age was also associated with higher morningness scores. After controlling for the effects of age, morningness was associated with earlier waketime, earlier bedtime, less time in bed, better alertness at waketime, less time spent asleep, more wake in the last 2 h of sleep, decreased REM activity, less stage REM (min and percentage), more Stage 1 (min and percentage) and fewer minutes of Stage 2. For one set of variables (night time in bed, waketime, total sleep time, wake in the last 2 h of sleep and minutes of REM and REM activity), morningness-eveningness accounted for about half of the relationship between age and sleep. For another set of variables (bedtime, alertness at waketime, percentages of REM and Stage 1), morningness-eveningness accounted for the entire relationship between age and sleep. In conclusion, age and morningness were both important predictors of the habitual sleep patterns and polysomnographic sleep characteristics of people in the middle years of life (20-59 y).

Lifespan changes in the human hypothalamus

The various cell groups in the human hypothalamus show different patterns of aging, which are the basis for changes in biological rhythms, hormone production, autonomic functions, and behavior. The suprachiasmatic nucleus (SCN), the clock of the brain, exhibits circadian and seasonal rhythms in vasopressin synthesis that are disrupted later in life. Furthermore, the age-related sexual differences in the number of vasoactive intestinal polypeptide neurons in this nucleus reinforces the idea that the SCN is not only involved in the timing of circadian rhythms but also in the temporal organization of reproductive functions. The sexually dimorphic nucleus of the preoptic are (SDN-POA), or intermediate nucleus, is twice as large in men as in women, a difference that arises between the ages of two to four years and puberty. During aging a dramatic, sex-dependent decrease in cell number occurs, leading to values which are only 10-15% of the cell number found in early childhood. The vasopressin and oxytocin producing cells in the supraoptic nucleus (SON) and paraventricular nucleus (PVN) are examples of neuron populations that seem to stay perfectly intact in old age. Parvocellular corticotropin-releasing hormone-containing neurons are found throughout the PVN and are even activated in the course of aging, as indicated by their increase in number and by their coexpression with vasopressin. Part of the arcuate nucleus of the hypothalamus (ARH), or tubero-infundibular nucleus, contains hypertrophic neurons in postmenopausal women. These hypertrophied neurons contain neurokinin-B, substance P, and estrogen receptors and probably act on LHRH neurons as interneurons. The tuberal lateral nucleus (NTL), involved in feeding behavior and energy metabolism, does not show any neuronal loss in senescence. These findings indicate that each cell group of the human hypothalamus has its own sex-specific pattern of aging. In fact, some hypothalamic nuclei show a dramatic functional decline with aging, whereas others seem to become more active later in life.

Long-term fitness training improves the circadian rest-activity rhythm in healthy elderly males

In old age, the circadian timing system loses optimal functioning. This process is even accelerated in Alzheimer's disease. Because pharmacological treatment of day-night rhythm disturbances usually is not very effective and may have considerable side effects, nonpharmacological treatments deserve attention. Bright light therapy has been shown to be effective. It is known from animal studies that increased activity, or an associated process, also strongly affects the circadian timing system, and the present study addresses the question of whether an increased level of physical activity may improve circadian rhythms in elderly. In the study, 10 healthy elderly males were admitted to a fitness training program for 3 months. The circadian rest-activity rhythm was assessed by means of actigraphy before and after the training period and again 1 year after discontinuation. As a control for possible seasonal effects, repeated actigraphic recordings were performed during the same times of the year as were the pre and post measurements in a control group of 8 healthy elderly males. Fitness training induced a significant reduction in the fragmentation of the rest-activity rhythm. Moreover, the fragmentation of the rhythm was negatively correlated with the level of fitness achieved after the training. No seasonal effect was found. Previous findings in human and animal studies are reviewed, and several possible mechanisms involved in the effect of fitness training on circadian rhythms are discussed. The results suggest that fitness training may be helpful in elderly people suffering from sleep problems related to circadian rhythm disturbances.

Caffeine and light effects on nighttime melatonin and temperature levels in sleep-deprived humans

The effects of caffeine ingestion and exposure to bright light, both separately and in combination, on salivary melatonin and tympanic temperature were assessed in humans. Four treatments during a 45.5 h sleep deprivation period were compared: Dim Light-Placebo, Dim Light-Caffeine, Bright Light-Placebo and Bright-Light Caffeine. The Dim Light-Caffeine condition (200 mg twice each night) relative to the Dim Light-Placebo condition suppressed nighttime melatonin levels and attenuated the normal decrease in temperature. Combining caffeine ingestion with bright light exposure (> or = 2000 lux) suppressed melatonin and attenuated the normal nighttime drop in temperature to a larger degree than either condition alone; i.e. effects were additive. Circadian effects were also observed in that the amplitude and phase of the temperature rhythm were altered during treatment. These findings establish that the human melatonin system is responsive to caffeine. Other evidence suggests that caffeine may influence melatonin and temperature levels through antagonism of the neuromodulator adenosine.

Circadian rhythms: basic neurobiology and clinical applications

Circadian rhythms are major features of adaptation to our environment. In mammals, circadian rhythms are generated and regulated by a circadian timing system. This system consists of entertainment pathways, pacemakers, and pace-maker output to effector systems that are under circadian control. The primary entertainment pathway is the retinohypothalamic tract, which terminates in the circadian pacemakers, the suprachiasmatic nuclei of the hypothalamus. The output of the suprachiasmatic nuclei is principally to the hypothalamus, the midline thalamus, and the basal forebrain. This provides a temporal organization to the sleep-wake cycle, to many physiological and endocrine functions, and to psychomotor performance functions. Disorders of circadian timing primarily affect entertainment and pacemaker functions. The pineal hormone, melatonin, appears to be promising agent for therapy of some circadian timing disorders.