Age-related changes in the sleep pattern of male adult rats

Sex and Sleep Disruption as Contributing Factors in Alzheimer's Disease

Alzheimer's disease (AD) affects more women than men, with women throughout the menopausal transition potentially being the most under researched and at-risk group. Sleep disruptions, which are an established risk factor for AD, increase in prevalence with normal aging and are exacerbated in women during menopause. Sex differences showing more disrupted sleep patterns and increased AD pathology in women and female animal models have been established in literature, with much emphasis placed on loss of circulating gonadal hormones with age. Interestingly, increases in gonadotropins such as follicle stimulating hormone are emerging to be a major contributor to AD pathogenesis and may also play a role in sleep disruption, perhaps in combination with other lesser studied hormones. Several sleep influencing regions of the brain appear to be affected early in AD progression and some may exhibit sexual dimorphisms that may contribute to increased sleep disruptions in women with age. Additionally, some of the most common sleep disorders, as well as multiple health conditions that impair sleep quality, are more prevalent and more severe in women. These conditions are often comorbid with AD and have bi-directional relationships that contribute synergistically to cognitive decline and neuropathology. The association during aging of increased sleep disruption and sleep disorders, dramatic hormonal changes during and after menopause, and increased AD pathology may be interacting and contributing factors that lead to the increased number of women living with AD.

Activity patterns are associated with fractional lifespan, memory, and gait speed in aged dogs

Maintaining an active lifestyle is considered a hallmark of successful aging. Physical activity significantly reduces the risk of cognitive decline and Alzheimer's disease in humans. However, pain and lack of motivation are important barriers to exercise. Dogs are a remarkable model for translational studies in aging and cognition as they are prone to Canine Cognitive Dysfunction syndrome, which has many similarities with Alzheimer's disease. According to owner reports, changes in activity levels are characteristic of this syndrome, with decreased daytime activity, but also excessive pacing, especially at sleep time. We used physical activity monitors to record the activity of 27 senior dogs and evaluated the association between activity level and age, fractional lifespan, cognitive status measured by an owner questionnaire and cognitive tests. We also assessed the relationship between activity and joint/spinal pain, and the off/on leash gait speed ratio (a potential marker of gait speed reserve and motivation). We found that activity patterns in dogs are associated with fractional lifespan and working memory. Additionally, dogs with higher on/off leash gait speed are more active in the afternoon of weekdays. These results encourage future studies evaluating how physical activity can improve or delay cognitive impairment in senior dogs.

To sleep or not to sleep - Effects on memory in normal aging and disease

Sleep behavior undergoes significant changes across the lifespan, and aging is associated with marked alterations in sleep amounts and quality. The primary sleep changes in healthy older adults include a shift in sleep timing, reduced slow-wave sleep, and impaired sleep maintenance. However, neurodegenerative and psychiatric disorders are more common among the elderly, which further worsen their sleep health. Irrespective of the cause, insufficient sleep adversely affects various bodily functions including energy metabolism, mood, and cognition. In this review, we will focus on the cognitive changes associated with inadequate sleep during normal aging and the underlying neural mechanisms.

Sleep and cognition in aging dogs. A polysomnographic study

Introduction

Sleep is fundamental for cognitive homeostasis, especially in senior populations since clearance of amyloid beta (key in the pathophysiology of Alzheimer's disease) occurs during sleep. Some electroencephalographic characteristics of sleep and wakefulness have been considered a hallmark of dementia. Owners of dogs with canine cognitive dysfunction syndrome (a canine analog to Alzheimer's disease) report that their dogs suffer from difficulty sleeping. The aim of this study was to quantify age-related changes in the sleep-wakefulness cycle macrostructure and electroencephalographic features in senior dogs and to correlate them with their cognitive performance.

Methods

We performed polysomnographic recordings in 28 senior dogs during a 2 h afternoon nap. Percentage of time spent in wakefulness, drowsiness, NREM, and REM sleep, as well as latency to the three sleep states were calculated. Spectral power, coherence, and Lempel Ziv Complexity of the brain oscillations were estimated. Finally, cognitive performance was evaluated by means of the Canine Dementia Scale Questionnaire and a battery of cognitive tests. Correlations between age, cognitive performance and sleep-wakefulness cycle macrostructure and electroencephalographic features were calculated.

Results

Dogs with higher dementia scores and with worse performance in a problem-solving task spent less time in NREM and REM sleep. Additionally, quantitative electroencephalographic analyses showed differences in dogs associated with age or cognitive performance, some of them reflecting shallower sleep in more affected dogs.

Discussion

Polysomnographic recordings in dogs can detect sleep-wakefulness cycle changes associated with dementia. Further studies should evaluate polysomnography's potential clinical use to monitor the progression of canine cognitive dysfunction syndrome.

Changes in sleep EEG with aging in humans and rodents

Sleep is one of the most ubiquitous but also complex animal behaviors. It is regulated at the global, systems level scale by circadian and homeostatic processes. Across the 24-h day, distribution of sleep/wake activity differs between species, with global sleep states characterized by defined patterns of brain electric activity and electromyography. Sleep patterns have been most intensely investigated in mammalian species. The present review begins with a brief overview on current understandings on the regulation of sleep, and its interaction with aging. An overview on age-related variations in the sleep states and associated electrophysiology and oscillatory events in humans as well as in the most common laboratory rodents follows. We present findings observed in different studies and meta-analyses, indicating links to putative physiological changes in the aged brain. Concepts requiring a more integrative view on the role of circadian and homeostatic sleep regulatory mechanisms to explain aging in sleep are emerging.

Cognitive Reserve in Model Systems for Mechanistic Discovery: The Importance of Longitudinal Studies

The goal of this review article is to provide a resource for longitudinal studies, using animal models, directed at understanding and modifying the relationship between cognition and brain structure and function throughout life. We propose that forthcoming longitudinal studies will build upon a wealth of knowledge gleaned from prior cross-sectional designs to identify early predictors of variability in cognitive function during aging, and characterize fundamental neurobiological mechanisms that underlie the vulnerability to, and the trajectory of, cognitive decline. Finally, we present examples of biological measures that may differentiate mechanisms of the cognitive reserve at the molecular, cellular, and network level.

Effects of Physical Exercise on Autophagy and Apoptosis in Aged Brain: Human and Animal Studies

The aging process is characterized by a series of molecular and cellular changes over the years that could culminate in the deterioration of physiological parameters important to keeping an organism alive and healthy. Physical exercise, defined as planned, structured and repetitive physical activity, has been an important force to alter physiology and brain development during the process of human beings' evolution. Among several aspects of aging, the aim of this review is to discuss the balance between two vital cellular processes such as autophagy and apoptosis, based on the fact that physical exercise as a non-pharmacological strategy seems to rescue the imbalance between autophagy and apoptosis during aging. Therefore, the effects of different types or modalities of physical exercise in humans and animals, and the benefits of each of them on aging, will be discussed as a possible preventive strategy against neuronal death.

Sex differences in age-related changes in the sleep-wake cycle

Age-related changes in sleep and circadian regulation occur as early as the middle years of life. Research also suggests that sleep and circadian rhythms are regulated differently between women and men. However, does sleep and circadian rhythms regulation age similarly in men and women? In this review, we present the mechanisms underlying age-related differences in sleep and the current state of knowledge on how they interact with sex. We also address how testosterone, estrogens, and progesterone fluctuations across adulthood interact with sleep and circadian regulation. Finally, we will propose research avenues to unravel the mechanisms underlying sex differences in age-related effects on sleep.

Progressive gene dose-dependent disruption of the methamphetamine-sensitive circadian oscillator-driven rhythms in a knock-in mouse model of Huntington's disease

Huntington's disease (HD) is a progressive genetic neurodegenerative disorder characterised by motor and cognitive deficits, as well as sleep and circadian abnormalities. In the R6/2 mouse, a fragment model of HD, rest-activity rhythms controlled by the suprachiasmatic nucleus disintegrate completely by 4months of age. Rhythms driven by a second circadian oscillator, the methamphetamine-sensitive circadian oscillator (MASCO), are disrupted even earlier, and cannot be induced after 2months of age. Here, we studied the effect of the HD mutation on the expression of MASCO-driven rhythms in a more slowly developing, genetically relevant mouse model of HD, the Q175 'knock-in' mouse. We induced expression of MASCO output by administering low dose methamphetamine (0.005%) chronically via the drinking water. We measured locomotor activity in constant darkness in wild-type and Q175 mice at 2 (presymptomatic), 6 (early symptomatic), and 12 (symptomatic) months of age. At 2months, all mice expressed MASCO-driven rhythms, regardless of genotype. At older ages, however, there was a progressive gene dose-dependent deficit in MASCO output in Q175 mice. At 6months of age, these rhythms could be observed in only 45% of heterozygous and 15% of homozygous mice. By 1year of age, 90% of homozygous mice had an impaired MASCO output. There was also an age-dependent disruption of MASCO output seen in wild-type mice. The fact that the progressive deficit in MASCO-driven rhythms in Q175 mice is HD gene dose-dependent suggests that, whatever its role in humans, abnormalities in MASCO output may contribute to the HD circadian phenotype.

Unraveling the Neurobiology of Sleep and Sleep Disorders Using Drosophila

Sleep disorders in humans are increasingly appreciated to be not only widespread but also detrimental to multiple facets of physical and mental health. Recent work has begun to shed light on the mechanistic basis of sleep disorders like insomnia, restless legs syndrome, narcolepsy, and a host of others, but a more detailed genetic and molecular understanding of how sleep goes awry is lacking. Over the past 15 years, studies in Drosophila have yielded new insights into basic questions regarding sleep function and regulation. More recently, powerful genetic approaches in the fly have been applied toward studying primary human sleep disorders and other disease states associated with dysregulated sleep. In this review, we discuss the contribution of Drosophila to the landscape of sleep biology, examining not only fundamental advances in sleep neurobiology but also how flies have begun to inform pathological sleep states in humans.

Aging in mice reduces the ability to sustain sleep/wake states

One of the most significant problems facing older individuals is difficulty staying asleep at night and awake during the day. Understanding the mechanisms by which the regulation of sleep/wake goes awry with age is a critical step in identifying novel therapeutic strategies to improve quality of life for the elderly. We measured wake, non-rapid eye movement (NREM) and rapid-eye movement (REM) sleep in young (2–4 months-old) and aged (22–24 months-old) C57BL6/NIA mice. We used both conventional measures (i.e., bout number and bout duration) and an innovative spike-and-slab statistical approach to characterize age-related fragmentation of sleep/wake. The short (spike) and long (slab) components of the spike-and-slab mixture model capture the distribution of bouts for each behavioral state in mice. Using this novel analytical approach, we found that aged animals are less able to sustain long episodes of wakefulness or NREM sleep. Additionally, spectral analysis of EEG recordings revealed that aging slows theta peak frequency, a correlate of arousal. These combined analyses provide a window into the mechanisms underlying the destabilization of long periods of sleep and wake and reduced vigilance that develop with aging.

Deep sleep and parietal cortex gene expression changes are related to cognitive deficits with age

BACKGROUND

Age-related cognitive deficits negatively affect quality of life and can presage serious neurodegenerative disorders. Despite sleep disruption's well-recognized negative influence on cognition, and its prevalence with age, surprisingly few studies have tested sleep's relationship to cognitive aging.

METHODOLOGY

We measured sleep stages in young adult and aged F344 rats during inactive (enhanced sleep) and active (enhanced wake) periods. Animals were behaviorally characterized on the Morris water maze and gene expression profiles of their parietal cortices were taken.

PRINCIPAL FINDINGS

Water maze performance was impaired, and inactive period deep sleep was decreased with age. However, increased deep sleep during the active period was most strongly correlated to maze performance. Transcriptional profiles were strongly associated with behavior and age, and were validated against prior studies. Bioinformatic analysis revealed increased translation and decreased myelin/neuronal pathways.

CONCLUSIONS

The F344 rat appears to serve as a reasonable model for some common sleep architecture and cognitive changes seen with age in humans, including the cognitively disrupting influence of active period deep sleep. Microarray analysis suggests that the processes engaged by this sleep are consistent with its function. Thus, active period deep sleep appears temporally misaligned but mechanistically intact, leading to the following: first, aged brain tissue appears capable of generating the slow waves necessary for deep sleep, albeit at a weaker intensity than in young. Second, this activity, presented during the active period, seems disruptive rather than beneficial to cognition. Third, this active period deep sleep may be a cognitively pathologic attempt to recover age-related loss of inactive period deep sleep. Finally, therapeutic strategies aimed at reducing active period deep sleep (e.g., by promoting active period wakefulness and/or inactive period deep sleep) may be highly relevant to cognitive function in the aging community.

The wake-promoting effects of hypocretin-1 are attenuated in old rats

Disruption of sleep is a frequent complaint among elderly humans and is also evident in aged laboratory rodents. The neurobiological bases of age-related sleep/wake disruption are unknown. Given the critical role of the hypocretins in sleep/wake regulation, we sought to determine whether the wake-promoting effect of hypocretin changes with age in Wistar rats, a strain in which age-related changes in both sleep and hypocretin signaling have been reported. Intracerebroventricular infusions of hypocretin-1 (10 and 30 μg) significantly increased wake time relative to vehicle in both young (3 mos) and old (25 mos) Wistar rats. However, the magnitude and duration of the wake-promoting effects were attenuated with age. An increase of parameters associated with homeostatic sleep recovery after sleep deprivation, including non-rapid eye movement (NR) sleep time, NR delta power, the ratio of NR to rapid eye movement (REM) sleep, and NR consolidation, occurred subsequent to Hcrt-induced waking in young but not old rats. ICV infusions of hypocretin-2 (10 and 30 μg) produced fewer effects in both young and old rats. These data demonstrate that activation of a major sleep/wake regulatory pathway is attenuated in old rats.

Protein expression is altered during spontaneous sleep in aged Sprague Dawley rats

Age-related changes in brain function include those affecting learning, memory, and sleep-wakefulness. Sleep-wakefulness is an essential behavior that results from the interaction of multiple brain regions, peptides, and neurotransmitters. The biological function(s) of sleep, however, remains unknown due to a paucity of information available at the cellular level. Aged rats exhibit alterations in the circadian and homeostatic influences associated with sleep-wake regulation. We recently showed that alterations in cortical profiles occur after timed bouts of spontaneous sleep in young rats. Examination of the cellular response to sleep-wake in old rats may thus provide insight(s) into the biological function(s) of sleep. To test this hypothesis, we monitored cortical profiles in the frontal cortex of young and old Sprague-Dawley rats after timed bouts of spontaneous sleep-wake behavior. Proteins were separated by two-dimensional electrophoresis (2-DE), visualized by fluorescent staining, imaged, and analyzed as a function of behavioral state and age. Old rats showed a 6-fold increase in total protein expression, independent of the behavioral state at sacrifice. When analyzed according to age and behavioral state, there was a decrease (approximately 46%) in the number of phospho-spots present during SWS in aged animals. SWS-associated spots present only in old animals were associated with multiple functions including vesicular transport, cell signaling, oxidation state, cytoskeletal support, and energy metabolism. These data suggest that the intracellular response to the signaling associated with spontaneous sleep is affected by age and is consistent with the idea that the ability of sleep to fulfill its function(s) may become diminished with age.

Midfrequency cortico-thalamic oscillations and the sleep cycle: Genetic, time of day and age effects

WAG/Rij rats have various types of mid frequency cortico-thalamic oscillations, such as anterior and posterior sleep spindles and two types of spike-wave discharges (SWD). The generalized SWD (type I) preferentially occur at transitions from wake to sleep, type II can be found at the occipital cortex during quite wakefulness. In the present experiment sleep spindles, SWD and sleep cycle characteristics of 6-month-old WAG/Rij rats were studied and compared with those of younger WAG/Rij rats with much less SWD and age-matched control (ACI) rats. EEG recordings were made during the beginning (morning) and end (afternoon) of the light period in these four groups of rats. Quantitative characteristics of SWD, sleep spindles and the sleep cycle were determined. There were strain-related and age-dependent effects in the various cortico-thalamic oscillations, older WAG/Rij had more SWDs than younger WAG/Rij rats (both types I and II) and there were more type I SWDs at the end of the light period compared to the beginning. Large strain, age and time of day effects on the sleep cycle were found. The duration of non-REM sleep and the sleep cycle was shorter in WAG/Rij rats but only at the end of the light period and only in older WAG/Rij rats. It can be concluded that the various phasic events and the length of the sleep cycle are under genetic control, and that the sleep cycle length is also controlled by time of day, age and genetic factors. Non-REM sleep and the sleep cycle are disrupted by absence seizures but only in fragile periods when drowsiness and light slow wave sleep dominate.

Beneficial effects of regular exercise on sleep in old F344 rats

With aging there is a significant decline in the normal architecture of sleep and a reduction in the diurnal amplitude of core body temperature. Regular moderate exercise has been shown to have a positive impact in the elderly and here we investigate whether sleep-wake patterning can also be improved. Young (3 months) and old (22 months) F344 rats were exercised once a day for 50min at night onset over an 8-week period. Thereafter, polysomnographic recordings were obtained immediately after exercise. To determine the lasting consequences of exercise, sleep was also recorded 2 days and 2 weeks after exercise had ended. Old rats that were exercised had a significant weight loss, were awake more during the last third of their active period, had less sleep fragmentation and the amplitude of the diurnal rhythm of core body temperature was significantly increased. Old exercised rats also had an overall increase in the amplitude of EEG power (0.5-16Hz) during wake and theta EEG power during REM sleep. In young rats regular exercise increased EEG delta power (0.5-4Hz) during NREM sleep. Our data indicate regular exercise in old rats improves sleep architecture, EEG power and diurnal rhythm of temperature.

Influence of estrus cycle and ageing on activity patterns in two inbred mouse strains

Despite the widespread use of inbred mice in research, little is known about aging of the circadian system in female mice, although interactions between female gonadal hormones and circadian rhythms have been established. We investigated the influence of the estrus cycle on circadian aspects of running-wheel activity and changes in the course of aging in female C57BL/6 and C3H/He mice recorded continuously between the ages of 3 and 19 months. In the young, cycling mice the second part of the proestrus night was often, but not consistently, characterized by increased motor activity compared to the remaining estrus cycle nights. After estrus cycling had ceased in the course of ageing, the estrus-dependent day-to-day variability in activity was reduced. The amplitude of the daily rest-activity rhythm decreased progressively after the age of 8 months in C3H/He and 10 months in C57BL/6 mice. The capacity for resynchronisation of activity onset to the LD-cycle was compared in young and old mice after an 8-h phase advance of the LD-cycle. Resynchronisation was significantly slower in old C3H/He mice and unaffected by age in C57BL/6 mice. The circadian period in constant darkness did not change with age in either strain. However, the period was shorter in 17-month old C57BL/6 mice compared to an additional group, which was recorded at the same age, after at least 1-month adaptation to the recording conditions. The results show that the reproductive state as well as ageing influence motor activity patterns of female mice in a strain- and cohort-dependent manner.

Women's sleep in health and disease

A huge amount of knowledge about sleep has accumulated during the last 5 decades following the discovery of rapid eye movement (REM) sleep. Nevertheless, there are numerous areas of considerable ignorance. One of these concerns the particularities of sleep in women. Most basic and clinical studies have been performed in male subjects, and only very recently research groups around the world have addressed women's sleep in health and disease. In this review, we summarize the present knowledge on the influence of oestrogens on the brain and on the distinctive changes of sleep across the menstrual cycle, during pregnancy and menopause. In addition, studies in female rodents are reviewed as well as the knowledge on female peculiarities regarding the interactions between sleep regulation and age-related changes in circadian rhythms. We also address specific aspects of sleep loss and sleep disorders in women. Finally, very recent studies on the sociology of sleep are summarized and future directions in the field are discussed.

The diurnal rhythm of hypocretin in young and old F344 rats

STUDY OBJECTIVES

Hypocretins (HCRT-1 and HCRT-2), also known as orexins, are neuropeptides localized in neurons surrounding the perifornical region of the posterior hypothalamus. These neurons project to major arousal centers in the brain and are implicated in regulating wakefulness. In young rats and monkeys, levels of HCRT-1 are highest at the end of the wake-active period and lowest toward the end of the sleep period. However, the effects of age on the diurnal rhythm of HCRT-1 are not known.

DESIGN

To provide such data, cerebrospinal fluid (CSF) was collected from the cisterna magna of young (2-month-old, n = 9), middle-aged (12 months, n = 10), and old (24 months, n = 10) F344 rats at 4-hour intervals, (beginning at zeitgeber [ZT]0, lights on). CSF was collected once from each rat every 4 days at 1 ZT point. After collecting the CSF at all of the time points, the rats were kept awake by gentle handling for 8 hours (ZT 0-ZT8), and the CSF was collected again at the end of the sleep-deprivation procedure. HCRT-1 levels in the CSF were determined by radioimmunoassay

SETTINGS

Basic neuroscience research lab.

MEASUREMENTS AND RESULTS

Old rats had significantly less HCRT-1 in the CSF versus young and middle-aged rats (P < .002) during the lights-on and lights-off periods and over the 24-hour period. In old rats, significantly low levels of HCRT-1 were evident at the end of the lights-off period (predominantly wake-active period). The old rats continued to have less HCRT-1 even after 8 hours of prolonged waking. Northern blot analysis did not show a difference in pre-proHCRT mRNA between age groups.

CONCLUSIONS

In old rats there is a 10% decline in CSF HCRT-1 over the 24-hour period. Functionally, if there is less HCRT-1, which our findings indicated, and there is also a decline in HCRT receptor mRNA, as has been previously found, then the overall consequence would be diminished action of HCRT at target sites. This would diminish the waking drive, which in the elderly could contribute to the increased tendency to fall asleep during the normal wake period.

Effects of age on circadian rhythms are similar in wild-type and heterozygous Clock mutant mice

The amplitudes of many circadian rhythms, at the behavioral, physiological, cellular, and biochemical levels, decrease with advanced age. Previous studies suggest that the amplitude of the central circadian pacemaker is decreased in old animals. Recently, it has been reported that expression of several circadian clock genes, including Clock, is lower in the master circadian pacemaker of old rodents. To test the hypothesis that decreased activity of a circadian clock gene renders animals more susceptible to the effects of aging, we analyzed the circadian rhythm of locomotor activity in young and old wild-type and heterozygous Clock mutant mice. We found that the effects of age and the Clock mutation were additive. These results indicate that age-related changes in circadian rhythmicity occur equally in wild-type and heterozygous Clock mutants, suggesting that the Clock mutation does not render mice more susceptible to the effects of age on the circadian pacemaker.

The diurnal rhythm of adenosine levels in the basal forebrain of young and old rats

There are significant decrements in sleep with age. These include fragmentation of sleep, increased wake time, decrease in the length of sleep bouts, decrease in the amplitude of the diurnal rhythm of sleep, decrease in rapid eye movement sleep and a profound decrease in electroencephalogram Delta power (0.3-4 Hz). Old rats also have less sleep in response to 12 h-prolonged wakefulness (W) indicating a reduction in sleep drive with age. The mechanism contributing to the decline in sleep with aging is not known but cannot be attributed to loss of neurons implicated in sleep since the numbers of neurons in the ventral lateral preoptic area, a region implicated in generating sleep, is similar between young (3.5 months) and old (21.5 months) rats. One possibility for the reduced sleep drive with age is that sleep-wake active neurons may be stimulated less as a result of a decline in endogenous sleep factors. Here, we test this hypothesis by focusing on the purine, adenosine (AD), one such sleep factor that increases after prolonged W. In experiment 1, microdialysis measurements of AD in the basal forebrain at 1 h intervals reveal that old (21.5 months) rats have more extracellular levels of AD compared with young rats across the 24 h diurnal cycle. In experiment 2, old rats kept awake for 6 h (first half of lights-on period) accumulated more AD compared with young rats. If old rats have more AD then why do they sleep less? To investigate whether changes in sensitivity of the AD receptor contribute to the decline in sleep, experiments 3 and 4 determined that for the same concentration of AD or the AD receptor 1 agonist, cyclohexyladenosine, old rats have less sleep compared with young rats. We conclude that even though old rats have more AD, a reduction in the sensitivity of the AD receptor to the ligand does not transduce the AD signal at the same strength as in young rats and may be a contributing factor to the decline in sleep drive in the elderly.

Changes in the sleep-wake cycle architecture and cortical nitric oxide release during ageing in the rat

Changes in sleep-wake states and nitric oxide release were examined in aged rats versus young-adult ones. Sleep-wake recordings and nitric oxide measurements were taken from animals chronically equipped with polygraphic and voltametric electrodes. Animals were examined in baseline conditions and in response to a 24-hour paradoxical sleep deprivation. In aged rats, basal amount of paradoxical sleep is decreased during the light phase versus young-adult animals. After paradoxical sleep deprivation, a paradoxical sleep rebound occurs with an amount and intensity that are less marked in aged animals than in young-adult rats. The amplitude of the circadian distribution for wakefulness, slow-wave sleep and paradoxical sleep amounts is reduced with age. Finally, delta-slow-wave sleep and theta-paradoxical sleep power spectra are attenuated either in baseline conditions or after paradoxical sleep deprivation in aged animals. It is also reported that cortical nitric oxide release exhibits a circadian rhythm with higher amplitude in aged rats than in young-adult ones. However, after paradoxical sleep deprivation, a limited overproduction of nitric oxide is obtained compared with young-adult ones. These results, evidencing the dynamics of the nitric oxide changes occurring in relation to the sleep-wake cycle, point out the homeostatic paradoxical sleep regulation as an age-dependent process in which the nitric oxide molecule is possibly involved.

Age-related decline in hypocretin (orexin) receptor 2 messenger RNA levels in the mouse brain

The hypocretin (Hcrt; also known as orexin) system has been implicated in arousal state regulation and energy metabolism. We hypothesize that age-related sleep problems can result from dysfunction of this system and thus measured messenger RNA (mRNA) levels of preprohcrt in the hypothalamus, and hcrt receptor 1 (hcrtr1) and hcrt receptor 2 (hcrtr2) in eight brain regions of 3, 12, 18 and 24 months old C57BL/6 mice. Expression of preprohcrt and the colocalized prodynorphin did not change with age. Whereas an age-related change in hcrtr1 mRNA expression was observed only in the hippocampus, hcrtr2 mRNA levels declined in the hippocampus, thalamus, pons, and medulla; these reductions ranged from 33 to 44%. Declining trends (P < 0.1) in hcrtr2 mRNA levels were also observed in the cortex, basal forebrain and hypothalamus. These results are consistent with the hypothesis that an age-related deterioration occurs in the Hcrt system that may contribute to age-related sleep disorders.

Sleep-related increase in activity of mesopontine neurons in old rats

Relationships between age-related changes in sleep patterns and neuronal activity have received scant attention. In the present study, reticularis pontis oralis (RPO) and ventral tegmental nucleus of Gudden (VTN) neurons were recorded in unanesthetized restrained young (3 months) and old (23 months) Sprague-Dawley rats during wakefulness (W), slow wave sleep (SWS) and rapid eye movement (REM) sleep. All RPO neurons displayed a tonic activity. Firing rates were similar during W in young and old rats. In contrast, firing rates were higher during SWS in old rats (P < 0.001). In both young and old rats, firing rates increased significantly during REM sleep as compared to W and SWS but this increase was markedly greater in old rats. Neurons recorded from VTN displayed bursting activity at theta frequencies during W and REM sleep. The frequency of VTN bursting neurons was higher during REM sleep as compared to W in both groups of age. This difference was significantly more pronounced in old as compared to young rats (P < 0.001). Sleep-related hyperactivity of pontine neurons is discussed in terms of a possible deficit in inhibitory processes in old rats.

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.

Distinct sleep-wake stages in rats depend differentially on age

The objective was to study age-related changes in sleep-wake stages in the rat by using precise polyphysiograph criteria for stage identification. Cortical and hippocampal electroencephalogram, and ocular and myographic activities were recorded in young, middle-aged, and old male Wistar rats to define 6 stages: active and quiet wake (AW, QW); light and deep slow wave sleep (SWS: S1, S2); intermediate stage of sleep (IS); and paradoxical sleep (PS). The old rats displayed a decrease in S1, S2, and IS, accompanied by an enhancement of AW. No age changes were found for QW and PS. It is suggested that the consolidation of SWS is primarily disturbed in the old rats, which may lead to a facilitation of wake.

Increased glutamate, GABA and glutamine in lateral geniculate nucleus but not in medial geniculate nucleus caused by visual attention to novelty

This study is concerned with cortico-thalamic neural mechanisms underlying attentional phenomena. Previous results from this laboratory demonstrated that the visual sector of the GABAergic thalamic reticular nucleus is selectively c-fos activated in rats that are naturally paying attention to features of a novel-complex environment, and that this activation is dependent on top-down glutamatergic inputs from the primary visual cortex. By contrast, the acoustic sector of the thalamic reticular nucleus is not activated despite noise generated by exploration and c-fos activation of brainstem acoustic centers (e.g. dorsal cochlear nucleus, inferior colliculus). A prediction of these results is that the levels of the neurotransmitters glutamate and GABA, and the glutamate-related amino acid glutamine, will be increased in the lateral geniculate nucleus (LGN), but not in the medial geniculate nucleus (MGN) of rats that explore a novel-complex environment in comparison to levels of these amino acids in control rats. By means of neurochemical analysis of these amino acids (HPLC) the results of this study confirmed this prediction. The results are consistent with the previously proposed 'focal attention' hypothesis postulating that a focus of attention in the primary visual cortex generates top-down center-surround facilitatory-inhibitory effects on geniculocortical transmission via corticoreticulogeniculate pathways. The results also supports the notion that a main function of corticothalamic pathways to relay thalamic nuclei is attention-dependent modulation of thalamocortical transmission.

Sleep changes induced by lipopolysaccharide in the rat are influenced by age

In mammals, aging is associated with immune senescense. To examine whether the sleep changes occurring during immune challenge are affected by age, we assessed sleep alterations induced by the administration of lipopolysaccharide (LPS) in young and middle-aged rats. During vehicle, the middle-aged rats exhibited less pre-rapid eye movement sleep (pre-REMS) as well as REMS, due to a smaller number and shorter duration of REMS episodes, than young rats. LPS elevated body temperature, increased non-REMS, and suppressed both pre-REMS and REMS in the young as well as in the middle-aged rats. However, in the young animals, LPS significantly enhanced slow-wave activity in the electroencephalogram (EEG) within non-REMS, reflecting an increase in sleep intensity. In contrast, LPS attenuated EEG power in most frequency bands in the older animals. This finding indicates age-related changes in the modulation of sleep by LPS.

Age-related changes in rhythmically bursting activity in the medial septum of rats

The effects of aging on the firing of septohippocampal neurons were estimated in unanesthetized, restrained young, old and very old rats (respectively 3, 23 and 30 months). Extracellular recordings were obtained during various states of arousal. The mean spontaneous activity for the overall neuronal population was not modified by aging. In contrast, the percentage of rhythmically bursting neurons was significantly lower in aged rats. During wakefulness, decrease of bursting activity was observed in old and very old rats (P<0.01 and P<0.001) whereas during rapid eye movement sleep it appeared only in the oldest group (P<0.01). The frequency of the bursts decreased in 30-month-old rats during wakefulness while it remained unchanged in both aged groups during rapid eye movement sleep. In old rats, at a time when the cholinergic septal neurons already deteriorated, a third of neurons recorded during rapid eye movement sleep exhibited a pattern of activity composed of long duration bursts with higher intraburst frequency than in young or very old rats. Our study shows that rhythmically bursting septal activity is impaired in aged rats and that the amplitude of the changes depends on advancing age and on states of arousal. Our findings suggest that age-induced loss and atrophy of cholinergic septal neurons contribute to the disorganization of the rhythmic activity but that functional alterations, influenced by the states of arousal, may also be considered.

Changes in sleep-wakefulness after 6-hydroxydopamine lesion of the preoptic area

This study was undertaken to assess the role of catecholamine fibers, terminating in the preoptic area, in regulating sleep-wakefulness in rats. Sleep-wakefulness was assessed on the basis of 24h electroencephalogram, electromyogram and electro-oculogram recordings before and after destruction of catecholaminergic terminals at the medial preoptic area by bilateral intracerebral injection of 6-hydroxydopamine (8 microg in 0.2 microl). There was a mild reduction in sleep and increase in wakefulness after the lesion. The increase in active wakefulness observed after eight days of lesion persisted even on the 12th day. In spite of the reduction in sleep, the day-night sleep ratio was not affected by 6-hydroxydopamine lesion of the preoptic area. The results indicate that the noradrenergic fibers at the preoptic area have a hypnogenic role.

Attentional activation of the visual thalamic reticular nucleus depends on 'top-down' inputs from the primary visual cortex via corticogeniculate pathways

This study is concerned with corticothalamic neural mechanisms underlying attentional phenomena. Previous results from this laboratory demonstrated that the visual sector of the GABAergic thalamic reticular nucleus is activated by attention in rats. Here it is demonstrated that Fos-detected activation of the visual reticular sector in rats, induced by attentive exploration of a novel-complex environment, is dependent on 'top-down' cortical inputs from the primary visual cortex, on the basis (a) that activation of the visual reticular sector is drastically diminished after ibotenate lesions mostly restricted to layer 6 of the primary visual cortex, which gives origin to the corticogeniculate pathway that innervates both the visual reticular sector and the dorsal lateral geniculate nucleus; and (b) the lesions did not induce retrograde degeneration nor diminution of Fos label in the geniculate. The results are consistent with the previously proposed hypothesis that a focus of attention in V1 generates a column of increased thalamocortical transmission in LGN by means of monosynaptic glutamatergic corticogeniculate inputs, and decreased transmission of surrounding regions by disynaptic cortico-reticulo-geniculate (ultimately GABAergic) inputs. The results also suggest that attentional modulation of thalamocortical transmission is a main function of corticothalamic pathways to sensory relay nuclei.

Compensatory sleep response to 12 h wakefulness in young and old rats

There is a pronounced decline in sleep with age. Diminished output from the circadian oscillator, the suprachiasmatic nucleus, might play a role, because there is a decrease in the amplitude of the day-night sleep rhythm in the elderly. However, sleep is also regulated by homeostatic mechanisms that build sleep drive during wakefulness, and a decline in these mechanisms could also decrease sleep. Because this question has never been addressed in old animals, the present study examined the effects of 12 h wakefulness on compensatory sleep response in young (3.5 mo) and old (21.5 mo) Sprague-Dawley and F344 rats. Old rats in both strains had a diminished compensatory increase in slow-wave sleep (SWS) after 12 h of wakefulness (0700-1900, light-on period) compared with the young rats. In contrast, compensatory REM sleep rebound was unaffected by age. To assess whether the reduced SWS rebound in old rats might result from loss of neurons implicated in sleep generation, we counted the number of c-Fos immunoreactive (c-Fos-ir) cells in the ventral lateral preoptic (VLPO) area and found no differences between young and old rats. These findings indicate that old rats, similar to elderly humans, demonstrate less sleep after prolonged wakefulness. The findings also indicate that although old rats have a decline in sleep, this cannot be attributed to loss of VLPO neurons implicated in sleep.

Immunolesion of the cholinergic basal forebrain: effects on functional properties of hippocampal and septal neurons

Deficits in cholinergic function have been documented in a variety of brain disorders including Alzheimer's Disease and, to a lesser extent, in normal ageing. In the present article, we have reviewed our recent findings on the effects of the loss of basal forebrain cholinergic neurons on the functional properties of the septohippocampal pathway. In vivo and ex vivo investigations were performed in rats following basal forebrain cholinergic lesion with the specific immunotoxin 192 IgG-saporin. Our results suggest a significant contribution of cholinergic neurons in the rhythmically bursting activity recorded within the medial septum. In addition, they give evidence that acetylcholine may tonically decrease the glutamatergic synaptic responses in the hippocampus whereas the GABAergic mediated inhibitory potentials are not affected. The possible contribution of these cholinergic mechanisms in the age-related functional alterations of the septohippocampal activity is discussed.

Age-related effect of ritanserin on the sleep-waking phases in rats

The age-related effect of the specific 5-hydroxytryptamine-2A/2C (5-HT(2A/2C)) antagonist ritanserin at two doses 0.63 mg/kg and 2.5 mg/kg) on six sleep-waking phases in young, middle-aged, and old male Wistar rats was electroencephalographically (EEG) examined. Only in the young and middle-aged rats, ritanserin enhanced slow wave sleep and reduced wakefulness in a dose-dependent manner. Ritanserin suppressed paradoxical sleep, such that this effect did not depend on the age. Although the effect of ritanserin on slow wave sleep was significantly smaller in the old compared to the young and the middle-aged rats, ritanserin produced an apparent sleep-improving effect in the old age group.

Post-trial sleep in old rats trained for a two-way active avoidance task

Nine male Wistar rats aged 27 months were trained for a two-way active avoidance task and tested for retention the following day. At variance with young adult rats, most of which succeed in mastering the task, all old rats displayed a large majority of freezing responses throughout the training and the retention sessions, thereby confirming the condition of learning impairment of aged rats. Comparison of baseline and post-trial sleep indicated the presence of a transient, but marked, increment in the average duration and total amount of post-trial slow-wave sleep followed by waking, and of a decrease in total amount of quiet waking. On the other hand, variables of paradoxical sleep and of slow-wave sleep followed by paradoxical sleep or by transition sleep did not show significant variations. Because these sleep variables are known to undergo significant variations in learning in young adult rats, the present data confirm that the latter effects are related to memory-processing events rather than to nonspecific effects of training. An additional outcome of training consisted in a marked post-trial decrement in the number of spike-wave discharges, which are known to occur in old rats during periods of quiet waking.

c-fos induction in sensory pathways of rats exploring a novel complex environment: shifts of active thalamic reticular sectors by predominant sensory cues

In normal rats exploring a novel, complex environment, in comparison to control nonexploring rats, there is induction of the FOS protein, a marker of neuronal activity, in all layers of the striate visual cortex (particularly in the granular and supragranular layers), in the stratum griseum superficiale of the superior colliculus, and in the dorsal lateral geniculate nucleus, as well as in all layers of the whiskers barrel field in the somatosensory cortex. A surprising finding was a selective activation of the visual sector of the thalamic reticular nucleus, in dorsocaudal parts of the nucleus. To the contrary, in visually deprived rats exploring a novel environment which would depend critically on whiskers tactile clues for exploration there was instead a selective activation of the somatic sector in central parts of the thalamic reticular nucleus, in conjunction with activation of cortical whiskers barrel field. From these results it is concluded: (1) Different sensory sectors of the rat thalamic reticular nucleus are activated depending on prevalent sensory channels used in recognition of the environment, suggesting a role of thalamic reticular nucleus in optimizing thalamocortical transmission of essential external cues to guide adequate behaviour. (2) In the awake state, the granular and supragranular layers of the visual and somatosensory cortices are more active when attention is paid to sensory stimuli that are essential for recognition of the environment. (3) The selective induction of c-fos in the visual and somatosensory cortices, and in the stratum griseum superficiale of superior colliculus of rats exploring a novel, complex environment might be related to plastic changes that have been demonstrated in these centres in rats raised in complex environments. These plastic changes are likely to be the result of target late-response genes activated by c-fos.

Age-related changes in diurnal acetylcholine release in the prefrontal cortex of male rats as measured by microdialysis

Extracellular levels of acetylcholine in the prefrontal cortex were measured using the micro-dialysis method in freely moving young (three to four months old) and old (23 to 24 months old) male rats over a period of 24 h to examine the effect of aging on prefrontal acetylcholine release. Prefrontal acetylcholine release during a 24 h period exhibited a diurnal variation with higher levels during the dark cycle than during the light cycle in young rats but not in old rats. In addition, prefrontal acetylcholine release was closely associated with spontaneous activity in young rats but not in old rats. The present study suggests that aging reduces diurnal changes in the prefrontal acetylcholine release and that there is a cross-correlation between the prefrontal acetylcholine release and spontaneous locomotor activity in male rats.

Effects of the GABAB antagonist CGP 35348 on sleep-wake states, behaviour, and spike-wave discharges in old rats

The GABAB antagonist CGP 35348 was intraperitoneally given in doses of 100, 300, and 900 mg/kg to old rats. These rats were earlier chronically provided with EEG and EMG electrodes. Sleep recordings based on visual inspection of EEG and EMG recordings were made for 3 h post injection, and spontaneous behaviour in the recording cage was additionally observed. With 100 and 300 mg/kg, the drug produced an increase in the duration of REM sleep compared to the saline-injected control group. The REM sleep latency was correspondingly reduced. Non-REM sleep and total sleep duration increased and an s-shaped dose-response relationship was found. Explorative behaviour was diminished after injections with 100 and 300 mg/kg CGP 35348. The number and duration of spike-wave discharges were reduced after all doses of CGP 35348 and during all 3 recording hours. The latter outcomes confirm the strong suppressive action of this drug on spike-wave discharges; these effects have also been reported in models of absence epilepsy. The hypnotic properties and especially the increase in REM sleep after the administration of CGP 35348 deserve attention considering the paucity of drugs which facilitate REM sleep. The discovery of drugs promoting REM sleep might have theoretical as well as clinical consequences.

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

Literature is reviewed indicating that aging is characterized by changes in circadian rhythms and sleep quality. The most marked change is an attenuation of amplitude. An advance of phase, a shortening of period, and a desynchronization of rhythms are also evident. The mechanisms underlying these changes are unknown. However, age-related changes in the retina, suprachiasmatic nucleus, and pineal gland seem relevant along with behavioral changes such as a reduction in physical activity and exposure to photic stimulation. Changes in circadian rhythms are frequently associated with a reduction in nighttime sleep quality, a decrease in daytime alertness, and an attenuation in cognitive performance; reversing such changes could enhance the quality of life for a large and rapidly increasing percentage of the population. Reversal appears possible by increasing melatonin levels with either appropriately timed exposure to photic stimulation and/or appropriately timed administration of exogenous melatonin. These interventions may increase aspects of genetic expression that have changed with aging. A hypothesis concerning the potential benefits of enhanced circadian amplitude is also offered.

Effects of chronic stress on sleep in rats

The present study was conducted to determine the effects of chronic stress on sleep using a rodent paradigm of around-the-clock signalled intermittent foot shock in which some rats can pull a chain to avoid/escape shock while another group of rats is yoked to the first group. We measured sleep using telemetry; four-channel EEG was collected 24 h/day in rats during 2 prestress days; days 1, 2, 3, 7, and 14 during chronic stress; and 3 poststress days. States of REM sleep, non-REM (NREM) sleep, and waking were scored for each 15-s period of the EEG recordings. During the prestress period, rats slept (REM plus NREM) 55% of available time during the light hours and 34% of the dark hours with the remainder represented by waking. On the first day of stress, total sleep and, especially REM sleep, decreased markedly. By the second day of stress, only REM sleep in the controllable stress group (but not the uncontrollable stress group) was still significantly decreased compared to prestress levels, and REM sleep returned to baseline levels by day 7 of stress. The recovery of sleep quantity was accomplished by increased sleep during the dark hours, resulting in a long-lasting disruption of normal circadian sleep patterning.

Sleep fragmentation, and changes in locomotor activity and body temperature in trypanosome-infected rats

The rest-activity and body temperature 24 h cycles, as well as the structure of spontaneous sleep, were studied in rats 3 weeks after infection with monomorphic Trypanosoma brucei brucei. This parasite belongs to the species of trypanosomes that causes in humans African sleeping sickness, a neuropsychiatric syndrome that involves alterations of endogenous biological rhythms. In the infected rats, entrained to a 12 h:12 h photoperiod, a considerable hypokinesia was detected during the hours of darkness. A significant oscillation of the body temperature during 24 h was lost in some infected animals. In the other infected animals, the body temperature cycle displayed a lower amplitude and a phase advance. The mean temperature was slightly higher in the infected than in control rats during the period of light. A detailed analysis of the structure of spontaneous sleep, based on daytime electroencephalographic recordings, revealed during trypanosome infection an increased relative proportion of wake, and a decreased percent value of synchronized sleep. A marked reduction of the mean REM latency and a fragmented pattern of synchronized sleep, resulting in a considerable alteration of the REM-non-REM sleep sequences, were also observed in the infected animals. These findings indicate that trypanosomiasis in the rat results in a striking sleep fragmentation, as well as in changes of locomotor activity and body temperature rhythm. Thus, trypanosome infection in the rat provides an experimental model of sleep dysregulation in a structurally intact brain, and may provide an animal model of endogenous rhythm changes documented in African sleeping sickness.

Spontaneous acetylcholine release in the hippocampus exhibits a diurnal variation in both young and old rats

Extracellular levels of acetylcholine (ACh) in the hippocampus were measured by the microdialysis method in freely moving young (3-4 months old) and old (18-24 months old) female rats over a period of 24 h to examine the effect of aging on hippocampal ACh release. Hippocampal ACh release during a 24-h period exhibited a diurnal variation with higher levels during the dark cycle than during the light cycle in old rats as well as young rats. The present study suggests that a diurnal variation in ACh release is maintained fairly well until the rats are at least 24 months old.

Non-pharmacological treatment of sleep and wake disturbances in aging and Alzheimer's disease: chronobiological perspectives

Numerous studies indicate a deterioration of nighttime sleep and daytime cognitive performance in elderly people and Alzheimer patients. As a result of the increasing number of elderly people and Alzheimer patients in the western society, attention for these problems has grown. However, so far, the major research effort has been concentrating on the development of pharmacological therapies for an isolated age-related problem. In the present review it is argued that several age-related problems with sleep and wakefulness may reflect a dampening of circadian rhythm amplitudes. Non-pharmacological manipulation of circadian rhythms by means of various external stimuli appears to be effective in improving sleep and cognitive functioning in elderly people and Alzheimer patients.

Effects of a novel melatonin analog on circadian rhythms of body temperature and activity in young, middle-aged, and old rats

Circadian rhythms of body temperature and activity were recorded in young, middle-aged, and old rats. A new melatonin analog, S20242, was administered daily around the onset of darkness for a 2-week period. Compared to the young animals, there was a significant age-related reduction in the amplitude and stability of body temperature and activity in both the middle-aged and old rats. In these two groups there was an improvement of the circadian rhythm of body temperature as a result of daily application of the melatonin analog.

Effect of light intensity on diurnal sleep-wake distribution in young and old rats

During the aging process, the amplitude of the circadian rhythms of many physiological variables is reduced. It has been hypothesized that increasing light intensity during the light phase of the light-dark cycle might result in a reduction of age-related changes in the circadian rhythms. Indeed, in the present sleep-wake study in young and old rats it was found that (a) various parameters, such as the light-dark differences and total amounts of each behavioral state responded positively to changes in environmental light intensity (i.e., age-related trends were reversed), (b) in both age groups, the logarithm of light intensity appeared to have a linear dose-response relationship with light-dark differences of the sleep-wake states, (c) the light-dark difference of active wakefulness and quiet sleep of old rats under high light intensity were comparable to those of young rats under low light intensity. The results of the present study suggest that, under appropriate conditions, light could be of clinical use in reducing age-related circadian sleep disturbances in humans. This may, in turn, reduce the use of sedatives in elderly people.

Enhancement of REM sleep with auditory stimulation in young and old rats

Auditory stimulation applied during rapid eye movement (REM) sleep enhances the duration of REM sleep in cats and humans. The present experiment investigated whether auditory stimulation would enhance REM sleep in young (3-6 months) rats, and also in old (22-24 months) rats which have impaired REM sleep. Baseline sleep records were obtained on two days. Sleep patterns were then assessed during auditory stimulation test sessions. In young rats, auditory stimulation was administered during each REM sleep bout. In old rats, auditory stimulation was administered on a fixed schedule (10 min of stimulation alternating with 15 min quiet). The day after the stimulation session, an additional sleep record (Day 2) was obtained for each rat. In young rats, auditory stimulation enhanced both REM sleep duration and total REM sleep time. In the old rats, which showed impaired sleep measures as compared to young animals, auditory stimulation enhanced both total REM sleep time and the number of REM sleep periods. Residual proactive effects of auditory stimulation (Day 2) were observed in both young and old rats. Thus, auditory stimulation is an effective manipulation with which to augment REM sleep in both young and old rats, and partially attenuates REM sleep impairments in old rats.

Glucose attenuation of paradoxical sleep deficits in old rats

Glucose administration enhances memory in several amnestic populations, including old humans and rodents. The present experiment demonstrates that glucose also enhances measures of sleep in old rats. Three-hour day-time sleep EEGs were assessed in 3- and 24-month-old rats. The animals received injections of saline or glucose (100, 500, and 1000 mg/kg) on different days in a counter-balanced order. At doses of 100 and 500 mg/kg, glucose augmented the duration of paradoxical sleep bouts and total paradoxical sleep time in old, but not young, rats. Within 2 weeks after the sleep tests, measures of several brain neurotransmitter functions were obtained. Glucose was more effective in enhancing paradoxical sleep in those individual aged rats with high levels of hippocampal choline acetyltransferase and occipital cortex serotonin concentrations than in aged rats with lower levels on these neurochemical measures. The findings suggest that glucose attenuates selective age-related sleep deficits in old rats. More generally, these results add to a growing body of evidence indicating that moderate doses of peripheral glucose can influence a variety of CNS measures.