Circadian rhythm sleep disorders

Cognitive performance as a zeitgeber: cognitive oscillators and cholinergic modulation of the SCN entrain circadian rhythms

The suprachiasmatic nucleus (SCN) is the primary circadian pacemaker in mammals that can synchronize or entrain to environmental cues. Although light exerts powerful influences on SCN output, other non-photic stimuli can modulate the SCN as well. We recently demonstrated that daily performance of a cognitive task requiring sustained periods of attentional effort that relies upon basal forebrain (BF) cholinergic activity dramatically alters circadian rhythms in rats. In particular, normally nocturnal rats adopt a robust diurnal activity pattern that persists for several days in the absence of cognitive training. Although anatomical and pharmacological data from non-performing animals support a relationship between cholinergic signaling and circadian rhythms, little is known about how endogenous cholinergic signaling influences SCN function in behaving animals. Here we report that BF cholinergic projections to the SCN provide the principal signal allowing for the expression of cognitive entrainment in light-phase trained animals. We also reveal that oscillator(s) outside of the SCN drive cognitive entrainment as daily timed cognitive training robustly entrains SCN-lesioned arrhythmic animals. Ablation of the SCN, however, resulted in significant impairments in task acquisition, indicating that SCN-mediated timekeeping benefits new learning and cognitive performance. Taken together, we conclude that cognition entrains non-photic oscillators, and cholinergic signaling to the SCN serves as a temporal timestamp attenuating SCN photic-driven rhythms, thereby permitting cognitive demands to modulate behavior.

Neurodegenerative Disease and REM Behavior Disorder

OPINION STATEMENT

Patients with cerebral degenerative conditions commonly suffer from a variety of sleep disorders, including sleep-disordered breathing, insomnia, parasomnias (REM sleep behavior disorder), circadian rhythm disturbances, and restless legs syndrome. When these sleep disorders go unrecognized and untreated, they can lead to decreased quality of life and worsening neurological symptoms related to the underlying condition. Appropriate management initially requires taking a careful history from the patient and bed partner regarding their sleep. In addition, polysomnography may be required to aid in the diagnosis of sleep-disordered breathing or parasomnias. Occasionally, adjusting the dosages of sedating or sleep disrupting medications and improving sleep hygiene may improve sleep complaints. However, in most cases restoring quality nighttime sleep requires specific therapeutic intervention. In patients that suffer from sleep apnea, this usually means treatment with continuous positive airway pressure (CPAP), positional therapy, dental appliances, upper airway surgery, or weight loss. Pharmacological treatment of insomnia in patients with cerebral degenerative conditions can be difficult due to side effects (worsening balance, cognition) and lack of data in this patient population. Behavioral strategies such as cognitive-behavioral therapy have been effective and are considered safer than hypnotic therapy, but can be limited due to access to trained providers (distance and number of providers) and limited cognitive functioning of the patient. Parasomnias, namely REM sleep behavior disorder, are managed by looking for any underlying cause of arousals (sleep apnea, periodic leg movements of sleep), implementing safety precautions, and pharmacologically with either benzodiazepines or melatonin. Restless legs syndrome may improve with iron replacement or dopamine agonist therapy, as it does in other patient populations. Light therapy may be beneficial in patients suffering from circadian rhythm disorders such as advanced sleep phase syndrome.

Sleep and circadian misalignment for the hospitalist: a review

Shift work is necessary for hospitalists to provide on-site 24-hour patient care. Like all shift workers, hospitalists working beyond daylight hours are subject to a misalignment between work obligations and the endogenous circadian system, which regulates sleep and alertness patterns. With chronic misalignment, sleep loss accumulates and can lead to shift work disorder or other chronic medical conditions. Hospitalists suffering from sleep deprivation also risk increased rates of medical errors. By realigning work and circadian schedules, a process called circadian adaptation, hospitalists can limit fatigue and potentially improve safety. Adaptation strategies include improving sleep hygiene before work, caffeine use at the start of the night shift, bright light exposure and planned naps during the shift, and short-term use of a mild hypnotic after night work. If these attempts fail and chronic fatigue persists, then a diagnosis of shift work disorder should be considered, which can be treated with stronger pharmacotherapy. Night float scheduling strategies may also help to limit chronic sleep loss. More research is urgently needed regarding the sleep patterns and job performance of hospitalists working at night to improve scheduling decisions and patient safety.

In a rat model of night work, activity during the normal resting phase produces desynchrony in the hypothalamus

Internal synchrony among external cycles and internal oscillators allows adaptation of physiology to cyclic demands for homeostasis. Night work and shift work lead to a disrupted phase relationship between external time cues and internal rhythms, also losing internal coherence among oscillations. This process results in internal desynchrony (ID) in which behavioral, hormonal, and metabolic variables cycle out of phase. It is still not clear whether ID originates at a peripheral or at a central level. In order to determine the possible role of hypothalamic oscillators in ID, we explored with a rat model of "night work" daily rhythms of activity and clock gene expression in the hypothalamus. This study provides evidence that wakefulness and activity during the normal resting phase lead to a shift in the diurnal rhythms of c-Fos and induce a rhythm of PER1 in the arcuate and dorsomedial nucleus of the hypothalamus, both associated with metabolism and regulation of the sleep/wake cycle. Moreover, the number of orexin (ORX)-positive neurons and c-Fos in the perifornical area increased during the working period, suggesting a relevant switch of activity in this brain region induced by the scheduled activity; however, the colocalization of c-Fos in ORX-positive cells was not increased. In contrast, the suprachiasmatic nucleus and the paraventricular nucleus remained locked to the light/dark cycle, resulting in ID in the hypothalamus. Present data suggest that ID occurs already at the level of the first output projections from the SCN, relaying nuclei that transmit temporal signals to other brain areas and to the periphery.

Circadian Rhythm Sleep Disorder: Irregular Sleep Wake Rhythm Type

Irregular Sleep Wake Rhythm Disorder (ISWRD) is characterized by the relative absence of a circadian pattern in an individual's sleep-wake cycle. Significant changes in circadian regulation occur with aging and with neurodegenerative diseases, such as Alzheimer's disease prevalent in older adults, which are likely to contribute to the prevalence of ISWRD seen in these populations, although ISWRD is also seen in traumatic brain injury and mental retardation populations. ISWRD is thought to result from some combination of; degeneration or decreased neuronal activity of suprachiasmatic nucleus (SCN) neurons, decreased responsiveness of the circadian clock to entraining agents such as light and activity, and decreased exposure to bright light and structured social and physical activity during the day. Treatment of ISWRD seeks to consolidate sleep during the night and wakefulness during the day; primarily through restoring or enhancing exposure to the various SCN time cues, or "zeitgebers". Studies of the effectiveness of pharmacologic treatments for ISWRD have generally yielded negative or inconsistent results. In general multi-modal non-pharmacological approaches involving increased exposure to light, increased physical and social activities and improved sleep hygiene have been the most successful therapeutic approaches.

Sleep disorders: causes, effects, and solutions

Until recently, sleep has been a mystery even to scientists. Research has defined sleep function and the effects of sleep deprivation. Sleep disorders are interrelated with medical and psychiatric illnesses. This article presents insomnia, jet lag, and shift work sleep disorders and reviews issues related to women's health and sleep. Pharmacologic and behavioral treatments for sleep conditions are explored.

Light measurement in the hospital: A comparison of two methods

Disrupted sleep in hospitalized patients is widely reported, and ambient environmental lighting may be both a contributor to and a modifier of sleep/wake patterns. This is the first study to examine the congruence between two types of light meters, a wrist-worn device and a stand-alone device, and their respective light intensity measurements. The study sample included 20 light trials in 17 patients for a total of 480 paired light measurements. Descriptive data analysis indicated that both light meters dependably recorded changes in light levels, and Bland Altman plots demonstrated congruence between data from the two types of light meters. The results provide promising data on how to measure patient exposure to ambient light dependably in the continuously changing and unpredictable clinical setting.

The brain's master circadian clock: implications and opportunities for therapy of sleep disorders

The suprachiasmatic nuclei (SCN) residing in the anterior hypothalamus maintains a near-24-h rhythm of electrical activity, even in the absence of environmental cues. This circadian rhythm is generated by intrinsic molecular mechanisms in the neurons of the SCN; however, the circadian clock is modulated by a wide variety of influences, including glutamate and pituitary adenylate cyclase-activating peptide (PACAP) from the retinohypothalamic tract, melatonin from the pineal gland, and neuropeptide Y from the intergeniculate leaflet. By virtue of these and other inputs, the SCN responds to environmental cues such as light, social and physical activities. In turn, the SCN controls or influences a wide variety of physiologic and behavioral functions, including attention, endocrine cycles, body temperature, melatonin secretion, and the sleep-wake cycle. Regulation of the sleep-wake cycle by the SCN has important implications for development of therapies for sleep disorders, including those involving desynchronization of circadian rhythms and insomnia.

Multi-target strategies for the improved treatment of depressive states: Conceptual foundations and neuronal substrates, drug discovery and therapeutic application

Major depression is a debilitating and recurrent disorder with a substantial lifetime risk and a high social cost. Depressed patients generally display co-morbid symptoms, and depression frequently accompanies other serious disorders. Currently available drugs display limited efficacy and a pronounced delay to onset of action, and all provoke distressing side effects. Cloning of the human genome has fuelled expectations that symptomatic treatment may soon become more rapid and effective, and that depressive states may ultimately be "prevented" or "cured". In pursuing these objectives, in particular for genome-derived, non-monoaminergic targets, "specificity" of drug actions is often emphasized. That is, priority is afforded to agents that interact exclusively with a single site hypothesized as critically involved in the pathogenesis and/or control of depression. Certain highly selective drugs may prove effective, and they remain indispensable in the experimental (and clinical) evaluation of the significance of novel mechanisms. However, by analogy to other multifactorial disorders, "multi-target" agents may be better adapted to the improved treatment of depressive states. Support for this contention is garnered from a broad palette of observations, ranging from mechanisms of action of adjunctive drug combinations and electroconvulsive therapy to "network theory" analysis of the etiology and management of depressive states. The review also outlines opportunities to be exploited, and challenges to be addressed, in the discovery and characterization of drugs recognizing multiple targets. Finally, a diversity of multi-target strategies is proposed for the more efficacious and rapid control of core and co-morbid symptoms of depression, together with improved tolerance relative to currently available agents.

The selective tachykinin neurokinin 1 (NK1) receptor antagonist, GR 205,171, stereospecifically inhibits light-induced phase advances of hamster circadian activity rhythms

Circadian rhythms in mammals are generated by master pacemaker cells located within the suprachiasmatic nucleus of the hypothalamus. In hamsters, the suprachiasmatic nucleus contains a small collection of cells immunoreactive for substance P, the endogenous ligand of tachykinin neurokinin 1 (NK1) receptors. In addition, two other nuclei which form part of the circadian system, the intergeniculate leaflet of the thalamus and the raphe nuclei, also contain fibers and/or cell bodies immunoreactive for substance P. In light of these observations, we evaluated the influence of the selective tachykinin NK1 receptor antagonist, GR 205,171, upon circadian activity rhythms in the hamster. Systemic injection of GR 205,171 dose-dependently (2.5-40.0 mg/kg, i.p.) inhibited light-induced phase advances in hamster circadian wheel running activity rhythms by approximately 50%. In contrast, GR 226,206, the less active enantiomer of GR 205,171, failed to affect light-induced phase advances. In addition, we examined the potential ability of GR 205,171 to induce non-photic phase shifts in hamster wheel running rhythms when injected at mid-day to late night circadian times. However, GR 205,171 (40 mg/kg) did not elicit non-photic phase shifts at these times indicating that tachykinin NK1 receptor antagonists are only effective when a light stimulus is applied to the pacemaker. Although GR 205,171 may, in theory, activate several sites within the circadian system, we suggest that GR 205,171 acts in the raphe nuclei to increase inhibitory serotonergic input to pacemaker cells in the suprachiasmatic nuclei, thereby suppressing photic modulation of the pacemaker. These findings have important implications for the use of tachykinin NK1 receptor antagonists in the treatment of depression and other central nervous system disorders.

Entrainment of the human circadian system by light

The periodic light-dark cycle is the dominant environmental synchronizer used by humans to entrain to the geophysical 24-h day. Entrainment is a fundamental property of circadian systems by which the period of the internal clock (tau) is synchronized to the period of the entraining stimuli (T cycle). An important aspect of entrainment in humans is the maintenance of an appropriate phase relationship between the circadian system, the timing of sleep and wakefulness, and environmental time (a.k.a. the phase angle of entrainment) to maintain wakefulness throughout the day and consolidated sleep at night. In this article, we review these concepts and the methods for assessing circadian phase and period in humans, as well as discuss findings on the phase angle of entrainment in healthy adults. We review findings from studies that examine how the phase, intensity, duration, and spectral characteristics of light affect the response of the human biological clock and discuss studies on entrainment in humans, including recent studies of the minimum light intensity required for entrainment. We briefly review conditions and disorders in which failure of entrainment occurs. We provide an integrated perspective on circadian entrainment in humans with respect to recent advances in our knowledge of circadian period and of the effects of light on the biological clock in humans.