Restricted and disrupted sleep: Effects on autonomic function, neuroendocrine stress systems and stress responsivity

Problems associated with short sleep: bridging the gap between laboratory and epidemiological studies

Existing data from laboratory studies suggest a number of negative consequences of acute reductions in sleep time. Also, epidemiological data suggest links between shorter self-reported sleep duration and negative health outcomes. These bodies of work are growing, revealing several key points of convergence and opportunities for future exploration. In addition, they begin to highlight possible problems experienced by "short sleepers," who sleep approximately 6h or less per night. While it is likely that this group is heterogeneous, comprised both of individuals with less need for sleep and those not sleeping enough, the laboratory and epidemiological findings point towards directions that can be more fully explored in verified short sleepers. This paper discusses problems associated with the terminology used to describe "short sleep," summarizes laboratory studies exploring neurobehavioral performance, metabolism and obesity, and psychological health and epidemiological studies exploring mortality risk, obesity and metabolism, cardiovascular disease, and general health/psychosocial stress, describes studies of verified short sleepers and explores areas of convergence, laying out possible future directions.

Paradoxical sleep deprivation activates hypothalamic nuclei that regulate food intake and stress response

A large body of evidence has shown that prolonged paradoxical sleep deprivation (PSD) results in hypothalamic-pituitary-adrenal (HPA) axis activation, and in loss of body weight despite an apparent increase of food intake, reflecting increased energy expenditure. The flowerpot technique for PSD is an efficient paradigm for investigating the relationships among metabolic regulation and stress response. The purpose of the present study was to examine the mechanisms involved in the effects of 96 h of PSD on metabolism regulation, feeding behaviour and stress response by studying corticotrophin-releasing hormone (CRH) and orexin (ORX) immunoreactivity in specific hypothalamic nuclei. Once-daily assessments of body weight, twice-daily measurements of (spillage-corrected) food intake, and once-daily determinations of plasma adrenocorticotropic hormone (ACTH) and corticosterone were made throughout PSD or at corresponding times in control rats (CTL). Immunoreactivity for CRH in the paraventricular nucleus of the hypothalamus and for ORX in the hypothalamic lateral area was evaluated at the end of the experimental period. PSD resulted in increased diurnal, but not nocturnal, food intake, producing no significant changes in global food intake. PSD augmented the immunoreactivity for CRH and plasma ACTH and corticosterone levels, characterizing activation of the HPA axis. PSD also markedly increased the ORX immunoreactivity. The average plasma level of corticosterone correlated negatively with body weight gain throughout PSD. These results indicate that augmented ORX and CRH immunoreactivity in specific hypothalamic nuclei may underlie some of the metabolic changes consistently described in PSD.

Effects of Ramadan fasting on physical performance and metabolic, hormonal, and inflammatory parameters in middle-distance runners

The Ramadan fasting (RF) period is associated with changes in sleep habits and increased sleepiness, which may affect physical performance in athletes, and may induce metabolic, hormonal, and inflammatory disturbances. In 8 middle-distance athletes (25.0 ± 1.3 years), a maximal aerobic velocity (MAV) test was performed 5 days before RF (day –5), and on days 7 and 21 of RF. The same days, saliva samples were collected to determine cortisol and testosterone concentrations before and after the MAV test. Blood samples were collected before RF (P1), at the end of RF (P2), and 1 week post RF (P3). Plasma levels of interleukin (IL)-6, a mediator of sleepiness and energy availability, were determined. We also evaluated changes in metabolic and hormonal parameters, mood state, and nutritional and sleep profiles. During RF, mean body mass and body fat did not statistically change. Compared with day –5, MAV values decreased at days 7 and 21 (p < 0.05, respectively), while testosterone/cortisol ratio values did not change significantly. Nocturnal sleep time and energy intake were lower at day 21 than before RF (day 0/P1) (p < 0.05). At the end of RF (day 31), the fatigue score on the Profile of Mood States questionnaire was increased (p < 0.001). For P2 vs. P1, IL-6 was increased (1.19 ± 0.25 vs. 0.51 ± 0.13 pg·mL–1; p < 0.05), melatonin levels were decreased (p < 0.05), and adrenalin and noradrenalin were increased (p < 0.01 and p < 0.001, respectively). At 7 days post RF, all parameters recovered to pre-RF values. In conclusion, RF is accompanied by significant metabolic, hormonal, and inflammatory changes. Sleep disturbances, energy deficiency, and fatigue during RF may decrease physical performance in Muslim athletes who maintain training. Reduction of work load and (or) daytime napping may represent adequate strategies to counteract RF effects for Muslim athletes.

New neurons in the adult brain: the role of sleep and consequences of sleep loss

Research over the last few decades has firmly established that new neurons are generated in selected areas of the adult mammalian brain, particularly the dentate gyrus of the hippocampal formation and the subventricular zone of the lateral ventricles. The function of adult-born neurons is still a matter of debate. In the case of the hippocampus, integration of new cells in to the existing neuronal circuitry may be involved in memory processes and the regulation of emotionality. In recent years, various studies have examined how the production of new cells and their development into neurons is affected by sleep and sleep loss. While disruption of sleep for a period shorter than one day appears to have little effect on the basal rate of cell proliferation, prolonged restriction or disruption of sleep may have cumulative effects leading to a major decrease in hippocampal cell proliferation, cell survival and neurogenesis. Importantly, while short sleep deprivation may not affect the basal rate of cell proliferation, one study in rats shows that even mild sleep restriction may interfere with the increase in neurogenesis that normally occurs with hippocampus-dependent learning. Since sleep deprivation also disturbs memory formation, these data suggest that promoting survival, maturation and integration of new cells may be an unexplored mechanism by which sleep supports learning and memory processes. Most methods of sleep deprivation that have been employed affect both non-rapid eye movement (NREM) and rapid eye movement (REM) sleep. Available data favor the hypothesis that decreases in cell proliferation are related to a reduction in REM sleep, whereas decreases in the number of cells that subsequently develop into adult neurons may be related to reductions in both NREM and REM sleep. The mechanisms by which sleep loss affects different aspects of adult neurogenesis are unknown. It has been proposed that adverse effects of sleep disruption may be mediated by stress and glucocorticoids. However, a number of studies clearly show that prolonged sleep loss can inhibit hippocampal neurogenesis independent of adrenal stress hormones. In conclusion, while modest sleep restriction may interfere with the enhancement of neurogenesis associated with learning processes, prolonged sleep disruption may even affect the basal rates of cell proliferation and neurogenesis. These effects of sleep loss may endanger hippocampal integrity, thereby leading to cognitive dysfunction and contributing to the development of mood disorders.

Neighborhood disorder, sleep quality, and psychological distress: testing a model of structural amplification

Using data from the 2004 Survey of Texas Adults (n=1504), we examine the association between perceived neighborhood disorder and psychological distress. Building on previous research, we test whether the effect of neighborhood disorder is mediated and moderated by sleep quality. Our specific analytic strategy follows a two-stage theoretical model of structural amplification. In the first stage, perceptions of neighborhood disorder increase psychological distress indirectly by reducing sleep quality. In the second stage, the effect of neighborhood disorder on psychological distress is amplified by poor sleep quality. The results of our analyses are generally consistent with our theoretical model. We find that neighborhood disorder is associated with poorer sleep quality and greater psychological distress. We also observe that the positive association between neighborhood disorder and psychological distress is mediated (partially) and moderated (amplified) by poor sleep quality.

How disturbed sleep may be a risk factor for adverse pregnancy outcomes

Adverse pregnancy outcomes associated with significant maternal and infant morbidity are on the rise in Western society despite advances of medical technology. Current risk factors are insufficient to identify women at greatest risk of developing an adverse outcome. An attempt to identify novel contributors to increased risk is warranted. Sleep disturbances are frequent during pregnancy, yet are often dismissed as irrelevant. Emerging evidence indicates that sleep disturbances are associated with poor health outcomes, including cardiovascular disease. Disturbed sleep is also linked with an increased inflammatory response. Increased inflammation is proposed as a key biological pathway through which chronic disease and adverse pregnancy outcomes develop. In this paper, we propose a model and a testable hypothesis of how disturbed sleep in the first 20 weeks of pregnancy could contribute to adverse pregnancy outcomes such as preeclampsia, intrauterine growth restriction, and preterm birth via increased inflammation.

TARGET AUDIENCE

Obstetricians & Gynecologists, Family Physicians Leaning Objectives: After completion of this article, the reader should be able to outline data linking sleep disturbances with an increased risk of some systemic disorders, recall characteristics of pregnancy complications which support the hypothesis that sleep disturbances may be related to these pregnancy outcomes, and summarize the likelihood and types of sleep disturbances that are common in pregnant women.

Delirium and long-term cognitive impairment

Delirium is a severe, acute neuropsychiatric syndrome that is highly prevalent in acute hospital populations. Delirium has noticeable effects on length of hospitalization, cost of care, mortality and morbidity. In addition to these well-established adverse consequences, there is increasing evidence linking delirium and a higher risk of long-term cognitive impairment (LTCI), including dementia. A prior review (Jackson, Gordon, Hart, Hopkins, & Ely, 2004), in which nine studies (total N = 1,885, years 1989-2003) were considered, concluded that there was evidence for an association between delirium and LTCI. Here we provide a review of studies published since Jackson's review. We included nine reports, with a total of 2,025 patients. The studies show diverse sample sizes, methodologies, designs and patient populations. However, taken together, the results of these new studies broadly confirm that there is a link between delirium and LTCI. We go on to discuss putative mechanisms and explanations. These include (1) delirium as a marker of chronic progressive pathology, but unrelated to any progression, (2) delirium as a consequence of acute brain damage which is also responsible for a 'single hit' or triggering of active processes causing LTCI, (3) delirium itself as a cause of LTCI, and (4) drug treatment of delirium or other conditions as a cause of LTCI. We conclude with suggestions for future research.

Chronically restricted sleep leads to depression-like changes in neurotransmitter receptor sensitivity and neuroendocrine stress reactivity in rats

STUDY OBJECTIVES

Frequently disrupted and restricted sleep is a common problem for many people in our Western society. In the long run, insufficient sleep may have repercussions for health and may sensitize individuals to psychiatric diseases. In this context, we applied an animal model of chronic sleep restriction to study effects of sleep loss on neurobiological and neuroendocrine systems that have been implied in the pathophysiology of depression, particularly the serotonergic system and the hypothalamic-pituitary-adrenal (HPA) axis.

DESIGN

Adult rats were exposed to a schedule of chronic partial sleep deprivation allowing them only 4 h of sleep per day. Sleep restriction was achieved by placing the animals in slowly rotating drums. To examine the regulation and reactivity of the HPA axis, blood samples were collected to measure adrenocorticotropin (ACTH) and corticosterone (CORT) responses.

MEASUREMENTS AND RESULTS

While one day of restricted sleep had no significant effect on HPA axis stress reactivity, sleep restriction for a week caused a blunted pituitary ACTH response in a conditioned fear paradigm. Despite this lower ACTH response, adrenal CORT release was normal. The blunted pituitary response may be related to reduced sensitivity of serotonin-1A receptors and/or receptors for corticotropin-releasing hormone (CRH), since sleep restricted rats showed similar reductions in ACTH release to direct pharmacological stimulation with a serotonin-1A agonist or CRH.

CONCLUSIONS

Chronic sleep restriction may lead to changes in neurotransmitter receptor systems and neuroendocrine reactivity in a manner similar to that seen in depression. This experimental study thus supports the hypothesis that disrupted and restricted sleep may contribute to the symptomatology of psychiatric disorders.