Slow wave sleep drives inhibition of pituitary-adrenal secretion in humans

Network analysis of the hair-based nine hormones from four neuroendocrine systems

INTRODUCTION

The stress response maintains the homeostasis of the body's internal environment and normal physiological activities, involving several neuroendocrine systems, such as the HPA axis, the HPG axis, the endocannabinoid system, and the melatonin system. However, studies on the intricate interactions among the four neuroendocrine systems are lacking, and it is not clear how these interactions are affected by demographic variables. The aim of this study was to investigate the network characteristics of hormonal networks comprising nine hormones from four neuroendocrine systems and how they were affected by demographic variables.

METHODS

252 healthy current students were recruited from Southeast University, China. The concentrations of nine hormones in their hair were measured by LC/MS methods, and hormonal network was constructed. Network analysis was used to characterize the interrelationships between hormones or neuroendocrine systems, central hormones, bridge hormones, hormonal network characteristics, and their changes in response to demographic variables.

RESULTS

Complex interactions between the HPA axis, the HPG axis, the ECS and the melatonin system formed a sparse and stable network, with cortisol and cortisone being the central hormones and melatonin as the bridge hormone. Demographic variables did not affect the overall characteristics of the network or the central hormone, but a number of specific connections in the network changed and the bridge hormones became cortisone and progesterone.

CONCLUSION

The interactions between the four stress-related neuroendocrine systems were relatively stable and were centered and initiated by the HPA axis. Demographic variables did not affect the overall structure of the network, but influenced local features of the network, such as edge weights and bridge centrality.

Insomnia and intestinal microbiota: a narrative review

PURPOSE

The intestinal microbiota and insomnia interact through the microbiota-gut-brain axis. The purpose of this review is to summarize and analyze the changes of intestinal microbiota in insomnia, the interaction mechanisms between intestinal microbiota and insomnia and the treatment methods based on the role of microbiota regulation in insomnia, in order to reveal the feasibility of artificial intervention of intestinal microbiota to improve insomnia.

METHODS

Pubmed/ Embase were searched through March 2024 to explore the relevant studies, which included the gut microbiota characteristics of insomnia patients, the mechanisms of interaction between insomnia and gut microbiota, and the relationship between gut microbiota and insomnia treatment.

RESULTS

Numerous studies implicated insomnia could induce intestinal microbiota disorder by activating the immune response, the hypothalamic-pituitary-adrenal axis, the neuroendocrine system, and affecting bacterial metabolites, resulting in intestinal ecological imbalance, intestinal barrier destruction and increased permeability. The intestinal microbiota exerted an influence on the central nervous system through its interactions with intestinal neurons, releasing neurotransmitters and inflammatory factors, which in turn, can exacerbate symptoms of insomnia. Artificial interventions of gut microbiota included probiotics, traditional Chinese medicine, fecal microbiota transplantation, diet and exercise, whose main pathway of action is to improve sleep by affecting the release of neurotransmitters and gut microbial metabolites.

CONCLUSION

There is an interaction between insomnia and gut microbiota, and it is feasible to diagnose and treat insomnia by focusing on changes in the gut microbiota of patients with insomnia. Large cross-sectional studies and fecal transplant microbiota studies are still needed in the future to validate its safety and efficacy.

Sleep-A brain-state serving systems memory consolidation

Although long-term memory consolidation is supported by sleep, it is unclear how it differs from that during wakefulness. Our review, focusing on recent advances in the field, identifies the repeated replay of neuronal firing patterns as a basic mechanism triggering consolidation during sleep and wakefulness. During sleep, memory replay occurs during slow-wave sleep (SWS) in hippocampal assemblies together with ripples, thalamic spindles, neocortical slow oscillations, and noradrenergic activity. Here, hippocampal replay likely favors the transformation of hippocampus-dependent episodic memory into schema-like neocortical memory. REM sleep following SWS might balance local synaptic rescaling accompanying memory transformation with a sleep-dependent homeostatic process of global synaptic renormalization. Sleep-dependent memory transformation is intensified during early development despite the immaturity of the hippocampus. Overall, beyond its greater efficacy, sleep consolidation differs from wake consolidation mainly in that it is supported, rather than impaired, by spontaneous hippocampal replay activity possibly gating memory formation in neocortex.

Histological study and immunohistochemical expression of StAR protein in the suprarenal cortex of adult male rats associated with sleep disturbance

The present study was designed to investigate the effects of sleep disturbance on histological features and evaluates the expression of StAR protein in the cortex of the adrenal gland of adult male rats. The suprarenal glands are endocrine organs that are directly affected by sleep deprivation. Sleep disturbance is a stress factor affecting steroidogenesis since it is regulated by the hypothalamic-pituitary axis (HPA). Its hormones are cholesterol-derived, and they use the Acut regulating protein of steroidogenesis StAR protein that plays an essential critical role in mediating cholesterol transfer to the inner mitochondrial membrane and the cholesterol side chain cleavage enzyme system. This research aims to investigate the effects of sleep disturbance (sleep disruption and deprivation) on the histological features and changes in StAR expression in the cortex of the adrenal glands of rats. Comparing experimental groups to controls, histological alterations such as cellular hypertrophy and vascular dilatation in the cortical zones of the adrenal cortex were found mainly in the Zona fasculata Zf. Immunohistochemistry was used to identify significant changes in the level of StAR, which showed a higher value in the sleep interruption group compared to the control and sleep deprivation groups at p-value ≤ 0.001. This indicates that sleep interruption has a more significant impact on steroidogenesis than sleep deprivation, which increases the level of StAR in the suprarenal gland. Keywords: suprarenal gland; sleep disturbance; StAR protein; steroidogenesis; circadian rhythms.

Hypnotic enhancement of slow-wave sleep increases sleep-associated hormone secretion and reduces sympathetic predominance in healthy humans

Sleep is important for normal brain and body functioning, and for this, slow-wave sleep (SWS), the deepest stage of sleep, is assumed to be especially relevant. Previous studies employing methods to enhance SWS have focused on central nervous components of this sleep stage. However, SWS is also characterized by specific changes in the body periphery, which are essential mediators of the health-benefitting effects of sleep. Here we show that enhancing SWS in healthy humans using hypnotic suggestions profoundly affects the two major systems linking the brain with peripheral body functions, i.e., the endocrine and the autonomic nervous systems (ANS). Specifically, hypnotic suggestions presented at the beginning of a 90-min afternoon nap to promote subsequent SWS strongly increased the release of growth hormone (GH) and, to a lesser extent, of prolactin and aldosterone, and shifted the sympathovagal balance towards reduced sympathetic predominance. Thus, the hypnotic suggestions induced a whole-body pattern characteristic of natural SWS. Given that the affected parameters regulate fundamental physiological functions like metabolism, cardiovascular activity, and immunity, our findings open up a wide range of potential applications of hypnotic SWS enhancement, in addition to advancing our knowledge on the physiology of human SWS.

The hypnotic enhancement of slow wave sleep, the deepest stage of sleep, goes beyond the central nervous system, causing changes at the level of the endocrine and the autonomic nervous systems.

Sleep in Normal Aging

Sleep is a key determinant of healthy and cognitive aging. Sleep patterns change with aging, independent of other factors, and include advanced sleep timing, shortened nocturnal sleep duration, increased frequency of daytime naps, increased number of nocturnal awakenings and time spent awake during the night, and decreased slow-wave sleep. The sleep-related hormone secretion changes with aging. Most changes seem to occur between young and middle adulthood; sleep parameters remain largely unchanged among healthy older adults. The circadian system and sleep homeostatic mechanisms become less robust with normal aging. The causes of sleep disturbances in older adults are multifactorial.

Neurochemical mechanisms for memory processing during sleep: basic findings in humans and neuropsychiatric implications

Sleep is essential for memory formation. Active systems consolidation maintains that memory traces that are initially stored in a transient store such as the hippocampus are gradually redistributed towards more permanent storage sites such as the cortex during sleep replay. The complementary synaptic homeostasis theory posits that weak memory traces are erased during sleep through a competitive down-selection mechanism, ensuring the brain's capability to learn new information. We discuss evidence from neuropharmacological experiments in humans to show how major neurotransmitters and neuromodulators are implicated in these memory processes. As to the major excitatory neurotransmitter glutamate that plays a prominent role in inducing synaptic consolidation, we show that these processes, while strengthening cortical memory traces during sleep, are insufficient to explain the consolidation of hippocampus-dependent declarative memories. In the inhibitory GABAergic system, we will offer insights how drugs may alter the intricate interplay of sleep oscillations that have been identified to be crucial for strengthening memories during sleep. Regarding the dopaminergic reward system, we will show how it is engaged during sleep replay, but that dopaminergic neuromodulation likely plays a side role for enhancing relevant memories during sleep. Also, we briefly go into basic evidence on acetylcholine and cortisol whose low tone during slow wave sleep (SWS) is crucial in supporting hippocampal-to-neocortical memory transmission. Finally, we will outline how these insights can be used to improve treatment of neuropsychiatric disorders focusing mainly on anxiety disorders, depression, and addiction that are strongly related to memory processing.

Overanxious and underslept

Are you feeling anxious? Did you sleep poorly last night? Sleep disruption is a recognized feature of all anxiety disorders. Here, we investigate the basic brain mechanisms underlying the anxiogenic impact of sleep loss. Additionally, we explore whether subtle, societally common reductions in sleep trigger elevated next-day anxiety. Finally, we examine what it is about sleep, physiologically, that provides such an overnight anxiety-reduction benefit. We demonstrate that the anxiogenic impact of sleep loss is linked to impaired medial prefrontal cortex activity and associated connectivity with extended limbic regions. In contrast, non-rapid eye movement (NREM) slow-wave oscillations offer an ameliorating, anxiolytic benefit on these brain networks following sleep. Of societal relevance, we establish that even modest night-to-night reductions in sleep across the population predict consequential day-to-day increases in anxiety. These findings help contribute to an emerging framework explaining the intimate link between sleep and anxiety and further highlight the prospect of non-rapid eye movement sleep as a therapeutic target for meaningfully reducing anxiety.

Sleep Matters: CD4+ T Cell Memory Formation and the Central Nervous System

The mechanisms of CD4⁺ T-cell memory formation in the immune system are debated. With the well-established concept of memory formation in the central nervous system (CNS), we propose that formation of CD4⁺ T-cell memory depends on the interaction of two different cell systems handling two types of stored information. First, information about antigen (event) and challenge (context) is taken up by antigen-presenting cells, as initial storage. Second, event and context information is transferred to CD4⁺ T cells. During activation, two categories of CD4⁺ T cell develop: effector CD4⁺ T cells, carrying event and context information, enabling them to efficiently focus their response to tissues under attack; and persisting CD4⁺ T cells, providing context-independent antigen-specific memories and long-term storage. This novel hypothesis is supported by the observation that mammalian sleep can improve both CNS and CD4⁺ T-cell memory.

The interplay between neuroendocrine and sleep alterations following traumatic brain injury

BACKGROUND

Sleep and endocrine disruptions are prevalent after traumatic brain injury (TBI) and are likely to contribute to morbidity.

OBJECTIVE

To describe the interaction between sleep and hormonal regulation following TBI and elucidate the impact that alterations of these systems have on cognitive responses during the posttraumatic chronic period.

METHODS

Review of preclinical and clinical literature describing long-lasting endocrine dysregulation and sleep alterations following TBI. The bidirectional relationship between sleep and hormones is described. Literature describing co-occurrence between sleep-wake disturbances and hormonal dysregulation will be presented. Review of literature describing cognitive effects of seep and hormones. The cognitive and functional impact of sleep disturbances and hormonal dysregulation is discussed within the context of TBI.

RESULTS/CONCLUSIONS

Sleep and hormonal alterations impact cognitive and functional outcome after TBI. Diagnosis and treatment of these disturbances will impact recovery following TBI and should be considered in the post-acute rehabilitative setting.

Sleep in Normal Aging

Sleep patterns change with aging, independent of other factors, and include advanced sleep timing, shortened nocturnal sleep duration, increased frequency of daytime naps, increased number of nocturnal awakenings and time spent awake during the night, and decreased slow wave sleep. Most of these changes seem to occur between young and middle adulthood; sleep parameters remain largely unchanged among healthy older adults. The circadian system and sleep homeostatic mechanisms become less robust with normal aging. The amount and pattern of sleep-related hormone secretion change as well. The causes of sleep disturbances in older adults are multifactorial.

Auditory closed-loop stimulation of EEG slow oscillations strengthens sleep and signs of its immune-supportive function

Sleep is essential for health. Slow wave sleep (SWS), the deepest sleep stage hallmarked by electroencephalographic slow oscillations (SOs), appears of particular relevance here. SWS is associated with a unique endocrine milieu comprising minimum cortisol and high aldosterone, growth hormone (GH), and prolactin levels, thereby presumably fostering efficient adaptive immune responses. Yet, whether SWS causes these changes is unclear. Here we enhance SOs in men by auditory closed-loop stimulation, i.e., by delivering tones in synchrony with endogenous SOs. Stimulation intensifies the hormonal milieu characterizing SWS (mainly by further reducing cortisol and increasing aldosterone levels) and reduces T and B cell counts, likely reflecting a redistribution of these cells to lymphoid tissues. GH remains unchanged. In conclusion, closed-loop stimulation of SOs is an easy-to-use tool for probing SWS functions, and might also bear the potential to ameliorate conditions like depression and aging, where disturbed sleep coalesces with specific hormonal and immunological dysregulations.

Circulating hormones undergo fluctuations during sleep. Here, the authors increase electroencephalographic slow oscillations (SO) during sleep in men using an auditory closed-loop stimulation, and show that the circulating level of cortisol, aldosterone and immune cell count can be altered.

Sleep Health: Reciprocal Regulation of Sleep and Innate Immunity

Sleep disturbances including insomnia independently contribute to risk of inflammatory disorders and major depressive disorder. This review and overview provides an integrated understanding of the reciprocal relationships between sleep and the innate immune system and considers the role of sleep in the nocturnal regulation of the inflammatory biology dynamics; the impact of insomnia complaints, extremes of sleep duration, and experimental sleep deprivation on genomic, cellular, and systemic markers of inflammation; and the influence of sleep complaints and insomnia on inflammaging and molecular processes of cellular aging. Clinical implications of this research include discussion of the contribution of sleep disturbance to depression and especially inflammation-related depressive symptoms. Reciprocal action of inflammatory mediators on the homeostatic regulation of sleep continuity and sleep macrostructure, and the potential of interventions that target insomnia to reverse inflammation, are also reviewed. Together, interactions between sleep and inflammatory biology mechanisms underscore the implications of sleep disturbance for inflammatory disease risk, and provide a map to guide the development of treatments that modulate inflammation, improve sleep, and promote sleep health.

Determinants of cortisol awakening responses to naps and nighttime sleep

The cortisol awakening response (CAR) is a phenomenon describing the sharp increase in basal cortisol levels shortly after waking from sleep. While extensively studied, little is known about the role of sleep architecture contributing to CAR. Furthermore, the potential for CAR after a shorter bout of sleep--a nap--has not been directly investigated. The current studies thus aimed at assessed sleep duration, time of day, and sleep architecture as potential determinants of the cortisol awakening response. Saliva samples were collected during the first hour (0, 30, 45, 60 min) following several EEG-monitored laboratory sleep conditions. Those included afternoon naps wherein 17 participants (4 men; ages 18-26) napped for 50 min and 24 participants (11 men; ages 18-24) napped for 90 min. Furthermore, 20 participants (10 men; ages 18-35) visited the lab twice and in addition to staying overnight, napped 90 min in the morning either under placebo conditions or pharmacologically-manipulated sleep conditions (5mg Zolpidem). Cortisol increases were observed in response to each sleep condition except to 50-min afternoon naps. Furthermore, CARs were predicted by Stage 2 sleep when following nighttime sleep (r=.46, p=.04) and by Stage 1 sleep when following placebo morning naps (r=.54, p=.01). The current study established cortisol awakening responses to naps and implicates sleep duration and architecture in the generation of CAR to both napping and nighttime sleep. Assessing CAR in conjunction with the specific type of sleep may thus contribute to our understanding of mechanisms underlying positive and negative health effects of napping.

The impact of sleep restriction while performing simulated physical firefighting work on cortisol and heart rate responses

PURPOSE

Physical work and sleep restriction are two stressors faced by firefighters, yet the combined impact these demands have on firefighters' acute stress responses is poorly understood. The purpose of the present study was to assess the effect firefighting work and sleep restriction have on firefighters' acute cortisol and heart rate (HR) responses during a simulated 3-day and 2-night fire-ground deployment.

METHODS

Firefighters completed multiple days of simulated physical work separated by either an 8-h (control condition; n = 18) or 4-h sleep opportunity (sleep restriction condition; n = 17). Salivary cortisol was sampled every 2 h, and HR was measured continuously each day.

RESULTS

On day 2 and day 3 of the deployment, the sleep restriction condition exhibited a significantly higher daily area under the curve cortisol level and an elevated cortisol profile in the afternoon and evening when compared with the control condition. Firefighters' HR decreased across the simulation, but there were no significant differences found between conditions.

CONCLUSION

Findings highlight the protective role an 8-h sleep opportunity between shifts of firefighting work has on preserving normal cortisol levels when compared to a 4-h sleep opportunity which resulted in elevated afternoon and evening cortisol. Given the adverse health outcomes associated with chronically high cortisol, especially later in the day, future research should examine how prolonged exposure to firefighting work (including restricted sleep) affects firefighters' cortisol levels long term. Furthermore, monitoring cortisol levels post-deployment will determine the minimum recovery time firefighters need to safely return to the fire-ground.

Effects of an interleukin-1 receptor antagonist on human sleep, sleep-associated memory consolidation, and blood monocytes

Pro-inflammatory cytokines like interleukin-1 beta (IL-1) are major players in the interaction between the immune system and the central nervous system. Various animal studies report a sleep-promoting effect of IL-1 leading to enhanced slow wave sleep (SWS). Moreover, this cytokine was shown to affect hippocampus-dependent memory. However, the role of IL-1 in human sleep and memory is not yet understood. We administered the synthetic IL-1 receptor antagonist anakinra (IL-1ra) in healthy humans (100mg, subcutaneously, before sleep; n=16) to investigate the role of IL-1 signaling in sleep regulation and sleep-dependent declarative memory consolidation. Inasmuch monocytes have been considered a model for central nervous microglia, we monitored cytokine production in classical and non-classical blood monocytes to gain clues about how central nervous effects of IL-1ra are conveyed. Contrary to our expectation, IL-1ra increased EEG slow wave activity during SWS and non-rapid eye movement (NonREM) sleep, indicating a deepening of sleep, while sleep-associated memory consolidation remained unchanged. Moreover, IL-1ra slightly increased prolactin and reduced cortisol levels during sleep. Production of IL-1 by classical monocytes was diminished after IL-1ra. The discrepancy to findings in animal studies might reflect species differences and underlines the importance of studying cytokine effects in humans.

Influence of sleep deprivation and circadian misalignment on cortisol, inflammatory markers, and cytokine balance

Cortisol and inflammatory proteins are released into the blood in response to stressors and chronic elevations of blood cortisol and inflammatory proteins may contribute to ongoing disease processes and could be useful biomarkers of disease. How chronic circadian misalignment influences cortisol and inflammatory proteins, however, is largely unknown and this was the focus of the current study. Specifically, we examined the influence of weeks of chronic circadian misalignment on cortisol, stress ratings, and pro- and anti-inflammatory proteins in humans. We also compared the effects of acute total sleep deprivation and chronic circadian misalignment on cortisol levels. Healthy, drug free females and males (N=17) aged 20-41 participated. After 3weeks of maintaining consistent sleep-wake schedules at home, six laboratory baseline days and nights, a 40-h constant routine (CR, total sleep deprivation) to examine circadian rhythms for melatonin and cortisol, participants were scheduled to a 25-day laboratory entrainment protocol that resulted in sleep and circadian disruption for eight of the participants. A second constant routine was conducted to reassess melatonin and cortisol rhythms on days 34-35. Plasma cortisol levels were also measured during sampling windows every week and trapezoidal area under the curve (AUC) was used to estimate 24-h cortisol levels. Inflammatory proteins were assessed at baseline and near the end of the entrainment protocol. Acute total sleep deprivation significantly increased cortisol levels (p<0.0001), whereas chronic circadian misalignment significantly reduced cortisol levels (p<0.05). Participants who exhibited normal circadian phase relationships with the wakefulness-sleep schedule showed little change in cortisol levels. Stress ratings increased during acute sleep deprivation (p<0.0001), whereas stress ratings remained low across weeks of study for both the misaligned and synchronized control group. Circadian misalignment significantly increased plasma tumor necrosis factor-alpha (TNF-α), interleukin 10 (IL-10) and C-reactive protein (CRP) (p<0.05). Little change was observed for the TNF-α/IL-10 ratio during circadian misalignment, whereas the TNF-α/IL-10 ratio and CRP levels decreased in the synchronized control group across weeks of circadian entrainment. The current findings demonstrate that total sleep deprivation and chronic circadian misalignment modulate cortisol levels and that chronic circadian misalignment increases plasma concentrations of pro- and anti-inflammatory proteins.

Association between sleep architecture and glucose tolerance in children and adolescents

BACKGROUND

Short sleep duration is a contributing factor for decreased insulin sensitivity and hyperglycemia. Sleep architecture represents a cyclical pattern of sleep that shifts between sleep Stages N1, N2, N3 (slow wave sleep) and Stage R (rapid eye movement sleep). The aim of the present study was to examine the association between sleep architecture and glucose and insulin metabolism in both normal weight and overweight/obese children and adolescents.

METHODS

A total of 118 subjects participated in the study. Subjects under-went overnight polysomnography (PSG) when the percentage of total sleep time (% TST) spent at each sleep stage was recorded and an oral glucose tolerance test together was performed the next morning. We assessed glucose tolerance, insulin sensitivity and pancreatic β-cell function using 2-h glucose levels, the Matsuda index (IS(OGTT)), and insulin secretion-sensitivity index-2 (ISSI-2), respectively.

RESULTS

After adjustment for age, gender, body mass index z-score, pubertal status, and obstructive apnea hypopnea index, Stage N3 (% TST) was positively associated with IS(OGTT), whereas Stage N1 (%TST) exerted an opposite effect on IS(OGTT). Higher sleep efficiency and longer TST were independently associated with lower 2-h glucose levels, higher ISSI-2 and/or higher IS(OGTT).

CONCLUSIONS

Stage N3, sleep efficiency and TST were protective factors in maintaining glucose and insulin homeostasis; however, Stage N1 functioned in the opposite direction.

Sleep and hormonal changes in aging

Age-related sleep and endocrinometabolic alterations frequently interact with each other. For many hormones, sleep curtailment in young healthy subjects results in alterations strikingly similar to those observed in healthy old subjects not submitted to sleep restriction. Thus, recurrent sleep restriction, which is currently experienced by a substantial and rapidly growing proportion of children and young adults, might contribute to accelerate the senescence of endocrine and metabolic function. The mechanisms of sleep-hormonal interactions, and therefore the endocrinometabolic consequences of age-related sleep alterations, which markedly differ from one hormone to another, are reviewed in this article.

About sleep's role in memory

Over more than a century of research has established the fact that sleep benefits the retention of memory. In this review we aim to comprehensively cover the field of "sleep and memory" research by providing a historical perspective on concepts and a discussion of more recent key findings. Whereas initial theories posed a passive role for sleep enhancing memories by protecting them from interfering stimuli, current theories highlight an active role for sleep in which memories undergo a process of system consolidation during sleep. Whereas older research concentrated on the role of rapid-eye-movement (REM) sleep, recent work has revealed the importance of slow-wave sleep (SWS) for memory consolidation and also enlightened some of the underlying electrophysiological, neurochemical, and genetic mechanisms, as well as developmental aspects in these processes. Specifically, newer findings characterize sleep as a brain state optimizing memory consolidation, in opposition to the waking brain being optimized for encoding of memories. Consolidation originates from reactivation of recently encoded neuronal memory representations, which occur during SWS and transform respective representations for integration into long-term memory. Ensuing REM sleep may stabilize transformed memories. While elaborated with respect to hippocampus-dependent memories, the concept of an active redistribution of memory representations from networks serving as temporary store into long-term stores might hold also for non-hippocampus-dependent memory, and even for nonneuronal, i.e., immunological memories, giving rise to the idea that the offline consolidation of memory during sleep represents a principle of long-term memory formation established in quite different physiological systems.

Predictors of slow-wave sleep in a clinic-based sample

Slow-wave sleep has been associated with several physiological phenomena, including glucose metabolism, sympathetic nervous system activity, hormonal secretion and blood pressure regulation. The aim of these analyses was to determine which sociodemographic and medical factors were associated with slow-wave sleep duration in a large clinical sample. We conducted cross-sectional analysis of clinical data from 1019 consecutive adults over a 10-month period who had their first in-laboratory polysomnogram for suspicion of obstructive sleep apnea. Patients either underwent in-laboratory full-night polysomnogram followed by full-night continuous positive airway pressure titration or split-night polysomnogram. Patients also completed questionnaires to assess race, education, marital status and medical co-morbidities. A multiple linear regression model that predicted the natural log of slow-wave sleep in minutes indicated that African Americans had approximately 48% less slow-wave sleep than non-African Americans. Increasing age and male gender were also associated with less slow-wave sleep. Overweight and obese individuals had significantly less slow-wave sleep than those not overweight, even after adjustment for obstructive sleep apnea severity. Finally, those with severe obstructive sleep apnea had significantly less slow-wave sleep than those with less severe obstructive sleep apnea even after adjustment for obesity. Results remained unchanged when patients who had a split-night polysomnogram were excluded. We observed less slow-wave sleep in African Americans, a group at increased risk of diabetes and hypertension compared with Caucasians, and in those who are overweight and obese and those with severe obstructive sleep apnea. Future research needs to explore potential reasons for reduced slow-wave sleep in these individuals.

Elucidation of neurobiology of anxiety disorders in children through pharmacological challenge tests and cortisol measurements: a systematic review

Anxiety disorders are common both in adults and children. While there have been major advances in understanding the neurobiology of anxiety disorders in adults, progress has been more limited in the elucidation of the mechanisms underlying these disorders in childhood. There is a need to delineate childhood biological models, since anxiety represents a significant clinical problem in children and is a risk factor for the subsequent development of anxiety and depression in adulthood. We conducted a review of the literature regarding pharmacological challenge tests and direct hypothalamic-pituitary-adrenal axis measurement in children with anxiety disorders, with emphasis on panic disorder and social anxiety disorder. Studies identified were contrasted with those in adult panic disorder and social anxiety disorder. Despite this broad approach few studies emerged in children, with only 22 studies meeting inclusion criteria. When contrasted with adult neurobiological models of panic disorder and social anxiety disorder, children studied showed some abnormalities which mirrored those reported in adults, such as altered baseline respiration, altered responses to CO(2) challenge tests and blunted growth hormone response to yohimbine. However, results differed from adults with panic disorder and social anxiety in some aspects of noradrenergic and serotonergic function. For endpoints studied in panic disorder children, unlike adults, displayed a lack of baseline end-tidal CO(2) abnormalities and a different hypothalamic-pituitary-adrenal pattern response under low-dose CO(2). The biology of these anxiety disorders in children may only partially mirror that of adult anxiety disorders. However, caution is required as the evidence is limited, and many studies combined patients with panic disorder and social anxiety disorder with other disorders or non-specific anxiety. Further research is required to fully understand the biology and progression of childhood anxiety disorders.

Sleep and immune function

Sleep and the circadian system exert a strong regulatory influence on immune functions. Investigations of the normal sleep–wake cycle showed that immune parameters like numbers of undifferentiated naïve T cells and the production of pro-inflammatory cytokines exhibit peaks during early nocturnal sleep whereas circulating numbers of immune cells with immediate effector functions, like cytotoxic natural killer cells, as well as anti-inflammatory cytokine activity peak during daytime wakefulness. Although it is difficult to entirely dissect the influence of sleep from that of the circadian rhythm, comparisons of the effects of nocturnal sleep with those of 24-h periods of wakefulness suggest that sleep facilitates the extravasation of T cells and their possible redistribution to lymph nodes. Moreover, such studies revealed a selectively enhancing influence of sleep on cytokines promoting the interaction between antigen presenting cells and T helper cells, like interleukin-12. Sleep on the night after experimental vaccinations against hepatitis A produced a strong and persistent increase in the number of antigen-specific Th cells and antibody titres. Together these findings indicate a specific role of sleep in the formation of immunological memory. This role appears to be associated in particular with the stage of slow wave sleep and the accompanying pro-inflammatory endocrine milieu that is hallmarked by high growth hormone and prolactin levels and low cortisol and catecholamine concentrations.

Reciprocal relations between objectively measured sleep patterns and diurnal cortisol rhythms in late adolescence

PURPOSE

To examine how hours of sleep and wake times relate to between-person differences and day-to-day changes in diurnal cortisol rhythms in late adolescence.

METHODS

Older adolescents (N = 119) provided six cortisol samples (wakeup, +30 minutes, +2 hours, +8 hours, +12 hours, and bedtime) on each of three consecutive days while wearing an actigraph. We examined how average (across 3 days) and day-to-day changes in hours of sleep and wake times related to diurnal cortisol patterns.

RESULTS

On average, more hours of sleep related to steeper decline in cortisol across the days. Day-to-day analyses revealed that the hours of sleep of the previous night predicted steeper diurnal slopes the next day, whereas greater waking cortisol levels and steeper slopes predicted more hours of sleep and a later wake time the next day.

CONCLUSION

Our results suggest a bidirectional relationship between sleep and hypothalamic-pituitary-adrenal axis activity.

Obstructive sleep apnea and metabolic dysfunction in polycystic ovary syndrome

Obstructive sleep apnea (OSA) is an underrecognized, yet significant factor in the pathogenesis of metabolic derangements in polycystic ovary syndrome (PCOS). Recent findings suggest that there may be two "subtypes" of PCOS, i.e. PCOS with or without OSA, and these two subtypes may be associated with distinct metabolic and endocrine alterations. PCOS women with OSA may be at much higher risk for diabetes and cardiovascular disease than PCOS women without OSA and may benefit from therapeutic interventions targeted to decrease the severity of OSA. The present chapter will review what is currently known about the roles of sex steroids and adiposity in the pathogenesis of OSA, briefly review the metabolic consequences of OSA as well as the metabolic abnormalities associated with PCOS, review the prevalence of OSA in PCOS and finally present early findings regarding the impact of treatment of OSA on metabolic measures in PCOS.

Sleep, hormones, and memory

Nocturnal sleep is characterized by a unique pattern of endocrine activity, which comprises reciprocal influences on the hypothalamo-pituitary-adrenal (HPA) and the somatotropic system. During early sleep, when slow wave sleep (SWS) prevails, HPA secretory activity is suppressed whereas growth hormone (GH) release reaches a maximum; this pattern is reversed during late sleep when rapid eye movement (REM) sleep predominates. SWS benefits the consolidation of hippocampus-dependent declarative memories, whereas REM sleep improves amygdala-dependent emotional memories and procedural skill memories involving striato-cortical circuitry. Manipulation of plasma cortisol and GH concentration during sleep revealed a primary role of HPA activity for memory consolidation. Pituitary-adrenal inhibition during SWS sleep represents a prerequisite for efficient consolidation of declarative memory; increased cortisol during late REM sleep seems to protect from an overshooting consolidation of emotional memories.

Impact of sleep and its disturbances on hypothalamo-pituitary-adrenal axis activity

The daily rhythm of cortisol secretion is relatively stable and primarily under the influence of the circadian clock. Nevertheless, several other factors affect hypothalamo-pituitary-adrenal (HPA) axis activity. Sleep has modest but clearly detectable modulatory effects on HPA axis activity. Sleep onset exerts an inhibitory effect on cortisol secretion while awakenings and sleep offset are accompanied by cortisol stimulation. During waking, an association between cortisol secretory bursts and indices of central arousal has also been detected. Abrupt shifts of the sleep period induce a profound disruption in the daily cortisol rhythm, while sleep deprivation and/or reduced sleep quality seem to result in a modest but functionally important activation of the axis. HPA hyperactivity is clearly associated with metabolic, cognitive and psychiatric disorders and could be involved in the well-documented associations between sleep disturbances and the risk of obesity, diabetes and cognitive dysfunction. Several clinical syndromes, such as insomnia, depression, Cushing's syndrome, sleep disordered breathing (SDB) display HPA hyperactivity, disturbed sleep, psychiatric and metabolic impairments. Further research to delineate the functional links between sleep and HPA axis activity is needed to fully understand the pathophysiology of these syndromes and to develop adequate strategies of prevention and treatment.

Association between sleep architecture and measures of body composition

STUDY OBJECTIVES

To determine whether slow wave sleep (SWS) is inversely associated with body mass index (BMI) and other measures of body composition.

DESIGN

Cross-sectional, observational study.

SETTING

Community-based.

PARTICIPANTS

2745 older men from the MrOS Sleep Study who completed polysomnography.

INTERVENTIONS

N/A.

MEASUREMENTS AND RESULTS

SWS as a percentage of total sleep duration was obtained from in-home, overnight polysomnography. Measures of body composition including BMI, weight, waist circumference and total body fat mass were determined by standard techniques. Other covariates in the analysis were age, race/ethnicity, clinic site, physical activity, respiratory disturbance index (RDI), total sleep time, and sleep efficiency. In the multivariate analysis, there was a significant inverse association between quartiles of SWS and BMI (P-trend = 0.0095). Older men in the lowest quartile of SWS had an average BMI of 27.4 kg/m2, compared to 26.8 for those in the highest quartile of SWS. This association was attenuated in men with RDI > or = 15. Furthermore, participants in the lowest quartile of SWS had a 1.4-fold increased odds for obesity (P = 0.03, 95% CI 1.0, 1.8) compared to those in the highest quartile. A similar inverse association between SWS and waist circumference as well as weight was observed. REM sleep was not associated with measures of body composition.

CONCLUSIONS

Independent of sleep duration, percentage time in SWS is inversely associated with BMI and other measures of body composition in this population of older men. Participants in the lowest quartile of SWS (compared to those in the highest quartile) are at increased risk for obesity.

Associations between HPA axis functioning and level of anxiety in children and adolescents with an anxiety disorder

The hypothalamus-pituitary-adrenal (HPA) axis becomes active in response to stress. Hence, increased levels of anxiety in children and adolescents may be associated with changes in HPA-axis functioning. The aim of this study was to test if level of anxiety or specific anxiety disorders were associated with basal HPA axis activity in children and adolescents with an anxiety disorder. In 99 8- to 16-year-olds with an anxiety disorder, basal cortisol levels were assessed. It was tested if (1) cortisol levels correlated with the level of self-reported anxiety and (2) if cortisol levels were different for individuals with different anxiety disorders. In girls, low levels of anxiety were associated with a stronger rise in early morning cortisol concentrations. In both boys and girls, harm avoidance predicted low cortisol concentrations after awakening. Separation anxiety and physical anxiety symptoms predicted cortisol concentrations at noon. Differences between individuals with different anxiety disorders were not found. More research is needed regarding mechanisms that explain the associations that were found, and to investigate if treatment may influence HPA axis functioning in children and adolescents with an anxiety disorder.

Altered neuroendocrine sleep architecture in patients with type 1 diabetes

OBJECTIVE

The modulatory influence of nocturnal sleep on neuroendocrine secretory activity is increasingly recognized as a factor critical to health. Disturbances of sleep may arise from and contribute to the disease process in chronically ill patients with type 1 diabetes.

RESEARCH DESIGN AND METHODS

Using standard polysomnography and repetitive blood sampling, neuroendocrine sleep architecture was assessed under well-controlled nonhypoglycemic conditions in 14 type 1 diabetic patients and 14 healthy control subjects matched for age, sex, and BMI.

RESULTS

As expected, plasma glucose (P = 0.02) and serum insulin (P < 0.001) levels were constantly higher in type 1 diabetic patients than in healthy subjects throughout the night. Beside these characteristic alterations of glucose metabolism, type 1 diabetic patients displayed higher blood levels of growth hormone (P = 0.001) and epinephrine (P = 0.02) during the entire night and higher levels of ACTH (P = 0.01) as well as a tendency toward higher cortisol levels (P = 0.072) during the first night-half, compared with healthy control subjects. Patients spent slightly less time in slow wave sleep (P = 0.09) during the first night-half (where this sleep stage predominates), and overall exhibited an increased proportion of stage 2 sleep (P = 0.01). Correspondingly, assessment of mood and symptoms after sleep revealed that subjective sleep was less restorative in type 1 diabetic patients than in healthy subjects.

CONCLUSIONS

Our data indicate distinct alterations in the neuroendocrine sleep architecture of patients with type 1 diabetes, which add to the generally adverse impact of the disease on the patients' health.

[Immune outcomes of sleep disorders: the hypothalamic-pituitary-adrenal axis as a modulatory factor]

OBJECTIVE

To review the literature on the interaction between sleep and the immune system.

METHOD

A search on Web of Science and Pubmed database including the keywords sleep, sleep deprivation, stress, hypothalamic-pituitary-adrenal axis, immune system, and autoimmune diseases.

RESULTS

On Web of Science, 588 publications were retrieved; 61 references, more significant and closer to our objective, were used, including original articles and review papers.

CONCLUSION

Sleep deprivation and immune system exert a bidirectional influence on each other. Since sleep deprivation is considered a stressor, inasmuch as it induces elevation of cortisol or corticosterone levels in humans and rodents, respectively, and given the well-known immunosuppressive effect of glucocorticoids, we propose that increased activation of the hypothalamic-pituitary-adrenal axis is a major mediator of the immune alterations observed in patients with insomnia or in sleep deprived subjects.

Memory consolidation during sleep: interactive effects of sleep stages and HPA regulation

Sleep is critically involved in the consolidation of previously acquired memory traces. However, nocturnal sleep is not uniform but is subject to distinct changes in electrophysiological and neuroendocrine activity. Specifically, the first half of the night is dominated by slow wave sleep (SWS), whereas rapid eye movement (REM) sleep prevails in the second half. Concomitantly, hypothalamo-pituitary-adrenal (HPA) activity as indicated by cortisol release is suppressed to a minimum during early sleep, while drastically increasing during late sleep. We have shown that the different sleep stages and the concomitant glucocorticoid release are interactively involved in the consolidation of different types of memories. SWS-rich early sleep has been demonstrated to benefit mainly the consolidation of hippocampus-dependent declarative memories (i.e. facts and episodes). In contrast, REM sleep-rich late sleep was shown to improve in particular emotional memories involving amygdalar function, as well as procedural memories (for skills) not depending on hippocampal or amygdalar function. Enhancing plasma glucocorticoid concentrations during SWS-rich early sleep counteracted hippocampus-dependent declarative memory consolidation, but did not affect hippocampus-independent procedural memory. Preventing the increase in cortisol during late REM sleep-rich sleep by administration of metyrapone impaired hippocampus-dependent declarative memory but enhanced amygdala-dependent emotional aspects of memory. The data underscore the importance of pituitary-adrenal inhibition during early SWS-rich sleep for efficient consolidation of declarative memory. The increase in cortisol release during late REM sleep-rich sleep may counteract an overshooting consolidation of emotional memories.

No effects of repeated forced wakings during three consecutive nights on morning cortisol awakening responses (CAR): a preliminary study

OBJECTIVE

The cortisol awakening response (CAR) is considered a reliable measure for the acute reagibility of the hypothalamus-pituitary-adrenal (HPA) axis. Whether repeated nightly awakenings at different times during the night also stimulate the HPA-axis and whether, consequently, the CAR is altered has not been tested, so far. We aimed to investigate whether three experimentally induced awakenings during three consecutive nights would be associated with HPA-axis stimulation and an altered morning CAR.

METHODS

The study sample consisted of 13 healthy adult women who were waken up three times in each of three consecutive nights. Cortisol levels were measured immediately and 15 min after each awakening in the night and in the morning, respectively. Also, the morning CARs after three nights of undisturbed sleep were assessed.

RESULTS

A significant difference between night time cortisol responses to awakening and the morning CAR was found. While cortisol levels during the first half of the night did not rise significantly after awakening in the night, some reactivity was seen during awakenings in the very early morning hours, and pronounced awakening responses were observed in the morning before getting out of bed. Interestingly, the morning CAR after disturbed sleep did not differ from the morning CAR following undisturbed sleep.

CONCLUSION

In healthy female individuals, the morning CAR appears to be unchanged even if sleep was repeatedly interrupted by forced wakings.

PreproTRH(158-183) fails to affect pituitary-adrenal response to CRH/vasopressin in man: a pilot study

Non-glucocorticoid inhibitors of the HPA-system are of utmost interest in the treatment of diseases with impaired regulation of this system, like the metabolic syndrome and depression. In rats, a fragment of the thyreotropin-releasing hormone (TRH) preprohormone, preproTRH((178-199)), has been demonstrated to inhibit basal and stimulated secretion of cortisol. Our pilot study aimed to explore the first time similar effects of the homologue peptide preproTRH((158-183)) in healthy humans. In a double-blind within-subject comparison, eight healthy young men were infused intravenously with placebo and preproTRH((158-183)) at varying doses of 5, 10, 25 and 50 mg/kg of body weight. After 15 min of infusion a corticotropin-releasing hormone (CRH)/vasopressin-test was performed. Plasma concentrations of pituitary hormones and free thyroxine, blood pressure, heart rate and feelings of activation and mood were assessed repeatedly at close intervals. Individual hormone profiles and collapsed data across all doses did not reveal any effects of preproTRH((158-183)) on HPA-activity, although it increased TSH and fT4, stimulated the release of GH and increased systolic blood pressure in the course of the experiment (p<0.05, for all effects). Self-reports indicated enhanced feelings of activation and general well-being following preproTRH (p<0.05). Our data exclude a substantial inhibitory effect of preproTRH((158-183)) on HPA secretory activity and, thus, contrast with findings in rats. In humans, the peptide appears to even exert an albeit weak stimulatory effect on autonomic stress systems as indicated by increased cardiovascular activity in combination with enhanced subjective arousal.

Is the cortisol awakening rise a response to awakening?

A distinct rise in cortisol levels that occurs after morning awakening is increasingly used as an indicator of adrenocortical activity which is associated with different pathologies. Although it was previously assumed that the transition from sleep to wake is essential for the occurrence of the cortisol morning rise, this has never been tested. Here, we examined 16 healthy young men (20-33 yrs) between 2300 and 0800 h under sleep laboratory conditions. Serum cortisol and plasma adrenocorticotropin (ACTH) as well as salivary cortisol levels (after subjects were woken up at 0700 h) were repeatedly assessed. In a supplementary study condition, salivary cortisol levels in the first hour after awakening were measured at the subjects' home on two consecutive days. Comparison of pre- and post awakening measurements revealed significantly steeper increases in cortisol and ACTH after awakening. The rise in cortisol upon awakening under laboratory conditions did not significantly differ from that observed at home. We conclude that the cortisol increase after awakening is a response to morning awakening that is distinct from the circadian rise in hypothalamo-pituitary-adrenal (HPA) activity in the morning hours. Although the cortisol awakening response is modulated by circadian influences, it primarily reflects phasic psychophysiological processes specific to the sleep-wake transition.

Sleep to remember

Recently, compelling evidence has accumulated that links sleep to learning and memory. Sleep has been identified as a state that optimizes the consolidation of newly acquired information in memory. Consolidation is an active process that is presumed to rely on the covert reactivation and reorganization of newly encoded representations. Hippocampus-dependent memories benefit primarily from slow-wave sleep (SWS), whereas memories not depending on the hippocampus show greater gains over periods containing high amounts of rapid eye movement sleep. One way sleep does this is by establishing different patterns of neurotransmitters and neurohormone secretion between sleep stages. Another central role for consolidating memories is played by the slow oscillation, that is, the oscillating field potential change dominating SWS. The emergence of slow oscillations in neocortical networks depends on the prior use of these networks for encoding of information. Via efferent pathways, they synchronize the occurrence of sharp wave ripples accompanying memory reactivations in the hippocampus with thalamocortical spindle activity. Thus, hippocampal memories are fed back into neocortical networks at a time when these networks are depolarized and, because of concurrent spindle activity, can most sensitively react to these inputs with plastic changes underlying the formation of long-term memory representations.

Melatonin does not inhibit hypothalamic-pituitary-adrenal activity in waking young men

The pineal hormone melatonin is mainly secreted during night-time which, in humans, is the normal time of sleep. It has been proposed that, during this period, melatonin exerts an inhibitory influence on secretory activity of the hypothalamic-pituitary-adrenal (HPA) system, although there is little evidence for this view in humans. In blind humans, a single oral dose of melatonin at bed time suppressed nocturnal cortisol secretion. However, suppression could have been secondary to an improved sleep after melatonin in these experiments. In the present study, we examined whether melatonin exerts a similar inhibitory effect on HPA activity in waking subjects. Fourteen healthy young men were tested at bed time, but kept awake throughout the experimental epoch. Thirty minutes after oral ingestion of 5 mg melatonin, activity of the HPA-system was stimulated through a standard insulin-induced hypoglycaemia. Adrenocorticotrophin hormone and cortisol concentrations under basal conditions before insulin injection, as well as in response to insulin-induced hypoglycaemia, were almost identical for the melatonin and placebo control conditions (P > 0.5). However, melatonin increased plasma prolactin concentrations (P < 0.01) and reduced systolic blood pressure in the time interval following hypoglycaemia (P < 0.05). Based on a review of the literature and our results, we conclude that melatonin per se has no substantially suppressing effect on HPA secretory activity, although such an effect can be gated by sleep-related processes.

Declarative memory consolidation: mechanisms acting during human sleep

Of late, an increasing number of studies have shown a strong relationship between sleep and memory. Here we summarize a series of our own studies in humans supporting a beneficial influence of slow-wave sleep (SWS) on declarative memory formation, and try to identify some mechanisms that might underlie this influence. Specifically, these experiments show that declarative memory benefits mainly from sleep periods dominated by SWS, whereas there is no consistent benefit of this memory from periods rich in rapid eye movement (REM) sleep. A main mechanism of declarative memory formation is believed to be the reactivation of newly acquired memory representations in hippocampal networks that stimulates a transfer and integration of these representations into neocortical neuronal networks. Consistent with this model, spindle activity and slow oscillation-related EEG coherence increase during early sleep after intense declarative learning in humans, signs that together point toward a neocortical reprocessing of the learned material. In addition, sleep seems to provide an optimal milieu for declarative memory reprocessing and consolidation by reducing cholinergic activation and the cortisol feedback to the hippocampus during SWS.

Ultradian rhythms in pituitary and adrenal hormones: their relations to sleep

Sleep and circadian rhythmicity both influence the 24-h profiles of the main pituitary and adrenal hormones. From studies using experimental strategies including complete and partial sleep deprivation, acute and chronic shifts in the sleep period, or complete sleep-wake reversal as occurs with transmeridian travel or shift-work, it appears that prolactin (PRL) and growth hormone (GH) profiles are mainly sleep related, while cortisol profile is mainly controlled by the circadian clock with a weak influence of sleep processes. Thyrotropin (TSH) profile is under the dual influence of sleep and circadian rhythmicity. Recent studies, in which we used spectral analysis of sleep electroencephalogram (EEG) rather than visual scoring of sleep stages, have evaluated the temporal associations between pulsatile hormonal release and the variations in sleep EEG activity. Pulses in PRL and in GH are positively linked to increases in delta wave activity, whereas TSH and cortisol pulses are related to decreases in delta wave activity. It is yet not clear whether sleep influences endocrine secretion, or conversely, whether hormone secretion affects sleep structure. These well-defined relationships raise the question of their physiological significance and of their clinical implications.

Twenty-four-hour cortisol secretion patterns in prepubertal children with anxiety or depressive disorders

BACKGROUND

Previous studies found few abnormalities in hypothalamic-pituitary-adrenal (HPA) axis function in prepubertal children with anxiety or depressive disorders. In this study, we combined data from two independent, consecutive studies to achieve a larger sample size. Our goal was to identify potential alterations in the circadian pattern of cortisol secretion in anxious or depressed children.

METHODS

A total of 124 prepubertal subjects from two independent samples (76 with major depressive disorder, 31 with anxiety disorders, and 17 healthy control subjects) were studied. Blood samples collected for cortisol at hourly intervals over a 24-hour period were examined. Analyses were performed aligning cortisol samples by clock-time. Additional analyses aligning samples by sleep-onset time were performed with a subsample of subjects.

RESULTS

In the combined sample, significant findings emerged that were previously undetected. Anxious children exhibited significantly lower nighttime cortisol levels and an initially sluggish rise in cortisol during the nighttime when compared with depressed and healthy control children. In contrast, depressed children did not show a clear-cut pattern of differences compared with healthy control children.

CONCLUSIONS

Anxious children seem to exhibit an altered pattern of nighttime cortisol secretion, with an initially sluggish or delayed nocturnal rise before reaching similar peak levels of cortisol near the time of awakening. These findings suggest subtle alterations in HPA axis function in prepubertal children with anxiety disorders.

A regulatory role of prolactin, growth hormone, and corticosteroids for human T-cell production of cytokines

The release of the pituitary hormones, prolactin and growth hormone (GH), and of adrenal corticosteroids is subject to a profound regulation by sleep. In addition these hormones are known to be involved in the regulation of the immune response. Here, we examined their role for in vitro production of T-cell cytokines. Specifically, we hypothesized that increased concentrations of prolactin and GH as well as a decrease in cortisol, i.e., hormonal changes characterizing early nocturnal sleep, could be responsible for a shift towards T helper 1 (Th1) cytokines during this time. Whole blood was sampled from 15 healthy humans in the morning after regular sleep and was activated in vitro with ionomycin and two concentrations of phorbol myrestate acetate (PMA, 8 and 25 ng/ml) in the absence or presence of prolactin, prolactin antibody, GH, glucocorticoid receptor (GR) antagonist RU-486, or mineralocorticoid receptor (MR) antagonist spironolactone. Hormones were examined at physiological concentrations. Production of T-cell derived cytokines was measured at the single cell level using multiparametric flow cytometry. Generally, effects were more pronounced after stimulation with 8 rather than 25 ng/ml PMA. The following changes reached significance (p <.05): prolactin (versus prolactin antibody) increased tumor necrosis factor-alpha (TNF-alpha) and interferon-gamma (IFN-gamma) producing CD4+ and CD8+ cells and interleukin-2 (IL-2) producing CD8+ cells. Compared with control, prolactin antibody decreased, whereas GH increased IFN-gamma+CD4+ cells. RU-486 increased TNF-alpha, IFN-gamma, and IL-2 producing CD4+ and CD8+ cells. Surprisingly strong effects were found after MR blocking with spironolactone which increased TNF-alpha, IFN-gamma, and IL-2 producing CD4+ and CD8+ cells. No effects on IL-4+CD4+ cells were observed, while the IFN-gamma/IL-4 ratio shifted towards Th1 after spironolactone and after RU-486 plus GH. Results suggest that enhanced prolactin and GH concentrations as well as low cortisol levels during early nocturnal sleep synergistically act to enhance Th1 cytokine activity.

Improvement of sleep and pituitary-adrenal inhibition after subchronic intranasal vasopressin treatment in elderly humans

Subchronic intranasal treatment with argininevasopressin (AVP) has been shown to exert a strong ameliorating effect on sleep and slow wave sleep (SWS) deficits in elderly. However, AVP is also a potent stimulus of the pituitary-adrenal stress system, which is usually inhibited during early, SWS-rich sleep. A disinhibition of pituitary-adrenal activity during sleep is correlated with aging and is considered a pathologic factor contributing to various age-related diseases. Here, we examined whether the beneficial effect of prolonged intranasal AVP administration on sleep in aged would be associated with a concomitant decrease in pituitary-adrenal inhibition and effects on other neuroendocrine features of sleep. Twenty-six healthy elderly (mean 72.9 yr) with mild sleep complaints were investigated in a placebo controlled double-blind study. One group was treated daily each morning and evening with intranasal AVP (2 x 20 IU) for 10 weeks, the other received placebo. During polysomnographical recordings taken at the beginning and end of the treatment period, blood was sampled every 15 min. Intranasal AVP increased SWS on average by +21.5 min (p<0.02). The effect persisted on the night after acute withdrawal of the peptide treatment with no rebound occurring. Notably, rather than increasing pituitary-adrenal activity, AVP decreased the early sleep cortisol nadir on average by 0.5 microg/dl (p<0.05). AVP did not induce any measurable changes in fluid balance or cardiovascular activity. Overall, results indicate a promoting effect of AVP on SWS in aged accompanied by a beneficial rather than impairing influence on the neuroendocrine pattern of sleep.

Growth hormone-releasing hormone facilitates hypoglycemia-induced release of cortisol

Early sleep in humans is characterized by a distinct suppression of pituitary-adrenal activity coinciding with enhanced activity of the somatotropic axis. Here, we tested in awake humans the hypothesis of an inhibiting influence of hypothalamic growth hormone-releasing hormone (GHRH) on pituitary-adrenal activity. For this purpose, pituitary-adrenal activity was stimulated in 10 men through a standard insulin-hypoglycemia-test (IHT) and in another 10 men through combined administration of CRH/vasopressin. Stimulation was performed in each man on three conditions following pretreatment with Placebo and GHRH administered intravenously (50 microg) or intranasally (300 microg) 1 h before. GH, ACTH and cortisol as well as blood pressure and heart rate were measured repeatedly. Contrary to expectations, pretreatment with GHRH did not suppress but enhanced secretion of cortisol upon insulin-induced hypoglycemia regardless of the route of GHRH pretreatment (p<0.05). In contrast, GHRH did not facilitate cortisol release after stimulation with CRH/vasopressin. Changes in ACTH remained inconsistent. Plasma levels of GH increased significantly after i.v. GHRH application, but remained unchanged after the intranasal administration. Blood pressure and heart rate were not influenced by the treatments. Results indicate facilitating effects of GHRH mediated at a suprapituitary (i.e. hypothalamic) level as suggested by restriction of the effect to the hypoglycemia-induced cortisol release with no effects after pituitary stimulation with CRH/vasopressin.

Immediate effects of an 8-h advance shift of the rest-activity cycle on 24-h profiles of cortisol

To investigate the adaptation of plasma cortisol profiles to an abrupt phase advance of the rest-activity cycle, eight normal young subjects were submitted in a sleep laboratory to an 8-h advance shift of their sleep-wake and dark-light cycles. The shift was achieved by advancing bedtimes from 2300-0700 to 1500-2300. Blood samples were obtained at 20-min intervals for 68 consecutive hours. The shift resulted within 6-9 h in a 3- to 4-h advance of timings of the nadir of the cortisol profile and of the end of the quiescent period but had no immediate effect on the timing of cortisol acrophase. The quiescent period of cortisol secretion was shortened and fragmented. Thus a major advance shift achieved without enforcing sleep deprivation results in a rapid partial adaptation of the temporal profiles of cortisol but also in a marked disruption of the cortisol quiescent period. Sleep onset was consistently followed by a decrease in cortisol concentrations. Conversely, both sleep-wake and dark-light transitions were consistently associated with cortisol secretory pulses.

Sleeping brain, learning brain. The role of sleep for memory systems

The hypothesis that sleep participates in the consolidation of recent memory traces has been investigated using four main paradigms: (1) effects of post-training sleep deprivation on memory consolidation, (2) effects of learning on post-training sleep, (3) effects of within sleep stimulation on the sleep pattern and on overnight memories, and (4) re-expression of behavior-specific neural patterns during post-training sleep. These studies convincingly support the idea that sleep is deeply involved in memory functions in humans and animals. However, the available data still remain too scarce to confirm or reject unequivocally the recently upheld hypothesis that consolidations of non-declarative and declarative memories are respectively dependent upon REM and NREM sleep processes.