Alpha-helical CRH exerts CRH agonistic effects on sleep-endocrine activity in humans

Neuroendocrine Control of Sleep

Sleep is a phenomenon in animal behavior as enigmatic as it is ubiquitous, and one deeply tied to endocrine function. Though there are still many unanswered questions about the neurochemical basis of sleep and its functions, extensive interactions have been identified between sleep and the endocrine system, in both the endocrine system's effect on sleep and sleep's effect on the endocrine system. Unfortunately, until recent years, much research on sleep behavior largely disregarded its connections with the endocrine system. Use of both clinical studies and rodent models to investigate interactions between neuroendocrine function, including biological sex, and sleep therefore presents a promising area of further exploration. Further investigation of the neurobiological and neuroendocrine basis of sleep could have wide impact on a number of clinical and basic science fields. In this review, we summarize the state of basic sleep biology and its connections to the field of neuroendocrine biology, as well as suggest key future directions for the neuroendocrine regulation of sleep that may significantly impact new therapies for sleep disorders in women and men.

Sleep-endocrine effects of growth hormone-releasing hormone (GHRH) in patients with schizophrenia

Changes in sleep-EEG after endocrine stimulation tests in patients with schizophrenia include reduced sleep efficiency, prolonged sleep latency and increased awaking after sleep onset Findings on sleep associated growth hormone (GH) secretion were ambiguous. The aim of this study was to elucidate the sleep-endocrine activity especially in the GH system of patients with schizophrenia after repeated administration of GHRH. The effect of repetitive injections of 4 × 50 μg GHRH between 22.00 and 01.00 h on sleep endocrine parameters was investigated in 9 patients diagnosed for schizophrenia. Patients did not receive any medication for one week. Concentrations of ACTH, cortisol, prolactin and GH were determined. Patients spent three consecutive nights in the sleep laboratory. Blood was taken every 20min. Results were compared with matched healthy controls. A non-significant prolonged sleep onset latency and increased time awake was found in patients compared to controls. Sleep stage 2 was significantly reduced in patients. No significant difference in ACTH and cortisol was detected, whereas the GH secretion in patients following GHRH stimulation was significantly elevated compared to controls. Our results in drug free patients confirm already known changes in sleep-EEG in these patients. The GH response to GHRH-stimulation indicates a different regulatory sensitivity of the system between daytime and night-time.

Influence of exogenous atrial natriuretic peptide on the nocturnal hypothalamic-pituitary-adrenal axis and sleep in healthy men

Atrial natriuretic peptide (ANP), originally found in the cardiac atria, is also widely distributed in the central nervous system (CNS) and has been predominantly found in the hypothalamus and the pituitary gland. Previous in vitro and in vivo studies have provided evidence for an inhibitory control of ANP at all regulatory levels of the hypothalamo-pituitary-adrenocortical (HPA) system. In vivo studies in man demonstrated that ANP inhibits stimulated pituitary-adrenal secretion during wakefulness. On the other hand, it has been reported that various neuropeptides not only influence the neuroendocrine compound of sleep, but also exert specific effects on the sleep electroencephalogram (EEG). To further characterize the role of ANP in the regulation of the nocturnal HPA axis activity and consecutive sleep regulation, we investigated sleep-endocrine effects of intravenously administered ANP in healthy men during nocturnal sleep. Eight volunteers underwent three trial conditions in random order and in a single-blind design receiving ANP infusion at the beginning of the 1st or the 2nd half of the night, or placebo. Sleep was assessed by polysomnography and blood samples were drawn in 30-min intervals for determination of adrenocorticotrophic hormone (ACTH) and cortisol during the entire night. While the ACTH and cortisol secretion during ANP infusions remained unchanged, an immediate increase of ACTH and cortisol secretion occurred after each infusion period for approximately 2h without changing basal levels and the circadian course of both hormones. Sleep EEG parameters were neither directly affected by ANP infusions nor by the following ANP-induced ACTH and cortisol secretion. The presence of such clear-cut enhancement of the pituitary-adrenal release indicates a rebound effect of ANP on HPA secretory activity and supports the idea that ANP acts as corticotropin-releasing hormone (CRH)-inhibiting factor.

Conditional corticotropin-releasing hormone overexpression in the mouse forebrain enhances rapid eye movement sleep

Impaired sleep and enhanced stress hormone secretion are the hallmarks of stress-related disorders, including major depression. The central neuropeptide, corticotropin-releasing hormone (CRH), is a key hormone that regulates humoral and behavioral adaptation to stress. Its prolonged hypersecretion is believed to play a key role in the development and course of depressive symptoms, and is associated with sleep impairment. To investigate the specific effects of central CRH overexpression on sleep, we used conditional mouse mutants that overexpress CRH in the entire central nervous system (CRH-COE-Nes) or only in the forebrain, including limbic structures (CRH-COE-Cam). Compared with wild-type or control mice during baseline, both homozygous CRH-COE-Nes and -Cam mice showed constantly increased rapid eye movement (REM) sleep, whereas slightly suppressed non-REM sleep was detected only in CRH-COE-Nes mice during the light period. In response to 6-h sleep deprivation, elevated levels of REM sleep also became evident in heterozygous CRH-COE-Nes and -Cam mice during recovery, which was reversed by treatment with a CRH receptor type 1 (CRHR1) antagonist in heterozygous and homozygous CRH-COE-Nes mice. The peripheral stress hormone levels were not elevated at baseline, and even after sleep deprivation they were indistinguishable across genotypes. As the stress axis was not altered, sleep changes, in particular enhanced REM sleep, occurring in these models are most likely induced by the forebrain CRH through the activation of CRHR1. CRH hypersecretion in the forebrain seems to drive REM sleep, supporting the notion that enhanced REM sleep may serve as biomarker for clinical conditions associated with enhanced CRH secretion.

Neurochemical regulation of sleep

This review summarizes recent developments in the field of sleep regulation, particularly in the role of hormones, and of synthetic GABA(A) receptor agonists. Certain hormones play a specific role in sleep regulation. A reciprocal interaction of the neuropeptides growth hormone (GH)-releasing hormone (GHRH) and corticotropin-releasing hormone (CRH) plays a key role in sleep regulation. At least in males GHRH is a common stimulus of non-rapid-eye-movement sleep (NREMS) and GH and inhibits the hypothalamo-pituitary adrenocortical (HPA) hormones, whereas CRH exerts opposite effects. Furthermore CRH may enhance rapid-eye-movement sleep (REMS). Changes in the GHRH:CRH ratio in favor of CRH appear to contribute to sleep EEG and endocrine changes during depression and normal ageing. In women, however, CRH-like effects of GHRH were found. Besides CRH somatostatin impairs sleep, whereas ghrelin, galanin and neuropeptide Y promote sleep. Vasoactive intestinal polypeptide appears to be involved in the temporal organization of human sleep. Beside of peptides, steroids participate in sleep regulation. Cortisol appears to promote REMS. Various neuroactive steroids exert specific effects on sleep. The beneficial effect of estrogen replacement therapy in menopausal women suggests a role of estrogen in sleep regulation. The GABA(A) receptor or GABAergic neurons are involved in the action of many of these hormones. Recently synthetic GABA(A) agonists, particularly gaboxadol and the GABA reuptake inhibitor tiagabine were shown to differ distinctly in their action from allosteric modulators of the GABA(A) receptor like benzodiazepines as they promote slow-wave sleep, decrease wakefulness and do not affect REMS.

Roles of peptides and steroids in sleep disorders

A bidirectional interaction exists between the electrophysiological and neuroendocrine components of sleep. The first is represented by the nonrapid eye movement sleep (NREMS) and rapid eye movement sleep (REMS) cycles, the latter by distinct patterns of the secretion of various hormones. Certain hormones (neuropeptides and steroids) play a specific role in sleep regulation. Changes in their activity contribute to the pathophysiology of sleep disorders. A reciprocal interaction of the peptides growth hormone-releasing hormone (GHRH) and corticotropin-releasing hormone (CRH) plays a key role in sleep regulation. GHRH promotes growth hormone secretion and, at least in males, NREMS, whereas CRH impairs NREMS, promotes REMS and stimulates the secretion of adrenocorticotropic hormone and cortisol. Changes in the CRH:GHRH ratio in favor of CRH contribute to impaired sleep, elevated cortisol secretion and blunted GH levels during depression and normal aging. However, in women, GHRH exerts CRH-like effects. Galanin, ghrelin and neuropeptide Y are other sleep-promoting peptides, whereas somatostatin impairs sleep. A decline of orexin activity causes narcolepsy. In addition to CRH overactivity, hypercortisolism appears to be involved in the pathophysiology of sleep- electroencephalogram (EEG) changes in depression. Various neuroactive steroids exert specific effects on sleep. The changes of sleep EEG in women after the menopause are related to the decline of estrogen and progesterone. Furthermore, sleep-EEG changes in dwarfism, acromegaly, Addison's disease, Cushing's disease, brain injury, sleep apnea syndrome, primary insomnia, prolactinoma and dementia appear to be related to changes in the activity of peptides and steroids.