Intraperitoneal injection of cholecystokinin elicits sleep in rabbits

A Systematic Review, Meta-Analysis and Meta-Regression on the Effects of Carbohydrates on Sleep

This study aimed to assess the effects of quantity, quality and periodization of carbohydrates consumption on sleep. PubMed, SCOPUS and Cochrane Library were searched through October 2020. Data were pooled using random-effects meta-analysis. Eleven articles were included in the meta-analysis which consisted of 27 separate nutrition trials, resulting in 16 comparison data sets (sleep quantity n = 11; sleep quality n = 5). Compared to high carbohydrate (HCI), low carbohydrate intake (LCI) moderately increased duration and proportion of N3 sleep stage (ES = 0.37; 95% CI = 0.18, 0.56; p < 0.001 and ES = 0.51; 95% CI = 0.33, 0.69; p < 0.001, respectively). HCI prolonged rapid eye movement (REM) stage duration (ES = −0.38; 95% CI = 0.05, −8.05; p < 0.001) and proportion (ES = −0.46; 95% CI = −0.83, −0.01; p < 0.001), compared to LCI. The quality of carbohydrate intake did not affect sleep stages. Meta-regression showed that the effectiveness of carbohydrate quantity and quality in sleep onset latency was significantly explained by alterations of carbohydrate intake as a percentage of daily energy intake (R² = 25.87, p = 0.018) and alterations in the glycemic load (R² = 50.8, p = 0.048), respectively. Alterations in glycemic load partially explained the variance of the effectiveness of carbohydrate quality in sleep efficiency (R² = 89.2, p < 0.001) and wake after sleep onset (R² = 64.9, p = 0.018). Carbohydrate quantity was shown to affect sleep architecture, and especially N3 and REM sleep stages. Alterations in both quantity and quality of carbohydrate intake showed a significant effect on sleep initiation. Variations in carbohydrate quality significantly affected measures of sleep continuation. Further studies are needed to assess the effect of long-term carbohydrate interventions on sleep.

Effect of Heweianshen Decoction on Orexin-A and Cholecystokinin-8 Expression in Rat Models of Insomnia

Objective. To study the effect of Heweianshen decoction (HAD) on orexin-A and cholecystokinin-8 (CCK-8) expression in rat models of insomnia caused by injecting parachlorophenylalanine (PCPA) intraperitoneally. Methods. Fifty male Wistar rats were randomly divided into five groups (10 rats in each group): blank group, model group, and low-, medium-, and high-dose HAD-treated groups. A rat model of insomnia was established by injecting intraperitoneally with PCPA (300 mg/kg body weight). Rats were given normal saline (10 mL/kg) or 5.25, 10.5, and 21 g/kg HAD by intragastric administration once a day for 6 days. After that, the rats were sacrificed to collect the hypothalamus for tests, using radioimmunoassay to detect the expression of orexin-A and CCK-8. Results. Heweianshen decoction reduced the expression of orexin-A and increased the expression of CCK-8 in the hypothalamus of rat model of insomnia. Conclusion. The therapeutic effect of HAD on insomnia is partially attributed to the decreased expression of orexin-A and increased expression of CCK-8.

The Neurobiology of Sleep and Wakefulness

Cortical electroencephalographic activity arises from corticothalamocortical interactions, modulated by wake-promoting monoaminergic and cholinergic input. These wake-promoting systems are regulated by hypothalamic hypocretin/orexins, while GABAergic sleep-promoting nuclei are found in the preoptic area, brainstem and lateral hypothalamus. Although pontine acetylcholine is critical for REM sleep, hypothalamic melanin-concentrating hormone/GABAergic cells may "gate" REM sleep. Daily sleep-wake rhythms arise from interactions between a hypothalamic circadian pacemaker and a sleep homeostat whose anatomical locus has yet to be conclusively defined. Control of sleep and wakefulness involves multiple systems, each of which presents vulnerability to sleep/wake dysfunction that may predispose to physical and/or neuropsychiatric disorders.

Effects of nutrient composition of dinner on sleep architecture and energy metabolism during sleep

Energy metabolism and substrate oxidation during sleep correlate with sleep stage, suggesting that energy metabolism affects sleep architecture or vice versa. The aim of the present study was to examine whether changes in energy metabolism during sleep, induced by a high-carbohydrate or high-fat meal for dinner, affect sleep architecture. Ten healthy males participated in this study, sleeping 3 nonconsecutive nights in a whole-room calorimeter. The first night was scheduled as an adaptation to the experimental environment. The other 2 nights were experimental calorimetry in a balanced cross-over design with intrasubject comparisons. In each session, subjects comsumed a high carbohydrate (HCD: PFC=10 : 10 : 80) or high fat (HFD: PFC=10 : 78 : 12) meal at 2000 h and slept with a polysomnographic recording in a metabolic chamber for indirect calorimetry (0000 h to 0800 h). Slow wave sleep was decreased during the first sleep cycle and not changed during the second or third sleep cycle under HCD conditions compared with those of HFD. Energy expenditure was not affected by dietary condition but substrate oxidation reflected differences in dietary composition of the dinner during the first and second sleep cycle. The present study suggested the possibility that substrate availability during sleep affects substrate oxidation during sleep, and affects sleep architecture during the first sleep cycle.

The effects of C75, an inhibitor of fatty acid synthase, on sleep and metabolism in mice

Sleep is greatly affected by changes in metabolic state. A possible mechanism where energy-sensing and sleep-regulatory functions overlap is related to lipid metabolism. Fatty acid synthase (FAS) plays a central role in lipid metabolism as a key enzyme in the formation of long-chain fatty acids. We studied the effects of systemic administration of C75, an inhibitor of FAS, on sleep, behavioral activity and metabolic parameters in mice. Since the effects of C75 on feeding and metabolism are the opposite of ghrelin's and C75 suppresses ghrelin production, we also tested the role of ghrelin signaling in the actions of C75 by using ghrelin receptor knockout (KO) mice. After a transient increase in wakefulness, C75 elicited dose-dependent and long lasting inhibition of REMS, motor activity and feeding. Simultaneously, C75 significantly attenuated slow-wave activity of the electroencephalogram. Energy expenditure, body temperature and respiratory exchange ratio were suppressed. The diurnal rhythm of feeding was completely abolished by C75. There was significant correlation between the anorectic effects, the decrease in motor activity and the diminished energy expenditure after C75 injection. We found no significant difference between wild-type and ghrelin receptor KO mice in their sleep and metabolic responses to C75. The effects of C75 resemble to what was previously reported in association with visceral illness. Our findings suggest that sleep and metabolic effects of C75 in mice are independent of the ghrelin system and may be due to its aversive actions in mice.

The hypothalamic peptidergic system, hypocretin/orexin and vigilance control

Using forward and reverse genetics, the genes (hypocretin/orexin ligand and its receptor) involved in the pathogenesis of the sleep disorder, narcolepsy, in animals, have been identified. Mutations in hypocretin related-genes are extremely rare in humans, but hypocretin-ligand deficiency is found in most narcolepsy-cataplexy cases. Hypocretin deficiency in humans can be clinically detected by CSF hypocretin-1 measures, and undetectably low CSF hypocretin-1 is now included in the revised international diagnostic criteria of narcolepsy. Since hypocretin-ligand deficiency is the major pathophysiology in human narcolepsy, hypocretin replacements (using hypocretin agonists or gene therapy) are promising future therapeutic options. New insights into the roles of hypocretin system on sleep physiology have also rapidly increased. Hypocretins are involved in various fundamental hypothalamic functions such as feeding, energy homeostasis and neuroendocrine regulation. Hypocretin neurons project to most ascending arousal systems (including monoaminergic and cholinergic systems), and generally exhibit excitatory inputs. Together with the recent finding of the sleep promoting system in the hypothalamus (especially in the GABA/galanin ventrolateral preoptic area which exhibits inhibitory inputs to these ascending systems), the hypothalamus is now recognized as the most important brain site for the sleep switch, and other peptidergic systems may also participate in this regulation. Meanwhile, narcolepsy now appears to be a more complex condition than previously thought. The pathophysiology of the disease is involved in the abnormalities of sleep and various hypothalamic functions due to hypocretin deficiency, such as the changes in energy homeostasis, stress reactions and rewarding. Narcolepsy is therefore, an important model to study the link between sleep regulation and other fundamental hypothalamic functions.

Neuropeptides as possible targets in sleep disorders

Insomnia and hypersomnia are frequent sleep disorders, and they are most often treated pharmacologically with hypnotics and wake-promoting compounds. These compounds act on classical neurotransmitter systems, such as benzodiazepines on GABA-A receptors, and amfetamine-like stimulants on monoaminergic terminals to modulate neurotransmission. In addition, acetylcholine, amino acids, lipids and proteins (cytokines) and peptides, are known to significantly modulate sleep and are, therefore, possibly involved in the pathophysiology of some sleep disorders. Due to the recent developments of molecular biological techniques, many neuropeptides have been newly identified, and some are found to significantly modulate sleep. It was also discovered that the impairment of the hypocretin/orexin neurotransmission (a recently isolated hypothalamic neuropeptide system) is the major pathophysiology of narcolepsy, and hypocretin replacement therapy is anticipated to treat the disease in humans. In this article, the authors briefly review the history of neuropeptide research, followed by the sleep modulatory effects of various neuropeptides. Finally, general strategies for the pharmacological therapeutics targeting the peptidergic systems for sleep disorders are discussed.

Relationship between antral distension and postprandial symptoms in functional dyspepsia

AIM: To investigate in patients with functional dyspepsia (FD) after an every-day meal whether (1) gastrointestinal (GI) and extra-GI symptoms had any relation with the degree of antral volume, (2) the onset of postprandial symptoms was associated with, and may predict, delayed gastric emptying.

METHODS: In 94 symptomatic FD patients, antral volume variations and gastric emptying were assessed with ultrasonography after a 1050 kcal meal. Symptoms were evaluated with a standardized questionnaire. The association of GI and extra-GI symptoms with antral volumes and gastric emptying were estimated with logistic regression analysis.

RESULTS: Forty percent of patients did not report any symptoms after a meal. Compared to the healthy controls, the antrum was more distended in patients throughout the entire observation period and 37 (39.4%) patients had delayed gastric emptying. Only postprandial drowsiness was associated with antral volume variations (AOR = 1.42; P < 0.001) and with delayed gastric emptying (AOR = 3.59; P < 0.03).

CONCLUSION: In FD patients, GI symptoms are neither associated with antral distension nor with gastric emptying. Drowsiness is associated with antral distension and delayed gastric emptying. The onset of drowsiness is preceded by an increment of antral distension and the duration of the symptom appears to be related to the persistence of antral distension.

Obestatin alters sleep in rats

Obestatin is a recently identified peptide derived from the ghrelin gene. Ghrelin stimulates food intake whereas obestatin has an opposite effect in rats. Previous experiments in our laboratory revealed that ghrelin also induces wakefulness in rats. The aim of the present experiments was to study the effect of obestatin on sleep. Rats received intraperitoneal (n = 7; 16 or 64 microg/kg) or intracerebroventricular (i.c.v.; n = 11) injection of pyrogen-free isotonic NaCl or obestatin (1, 4 and 16 microg in a volume of 4 microl) at dark onset. Sleep-wake activity was recorded for 23 h. I.c.v. administration of 16 microg obestatin induced a significant increase (approximately 58%) in the time spent in non-rapid-eye-movement sleep (NREMS) in the first hour after the injection. This resulted from an increase in the number of NREMS episodes and shortened sleep latency. Electroencephalographic (EEG) slow-wave activity (0.5-4 Hz) was reduced by obestatin treatment. The initial increase in NREMS time was followed by a decrease in both NREMS and REMS in the second hour after the injection. Peripheral injection of obestatin did not induce significant changes in sleep in any post-injection hours. Results suggest that the sleep-promoting effect of centrally administered obestatin may be part of the behavioral manifestation of satiety elicited by the peptide. Current results confirm the finding that two regulatory peptides derived from the same gene have opposite actions in the same species.

Neuropeptide-Y Y2-receptor agonist, PYY3–36 promotes non-rapid eye movement sleep in rat

PYY3-36 is a major component of the gut-brain axis and peripheral administration has been reported to exert significant effects on feeding, brain function and is more selective for neuropeptide Y2 receptor. Therefore, we investigated the effects of nocturnal intraperitoneal administration of single doses of PYY3-36 (30 and 100 microg/kg i.p.) on food intake, water intake and the sleep-wake cycle in rats. Sleep recordings were carried out in male Sprague-Dawley rats implanted with cortical electroencephalogram (EEG) and neck electromyogram (EMG) electrodes. The EEG, EMG, food intake and water intake were assessed. The electrographic recordings obtained were scored visually as rapid eye movement (REM) sleep, non-REM (NREM) sleep and wakefulness. PYY3-36 administration 15 min prior to dark onset significantly (p<0.05) increased non-rapid eye movement (NREM) sleep and decreased wakefulness. Analysis of the dark-period at 4-h time intervals showed that nocturnal administration of PYY3-36 (30 and 100 microg/kg) significantly suppressed wakefulness and increased non-REM sleep during the first 4-h time interval. Time spent in wakefulness was significantly decreased after administration of PYY3-36 (30 and 100 microg/kg) when compared with administration of vehicle. In addition, PYY3-36 (30 and 100 microg/kg i.p.) induced an increase in the time spent in NREM sleep. The nocturnal intraperitoneal administration of the lower dose of PYY3-36 (30 microg/kg) also significantly decreased food intake [F (2,23)=4.90, p<0.05] but had no effect on water intake. These findings suggest that PYY3-36 may play an important role in the enhancement of NREM sleep and feeding behavior.

Sleep is increased in mice with obesity induced by high-fat food

Excessive daytime sleepiness has been associated with obesity in humans. However, experimental studies on sleep in obese animals are scarce and the results are not consistent. To test the hypothesis that obesity is associated with increased sleep, we examined the effects of obesity, induced by high-fat food, on sleep in mice. We first determined baseline sleep in adult C57BL/6 mice (6 months of age). In the following 6 weeks, the experimental mice (n = 12) were switched to high-fat food, in which fat provided 59% of calories, and the control mice (n = 11) were continuously fed with regular lab chows, in which fat provided 16% of calories. The body weights increased steadily in the high-fat group, but maintained constant in the controls. Wakefulness was reduced when assessed after 2, 4, and 6 weeks of high-fat feeding. Concurrently, there were large increases (about 80-100 min/day) in non-rapid eye movement sleep (NREMS). Rapid eye movement sleep (REMS) was not altered. The numbers of NREMS and REMS episodes were increased, whereas the duration of waking episodes was reduced, mainly during the dark period. These alterations in sleep were not observed in the controls. In the high-fat group, the increases of body weight, but not the amounts of energy intake, were negatively correlated with the change in the amounts of wakefulness and positively correlated with the change in the amounts of NREMS. These results indicate that the obese animals have increased sleep pressure and difficulties in maintaining wakefulness during the active phase.

Neurobiological mechanisms involved in sleep bruxism

Sleep bruxism (SB) is reported by 8% of the adult population and is mainly associated with rhythmic masticatory muscle activity (RMMA) characterized by repetitive jaw muscle contractions (3 bursts or more at a frequency of 1 Hz). The consequences of SB may include tooth destruction, jaw pain, headaches, or the limitation of mandibular movement, as well as tooth-grinding sounds that disrupt the sleep of bed partners. SB is probably an extreme manifestation of a masticatory muscle activity occurring during the sleep of most normal subjects, since RMMA is observed in 60% of normal sleepers in the absence of grinding sounds. The pathophysiology of SB is becoming clearer, and there is an abundance of evidence outlining the neurophysiology and neurochemistry of rhythmic jaw movements (RJM) in relation to chewing, swallowing, and breathing. The sleep literature provides much evidence describing the mechanisms involved in the reduction of muscle tone, from sleep onset to the atonia that characterizes rapid eye movement (REM) sleep. Several brainstem structures (e.g., reticular pontis oralis, pontis caudalis, parvocellularis) and neurochemicals (e.g., serotonin, dopamine, gamma aminobutyric acid [GABA], noradrenaline) are involved in both the genesis of RJM and the modulation of muscle tone during sleep. It remains unknown why a high percentage of normal subjects present RMMA during sleep and why this activity is three times more frequent and higher in amplitude in SB patients. It is also unclear why RMMA during sleep is characterized by co-activation of both jaw-opening and jaw-closing muscles instead of the alternating jaw-opening and jaw-closing muscle activity pattern typical of chewing. The final section of this review proposes that RMMA during sleep has a role in lubricating the upper alimentary tract and increasing airway patency. The review concludes with an outline of questions for future research.

L-364,718, a cholecystokinin-A receptor antagonist, suppresses feeding-induced sleep in rats

Feeding induces increased sleep in several species, including rats. The aim of the study was to determine if CCK plays a role in sleep responses to feeding. We induced excess eating in rats by 4 days of starvation and studied the sleep responses to refeeding in control and CCK-A receptor antagonist-treated animals. Sleep was recorded on 2 baseline days when food was provided ad libitum. After the starvation period, sleep was recorded on 2 refeeding days when the control rats (n = 8) were injected with vehicle and the experimental animals (n = 8) received intraperitoneal injections of L-364,718 (500 microg/kg, on both refeeding days). In the control group, refeeding caused increases in rapid eye movement sleep (REMS) and non-REMS (NREMS) and decreases in NREMS intensity as indicated by the slow-wave activity (SWA) of the electroencephalogram. CCK-A receptor antagonist treatment completely prevented the SWA responses and delayed the NREMS responses to refeeding; REMS responses were not simply abolished, but the amount of REMS was below baseline after the antagonist treatment. These results suggest that endogenous CCK, acting on CCK-A receptors, may play a key role in eliciting postprandial sleep.

Albumin enhances sleep in the young rat

Rats 4 to 7 days after weaning received intraperitoneal (i.p.) injections of vehicle (baseline day), and either serum (2 mL of lyophilized rabbit serum), 140 mg of rat albumin, or hyperosmotic NaCl (experimental day). Injections were given 1 h before light onset. Sleep-wake activity and cortical brain temperature were recorded during the subsequent 12-h light period. The intensity of non-rapid eye movement sleep (NREMS) was characterized by the power density values of the electroencephalogram slow-wave activity. The sera and albumin preparations enhanced both NREMS and slow-wave activity for 5 to 6 h starting during Hour 2 after light onset. Rapid eye movement sleep (REMS) tended to decrease. Modest (0.6 degrees C maximum deviation) biphasic changes were observed in cortical brain temperature with initial decreases for 3 h followed by rises between Hours 3 and 9 of the light period. There were no differences in the sleep responses to albumin between male and female rats. Albumin also enhanced NREMS in young rats on a protein-rich diet. A significant negative correlation was found between the NREMS promoting activity of albumin injections and the body weight of the rats. NaCl solution with the same osmolarity as that of the albumin solution failed to alter sleep. I.p. albumin injection elicited significant increases in the concentrations of cholecystokinin-like immunoreactivity in the plasma. Sleep-promoting materials (hormones) in the albumin fraction, the calorigenic or nutritional value of proteins, the release of somnogenic cytokines by albumin, or endogenous humoral mechanisms stimulated by proteins (e.g., cholecystokinin or the somatotropic axis) might mediate the enhanced sleep after albumin.

A comparison of feeding to cephalic stimulation on postprandial sleepiness

This study investigated the effects of ingestion of a meal compared to a sham feeding on objectively measured sleepiness. It was hypothesized that the ingestion of a solid meal would produce significantly greater postprandial sleepiness evidenced by shorter sleep onset latencies (SOL) when compared to a sham feeding. Eleven men and eight women without evidence of gastrointestinal disease or sleep disorders participated in the 2-day study. Subjects underwent a premeal baseline nap at 1600 hours and were given a standardized meal at 1700 hours. On one study day, subjects consumed the entire meal, whereas on another study day, they were asked to chew and then expectorate the meal. Naps with polysomnographic monitoring followed at 1730, 1800, and 1900 hours. Sleep onset latencies were determined by standard polysomnographic measures. Statistical analyses revealed the sleep onset latencies for the two meal conditions differed significantly at the 1800 hours postprandial nap only. Individuals demonstrated a transient decrease in sleep latency after consuming a meal compared to a sham feeding. These results lend support to the existence of a gastrointestinal effect on postprandial sleepiness.

Cafeteria diet-induced sleep is blocked by subdiaphragmatic vagotomy in rats

Feeding rats a cafeteria diet results in increased food intake and excess sleep. Furthermore, vagal afferent activity is altered by a variety of gastrointestinal factors, and vagal stimulation can induce sleep. We investigated, therefore, the hypothesis that the vagal nerve plays a critical role in mediating the sleep-inducing effects of cafeteria feeding. We examined the effects of a cafeteria diet on sleep, electroencephalographic (EEG) slow-wave activity (SWA), and brain temperature (Tbr) in control and vagotomized rats. EEG, electromyogram, and Tbr were recorded for 7 consecutive days. Day 1 was considered a baseline day; normal rat chow was available ad libitum. On days 2-4, the animals were fed, in addition to normal chow, a mixed, energy-rich diet (cafeteria diet). On days 5-7, the rats were again fed only normal rat chow. In control rats, the cafeteria diet resulted in an increase in non-rapid eye movement sleep (NREMS), which was the result of a significant lengthening of the NREMS episodes. In contrast, feeding vagotomized rats the cafeteria diet resulted in a decrease in NREMS. Cafeteria feeding decreased REMS and EEG SWA and increased Tbr in both control and vagotomized rats. These results suggest that an intact vagus plays a key role in the NREMS-inducing effects of the cafeteria diet.

Meal composition and its effect on postprandial sleepiness

Drowsiness is a commonly experienced phenomenon following food ingestion. The present two experiments were designed to assess separately the effects of a solid meal compared to a liquid meal and to an equal volume of water, and the effects of meal constituents (high-fat, high-carbohydrate, or mixed meal) on objective postprandial sleep latencies. Ten normal male subjects participated in each study. Both studies used identical protocols, differing only in the meals the subjects were fed. All subjects underwent a pre-meal baseline nap at 1600 hours. At 1700 hours, subjects consumed a test meal. Naps followed at 1730, 1800, 1900, and 2000 hours. Sleep onset latency was determined by standard polysomnographic measures. In both studies, a one-way repeated-measures ANOVA procedure revealed no significant difference in sleep latencies among the meal conditions for the nap at 1600 hours. However, for the postprandial naps at 1730, 1800, and 2000 hours, the solid meal demonstrated a significant decrease in postprandial sleep latency compared with an equivalent volume of water (control). No significant differences in sleep latency were found between the food constituents. Results indicate that in contrast to a liquid meal, a solid meal produces a decrease in sleep onset latency when compared to an equivalent volume of water. Further, it was demonstrated that meal constituents have no effect on postprandial sleepiness.

Selective activation of CCK-B receptors does not induce sleep and does not affect EEG slow-wave activity and brain temperature in rats

Systemic injections of cholecystokinin octapeptide sulfate ester (CCK-8-SE) elicit various behavioral and autonomic responses, such as increases in nonrapid-eye-movement sleep (NREMS) and hypothermia. There are two CCK receptors; both CCK-A and CCK-B receptors are stimulated by CCK-8-SE. The relative importance of the CCK-A and CCK-B receptors in the somnogenic and hypothermic effects of CCK-8-SE is not well understood. In the present experiments, we studied the effects of the selective activation of CCK-B receptors by CCK tetrapeptide (CCK-4) or nonsulfated CCK-8 (CCK-8-NS) on sleep and brain temperature (Tbr). Rats were injected intraperitoneally with saline on the control day and with CCK-8-NS (10, 50, or 250 microg/kg) or CCK-4 (10, 50, or 250 microg/kg) on the test day 5-10 min before dark onset. Electroencephalogram, electromyogram, and Tbr were recorded for 12 h. None of the treatments affected sleep or Tbr significantly, with the exception of 10 microg/kg CCK-4, which transiently decreased the amount of NREMS, and 10 microg/kg CCK-8-NS, which slightly increased REMS. These results suggest that the activation of CCK-B receptors by systemic injection of CCK-4 or CCK-8-NS is not sufficient to elicit increased NREMS and hypothermia in rats.