Sleep: Giving it up to get it on.

A new study presents evidence of sex-related sleep reduction in males of two marsupial mice species but not in females. The growing experimental data suggest that seasonal sleep reduction, linked to migrations and reproductive periods, is common among animals.

Opiate anticipation, opiate induced anatomical changes in hypocretin (Hcrt, orexin) neurons and opiate induced microglial activation are blocked by the dual Hcrt receptor antagonist suvorexant, while opiate analgesia is maintained.

We previously found that heroin addiction in humans is accompanied by an increase in the number of detected Hcrt neurons and a decrease in their soma size. We now show that the increased number of Hcrt cells visible after morphine treatment is likely the result of increased Hcrt production in neurons having sub-detection levels of the peptides. We find that morphine increases Hcrt projections to the ventral tegmental area (VTA), the level of tyrosine hydroxylase enzyme (TH) and the number of TH positive cells in VTA, with no changes in the adjacent substantia nigra. We find that the dual Hcrt receptor antagonist suvorexant prevents morphine-induced changes in the number and size of Hcrt neurons, microglial activation and morphine anticipatory behavior, but does not diminish morphine analgesia. These findings suggest that combined administration of opiates and suvorexant may be a less addictive way of administering opiates for pain relief in humans.

A 108-h total sleep deprivation did not impair fur seal performance in delayed matching to sample task.

While the majority of studies have concluded that sleep deprivation causes detrimental effects on various cognitive processes, some studies reported conflicting results. We examined the effects of a 108-h total sleep deprivation (TSD) on working memory in the northern fur seal, an animal with unusual sleep phenomenology and long-range annual migrations. The performance of fur seals was evaluated in a two-choice visual delayed matching to sample (DMTS) task, which is commonly used to evaluate working memory. In baseline conditions, the performance of fur seals in a DMTS task based on the percentage of errors was somewhat comparable with that in nonhuman primates at similar delays. We have determined that a 108-h TSD did not affect fur seals' performance in a visual DMTS task as measured by overall percentage of errors and response latencies. On the contrary, all fur seals improved task performance over the study, including the baseline, TSD and recovery conditions. In addition, TSD did not change the direction and strength of the pattern of behavioral lateralization in fur seals. We conclude that a 108-h TSD did not interfere with working memory in a DMTS test in northern fur seals.

Effects of sodium oxybate on hypocretin/orexin and locus coeruleus neurons.

Long-term use of sodium oxybate (SXB), (also called gamma-hydroxybutyrate [GHB]) attenuates the cataplexy and sleepiness of human narcolepsy. We had previously found that chronic opiate usage in humans and long-term opiate administration to mice significantly increased the number of detected hypocretin/orexin (Hcrt) neurons, decreased their size, and increased Hcrt level in the hypothalamus. We also found that opiates significantly decreased cataplexy in human narcoleptics as well as in narcoleptic mice and that cessation of locus coeruleus neuronal activity preceded and was tightly linked to cataplectic attacks in narcoleptic dogs. We tested the hypothesis that SXB produces changes similar to opiates and now report that chronic SXB administration significantly increased the size of Hcrt neurons, the reverse of what we had seen with opiates in humans and mice. Levels of Hcrt in the hypothalamus were nonsignificantly lower, in contrast to the significant increase in hypothalamic Hcrt level after opiates. SXB decreased tyrosine hydroxylase levels in the locus coeruleus, the major descending projection of the hypocretin system, also the reverse of what we saw with opioids. Therefore despite some similar effects on narcoleptic symptomatology, SXB does not produce anatomical changes similar to those elicited by opiates. Analysis of changes in other links in the cataplexy pathway might further illuminate SXB's mechanism of action on narcolepsy.

Sensitivity of Hypocretin System to Chronic Alcohol Exposure: A Human and Animal Study.

Human heroin addicts and mice administered morphine for a 2 week period show a greatly increased number of hypothalamic hypocretin (Hcrt or orexin) producing neurons with a concomitant reduction in Hcrt cell size. Male rats addicted to cocaine similarly show an increased number of detectable Hcrt neurons. These findings led us to hypothesize that humans with alcohol use disorder (AUD) would show similar changes. We now report that humans with AUD have a decreased number and size of detectable Hcrt neurons. In addition, the intermingled melanin concentrating hormone (MCH) neurons are reduced in size. We saw no change in the size and number of tuberomammillary histamine neurons in AUD. Within the Hcrt/MCH neuronal field we found that microglia cell size was increased in AUD brains. In contrast, male rats with 2 week alcohol exposure, sufficient to elicit withdrawal symptoms, show no change in the number or size of Hcrt, MCH and histamine neurons, and no change in the size of microglia. The present study indicates major differences between the response of Hcrt neurons to opioids and that to alcohol in human subjects with a history of substance abuse.

Sleep function: an evolutionary perspective.

Prospective epidemiological studies in industrial societies indicate that 7 h of sleep per night in people aged 18 years or older is optimum, with higher and lower amounts of sleep predicting a shorter lifespan. Humans living a hunter-gatherer lifestyle (eg, tribal groups) sleep for 6-8 h per night, with the longest sleep durations in winter. The prevalence of insomnia in hunter-gatherer populations is low (around 2%) compared with the prevalence of insomnia in industrial societies (around 10-30%). Sleep deprivation studies, which are done to gain insights into sleep function, are often confounded by the effects of stress. Consideration of the duration of spontaneous daily sleep across species of mammals, which ranges from 2 h to 20 h, can provide important insights into sleep function without the stress of deprivation. Sleep duration is not related to brain size or cognitive ability. Rather, sleep duration across species is associated with their ecological niche and feeding requirements, indicating a role for wake-sleep balance in food acquisition and energy conservation. Brain temperature drops from waking levels during non-rapid eye movement (non-REM) sleep and rises during REM sleep. Average daily REM sleep time of homeotherm orders is negatively correlated with average body and brain temperature, with the largest amount of REM sleep in egg laying (monotreme) mammals, moderate amounts in pouched (marsupial) mammals, lower amounts in placental mammals, and the lowest amounts in birds. REM sleep might, therefore, have a key role in the regulation of temperature and metabolism of the brain during sleep and in the facilitation of alert awakening.

Consensus guidelines on the construct validity of rodent models of restless legs syndrome.

Our understanding of the causes and natural course of restless legs syndrome (RLS) is incomplete. The lack of objective diagnostic biomarkers remains a challenge for clinical research and for the development of valid animal models. As a task force of preclinical and clinical scientists, we have previously defined face validity parameters for rodent models of RLS. In this article, we establish new guidelines for the construct validity of RLS rodent models. To do so, we first determined and agreed on the risk, and triggering factors and pathophysiological mechanisms that influence RLS expressivity. We then selected 20 items considered to have sufficient support in the literature, which we grouped by sex and genetic factors, iron-related mechanisms, electrophysiological mechanisms, dopaminergic mechanisms, exposure to medications active in the central nervous system, and others. These factors and biological mechanisms were then translated into rodent bioequivalents deemed to be most appropriate for a rodent model of RLS. We also identified parameters by which to assess and quantify these bioequivalents. Investigating these factors, both individually and in combination, will help to identify their specific roles in the expression of rodent RLS-like phenotypes, which should provide significant translational implications for the diagnosis and treatment of RLS.

Striatal mechanism of the restless legs syndrome.

STUDY OBJECTIVES: Brain iron deficiency has been reported to be associated with the restless legs syndrome (RLS). However, 30%-50% of RLS patients do not respond to iron therapy, indicating that mechanisms other than brain iron deficiency may also participate in this disease. The striatum is known to be involved in the modulation of motor activity. We speculated that dysfunction of the striatum may induce RLS. METHODS: Two groups, wild-type (WT) and iron-deficient (ID) rats were used. Each group was divided into two subgroups, control and N-methyl-d-aspartate striatal-lesioned. After baseline recording, striatal-lesioned wild-type (WT-STL) and striatal-lesioned iron-deficient (ID-STL) rats were given pramipexole and thioperamide injections. Iron-deficient and ID-STL rats were then given a standard rodent diet for 4 weeks, and their sleep and motor activity were recorded. RESULTS: WT-STL rats showed periodic leg movements (PLM) in wake, an increase in PLM in slow wave sleep (SWS), a decrease in rapid-eye-movement sleep, and a decrease in the daily average duration of episodes in SWS. The sleep-wake pattern and motor activity did not differ between ID and ID-STL rats. Thioperamide or pramipexole injection decreased PLM in sleep and in wake in WT-STL rats and ID-STL rats. Unlike ID rats, whose motor hyperactivity can be reversed by iron replacement, PLM in wake and in sleep in ID-STL rats were not fully corrected by iron treatment. CONCLUSIONS: Lesions of the striatum generate RLS-like activity in rats. Dysfunction of the striatum may be responsible for failure to respond to iron treatment in some human RLS patients.

Nuclear organization of orexinergic neurons in the hypothalamus of a lar gibbon and a chimpanzee.

Employing orexin-A immunohistochemical staining we describe the nuclear parcellation of orexinergic neurons in the hypothalami of a lar gibbon and a chimpanzee. The clustering of orexinergic neurons within the hypothalamus and the terminal networks follow the patterns generally observed in other mammals, including laboratory rodents, strepsirrhine primates and humans. The orexinergic neurons were found within three distinct clusters in the ape hypothalamus, which include the main cluster, zona incerta cluster and optic tract cluster. In addition, the orexinergic neurons of the optic tract cluster appear to extend to a more rostral and medial location than observed in other species, being observed in the tuberal region in the anterior ventromedial aspect of the hypothalamus. While orexinergic terminal networks were observed throughout the brain, high density terminal networks were observed within the hypothalamus, medial and intralaminar nuclei of the dorsal thalamus, and within the serotonergic and noradrenergic regions of the midbrain and pons, which is typical for mammals. The expanded distribution of orexinergic neurons into the tuberal region of the ape hypothalamus, is a feature that needs to be investigated in other primate species, but appears to correlate with orexin gene expression in the same region of the human hypothalamus, but these neurons are not revealed with immunohistochemical staining in humans. Thus, it appears that apes have a broader distribution of orexinergic neurons compared to other primate species, but that the neurons within this extension of the optic tract cluster in humans, while expressing the orexin gene, do not produce the neuropeptide.

Hypocretin/Orexin Interactions with Norepinephrine Contribute to the Opiate Withdrawal Syndrome.

We previously found that human heroin addicts and mice chronically exposed to morphine exhibit a significant increase in the number of detected hypocretin/orexin (Hcrt)-producing neurons. However, it remains unknown how this increase affects target areas of the hypocretin system involved in opioid withdrawal, including norepinephrine containing structures locus coeruleus (LC) and A1/A2 medullary regions. Using a combination of immunohistochemical, biochemical, imaging, and behavioral techniques, we now show that the increase in detected hypocretin cell number translates into a significant increase in hypocretin innervation and tyrosine hydroxylase (TH) levels in the LC without affecting norepinephrine-containing neuronal cell number. We show that the increase in TH is completely dependent on Hcrt innervation. The A1/A2 regions were unaffected by morphine treatment. Manipulation of the Hcrt system may affect opioid addiction and withdrawal.SIGNIFICANCE STATEMENT Previously, we have shown that the hypothalamic hypocretin system undergoes profound anatomic changes in human heroin addicts and in mice exposed to morphine, suggesting a role of this system in the development of addictive behaviors. The locus coeruleus plays a key role in opioid addiction. Here we report that the hypothalamic hypocretin innervation of the locus coeruleus increases dramatically with morphine administration to mice. This increase is correlated with a massive increase in tyrosine hydroxylase expression in locus coeruleus. Elimination of hypocretin neurons prevents the tyrosine hydroxylase increase in locus coeruleus and dampens the somatic and affective components of opioid withdrawal.

Sleep in the lesser mouse-deer (Tragulus kanchil).

The mouse-deer or chevrotains are the smallest of the ungulates and ruminants. They are characterized by a number of traits which are considered plesiomorphic for the Artiodactyla order. The objective of this study was to examine sleep in the lesser mouse-deer (Tragulus kanchil), which is the smallest in this group (body mass < 2.2 kg). Electroencephalogram, nuchal electromyogram, electrooculogram, and body acceleration were recorded in four adult mouse-deer females using a telemetry system in Bu Gia Map National Park in Vietnam. The mouse-deer spent on average 49.7 ± 3.0% of 24 h in non-rapid eye movement (NREM) sleep. REM sleep occupied 1.7 ± 0.3% of 24 h or 3.2 ± 0.5% of total sleep time. The average duration of REM sleep episodes was 2.0 ± 0.2 min, the average maximum was 5.1 ± 1.1 min, and the longest episodes lasted 8 min. NREM sleep occurred in sternal recumbency with the head held above the ground while 64.7 ± 6.4% of REM sleep occurred with the head resting on the ground. The eyes were open throughout most of the NREM sleep period. The mouse-deer displayed polyphasic sleep and crepuscular peaks in activity (04:00-06:00 and 18:00-19:00). The largest amounts of NREM occurred in the morning (06:00-09:00) and the smallest before dusk (at 04:00-06:00). REM sleep occurred throughout most of the daylight hours (08:00-16:00) and in the first half of the night (19:00-02:00). We suggest that the pattern and timing of sleep in the lesser mouse-deer is adapted to the survival of a small herbivorous animal, subject to predation, living in high environmental temperatures in the tropical forest undergrowth.

Orexin receptors in GtoPdb v.2021.3.

Orexin receptors (nomenclature as agreed by the NC-IUPHAR Subcommittee on Orexin receptors [42]) are activated by the endogenous polypeptides orexin-A and orexin-B (also known as hypocretin-1 and -2; 33 and 28 aa) derived from a common precursor, preproorexin or orexin precursor, by proteolytic cleavage and some typical peptide modifications [109]. Currently the only orexin receptor ligands in clinical use are suvorexant and lemborexant, which are used as hypnotics. Orexin receptor crystal structures have been solved [134, 133, 54, 117, 46].

Memory Consolidation Is Similar in Waking and Sleep.

PURPOSE OF REVIEW: I review the current status of the hypothesis that sleep is critically involved in memory consolidation and conclude that there are major methodological problems with the studies used to support this hypothesis. RECENT FINDINGS: Memory consolidation is similar in quiet waking and sleep (Humiston GB, Tucker MA, Summer T, Wamsley EJ. Sci Rep 18;9(1):19345, 2019), and suppression of REM sleep for long periods is compatible with learning and highly adaptive behavior (Lyamin OI, Korneva SM, Obukhova ED, Mukhametov LM, Siegel JM. Dokl Biol Sci 463:211-4, 2015; Lyamin OI, Kosenko PO, Korneva SM, Vyssotski AL, Mukhametov LM, Siegel JM. Current Biology 28(12):2000-5, 2018); despite their considerable abilities to navigate and remember, African elephants have very small amount of sleep, and learning interference effects have not been adequately controlled for in studies purporting to show sleep-dependent memory consolidation (Sosic-Vasic Z, Hille K, Kroner J, Spitzer M, Kornmeier J. Frontiers in psychology 9:82, 2018; Yonelinas AP, Ranganath C, Ekstrom AD, Wiltgen BJ. Nat Rev Neurosci 20(6):364-75, 2019). SUMMARY: Memory consolidation clearly occurs in both sleep and waking. Whether, and the extent to which, consolidation might differ in these two states has not been conclusively determined.

Pleasure, addiction, and hypocretin (orexin).

The hypocretins/orexins were discovered in 1998. Within 2 years, this led to the discovery of the cause of human narcolepsy, a 90% loss of hypothalamic neurons containing these peptides. Further work demonstrated that these neurons were not simply linked to waking. Rather these neurons were active during pleasurable behaviors in waking and were silenced by aversive stimulation. This was seen in wild-type mice, rats, cats, and dogs. It was also evident in humans, with increased Hcrt release during pleasurable activities and decreased release, to the levels seen in sleep, during pain. We found that human heroin addicts have, on average, an increase of 54% in the number of detectable Hcrt neurons compared to "control" human brains and that these Hcrt neurons are substantially smaller than those in control brains. We found that in mice, chronic morphine administration induced the same changes in Hcrt neuron number and size. Our studies in the mouse allowed us to determine the specificity, dose response relations, time course of the change in the number of Hcrt neurons, and that the increased number of Hcrt neurons after opiates was not due to neurogenesis. Furthermore, we found that it took a month or longer for these anatomical changes in the mouse brain to return to baseline. Human narcoleptics, despite their prescribed use of several commonly addictive drugs, do not show significant evidence of dose escalation or substance use disorder. Similarly, mice in which the peptide has been eliminated are resistant to addiction. These findings are consistent with the concept that an increased number of Hcrt neurons may underlie and maintain opioid or cocaine use disorders.

Consensus Guidelines on Rodent Models of Restless Legs Syndrome.

Restless legs syndrome (RLS) is a chronic sensorimotor disorder diagnosed by clinical symptoms. It is challenging to translate the diagnostic self-reported features of RLS to animals. To help researchers design their experiments, a task force was convened to develop consensus guidelines for experimental readouts in RLS animal models. The RLS clinical diagnostic criteria were used as a starting point. After soliciting additional important clinical features of RLS, a consensus set of methods and outcome measures intent on capturing these features-in the absence of a face-to-face interview-was generated and subsequently prioritized by the task force. These were, in turn, translated into corresponding methods and outcome measures for research on laboratory rats and mice and used to generate the final recommendations. The task force recommended activity monitoring and polysomnography as principal tools in assessing RLS-like behavior in rodents. Data derived from these methods were determined to be the preferred surrogate measures for the urge to move, the principal defining feature of RLS. The same tools may be used to objectively demonstrate sleep-state features highly associated with RLS, such as sleep disturbance and number and periodicity of limb movements. Pharmacological challenges and dietary or other manipulations that affect iron availability are desirable to aggravate or improve RLS-like behavior and lend greater confidence that the animal model being proffered replicates key clinical features of RLS. These guidelines provide the first consensus experimental framework for researchers to use when developing new rodent models of RLS. © 2020 International Parkinson and Movement Disorder Society.

Sleep in ostrich chicks (Struthio camelus).

It has been reported that adult ostriches displayed the longest episodes of rapid eye movement (REM) sleep (up to 5 min) and more REM sleep (24% of the nighttime) than any other bird species. If the mammalian ontogenetic trend exists in the ostrich, then the amounts of REM and the duration of sleep episodes in young ostriches may be greater than those reported in adults. We investigated sleep in 1.5-3.5 month old ostrich chicks. Recordings were conducted during nighttime (20:00-08:00), the main sleep period in ostriches, which are diurnal. The polygrams were scored in 4-s epochs for waking, non-rapid eye movement (NREM) sleep and REM sleep, as in other bird studies. REM sleep in ostrich chicks occurred during both cortical EEG activation and during slow waves, as was described in adult ostriches. The chicks spent 69.3% ± 1.5% of the night in NREM sleep. REM sleep occupied 14.1% ± 1.8% of the night or 16.8% ± 2.0% of nighttime sleep. Episodes of REM sleep lasted on average 10 ± 1 s and ranged between 4 and 40 s. Therefore, the total amount and duration of REM sleep episodes in ostrich chicks were substantially smaller than reported in adult ostriches while the amounts of NREM sleep did not greatly differ. The developmental profile of REM sleep ontogenesis in the ostrich may be remarkably different from what has been reported in all studied mammals and birds.

Substantia nigra pars reticulata-mediated sleep and motor activity regulation.

STUDY OBJECTIVES: The substantia nigra pars reticulata (SNR) is a major output nucleus of the basal ganglia. Animal studies have shown that lesions of the SNR cause hyposomnia and motor hyperactivity, indicating that the SNR may play a role in the control of sleep and motor activity. METHODS: Eight 8- to 10-week-old adult male Sprague-Dawley rats were used. After 3 days of baseline polysomnographic recording, dialysates were collected from the lateral SNR across natural sleep-wake states. Muscimol and bicuculline were microinfused into the lateral SNR. RESULTS: We found that GABA release in the lateral SNR is negatively correlated with slow wave sleep (SWS; R = -0.266, p < 0.01, n = 240) and positively correlated with waking (R = 0.265, p < 0.01, n = 240) in rats. Microinfusion of muscimol into the lateral SNR decreased sleep time and sleep quality, as well as eliciting motor hyperactivity in wake and increased periodic leg movement in SWS, while bicuculline infused into the lateral SNR increased sleep and decreased motor activity in SWS in rats. Muscimol infusion skewed the distribution of inter-movement intervals, with most between 10 and 20 s, while a flat distribution of intervals between 10 and 90 s was seen in baseline conditions. CONCLUSIONS: Activation of the lateral SNR is important for inducing sleep and inhibiting motor activity prior to and during sleep, and thus to the maintenance of sleep. Abnormal function of the lateral SNR may cause hyposomnia and motor hyperactivity in quiet wake and in sleep.

Do all mammals dream?

The presence of dreams in human sleep, especially in REM sleep, and the detection of physiologically similar states in mammals has led many to ponder whether animals experience similar sleep mentation. Recent advances in our understanding of the anatomical and physiological correlates of sleep stages, and thus dreaming, allow a better understanding of the possibility of dream mentation in nonhuman mammals. Here, we explore the potential for dream mentation, in both non-REM and REM sleep across mammals. If we take a hard-stance, that dream mentation only occurs during REM sleep, we conclude that it is unlikely that monotremes, cetaceans, and otariid seals while at sea, have the potential to experience dream mentation. Atypical REM sleep in other species, such as African elephants and Arabian oryx, may alter their potential to experience REM dream mentation. Alternatively, evidence that dream mentation occurs during both non-REM and REM sleep, indicates that all mammals have the potential to experience dream mentation. This non-REM dream mentation may be different in the species where non-REM is atypical, such as during unihemispheric sleep in aquatic mammals (cetaceans, sirens, and Otariid seals). In both scenarios, the cetaceans are the least likely mammalian group to experience vivid dream mentation due to the morphophysiological independence of their cerebral hemispheres. The application of techniques revealing dream mentation in humans to other mammals, specifically those that exhibit unusual sleep states, may lead to advances in our understanding of the neural underpinnings of dreams and conscious experiences.

Sex- and Age-dependent Differences in Sleep-wake Characteristics of Fisher-344 Rats.

Aging is a well-recognized risk factor for sleep disruption. The characteristics of sleep in aging include its disruption by frequent awakenings, a decline in both non-rapid eye movement (nonREM) and REM sleep amounts, and a weaker homeostatic response to sleep loss. Evidence also suggests that sleep in females is more sensitive to changes in the ovarian steroidal milieu. The Fischer-344 rats are commonly used experimental subjects in behavioral and physiological studies, including sleep and aging. Most sleep studies in Fischer-344 rats have used male subjects to avoid interactions between the estrus and sleep-waking cycles. The changes in the sleep-wake organization of female Fischer-344 rats, especially with advancing age, are not well-characterized. We determined sleep-waking features of cycling females across estrus stages. We also compared spontaneous and homeostatic sleep response profiles of young (3-4 months) and old (24-25 months) male and female Fischer-344 rats. The results suggest that: i) sleep-wake architectures across stages of estrus cycle in young females were largely comparable except for a significant suppression of REM sleep at proestrus night and an increase in REM sleep the following day; ii) despite hormonal differences, sleep-wake architecture in male and female rats of corresponding ages were comparable except for the suppression of REM sleep at proestrus night and higher nonREM delta power in recovery sleep; and iii) aging significantly affected sleep-wake amounts, sleep-wake stability, and homeostatic response to sleep loss in both male and female rats and that the adverse effects of aging were largely comparable in both sexes.