Sleep Bouts Research Articles

Hypnotic effects of a novel anti-insomnia formula on Drosophila insomnia model.

To assess the biological effects of the six-herb mixture Anti-Insomia Formula (AIF) extract using caffeine-induced insomnia Drosophila model and short-sleep mutants. Caffeineinduced insomnia wild-type Drosophila and short-sleep mutant flies minisleep (mns) and Hyperkinetic(Y) (Hk(Y)) were used to assess the hypnotic effects of the AIF in vivo. The night time activity, the amount of night time sleep and the number of sleep bouts were determined using Drosophila activity monitoring system. Sleep was defined as any period of uninterrupted behavioral immobility (0 count per minute) lasting > 5 min. Night time sleep was calculated by summing up the sleep time in the dark period. Number of sleep bouts was calculated by counting the number of sleep episodes in the dark period. AIF at the dosage of 50 mg/mL, effectively attenuated caffeine-induced wakefulness (P<0.01) in wild-type Canton-S flies as indicated by the reduction of the sleep bouts, night time activities and increase of the amount of night time sleep. AIF also significantly reduced sleeping time of short-sleep Hk(Y) mutant flies (P<0.01). However, AIF did not produce similar effect in mns mutants. AIF might be able to rescue the abnormal condition caused by mutated modulatory subunit of the tetrameric potassium channel, but not rescuing the abnormal nerve firing caused by Shaker gene mutation. This study provides the scientific evidence to support the use of AIF in Chinese medicine for promoting sleep quality in insomnia.

Sleep and vigilance linked to melanism in wild barn owls.

Understanding the function of variation in sleep requires studies in the natural ecological conditions in which sleep evolved. Sleep has an impact on individual performance and hence may integrate the costs and benefits of investing in processes that are sensitive to sleep, such as immunity or coping with stress. Because dark and pale melanic animals differentially regulate energy homeostasis, immunity and stress hormone levels, the amount and/or organization of sleep may covary with melanin-based colour. We show here that wild, cross-fostered nestling barn owls (Tyto alba) born from mothers displaying more black spots had shorter non-REM (rapid eye movement) sleep bouts, a shorter latency until the occurrence of REM sleep after a bout of wakefulness and more wakefulness bouts. In male nestlings, the same sleep traits also correlated with their own level of spotting. Because heavily spotted male nestlings and the offspring of heavily spotted biological mothers switched sleep-wakefulness states more frequently, we propose the hypothesis that they could be also behaviourally more vigilant. Accordingly, nestlings from mothers displaying many black spots looked more often towards the nest entrance where their parents bring food and towards their sibling against whom they compete. Owlets from heavily spotted mothers might invest more in vigilance, thereby possibly increasing associated costs due to sleep fragmentation. We conclude that different strategies of the regulation of brain activity have evolved and are correlated with melanin-based coloration.

Effects of acute sleep deprivation on motor and reversal learning in mice

Sleep supports the formation of a variety of declarative and non-declarative memories, and sleep deprivation often impairs these types of memories. In human subjects, natural sleep either during a nap or overnight leads to long-lasting improvements in visuomotor and fine motor tasks, but rodent models recapitulating these findings have been scarce. Here we present evidence that 5h of acute sleep deprivation impairs mouse skilled reach learning compared to a matched period of ad libitum sleep. In sleeping mice, the duration of total sleep time during the 5h of sleep opportunity or during the first bout of sleep did not correlate with ultimate gain in motor performance. In addition, we observed that reversal learning during the skilled reaching task was also affected by sleep deprivation. Consistent with this observation, 5h of sleep deprivation also impaired reversal learning in the water-based Y-maze. In conclusion, acute sleep deprivation negatively impacts subsequent motor and reversal learning and memory.

The Role of Circadian Rhythms, Light and Melatonin in SAD and Nonseasonal Affective and Anxiety Disorders

More than three decades ago, bright light was found to be able to suppress melatonin production in humans, a finding which quickly led to identification of seasonal affective disorder (SAD) and its treatment with light. However, current thinking supports a phase shift hypothesis (PSH), according to which SAD is a disorder primarily of phasedelayed circadian misalignment {best assessed by the time interval [or phase angle difference (PAD)]} between the dim light melatonin onset (DLMO) and the midpoint of the sleep bout. It has been heuristically useful to use PAD 6 (a time interval of six hours) as the “sweet spot” for SAD: most patients with SAD have phase-delayed circadian misalignment (that is, have PADs ≤ 6), which explains why bright light exposure scheduled at waketime is the optimal treatment for most patients with SAD. Low-dose melatonin taken in the afternoon/evening also provides a corrective phase advance and is therefore an alternative or “add-on” treatment for these patients. The other SAD patients appear to be phase advanced (with PADs > 6) and respond to evening light and morning melatonin. Other hypotheses have not stood the test of time, including the two-oscillator dawn/dusk model of the endogenous circadian pacemaker which has been at least heuristically useful in rodents. However, recent research on multiple oscillators in the SCN and brain, as well as in other tissues and organs, may yet yield a more refined understanding of circadian misalignment. The salivary home DLMO may soon be the first laboratory test for a psychiatric disorder.

Correlations between depression behaviors and sleep parameters after repeated corticosterone injections in rats.

Disrupted sleep may be a prodromal symptom or a predictor of depressive disorders. In this study we investigated the relationship between depression symptoms and disrupted sleep using a novel model of stress-mimicked sleep disorders in rats. SD rats were injected with corticosterone (10, 20 or 40 mg/kg, sc) or vehicle for 7 d. Their sleep-wake behavior was monitored through implanted EEG and EMG electrodes. Their depressive behaviors were assessed using forced swim test, open field test and sucrose preference test. The corticosterone-treated rats showed significantly reduced sleep time, disinhibition of rapid-eye-movement (REM) sleep and altered power spectra during non-REM sleep. All depressive behavioral tests did not show significant difference across the groups. However, individual correlation analysis revealed statistically significance: the immobility time (despair) was negatively correlated with REM sleep latency, slow wave sleep (SWS) time ratio, SWS bouts and delta power density, and it was positively correlated with REM sleep bouts and beta power density. Meanwhile, sucrose preference (anhedonia) was positively correlated with total sleep time and light sleep bouts, and it was negatively correlated with the REM sleep time ratio. In stress-mimicked rats, sleep disturbances are a predictor of depressive disorders, and certain symptoms of depression may be related to the disruption of several specific sleep parameters.

MODELING SLEEP AND WAKE BOUTS IN DROSOPHILA MELANOGASTER

Adequate sleep restores vital processes required for health and well-being; but the function and regulation of sleep is not well understood. Unfortunately, a definition of adequate sleep is unclear. On an hours-long timescale, consolidated and cycling sleep results in better health and performance outcomes. At shorter timescales, older studies report conflicting results regarding the relationship between sleep and wake bout durations. One approach to this problem has been to simply analyze the distribution of bout durations. While informative, this method eliminates the time relationship between bouts, which may be important. Here, we develop a model that describes the relationship between sleep and wake bout durations using the model organism, Drosophila melanogaster, which exhibits behavioral and molecular homology to human sleep. We present an exploratory analysis of the data to gain a better understanding of the sleep bout duration distribution by considering a broader range of potential distributions than considered in previous studies. We use the results of the distribution analysis to develop a model for sleep bout durations in the fly based upon their past sleep and wake history and find that this relationship should not be ignored.

The incidence and temporal patterning of insomnia: a second study

Whether subjects with insomnia exhibit good sleep on some interval basis is unclear. Prior research suggests that patients with insomnia are highly variable with respect to night-to-night sleep continuity, that more than 40% of patients exhibit temporal patterning of good sleep, and that nearly 90% of patients exhibit better than average sleep following 1 to 3 nights of relatively poor sleep. The aim of the present study was to replicate and extend the above-noted findings utilizing: (i) a large sample studied over an extended time interval (ii) absolute standards for 'good' and 'poor' sleep; and (iii) a formal statistical methodology to assess temporal patterning and the association of time in bed with bout duration of poor or average sleep. Thirty-three subjects with insomnia and 33 good sleepers completed sleep diaries over the course of 110 days. It was found that subjects with insomnia (compared to good sleepers) had more poor nights (e.g. about 39 versus 7% of the assessed nights), a higher probability of a having a poor night on any given occasion (60% greater probability than good sleepers) and more consecutive nights of poor sleep between good sleep nights (median bout duration of approximately three versus one night). Lastly, it was found that (as would be predicted by both the Spielman model and the two-process model) time in bed moderated bout duration in the insomnia group. That is, longer times in bed were associated with longer bouts of poor sleep.

Diffuse brain injury does not affect chronic sleep patterns in the mouse

Primary objective: To test if the current model of diffuse brain injury produces chronic sleep disturbances similar to those reported by TBI patients.Methods and procedures: Adult male C57BL/6 mice were subjected to moderate midline fluid percussion injury (n = 7; 1.4 atm; 6–10 minutes righting reflex time) or sham injury (n = 5). Sleep–wake activity was measured post-injury using a non-invasive, piezoelectric cage system. Chronic sleep patterns were analysed weekly for increases or decreases in percentage sleep (hypersomnia or insomnia) and changes in bout length (fragmentation).Main outcomes and results: During the first week after diffuse TBI, brain-injured mice exhibited increased mean percentage sleep and mean bout length compared to sham-injured mice. Further analysis indicated the increase in mean percentage sleep occurred during the dark cycle. Injury-induced changes in sleep, however, did not extend beyond the first week post-injury and were not present in weeks 2–5 post-injury.Conclusions: Previously, it has been shown that the midline fluid percussion model used in this study immediately increased post-traumatic sleep. The current study extended the timeline of investigation to show that sleep disturbances extended into the first week post-injury, but did not develop into chronic sleep disturbances. However, the clinical prevalence of TBI-related sleep–wake disturbances warrants further experimental investigation.

The Circadian Clock Gene Csnk1e Regulates Rapid Eye Movement Sleep Amount, and Nonrapid Eye Movement Sleep Architecture in Mice

Efforts to identify the genetic basis of mammalian sleep have included quantitative trait locus (QTL) mapping and gene targeting of known core circadian clock genes. We combined three different genetic approaches to identify and test a positional candidate sleep gene - the circadian gene casein kinase 1 epsilon (Csnk1e), which is located in a QTL we identified for rapid eye movement (REM) sleep on chromosome 15. Using electroencephalographic (EEG) and electromyographic (EMG) recordings, baseline sleep was examined in a 12-h light:12-h dark (LD 12:12) cycle in mice of seven genotypes, including Csnk1e(tau/tau) and Csnk1e(-/-) mutant mice, Csnk1e (B6.D2) and Csnk1e (D2.B6) congenic mice, and their respective wild-type littermate control mice. Additionally, Csnk1e(tau/tau) and wild-type mice were examined in constant darkness (DD). Csnk1e(tau/tau) mutant mice and both Csnk1e (B6.D2) and Csnk1e (D2.B6) congenic mice showed significantly higher proportion of sleep time spent in REM sleep during the dark period than wild-type controls - the original phenotype for which the QTL on chromosome 15 was identified. This phenotype persisted in Csnk1e(tau/tau) mice while under free-running DD conditions. Other sleep phenotypes observed in Csnk1e(tau/tau) mice and congenics included a decreased number of bouts of nonrapid eye movement (NREM) sleep and an increased average NREM sleep bout duration. These results demonstrate a role for Csnk1e in regulating not only the timing of sleep, but also the REM sleep amount and NREM sleep architecture, and support Csnk1e as a causal gene in the sleep QTL on chromosome 15.

Agomelatine restores a physiological response to stress in the aged rat

Short duration immobilization stress (IS) in younger rats is followed by a sleep rebound involving slow wave sleep (SWS) and, more particularly, rapid eye movement (REM) sleep. This rebound, expressing the ability of the brain to confront a stress challenge, is now accepted as a marker of the homeostasis. In older rats (24–25 months), however, an IS of 1h is not followed by a sleep rebound. To determine whether this impairment is reversible, we analyzed the effects of the antidepressant agomelatine, on stress-related sleep rebound in older animals. Older and younger (3–5 months) rats were equipped with electroencephalographic (EEG) and electromyographic (EMG) electrodes and polygraphic recordings were achieved under basal conditions with a digitized set-up. Older rats were pretreated with agomelatine (40mg/kg/day) for 3 days, with IS applied on the third day, whereas younger rats were only subjected to IS. Polygraphic recordings achieved under basal conditions confirmed the conventional impairments of the sleep/wake architecture in older animals, including decreased delta power, shortened REM sleep bouts, and modified sleep/wake circadian rhythms. Older rats pretreated with agomelatine for 3 days showed a reversal of the deficit observed in the beta-1, but not in the delta, EEG power band. Application of an IS to older rats after agomelatine pretreatment resulted in a REM sleep rebound in response to stress. These findings indicate that agomelatine, by improving beta-1 EEG power band and by inducing stress-related sleep rebound in older animals, contributes to the homeostasis maintenance.

Endocannabinoid Modulation of Cortical Up-States and NREM Sleep

Up-/down-state transitions are a form of network activity observed when sensory input into the cortex is diminished such as during non-REM sleep. Up-states emerge from coordinated signaling between glutamatergic and GABAergic synapses and are modulated by systems that affect the balance between inhibition and excitation. We hypothesized that the endocannabinoid (EC) system, a neuromodulatory system intrinsic to the cortical microcircuitry, is an important regulator of up-states and sleep. To test this hypothesis, up-states were recorded from layer V/VI pyramidal neurons in organotypic cultures of wild-type or CB1R knockout (KO) mouse prefrontal cortex. Activation of the cannabinoid 1 receptor (CB1) with exogenous agonists or by blocking metabolism of endocannabinoids, anandamide or 2-arachidonoyl glycerol, increased up-state amplitude and facilitated action potential discharge during up-states. The CB1 agonist also produced a layer II/III-selective reduction in synaptic GABAergic signaling that may underlie its effects on up-state amplitude and spiking. Application of CB1 antagonists revealed that an endogenous EC tone regulates up-state duration. Paradoxically, the duration of up-states in CB1 KO cultures was increased suggesting that chronic absence of EC signaling alters cortical activity. Consistent with increased cortical excitability, CB1 KO mice exhibited increased wakefulness as a result of reduced NREM sleep and NREM bout duration. Under baseline conditions, NREM delta (0.5–4 Hz) power was not different in CB1 KO mice, but during recovery from forced sleep deprivation, KO mice had reduced NREM delta power and increased sleep fragmentation. Overall, these findings demonstrate that the EC system actively regulates cortical up-states and important features of NREM sleep such as its duration and low frequency cortical oscillations.

Diffuse Brain Injury Induces Acute Post-Traumatic Sleep

ObjectiveClinical observations report excessive sleepiness immediately following traumatic brain injury (TBI); however, there is a lack of experimental evidence to support or refute the benefit of sleep following a brain injury. The aim of this study is to investigate acute post-traumatic sleep.MethodsSham, mild or moderate diffuse TBI was induced by midline fluid percussion injury (mFPI) in male C57BL/6J mice at 9:00 or 21:00 to evaluate injury-induced sleep behavior at sleep and wake onset, respectively. Sleep profiles were measured post-injury using a non-invasive, piezoelectric cage system. In separate cohorts of mice, inflammatory cytokines in the neocortex were quantified by immunoassay, and microglial activation was visualized by immunohistochemistry.ResultsImmediately after diffuse TBI, quantitative measures of sleep were characterized by a significant increase in sleep (>50%) for the first 6 hours post-injury, resulting from increases in sleep bout length, compared to sham. Acute post-traumatic sleep increased significantly independent of injury severity and time of injury (9:00 vs 21:00). The pro-inflammatory cytokine IL-1β increased in brain-injured mice compared to sham over the first 9 hours post-injury. Iba-1 positive microglia were evident in brain-injured cortex at 6 hours post-injury.ConclusionPost-traumatic sleep occurs for up to 6 hours after diffuse brain injury in the mouse regardless of injury severity or time of day. The temporal profile of secondary injury cascades may be driving the significant increase in post-traumatic sleep and contribute to the natural course of recovery through cellular repair.

The development of sleep–wake rhythms and the search for elemental circuits in the infant brain.

Despite the predominance of sleep in early infancy, developmental science has yet to play a major role in shaping concepts and theories about sleep and its associated ultradian and circadian rhythms. Here we argue that developmental analyses help us to elucidate the relative contributions of the brainstem and forebrain to sleep-wake control and to dissect the neural components of sleep-wake rhythms. Developmental analysis also makes it clear that sleep-wake processes in infants are the foundation for those of adults. For example, the infant brainstem alone contains a fundamental sleep-wake circuit that is sufficient to produce transitions among wakefulness, quiet sleep, and active sleep. In addition, consistent with the requirements of a "flip-flop" model of sleep-wake processes, this brainstem circuit supports rapid transitions between states. Later in development, strengthening bidirectional interactions between the brainstem and forebrain contribute to the consolidation of sleep and wake bouts, the elaboration of sleep homeostatic processes, and the emergence of diurnal or nocturnal circadian rhythms. The developmental perspective promoted here critically constrains theories of sleep-wake control and provides a needed framework for the creation of fully realized computational models. Finally, with a better understanding of how this system is constructed developmentally, we will gain insight into the processes that govern its disintegration due to aging and disease.

Effects of Chronic Sleep Fragmentation on Wake-Active Neurons and the Hypercapnic Arousal Response

Delayed hypercapnic arousals may occur in obstructive sleep apnea. The impaired arousal response is expected to promote more pronounced oxyhemoglobin desaturations. We hypothesized that long-term sleep fragmentation (SF) results in injury to or dysfunction of wake-active neurons that manifests, in part, as a delayed hypercapnic arousal response. Adult male mice were implanted for behavioral state recordings and randomly assigned to 4 weeks of either orbital platform SF (SF4wk, 30 events/h) or control conditions (Ct4wk) prior to behavioral, histological, and locus coeruleus (LC) whole cell electrophysiological evaluations. SF was successfully achieved across the 4 week study, as evidenced by a persistently increased arousal index, P < 0.01 and shortened sleep bouts, P < 0.05, while total sleep/wake times and plasma corticosterone levels were unaffected. A multiple sleep latency test performed at the onset of the dark period showed a reduced latency to sleep in SF4wk mice (P < 0.05). The hypercapnic arousal latency was increased, Ct4wk 64 ± 5 sec vs. SF4wk 154 ± 6 sec, P < 0.001, and remained elevated after a 2 week recovery (101 ± 4 sec, P < 0.001). C-fos activation in noradrenergic, orexinergic, histaminergic, and cholinergic wake-active neurons was reduced in response to hypercapnia (P < 0.05-0.001). Catecholaminergic and orexinergic projections into the cingulate cortex were also reduced in SF4wk (P < 0.01). In addition, SF4wk resulted in impaired LC neuron excitability (P < 0.01). Four weeks of sleep fragmentation (SF4wk) impairs arousal responses to hypercapnia, reduces wake neuron projections and locus coeruleus neuronal excitability, supporting the concepts that some effects of sleep fragmentation may contribute to impaired arousal responses in sleep apnea, which may not reverse immediately with therapy.

PTPRD expression regulates sleep consolidation in Drosophila

Restless legs syndrome/Willis-Ekbom Disease (RLS/WED) is a common sleep disorder, yet its underlying pathophysiology is poorly understood. Genome-wide association studies (GWAS) point to allelic variants in multiple genes that confer susceptibility to RLS/WED. They offer potential insights into molecular pathways that govern expressivity of symptoms and signs. We used Drosophila melanogaster to explore sleep related physiology of two genes harboring at-risk alleles for RLS which also have highly conserved fly homologs, BTBD9 and PTPRD. Here, we complement our recent report of RLS phenotypes in BTBD9 mutants by exploring whether similar phenotypes exist in PTPRD mutants and probe whether sleep phenotypes are mimicked by dual mutants (i.e., suggesting a common molecular pathway) or are more severely disrupted (i.e., consistent with parallel pathways). Sleep phenotypes resulting from mutations in the fly homolog of PTPRD (dLar) were assayed with the Drosophila Activity Monitor. Flies transgenic for either mutated or wild-type dLar protein allowed for cell-specific manipulation of expression levels. The impact of combined dLar and BTBD9 mutations on sleep architecture was also assessed. Disruption of dLar/PTPRD expression in flies yielded viable, hyperlocomotive animals. dLar mutants exhibit sleep fragmentation and increased wake after sleep onset similar to that observed in BTBD9 mutant flies, the latter of which bears close resemblance to human RLS. The magnitude of fragmentation, as measured by sleep bout number and average sleep bout length, was not further increased by introduction of BTBD9 mutations into the dLar mutant background. Neuron specific expression of dLar constructs, using the GAL4-UAS system, yielded disrupted sleep consolidation similar to whole animal dLar mutants. These results further validate GWAS as a hypothesis independent means to delineate the molecular pathophysiology underlying RLS/WED. While the role of PTPRD in neuronal development and plasticity has been studied previously in flies, this is the first exploration of its function in the context of sleep and, more specifically, RLS/WED. Our results suggest neuronal PTPRD expression regulates sleep architecture and most likely operates in a molecular pathway that also includes BTBD9. Ongoing efforts to delineate the mechanistic basis of sleep regulation by PTPRD and BTBD9 are underway. Supported by RLS Foundation, Sleep Research Society, and Emory Neuroscience Initiative grants to S.S.

Maternal accounts of their breast-feeding intent and early challenges after caesarean childbirth

Backgroundbreast-feeding outcomes are often worse after caesarean section compared to vaginal childbirth. Objectivesthis study characterises mothers' breast-feeding intentions and their infant feeding experiences after caesarean childbirth. Methodsdata are from 115 mothers on a postnatal unit in Northeast England during February 2006–March 2009. Interviews were conducted an average of 1.5 days (range 1–6 days) after the women underwent unscheduled or scheduled caesarean. Resultsthematic analysis of the data suggested was mostly considered the ‘right thing to do,’ preferable, natural, and ‘supposedly healthier,’ but tiring and painful. Advantages of supplementation involved more satiated infants, feeding ease, and longer sleep bouts. The need for ‘thinking about yourself’ was part of caesarean recovery. Infrequent feeding was concerning but also enabled maternal rest. Other breast-feeding obstacles were maternal mobility limitations, positioning difficulties, and frustration at the need for assistance. Participants were confused about nocturnal infant wakings, leading many to determine that they had insufficient milk. Mothers were surprised that sub-clinically poor infant condition was common following caesarean section. Some breast-feeding difficulty stemmed from ‘mucus’ expulsion that had to occur before the infants could be ‘interested’ in feeding. Women who cited motivations for breast feeding that included benefit to themselves were more likely to exclusively breast feed on the postnatal unit after their caesareans than those who reported infant-only motivations. Conclusionsfor the majority of mothers, breast feeding after a caesarean is affected by interrelated and compounding difficulties. Provision of more relational breast-feeding information may enable families to better anticipate early feeding experiences after caesarean section childbirth.

Essential Roles of GABA Transporter-1 in Controlling Rapid Eye Movement Sleep and in Increased Slow Wave Activity after Sleep Deprivation

GABA is the major inhibitory neurotransmitter in the mammalian central nervous system that has been strongly implicated in the regulation of sleep. GABA transporter subtype 1 (GAT1) constructs high affinity reuptake sites for GABA and regulates GABAergic transmission in the brain. However, the role of GAT1 in sleep-wake regulation remains elusive. In the current study, we characterized the spontaneous sleep-wake cycle and responses to sleep deprivation in GAT1 knock-out (KO) mice. GAT1 KO mice exhibited dominant theta-activity and a remarkable reduction of EEG power in low frequencies across all vigilance stages. Under baseline conditions, spontaneous rapid eye movement (REM) sleep of KO mice was elevated both during the light and dark periods, and non-REM (NREM) sleep was reduced during the light period only. KO mice also showed more state transitions from NREM to REM sleep and from REM sleep to wakefulness, as well as more number of REM and NREM sleep bouts than WT mice. During the dark period, KO mice exhibited more REM sleep bouts only. Six hours of sleep deprivation induced rebound increases in NREM and REM sleep in both genotypes. However, slow wave activity, the intensity component of NREM sleep was briefly elevated in WT mice but remained completely unchanged in KO mice, compared with their respective baselines. These results indicate that GAT1 plays a critical role in the regulation of REM sleep and homeostasis of NREM sleep.

Hypersomnolence and Reduced Activity in Pan-Leptin Receptor Knockout Mice

Excessive obesity correlates with hypersomnolence and impaired cognitive function, presumably induced by metabolic factors and cytokines. Production of the adipokine leptin correlates with the amount of adiposity, and leptin has been shown to promote sleep. To determine whether leptin plays a major role in the hypersomnolence of obesity, we measured sleep architecture in pan-leptin receptor knockout (POKO) mice that do not respond to leptin because of the production of a mutant, non-signaling receptor. The obese POKO mice had more non-rapid eye movement (NREM) sleep and less waking time than their littermate controls. This was mainly seen during the light span, although increased bouts of rapid eye movement sleep were also seen in the dark span. The increase of NREM sleep correlated with the extent of obesity. The POKO mice also had decreased locomotor activity and more immobility in the open field test, but there was no increase of forced immobility nor reduction of sucrose intake as would be seen in depression. The increased NREM sleep and reduced locomotor activity in the POKO mice suggest that it was obesity, rather than leptin signaling, that played a predominant role in altering sleep architecture and activity.

Chronic Alterations in Monoaminergic Cells in the Locus Coeruleus in Orexin Neuron-Ablated Narcoleptic Mice

Narcolepsy patients often suffer from insomnia in addition to excessive daytime sleepiness. Narcoleptic animals also show behavioral instability characterized by frequent transitions between all vigilance states, exhibiting very short bouts of NREM sleep as well as wakefulness. The instability of wakefulness states in narcolepsy is thought to be due to deficiency of orexins, neuropeptides produced in the lateral hypothalamic neurons, which play a highly important role in maintaining wakefulness. However, the mechanism responsible for sleep instability in this disorder remains to be elucidated. Because firing of orexin neurons ceases during sleep in healthy animals, deficiency of orexins does not explain the abnormality of sleep. We hypothesized that chronic compensatory changes in the neurophysiologica activity of the locus coeruleus (LC) and dorsal raphe (DR) nucleus in response to the progressive loss of endogenous orexin tone underlie the pathological regulation of sleep/wake states. To evaluate this hypothesis, we examined firing patterns of serotonergic (5-HT) neurons and noradrenergic (NA) neurons in the brain stem, two important neuronal populations in the regulation of sleep/wakefulness states. We recorded single-unit activities of 5-HT neurons and NA neurons in the DR nucleus and LC of orexin neuron-ablated narcoleptic mice. We found that while the firing pattern of 5-HT neurons in narcoleptic mice was similar to that in wildtype mice, that of NA neurons was significantly different from that in wildtype mice. In narcoleptic mice, NA neurons showed a higher firing frequency during both wakefulness and NREM sleep as compared with wildtype mice. In vitro patch-clamp study of NA neurons of narcoleptic mice suggested a functional decrease of GABAergic input to these neurons. These alterations might play roles in the sleep abnormality in narcolepsy.

Regulation of sleep by the short neuropeptide F (sNPF) in Drosophila melanogaster

The short neuropeptide F (sNPF), a neuropeptide in the central nervous system (CNS) of Drosophila melanogaster, is expressed in a large population of diverse neurons of brain. Most of these neurons are intrinsic interneurons of the mushroom bodies, which are the most prominent insect bilateral CNS structures that regulate memory and sleep. However, its role in sleep regulation still remains elusive. Here, we showed that sNPF-deficient female and male flies exhibit sleep enhancement with an increase of sleep bout duration. Loss of function of sNPF and sNPFR1 also elevated sleep. Moreover, the homeostatic regulation of flies after sleep deprivation was disrupted by aberrant sNPF signaling, since sleep deprivation increased transcription of sNPF and wakefulness at night in control flies but not in the sNPF mutant flies, suggesting that sNPF autoregulation plays an important role in sleep homeostasis. We further verified that sNPF signal elevated cAMP levels, and subsequently activated the downstream CREB transcription factor. The duration of sleep was found to be inversely related to cAMP signaling and CREB activity in the mushroom bodies. Thus, we concluded that sleep might be regulated by sNPF through modulating the cAMP-PKA-CREB signal pathway in vivo.