Spontaneous sleep and homeostatic sleep regulation in ghrelin knockout mice

Ghrelin is well known for its feeding and growth hormone-releasing actions. It may also be involved in sleep regulation; intracerebroventricular administration and hypothalamic microinjections of ghrelin stimulate wakefulness in rats. Hypothalamic ghrelin, together with neuropeptide Y and orexin form a food intake-regulatory circuit. We hypothesized that this circuit also promotes arousal. To further investigate the role of ghrelin in the regulation of sleep-wakefulness, we characterized spontaneous and homeostatic sleep regulation in ghrelin knockout (KO) and wild-type (WT) mice. Both groups of mice exhibited similar diurnal rhythms with more sleep and less wakefulness during the light period. In ghrelin KO mice, spontaneous wakefulness and rapid-eye-movement sleep (REMS) were slightly elevated, and non-rapid-eye-movement sleep (NREMS) was reduced. KO mice had more fragmented NREMS than WT mice, as indicated by the shorter and greater number of NREMS episodes. Six hours of sleep deprivation induced rebound increases in NREMS and REMS and biphasic changes in electroencephalographic slow-wave activity (EEG SWA) in both genotypes. Ghrelin KO mice recovered from NREMS and REMS loss faster, and the delayed reduction in EEG SWA, occurring after sleep loss-enhanced increases in EEG SWA, was shorter-lasting compared with WT mice. These findings suggest that the basic sleep-wake regulatory mechanisms in ghrelin KO mice are not impaired and they are able to mount adequate rebound sleep in response to a homeostatic challenge. It is possible that redundancy in the arousal systems of the brain or activation of compensatory mechanisms during development allow for normal sleep-wake regulation in ghrelin KO mice.     

Central administration of neuropeptide Y induces wakefulness in rats

Neuropeptide Y (NPY) is a well-characterized neuromodulator in the central nervous system, primarily implicated in the regulation of feeding. NPY, orexins, and ghrelin form a hypothalamic food intake regulatory circuit. Orexin and ghrelin are also implicated in sleep-wake regulation. In the present experiments, we studied the sleep-modulating effects of central administration of NPY in rats. Rats received intracerebroventricular injection of physiological saline or three different doses of NPY (0.4, 2, and 10 microg in a volume of 4 microl) at light onset. Another group of rats received bilateral microinjection of saline or 2 microg NPY in the lateral hypothalamus in a volume of 0.2 microl. Sleep-wake activity and motor activity were recorded for 23 h. Food intake after the control and treatment injections was also measured on separate days. Intracerebroventricular and lateral hypothalamic administration of NPY suppressed non-rapid-eye-movement sleep and rapid-eye-movement sleep in rats during the first hour after the injection and also induced changes in electroencephalogram delta power spectra. NPY stimulated food intake in the first hour after both routes of administration. Data are consistent with the hypothesis that NPY has a role in the integration of feeding, metabolism, and sleep regulation.     

Altered sleep and behavioral activity phenotypes in PER3-deficient mice

Sleep homeostasis and circadian rhythmicity interact to determine the timing of behavioral activity. Circadian clock genes contribute to circadian rhythmicity centrally and in the periphery, but some also have roles within sleep regulation. The clock gene Period3 (Per3) has a redundant function within the circadian system and is associated with sleep homeostasis in humans. This study investigated the role of PER3 in sleep/wake activity and sleep homeostasis in mice by recording wheel-running activity under baseline conditions in wild-type (WT; n = 54) and in PER3-deficient (Per3(-/-); n = 53) mice, as well as EEG-assessed sleep before and after 6 h of sleep deprivation in WT (n = 7) and Per3(-/-) (n = 8) mice. Whereas total activity and vigilance states did not differ between the genotypes, the temporal distribution of wheel-running activity, vigilance states, and EEG delta activity was affected by genotype. In Per3(-/-) mice, running wheel activity was increased, and REM sleep and NREM sleep were reduced in the middle of the dark phase, and delta activity was enhanced at the end of the dark phase. At the beginning of the baseline light period, there was less wakefulness and more REM and NREM sleep in Per3(-/-) mice. Per3(-/-) mice spent less time in wakefulness and more time in NREM sleep in the light period immediately after sleep deprivation, and REM sleep accumulated more slowly during the recovery dark phase. These data confirm a role for PER3 in sleep-wake timing and sleep homeostasis.     

Rhythms of ghrelin, leptin, and sleep in rats: effects of the normal diurnal cycle, restricted feeding, and sleep deprivation

To determine the relationships among plasma ghrelin and leptin concentrations and hypothalamic ghrelin contents, and sleep, cortical brain temperature (Tcrt), and feeding, we determined these parameters in rats in three experimental conditions: in free-feeding rats with normal diurnal rhythms, in rats with feeding restricted to the 12-h light period (RF), and in rats subjected to 5-h of sleep deprivation (SD) at the beginning of the light cycle. Plasma ghrelin and leptin displayed diurnal rhythms with the ghrelin peak preceding and the leptin peak following the major daily feeding peak in hour 1 after dark onset. RF reversed the diurnal rhythm of these hormones and the rhythm of rapid-eye-movement sleep (REMS) and significantly altered the rhythm of Tcrt. In contrast, the duration and intensity of non-REMS (NREMS) were hardly responsive to RF. SD failed to change leptin concentrations, but it promptly stimulated plasma ghrelin and induced eating. SD elicited biphasic variations in the hypothalamic ghrelin contents. SD increased plasma corticosterone, but corticosterone did not seem to influence either leptin or ghrelin. The results suggest a strong relationship between feeding and the diurnal rhythm of leptin and that feeding also fundamentally modulates the diurnal rhythm of ghrelin. The variations in hypothalamic ghrelin contents might be associated with sleep-wake activity in rats, but, unlike the previous observations in humans, obvious links could not be detected between sleep and the diurnal rhythms of plasma concentrations of either ghrelin or leptin in the rat.     

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.     

Ghrelin microinjection into forebrain sites induces wakefulness and feeding in rats

Ghrelin, a gut-brain peptide, is best known for its role in the stimulation of feeding and growth hormone release. In the brain, orexin, neuropeptide Y (NPY), and ghrelin are parts of a food intake regulatory circuit. Orexin and NPY are also implicated in maintaining wakefulness. Previous experiments in our laboratory revealed that intracerebroventricular injections of ghrelin induce wakefulness in rats. To further elucidate the possible role of ghrelin in the regulation of arousal, we studied the effects of microinjections of ghrelin into hypothalamic sites, which are implicated in the regulation of feeding and sleep, such as the lateral hypothalamus (LH), medial preoptic area (MPA), and paraventricular nucleus (PVN) on sleep in rats. Sleep responses, motor activity, and food intake after central administration of 0.04, 0.2, or 1 mug (12, 60, or 300 pmol) ghrelin were recorded. Microinjections of ghrelin into the LH had strong wakefulness-promoting effects lasting for 2 h. Wakefulness was also stimulated by ghrelin injection into the MPA and PVN; the effects were confined to the first hour after the injection. Ghrelin's non-rapid-eye-movement sleep-suppressive effect was accompanied by attenuation in the electroencephalographic (EEG) slow-wave activity and changes in the EEG power spectrum. Food consumption was significantly stimulated after microinjections of ghrelin into each hypothalamic site. Together, these results are consistent with the hypothesis that forebrain ghrelinergic mechanisms play a role in the regulation of vigilance, possibly through activating the components of the food intake- and arousal-promoting network formed by orexin and NPY.     

Antagonism of corticotropin-releasing hormone alters serotonergic-induced changes in brain temperature, but not sleep, of rats

Serotonin is involved in many physiological processes, including the regulation of sleep and body temperature. Administration into rats of low doses (25, 50 mg/kg) of the 5-HT precursor l-5-hydroxytryptophan (5-HTP) at the beginning of the dark period of the 12:12-h light-dark cycle initially increases wakefulness. Higher doses (75, 100 mg/kg) increase nonrapid eye movement (NREM) sleep. The initial enhancement of wakefulness after low-dose 5-HTP administration may be a direct action of 5-HT in brain or due to 5-HT-induced activation of other arousal-promoting systems. One candidate arousal-promoting system is corticotropin-releasing hormone (CRH) and the hypothalamic-pituitary-adrenal axis. Serotonergic activation by 5-HTP at the beginning of the dark period also induces hypothermia. Because sleep and body temperature are influenced by circadian factors, one aim of this study was to determine responses to 5-HTP when administered at a different circadian time, the beginning of the light period. Results obtained show that all doses of 5-HTP (25-100 mg/kg) administered at light onset initially increase wakefulness; NREM sleep increases only after a long delay, during the subsequent dark period. Serotonergic activation by 5-HTP at light onset induces hypothermia, the time course of which is biphasic after higher doses (75, 100 mg/kg). Intracerebroventricular pretreatment with the CRH receptor antagonist alpha-helical CRH does not alter the impact of 5-HTP on sleep-wake behavior but potentiates the hypothermic response to 50 mg/kg 5-HTP. These data suggest that serotonergic activation by peripheral administration of 5-HTP may modulate sleep-wake behavior by mechanisms in addition to direct actions in brain and that circadian systems are important determinants of the impact of serotonergic activation on sleep and body temperature.     

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.     

Day- and nighttime injection of a nitric oxide synthase inhibitor elicits opposite sleep responses in rats

Previous studies suggest that nitric oxide (NO) may play a role in sleep regulation, particularly in the homeostatic process. The present studies were undertaken to compare the sleep effects of injecting a NO synthase (NOS) inhibitor when homeostatic sleep pressure is naturally highest (light onset) or when it is at its nadir (dark onset) in rats. Sleep, electroencephalogram delta-wave activity during nonrapid eye movement sleep (NREMS), also known as slow-wave activity (SWA), and brain temperature responses to three doses of the NOS inhibitor N(omega)-nitro-L-arginine methyl ester (L-NAME ; 5, 50, and 100 mg/kg) injected intraperitoneally at light or dark onset were examined in rats (n = 6 to 8). The effects of 5 mg/kg L-NAME were determined in both normal and vagotomized (VX) rats. Light onset administration of 50 mg/kg L-NAME decreased NREMS amounts and suppressed SWA and increased rapid eye movement sleep (REMS) amounts. At dark onset, L-NAME injection also dose dependently suppressed SWA; however, unlike light onset injections, both NREMS and REMS amounts were increased after all three doses. Sleep responses to 5 mg/kg L-NAME were not different in control and VX rats, suggesting that the sleep effects of L-NAME are not mediated through the activation of sensory vagal mechanisms. The present findings suggest that timing of the injection is a major determinant of the sleep responses observed after systemic L-NAME injection in rats.     

Promotion of non-rapid eye movement sleep in mice after oral administration of ornithine

We examined the effects of ornithine on the sleep-wake cycle by monitoring the electroencephalo-gram, electromyogram, and locomotor activity of freely moving mice after oral administration of it at lights-off time (18:00). Ornithine (1.0 and 3.0 g/kg of body weight) increased the amount of non-rapid eye movement (non-REM, NREM) sleep for 2 h after its administration, with a peak at 60 min post administration, to 164% and 198%, respectively, of that of the vehicle-administered mice, without changing the amount of REM sleep. The administration of ornithine at a lower dose (0.3 g/kg of body weight) did not increase the amount of NREM sleep compared with the vehicle administration. Ornithine did not affect the power spectrum density of NREM sleep but increased the number of episodes of wakefulness and NREM sleep and that of transitions between wakefulness and NREM sleep, and decreased the mean duration of wake episodes in a dose-dependent manner for 2 h after the oral administration. These results indicate that ornithine increased the amount of NREM sleep without reducing the power spectrum density of NREM sleep.

     

Ghrelin induces time-dependent modulation of thermoregulation in the cold

Fasted mice show torpor-like hypothermia in the cold in their inactive phase. The aim of the present study was to elucidate whether leptin and/or ghrelin are involved in this reaction and to identify its neurophysiological mechanisms. In ob/ob mice, which lack leptin, metabolic heat production (oxygen consumption, Vo(2)) was suppressed in 20°C cold in both the light and dark phases, resulting in hypothermia. When wild-type mice received a systemic injection of 8 μg ghrelin in the early light phase, followed by a 2-h cold exposure to 10°C, their core body temperature (T(b)) decreased by 1.7°C, and they displayed a less marked increase in Vo(2) compared with vehicle-injected mice. However, ghrelin injection in the early dark phase resulted in the maintenance of T(b) and increased Vo(2) in the mice, which was similar to the result observed in the vehicle-injected mice. The number of doubly labeled neurons with cFos and neuropeptide Y (NPY) in the suprachiasmatic nucleus was greater in the light phase in the ghrelin-injected mice, which may suggest that ghrelin activates NPY neurons. On the contrary, in the paraventricular nucleus, the counts became greater only when they were exposed to the cold in the dark phase. These results indicate that ghrelin plays an important role in inducing time-dependent changes in thermoregulation in the cold via hypothalamic pathways.     

Sleep Deprivation in the Dark Period Does Not Impair Memory in OF1 Mice

There is increasing evidence that sleep facilitates memory acquisition and consolidation. Moreover, the sleep-wake history preceding memory acquisition and retention as well as circadian timing may be important. We showed previously that sleep deprivation (SD) following learning in OF1 mice impaired their performance on an object recognition task. The learning task was scheduled at the end of the 12 h dark period and the test 24 h later. To investigate the influence of the prominent circadian sleep-wake distribution typical for rodents, we now scheduled the learning task at the beginning of the dark period. Wakefulness following immediately after the learning task was attained either by gentle interference (SD; n?=?20) or by spontaneous wheel running (RW; n?=?20). Two control groups were used: one had no RW throughout the experiment (n?=?23), while the other group's wheel was blocked immediately after acquisition (n?=?16), thereby preventing its use until testing. Recognition memory, defined as the difference in exploration of a novel and of familiar objects, was assessed 24 h later during the test phase. Motor activity and RW use were continuously recorded. Remarkably, performance on the object recognition task was not influenced by the protocols; the waking period following acquisition did not impair memory, independent of the method inducing wakefulness (i.e., sleep deprivation or spontaneous running). Thus, all groups explored the novel object significantly longer than the familiar ones during the test phase. Interestingly, neither the amount of rest lost during the SD interventions nor the amount of rest preceding acquisition influenced performance. However, the total amount of rest obtained by the control and SD mice subjected to acquisition at “dark offset” correlated positively (r?=?0.66) with memory at test, while no such relationship occurred in the corresponding groups tested at dark onset. Neither the amount of running nor intermediate rest correlated with performance at test in the RW group. We conclude that interfering with sleep during the dark period does not affect object recognition memory consolidation.     

Characteristics of Sleep and Wakefulness inWild-Derived Inbred Mice

Genetic variations in the wild-derived inbred mouse strains are more diverse than that of classical laboratory inbred mouse strains, including C57BL/6J (B6). The sleep/wake and monoamine properties of six wild-derived inbred mouse strains (PGN2, NJL, BLG2, KJR, MSM, HMI) were characterized and compared with those of B6 mice. All examined mice were nocturnal and had a polyphasic sleep pattern with a “main sleep period” identified during the light period. However, there were three sleep/wake phenotypic differences between the wild-derived mouse strains and B6 strain. First, the amount of sleep during the dark phase was comparable with that of B6 mice. However, the amount of sleep during the light phase was more varied among strains, in particular, NJL and HMI had significantly less sleep compared with that of B6 mice. Second, PGN2, NJL, BLG2, and KJR mice showed a “highly awake period” (in which the hourly total sleep time was <10%) immediately after the onset of the dark period, which was not seen in B6 mice. Third, relative to that of B6 mice, PGN2 and KJR mice showed longer duration of wakefulness episodes during the 12-h dark phase. Differences in whole brain noradrenaline, dopamine, and 5-hydroxy-tryptamine contents between the wild-derived mouse strains and B6 strain were also found. These identified phenotypes might be potentially under strong genetic control. Hence, wild-derived inbred mice could be useful for identifying the genetic factors underlying the regulation of sleep and wakefulness.     

Ozone-induced paradoxical sleep decrease is related to diminished acetylcholine levels in the medial preoptic area in rats

Ozone (O3) produces significant effects on sleep, characterized specially by a decrease in paradoxical sleep (PS) and increase in slow-wave sleep (SWS), which in turn represent a sleep-wake cycle disruption. On the other hand, neuronal activity recorded in the cholinoceptive hypothalamic medial preoptic area (MPO) has been involved in the regulation of sleep. However, there is no direct evidence on the role that acetylcholine (Ach) release in the MPO plays in the sleep-wake cycle. In order to study this relation, we measured the Ach concentration in dialysates collected from MPO in rats exposed to coal-filtered air (clean air) for 48 h and in rats exposed to clean air for 24 h followed by 24-h of O3 exposure to 0.5 ppm. Polygraphic sleep records were taken simultaneously to neurochemical sampling. O3 was employed to disrupt the sleep-wake cycle and relate these changes with concomitant disruptions in Ach concentration dialyzed from MPO. A clear circadian pattern of Ach concentration was observed in dialysates from MPO and also in PS, SWS and wakefulness of rats exposed to filtered air. However, O3 exposure decreased the PS by 65% (Mann-Whitney's U-test, p相似文献   

Subchronic 17alpha-ethinyl estradiol differentially affects subtypes of sleep and wakefulness in ovariectomized rats

In ovariectomized (OVX) Sprague-Dawley rats, estradiol benzoate (EB) has been reported to decrease rapid eye movement (REM) and non-REM (NREM) sleep during the dark phase for up to 3 days. It is unknown, however, if estrogenic effects on sleep extend beyond 3 days or if other estrogens could induce the same changes. Furthermore, it is unclear whether the increased wakefulness in the dark phase was due to changes in active or quiet wakefulness. Therefore, we examined the effects of daily injections of 17alpha-ethinyl estradiol (EE) for 6 days on sleep and wakefulness in the OVX rat. After 3 days of baseline recording using a telemetric system, rats were administered sesame oil (sc) for 3 days followed by injection with EE (20 mug/rat/day, sc) for 6 days. After treatment, sleep was recorded during hormone withdrawal for an additional 5 days. A few sporadic but statistically significant increases in light phase sleep occurred during the last 3 days of EE treatment. Starting on day 2 of the study, EE caused statistically significant decreases in dark phase REM sleep that were maintained throughout the treatment period and persisted until the 3rd day of hormone withdrawal. During the dark phase, statistically significant decreases in NREM sleep and increases in active wakefulness started on the second day of treatment and abated by the end of treatment. This study demonstrated that EE had similar effects on sleep-wakefulness to EB and demonstrates the utility of telemetric polysomnographic recording of the female OVX rat as a model for understanding the estrogen-induced changes on sleep-wakefulness.     

Elevated body temperature during sleep in orexin knockout mice

Core body temperature (Tb) is influenced by many physiological factors, including behavioral state, locomotor activity, and biological rhythms. To determine the relative roles of these factors, we examined Tb in orexin knockout (KO) mice, which have a narcolepsy-like phenotype with severe sleep-wake fragmentation. Because orexin is released during wakefulness and is thought to promote heat production, we hypothesized that orexin KO mice would have lower Tb while awake. Surprisingly, Tb was the same in orexin KO mice and wild-type (WT) littermates during sustained wakefulness. Orexin KO mice had normal diurnal variations in Tb, but the ultradian rhythms of Tb, locomotor activity, and wakefulness were markedly reduced. During the first 15 min of spontaneous sleep, the Tb of WT mice decreased by 1.0 degrees C, but Tb in orexin KO mice decreased only 0.4 degrees C. Even during intense recovery sleep after 8 h of sleep deprivation, the Tb of orexin KO mice remained 0.7 degrees C higher than in WT mice. This blunted fall in Tb during sleep may be due to inadequate activation of heat loss mechanisms or sustained activity in heat-generating systems. These observations reveal an unexpected role for orexin in thermoregulation. In addition, because heat loss is an essential aspect of sleep, the blunted fall in Tb of orexin KO mice may provide an explanation for the fragmented sleep of narcolepsy.     

miR-155 deletion modulates lipopolysaccharide-induced sleep in female mice

Immune signaling is known to regulate sleep. miR-155 is a microRNA that regulates immune responses. We hypothesized that miR-155 would alter sleep regulation. Thus, we investigated the potential effects of miR-155 deletion on sleep-wake behavior in adult female homozygous miR-155 knockout (miR-155^KO) mice and littermate controls (WT). Mice were implanted with biotelemetry units and EEG/EMG biopotentials were recorded continuously for three baseline days. miR-155^KO mice had decreased bouts of NREM and REM sleep compared with WT mice, but no differences were observed in the length of sleep bouts or total time spent in sleep-wake states. Locomotor activity and subcutaneous temperature did not differ between WT and miR-155^KO mice. Following baseline recordings, mice were sleep-deprived during the first six hours of the rest phase (light phase; ZT 0–6) followed by an 18 h recovery period. There were no differences between groups in sleep rebound (% sleep and NREM δ power) after sleep deprivation. Following recovery from sleep deprivation, mice were challenged with a somnogen (viz., lipopolysaccharide (LPS)) one hour prior to the initiation of the dark (active) phase. Biopotentials were continuously recorded for the following 24 h, and miR-155^KO mice displayed increased wakefulness and decreased NREM sleep during the dark phase following LPS injection. Additionally, miR-155^KO mice had reduced EEG slow-wave responses (0.5–4 Hz) compared to WT mice. Together, our findings indicate that miR-155 deletion attenuates the somnogenic and EEG delta-enhancing effects of LPS.

Abbreviations: ANOVA: analysis of variance; EEG: electroencephalogram; EMG: electromyogram; h: hour; IL-1: interleukin-1; IL-6: interleukin-6; IP: intra-peritoneal; LPS: lipopolysaccharide; miR/miRNA: microRNA; miR-155^KO: miR-155 knockout; NREM: non-rapid eye movement; REM: rapid eye movement; TNF: tumor necrosis factor; SWS: slow-wave sleep; WT: wild-type.     

Activation of extracellular signal-regulated kinase signaling in the pedunculopontine tegmental cells is involved in the maintenance of sleep in rats

Considerable evidence suggests that receptor-mediated excitation and inhibition of brainstem pedunculopontine tegmental (PPT) neurons are critically involved in the regulation of sleep-wake states. However, the molecular mechanisms operating within the PPT-controlling sleep-wake states remain relatively unknown. This study was designed to examine sleep-wake state-associated extracellular-signal-regulated kinase 1 and 2 (ERK1/2) transduction changes in the PPT of freely moving rats. The results of this study demonstrate that the levels of ERK1/2 expression, phosphorylation, and activity in the PPT increased with increased amount of time spent in sleep. The sleep-associated increases in ERK1/2 expression, phosphorylation, and activity were not observed in the cortex, or in the immediately adjacent medial pontine reticular formation. The results of regression analyses revealed significant positive relationships between the levels of ERK1/2 expression, phosphorylation, and activity in the PPT and amounts of time spent in slow-wave sleep, rapid eye movement sleep, and total sleep. Additionally, these regression analyses revealed significant negative relationships between the levels of ERK1/2 expression, phosphorylation, and activity in the PPT and amounts of time spent in wakefulness. Collectively, these results, for the first time, suggest that the increased ERK1/2 signaling in the PPT is associated with maintenance of sleep via suppression of wakefulness.     

Sleep-Wake Cycle Dysfunction in the TgCRND8 Mouse Model of Alzheimer’s Disease: From Early to Advanced Pathological Stages

In addition to cognitive decline, individuals affected by Alzheimer’s disease (AD) can experience important neuropsychiatric symptoms including sleep disturbances. We characterized the sleep-wake cycle in the TgCRND8 mouse model of AD, which overexpresses a mutant human form of amyloid precursor protein resulting in high levels of β-amyloid and plaque formation by 3 months of age. Polysomnographic recordings in freely-moving mice were conducted to study sleep-wake cycle architecture at 3, 7 and 11 months of age and corresponding levels of β-amyloid in brain regions regulating sleep-wake states were measured. At all ages, TgCRND8 mice showed increased wakefulness and reduced non-rapid eye movement (NREM) sleep during the resting and active phases. Increased wakefulness in TgCRND8 mice was accompanied by a shift in the waking power spectrum towards fast frequency oscillations in the beta (14-20 Hz) and low gamma range (20-50 Hz). Given the phenotype of hyperarousal observed in TgCRND8 mice, the role of noradrenergic transmission in the promotion of arousal, and previous work reporting an early disruption of the noradrenergic system in TgCRND8, we tested the effects of the alpha-1-adrenoreceptor antagonist, prazosin, on sleep-wake patterns in TgCRND8 and non-transgenic (NTg) mice. We found that a lower dose (2 mg/kg) of prazosin increased NREM sleep in NTg but not in TgCRND8 mice, whereas a higher dose (5 mg/kg) increased NREM sleep in both genotypes, suggesting altered sensitivity to noradrenergic blockade in TgCRND8 mice. Collectively our results demonstrate that amyloidosis in TgCRND8 mice is associated with sleep-wake cycle dysfunction, characterized by hyperarousal, validating this model as a tool towards understanding the relationship between β-amyloid overproduction and disrupted sleep-wake patterns in AD.     

Neurophysiological analysis of the effects of partial paradoxical sleep deprivation

A neurophysiological study was made of the effects of partial and complete paradoxial sleep deprivation by substituting episodes of active wakefulness for spells of paradoxical sleep (PS) of the same duration in the sleep-wake cycle. Neither accumulated need for paradoxical sleep (culminating in increased onset of PS during deprivation), PS rebound during the post-deprivation period, nor dissociation of the stages of paradoxical sleep resulting in their intervening individually at unaccustomed points in the sleep-wake cycle were observed during our experimental procedure. The phenomenon of self-deprivation, increased heart rate, eye movements, and pontogeniculooccipital (PGO) action potentials also failed to occur during the post-deprivation period. It is postulated that PS requirement and the need for periods of wakefulness stem from the same neurochemical alterations.I. S. Beritashvili Institute of Physiology, Academy of Sciences of the Georgian SSR, Tbilisi. Translated from Neirofiziologiya, Vol. 20, No. 1, pp. 20–28, January–February, 1988.