Contribution of default mode network to game and delayed-response task performance: Power and connectivity analyses of theta oscillation in the monkey.

Neuroimaging studies have demonstrated the presence of a default mode network (DMN) which shows greater activity during rest, and an executive network (EN) which is activated during cognitive tasks. DMN and EN are thought to have competing functions. However, recent studies reported that the two networks show coactivation during some cognitive tasks. To clarify how DMN works and how DMN interacts with EN for cognitive control, we recorded EEG activities in the medial prefrontal (anterior DMN: aDMN), posterior cingulate/precuneus (posterior DMN: pDMN), and lateral prefrontal (EN) areas in the monkey. As cognitive tasks, we employed a monkey-monkey competitive video game (GAME) and a delayed-response (DR) task. We focused on theta oscillation because of its importance in cognitive control. We also examined theta band connectivity among the three network areas using the Granger causality analysis. DMN and EN were found to work cooperatively in both tasks. In all the three network areas, we found GAME-task-related, but no DR-task-related, increase in theta power from the resting level, maybe because of the higher cognitive demand associated with the GAME task performance. The information flow conveyed by the theta oscillation was directed more to aDMN than from aDMN for both tasks. The GAME-task-related increase in theta power in aDMN is supposed to be supported by more information flow conveyed by the theta oscillation from EN and pDMN.

A rare genetic variant in the cleavage site of prepro-orexin is associated with idiopathic hypersomnia.

Idiopathic hypersomnia (IH) is a rare, heterogeneous sleep disorder characterized by excessive daytime sleepiness. In contrast to narcolepsy type 1, which is a well-defined type of central disorders of hypersomnolence, the etiology of IH is poorly understood. No susceptibility loci associated with IH have been clearly identified, despite the tendency for familial aggregation of IH. We performed a variation screening of the prepro-orexin/hypocretin and orexin receptors genes and an association study for IH in a Japanese population, with replication (598 patients and 9826 controls). We identified a rare missense variant (g.42184347T>C; p.Lys68Arg; rs537376938) in the cleavage site of prepro-orexin that was associated with IH (minor allele frequency of 1.67% in cases versus 0.32% in controls, P = 2.7 × 10-8, odds ratio = 5.36). Two forms of orexin (orexin-A and -B) are generated from cleavage of one precursor peptide, prepro-orexin. The difference in cleavage efficiency between wild-type (Gly-Lys-Arg; GKR) and mutant (Gly-Arg-Arg; GRR) peptides was examined by assays using proprotein convertase subtilisin/kexin (PCSK) type 1 and PCSK type 2. In both PCSK1 and PCSK2 assays, the cleavage efficiency of the mutant peptide was lower than that of the wild-type peptide. We also confirmed that the prepro-orexin peptides themselves transmitted less signaling through orexin receptors than mature orexin-A and orexin-B peptides. These results indicate that a subgroup of IH is associated with decreased orexin signaling, which is believed to be a hallmark of narcolepsy type 1.

A variant in orexin receptor-2 is associated with self-reported daytime sleepiness in the Japanese population.

Excessive daytime sleepiness is characterized by a persistent feeling of having trouble staying awake, typically with inappropriate sleep episodes. Orexin (hypocretin) is a neuropeptide that regulates sleep-wake cycles and rapid eye movement sleep. Several large-scale genome-wide association studies (GWASs) in European populations have found genetic variants in orexin receptor-1 (OX1R) and -2 (OX2R) that are associated with sleep traits including daytime sleepiness. To identify genetic variants associated with daytime sleepiness, we performed an association study of genetic variants in prepro-orexin, OX1R, and OX2R in 14,329 Japanese individuals from the Tohoku Medical Megabank Project cohort. A genetic variant in OX2R was significantly associated with self-reported daytime sleepiness after Bonferroni correction (rs188018846: P = 8.4E-05). In addition, a missense variant in OX2R identified by the European GWASs showed a nominally significant association with daytime sleepiness in a Japanese population (p.Ile308Val, rs2653349: P = 0.044). Multiple genetic variants in OX2R can affect daytime sleepiness in general populations.

Genome-wide association study of idiopathic hypersomnia in a Japanese population.

Idiopathic hypersomnia (IH) is a rare sleep disorder characterized by excessive daytime sleepiness, great difficulty upon awakening, and prolonged sleep time. In contrast to narcolepsy type 1, which is a well-recognized hypersomnia, the etiology of IH remains poorly understood. No susceptibility loci for IH have been identified, although familial aggregations have been observed among patients with IH. Narcolepsy type 1 is strongly associated with human leukocyte antigen (HLA)-DQB1*06:02; however, no significant associations between IH and HLA alleles have been reported. To identify genetic variants that affect susceptibility to IH, we performed a genome-wide association study (GWAS) and two replication studies involving a total of 414 Japanese patients with IH and 6587 healthy Japanese individuals. A meta-analysis of the three studies found no single-nucleotide polymorphisms (SNPs) that reached the genome-wide significance level. However, we identified several candidate SNPs for IH. For instance, a common genetic variant (rs2250870) within an intron of PDE9A was suggestively associated with IH. rs2250870 was significantly associated with expression levels of PDE9A in not only whole blood but also brain tissues. The leading SNP in the PDE9A region was the same in associations with both IH and PDE9A expression. PDE9A is a potential target in the treatment of several brain diseases, such as depression, schizophrenia, and Alzheimer's disease. It will be necessary to examine whether PDE9A inhibitors that have demonstrated effects on neurophysiologic and cognitive function can contribute to the development of new treatments for IH, as higher expression levels of PDE9A were observed with regard to the risk allele of rs2250870. The present study constitutes the first GWAS of genetic variants associated with IH. A larger replication study will be required to confirm these associations. Supplementary Information: The online version contains supplementary material available at 10.1007/s41105-021-00349-2.

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.

Intracellular ATP levels in mouse cortical excitatory neurons varies with sleep-wake states.

Whilst the brain is assumed to exert homeostatic functions to keep the cellular energy status constant under physiological conditions, this has not been experimentally proven. Here, we conducted in vivo optical recordings of intracellular concentration of adenosine 5'-triphosphate (ATP), the major cellular energy metabolite, using a genetically encoded sensor in the mouse brain. We demonstrate that intracellular ATP levels in cortical excitatory neurons fluctuate in a cortex-wide manner depending on the sleep-wake states, correlating with arousal. Interestingly, ATP levels profoundly decreased during rapid eye movement sleep, suggesting a negative energy balance in neurons despite a simultaneous increase in cerebral hemodynamics for energy supply. The reduction in intracellular ATP was also observed in response to local electrical stimulation for neuronal activation, whereas the hemodynamics were simultaneously enhanced. These observations indicate that cerebral energy metabolism may not always meet neuronal energy demands, consequently resulting in physiological fluctuations of intracellular ATP levels in neurons.

Metabolome analysis using cerebrospinal fluid from narcolepsy type 1 patients.

Narcolepsy type 1 (NT1) is a hypersomnia characterized by excessive daytime sleepiness and cataplexy. Inappropriate regulation of fatty acid metabolism has been suggested to be involved in the pathophysiology of NT1, but the detailed mechanisms remain uncertain. Here we performed a metabolomic analysis of cerebrospinal fluid samples from 14 NT1 and 17 control subjects using a novel capillary electrophoresis coupled with Fourier transform mass spectrometry. A total of 268 metabolites were identified and the amount of histidine was the most significantly increased in NT1 patients (p = 4.0 × 10-4). Validation analysis using high-performance liquid chromatography (HPLC) including independent replication samples also identified the association of histidine (p = 2.02 × 10-3). Further, levels of histamine, which is synthesized from histidine, were also examined using HPLC and were found to be significantly decreased in NT1 patients (p = 6.12 × 10-4). Pathway analysis with nominally significant metabolites identified several pathways related to the metabolism of glycogenic amino acids, suggesting that glycogenesis is enhanced in NT1 as a compensatory mechanism for fatty acid metabolism. We performed further exploratory analysis, searching for metabolites associated with sleep variables from polysomnography and the multiple sleep latency test. As a result, 5'-deoxy-5'-methylthioadenosine showed a significant association with apnea-hypopnea index (p = 2.66 ×10-6). Moreover, gamma aminobutyric acid displayed a negative correlation with rapid eye movement sleep latency (REML), and thus might represent an intriguing target for future studies to elucidate how the controlling circuit of REM sleep is associated with abnormally short REML in NT1.

A Susceptible Period of Photic Day-Night Rhythm Loss in Common Marmoset Social Behavior Development.

The prevalence of neurodevelopmental psychiatric disorders such as pervasive developmental disorders is rapidly increasing worldwide. Although these developmental disorders are known to be influenced by an individual's genetic background, the potential biological responses to early life's environmental exposure to both physical and psychological factors must also be considered. Many studies have acknowledged the influence of shorter time for rest at night and the simultaneous occurrence of various kinds of complications involving developmental disorders. In a prior study, we examined how a common marmoset's (Callithrix jacchus) psychosocial development was affected when it was reared under constant daylight from birth and then reared individually by humans nursing them under constant light (LL) during their juvenile development stages. The behaviors of these marmosets were compared with those of normal day-night cycle (LD) marmosets using a multivariate analysis based on principal component analysis (PCA). That study found that LL marmosets relatively elicited egg-like calls (Ecall) and side-to-side shakes of the upper body with rapid head rotation through adulthood frequently. Based on the PCA, these behaviors were interpreted as "alert" or "hyperactive" states. However, we did not clarify susceptible periods of the photic rhythm loss experience and the psychological development output. In this study we summarize the following studies in our model animal colonies involving 30 animals (11 female, 19 males) to further explore critical age states of inquiry about each social behavior profiling. We compared social behaviors of three age stages, juvenile, adolescent and young adult equivalent to one another in four LL experience conditions, LL (postnatal day (P) 0 to around 150), Middle (P60-149, 90 days), Late (P150-239, 90 days), and LD (no experience). In the most representative 1st and 2nd principal component scores, the shifting to higher frequency of alert behaviors developed at the adult stage in LL, Middle, then Late in turn. The no LL experience group, LD, generally featured higher frequency of local preference of high position compared to LL experience present groups, in adulthood. This limited model primate study might inspire different developmental age sensitive mechanisms of neuronal network to control socio-emotional functions by utilizing the multivariate visualization method, BOUQUET. This study could potentially contribute to nurturing educational designs for social developmental disorders.

The Effects of Frankincense Essential Oil on Stress in Rats.

Frankincense essential oil, obtained from Boswellia carteri, is a popular essential oil, which is widely used in many parts of the world. While some of its properties are known, its effects on stress and sleep have not been studied. The effects of frankincense essential oil and its major components, limonene and α-pinene, on plasma corticosterone and glutathione (GSH) levels, as well as on sleep and wakefulness behaviour, were studied in sleep-deprived rats. The substances were applied topically after dilution in jojoba oil (vehicle). As compared to vehicle, frankincense essential oil at a dilution of 1/1000 (1:103) significantly reduced corticosterone levels (p < 0.05). In contrast, its major constituents (α-pinene and limonene), elevated levels of this stress hormone. Frankincense, limonene and α-pinene, all led to significant reductions in plasma GSH levels. Although frankincense dose-dependently reduced plasma concentrations of antioxidant ions albeit to levels insufficient to neutralize oxidative stress; levels of products of oxidative metabolism metabolites were decreased by the frankincense. In sleep-deprived rats, frankincense 1:103 respectively increased and decreased the amount of wakefulness and non-rapid eye movement sleep. Frankincense essential oil can counter the effects of stress by effectively relieving sleep debt and maintaining antioxidant capacity without increasing oxidative stress, and, therefore, may be beneficial in the management of stress.

In situ estimation of optical properties of rat and monkey brains using femtosecond time-resolved measurements.

An accurate knowledge of tissue optical properties (absorption coefficients, µa, and reduced scattering coefficients, µs') is critical for precise modeling of light propagation in biological tissue, essential for developing diagnostic and therapeutic optical techniques that utilize diffusive photons. A great number of studies have explored the optical properties of various tissue, and these values are not known in detail due to difficulties in the experimental determination and significant variations in tissue constitution. Especially, in situ estimates of the optical properties of brain tissue, a common measurement target in optical imaging, is a challenge because of its layer structure (where the thin gray matter covers the white matter). Here, we report an approach to in situ estimates of the µa and µs' of the gray and white matter in living rat and monkey brains by using femtosecond time-resolved measurements and Monte Carlo simulation. The results demonstrate that the µa of the gray matter is larger than that of the white matter, while there was no significant difference in the µs' between the gray and white matter. The optical properties of the rat brain were very similar to those of the monkey brain except for the µa of the gray matter here.

Involvement of PLAGL1/ZAC1 in hypocretin/orexin transcription.

The hypocretin/orexin neuropeptide system coordinates the regulation of various physiological processes. Our previous study reported that a reduction in the expression of pleomorphic adenoma gene­like 1 (Plagl1), which encodes a C2H2 zinc­finger transcription factor, occurs in hypocretin neuron­ablated transgenic mice, suggesting that PLAGL1 is co­expressed in hypocretin neurons and regulates hypocretin transcription. The present study examined whether canonical prepro­hypocretin transcription is functionally modulated by PLAGL1. Double immunostaining indicated that the majority of hypocretin neurons were positive for PLAGL1 immunoreactivity in the nucleus. Notably, PLAGL1 immunoreactivity in hypocretin neurons was altered in response to several conditions affecting hypocretin function. An uneven localization of PLAGL1 was detected in the nuclei of hypocretin neurons following sleep deprivation. Chromatin immunoprecipitation revealed that endogenous PLAGL1 may bind to a putative PLAGL1­binding site in the proximal region of the hypocretin gene, in the murine hypothalamus. In addition, electroporation of the PLAGL1 expression vector into the fetal hypothalamus promoted hypothalamic hypocretin transcription. These results suggested that PLAGL1 may regulate hypothalamic hypocretin transcription.

Narcolepsy susceptibility gene CCR3 modulates sleep-wake patterns in mice.

Narcolepsy is caused by the loss of hypocretin (Hcrt) neurons and is associated with multiple genetic and environmental factors. Although abnormalities in immunity are suggested to be involved in the etiology of narcolepsy, no decisive mechanism has been established. We previously reported chemokine (C-C motif) receptor 3 (CCR3) as a novel susceptibility gene for narcolepsy. To understand the role of CCR3 in the development of narcolepsy, we investigated sleep-wake patterns of Ccr3 knockout (KO) mice. Ccr3 KO mice exhibited fragmented sleep patterns in the light phase, whereas the overall sleep structure in the dark phase did not differ between Ccr3 KO mice and wild-type (WT) littermates. Intraperitoneal injection of lipopolysaccharide (LPS) promoted wakefulness and suppressed both REM and NREM sleep in the light phase in both Ccr3 KO and WT mice. Conversely, LPS suppressed wakefulness and promoted NREM sleep in the dark phase in both genotypes. After LPS administration, the proportion of time spent in wakefulness was higher, and the proportion of time spent in NREM sleep was lower in Ccr3 KO compared to WT mice only in the light phase. LPS-induced changes in sleep patterns were larger in Ccr3 KO compared to WT mice. Furthermore, we quantified the number of Hcrt neurons and found that Ccr3 KO mice had fewer Hcrt neurons in the lateral hypothalamus compared to WT mice. We found abnormalities in sleep patterns in the resting phase and in the number of Hcrt neurons in Ccr3 KO mice. These observations suggest a role for CCR3 in sleep-wake regulation in narcolepsy patients.

Anti-Tribbles Pseudokinase 2 (TRIB2)-Immunization Modulates Hypocretin/Orexin Neuronal Functions.

Study Objectives: Recent findings showed that 16%-26% of narcolepsy patients were positive for anti-tribbles pseudokinase 2 (TRIB2) antibody, and the intracerebroventricular administration of immunoglobulin-G purified from anti-TRIB2 positive narcolepsy patients caused hypocretin/orexin neuron loss. We investigated the pathophysiological role of TRIB2 antibody using TRIB2-immunized rats and hypocretin/ataxin-3 transgenic (ataxin-3) mice. Methods: Plasma, cerebrospinal fluid (CSF), and hypothalamic tissues from TRIB2-immunized rats were collected. Anti-TRIB2 titers, hypocretin contents, mRNA expressions, the cell count of hypocretin neurons, and immunoreactivity of anti-TRIB2 antibodies on hypocretin neurons were investigated. The plasma from ataxin-3 mice was also used to determine the anti-TRIB2 antibody titer changes following the loss of hypocretin neurons. Results: TRIB2 antibody titers increased in the plasma and CSF of TRIB2-immunized rats. The hypothalamic tissue immunostained with the sera from TRIB2-immunized rats revealed positive signals in the cytoplasm of hypcretin neurons. While no changes were found regarding hypothalamic hypocretin contents or cell counts, but there were significant decreases of the hypocretin mRNA level and release into the CSF. The plasma from over 26-week-old ataxin-3 mice, at the advanced stage of hypocretin cell destruction, showed positive reactions against TRIB2 antigen, and positive plasma also reacted with murine hypothalamic hypocretin neurons. Conclusions: Our results suggest that the general activation of the immune system modulates the functions of hypocretin neurons. The absence of a change in hypocretin cell populations suggested that factors other than anti-TRIB2 antibody play a part in the loss of hypocretin neurons in narcolepsy. The increased anti-TRIB2 antibody after the destruction of hypocretin neurons suggest that anti-TRIB2 antibody in narcolepsy patients is the consequence rather than the inciting cause of hypocretin cell destruction.

Oral Administration of Methylphenidate (Ritalin) Affects Dopamine Release Differentially Between the Prefrontal Cortex and Striatum: A Microdialysis Study in the Monkey.

Methylphenidate (MPH; trade name Ritalin) is a widely used drug for the treatment of attention deficit hyperactivity disorder (ADHD) and is often used as a cognitive enhancer. Because MPH increases dopamine (DA) release by blocking the DA transporter in the human striatum, MPH is supposed to work on attention and cognition through a DA increase in the striatum. However, ADHD patients show impaired prefrontal cortex (PFC) function and MPH administration is associated with increased neural activity in the PFC. Although MPH is indicated to increase DA release in the rat PFC, there has been no study to examine MPH-induced DA changes in the human PFC because of technical difficulties associated with the low level of PFC DA receptors. Using the microdialysis technique, we examined the effects of oral administration of MPH on DA release in both the PFC and striatum in the monkey. We also tested the effect of MPH on cognitive task performance. As in human studies, in the striatum, both high and low doses of MPH induced consistent increases in DA release ∼30 min after their administrations. In the PFC, a consistent increase in DA release was observed 1 h after a high dose, but not low doses, of MPH. Low doses of MPH improved cognitive task performance, but a high dose of MPH made the monkey drowsy. Therefore, low-dose MPH-induced cognitive enhancement is supported by striatum DA increase.SIGNIFICANCE STATEMENT Methylphenidate (MPH) is a widely used drug for the treatment of attention deficit hyperactivity disorder and is often used as a cognitive enhancer. Although human positron emission tomography studies suggest that MPH works on attention and cognition through dopamine (DA) changes in the striatum, there has been no study to examine MPH-induced DA changes in the human prefrontal cortex (PFC). Using the microdialysis technique in monkeys, we found, for the first time, that low doses of MPH consistently increased DA release in the striatum but did not in the PFC. Cognitive enhancement effects of low doses of MPH are supposed to be supported by the striatum DA increase.

Hypocretin/orexin loss changes the hypothalamic immune response.

Hypocretin, also known as orexin, maintains the vigilance state and regulates various physiological processes, such as arousal, sleep, food intake, energy expenditure, and reward. Previously, we found that when wild-type mice and hypocretin/ataxin-3 littermates (which are depleted of hypothalamic hypocretin-expressing neurons postnatally) were administered lipopolysaccharide (LPS), the two genotypes exhibited significant differences in their sleep/wake cycle, including differences in the degree of increase in sleep periods and in recovery from sickness behaviour. In the present study, we examined changes in the hypothalamic vigilance system and in the hypothalamic expression of inflammatory factors in response to LPS in hypocretin/ataxin-3 mice. Peripheral immune challenge with LPS affected the hypothalamic immune response and vigilance states. This response was altered by the loss of hypocretin. Hypocretin expression was inhibited after LPS injection in both hypocretin/ataxin-3 mice and their wild-type littermates, but expression was completely abolished only in hypocretin/ataxin-3 mice. Increases in the number of histidine decarboxylase (HDC)-positive cells and in Hdc mRNA expression were found in hypocretin/ataxin-3 mice, and this increase was suppressed by LPS. Hypocretin loss did not impact the change in expression of hypothalamic inflammatory factors in response to LPS, except for interferon gamma and colony stimulating factor 3. The number of c-Fos-positive/HDC-positive cells in hypocretin/ataxin-3 mice administered LPS injections was elevated, even during the rest period, in all areas, suggesting that there is an increase in the activity of histaminergic neurons in hypocretin/ataxin-3 mice following LPS injection. Taken together, our results suggest a novel role for hypocretin in the hypothalamic response to peripheral immune challenge. Our findings contribute to the understanding of the pathophysiology of narcolepsy.

Novel psychoactive benzofurans strongly increase extracellular serotonin level in mouse corpus striatum.

We examined the effects of three benzofurans [1-(Benzofuran-5-yl)-N-methylpropan-2-amine (5-MAPB), 1-(Benzofuran-2-yl)-N-methylpropan-2-amine (2-MAPB), and 1-(Benzofuran-5-yl)-N-ethylpropan-2-amine (5-EAPB)] on the extracellular monoamine level in mouse corpus striatum by the microdialysis method and compared them with the effects of psychoactive 3,4-Methylenedioxymethamphetamine (MDMA). The effects of benzofurans on the extracellular monoamine level were qualitatively analogous to that of MDMA, with an increase in serotonin (5-HT) level exceeding dopamine (DA) level. The effects of 2-MAPB and 5-EAPB were almost the same as the effect of MDMA. However, 5-MAPB strongly increased extracellular monoamine level than MDMA. These differences in the potency appear to have a structure-activity relationship. The administration of 5-MAPB (1.6 × 10(-4) mol/kg B.W.) resulted in the death of two-thirds of the mice. The same dose of MDMA did not cause any deaths. The administration of 5-MAPB (1.6 × 10(-4) mol/kg B.W.) produced a 3.41°C ± 0.28°C rise in rectal temperature after 1 hr, whereas the administration of MDMA (1.6 × 10(-4) mol/kg B.W.) produced an approximate 1.85°C ± 0.26°C rise. These results suggest that benzofurans have 5-HT toxicity similar to MDMA, and 5-MAPB has a higher risk of lethal intoxication than MDMA. Furthermore, 5-APB, the metabolic product of 5-MAPB demethylation, may be involved in the acute 5-HT toxicity and may cause lethal intoxication in mice.

Monoamine Release during Unihemispheric Sleep and Unihemispheric Waking in the Fur Seal.

STUDY OBJECTIVES: Our understanding of the role of neurotransmitters in the control of the electroencephalogram (EEG) has been entirely based on studies of animals with bilateral sleep. The study of animals with unihemispheric sleep presents the opportunity of separating the neurochemical substrates of waking and sleep EEG from the systemic, bilateral correlates of sleep and waking states. METHODS: The release of histamine (HI), norepinephrine (NE), and serotonin (5HT) in cortical and subcortical areas (hypothalamus, thalamus and caudate nucleus) was measured in unrestrained northern fur seals (Callorhinus ursinus) using in vivo microdialysis, in combination with, polygraphic recording of EEG, electrooculogram, and neck electromyogram. RESULTS: The pattern of cortical and subcortical HI, NE, and 5HT release in fur seals is similar during bilaterally symmetrical states: highest in active waking, reduced in quiet waking and bilateral slow wave sleep, and lowest in rapid eye movement (REM) sleep. Cortical and subcortical HI, NE, and 5HT release in seals is highly elevated during certain waking stimuli and behaviors, such as being sprayed with water and feeding. However, in contrast to acetylcholine (ACh), which we have previously studied, the release of HI, NE, and 5HT during unihemispheric sleep is not lateralized in the fur seal. CONCLUSIONS: Among the studied neurotransmitters most strongly implicated in waking control, only ACh release is asymmetric in unihemispheric sleep and waking, being greatly increased on the activated side of the brain. COMMENTARY: A commentary on this article appears in this issue on page 491.

Chronic restraint stress triggers dopaminergic and noradrenergic neurodegeneration: Possible role of chronic stress in the onset of Parkinson's disease.

Parkinson's disease (PD) is a neurodegenerative disease characterized by the loss of dopaminergic (DA) neurons in the substantia nigra pars compacta (SNpc) and, to a lesser extent, in the noradrenergic neurons of the locus coeruleus (LC). Most cases of PD are idiopathic and sporadic and are believed to be the result of both environmental and genetic factors. Here, to the best of our knowledge, we report the first evidence that chronic restraint stress (8h/day, 5days/week) substantially reduces nigral DA and LC noradrenergic neuronal cell numbers in rats. Loss of DA neurons in the SNpc was evident after 2weeks of stress and progressed in a time-dependent manner, reaching up to 61% at 16weeks. This reduction was accompanied by robust microglial activation and oxidative stress and was marked by nitrotyrosine in the SNpc and LC of the midbrain. These results indicate that chronic stress triggers DA and noradrenergic neurodegeneration by increasing oxidative stress, and that activated microglia in the substantia nigra and LC may play an important role in modulating the neurotoxic effects of oxidative stress. Taken together, these data suggest that exposure to chronic stress triggers DA and noradrenergic neurodegeneration, which is a cause of PD.

Hypocretin/orexin prevents recovery from sickness.

Sickness behavior is defined as states of lethargy, depression, anxiety, loss of appetite, hypersomnia, hyperalgesia, reduction of grooming and failure to concentrate that can be induced by inflammatory diseases, such as infections and cancer. Recent findings revealed that the lipopolysaccharide (LPS) injection causes lethargy as a consequence of the inhibition of hypocretin signaling. The hypocretin system maintains the vigilance state in various physiological processes. In order to investigate the sleep arousal system against sickness behavior, LPS-induced sickness behavior was examined in hypocretin-ataxin-3 transgenic mice, whose hypocretin neurons were postnatally ablated. Sleep-wake activity was determined following the administration of LPS at Zeitgeber time (ZT) 8.0 in ataxin-3 transgenic mice, and the age-, gender-matched wild-type littermates. LPS injection induced increases in non-rapid eye movement (REM) sleep in the matched wild-type littermates. In addition, a further increase in periods of sleep according to the loss of hypocretin neurons was identified in the ataxin-3 transgenic mice. A marked reduction of awakening during ZT12-ZT18 was observed as expected following LPS injection in the mouse lines. The increase in the period of non-REM sleep was not observed on the next day following LPS administration in either of the mouse lines. Complete recovery of physical activity was not observed in the matched wild-type littermates. Ataxin-3 transgenic mice recovered their physical activity to the same level as that on the first day before LPS administration. These results suggest the possibility that a faster recovery is the result of deeper resting according to the absence of hypocretin neurons, as ataxin-3 transgenic mice demonstrated more non-REM sleep.