Underlying Brain Mechanisms that Regulate Sleep–Wakefulness Cycles

Targeted metabolomics-based understanding of the sleep disturbances in drug-naïve patients with schizophrenia

BACKGROUND

Sleep disturbances are a common occurrence in patients with schizophrenia, yet the underlying pathogenesis remain poorly understood. Here, we performed a targeted metabolomics-based approach to explore the potential biological mechanisms contributing to sleep disturbances in schizophrenia.

METHODS

Plasma samples from 59 drug-naïve patients with schizophrenia and 36 healthy controls were subjected to liquid chromatography-mass spectrometry (LC-MS) targeted metabolomics analysis, allowing for the quantification and profiling of 271 metabolites. Sleep quality and clinical symptoms were assessed using the Pittsburgh Sleep Quality Index (PSQI) and the Positive and Negative Symptom Scale (PANSS), respectively. Partial correlation analysis and orthogonal partial least squares discriminant analysis (OPLS-DA) model were used to identify metabolites specifically associated with sleep disturbances in drug-naïve schizophrenia.

RESULTS

16 characteristic metabolites were observed significantly associated with sleep disturbances in drug-naïve patients with schizophrenia. Furthermore, the glycerophospholipid metabolism (Impact: 0.138, p<0.001), the butanoate metabolism (Impact: 0.032, p=0.008), and the sphingolipid metabolism (Impact: 0.270, p=0.104) were identified as metabolic pathways associated with sleep disturbances in drug-naïve patients with schizophrenia.

CONCLUSIONS

Our study identified 16 characteristic metabolites (mainly lipids) and 3 metabolic pathways related to sleep disturbances in drug-naïve schizophrenia. The detection of these distinct metabolites provide valuable insights into the underlying biological mechanisms associated with sleep disturbances in schizophrenia.

Investigating functional brain connectivity patterns associated with two hypnotic states

While there's been clinical success and growing research interest in hypnosis, neurobiological underpinnings induced by hypnosis remain unclear. In this fMRI study (which is part of a larger hypnosis project) with 50 hypnosis-experienced participants, we analyzed neural and physiological responses during two hypnosis states, comparing them to non-hypnotic control conditions and to each other. An unbiased whole-brain analysis (multi-voxel- pattern analysis, MVPA), pinpointed key neural hubs in parieto-occipital-temporal areas, cuneal/precuneal and occipital cortices, lingual gyri, and the occipital pole. Comparing directly both hypnotic states revealed depth-dependent connectivity changes, notably in left superior temporal/supramarginal gyri, cuneus, planum temporale, and lingual gyri. Multi-voxel- pattern analysis (MVPA) based seeds were implemented in a seed-to-voxel analysis unveiling region-specific increases and decreases in functional connectivity patterns. Physiologically, the respiration rate significantly slowed during hypnosis. Summarized, these findings foster fresh insights into hypnosis-induced functional connectivity changes and illuminate further knowledge related with the neurobiology of altered consciousness.

Median preoptic GABA and glutamate neurons exert differential control over sleep behavior

Previous studies suggest that the median preoptic nucleus (MnPO) of the hypothalamus plays an important role in regulating the wake-sleep cycle and, in particular, homeostatic sleep drive. However, the precise cellular phenotypes, targets, and central mechanisms by which the MnPO neurons regulate the wake-sleep cycle remain unknown. Both excitatory and inhibitory MnPO neurons innervate brain regions implicated in sleep promotion and maintenance, suggesting that both cell types may participate in sleep control. Using genetically targeted approaches, we investigated the role of the MnPO GABAergic (MnPO^Vgat) and glutamatergic (MnPO^Vglut2) neurons in modulating wake-sleep behavior of mice. We found that both neuron populations differentially participate in wake-sleep control, with MnPO^Vgat neurons being involved in sleep homeostasis and MnPO^Vglut2 neurons facilitating sleep during allostatic (stressful) challenges.

Assessing the treatment of cannabidiolic acid methyl ester: a stable synthetic analogue of cannabidiolic acid on c-Fos and NeuN expression in the hypothalamus of rats

BACKGROUND

Cannabidiol (CBD), the non-psychotropic compound from Cannabis sativa, shows positive results on controlling several health disturbances; however, comparable data regarding additional chemical from C. sativa, such as cannabidiolic acid (CBDA), is scarce due to its instability. To address this limitation, a stable CBDA analogue, CBDA methyl ester (HU-580), was synthetized and showed CBDA-like effects. Recently, we described that HU-580 increased wakefulness and wake-related neurochemicals.

OBJECTIVE

To extend the comprehension of HU-580´s properties on waking, the c-Fos and NeuN expression in a wake-linked brain area, the hypothalamus was evaluated.

METHODS

c-Fos and NeuN expression in hypothalamic sections were analyzed after the injections of HU-580 (0.1 or 100 μg/kg, i.p.).

RESULTS

Systemic administrations of HU-580 increased c-Fos and neuronal nuclei (NeuN) expression in hypothalamic nuclei, including the dorsomedial hypothalamic nucleus dorsal part, dorsomedial hypothalamic nucleus compact part, and dorsomedial hypothalamic nucleus ventral part.

CONCLUSION

HU-580 increased c-Fos and NeuN immunoreactivity in hypothalamus nuclei suggesting that this drug might modulate the sleep-wake cycle by engaging the hypothalamus.

Saporin from Saponaria officinalis as a Tool for Experimental Research, Modeling, and Therapy in Neuroscience

Saporin, which is extracted from Saponaria officinalis, is a protein toxin that inactivates ribosomes. Saporin itself is non-selective toxin but acquires high specificity after conjugation with different ligands such as signaling peptides or antibodies to some surface proteins expressed in a chosen cell subpopulation. The saporin-based conjugated toxins were widely adopted in neuroscience as a convenient tool to induce highly selective degeneration of desired cell subpopulation. Induction of selective cell death is one of approaches used to model neurodegenerative diseases, study functions of certain cell subpopulations in the brain, and therapy. Here, we review studies where saporin-based conjugates were used to analyze cell mechanisms of sleep, general anesthesia, epilepsy, pain, and development of Parkinson’s and Alzheimer’s diseases. Limitations and future perspectives of use of saporin-based toxins in neuroscience are discussed.

Diversity of simultaneous sleep in the motor cortex and hippocampus in rats

We investigated the homogeneity/heterogeneity of spontaneous sleep, simultaneously recorded in the motor cortex and the hippocampus of control rats, and particularly analysed simultaneous and non-simultaneous motor cortical and hippocampal non-rapid eye movement (NREM)/rapid eye movement (REM) sleep. We demonstrate that the sleep architectures of the motor cortex and hippocampus are different in control rats. There was an increase of NREM duration and a decrease of REM duration in the hippocampus versus the motor cortex. In terms of duration, NREM state is the most heterogeneous in the hippocampus, whereas the REM state is the most heterogeneous in the motor cortex. Whereas the hippocampal NREM duration was increased due to the prolongation of NREM episodes, the hippocampal REM duration decreased due to the decreased number of REM episodes. The heterogeneity of sleep in the motor cortex and hippocampus in control rats was particularly expressed through the inverse alteration of sigma amplitude during NREM sleep and beta/gamma amplitudes during REM sleep in the hippocampus, along with the delta, sigma, beta and gamma amplitudes only during non-simultaneous NREM/REM sleep in the hippocampus. We demonstrated the brain structure-related and NREM/REM state-related heterogeneity of the motor cortical and hippocampal local sleep in control rats. The distinctly altered local NREM/REM states, alongside their episode dynamics and electroencephalographic (EEG) microstructures, suggest the importance of both the local neuronal network substrate and the NREM/REM neurochemical substrate in the control mechanisms of sleep.

Sleep quality is related to brain glutamate and symptom severity in schizophrenia

Up to 80% of patients with schizophrenia experience sleep disturbances, which negatively impact daytime functioning. Given that the glutamatergic system is involved in the pathophysiology of schizophrenia as well as normal sleep-wake neurobiology, the current project aimed to determine whether sleep quality was related to brain glutamate levels in schizophrenia. The Pittsburgh Sleep Quality Index (PSQI) was used to assess subjective sleep quality and proton magnetic resonance spectroscopy (MRS) was used to quantify glutamate in the bilateral anterior cingulate, left parietal cortex, and left hippocampus. Results indicate that global PSQI scores were negatively correlated with the anterior cingulate and parietal glutamate levels. In patients with schizophrenia, poorer sleep quality correlated with greater positive symptom severity. Our findings suggest that poor sleep quality is related to greater positive symptom severity and lower levels of anterior cingulate glutamate in individuals with schizophrenia. Interventions to enhance sleep quality may prove beneficial for patients. Future studies will examine whether glutamate relates to objective measures of sleep quality, and whether glutamate may mediate the relationship between sleep quality and symptom severity across the schizophrenia-spectrum.

Circadian Rhythms and Measures of CNS/Autonomic Interaction

The physiological role and relevance of the mechanisms sustaining circadian rhythms have been acknowledged. Abnormalities of the circadian and/or sleep-wakefulness cycles can result in major metabolic disorders or behavioral/professional inadequacies and stand as independent risk factors for metabolic, psychiatric, and cerebrovascular disorders and early markers of disease. Neuroimaging and clinical evidence have documented functional interactions between autonomic (ANS) and CNS structures that are described by a concept model (Central Autonomic Network) based on the brain-heart two-way interplay. The circadian rhythms of autonomic function, ANS-mediated processes, and ANS/CNS interaction appear to be sources of variability adding to a variety of environmental factors, and may become crucial when considering the ANS major role in internal environment constancy and adaptation that are fundamental to homeostasis. The CNS/ANS interaction has not yet obtained full attention and systematic investigation remains overdue.

Autonomic regulation during sleep and wakefulness: a review with implications for defining the pathophysiology of neurological disorders

Cardiovascular and respiratory parameters change during sleep and wakefulness. This observation underscores an important, albeit incompletely understood, role for the central nervous system in the differential regulation of autonomic functions. Understanding sleep/wake-dependent sympathetic modulations provides insights into diseases involving autonomic dysfunction. The purpose of this review was to define the central nervous system nuclei regulating sleep and cardiovascular function and to identify reciprocal networks that may underlie autonomic symptoms of disorders such as insomnia, sleep apnea, restless leg syndrome, rapid eye movement sleep behavior disorder, and narcolepsy/cataplexy. In this review, we examine the functional and anatomical significance of hypothalamic, pontine, and medullary networks on sleep, cardiovascular function, and breathing.

The Mutual Interaction Between Sleep and Epilepsy on the Neurobiological Basis and Therapy

BACKGROUND

Sleep and epilepsy are mutually related in a complex, bidirectional manner. However, our understanding of this relationship remains unclear.

RESULTS

The literatures of the neurobiological basis of the interactions between sleep and epilepsy indicate that non rapid eye movement sleep and idiopathic generalized epilepsy share the same thalamocortical networks. Most of neurotransmitters and neuromodulators such as adenosine, melatonin, prostaglandin D2, serotonin, and histamine are found to regulate the sleep-wake behavior and also considered to have antiepilepsy effects; antiepileptic drugs, in turn, also have effects on sleep. Furthermore, many drugs that regulate the sleep-wake cycle can also serve as potential antiseizure agents. The nonpharmacological management of epilepsy including ketogenic diet, epilepsy surgery, neurostimulation can also influence sleep.

CONCLUSION

In this paper, we address the issues involved in these phenomena and also discuss the various therapies used to modify them.

The Sleep in Caenorhabditis elegans: What We Know Until Now

Sleep, as one of the most important requirements of our brain, has a mystical nature. Despite long-standing studies, the molecular mechanisms and physiological properties of sleep have not been defined well as the complexity of the mammals' brain make it difficult to investigate the mechanisms and properties of sleep. Although some features of sleep have changed during evolution, its existence in such a simple animal, Caenorhabditis elegans, not only signifies the importance of sleep in even simple animals, but also allows the scientist to assess the core mechanism and biological events in an uncomplicated organism. This article reviews the information which exists about the characteristics of sleep in C. elegans, its circadian rhythm, the neurons and neurotransmitters responsible for each state, and the signaling molecules involved. Although much still remains to be resolved about the sleep of C. elegans, the available knowledge helps the scientists to recognize the properties better of this mysterious function of the brain.

Different Simultaneous Sleep States in the Hippocampus and Neocortex

STUDY OBJECTIVES

Investigators assign sleep-waking states using brain activity collected from a single site, with the assumption that states occur at the same time throughout the brain. We sought to determine if sleep-waking states differ between two separate structures: the hippocampus and neocortex.

METHODS

We measured electrical signals (electroencephalograms and electromyograms) during sleep from the hippocampus and neocortex of five freely behaving adult male rats. We assigned sleep-waking states in 10-sec epochs based on standard scoring criteria across a 4-h recording, then analyzed and compared states and signals from simultaneous epochs between sites.

RESULTS

We found that the total amount of each state, assigned independently using the hippocampal and neocortical signals, was similar between the hippocampus and neocortex. However, states at simultaneous epochs were different as often as they were the same (P = 0.82). Furthermore, we found that the progression of states often flowed through asynchronous state-pairs led by the hippocampus. For example, the hippocampus progressed from transition-to-rapid eye movement sleep to rapid eye movement sleep before the neocortex more often than in synchrony with the neocortex (38.7 ± 16.2% versus 15.8 ± 5.6% mean ± standard error of the mean).

CONCLUSIONS

We demonstrate that hippocampal and neocortical sleep-waking states often differ in the same epoch. Consequently, electrode location affects estimates of sleep architecture, state transition timing, and perhaps even percentage of time in sleep states. Therefore, under normal conditions, models assuming brain state homogeneity should not be applied to the sleeping or waking brain.

Controversies in the use of second generation antipsychotics as sleep agent

A growing number of patients present in clinics with complaints of insomnia. Over the past century, great advances have been made in our knowledge of mechanisms of sleep and wakefulness. Understanding sleep neurochemistry has led to better management of different types of insomnias with a variety of non-pharmacological and pharmacological treatments. Unfortunately, the increasing development and availability of second generation antipsychotics (SGA) have prompted their frequent use exclusively for insomnia. However, to date, no large randomized-controlled or placebo-controlled studies have shown the utility of SGAs in the realm of treating insomnia. Many clinicians use SGAs as "off-label" for sleep induction and maintenance, but this practice needs to be readdressed given their potential risks and the current lack of evidence base. This review will highlight the neurochemistry related to sleep, the mechanisms of action by which SGA may have some benefit in treating insomnia, and the risks associated with their utilization.

Reduced cerebral blood flow and white matter hyperintensities predict poor sleep in heart failure

BACKGROUND

Poor sleep is common in heart failure (HF), though mechanisms of sleep difficulties are not well understood. Adverse brain changes among regions important for sleep have been demonstrated in patients with HF. Cerebral hypoperfusion, a correlate of sleep quality, is also prevalent in HF and a likely contributor to white matter hyperintensities (WMH). However, no study to date has examined the effects of cerebral blood flow, WMH, and brain volume on sleep quality in HF.

METHODS

Fifty-three HF patients completed the Pittsburgh Sleep Quality Index and underwent brain magnetic resonance imaging to quantify brain and WMH volume. Transcranial Doppler ultrasonography assessed cerebral blood flow velocity of the middle cerebral artery (CBF-V of the MCA).

RESULTS

75.5% of HF patients reported impaired sleep. Regression analyses adjusting for medical and demographic factors showed decreased CBF-V of the MCA and greater WMH volume were associated with poor sleep quality. No such pattern emerged on total brain or regional volume indices.

CONCLUSIONS

Decreased cerebral perfusion and greater WMH may contribute to sleep difficulties in HF. Future studies are needed to confirm these findings and clarify the effects of cerebral blood flow and WMH on sleep in healthy and patient samples.

Reward-related ventral striatum reactivity mediates gender-specific effects of a galanin remote enhancer haplotype on problem drinking

The neuropeptide galanin has been implicated in the regulation of appetitive and consummatory behaviors. Prior studies have shown that direct injection of galanin into the hypothalamus results in increased release of dopamine (DA) in the nucleus accumbens (NAcc), and parallel increases in food and alcohol consumption. These studies are consistent with a role of hypothalamic galanin in regulating reward system reactivity. In humans, a common functional haplotype (GAL5.1) within a remote enhancer region upstream of the galanin gene (GAL) affects promoter activity and galanin expression in hypothalamic neurons in vitro. Given the effects of hypothalamic galanin on NAcc DA release and the effects of the GAL5.1 haplotype on GAL expression, we examined the impact of this functional genetic variation on human reward-related ventral striatum (VS) reactivity. Using an imaging genetics strategy in Caucasian individuals (N = 138, 72 women) participating in the ongoing Duke Neurogenetics Study, we report a significant gender-by-genotype interaction (right hemisphere: F1,134  = 8.08, P = 0.005; left hemisphere: F1,134  = 5.39, P = 0.022), such that homozygosity for the GG haplotype, which predicts greater GAL expression, is associated with relatively increased VS reactivity in women (n = 50, right hemisphere: P = 0.015; left hemisphere: P = 0.060), but not in men (N = 49, P-values > 0.10). Furthermore, these differences in VS reactivity correlated positively with differences in alcohol use, such that VS reactivity mediated a gender-specific association between GAL5.1 haplotype and problem drinking. Our current results support those in animal models implicating galanin signaling in neural pathways associated with appetitive and consummatory behaviors of relevance for understanding risk for substance use and abuse.

Association of common genetic variants with risperidone adverse events in a Spanish schizophrenic population

Risperidone non-compliance is often high due to undesirable side effects, whose development is in part genetically determined. Studies with genetic variants involved in the pharmacokinetics and pharmacodynamics of risperidone have yielded inconsistent results. Thus, the aim of this study was to investigate the putative association of genetic markers with the occurrence of four frequently observed adverse events secondary to risperidone treatment: sleepiness, weight gain, extrapyramidal symptoms and sexual adverse events. A series of 111 schizophrenia inpatients were genotyped for genetic variants previously associated with or potentially involved in risperidone response. Presence of adverse events was the main variable and potential confounding factors were considered. Allele 16Gly of ADRB2 was significantly associated with a higher risk of sexual adverse events. There were other non-significant trends for DRD3 9Gly and SLC6A4 S alleles. Our results, although preliminary, provide new candidate variants of potential use in risperidone safety prediction.

A molecular basis for interactions between sleep and memory

The electrophysiological properties of the sleeping brain profoundly influence memory function in various species, yet the molecular nature by which sleep and memory interact remains unclear. We summarize work that has established the cAMP-PKA-CREB intracellular signaling pathway as a major mechanism involved in the wakeful consolidation of memory in many organisms while highlighting newer evidence that this pathway has a role in sleep regulation, sleep deprivation and potentially sleep-memory interactions. We explore the possibility that sleep might influence memory processing by reactivating the same molecular cascades first recruited during learning during a sort of "molecular replay". Lastly, we discuss how new approaches together with established techniques will aid in our understanding of the nature of sleep-memory interactions.