Neurotransmitters of the suprachiasmatic nuclei

Circadian rhythm mechanism in the suprachiasmatic nucleus and its relation to the olfactory system

Animals need sleep, and the suprachiasmatic nucleus, the center of the circadian rhythm, plays an important role in determining the timing of sleep. The main input to the suprachiasmatic nucleus is the retinohypothalamic tract, with additional inputs from the intergeniculate leaflet pathway, the serotonergic afferent from the raphe, and other hypothalamic regions. Within the suprachiasmatic nucleus, two of the major subtypes are vasoactive intestinal polypeptide (VIP)-positive neurons and arginine-vasopressin (AVP)-positive neurons. VIP neurons are important for light entrainment and synchronization of suprachiasmatic nucleus neurons, whereas AVP neurons are important for circadian period determination. Output targets of the suprachiasmatic nucleus include the hypothalamus (subparaventricular zone, paraventricular hypothalamic nucleus, preoptic area, and medial hypothalamus), the thalamus (paraventricular thalamic nuclei), and lateral septum. The suprachiasmatic nucleus also sends information through several brain regions to the pineal gland. The olfactory bulb is thought to be able to generate a circadian rhythm without the suprachiasmatic nucleus. Some reports indicate that circadian rhythms of the olfactory bulb and olfactory cortex exist in the absence of the suprachiasmatic nucleus, but another report claims the influence of the suprachiasmatic nucleus. The regulation of circadian rhythms by sensory inputs other than light stimuli, including olfaction, has not been well studied and further progress is expected.

Circadian neurogenetics and its implications in neurophysiology, behavior, and chronomedicine

The circadian rhythm affects multiple physiological processes, and disruption of the circadian system can be involved in a range of disease-related pathways. The genetic underpinnings of the circadian rhythm have been well-studied in model organisms. Significant progress has been made in understanding how clock genes affect the physiological functions of the nervous system. In addition, circadian timing is becoming a key factor in improving drug efficacy and reducing drug toxicity. The circadian biology of the target cell determines how the organ responds to the drug at a specific time of day, thus regulating pharmacodynamics. The current review brings together recent advances that have begun to unravel the molecular mechanisms of how the circadian clock affects neurophysiological and behavioral processes associated with human brain diseases. We start with a brief description of how the ubiquitous circadian rhythms are regulated at the genetic, cellular, and neural circuit levels, based on knowledge derived from extensive research on model organisms. We then summarize the latest findings from genetic studies of human brain disorders, focusing on the role of human clock gene variants in these diseases. Lastly, we discuss the impact of common dietary factors and medications on human circadian rhythms and advocate for a broader application of the concept of chronomedicine.

The subjective amplitude of the diurnal rhythm matters - Chronobiological insights for neuroimaging studies

Multiple aspects of human psychophysiology, including mood and cognition, are subjected to diurnal rhythms. While the previous magnetic resonance imaging (MRI) studies have focused solely on the morningness-eveningness (ME) preference dichotomy, i.e. the circadian phase, the second key dimension of the diurnal rhythms, i.e. the strength of these preferences (amplitude; AM), has been completely overlooked. Uncovering the neural correlates of AM is especially important considering its link with negative emotionality. Structural T1-weighted neuroimaging data from 79 early (EC) and 74 late (LC) chronotypes were analysed to compare grey matter (GM) volume and cortical thickness. The study aimed to elucidate whether the subjective AM and its interaction with ME was a significant predictor of individual brain structure. Both GM volume and cortical thickness of the left primary visual cortex was negatively correlated with AM scores across the entire sample. Furthermore, EC and LC differed in their association between AM scores and the GM volume in the right middle temporal gyrus, with the positive and negative correlations reported respectively in the two groups. The current study underlines the importance of the visual system in circadian rhythmicity and provides possible neural correlates for AM-related differences in negative affect processing. Furthermore, the presence of the opposite correlations between brain anatomy and AM in the two groups suggests that the behavioural and neuronal chronotype differences might become more pronounced in individuals with extreme diurnal differences in mood and cognition, highlighting the necessity to additionally account for AM in neuroimaging studies.

Circadian Regulation of the Neuroimmune Environment Across the Lifespan: From Brain Development to Aging

Circadian clocks confer 24-h periodicity to biological systems, to ultimately maximize energy efficiency and promote survival in a world with regular environmental light cycles. In mammals, circadian rhythms regulate myriad physiological functions, including the immune, endocrine, and central nervous systems. Within the central nervous system, specialized glial cells such as astrocytes and microglia survey and maintain the neuroimmune environment. The contributions of these neuroimmune cells to both homeostatic and pathogenic demands vary greatly across the day. Moreover, the function of these cells changes across the lifespan. In this review, we discuss circadian regulation of the neuroimmune environment across the lifespan, with a focus on microglia and astrocytes. Circadian rhythms emerge in early life concurrent with neuroimmune sculpting of brain circuits and wane late in life alongside increasing immunosenescence and neurodegeneration. Importantly, circadian dysregulation can alter immune function, which may contribute to susceptibility to neurodevelopmental and neurodegenerative diseases. In this review, we highlight circadian neuroimmune interactions across the lifespan and share evidence that circadian dysregulation within the neuroimmune system may be a critical component in human neurodevelopmental and neurodegenerative diseases.

Microbial circadian clocks: host-microbe interplay in diel cycles

BACKGROUND

Circadian rhythms, observed across all domains of life, enable organisms to anticipate and prepare for diel changes in environmental conditions. In bacteria, a circadian clock mechanism has only been characterized in cyanobacteria to date. These clocks regulate cyclical patterns of gene expression and metabolism which contribute to the success of cyanobacteria in their natural environments. The potential impact of self-generated circadian rhythms in other bacterial and microbial populations has motivated extensive research to identify novel circadian clocks.

MAIN TEXT

Daily oscillations in microbial community composition and function have been observed in ocean ecosystems and in symbioses. These oscillations are influenced by abiotic factors such as light and the availability of nutrients. In the ocean ecosystems and in some marine symbioses, oscillations are largely controlled by light-dark cycles. In gut systems, the influx of nutrients after host feeding drastically alters the composition and function of the gut microbiota. Conversely, the gut microbiota can influence the host circadian rhythm by a variety of mechanisms including through interacting with the host immune system. The intricate and complex relationship between the microbiota and their host makes it challenging to disentangle host behaviors from bacterial circadian rhythms and clock mechanisms that might govern the daily oscillations observed in these microbial populations.

CONCLUSIONS

While the ability to anticipate the cyclical behaviors of their host would likely be enhanced by a self-sustained circadian rhythm, more evidence and further studies are needed to confirm whether host-associated heterotrophic bacteria possess such systems. In addition, the mechanisms by which heterotrophic bacteria might respond to diel cycles in environmental conditions has yet to be uncovered.

Hair Follicles as a Critical Model for Monitoring the Circadian Clock

Clock (circadian) genes are heterogeneously expressed in hair follicles (HFs). The genes can be modulated by both the central circadian system and some extrinsic factors, such as light and thyroid hormones. These circadian genes participate in the regulation of several physiological processes of HFs, including hair growth and pigmentation. On the other hand, because peripheral circadian genes are synchronized with the central clock, HFs could provide a noninvasive and practical method for monitoring and evaluating multiple circadian-rhythm-related conditions and disorders among humans, including day and night shifts, sleep-wake disorders, physical activities, energy metabolism, and aging. However, due to the complexity of circadian biology, understanding how intrinsic oscillation operates using peripheral tissues only may be insufficient. Combining HF sampling with multidimensional assays such as detection of body temperature, blood samples, or certain validated questionnaires may be helpful in improving HF applications. Thus, HFs can serve as a critical model for monitoring the circadian clock and can help provide an understanding of the potential mechanisms of circadian-rhythm-related conditions; furthermore, chronotherapy could support personalized treatment scheduling based on the gene expression profile expressed in HFs.

Melatonin as a Chronobiotic with Sleep-promoting Properties

The use of exogenous melatonin (exo-MEL) as a sleep-promoting drug has been under extensive debate due to the lack of consistency of its described effects. In this study, we conduct a systematic and comprehensive review of the literature on the chronobiotic, sleep-inducing, and overall sleep-promoting properties of exo-MEL. To this aim, we first describe the possible pharmacological mechanisms involved in the sleep-promoting properties and then report the corresponding effects of exo-MEL administration on clinical outcomes in: a) healthy subjects, b) circadian rhythm sleep disorders, c) primary insomnia. Timing of administration and doses of exo-MEL received particular attention in this work. The exo-MEL pharmacological effects are hereby interpreted in view of changes in the physiological properties and rhythmicity of endogenous melatonin. Finally, we discuss some translational implications for the personalized use of exo-MEL in the clinical practice.

Intertwining Neuropathogenic Impacts of Aberrant Circadian Rhythm and Impaired Neuroregenerative Plasticity in Huntington’s Disease: Neurotherapeutic Significance of Chemogenetics

Huntington’s disease (HD) is a progressive neurodegenerative disorder characterized by abnormal progressive involuntary movements, cognitive deficits, sleep disturbances, and psychiatric symptoms. The onset and progression of the clinical symptoms have been linked to impaired adult neurogenesis in the brains of subjects with HD, due to the reduced neurogenic potential of neural stem cells (NSCs). Among various pathogenic determinants, an altered clock pathway appears to induce the dysregulation of neurogenesis in neurodegenerative disorders. Notably, gamma-aminobutyric acid (GABA)-ergic neurons that express the vasoactive intestinal peptide (VIP) in the brain play a key role in the regulation of circadian rhythm and neuroplasticity. While an abnormal clock gene pathway has been associated with the inactivation of GABAergic VIP neurons, recent studies suggest the activation of this neuronal population in the brain positively contributes to neuroplasticity. Thus, the activation of GABAergic VIP neurons in the brain might help rectify the irregular circadian rhythm in HD. Chemogenetics refers to the incorporation of genetically engineered receptors or ion channels into a specific cell population followed by its activation using desired chemical ligands. The recent advancement of chemogenetic-based approaches represents a potential scientific tool to rectify the aberrant circadian clock pathways. Considering the facts, the defects in the circadian rhythm can be rectified by the activation of VIP-expressing GABAergic neurons using chemogenetics approaches. Thus, the chemogenetic-based rectification of an abnormal circadian rhythm may facilitate the neurogenic potentials of NSCs to restore the neuroregenerative plasticity in HD. Eventually, the increased neurogenesis in the brain can be expected to mitigate neuronal loss and functional deficits.

Circadian dysregulation and Alzheimer’s disease: A comprehensive review

Alzheimer’s disease (AD), the foremost variant of dementia, has been associated with a menagerie of risk factors, many of which are considered to be modifiable. Among these modifiable risk factors is circadian rhythm, the chronobiological system that regulates sleep‐wake cycles, food consumption timing, hydration timing, and immune responses amongst many other necessary physiological processes. Circadian rhythm at the level of the suprachiasmatic nucleus (SCN), is tightly regulated in the human body by a host of biomolecular substances, principally the hormones melatonin, cortisol, and serotonin. In addition, photic information projected along afferent pathways to the SCN and peripheral oscillators regulates the synthesis of these hormones and mediates the manner in which they act on the SCN and its substructures. Dysregulation of this cycle, whether induced by environmental changes involving irregular exposure to light, or through endogenous pathology, will have a negative impact on immune system optimization and will heighten the deposition of Aβ and the hyperphosphorylation of the tau protein. Given these correlations, it appears that there is a physiologic association between circadian rhythm dysregulation and AD. This review will explore the physiology of circadian dysregulation in the AD brain, and will propose a basic model for its role in AD‐typical pathology, derived from the literature compiled and referenced throughout.

Melatonin and melatonergic drugs in sleep disorders

Melatonin is an endogenous chronobiological regulator secreted mainly from the pineal gland, which has been used as a dietary supplement in the treatment of sleep problems, including insomnia, parasomnia, and circadian rhythm sleep disorders. However, the short half-life and rapid metabolism of melatonin limit its suitability as a drug. There are many melatonergic drugs used in the treatment of sleep disorders and several drugs are under investigation for approval. Ramelteon was the first melatonergic agonist approved as hypnotic agent by U.S. Food and Drug Administration for the treatment of insomnia. It exhibits higher selective affinity for melatonin 1a (MT₁) receptor than melatonin 1b (MT₂) receptor. This selectivity suggests that it targets sleep onset with no significant adverse effect or dependency. Agomelatin, naphtahalenic compound, act as a potent MT₁/MT₂ melatonergic receptor agonist and serotonergic receptor antagonist was approved for treatment of depression in 2009. This dual action drug is the first melatonergic agent used in depression. Another melatonergic agonist, tasimelteon has high affinity for the MT₁/MT₂ receptors in humans. It was approved for the treatment of non-24 hours sleep-wake rhythm disorder. The newly developed melatonin and melatonergic drugs have the potential to be used extensively in various clinical situations and substitute the old benzodiazepine and its derivatives in the treatment of insomnia. However, the efficacy and safety of newly developed melatonergic drugs should be elucidated through long-term clinical trials.

The associations between central serous chorioretinopathy and muscle relaxants: A case-control study

PURPOSE

To evaluate the role of muscle-relaxants as risk factors for the development of central serous chorioretinopathy (CSC) - the second most common retinopathy in our settings; despite multiple risk factors seen in our patients, 21% were initially labelled as idiopathic.

MATERIALS AND METHODS

Retrospective case-control study at a tertiary hospital in the United Arab Emirates, where we reviewed the medical records of 273 patients with CSC examined between 2010 and 2019 for use of muscle-relaxants including tolperisone/eperisone, carisoprodol and gabapentin/pregabalin within a year of onset/recurrence of the disease. Intake of drugs with known association with CSC (including corticosteroids/sympathomimetics) was also recorded. Two hundred eighty-six subjects with adverse events seen at the same institute during the same study period served as controls. Odds ratios, Chi-Square tests and multivariate logistic regression were carried out to determine any associations with the muscle-relaxants and other pharmacological confounders - corticosteroids/sympathomimetics.

RESULTS

Muscle relaxants may increase the risk of CSC as evident on multivariate regression analysis (OR: 2.55; confidence interval [CI]: 1.208-5.413); the significance was retained on removing the 6 subjects who had corticosteroids/sympathomimetics (OR: 2.30; CI: 1.073-4.939). Univariate analysis yielded an OR of 2.52 for muscle relaxants (CI: 1.2149-5.2276), 2.96 for eperisone/tolperisone (CI: 1.3531-6.5038), and 6.26 for eperisone as an individual agent (CI: 1.8146-21.6252).

CONCLUSION

We found muscle relaxants to be associated factors of CSC regardless of inclusion of corticosteroids/sympathomimetics (P < 0.05). Among individual classes of muscle relaxants in this study, only eperisone/tolperisone posed a significant risk (P < 0.05). The vascular smooth muscle relaxation could be the possible mechanism that affects the choroidal blood flow and indirectly predisposes to CSC.

Circadian rhythm-related factors of PER and CRY family genes function as novel therapeutic targets and prognostic biomarkers in lung adenocarcinoma

The period (PER) and cryptochrome (CRY) families play critical roles in circadian rhythms. The imbalance of circadian factors may lead to the occurrence of cancer. Expressions of PER and CRY family members decrease in various cancers. Nevertheless, expression levels, genetic variations, and molecular mechanisms of PER and CRY family members in lung adenocarcinoma (LUAD) and their correlations with prognoses and immune infiltration in LUAD patients are still unclear. In this study, to identify their biological functions in LUAD development, comprehensive high-throughput techniques were applied to analyze the relationships of expressions of PER and CRY family members with genetic variations, molecular mechanisms, and immune infiltration. The present results showed that transcription levels of PER1 and CRY2 in LUAD were significantly downregulated. High expression levels of PER2, PER3, CRY1, and CRY2 indicated longer overall survival. Some cancer signaling pathways were related to PER and CRY family members, such as cell-cycle, histidine metabolism, and progesterone-mediated oocyte maturation pathways. Expressions of PER and CRY family members significantly affected the infiltration of different immune cells. In conclusion, our findings may help better understand the molecular basis of LUAD, and provide new perspectives of PER and CRY family members as novel biomarkers for LUAD.

Melatonergic Receptors (Mt1/Mt2) as a Potential Additional Target of Novel Drugs for Depression

A complex pathogenesis involving several physiological systems is theorized to underline the development of depressive disorders. Depression is accompanied by circadian regulation disruption and interaction with the functioning of both central and peripheral oscillators. Many aspects of melatonin function unite these systems. The use of drugs for circadian rhythm disorders could inspire a potential treatment strategy for depression. Melatonin plays an essential role in the regulation of circadian rhythms. It exerts effect by activating two types of melatonin receptors, type 1A (MT1) and 1B (MT2). These are G-protein-coupled receptors, predominantly located in the central nervous system. MT1/MT2 agonists could be a useful treatment approach according to all three prevalent theories of the pathogenesis of depression involving either monoamines, synaptic remodeling, or immune/inflammatory events. MT1/MT2 receptors can be a potential target for novel antidepressants with impact on concentrations of neurotrophins or neurotransmitters, and reducing levels of pro-inflammatory cytokines. There is an interesting cross-talk mediated via the physical association of melatonin and serotonin receptors into functional heteromers. The antidepressive and neurogenetic effects of MT1/MT2 agonists can also be caused by the inhibition of the acid sphingomyelinase, leading to reduced ceramide, or increasing monoamine oxidase A levels in the hippocampus. Compounds targeting MT1 and MT2 receptors could have potential for new anti-depressants that may improve the quality of therapeutic interventions in treating depression and relieving symptoms. In particular, a combined effect on MT1 and/or MT2 receptors and neurotransmitter systems may be useful, since the normalization of the circadian rhythm through the melatonergic system will probably contribute to improved treatment. In this review, we discuss melatonergic receptors as a potential additional target for novel drugs for depression.

Circadian and Immunity Cycle Talk in Cancer Destination: From Biological Aspects to In Silico Analysis

Simple Summary

The circadian cycle is a natural cycle of the body repeated every 24 h, based on a day and night rhythm, and it affects many body processes. The present article reviews the importance and role of the circadian cycle in cancer and its association with the immune system and immunotherapy drugs at the cellular and molecular levels. It also examines the genes and cellular pathways involved in both circadian and immune systems. It offers possible computational solutions to increase the effectiveness of cancer treatment concerning the circadian cycle.

Abstract

Cancer is the leading cause of death and a major problem to increasing life expectancy worldwide. In recent years, various approaches such as surgery, chemotherapy, radiation, targeted therapies, and the newest pillar, immunotherapy, have been developed to treat cancer. Among key factors impacting the effectiveness of treatment, the administration of drugs based on the circadian rhythm in a person and within individuals can significantly elevate drug efficacy, reduce adverse effects, and prevent drug resistance. Circadian clocks also affect various physiological processes such as the sleep cycle, body temperature cycle, digestive and cardiovascular processes, and endocrine and immune systems. In recent years, to achieve precision patterns for drug administration using computational methods, the interaction of the effects of drugs and their cellular pathways has been considered more seriously. Integrated data-derived pathological images and genomics, transcriptomics, and proteomics analyses have provided an understanding of the molecular basis of cancer and dramatically revealed interactions between circadian and immunity cycles. Here, we describe crosstalk between the circadian cycle signaling pathway and immunity cycle in cancer and discuss how tumor microenvironment affects the influence on treatment process based on individuals’ genetic differences. Moreover, we highlight recent advances in computational modeling that pave the way for personalized immune chronotherapy.

DAT-truncated epigenetics: heterozigosity of the grand-mother rat temperates the vulnerable phenotype in second-generation offspring

Behavioral phenotype differs among epigenotypes of dopamine-transporter heterozygous (DAT-HET) rats. Epigenetic regulations act through trans-generational effects, referring to phenotypic variations emerging at second or third generation. To investigate trans-generational influences exerted by maternal grandmothers, we developed breeding schemes where only the genotype of maternal grandmothers varied. Heterozygous females, to serve as MAT vs MIX mothers, were generated, respectively, from WTxKO=MAT and MATxKO=MIX breeding, with KO males acting as grandfather. The HET experimental groups, generated from either MAT or MIX mothers, were called MIX-by-MAT and MIX² (male-fathers KO; asset-M: wild\healthy-allele from dam); or SOT and SIX (male-fathers WT; asset-P: mutated-allele from dam). Thus, sequelae of first-encounter between wild\healthy and mutated DAT-alleles (in maternal-lineage) were compared at first- (MAT-dam, WT-grandmother) vs. at second- (MIX-dam, HET-grandmother) generation. We characterized, within these epigenotypes, (1) circadian home-cage activity; (2) preference for social stimuli. Marked alterations of circadian activity appeared in HETs, if offspring of MAT-dams, compared to MIX² (HET offspring of MIX-dams) which, in turn, were undistinguishable from WT-controls. A clear-cut social preference by WT-rats was expressed towards SIX compared to SOT stimulus-rats, confirming reduced social motivations. In conclusion, significant epigenetic modulations took place in DAT-HET rats, as a function of maternal grandmother's genotype.

Motif structure for the four subgroups within the suprachiasmatic nuclei affects its entrainment ability

Circadian rhythms of physiological and behavioral activities are regulated by a central clock. This clock is located in the bilaterally symmetrical suprachiasmatic nucleus (SCN) of mammals. Each nucleus contains a light-sensitive group of neurons, named the ventrolateral (VL) part, with the rest of the neurons being insensitive to light, named the dorsomedial (DM) group. While the coupling between the VL and DM subgroups have been investigated quite well, the communication among the four subgroups across the nuclei did not get a lot of attention. In this article, we theoretically analyzed seven motiflike connection patterns to investigate the network of the two nuclei of the SCN as a whole in relation to the function of the SCN. We investigated the entrainment ability of the SCN and found that the entrainment range is larger in the motifs containing a link between the two VL parts across the nuclei, but it is smaller in the motifs that contain a link between the two DM parts across the nuclei. The SCN may strengthen or weaken connections between the left and right nucleus to accomodate changes in external conditions, such as resynchronization after a jet lag, adjustment to photoperiod or for the aging SCN.

MicroRNAs as Potential Orchestrators of Alzheimer's Disease-Related Pathologies: Insights on Current Status and Future Possibilities

Alzheimer's disease (AD) is a progressive and deleterious neurodegenerative disease, strongly affecting the cognitive functions and memory of seniors worldwide. Around 58% of the affected patients live in low and middle-income countries, with estimates of increasing deaths caused by AD in the coming decade. AD is a multifactor pathology. Mitochondrial function declines in AD brain and is currently emerging as a hallmark of this disease. It has been considered as one of the intracellular processes severely compromised in AD. Many mitochondrial parameters decline already during aging; mitochondrial efficiency for energy production, reactive oxygen species (ROS) metabolism and the de novo synthesis of pyrimidines, to reach an extensive functional failure, concomitant with the onset of neurodegenerative conditions. Besides its impact on cognitive functions, AD is characterized by loss of synapses, extracellular amyloid plaques composed of the amyloid-β peptide (Aβ), and intracellular aggregates of hyperphosphorylated Tau protein, accompanied by drastic sleep disorders, sensory function alterations and pain sensitization. Unfortunately, till date, effective management of AD-related disorders and early, non-invasive AD diagnostic markers are yet to be found. MicroRNAs (miRNAs) are small non-coding nucleic acids that regulate key signaling pathway(s) in various disease conditions. About 70% of experimentally detectable miRNAs are expressed in the brain where they regulate neurite outgrowth, dendritic spine morphology, and synaptic plasticity. Increasing studies suggest that miRNAs are intimately involved in synaptic function and specific signals during memory formation. This has been the pivotal key for considering miRNAs crucial molecules to be studied in AD. MicroRNAs dysfunctions are increasingly acknowledged as a pivotal contributor in AD via deregulating genes involved in AD pathogenesis. Moreover, miRNAs have been proved to control pain sensitization processes and regulate circadian clock system that affects the sleep process. Interestingly, the differential expression of miRNA panels implies their emerging potential as diagnostic AD biomarkers. In this review, we will present an updated analysis of miRNAs role in regulating signaling processes that are involved in AD-related pathologies. We will discuss the current challenges against wider use of miRNAs and the future promising capabilities of miRNAs as diagnostic and therapeutic means for better management of AD.

Modelling the functional roles of synaptic and extra-synaptic γ-aminobutyric acid receptor dynamics in circadian timekeeping

In the suprachiasmatic nucleus (SCN), γ-aminobutyric acid (GABA) is a primary neurotransmitter. GABA can signal through two types of GABAA receptor subunits, often referred to as synaptic GABAA (gamma subunit) and extra-synaptic GABAA (delta subunit). To test the functional roles of these distinct GABAA in regulating circadian rhythms, we developed a multicellular SCN model where we could separately compare the effects of manipulating GABA neurotransmitter or receptor dynamics. Our model predicted that blocking GABA signalling modestly increased synchrony among circadian cells, consistent with published SCN pharmacology. Conversely, the model predicted that lowering GABAA receptor density reduced firing rate, circadian cell fraction, amplitude and synchrony among individual neurons. When we tested these predictions, we found that the knockdown of delta GABAA reduced the amplitude and synchrony of clock gene expression among cells in SCN explants. The model further predicted that increasing gamma GABAA densities could enhance synchrony, as opposed to increasing delta GABAA densities. Overall, our model reveals how blocking GABAA receptors can modestly increase synchrony, while increasing the relative density of gamma over delta subunits can dramatically increase synchrony. We hypothesize that increased gamma GABAA density in the winter could underlie the tighter phase relationships among SCN cells.

Aging of the Suprachiasmatic Nucleus, CIRCLONSA Syndrome, Implications for Regenerative Medicine and Restoration of the Master Body Clock

The suprachiasmatic nucleus (SCN) in the brain is the master regulator of the circadian clocks throughout the human body. With increasing age the circadian clock in humans and other mammals becomes increasingly disorganized leading to a large number of more or less well-categorized problems. While a lot of aging research has focused on the peripheral clocks in tissues across organisms, it remains a paramount task to quantify aging of the most important master clock, the human SCN. Furthermore, a pipeline needs to be developed with therapies to mitigate the systemic cellular circadian dysfunction in the elderly and ultimately repair and reverse aging of the SCN itself. A disease classification for the aging SCN, Circadian Clock Neuronal Senile Atrophy (CIRCLONSA syndrome), would improve research funding and goal-oriented biotechnological entrepreneurship.

Adult hypothalamic neurogenesis and sleep-wake dysfunction in aging

In the mammalian brain, adult neurogenesis has been extensively studied in the hippocampal sub-granular zone and the sub-ventricular zone of the anterolateral ventricles. However, growing evidence suggests that new cells are not only "born" constitutively in the adult hypothalamus, but many of these cells also differentiate into neurons and glia and serve specific functions. The preoptic-hypothalamic area plays a central role in the regulation of many critical functions, including sleep-wakefulness and circadian rhythms. While a role for adult hippocampal neurogenesis in regulating hippocampus-dependent functions, including cognition, has been extensively studied, adult hypothalamic neurogenic process and its contributions to various hypothalamic functions, including sleep-wake regulation are just beginning to unravel. This review is aimed at providing the current understanding of the hypothalamic adult neurogenic processes and the extent to which it affects hypothalamic functions, including sleep-wake regulation. We propose that hypothalamic neurogenic processes are vital for maintaining the proper functioning of the hypothalamic sleep-wake and circadian systems in the face of regulatory challenges. Sleep-wake disturbance is a frequent and challenging problem of aging and age-related neurodegenerative diseases. Aging is also associated with a decline in the neurogenic process. We discuss a hypothesis that a decrease in the hypothalamic neurogenic process underlies the aging of its sleep-wake and circadian systems and associated sleep-wake disturbance. We further discuss whether neuro-regenerative approaches, including pharmacological and non-pharmacological stimulation of endogenous neural stem and progenitor cells in hypothalamic neurogenic niches, can be used for mitigating sleep-wake and other hypothalamic dysfunctions in aging.

Chronobiology and Chronotherapy in Depression: Current Knowledge and Chronotherapeutic Promises

Background:

Depression is a heavily prevalent mental disorder. Symptoms of depression extend beyond mood, cognition, and behavior to include a spectrum of somatic manifestations in all organic systems. Changes in sleep and neuroendocrine rhythms are especially prominent, and disruptions of circadian rhythms have been closely related to the neurobiology of depression. With the advent of increased research in chronobiology, various pathophysiologic mechanisms have been proposed, including anomalies of sleep architecture, the effects of clock gene polymorphisms in monoamine metabolism, and the deleterious impact of social zeitgebers. The identification of these chronodisruptions has propelled the emergence of several chronotherapeutic strategies, both pharmacological and non-pharmacological, with varying degrees of clinical evidence.

Methods:

The fundamental objective of this review is to integrate current knowledge about the role of chronobiology and depression and to summarize the interventions developed to resynchronize biorhythms both within an individual and with geophysical time.

Results:

We have found that among the non-pharmacological alternatives, triple chronotherapywhich encompasses bright light therapy, sleep deprivation therapy, and consecutive sleep phase advance therapy-has garnered the most considerable scientific interest. On the other hand, agomelatine appears to be the most promising pharmacological option, given its unique melatonergic pharmacodynamics.

Conclusions:

Research in chronotherapy as a treatment for depression is currently booming. Novel interventions could play a significant role in adopting new options for the treatment of depression, with Tripe Cronotherapy standing out as the most promising treatment.

Lipocalin-type prostaglandin D synthase regulates light-induced phase advance of the central circadian rhythm in mice

We previously showed that mice lacking pituitary adenylate cyclase-activating polypeptide (PACAP) exhibit attenuated light-induced phase shift. To explore the underlying mechanisms, we performed gene expression analysis of laser capture microdissected suprachiasmatic nuclei (SCNs) and found that lipocalin-type prostaglandin (PG) D synthase (L-PGDS) is involved in the impaired response to light stimulation in the late subjective night in PACAP-deficient mice. L-PGDS-deficient mice also showed impaired light-induced phase advance, but normal phase delay and nonvisual light responses. Then, we examined the receptors involved in the response and observed that mice deficient for type 2 PGD₂ receptor DP2/CRTH2 (chemoattractant receptor homologous molecule expressed on Th2 cells) show impaired light-induced phase advance. Concordant results were observed using the selective DP2/CRTH2 antagonist CAY10471. These results indicate that L-PGDS is involved in a mechanism of light-induced phase advance via DP2/CRTH2 signaling.

Kawaguchi et al. show that mice deficient in lipocalin-type prostaglandin (PG) D synthase (L-PGDS) exhibit impaired light-induced phase advance, but normal phase delay and nonvisual light responses. This study suggests the role of L-PGDS for the light-induced phase advance possibly via a chemoattractant receptor DP2/CRTH2.

A role for the neuropeptide somatostatin in the neurobiology of behaviors associated with substances abuse and affective disorders

In recent years, neuropeptides which display potent regulatory control of stress-related behaviors have been extensively demonstrated to play a critical role in regulating behaviors associated with substance abuse and affective disorders. Somatostatin (SST) is one neuropeptide known to significantly contribute to emotionality and stress behaviors. However, the role of SST in regulating behavior has received relatively little attention relative to other stress-involved peptides, such as neuropeptide Y or corticotrophin releasing factor. This review characterizes our current understanding of the role of SST and SST-expressing cells in general in modulating several behaviors intrinsically linked to substance abuse and affective disorders, specifically: anxiety and fear; stress and depression; feeding and drinking; and circadian rhythms. We further summarize evidence of a direct role for the SST system, and specifically somatostatin receptors 2 and 4, in substance abuse disorders. This article is part of the special issue on 'Neuropeptides'.

Systems Biology Approaches and Precision Oral Health: A Circadian Clock Perspective

A vast majority of the pathophysiological and metabolic processes in humans are temporally controlled by a master circadian clock located centrally in the hypothalamic suprachiasmatic nucleus of the brain, as well as by specialized peripheral oscillators located in other body tissues. This circadian clock system generates a rhythmical diurnal transcriptional-translational cycle in clock genes and protein expression and activities regulating numerous downstream target genes. Clock genes as key regulators of physiological function and dysfunction of the circadian clock have been linked to various diseases and multiple morbidities. Emerging omics technologies permits largescale multi-dimensional investigations of the molecular landscape of a given disease and the comprehensive characterization of its underlying cellular components (e.g., proteins, genes, lipids, metabolites), their mechanism of actions, functional networks and regulatory systems. Ultimately, they can be used to better understand disease and interpatient heterogeneity, individual profile, identify personalized targetable key molecules and pathways, discover novel biomarkers and genetic alterations, which collectively can allow for a better patient stratification into clinically relevant subgroups to improve disease prediction and prevention, early diagnostic, clinical outcomes, therapeutic benefits, patient's quality of life and survival. The use of “omics” technologies has allowed for recent breakthroughs in several scientific domains, including in the field of circadian clock biology. Although studies have explored the role of clock genes using circadiOmics (which integrates circadian omics, such as genomics, transcriptomics, proteomics and metabolomics) in human disease, no such studies have investigated the implications of circadian disruption in oral, head and neck pathologies using multi-omics approaches and linking the omics data to patient-specific circadian profiles. There is a burgeoning body of evidence that circadian clock controls the development and homeostasis of oral and maxillofacial structures, such as salivary glands, teeth and oral epithelium. Hence, in the current era of precision medicine and dentistry and patient-centered health care, it is becoming evident that a multi-omics approach is needed to improve our understanding of the role of circadian clock-controlled key players in the regulation of head and neck pathologies. This review discusses current knowledge on the role of the circadian clock and the contribution of omics-based approaches toward a novel precision health era for diagnosing and treating head and neck pathologies, with an emphasis on oral, head and neck cancer and Sjögren's syndrome.

Mechanisms underlying the association between insomnia, anxiety, and depression in adolescence: Implications for behavioral sleep interventions

There is robust evidence of an association between insomnia, anxiety, and depression in adolescence. The aim of this review is to describe and synthesize potential mechanisms underlying this association and explore implications for the design of adolescent behavioral sleep interventions. Specifically, we examine whether insomnia symptoms are a mechanism for the development of internalizing symptoms in adolescence and whether sleep interventions are an effective treatment for both insomnia and internalizing symptoms in adolescence because they target the shared mechanisms underlying these disorders. Research using different methodologies points to the role of sequential, parallel, and interacting mechanisms. In this paper, we review a wide range of relevant biological (i.e., polymorphisms and dysregulation in serotonin, dopamine, and circadian clock genes; alterations in corticolimbic and mesolimbic brain circuits; cortisol reactivity to stress; inflammatory cytokine dysregulation; biased memory consolidation; changes in sleep architecture), psychological (i.e., cognitive inflexibility, interpretational biases, judgment biases, negative attribution styles, worry, rumination, biased attention to threat, dysfunctional beliefs and attitudes about sleep, misperception of sleep deficit), and social mechanisms (i.e., reduced and impaired social interactions, unhelpful parenting behaviors, family stress) and propose an integrative multilevel model of how these phenomena may interact to increase vulnerability to both insomnia and internalizing disorders. Several 'biopsychosocial' mechanisms hold promise as viable treatment targets for adolescent behavioral sleep interventions, which may reduce both insomnia and internalizing symptoms.

Photoperiod-Induced Neuroplasticity in the Circadian System

Seasonal changes in light exposure have profound effects on behavioral and physiological functions in many species, including effects on mood and cognitive function in humans. The mammalian brain's master circadian clock, the suprachiasmatic nucleus (SCN), transmits information about external light conditions to other brain regions, including some implicated in mood and cognition. Although the detailed mechanisms are not yet known, the SCN undergoes highly plastic changes at the cellular and network levels under different light conditions. We therefore propose that the SCN may be an essential mediator of the effects of seasonal changes of day length on mental health. In this review, we explore various forms of neuroplasticity that occur in the SCN and other brain regions to facilitate seasonal adaptation, particularly altered phase distribution of cellular circadian oscillators in the SCN and changes in hypothalamic neurotransmitter expression.

Central Circadian Clock Regulates Energy Metabolism

Our body not only responds to environmental changes but also anticipates them. The light and dark cycle with the period of about 24 h is a recurring environmental change that determines the diurnal variation in food availability and safety from predators in nature. As a result, the circadian clock is evolved in most animals to align locomotor behaviors and energy metabolism with the light cue. The central circadian clock in mammals is located at the suprachiasmatic nucleus (SCN) of the hypothalamus in the brain. We here review the molecular and anatomic architecture of the central circadian clock in mammals, describe the experimental and observational evidence that suggests a critical role of the central circadian clock in shaping systemic energy metabolism, and discuss the involvement of endocrine factors, neuropeptides, and the autonomic nervous system in the metabolic functions of the central circadian clock.

The Suprachiasmatic Nucleus of the Dromedary Camel (Camelus dromedarius): Cytoarchitecture and Neurochemical Anatomy

In mammals, biological rhythms are driven by a master circadian clock located in the suprachiasmatic nucleus (SCN) of the hypothalamus. Recently, we have demonstrated that in the camel, the daily cycle of environmental temperature is able to entrain the master clock. This raises several questions about the structure and function of the SCN in this species. The current work is the first neuroanatomical investigation of the camel SCN. We carried out a cartography and cytoarchitectural study of the nucleus and then studied its cell types and chemical neuroanatomy. Relevant neuropeptides involved in the circadian system were investigated, including arginine-vasopressin (AVP), vasoactive intestinal polypeptide (VIP), met-enkephalin (Met-Enk), neuropeptide Y (NPY), as well as oxytocin (OT). The neurotransmitter serotonin (5-HT) and the enzymes tyrosine hydroxylase (TH) and aromatic L-amino acid decarboxylase (AADC) were also studied. The camel SCN is a large and elongated nucleus, extending rostrocaudally for 9.55 ± 0.10 mm. Based on histological and immunofluorescence findings, we subdivided the camel SCN into rostral/preoptic (rSCN), middle/main body (mSCN) and caudal/retrochiasmatic (cSCN) divisions. Among mammals, the rSCN is unusual and appears as an assembly of neurons that protrudes from the main mass of the hypothalamus. The mSCN exhibits the triangular shape described in rodents, while the cSCN is located in the retrochiasmatic area. As expected, VIP-immunoreactive (ir) neurons were observed in the ventral part of mSCN. AVP-ir neurons were located in the rSCN and mSCN. Results also showed the presence of OT-ir and TH-ir neurons which seem to be a peculiarity of the camel SCN. OT-ir neurons were either scattered or gathered in one isolated cluster, while TH-ir neurons constituted two defined populations, dorsal parvicellular and ventral magnocellular neurons, respectively. TH colocalized with VIP in some rSCN neurons. Moreover, a high density of Met-Enk-ir, 5-HT-ir and NPY-ir fibers were observed within the SCN. Both the cytoarchitecture and the distribution of neuropeptides are unusual in the camel SCN as compared to other mammals. The presence of OT and TH in the camel SCN suggests their role in the modulation of circadian rhythms and the adaptation to photic and non-photic cues under desert conditions.

Are circadian rhythms new pathways to understand Autism Spectrum Disorder?

Autism Spectrum Disorder (ASD) is a frequent neurodevelopmental disorder. ASD is probably the result of intricate interactions between genes and environment altering progressively the development of brain structures and functions. Circadian rhythms are a complex intrinsic timing system composed of almost as many clocks as there are body cells. They regulate a variety of physiological and behavioral processes such as the sleep-wake rhythm. ASD is often associated with sleep disorders and low levels of melatonin. This first point raises the hypothesis that circadian rhythms could have an implication in ASD etiology. Moreover, circadian rhythms are generated by auto-regulatory genetic feedback loops, driven by transcription factors CLOCK and BMAL1, who drive transcription daily patterns of a wide number of clock-controlled genes (CCGs) in different cellular contexts across tissues. Among these, are some CCGs coding for synapses molecules associated to ASD susceptibility. Furthermore, evidence emerges about circadian rhythms control of time brain development processes.

Day/night expression of MT1 and MT2 receptors in hypothalamic nuclei of the primate Sapajus apella

Melatonin is involved in the temporal organization of several physiological and behavioral events, controlled by hypothalamic nuclei, like sleep, feeding, reproduction and metabolic modulation and acts through two types of high-affinity G protein-coupled membrane receptors: MT₁ and MT₂. This study aimed to investigate the expression of MT₁ and MT₂ receptors proteins in four hypothalamic nuclei, i.e., SCN, supraoptic (SON), paraventricular (PVN) and anteroventral periventricular nuclei (AVPV), of the diurnal primate Sapajus apella using immunohistochemistry. Since these areas are involved in the expression of biological rhythms, they are candidates to have variations in their neurochemistry, so the MT₁ and MT₂ expression has been analyzed at a point in light and another in the dark phase. Both receptors were found to have day/night differences in the four hypothalamic nuclei with an apparent inverse expression in the SCN compared with the other areas. These differences could be related to the idea that the individual should be prepared to respond by different ways to melatonin signal within the several processes and can contribute to the efficacy of melatonin ligands or melatonin in therapies.

Disruption of the Suprachiasmatic Nucleus in Fibroblast Growth Factor Signaling-Deficient Mice

Fibroblast growth factor (Fgf) 8 is essential for the development of multiple brain regions. Previous studies from our laboratory showed that reduced Fgf8 signaling led to the developmental alterations of neuroendocrine nuclei that originated within the diencephalon, including the paraventricular (PVN) and supraoptic (SON) nuclei. To further understand the role of Fgf8 in the development of other hypothalamic nuclei, we examined if Fgf8 and its cognate receptor, Fgfr1, also impact the integrity of the suprachiasmatic nuclei (SCN). The SCN control an organism's circadian rhythm and contain vasoactive intestinal peptide (VIP)-producing neurons as the main input neurons. Mice hypomorphic for Fgf8, Fgfr1, or both were examined for their SCN volume and the number of VIP neurons on postnatal day (PN) 0; adult hypomorphic mice were further examined for SCN function by quantifying SCN neuronal activation using cFos as a marker. On PN0, mice homozygous for Fgf8 hypomorphy displayed the most severe reduction of the SCN volume and VIP neurons. Those heterozygous for Fgf8 hypomorphy alone or Fgf8 combined with Fgfr1 hypomorphy, called double heterozygotes (DH), showed normal SCN volume but significantly reduced VIP neurons, albeit less severely than the homozygotes. Adult wild type, heterozygous Fgf8 hypomorphs (F8 Het), and DH mice were also examined for SCN cFos activation at three time points: 1 h (morning), 6 h (afternoon), and 11 h (evening) after light onset. In F8 Het mice, a significant change in the pattern of cFos immunostaining that may reflect delayed morning SCN activation was observed. Overall, our studies provide evidence supporting that deficiencies in Fgf8 not only impact the structural integrity of the SCN but also the pattern of SCN activation in response to light.

Light therapy for better mood and insulin sensitivity in patients with major depression and type 2 diabetes: a randomised, double-blind, parallel-arm trial

BACKGROUND

Major depression and type 2 diabetes often co-occur. Novel treatment strategies for depression in type 2 diabetes patients are warranted, as depression in type 2 diabetes patients is associated with poor prognosis and treatment results. Major depression and concurrent sleep disorders have been related to disturbances of the biological clock. The biological clock is also involved in regulation of glucose metabolism by modulating peripheral insulin sensitivity. Light therapy has been shown to be an effective antidepressant that 'resets' the biological clock. We here describe the protocol of a study that evaluates the hypothesis that light therapy improves mood as well as insulin sensitivity in patients with a major depressive episode and type 2 diabetes.

METHODS/DESIGN

This study is a randomised, double-blind, parallel-arm trial in 98 participants with type 2 diabetes and a major depressive episode, according to DSM-IV criteria. We will assess whether light therapy improves depressive symptoms and insulin sensitivity, our primary outcome measures, and additionally investigate whether these effects are mediated by restoration of the circadian rhythmicity, as measured by sleep and hypothalamic-pituitary-adrenal axis activity. Participants will be randomly allocated to a bright white-yellowish light condition or dim green light condition. Participants will undergo light therapy for half an hour every morning for 4 weeks at home. At several time points, namely before the start of light therapy, during light therapy, after completion of 4 weeks of light therapy and after 4 weeks follow-up, several psychometrical, psychophysiological and glucometabolic measures will be performed.

DISCUSSION

If light therapy effectively improves mood and insulin sensitivity in type 2 diabetes patients with a major depressive episode, light therapy may be a valuable patient friendly addition to the currently available treatment strategies. Additionally, if our data support the role of restoration of circadian rhythmicity, such an observation may guide further development of chronobiological treatment strategies in this patient population.

TRIAL REGISTRATION

The Netherlands Trial Register (NTR) NTR4942 . Registered 13 January 2015.

Candidate genes underlying heritable differences in reproductive seasonality between wild and domestic rabbits

Reproductive seasonality is a trait that often differs between domestic animals and their wild ancestors, with domestic animals showing prolonged or even continuous breeding seasons. However, the genetic basis underlying this trait is still poorly understood for most species, and because environmental factors and resource availability are known to play an important role in determining breeding seasons, it is also not clear in most cases to what extent this phenotypic shift is determined by the more lenient captive conditions or by genetic factors. Here, using animals resulting from an initial cross between wild and domestic rabbits followed by two consecutive backcrosses (BC1 and BC2) to wild rabbits, we evaluated the yearly distribution of births for the different generations. Similar to domestic rabbits, F1 animals could be bred all year round but BC1 and BC2 animals showed a progressive and significant reduction in the span of the breeding season, providing experimental evidence that reduced seasonal breeding in domestic rabbits has a clear genetic component and is not a simple by-product of rearing conditions. We then took advantage of a recently published genome-wide scan of selection in the domesticated lineage and searched for candidate genes potentially associated with this phenotypic shift. Candidate genes located within regions targeted by selection include well-known examples of genes controlling clock functions (CRY1 and NR3C1) and reproduction (PRLR).

Sleep- and circadian rhythm-associated pathways as therapeutic targets in bipolar disorder

INTRODUCTION

Disruptions in sleep and circadian rhythms are observed in individuals with bipolar disorders (BD), both during acute mood episodes and remission. Such abnormalities may relate to dysfunction of the molecular circadian clock and could offer a target for new drugs.

AREAS COVERED

This review focuses on clinical, actigraphic, biochemical and genetic biomarkers of BDs, as well as animal and cellular models, and highlights that sleep and circadian rhythm disturbances are closely linked to the susceptibility to BDs and vulnerability to mood relapses. As lithium is likely to act as a synchronizer and stabilizer of circadian rhythms, we will review pharmacogenetic studies testing circadian gene polymorphisms and prophylactic response to lithium. Interventions such as sleep deprivation, light therapy and psychological therapies may also target sleep and circadian disruptions in BDs efficiently for treatment and prevention of bipolar depression.

EXPERT OPINION

We suggest that future research should clarify the associations between sleep and circadian rhythm disturbances and alterations of the molecular clock in order to identify critical targets within the circadian pathway. The investigation of such targets using human cellular models or animal models combined with 'omics' approaches are crucial steps for new drug development.

Efferent projections of the suprachiasmatic nucleus based on the distribution of vasoactive intestinal peptide (VIP) and arginine vasopressin (AVP) immunoreactive fibers in the hypothalamus of Sapajus apella

The suprachiasmatic nucleus (SCN), which is considered to be the master circadian clock in mammals, establishes biological rhythms of approximately 24 h that several organs exhibit. One aspect relevant to the study of the neurofunctional features of biological rhythmicity is the identification of communication pathways between the SCN and other brain areas. As a result, SCN efferent projections have been investigated in several species, including rodents and a few primates. The fibers originating from the two main intrinsic fiber subpopulations, one producing vasoactive intestinal peptide (VIP) and the other producing arginine vasopressin (AVP), exhibit morphological traits that distinguish them from fibers that originate from other brain areas. This distinction provides a parameter to study SCN efferent projections. In this study, we mapped VIP (VIP-ir) and AVP (AVP-ir) immunoreactive (ir) fibers and endings in the hypothalamus of the primate Sapajus apella via immunohistochemical and morphologic study. Regarding the fiber distribution pattern, AVP-ir and VIP-ir fibers were identified in regions of the tuberal hypothalamic area, retrochiasmatic area, lateral hypothalamic area, and anterior hypothalamic area. VIP-ir and AVP-ir fibers coexisted in several hypothalamic areas; however, AVP-ir fibers were predominant over VIP-ir fibers in the posterior hypothalamus and medial periventricular area. This distribution pattern and the receiving hypothalamic areas of the VIP-ir and AVP-ir fibers, which shared similar morphological features with those found in SCN, were similar to the patterns observed in diurnal and nocturnal animals. This finding supports the conservative nature of this feature among different species. Morphometric analysis of SCN intrinsic neurons indicated homogeneity in the size of VIP-ir neurons in the SCN ventral portion and heterogeneity in the size of two subpopulations of AVP-ir neurons in the SCN dorsal portion. The distribution of fibers and morphometric features of these neuronal populations are described and compared with those of other species in the present study.

Efficacy of vestipitant, a neurokinin-1 receptor antagonist, in primary insomnia

STUDY OBJECTIVES

Investigate the hypnotic effects of repeated doses of neurokinin-1 receptor antagonist, vestipitant, in primary insomnia.

DESIGN

Randomized, double-blind, placebo-controlled 28-day parallel-group study.

SETTING

Eleven sleep centers in Germany.

PATIENTS

One hundred sixty-one patients with primary insomnia.

INTERVENTIONS

Patients received vestipitant (15 mg) or placebo for 28 days; 2-night polysomnographic assessment occurred on nights 1/2 and 27/28.

MEASUREMENTS AND RESULTS

Wake after sleep onset (WASO) was improved on nights 1/2 and 27/28 (ratio, vestipitant versus placebo [95% confidence interval]: 0.76 [0.65, 0.90], P = 0.001 and 0.79 [0.65, 0.96], P = 0.02, respectively), demonstrating maintenance of the effect following repeated dosing. Latency to persistent sleep was shorter with vestipitant on nights 1/2 (P = 0.0006 versus placebo), but not on nights 27/28. Total sleep time (TST) improved with vestipitant (nights 1/2: P < 0.0001, nights 27/28: P = 0.02 versus placebo). Next-day cognitive function tests demonstrated no residual effects of vestipitant (P > 0.05 versus placebo). Adverse events (AEs) occurred in 25% of vestipitant patients versus 22% for placebo. Headache was the most common AE (8% of vestipitant patients versus 9% for placebo).

CONCLUSIONS

Vestipitant improved sleep maintenance in patients with primary insomnia, with no associated next-day cognitive impairment. The effects on wake after sleep onset and total sleep time were maintained following repeated dosing.

Fractal patterns of neural activity exist within the suprachiasmatic nucleus and require extrinsic network interactions

The mammalian central circadian pacemaker (the suprachiasmatic nucleus, SCN) contains thousands of neurons that are coupled through a complex network of interactions. In addition to the established role of the SCN in generating rhythms of ~24 hours in many physiological functions, the SCN was recently shown to be necessary for normal self-similar/fractal organization of motor activity and heart rate over a wide range of time scales--from minutes to 24 hours. To test whether the neural network within the SCN is sufficient to generate such fractal patterns, we studied multi-unit neural activity of in vivo and in vitro SCNs in rodents. In vivo SCN-neural activity exhibited fractal patterns that are virtually identical in mice and rats and are similar to those in motor activity at time scales from minutes up to 10 hours. In addition, these patterns remained unchanged when the main afferent signal to the SCN, namely light, was removed. However, the fractal patterns of SCN-neural activity are not autonomous within the SCN as these patterns completely broke down in the isolated in vitro SCN despite persistence of circadian rhythmicity. Thus, SCN-neural activity is fractal in the intact organism and these fractal patterns require network interactions between the SCN and extra-SCN nodes. Such a fractal control network could underlie the fractal regulation observed in many physiological functions that involve the SCN, including motor control and heart rate regulation.

Overlapping prefrontal systems involved in cognitive and emotional processing in euthymic bipolar disorder and following sleep deprivation: a review of functional neuroimaging studies

Prefrontal cortex (PFC) mediated cognitive and emotional processing deficits in bipolar disorder lead to functional limitations even during periods of mood stability. Alterations of sleep and circadian functioning are well-documented in bipolar disorder, but there is little research directly examining the mechanistic role of sleep and/or circadian rhythms in the observed cognitive and emotional processing deficits. We systematically review the cognitive and emotional processing deficits reliant upon PFC functioning of euthymic patients with bipolar disorder and in healthy individuals deprived of sleep. The evidence from two parallel lines of investigation suggests that sleep and circadian rhythms may be involved in the cognitive and emotional processing deficits seen in bipolar disorder through overlapping neurobiological systems. We discuss current models of bipolar highlighting the PFC-limbic connections and discuss inclusion of sleep-related mechanisms. Sleep and circadian dysfunction is a core feature of bipolar disorder and models of neurobiological abnormalities should incorporate chronobiological measures. Further research into the role of sleep and circadian rhythms in cognition and emotional processing in bipolar disorder is warranted.

Melatonin and its analogs in insomnia and depression

Benzodiazepine sedative-hypnotic drugs are widely used for the treatment of insomnia. Nevertheless, their adverse effects, such as next-day hangover, dependence and impairment of memory, make them unsuitable for long-term treatment. Melatonin has been used for improving sleep in patients with insomnia mainly because it does not cause hangover or show any addictive potential. However, there is a lack of consistency on its therapeutic value (partly because of its short half-life and the small quantities of melatonin employed). Thus, attention has been focused either on the development of more potent melatonin analogs with prolonged effects or on the design of slow release melatonin preparations. The MT(1) and MT(2) melatonergic receptor ramelteon was effective in increasing total sleep time and sleep efficiency, as well as in reducing sleep latency, in insomnia patients. The melatonergic antidepressant agomelatine, displaying potent MT(1) and MT(2) melatonergic agonism and relatively weak serotonin 5HT(2C) receptor antagonism, was found effective in the treatment of depressed patients. However, long-term safety studies are lacking for both melatonin agonists, particularly considering the pharmacological activity of their metabolites. In view of the higher binding affinities, longest half-life and relative higher potencies of the different melatonin agonists, studies using 2 or 3mg/day of melatonin are probably unsuitable to give appropriate comparison of the effects of the natural compound. Hence, clinical trials employing melatonin doses in the range of 50-100mg/day are warranted before the relative merits of the melatonin analogs versus melatonin can be settled.

Disrupted circadian rhythms in a mouse model of schizophrenia

Sleep and circadian rhythm disruption has been widely observed in neuropsychiatric disorders including schizophrenia [1] and often precedes related symptoms [2]. However, mechanistic basis for this association remains unknown. Therefore, we investigated the circadian phenotype of blind-drunk (Bdr), a mouse model of synaptosomal-associated protein (Snap)-25 exocytotic disruption that displays schizophrenic endophenotypes modulated by prenatal factors and reversible by antipsychotic treatment [3, 4]. Notably, SNAP-25 has been implicated in schizophrenia from genetic [5-8], pathological [9-13], and functional studies [14-16]. We show here that the rest and activity rhythms of Bdr mice are phase advanced and fragmented under a light/dark cycle, reminiscent of the disturbed sleep patterns observed in schizophrenia. Retinal inputs appear normal in mutants, and clock gene rhythms within the suprachiasmatic nucleus (SCN) are normally phased both in vitro and in vivo. However, the 24 hr rhythms of arginine vasopressin within the SCN and plasma corticosterone are both markedly phase advanced in Bdr mice. We suggest that the Bdr circadian phenotype arises from a disruption of synaptic connectivity within the SCN that alters critical output signals. Collectively, our data provide a link between disruption of circadian activity cycles and synaptic dysfunction in a model of neuropsychiatric disease.