Circadian regulation of pineal gland rhythmicity

The circadian rhythm: A new target of natural products that can protect against diseases of the metabolic system, cardiovascular system, and nervous system

BACKGROUND

The treatment of metabolic system, cardiovascular system, and nervous system diseases remains to be explored. In the internal environment of organisms, the metabolism of substances such as carbohydrates, lipids and proteins (including biohormones and enzymes) exhibit a certain circadian rhythm to maintain the energy supply and material cycle needed for the normal activities of organisms. As a key factor for the health of organisms, the circadian rhythm can be disrupted by pathological conditions, and this disruption accelerates the progression of diseases and results in a vicious cycle. The current treatments targeting the circadian rhythm for the treatment of metabolic system, cardiovascular system, and nervous system diseases have certain limitations, and the identification of safer and more effective circadian rhythm regulators is needed.

AIM OF THE REVIEW

To systematically assess the possibility of using the biological clock as a natural product target for disease intervention, this work reviews a range of evidence on the potential effectiveness of natural products targeting the circadian rhythm to protect against diseases of the metabolic system, cardiovascular system, and nervous system. This manuscript focuses on how natural products restore normal function by affecting the amplitude of the expression of circadian factors, sleep/wake cycles and the structure of the gut microbiota.

KEY SCIENTIFIC CONCEPTS OF THE REVIEW

This work proposes that the circadian rhythm, which is regulated by the amplitude of the expression of circadian rhythm-related factors and the sleep/wake cycle, is crucial for diseases of the metabolic system, cardiovascular system and nervous system and is a new target for slowing the progression of diseases through the use of natural products. This manuscript provides a reference for the molecular modeling of natural products that target the circadian rhythm and provides a new perspective for the time-targeted action of drugs.

Melatonin: A potential nighttime guardian against Alzheimer's

In the context of the escalating global health challenge posed by Alzheimer's disease (AD), this comprehensive review considers the potential of melatonin in both preventive and therapeutic capacities. As a naturally occurring hormone and robust antioxidant, accumulating evidence suggests melatonin is a compelling candidate to consider in the context of AD-related pathologies. The review considers several mechanisms, including potential effects on amyloid-beta and pathologic tau burden, antioxidant defense, immune modulation, and regulation of circadian rhythms. Despite its promise, several gaps need to be addressed prior to clinical translation. These include conducting additional randomized clinical trials in patients with or at risk for AD dementia, determining optimal dosage and timing, and further determining potential side effects, particularly of long-term use. This review consolidates existing knowledge, identifies gaps, and suggests directions for future research to better understand the potential of melatonin for neuroprotection and disease mitigation within the landscape of AD.

Sleep-wake modulation and pathogenesis of Alzheimer disease: Suggestions for postponement and treatment

Sleep-wake disorders are recognized as one of the earliest symptoms of Alzheimer disease (AD). Accumulating evidence has highlighted a significant association between sleep-wake disorders and AD pathogenesis, suggesting that sleep-wake modulation could be a promising approach for postponing AD onset. The suprachiasmatic nucleus (SCN) and the pineal hormone melatonin are major central modulating components of the circadian rhythm system. Cerebrospinal fluid (CSF) melatonin levels are dramatically decreased in AD. Interestingly, the number of neurofibrillary tangles in the hippocampus, which is one of the two major neuropathologic AD biomarkers, increases in parallel with the decrease in CSF melatonin levels. Furthermore, a decrease in salivary melatonin levels in middle-aged persons is a significant risk factor for the onset of the early stages of AD. Moreover, the disappearance of rhythmic fluctuations in melatonin may be one of the best biomarkers for AD diagnosis. Light therapy combined with melatonin supplementation is the recommended first-line treatment for sleep-wake disorders in AD patients and may be beneficial for ameliorating cognitive impairment. Sleep-wake cycle modulation based on AD risk gene presence is a promising early intervention for AD onset postponement.

Melatonin and brain barriers: The protection conferred by melatonin to the blood-brain barrier and blood-cerebrospinal fluid barrier

The blood-brain barrier and the blood-cerebrospinal fluid barrier separate the blood from brain tissue and cerebrospinal fluid. These brain barriers are important to maintain homeostasis and complex functions by protecting the brain from xenobiotics and harmful endogenous compounds. The disruption of brain barriers is a characteristic of neurologic diseases. Melatonin is a lipophilic hormone that is mainly produced by the pineal gland. The blood-brain barrier and the blood-cerebrospinal fluid barriers are melatonin-binding sites. Among the several melatonin actions, the most characteristic one is the regulation of sleep-wake cycles, melatonin has anti-inflammatory and antioxidant properties. Since brain barriers disruption can arise from inflammation and oxidative stress, knowing the influence of melatonin on the integrity of brain barriers is extremely important. Therefore, the objective of this review is to gather and discuss the available literature about the regulation of brain barriers by melatonin.

Circadian disturbances by altering the light-dark cycle negatively affects hematopoietic function of bone marrow in mice

Circadian rhythms in metabolically active tissues are crucial for maintaining physical health. Circadian disturbance (CD) can cause various health issues, such as metabolic abnormalities and immune and cognitive dysfunctions. However, studies on the role of CD in immune cell development and differentiation, as well as the rhythmic expression of the core clock genes and their altered expression under CD, remain unclear. Therefore, we exposed C57bl/6j mice to repeated reversed light-dark cycles for 90 days to research the effects of CD on bone marrow (BM) hematopoietic function. We also researched the effects of CD on endogenous circadian rhythms, temporally dependent expression in peripheral blood and myeloid leukocytes, environmental homeostasis within BM, and circadian oscillations of hematopoietic-extrinsic cues. Our results confirmed that when the light and dark cycles around mice were frequently reversed, the circadian rhythmic expression of the two main circadian rhythm markers, the hypothalamic clock gene, and serum melatonin, was disturbed, indicating that the body was in a state of endogenous CD. Furthermore, CD altered the temporally dependent expression of peripheral blood and BM leukocytes and destroyed environmental homeostasis within the BM as well as circadian oscillations of hematopoietic-extrinsic cues, which may negatively affect BM hematopoiesis in mice. Collectively, these results demonstrate that circadian rhythms are vital for maintaining health and suggest that the association between CD and hematopoietic dysfunction warrants further investigation.

Fundamentals of sleep regulation: Model and benchmark values for fractal and oscillatory neurodynamics

Homeostatic, circadian and ultradian mechanisms play crucial roles in the regulation of sleep. Evidence suggests that ratios of low-to-high frequency power in the electroencephalogram (EEG) spectrum indicate the instantaneous level of sleep pressure, influenced by factors such as individual sleep-wake history, current sleep stage, age-related differences and brain topography characteristics. These effects are well captured and reflected in the spectral exponent, a composite measure of the constant low-to-high frequency ratio in the periodogram, which is scale-free and exhibits lower interindividual variability compared to slow wave activity, potentially serving as a suitable standardization and reference measure. Here we propose an index of sleep homeostasis based on the spectral exponent, reflecting the level of membrane hyperpolarization and/or network bistability in the central nervous system in humans. In addition, we advance the idea that the U-shaped overnight deceleration of oscillatory slow and fast sleep spindle frequencies marks the biological night, providing somnologists with an EEG-index of circadian sleep regulation. Evidence supporting this assertion comes from studies based on sleep replacement, forced desynchrony protocols and high-resolution analyses of sleep spindles. Finally, ultradian sleep regulatory mechanisms are indicated by the recurrent, abrupt shifts in dominant oscillatory frequencies, with spindle ranges signifying non-rapid eye movement and non-spindle oscillations - rapid eye movement phases of the sleep cycles. Reconsidering the indicators of fundamental sleep regulatory processes in the framework of the new Fractal and Oscillatory Adjustment Model (FOAM) offers an appealing opportunity to bridge the gap between the two-process model of sleep regulation and clinical somnology.

Targeting the blood-brain barrier to delay aging-accompanied neurological diseases by modulating gut microbiota, circadian rhythms, and their interplays

The blood-brain barrier (BBB) impairment plays a crucial role in the pathological processes of aging-accompanied neurological diseases (AAND). Meanwhile, circadian rhythms disruption and gut microbiota dysbiosis are associated with increased morbidity of neurological diseases in the accelerated aging population. Importantly, circadian rhythms disruption and gut microbiota dysbiosis are also known to induce the generation of toxic metabolites and pro-inflammatory cytokines, resulting in disruption of BBB integrity. Collectively, this provides a new perspective for exploring the relationship among circadian rhythms, gut microbes, and the BBB in aging-accompanied neurological diseases. In this review, we focus on recent advances in the interplay between circadian rhythm disturbances and gut microbiota dysbiosis, and their potential roles in the BBB disruption that occurs in AAND. Based on existing literature, we discuss and propose potential mechanisms underlying BBB damage induced by dysregulated circadian rhythms and gut microbiota, which would serve as the basis for developing potential interventions to protect the BBB in the aging population through targeting the BBB by exploiting its links with gut microbiota and circadian rhythms for treating AAND.

Role of Melatonin in the Onset of Metabolic Syndrome in Women

Metabolic syndrome (MetS) is a constellation of several associated cardiometabolic risk factors that increase the risk of developing type 2 diabetes mellitus (T2DM), cardiovascular diseases, and mortality. The role of hormonal factors in the development of MetS is assumed. In women, an insulin-resistant state that is associated with polycystic ovarian syndrome and increased deposition of intra-abdominal adipose tissue promotes the development of MetS and increases cardiovascular risk. The neuroendocrine hormone melatonin is secreted mainly at night under the regulatory action of the suprachiasmatic nucleus in the hypothalamus. Melatonin secretion is influenced by exogenous factors such as light and seasons and endogenous factors such as age, sex, and body weight. At present, the role of melatonin in metabolic disorders in humans is not fully understood. In this review, we set out to analyze the relationship of melatonin with the main features of MetS in women. Data from experimental and clinical studies on the role of melatonin in glucose metabolism and on the involvement of melatonin in lipid disturbances in MetS are reviewed. The complex influence of melatonin on hypertension is discussed. The changes in melatonin, leptin, and ghrelin and their relation to various metabolic processes and vascular dysfunction are discussed.

In vitro deacetylation of N-acetylserotonin by arylacetamide deacetylase

Arylacetamide deacetylase (AADAC) is a deacetylation enzyme present in the mammalian liver, gastrointestinal tract, and brain. During our search for mammalian enzymes capable of metabolizing N-acetylserotonin (NAS), AADAC was identified as having the ability to convert NAS to serotonin. Both human and rodent recombinant AADAC proteins can deacetylate NAS in vitro, although the human AADAC shows markedly higher activity compared with rodent enzyme. The AADAC-mediated deacetylation reaction can be potently inhibited by eserine in vitro. In addition to NAS, recombinant hAADAC can deacetylate melatonin (to form 5-methoxytryptamine) and N-acetyltryptamine (NAT) (to form tryptamine). In addition to the in vitro deacetylation of NAS by the recombinant AADAC proteins, liver (mouse and human) and brain (human) extracts were able to deacetylate NAS; these activities were sensitive to eserine. Taken together, these results demonstrate a new role for AADAC and suggest a novel pathway for the AADAC-mediated metabolism of pineal indoles in mammals.

Neuroprotective Effects of N-acetylserotonin and Its Derivative

N-acetylserotonin (NAS) is a chemical intermediate in melatonin biosynthesis. NAS and its derivative N-(2-(5-hydroxy-1H-indol-3-yl) ethyl)-2-oxopiperidine-3-carboxamide (HIOC) are potential therapeutic agents for traumatic brain injury, autoimmune encephalomyelitis, hypoxic-ischemic encephalopathy, and other diseases. Evidence shows that NAS and its derivative HIOC have neuroprotective properties, and can exert neuroprotective effects by inhibiting oxidative stress, anti-apoptosis, regulating autophagy dysfunction, and anti-inflammatory. In this review, we discussed the neuroprotective effects and related mechanisms of NAS and its derivative HIOC to provide a reference for follow-up research and applications.

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.

Impacts of vitamin A deficiency on biological rhythms: Insights from the literature

Vitamin A is essential for brain function, in addition to its important roles in vision, immunity, and reproduction. Previous studies have shown that retinoic acid (RA), the bioactive form of vitamin A, is involved in the regulation of various intracellular responses related to biological rhythms. RA is reported to affect the circadian rhythm by binding to RA receptors, such as receptors in the circadian feedback loops in the mammalian suprachiasmatic nucleus. However, evidence of the impacts of vitamin A deficiency (VAD) on biological rhythms is limited, and most of the related studies were conducted on animals. In this review, we described the physiological functions of biological rhythms and physiological pathways/molecular mechanisms regulating the biological rhythms. We then discussed the current understanding of the associations of VAD with biological rhythm disorders/diseases (sleep disorders, impairments in learning/memory, emotional disorders, and other immune or metabolism diseases) and summarized the currently proposed mechanisms (mainly by retinoid nuclear receptors and related proteins) for the associations. This review may help recognize the role of VAD in biological rhythm disorders and stimulate clinical or epidemiological studies to confirm the findings of related animal studies.

Mammalian circadian networks mediated by the suprachiasmatic nucleus

The brain has a complex structure composed of hundreds of regions, forming networks to cooperate body functions. Therefore, understanding how various brain regions communicate with each other and with peripheral organs is important to understand human physiology. The suprachiasmatic nucleus (SCN) in the brain is the circadian pacemaker. The SCN receives photic information from the environment and conveys this to other parts of the brain and body to synchronize all circadian clocks. The circadian clock is an endogenous oscillator that generates daily rhythms in metabolism and physiology in almost all cells via a conserved transcriptional-translational negative feedback loop. So, the information flow from the environment to the SCN to other tissues synchronizes locally distributed circadian clocks to maintain homeostasis. Thus, understanding the circadian networks and how they adjust to environmental changes will better understand human physiology. This review will focus on circadian networks mediated by the SCN to understand how the environment, brain, and peripheral tissues form networks for cooperation.

Pineal Gland from the Cell Culture to Animal Models: A Review

This review demonstrates current literature on pineal gland physiology, pathology, and animal model experiments to concisely explore future needs in research development with respect to pineal gland function and neuro-regenerative properties. The pineal gland plays an integral role in sleep and recovery by promoting physiologic circadian rhythms via production and release of melatonin. Yet, the current literature shows that the pineal gland has neuroprotective effects that modulate both peripheral and central nerve injuries through several direct and indirect mechanisms, such as angiogenesis and induction of growth factors and anti-inflammatory mediators. Animal models have also shown correlations between pineal gland function and metabolic homeostasis. Studies have shown that a functional pineal gland is essential in preventing and slowing the progression of certain diseases such as diabetes, osteoporosis, vertebral osteoarthritis, and neurodegenerative processes. Lastly, the array of cell culturing methods and animal models that can be used to further develop the study of pineal gland function and nervous system injury were reviewed.

Luxotonic signals in human prefrontal cortex as a possible substrate for effects of light on mood and cognition

Studies with experimental animals have revealed a mood-regulating neural pathway linking intrinsically photosensitive retinal ganglion cells (ipRGCs) and the prefrontal cortex (PFC), involved in the pathophysiology of mood disorders. Since humans also have light-intensity-encoding ipRGCs, we asked whether a similar pathway exists in humans. Here, functional MRI was used to identify PFC regions and other areas exhibiting light-intensity-dependent signals. We report 26 human brain regions having activation that either monotonically decreases or monotonically increases with light intensity. Luxotonic-related activation occurred across the cerebral cortex, in diverse subcortical structures, and in the cerebellum, encompassing regions with functions related to visual image formation, motor control, cognition, and emotion. Light suppressed PFC activation, which monotonically decreased with increasing light intensity. The sustained time course of light-evoked PFC responses and their susceptibility to prior light exposure resembled those of ipRGCs. These findings offer a functional link between light exposure and PFC-mediated cognitive and affective phenomena.

Pineal morphology of the clinical high-risk state for psychosis and different psychotic disorders

BACKGROUND

Pineal volume reductions have been reported in schizophrenia and clinical high-risk states for the development of psychosis, supporting the role of melatonin dysregulation in the pathophysiology of psychosis. However, it remains unclear whether pineal volume is associated with the later onset of psychosis in individuals at clinical high-risk (CHR) of psychosis or if pineal atrophy is specific to schizophrenia among different psychotic disorders.

METHODS

This magnetic resonance imaging study examined the volume of and cyst prevalence in the pineal gland in 135 individuals at CHR of psychosis [52 (38.5%) subsequently developed psychosis], 162 with first-episode psychosis (FEP), 89 with chronic schizophrenia, and 87 healthy controls. The potential contribution of the pineal morphology to clinical characteristics was also examined in the CHR and FEP groups.

RESULTS

Pineal volumes did not differ significantly between the CHR, FEP, and chronic schizophrenia groups, but were significantly smaller than that in healthy controls. However, pineal volumes were not associated with the later onset of psychosis in the CHR group or FEP sub-diagnosis (i.e., schizophrenia, schizophreniform disorder, affective psychosis, and other psychoses). No significant differences were observed in the prevalence of pineal cysts between the groups, and it also did not correlate with clinical characteristics in the CHR and FEP groups.

CONCLUSION

These results suggest that pineal atrophy is a general vulnerability marker of psychosis, while pineal cysts do not appear to contribute to the pathophysiology of psychosis.

The rationale for treating uveal melanoma with adjuvant melatonin: a review of the literature

BACKGROUND

Uveal melanoma is a rare form of cancer with high mortality. The incidence of metastases is attributed to early seeding of micrometastases from the eye to distant organs, primarily the liver. Once these seeded clusters of dormant tumor cells grow into larger radiologically detectable macrometastases, median patient survival is about 1 year. Melatonin is an important hormone for synchronizing circadian rhythms. It is also involved in other aspects of human physiology and may offer therapeutic benefits for a variety of diseases including cancer.

METHODS

Articles involving the physiological effects of melatonin, pharmacokinetics, and previous use in cancer studies were acquired using a comprehensive literature search in the Medline (PubMed) and Web of Science databases. In total, 147 publications were selected and included in the review.

RESULTS

Melatonin has been observed to suppress the growth of cancer cells, inhibit metastatic spread, enhance immune system functions, and act as an anti-inflammatory in both in vitro and in vivo models. Melatonin may also enhance the efficacy of cancer treatments such as immuno- and chemotherapy. Numerous studies have shown promising results for oral melatonin supplementation in patients with other forms of cancer including cutaneous malignant melanoma. Cell line and animal studies support a hypothesis in which similar benefits may exist for uveal melanoma.

CONCLUSIONS

Given its low cost, good safety profile, and limited side effects, there may be potential for the use of melatonin as an adjuvant oncostatic treatment. Future avenues of research could include clinical trials to evaluate the effect of melatonin in prevention of macrometastases of uveal melanoma.

Profiling Temporal Changes of the Pineal Transcriptomes at Single Cell Level Upon Neonatal HIBD

Neonatal hypoxic-ischemic brain damage (HIBD) often results in various neurological deficits. Among them, a common, yet often neglected, symptom is circadian rhythm disorders. Previous studies revealed that the occurrence of cysts in the pineal gland, an organ known to regulate circadian rhythm, is associated with circadian problems in children with HIBD. However, the underlying mechanisms of pineal dependent dysfunctions post HIBD remain largely elusive. Here, by performing 10x single cell RNA sequencing, we firstly molecularly identified distinct pineal cell types and explored their transcriptome changes at single cell level at 24 and 72 h post neonatal HIBD. Bioinformatic analysis of cell prioritization showed that both subtypes of pinealocytes, the predominant component of the pineal gland, were mostly affected. We then went further to investigate how distinct pineal cell types responded to neonatal HIBD. Within pinealocytes, we revealed a molecularly defined β to α subtype conversion induced by neonatal HIBD. Within astrocytes, we discovered that all three subtypes responded to neonatal HIBD, with differential expression of reactive astrocytes markers. Two subtypes of microglia cells were both activated by HIBD, marked by up-regulation of Ccl3. Notably, microglia cells showed substantial reduction at 72 h post HIBD. Further investigation revealed that pyroptosis preferentially occurred in pineal microglia through NLRP3-Caspase-1-GSDMD signaling pathway. Taken together, our results delineated temporal changes of molecular and cellular events occurring in the pineal gland following neonatal HIBD. By revealing pyroptosis in the pineal gland, our study also provided potential therapeutic targets for preventing extravasation of pineal pathology and thus improving circadian rhythm dysfunction in neonates with HIBD.

Associations between solar and geomagnetic activity and peripheral white blood cells in the Normative Aging Study

It has been hypothesized that solar and geomagnetic activity can affect the function of the autonomic nervous system (ANS) and melatonin secretion, both of which may influence immune response. We investigated the association between solar geomagnetic activity and white blood cell counts in the Normative Aging Study (NAS) Cohort between 2000 and 2013. Linear mixed effects models with moving day averages ranging from 0 to 28 days were used to evaluate the effects of solar activity measures, interplanetary magnetic field (IMF), and sunspot number (SSN), and a measure of geomagnetic activity, K Index (K), on total white blood cell (WBC), neutrophil, monocytes, lymphocyte, eosinophil, and basophil concentrations. After adjusting for demographic and health-related factors, there were consistently significant associations between IMF, SSN, and K_p index, with reductions in total WBC, neutrophils, and basophil counts. These associations were stronger with longer moving averages. The associations were similar after adjusting for ambient air particulate pollution and particle radioactivity. Our findings suggest that periods of increased solar and geomagnetic activity result in lower WBC, neutrophil, and basophil counts that may contribute to mil mild immune suppression.

Prednisolone induces sleep disorders via inhibition of melatonin secretion by the circadian rhythm in zebrafish

Prednisolone (PN) is a glucocorticoid (GC) analog that is clinically used to treat allergic inflammation and autoimmune diseases. However, the long-term use of GC-like drugs results in many side effects, among which sleep disorders caused by PN have attracted much attention. Many studies have showed that GCs indirectly cause sleep disorders by disrupting the circadian rhythm of the peripheral biological clock. However, the detailed mechanism of this effect in zebrafish remains unclear. In the present study, we aimed to study the pharmacology and toxicology of PN by analyzing the sleep phenotype and internal circadian oscillation of zebrafish. Exposure of zebrafish to PN resulted in decreased melatonin secretion and shortened sleep time. Additionally, analysis of the internal circadian rhythm of the zebrafish revealed that the expression of per and cry was significantly upregulated, resulting in a significant delay in the phase of the zebrafish behavioral rhythm. A dual-luciferase reporter assay further revealed that PN repressed per2 and cry1aa expression via the GC receptor (GR), which inhibited aanat2 expression. This caused a decrease in melatonin secretion and led to sleep disorders. The findings of this study highlight the mechanisms underlying the effects of GCs on sleep.

Adult Neurogenesis under Control of the Circadian System

The mammalian circadian system is a hierarchically organized system, which controls a 24-h periodicity in a wide variety of body and brain functions and physiological processes. There is increasing evidence that the circadian system modulates the complex multistep process of adult neurogenesis, which is crucial for brain plasticity. This modulatory effect may be exercised via rhythmic systemic factors including neurotransmitters, hormones and neurotrophic factors as well as rhythmic behavior and physiology or via intrinsic factors within the neural progenitor cells such as the redox state and clock genes/molecular clockwork. In this review, we discuss the role of the circadian system for adult neurogenesis at both the systemic and the cellular levels. Better understanding of the role of the circadian system in modulation of adult neurogenesis can help develop new treatment strategies to improve the cognitive deterioration associated with chronodisruption due to detrimental light regimes or neurodegenerative diseases.

Melatonin

Foster provides an overview of the hormone melatonin, discussing its role in seasonal biology and its more controversial function in human sleep.

Association Between CLOCK Gene Variants and Restless Legs Syndrome in Koreans

OBJECTIVE

Previous studies have suggested various causes of restless legs syndrome (RLS), including iron and dopamine concentrations in the brain. Genetic influences have also been reported in many studies. There is also a possibility that circadian clock genes may be involved because symptoms of RLS worsen at night. We investigated whether CLOCK and NPAS2 gene polymorphisms were associated with RLS.

METHODS

A total of 227 patients with RLS and 229 non-RLS matched controls were assessed according to the International Restless Legs Syndrome Study Group diagnostic criteria. Genotyping was performed using reverse transcription polymerase chain reaction and high-resolution melting curve analyses.

RESULTS

Although the genotype distributions of the CLOCK variants (rs1801260 and rs2412646) were not significantly different between patients with RLS and non-RLS controls, the allele frequencies of CLOCK rs1801260 showed marginally significant differences between the two groups (X2 =2.98, p=0.085). Furthermore, there was a significant difference in the distribution of CLOCK haplotypes (rs1801260-rs2412646) between patients with RLS and non-RLS controls (p=0.013). The distributions of allelic, genotypic, and haplotypic variants of NPAS2 (rs2305160 and rs6725296) were not significantly different between the two groups.

CONCLUSION

Our results suggest that CLOCK variants may be associated with decreased susceptibility to RLS.

Empowering Melatonin Therapeutics with Drosophila Models

Melatonin functions as a central regulator of cell and organismal function as well as a neurohormone involved in several processes, e.g., the regulation of the circadian rhythm, sleep, aging, oxidative response, and more. As such, it holds immense pharmacological potential. Receptor-mediated melatonin function mainly occurs through MT1 and MT2, conserved amongst mammals. Other melatonin-binding proteins exist. Non-receptor-mediated activities involve regulating the mitochondrial function and antioxidant cascade, which are frequently affected by normal aging as well as disease. Several pathologies display diseased or dysfunctional mitochondria, suggesting melatonin may be used therapeutically. Drosophila models have extensively been employed to study disease pathogenesis and discover new drugs. Here, we review the multiple functions of melatonin through the lens of functional conservation and model organism research to empower potential melatonin therapeutics to treat neurodegenerative and renal diseases.

Potential contribution of pineal atrophy and pineal cysts toward vulnerability and clinical characteristics of psychosis

BACKGROUND

Magnetic resonance imaging (MRI) studies reported pineal gland atrophy in schizophrenia patients and individuals at a clinical high risk of developing psychosis, implicating abnormalities in melatonin secretion in the pathophysiology of psychosis. However, it currently remains unclear whether the morphology of the pineal gland contributes to symptomatology and sociocognitive functions.

METHODS

This MRI study examined pineal gland volumes and the prevalence of pineal cysts as well as their relationship with clinical characteristics in 57 at risk mental state (ARMS) subjects, 63 patients with schizophrenia, and 61 healthy controls. The Social and Occupational Functioning Assessment Scale (SOFAS), the Schizophrenia Cognition Rating Scale (SCoRS), and the Brief Assessment of Cognition in Schizophrenia (BACS) were used to assess sociocognitive functions, while the Positive and Negative Syndrome Scale was employed to evaluate clinical symptoms in ARMS subjects and schizophrenia patients.

RESULTS

Pineal gland volumes were significantly smaller in the ARMS and schizophrenia groups than in the controls, while no significant differences were observed in the prevalence of pineal cysts. Although BACS, SCoRS, and SOFAS scores were not associated with pineal morphology, patients with pineal cysts in the schizophrenia group exhibited severe positive psychotic symptoms with rather mild negative symptoms.

CONCLUSION

The present results indicate the potential of pineal atrophy as a vulnerability marker in various stages of psychosis and suggest that pineal cysts influence the clinical subtype of schizophrenia.

Expanding the link between circadian rhythms and redox metabolism of epigenetic control

Circadian rhythms play a central role in physiological and metabolic processes. This is mostly achieved through rhythmic regulation of myriad genes via dynamic epigenome changes. Accumulating evidence indicates that oxidative stress and redox balance are under circadian control and feedback on the clock system. Circadian perturbations induce oxidative stress accumulation and disturb redox balance. Along with these changes, epigenomic landscape changes are a remarkable hallmark of clock disruption. This review aims to summarize evidence supporting the link between the circadian clock and redox metabolism, focusing on possible connections through epigenetic mechanisms.

Ameliorating effect of melatonin against nicotine induced lung and heart toxicity in rats

The present study was carried out to investigate the ameliorative effects of melatonin against nicotine-induced heart and lung toxicity. For this purpose, 75 mature male Sprague Dawley (SD) rats weighing 150-170 g were randomly divided into five groups (15 rats each): control group (rats were I/P injected with 1% ethanol in saline), nicotine group (rats were I/P injected with 0.6 mg/kg body weight), and combined nicotine and melatonin groups (rats received nicotine as in the previous group and melatonin at a dose of 1, 5, or 10 mg/kg body weight, respectively); all treatments were continued for 21 days. Fasting blood samples were collected from each rat at the 11th day and one day after the end of the last injection (22nd day) for complete blood count (CBC) determination, while sera were collected for the determination of lipid profiles. Malondialdehyde (MDA) concentration, superoxide dismutase (SOD) activity, and reduced glutathione (GSH) as well as DNA fragmentation percentage were assessed in cardiac tissue. Heart and lung samples were collected for estimation of caspase-3 expression and histopathological examination. The results revealed that nicotine increased the number of RBCs, Hb concentration, total cholesterol, and low density lipoprotein (LDL) and decreased high density lipoprotein (HDL). In addition, it decreased SOD activity and GSH concentration with increased MDA concentration, and DNA fragmentation in the heart, as well as caspase-3 expression in both heart and lungs. It also induced histopathological changes in the heart and lung tissues. Melatonin could ameliorate the deleterious effect of nicotine on the previous parameters either partially or completely, where melatonin restored complete blood count, improved lipid profile, mended lipid peroxidation and antioxidant parameters in the cardiac tissue, rectified caspase-3 expression in the heart and lungs, ameliorated DNA fragmentation percentage in the heart, and protected both heart and lung tissue against the harmful effect of nicotine. It is concluded that melatonin has a protective effect on the heart and lungs against the harmful effect of nicotine.

Germline and somatic mutations in the pathology of pineal cyst: A whole-exome sequencing study of 93 individuals

Background

Pineal cyst is a benign lesion commonly occurring in people of any age. Until now, the underlying molecular alterations have not been explored.

Methods

We performed whole exome sequencing of 93 germline samples and 21 pineal cyst tissue samples to illustrate its genetic architecture and somatic mutations. The dominant and recessive inheritance modes were considered, and a probability was calculated to evaluate the significance of variant overrepresentation.

Results

By analyzing pineal cyst as a Mendelian disease with a dominant inheritance pattern, we identified 42,325 rare germline variants, and NM_001004711.1:c.476A>G was highly enriched (FDR<0.2). By analyzing it as a recessive disorder, we identified 753 homozygous rare variants detected in at least one pineal cyst sample each. One STIM2 rare variant, NM_001169117.1:c.1652C>T, was overrepresented (FDR<0.05). Analyzing at a gene‐based level, we identified a list of the most commonlymutated germline genes, including POP4, GNGT2 and TMEM254. A somatic mutation analysis of 21 samples identified 16 variants in 15 genes, which mainly participated in the biological processes of gene expression and epigenetic regulation, immune response modulation, and transferase activity.

Conclusion

These molecular profiles are novel for this condition and provide data for investigators interested in pineal cysts.

A cross-species analysis of systemic mediators of repair and complex tissue regeneration

Regeneration is an elegant and complex process informed by both local and long-range signals. Many current studies on regeneration are largely limited to investigations of local modulators within a canonical cohort of model organisms. Enhanced genetic tools increasingly enable precise temporal and spatial perturbations within these model regenerators, and these have primarily been applied to cells within the local injury site. Meanwhile, many aspects of broader spatial regulators of regeneration have not yet been examined with the same level of scrutiny. Recent studies have shed important insight into the significant effects of environmental cues and circulating factors on the regenerative process. These observations highlight that consideration of more systemic and possibly more broadly acting cues will also be critical to fully understand complex tissue regeneration. In this review, we explore the ways in which systemic cues and circulating factors affect the initiation of regeneration, the regenerative process, and its outcome. As this is a broad topic, we conceptually divide the factors based on their initial input as either external cues (for example, starvation and light/dark cycle) or internal cues (for example, hormones); however, all of these inputs ultimately lead to internal responses. We consider studies performed in a diverse set of organisms, including vertebrates and invertebrates. Through analysis of systemic mediators of regeneration, we argue that increased investigation of these "systemic factors" could reveal novel insights that may pave the way for a diverse set of therapeutic avenues.

Circadian Rhythms of the Hypothalamus: From Function to Physiology

The nearly ubiquitous expression of endogenous 24 h oscillations known as circadian rhythms regulate the timing of physiological functions in the body. These intrinsic rhythms are sensitive to external cues, known as zeitgebers, which entrain the internal biological processes to the daily environmental changes in light, temperature, and food availability. Light directly entrains the master clock, the suprachiasmatic nucleus (SCN) which lies in the hypothalamus of the brain and is responsible for synchronizing internal rhythms. However, recent evidence underscores the importance of other hypothalamic nuclei in regulating several essential rhythmic biological functions. These extra-SCN hypothalamic nuclei also express circadian rhythms, suggesting distinct regions that oscillate either semi-autonomously or independent of SCN innervation. Concurrently, the extra-SCN hypothalamic nuclei are also sensitized to fluctuations in nutrient and hormonal signals. Thus, food intake acts as another powerful entrainer for the hypothalamic oscillators' mediation of energy homeostasis. Ablation studies and genetic mouse models with perturbed extra-SCN hypothalamic nuclei function reveal their critical downstream involvement in an array of functions including metabolism, thermogenesis, food consumption, thirst, mood and sleep. Large epidemiological studies of individuals whose internal circadian cycle is chronically disrupted reveal that disruption of our internal clock is associated with an increased risk of obesity and several neurological diseases and disorders. In this review, we discuss the profound role of the extra-SCN hypothalamic nuclei in rhythmically regulating and coordinating body wide functions.

Hormonal Regulation of Oligodendrogenesis I: Effects across the Lifespan

The brain’s capacity to respond to changing environments via hormonal signaling is critical to fine-tuned function. An emerging body of literature highlights a role for myelin plasticity as a prominent type of experience-dependent plasticity in the adult brain. Myelin plasticity is driven by oligodendrocytes (OLs) and their precursor cells (OPCs). OPC differentiation regulates the trajectory of myelin production throughout development, and importantly, OPCs maintain the ability to proliferate and generate new OLs throughout adulthood. The process of oligodendrogenesis, the creation of new OLs, can be dramatically influenced during early development and in adulthood by internal and environmental conditions such as hormones. Here, we review the current literature describing hormonal regulation of oligodendrogenesis within physiological conditions, focusing on several classes of hormones: steroid, peptide, and thyroid hormones. We discuss hormonal regulation at each stage of oligodendrogenesis and describe mechanisms of action, where known. Overall, the majority of hormones enhance oligodendrogenesis, increasing OPC differentiation and inducing maturation and myelin production in OLs. The mechanisms underlying these processes vary for each hormone but may ultimately converge upon common signaling pathways, mediated by specific receptors expressed across the OL lineage. However, not all of the mechanisms have been fully elucidated, and here, we note the remaining gaps in the literature, including the complex interactions between hormonal systems and with the immune system. In the companion manuscript in this issue, we discuss the implications of hormonal regulation of oligodendrogenesis for neurological and psychiatric disorders characterized by white matter loss. Ultimately, a better understanding of the fundamental mechanisms of hormonal regulation of oligodendrogenesis across the entire lifespan, especially in vivo, will progress both basic and translational research.

Cross-species physiological interactions of endocrine disrupting chemicals with the circadian clock

Endocrine disrupting chemicals (EDCs) are endocrine-active chemical pollutants that disrupt reproductive, neuroendocrine, cardiovascular and metabolic health across species. The circadian clock is a transcriptional oscillator responsible for entraining 24-hour rhythms of physiology, behavior and metabolism. Extensive bidirectional cross talk exists between circadian and endocrine systems and circadian rhythmicity is present at all levels of endocrine control, from synthesis and release of hormones, to sensitivity of target tissues to hormone action. In mammals, a range of hormones directly alter clock gene expression and circadian physiology via nuclear receptor (NR) binding and subsequent genomic action, modulating physiological processes such as nutrient and energy metabolism, stress response, reproductive physiology and circadian behavioral rhythms. The potential for EDCs to perturb circadian clocks or circadian-driven physiology is not well characterized. For this reason, we explore evidence for parallel endocrine and circadian disruption following EDC exposure across species. In the reviewed studies, EDCs dysregulated core clock and circadian rhythm network gene expression in brain and peripheral organs, and altered circadian reproductive, behavioral and metabolic rhythms. Circadian impacts occurred in parallel to endocrine and metabolic alterations such as impaired fertility and dysregulated metabolic and energetic homeostasis. Further research is warranted to understand the nature of interaction between circadian and endocrine systems in mediating physiological effects of EDC exposure at environmental levels.

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.

Do malignant cells sleep at night?

Biological rhythms regulate the biology of most, if not all living creatures, from whole organisms to their constitutive cells, their microbiota, and also parasites. Here, we present the hypothesis that internal and external ecological variations induced by biological cycles also influence or are exploited by cancer cells, especially by circulating tumor cells, the key players in the metastatic cascade. We then discuss the possible clinical implications of the effect of biological cycles on cancer progression, and how they could be exploited to improve and standardize methods used in the liquid biopsy field.

Management of primary aldosteronism and mineralocorticoid receptor-associated hypertension

Resistant hypertension is associated with a poor prognosis due to organ damage caused by prolonged suboptimal blood pressure control. The concomitant use of mineralocorticoid receptor (MR) antagonists with other antihypertensives has been shown to improve blood pressure control in some patients with resistant hypertension, and such patients are considered to have MR-associated hypertension. MR-associated hypertension is classified into two subtypes: one with a high plasma aldosterone level, which includes primary aldosteronism (PA), and the other with a normal aldosterone level. In patients with unilateral PA, adrenalectomy may be the first-choice procedure, while in patients with bilateral PA, MR antagonists are selected. In addition, in patients with other types of MR-associated hypertension with high aldosterone levels, MR antagonists may be selected as a first-line therapy. In patients with normal aldosterone levels, ARBs or ACE inhibitors are used as a first-line therapy, and MR antagonists may be used as an add-on agent. Since MR antagonist therapy may have efficacy as a first-line or add-on agent in these patients, it is important to recognize this type of hypertension. Further studies are needed to elucidate the pathogenesis and management of MR-associated hypertension in more detail to improve the clinical outcomes of patients with MR-associated hypertension.

Two indoleamines are secreted from rat pineal gland at night and act on melatonin receptors but are not night hormones

INTRODUCTION

At night, the pineal gland produces the indoleamines, melatonin, N-acetylserotonin (NAS), and N-acetyltryptamine (NAT). Melatonin is accepted as a hormone of night. Could NAS and NAT serve that role too?

METHODS

Concentration-response measurements with overexpressed human melatonin receptors MT₁ and MT₂ ; mass spectrometry analysis of norepinephrine-stimulated secretions from isolated rat pineal glands; analysis of 24-hour periodic samples of rat blood.

RESULTS

We show that NAT and NAS do activate melatonin receptors MT₁ and MT₂ , although with lower potency than melatonin, and that in vitro, melatonin and NAS are secreted from stimulated, isolated pineal glands in roughly equimolar amounts, but secretion of NAT was much less. All three were found at roughly equal concentrations in blood during the night. However, during the day, serum melatonin fell to very low values creating a high-amplitude circadian rhythm that was absent after pinealectomy, whereas NAS and NAT showed only small or no circadian variation.

CONCLUSION

Blood levels of NAS and NAT were insufficient to activate peripheral melatonin receptors, and they were invariant, so they could not serve as circulating hormones of night. However, they could instead act in paracrine circadian fashion near the pineal gland or via other higher-affinity receptors.

Temporal organization of pineal melatonin signaling in mammals

In mammals, the pineal gland is the sole endocrine source of melatonin, which is secreted according to daily and seasonal patterns. This mini-review synthesizes the established endocrine actions of melatonin in the following temporal contexts. Melatonin is a strictly regulated output of the circadian timing system, but under certain conditions, may also entrain the circadian pacemaker and clocks in peripheral tissues. As the waveform of nightly melatonin secretion varies seasonally, melatonin provides a hormonal representation of the time of year. The duration of elevated melatonin secretion regulates reproductive physiology and other seasonal adaptations either by entraining a circannual rhythm or by inducing seasonal responses directly. An entrainment action of nightly melatonin on clock gene expression in the pars tuberalis of the anterior pituitary may partly underly its mechanistic role as a photoperiodic switch. Melatonin has important functions developmentally to regulate multiple physiological systems and program timing of puberty. Endogenous melatonergic systems are disrupted by modern lifestyles of humans through altered circadian entrainment, acute suppression by light and self-administration of pharmacological melatonin. Non-endocrine actions of locally synthesized melatonin fall outside of the scope of this mini-review.

Dysregulation of Circadian Rhythms in Autism Spectrum Disorders

Background:

The alterations in neurological and neuroendocrine functions observed in the autism spectrum disorder (ASD) involves environmentally dependent dysregulation of neurodevelopment, in interaction with multiple coding gene defects. Disturbed sleep-wake patterns, as well as abnormal melatonin and glucocorticoid secretion, show the relevance of an underlying impairment of the circadian timing system to the behavioral phenotype of ASD. Thus, understanding the mechanisms involved in the circadian dysregulation in ASD could help to identify early biomarkers to improve the diagnosis and therapeutics as well as providing a significant impact on the lifelong prognosis.

Objective:

In this review, we discuss the organization of the circadian timing system and explore the connection between neuroanatomic, molecular, and neuroendocrine responses of ASD and its clinical manifestations. Here we propose interconnections between circadian dysregulation, inflammatory baseline and behavioral changes in ASD. Taking into account, the high relevancy of melatonin in orchestrating both circadian timing and the maintenance of physiological immune quiescence, we raise the hypothesis that melatonin or analogs should be considered as a pharmacological approach to suppress inflammation and circadian misalignment in ASD patients.

Strategy:

This review provides a comprehensive update on the state-of-art of studies related to inflammatory states and ASD with a special focus on the relationship with melatonin and clock genes. The hypothesis raised above was analyzed according to the published data.

Conclusion:

Current evidence supports the existence of associations between ASD to circadian dysregulation, behavior problems, increased inflammatory levels of cytokines, sleep disorders, as well as reduced circadian neuroendocrine responses. Indeed, major effects may be related to a low melatonin rhythm. We propose that maintaining the proper rhythm of the circadian timing system may be helpful to improve the health and to cope with several behavioral changes observed in ASD subjects.

Pineal Gland Volume in Major Depressive and Bipolar Disorders

Abnormal melatonin secretion has been demonstrated in patients with affective disorders such as major depressive disorder (MDD) and bipolar disorder (BD). However, magnetic resonance imaging (MRI) studies that previously investigated the volume of the pineal gland, which regulates circadian rhythms by secreting melatonin, in these patients reported inconsistent findings. The present study employed MRI to examine pineal gland volumes and pineal cyst prevalence in 56 MDD patients (29 currently depressed and 27 remitted patients), 26 BD patients, and matched controls (33 for MDD and 24 for BD). Pineal volumes and cyst prevalence in the current MDD, remitted MDD, and BD groups did not significantly differ from those of the healthy controls. However, pineal gland volumes were significantly smaller in the current MDD subgroup of non-melancholic depression than in the melancholic MDD subgroup. Interestingly, pineal volumes correlated negatively with the severity of loss of interest in the current MDD group. Medication and the number of affective episodes were not associated with pineal volumes in the MDD or BD group. While these results do not suggest that pineal volumes reflect abnormal melatonin secretion in affective disorders, they do point to the possibility that pineal abnormalities are associated with clinical subtypes of MDD and its symptomatology.

Circadian blueprint of metabolic pathways in the brain

The circadian clock is an endogenous, time-tracking system that directs multiple metabolic and physiological functions required for homeostasis. The master or central clock located within the suprachiasmatic nucleus in the hypothalamus governs peripheral clocks present in all systemic tissues, contributing to their alignment and ultimately to temporal coordination of physiology. Accumulating evidence reveals the presence of additional clocks in the brain and suggests the possibility that circadian circuits may feed back to these from the periphery. Here, we highlight recent advances in the communications between clocks and discuss how they relate to circadian physiology and metabolism.

The impact of light during the night

Exposing chicks to one hour of light during the night disrupts the release of a hormone that is needed by cells in the developing brain to survive.

Melatonin synthesis and clock gene regulation in the pineal organ of teleost fish compared to mammals: Similarities and differences

The pineal organ of all vertebrates synthesizes and secretes melatonin in a rhythmic manner due to the circadian rhythm in the activity of arylalkylamine N-acetyltransferase (AANAT) - the rate-limiting enzyme in melatonin synthesis pathway. Nighttime increase in AANAT activity and melatonin synthesis depends on increased expression of aanat gene (a clock-controlled gene) and/or post-translation modification of AANAT protein. In mammalian and avian species, only one aanat gene is expressed. However, three aanat genes (aanat1a, aanat1b, and aanat2) are reported in fish species. While aanat1a and aanat1b genes are expressed in the fish retina, the nervous system and other peripheral tissues, aanat2 gene is expressed exclusively in the fish pineal organ. Clock genes form molecular components of the clockwork, which regulates clock-controlled genes like aanat gene. All core clock genes (i.e., clock, bmal1, per1, per2, per3, cry1 and cry2) and aanat2 gene (a clock-controlled gene) are expressed in the pineal organ of several fish species. There is a large body of information on regulation of clock genes, aanat gene and melatonin synthesis in the mammalian pineal gland. However, the information available on clock genes, aanat genes and melatonin synthesis in photoreceptive pineal organ of teleosts is fragmentary and not well documented. Therefore, we have reviewed published information on rhythmic expression of clock genes, aanat genes as well as synthesis of melatonin, and their regulation by photoperiod and temperature in teleostean pineal organ as compared to mammalian pineal gland. A critical analysis of the literature suggests that in contrast to the mammalian pineal gland, the pineal organ of teleosts (except salmonids) possesses a well developed indigenous clock composed of clock genes for regulation of rhythmic expression of aanat2 gene and melatonin synthesis. Further, the fish pineal organ also possesses essential molecular components for responding to light and temperature directly. The fish pineal organ seems to act as a potential master biological clock in most of the teleosts.

Melatonin in Medicinal and Food Plants: Occurrence, Bioavailability, and Health Potential for Humans

Melatonin is a widespread molecule among living organisms involved in multiple biological, hormonal, and physiological processes at cellular, tissue, and organic levels. It is well-known for its ability to cross the blood–brain barrier, and renowned antioxidant effects, acting as a free radical scavenger, up-regulating antioxidant enzymes, reducing mitochondrial electron leakage, and interfering with proinflammatory signaling pathways. Detected in various medicinal and food plants, its concentration is widely variable. Plant generative organs (e.g., flowers, fruits), and especially seeds, have been proposed as having the highest melatonin concentrations, markedly higher than those found in vertebrate tissues. In addition, seeds are also rich in other substances (lipids, sugars, and proteins), constituting the energetic reserve for a potentially growing seedling and beneficial for the human diet. Thus, given that dietary melatonin is absorbed in the gastrointestinal tract and transported into the bloodstream, the ingestion of medicinal and plant foods by mammals as a source of melatonin may be conceived as a key step in serum melatonin modulation and, consequently, health promotion.

Interplay of central and peripheral circadian clocks in energy metabolism regulation

Metabolic health founds on a homeostatic balance that has to integrate the daily changes of rest/activity and feeding/fasting cycles. A network of endogenous 24-hour circadian clocks helps to anticipate daily recurring events and adjust physiology and behavioural functions accordingly. Circadian clocks are self-sustained cellular oscillators based on a set of clock genes/proteins organised in interlocked transcriptional-translational feedback loops. The body's clocks need to be regularly reset and synchronised with each other to achieve coherent rhythmic output signals. This synchronisation is achieved by interplay of a master clock, which resides in the suprachiasmatic nucleus, and peripheral tissue clocks. This clock network is reset by time signals such as the light/dark cycle, food intake and activity. The balanced interplay of clocks is easily disturbed in modern society by shiftwork or high-energy diets, which may further promote the development of metabolic disorders. In this review, we summarise the current model of central-peripheral clock interaction in metabolic health. Different established mouse models for central or peripheral clock disruption and their metabolic phenotypes are compared and the possible relevance of clock network interaction for the development of therapeutic approaches in humans is discussed.

Reduced pineal gland volume across the stages of schizophrenia

A few magnetic resonance imaging (MRI) studies reported reduced pineal gland volume in chronic schizophrenia (Sz), implicating the involvement of melatonin in the pathophysiology of the illness. However, it is not known whether this abnormality, if present, exists at the early illness stages and/or develops progressively over the course of the illness. This MRI study examined pineal gland volume in 64 patients with first-episode schizophrenia (FESz), 40 patients with chronic Sz, 22 individuals with at-risk mental state (ARMS), and 84 healthy controls. Longitudinal changes in pineal volume (mean inter-scan interval = 2.5 ± 0.7 years) were also examined in a subsample of 23 FESz, 16 chronic Sz, and 21 healthy subjects. In the cross-sectional comparison, the ARMS, FESz, and chronic Sz groups had significantly smaller pineal volume to the same degree as compared with healthy controls. A longitudinal comparison demonstrated that pineal volume did not change over time in any group. There was no association between pineal volume and clinical variables (e.g., symptom severity, medication) in the ARMS and Sz groups. The results suggest that a smaller pineal gland may be a static vulnerability marker of Sz, which probably reflects an early neurodevelopmental abnormality.

Differential Function of Melatonin MT1 and MT2 Receptors in REM and NREM Sleep

The pathophysiological function of the G-protein coupled melatonin MT1 and MT2 receptors has not yet been well-clarified. Recent advancements using selective MT1/ MT2 receptor ligands and MT1/MT2 receptor knockout mice have suggested that the activation of the MT1 receptors are mainly implicated in the regulation of rapid eye movement (REM) sleep, whereas the MT2 receptors selectively increase non-REM (NREM) sleep. Studies in mutant mice show that MT1 knockout mice have an increase in NREM sleep and a decrease in REM sleep, while MT2 knockout mice a decrease in NREM sleep. The localization of MT1 receptors is also distinct from MT2 receptors; for example, MT2 receptors are located in the reticular thalamus (NREM area), while the MT1 receptors in the Locus Coeruleus and lateral hypothalamus (REM areas). Altogether, these findings suggest that these two receptors not only have a very specialized function in sleep, but that they may also modulate opposing effects. These data also suggest that mixed MT1-MT2 receptors ligands are not clinically recommended given their opposite roles in physiological functions, confirmed by the modest effects of melatonin or MT1/MT2 non-selective agonists when used in both preclinical and clinical studies as hypnotic drugs. In sum, MT1 and MT2 receptors have specific roles in the modulation of sleep, and consequently, selective ligands with agonist, antagonist, or partial agonist properties could have therapeutic potential for sleep; while the MT2 agonists or partial agonists might be indicated for NREM-related sleep and/or anxiety disorders, the MT1 agonists or partial agonists might be so for REM-related sleep disorders. Furthermore, MT1 but not MT2 receptors seem involved in the regulation of the circadian rhythm. Future research will help further develop MT1 and/or MT2 receptors as targets for neuropsychopharmacology drug development.

Sex Difference in the Morphology of Pineal Gland in Adults Based on Brain Magnetic Resonance Imaging

PURPOSE

We aimed to figure out the anatomical features of pineal gland region on magnetic resonance imaging (MRI) and to explore the sex difference in pineal gland-related parameters with increasing age.

METHODS

We measured the pineal gland on MRI images from 198 healthy adults (96 males and 102 females). Included subjects were divided into 4 age groups. After 3-dimensional reconstruction, the anatomic features of pineal gland and its distances to superior colliculus and splenium of corpus callosum were analyzed in each group. The prevalence of cystic pineal gland was calculated. Moreover, we calculated the volume of pineal gland (PGV) and explored the differences of PGV in males and females across different age groups. Linear regression analysis was performed to detect the relationship between age and pineal gland-related parameters.

RESULTS

In 198 subjects, the mean length, width, and height of pineal gland were 7.58 ± 0.45 mm, 4.92 ± 0.40 mm, and 2.90 ± 0.20 mm. The distances between pineal gland and superior colliculus as well as splenium of corpus callosum were 3.96 ± 0.92 mm and 4.3 ± 1.89 mm, respectively. The PGV was 54.1 ± 7.02 mm. Significant sex differences were found in pineal gland length (P < 0.001), cranial cavity diameter (P < 0.001), pineal gland index (P < 0.001) and PGV values (P = 0.02). The prevalence of cystic pineal gland was 36.4% in total subjects, 41.7% in males and 32.4% in females. No linear relationship was found between age and pineal gland parameters.

CONCLUSION

We measured the pineal gland morphology based on MRI images. Significant influences on pineal gland parameters were found in subjects with different sex, whereas no effect was observed from age.

Effect of Monochromatic Light on Circadian Rhythm of Clock Genes in Chick Pinealocytes

The avian circadian system is a complex of mutually coupled pacemakers residing in pineal gland, retina and suprachiasmatic nucleus. In this study, the self-regulation mechanism of pineal circadian rhythm was investigated by culturing chick primary pinealocytes exposed to red light (RL), green light (GL), blue light (BL), white light (WL) and constant darkness (DD), respectively. All illuminations were set up with a photoperiod of 12 light: 12 dark. The 24-h expression profiles of seven core clock genes (cBmal1/2, cClock, cCry1/2 and cPer2/3), cAanat and melatonin showed significant circadian oscillation in all groups, except for the loss of cCry1 rhythm in BL. Compared to WL, GL increased the amplitudes and mesors of positive elements (cClock and cBmal1/2) and reduced those of negative elements (cCry1/2 and cPer2/3), in contrast to RL. The temporal patterns of cAanatmRNA and melatonin secretion have always been consistent with the positive genes. Besides, GL advanced the acrophases of the positive elements, cAanat and melatonin, but RL and BL showed the opposite effect. Thereby, GL could promote the secretion of melatonin by enhancing the expressions of positive clock genes and repressing the expressions of negative clock genes.

d-Leucine: Evaluation in an epilepsy model

BACKGROUND

Current medicines do not provide sufficient seizure control for nearly one-third of patients with epilepsy. New options are needed to address this treatment gap. We recently found that the atypical amino acid d-leucine protected against acutely-induced seizures in mice, but its effect in chronic seizures has not been explored. We hypothesized that d-leucine would protect against spontaneous recurrent seizures. We also investigated whether mice lacking a previously-described d-leucine receptor (Tas1R2/R3) would be protected against acutely-induced seizures.

METHODS

Male FVB/NJ mice were subjected to kainic acid-induced status epilepticus and monitored by video-electroencephalography (EEG) (surgically implanted electrodes) for 4weeks before, during, and after treatment with d-leucine. Tas1R2/R3 knockout mice and controls underwent the maximal electroshock threshold (MES-T) and 6-Hz tests.

RESULTS

There was no difference in number of calendar days with seizures or seizure frequency with d-leucine treatment. In an exploratory analysis, mice treated with d-leucine had a lower number of dark cycles with seizures. Tas1R2/R3 knockout mice had elevated seizure thresholds in the MES-T test but not the 6-Hz test.

CONCLUSIONS

d-Leucine treatment was ineffective against chronic seizures after kainic acid-induced status epilepticus, but there was some efficacy during the dark cycle. Because d-leucine is highly concentrated in the pineal gland, these data suggest that d-leucine may be useful as a tool for studying circadian patterns in epilepsy. Deletion of the Tas1R2/R3 receptor protected against seizures in the MES-T test and, therefore, may be a novel target for treating seizures.