Melatonin, consciousness, and traumatic stress

Melatonin-mediated FKBP4 downregulation protects against stress-induced neuronal mitochondria dysfunctions by blocking nuclear translocation of GR

The physiological crosstalk between glucocorticoid and melatonin maintains neuronal homeostasis in regulating circadian rhythms. However, the stress-inducing level of glucocorticoid triggers mitochondrial dysfunction including defective mitophagy by increasing the activity of glucocorticoid receptors (GRs), leading to neuronal cell death. Melatonin then suppresses glucocorticoid-induced stress-responsive neurodegeneration; however, the regulatory mechanism of melatonin, i.e., associated proteins involved in GR activity, has not been elucidated. Therefore, we investigated how melatonin regulates chaperone proteins related to GR trafficking into the nucleus to suppress glucocorticoid action. In this study, the effects of glucocorticoid on suppressing NIX-mediated mitophagy, followed by mitochondrial dysfunction, neuronal cell apoptosis, and cognitive deficits were reversed by melatonin treatment by inhibiting the nuclear translocation of GRs in both SH-SY5Y cells and mouse hippocampal tissue. Moreover, melatonin selectively suppressed the expression of FKBP prolyl isomerase 4 (FKBP4), which is a co-chaperone protein that works with dynein, to reduce the nuclear translocation of GRs among the chaperone proteins and nuclear trafficking proteins. In both cells and hippocampal tissue, melatonin upregulated melatonin receptor 1 (MT1) bound to Gαq, which triggered the phosphorylation of ERK1. The activated ERK then enhanced DNA methyltransferase 1 (DNMT1)-mediated hypermethylation of FKBP52 promoter, reducing GR-mediated mitochondrial dysfunction and cell apoptosis, the effects of which were reversed by knocking down DNMT1. Taken together, melatonin has a protective effect against glucocorticoid-induced defective mitophagy and neurodegeneration by enhancing DNMT1-mediated FKBP4 downregulation that reduced the nuclear translocation of GRs.

Ectopic expression of MmCYP1A1, a mouse cytochrome P450 gene, positively regulates stress tolerance in apple calli and Arabidopsis

Ectopic expression of MmCYP1A1 gene from Mus musculus in apple calli and Arabidopsis increased the levels of melatonin and 6-hydroxymelatonin, and improved their stress resistance. Melatonin occurs widely in organisms, playing a key regulatory role. CYP1A1 is a cytochrome P450 monooxygenase, involved in the melatonin metabolism, and is responsible for the synthesis of 6-hydroxymelatonin from melatonin. Melatonin and 6-hydroxymelatonin have strong antioxidant activities in animals. Here, we cloned MmCYP1A1 from Mus musculus and found that ectopic expression of MmCYP1A1 improved the levels of melatonin and 6-hydroxymelatonin in transgenic apple calli and Arabidopsis. Subsequently, we observed that MmCYP1A1 increased the tolerance of transgenic apple calli and Arabidopsis to osmotic stress simulated by polyethylene glycol 6000 (PEG 6000), as well as resistance of transgenic Arabidopsis to drought stress. Further, the number of lateral roots of MmCYP1A1 transgenic Arabidopsis were enhanced significantly after PEG 6000 treatment. The expression of MmCYP1A1 remarkably reduced malondialdehyde (MDA) content, electrolyte leakage, accumulation of H₂O₂ and O₂^- during stress treatment. Moreover, MmCYP1A1 enhanced stress tolerance in apple calli and Arabidopsis by increasing the expression levels of resistance genes. MmCYP1A1 also promoted stomatal closure in transgenic Arabidopsis to reduce leaf water loss during drought. Our results indicate that MmCYP1A1 plays a key role in plant stress tolerance, which may provide a reference for future plant stress tolerance studies.

It's About Time: The Circadian Network as Time-Keeper for Cognitive Functioning, Locomotor Activity and Mental Health

A variety of organisms including mammals have evolved a 24h, self-sustained timekeeping machinery known as the circadian clock (biological clock), which enables to anticipate, respond, and adapt to environmental influences such as the daily light and dark cycles. Proper functioning of the clock plays a pivotal role in the temporal regulation of a wide range of cellular, physiological, and behavioural processes. The disruption of circadian rhythms was found to be associated with the onset and progression of several pathologies including sleep and mental disorders, cancer, and neurodegeneration. Thus, the role of the circadian clock in health and disease, and its clinical applications, have gained increasing attention, but the exact mechanisms underlying temporal regulation require further work and the integration of evidence from different research fields. In this review, we address the current knowledge regarding the functioning of molecular circuits as generators of circadian rhythms and the essential role of circadian synchrony in a healthy organism. In particular, we discuss the role of circadian regulation in the context of behaviour and cognitive functioning, delineating how the loss of this tight interplay is linked to pathological development with a focus on mental disorders and neurodegeneration. We further describe emerging new aspects on the link between the circadian clock and physical exercise-induced cognitive functioning, and its current usage as circadian activator with a positive impact in delaying the progression of certain pathologies including neurodegeneration and brain-related disorders. Finally, we discuss recent epidemiological evidence pointing to an important role of the circadian clock in mental health.

Impairment of aversive episodic memories during Covid-19 pandemic: The impact of emotional context on memory processes

The threatening context of the COVID-19 pandemic provided a unique setting to study the effects of negative psychological symptoms on memory processes. Episodic memory is an essential function of the human being related to the ability to store and remember experiences and anticipate possible events in the future. Studying this function in this context is crucial to understand what effects the pandemic will have on the formation of episodic memories. To study this, the formation of episodic memories was evaluated by free recall, recognition, and episode order tasks for an aversive and neutral content. The results indicated that aversive episodic memory is impaired both in the free recall task and in the recognition task. Even the beneficial effect that emotional memory usually has for the episodic order was undermined as there were no differences between the neutral and aversive condition. The present work adds to the evidence that indicates that the level of activation does not modify memory processes in a linear way, which also depends on the type of recall and the characteristics of the content to be encoded.

"Seat of the soul"? The structure and function of the pineal gland in women with alleged spirit possession-Results of two experimental studies

BACKGROUND

Cultural traditions attribute to pineal gland an important role for spiritual experiences. Mediumship and spirit possession are cultural phenomena found worldwide which have been described as having dissociative and psychotic-like characteristics, but with nonpathological aspects. A sympathetic activation pattern in response to spirit possession has been reported in some studies, but empirical data on pineal gland is scarce in this context.

METHODS

We aimed to investigate pineal gland and pituitary volumes, as well as urinary 6-sulfatoxymelatonin levels in 16 alleged mediums (Medium Group-MG) compared with 16 healthy nonmedium controls (Control Group) (Experiment 1). Furthermore, we aimed to evaluate urinary 6-sulfatoxymelatonin and stress reactivity in GM (n = 10) under different physiological conditions (Experiment 2).

RESULTS

In Experiment 1, MG presented higher scores of anomalous experiences, but there were no between-group differences regarding mental health or subjective sleep quality. Similar pineal gland and pituitary volumes were observed between groups. There were no between-group differences in urinary 6-sulfatoxymelatonin collected under equivalent baseline conditions. In Experiment 2, the rise of anxiety and heart rate in response to mediumistic experience was intermediate between a nonstressful control task (reading) and a stressful control task (Trier Social Stress Test-TSST). No significant differences were observed in 6-sulfatoxymelatonin urinary levels between the three conditions. The pattern of stress reactivity during the TSST was normal, but with an attenuated salivary cortisol response.

CONCLUSION

The normal neuroimaging and stress reactivity findings in MG contrast with the abnormal results usually observed in subjects with psychotic and dissociative disorders.

Effects of agomelatine on behaviour, circadian expression of period 1 and period 2 clock genes and neuroplastic markers in the predator scent stress rat model of PTSD

Objectives: The therapeutic value of the antidepressant agomelatine in the aftermath of traumatic experience and early post-reminder has been questioned. Herein, agomelatine, its vehicle or melatonin agonist were administered either acutely 1 h post-stressor or repeatedly (7 days) after early post-reminder in a post-traumatic stress rat model (PSS) using the scent of predator urine.Methods: Behavioural responses, and brain molecular and morphological changes were evaluated after each treatment procedure in PSS-exposed and unexposed rats.Results: When administered immediately after PSS, agomelatine induced a significant reduction of anxiety-like behaviour as assessed in the elevated-plus-maze and acoustic startle response at 8 days post-administration. Concomitantly, agomelatine significantly decreased Per1/Per2 expression in the CA1/CA3 areas, suprachiasmatic nucleus and basolateral amygdala, thereby partially restoring genes expression overregulated by PSS. Agomelatine further significantly increased cell growth and facilitated dendritic growth and arbour in dentate gyrus (DG) granule and apical CA1 cells and upregulated brain-derived neurotrophic factor protein in the DG and cortex III versus vehicle. When administered early post-reminder over 7 days before testing, agomelatine was ineffective on behavioural responses pattern, molecular and morphological changes induced by PSS.Conclusions: These findings suggest that agomelatine may be a potential agent in the acute aftermath of traumatic stress exposure.

Melatonin in Synaptic Impairments of Alzheimer's Disease

Alzheimer's disease (AD) underlies dementia for millions of people worldwide with no effective treatment. The dementia of AD is thought stem from the impairments of the synapses because of their critical roles in cognition. Melatonin is a neurohormone mainly released by the pineal gland in a circadian manner and it regulates brain functions in various manners. It is reported that both the melatonin deficit and synaptic impairments are present in the very early stage of AD and strongly contribute to the progress of AD. In the mammalian brains, the effects of melatonin are mainly relayed by two of its receptors, melatonin receptor type 1a (MT1) and 1b (MT2). To have a clear idea on the roles of melatonin in synaptic impairments of AD, this review discussed the actions of melatonin and its receptors in the stabilization of synapses, modulation of long-term potentiation, as well as their contributions in the transmissions of glutamatergic, GABAergic and dopaminergic synapses, which are the three main types of synapses relevant to the synaptic strength. The synaptic protective roles of melatonin in AD treatment were also summarized. Regarding its protective roles against amyloid-β neurotoxicity, tau hyperphosphorylation, oxygenation, inflammation as well as synaptic dysfunctions, melatonin may be an ideal therapeutic agent against AD at early stage.

The emergence of melatonin in oncology: Focus on colorectal cancer

Within the last few decades, melatonin has increasingly emerged in clinical oncology as a naturally occurring bioactive molecule with substantial anticancer properties and a pharmacological profile optimal for joining the currently available pharmacopeia. In addition, extensive experimental data shows that this chronobiotic agent exerts oncostatic effects throughout all stages of tumor growth, from initial cell transformation to mitigation of malignant progression and metastasis; additionally, melatonin alleviates the side effects and improves the welfare of radio/chemotherapy-treated patients. Thus, the support of clinicians and oncologists for the use of melatonin in both the treatment and proactive prevention of cancer is gaining strength. Because of its epidemiological importance and symptomatic debut in advanced stages of difficult clinical management, colorectal cancer (CRC) is a preferential target for testing new therapies. In this regard, the development of effective forms of clinical intervention for the improvement of CRC outcome, specifically metastatic CRC, is urgent. At the same time, the need to reduce the costs of conventional anti-CRC therapy results is also imperative. In light of this status quo, the therapeutic potential of melatonin, and the direct and indirect critical processes of CRC malignancy it modulates, have aroused much interest. To illuminate the imminent future on CRC research, we focused our attention on the molecular mechanisms underlying the multiple oncostatic actions displayed by melatonin in the onset and evolution of CRC and summarized epidemiological evidence, as well as in vitro, in vivo and clinical findings that support the broadly protective potential demonstrated by melatonin.

Multilevel Interactions of Stress and Circadian System: Implications for Traumatic Stress

The dramatic fluctuations in energy demands by the rhythmic succession of night and day on our planet has prompted a geophysical evolutionary need for biological temporal organization across phylogeny. The intrinsic circadian timing system (CS) represents a highly conserved and sophisticated internal "clock," adjusted to the 24-h rotation period of the earth, enabling a nyctohemeral coordination of numerous physiologic processes, from gene expression to behavior. The human CS is tightly and bidirectionally interconnected to the stress system (SS). Both systems are fundamental for survival and regulate each other's activity in order to prepare the organism for the anticipated cyclic challenges. Thereby, the understanding of the temporal relationship between stressors and stress responses is critical for the comprehension of the molecular basis of physiology and pathogenesis of disease. A critical loss of the harmonious timed order at different organizational levels may affect the fundamental properties of neuroendocrine, immune, and autonomic systems, leading to a breakdown of biobehavioral adaptative mechanisms with increased stress sensitivity and vulnerability. In this review, following an overview of the functional components of the SS and CS, we present their multilevel interactions and discuss how traumatic stress can alter the interplay between the two systems. Circadian dysregulation after traumatic stress exposure may represent a core feature of trauma-related disorders mediating enduring neurobiological correlates of trauma through maladaptive stress regulation. Understanding the mechanisms susceptible to circadian dysregulation and their role in stress-related disorders could provide new insights into disease mechanisms, advancing psychochronobiological treatment possibilities and preventive strategies in stress-exposed populations.

Pretraining hippocampal stimulation of melatonin type 2 receptors can improve memory acquisition in rats

BACKGROUND

Learning and memory are among the most important cognitive functions of the brain. Melatonin receptor type 2 (MT2R) is located in the hippocampus and participates in learning and memory processes. In the present study, we examined the role of hippocampal MT2R activation in the acquisition, consolidation, and retrieval of learning and memory in novel object recognition (NOR) and passive avoidance (PA) tasks.

METHODS

IIK7 (0.03, 0.3, and 3 μg/μl/side), as a selective MT2R agonist, or vehicle was injected bilaterally into the dentate gyrus (DG) region of the hippocampus in rats five minutes before training, immediately after training, and five minutes before the retrieval-behavioral tasks, respectively. The discrimination index (DI) was measured in the NOR task, while step-through latency in acquisition (STLa), number of trials to acquisition (NOT), step-through latency in the retention trial (STLr), and time spent in the dark compartment (TDC) were determined in the PA task.

RESULTS

The pretraining intrahippocampal injection of IIK7 at all doses significantly improved acquisition in the PA task. On the other hand, the posttraining intrahippocampal administration of IIK7 had no significant effects on consolidation. The preretrieval intrahippocampal injection of IIK7 at different doses attenuated the retrieval of memory. However, the NOR data showed that the intrahippocampal injection of IIK7 at different doses had no significant effects on the acquisition, consolidation, or retrieval in this task.

DISCUSSION

Based on the findings, stimulation of MT2R could improve acquisition, whereas it had no effects on consolidation. It could impair retrieval in the PA task, while it had no effects on object recognition in rats.

The Glymphatic System in Diabetes-Induced Dementia

The glymphatic system has emerged as an important player in central nervous system (CNS) diseases, by regulating the vasculature impairment, effectively controlling the clearance of toxic peptides, modulating activity of astrocytes, and being involved in the circulation of neurotransmitters in the brain. Recently, several studies have indicated decreased activity of the glymphatic pathway under diabetes conditions such as in insulin resistance and hyperglycemia. Furthermore, diabetes leads to the disruption of the blood-brain barrier and decrease of apolipoprotein E (APOE) expression and the secretion of norepinephrine in the brain, involving the impairment of the glymphatic pathway and ultimately resulting in cognitive decline. Considering the increased prevalence of diabetes-induced dementia worldwide, the relationship between the glymphatic pathway and diabetes-induced dementia should be investigated and the mechanisms underlying their relationship should be discussed to promote the development of an effective therapeutic approach in the near future. Here, we have reviewed recent evidence for the relationship between glymphatic pathway dysfunction and diabetes. We highlight that the enhancement of the glymphatic system function during sleep may be beneficial to the attenuation of neuropathology in diabetes-induced dementia. Moreover, we suggest that improving glymphatic system activity may be a potential therapeutic strategy for the prevention of diabetes-induced dementia.

Evaluation of Oxidant-Antioxidant Balance in Children with Atopic Dermatitis: A Case-Control Study

BACKGROUND

Increased reactive oxygen species (ROS) and oxidative stress (OS) has been reported in many allergic and inflammatory skin diseases, including urticaria, psoriasis, and atopic dermatitis (AD). Melatonin is a hormone secreted from the pineal gland and is a potent antioxidant.

OBJECTIVE

The aim of the study was to measure serum antioxidant melatonin, oxidants of nitric oxide (NO), and malondialdehyde levels to calculate the serum oxidant-antioxidant balance based on the NO/melatonin and malondialdehyde/melatonin ratios and to determine the correlation with the disease severity in children with AD.

METHODS

Seventy-three children with AD and 67 healthy controls were included in the study. The clinical diagnosis of AD was based on the diagnostic criteria of Hanifin-Rajka. The severity of AD was evaluated by the scoring AD (SCORAD) index, and atopy was determined by skin prick tests (SPTs) with commercial extracts. The OS-related parameters of serum melatonin, NO, malondialdehyde, and the NO/melatonin and malondialdehyde/melatonin ratios were calculated and compared with the results of healthy controls.

RESULTS

Serum melatonin levels were higher (p < 0.0001) and serum NO levels and the NO/melatonin and malondialdehyde/melatonin ratios were lower in children with AD than in healthy controls (p = 0.045, p < 0.0001, p < 0.0001, respectively). There was no difference between children with AD and healthy controls in terms of serum malondialdehyde levels (p = 0.119). Serum melatonin levels were significantly lower in severe AD than in mild AD (p = 0.012). However, in terms of serum melatonin levels, there was no difference between mild and moderate AD (p = 0.742) and moderate to severe AD (p = 0.301). There was no significant difference in serum NO and malondialdehyde levels and NO/melatonin and malondialdehyde/melatonin ratios among children with mild, moderate, and severe AD (p > 0.05). A negative correlation was found between serum melatonin levels and the SCORAD index (r = -0.252, p = 0.031), and a positive correlation was found between NO/melatonin and malondialdehyde/melatonin ratios (r = 0.511, p < 0.0001). There was no statistically significant relationship between age (≤24 or >24 months), disease duration (≤6 or >6 months), and sex for the OS-related parameters (p > 0.05).

CONCLUSION

The serum oxidant-antioxidant balance was impaired in children with AD. Serum melatonin levels were higher in children with AD; however, this was negatively correlated with disease severity. Serum NO levels and NO/melatonin and malondialdehyde/melatonin ratios were lower in children with AD than in healthy controls. Melatonin might be used as a promising antioxidant to evaluate disease severity in children with AD. Thus, further studies are needed to clarify the role of melatonin in AD pathogenesis.

Potential pleiotropic beneficial effects of adjuvant melatonergic treatment in posttraumatic stress disorder

Loss of circadian rhythmicity fundamentally affects the neuroendocrine, immune, and autonomic system, similar to chronic stress and may play a central role in the development of stress-related disorders. Recent articles have focused on the role of sleep and circadian disruption in the pathophysiology of posttraumatic stress disorder (PTSD), suggesting that chronodisruption plays a causal role in PTSD development. Direct and indirect human and animal PTSD research suggests circadian system-linked neuroendocrine, immune, metabolic and autonomic dysregulation, linking circadian misalignment to PTSD pathophysiology. Recent experimental findings also support a specific role of the fundamental synchronizing pineal hormone melatonin in mechanisms of sleep, cognition and memory, metabolism, pain, neuroimmunomodulation, stress endocrinology and physiology, circadian gene expression, oxidative stress and epigenetics, all processes affected in PTSD. In the current paper, we review available literature underpinning a potentially beneficiary role of an add-on melatonergic treatment in PTSD pathophysiology and PTSD-related symptoms. The literature is presented as a narrative review, providing an overview on the most important and clinically relevant publications. We conclude that adjuvant melatonergic treatment could provide a potentially promising treatment strategy in the management of PTSD and especially PTSD-related syndromes and comorbidities. Rigorous preclinical and clinical studies are needed to validate this hypothesis.

Melatonin, noncoding RNAs, messenger RNA stability and epigenetics--evidence, hints, gaps and perspectives

Melatonin is a highly pleiotropic regulator molecule, which influences numerous functions in almost every organ and, thus, up- or down-regulates many genes, frequently in a circadian manner. Our understanding of the mechanisms controlling gene expression is actually now expanding to a previously unforeseen extent. In addition to classic actions of transcription factors, gene expression is induced, suppressed or modulated by a number of RNAs and proteins, such as miRNAs, lncRNAs, piRNAs, antisense transcripts, deadenylases, DNA methyltransferases, histone methylation complexes, histone demethylases, histone acetyltransferases and histone deacetylases. Direct or indirect evidence for involvement of melatonin in this network of players has originated in different fields, including studies on central and peripheral circadian oscillators, shift work, cancer, inflammation, oxidative stress, aging, energy expenditure/obesity, diabetes type 2, neuropsychiatric disorders, and neurogenesis. Some of the novel modulators have also been shown to participate in the control of melatonin biosynthesis and melatonin receptor expression. Future work will need to augment the body of evidence on direct epigenetic actions of melatonin and to systematically investigate its role within the network of oscillating epigenetic factors. Moreover, it will be necessary to discriminate between effects observed under conditions of well-operating and deregulated circadian clocks, and to explore the possibilities of correcting epigenetic malprogramming by melatonin.

When time stands still: an integrative review on the role of chronodisruption in posttraumatic stress disorder

PURPOSE OF REVIEW

The human circadian system creates and maintains cellular and systemic rhythmicity essential to homeostasis. Loss of circadian rhythmicity fundamentally affects the neuroendocrine, immune and autonomic system, similar to chronic stress and, thus, may play a central role in the development of stress-related disorders. This article focuses on the role of circadian misalignment in the pathophysiology of posttraumatic stress disorder (PTSD).

RECENT FINDINGS

Sleep disruption is a core feature of PTSD supporting the important supraordinate pathophysiological role of circadian system in PTSD. Furthermore, direct and indirect human and animal PTSD research suggests circadian system linked neuroendocrine, immune, metabolic and autonomic dysregulation with blunted diurnal rhythms, specific sleep pattern pathologies and cognitive deficits, as well as endocannabinoid and neuropeptide Y system alterations and altered circadian gene expression, linking circadian misalignment to PTSD pathophysiology.

SUMMARY

PTSD development is associated with chronodisruption findings. Evaluation and treatment of sleep and circadian disruption should be the first steps in PTSD management. State-of-the-art methods of circadian rhythm assessment should be applied to bridge the gap between clinical significance and limited understanding of the relationship between traumatic stress, sleep and circadian system.

Unveiling the role of melatonin MT2 receptors in sleep, anxiety and other neuropsychiatric diseases: a novel target in psychopharmacology

BACKGROUND

Melatonin (MLT) is a pleiotropic neurohormone controlling many physiological processes and whose dysfunction may contribute to several different diseases, such as neurodegenerative diseases, circadian and mood disorders, insomnia, type 2 diabetes and pain. Melatonin is synthesized by the pineal gland during the night and acts through 2 G-protein coupled receptors (GPCRs), MT1 (MEL1a) and MT2 (MEL1b). Although a bulk of research has examined the physiopathological effects of MLT, few studies have investigated the selective role played by MT1 and MT2 receptors. Here we have reviewed current knowledge about the implications of MT2 receptors in brain functions.

METHODS

We searched PubMed, Web of Science, Scopus, Google Scholar and articles' reference lists for studies on MT2 receptor ligands in sleep, anxiety, neuropsychiatric diseases and psychopharmacology, including genetic studies on the MTNR1B gene, which encodes the melatonin MT2 receptor.

RESULTS

These studies demonstrate that MT2 receptors are involved in the pathophysiology and pharmacology of sleep disorders, anxiety, depression, Alzheimer disease and pain and that selective MT2 receptor agonists show hypnotic and anxiolytic properties.

LIMITATIONS

Studies examining the role of MT2 receptors in psychopharmacology are still limited.

CONCLUSION

The development of novel selective MT2 receptor ligands, together with further preclinical in vivo studies, may clarify the role of this receptor in brain function and psychopharmacology. The superfamily of GPCRs has proven to be among the most successful drug targets and, consequently, MT2 receptors have great potential for pioneer drug discovery in the treatment of mental diseases for which limited therapeutic targets are currently available.

Diurnal alterations in circadian genes and peptides in major depressive disorder before and after escitalopram treatment

BACKGROUND

Strong links exist between circadian disturbances and some of the most characteristic symptoms of clinical major depressive disorder (MDD). However, changes in the expression of clock genes or neuropeptides related to the regulation of circadian rhythm that may influence the susceptibility to recurrence after antidepressant treatment in MDD have not been investigated.

METHODS

Blood samples were collected at 4h intervals for 24h from 12 male healthy controls and 12 male MDD patients before and after treatment with escitalopram for 8 weeks. The outcome measures included the relative expression of clock gene mRNA (PERIOD1, PERIOD2, PERIOD3, CRY1, BMAL1, NPAS2, and GSK-3β), and the levels of serum melatonin, vasoactive intestinal polypeptide (VIP), cortisol, adrenocorticotropic hormone (ACTH), insulin-like growth factor-1 (IGF-1), and growth hormone (GH).

RESULTS

Compared with healthy controls, MDD patients showed disruptions in the diurnal rhythms of the expression of PERIOD1, PERIOD2, CRY1, BMAL1, NPAS2, and GSK-3β and disruptions in the diurnal rhythms of the release of melatonin, VIP, cortisol, ACTH, IGF-1, and GH. Several of these disruptions (i.e., PER1, CRY1, melatonin, VIP, cortisol, ACTH, and IGF-1) persisted 8 weeks after escitalopram treatment, similar to the increase in the 24h levels of VIP and decreases in the 24h levels of cortisol and ACTH.

CONCLUSION

These persistent neurobiological changes may play a role in MDD symptoms that are thought to contribute to the vulnerability to recurrence and long-term maintenance therapy.

Potency of melatonin in living beings

Living beings are surrounded by various changes exhibiting periodical rhythms in environment. The environmental changes are imprinted in organisms in various pattern. The phenomena are believed to match the external signal with organisms in order to increase their survival rate. The signals are categorized into circadian, seasonal, and annual cycles. Among the cycles, the circadian rhythm is regarded as the most important factor because its periodicity is in harmony with the levels of melatonin secreted from pineal gland. Melatonin is produced by the absence of light and its presence displays darkness. Melatonin plays various roles in creatures. Therefore, this review is to introduce the diverse potential ability of melatonin in manifold aspects in living organism.

The hormonal Zeitgeber melatonin: role as a circadian modulator in memory processing

The neuroendocrine substance melatonin is a hormone synthesized rhythmically by the pineal gland under the influence of the circadian system and alternating light/dark cycles. Melatonin has been shown to have broad applications, and consequently becoming a molecule of great controversy. Undoubtedly, however, melatonin plays an important role as a time cue for the endogenous circadian system. This review focuses on melatonin as a regulator in the circadian modulation of memory processing. Memory processes (acquisition, consolidation, and retrieval) are modulated by the circadian system. However, the mechanism by which the biological clock is rhythmically influencing cognitive processes remains unknown. We also discuss, how the circadian system by generating cycling melatonin levels can implant information about daytime into memory processing, depicted as day and nighttime differences in acquisition, memory consolidation and/or retrieval.

Neuroprotection by melatonin after germinal matrix hemorrhage in neonatal rats

BACKGROUND

Germinal matrix hemorrhage (GMH) is a devastating neurological disorder of very low birth weight premature infants that leads to post-hemorrhagic hydrocephalus, cerebral palsy, and mental retardation. Melatonin is a potent antioxidant known to reverse free-radical mediated injury in the brain. This study investigated the effect of melatonin treatment after GMH injury.

METHODS

Clostridial collagenase was infused into the right germinal matrix region of neonatal rats with stereotaxic technique. Cognitive function, sensorimotor ability, cerebral, cardiac and splenic growths were measured in juvenile animals.

RESULTS

Systemic melatonin treatment ameliorated cognitive and sensorimotor dysfunction at the juvenile developmental stage. This hormone also normalized brain atrophy, splenomegaly, and cardiac hypertrophy consequences at 1 month after injury.

CONCLUSION

This study supports the role of free radicals in acute neonatal hemorrhagic brain injury. Melatonin is an effective antioxidant that can protect the infant's brain from the post-hemorrhagic consequences of mental retardation and cerebral palsy. Further mechanistic studies are warranted to determine the mechanisms behind these neuroprotective effects.

The relationship between urinary melatonin metabolite excretion and posttraumatic symptoms following traumatic injury

BACKGROUND

Associations between 24-hour urinary 6-sulphatoxy melatonin excretion and symptoms of posttraumatic stress disorder were assessed 2 days, 1 month and 6 months after traumatic injury requiring hospitalisation.

METHODS

Forty-eight participants were recruited following an admission to hospital for an acute traumatic injury. They completed assessments 48h after the accident, 1 month and 6 months later. A 24-hour urine collection was initiated the morning before questionnaires were administered. PTSD symptoms and caseness was determined using the Impact of Event Scale (IES-R) and the Clinician Administered PTSD Scale respectively. Urinary 6-sulphatoxy melatonin was assayed by radioimmunoassay.

RESULTS

Mean age of participants was 34 years (SD=12.72) and 75% were males. Ten (27%) participants met the criteria for PTSD 1 month post trauma and 6 (21%) met the criteria for PTSD at 6 months. Four of the six (67%) participants with PTSD at 6 months were also positive for major depression. Significant negative correlations were found between 6-sulphatoxy melatonin excretion at day 2 and all subscales and total score of the IES-R at the six month assessment. Controlling for depression, every one unit decrease in 6-sulphatoxy melatonin excretion was associated with a 13% increase in PTSD risk at six months (OR=1.13, 95% CI 1.00-1.27). However, this association was lost when self-reported pain, gender and employment was added to the model (OR=1.11, 0.93-1.32).

CONCLUSION

This study provides preliminary data suggesting disrupted melatonin levels in the first 48h following trauma may place individuals at increased risk of PTSD.

Long-term sleep disturbances in children: a cause of neuronal loss

Short-term sleep loss is known to cause temporary difficulties in cognition, behaviour and health but the effects of persistent sleep deprivation on brain development have received little or no attention. Yet, severe sleep disorders that last for years are common in children especially when they have neurodevelopmental disabilities. There is increasing evidence that chronic sleep loss can lead to neuronal and cognitive loss in children although this is generally unrecognized by the medical profession and the public. Without the restorative functions of sleep due to total sleep deprivation, death is inevitable within a few weeks. Chronic sleep disturbances at any age deprive children of healthy environmental exposure which is a prerequisite for cognitive growth more so during critical developmental periods. Sleep loss adversely effects pineal melatonin production which causes disturbance of circadian physiology of cells, organs, neurochemicals, neuroprotective and other metabolic functions. Through various mechanisms sleep loss causes widespread deterioration of neuronal functions, memory and learning, gene expression, neurogenesis and numerous other changes which cause decline in cognition, behaviour and health. When these changes are long-standing, excessive cellular stress develops which may result in widespread neuronal loss. In this review, for the first time, recent research advances obtained from various fields of sleep medicine are integrated in order to show that untreated chronic sleep disorders may lead to impaired brain development, neuronal damage and permanent loss of developmental potentials. Further research is urgently needed because these findings have major implications for the treatment of sleep disorders.

Melatonin, cardiolipin and mitochondrial bioenergetics in health and disease

Melatonin is a natural occurring compound with well-known antioxidant properties. Melatonin is ubiquitously distributed and because of its small size and amphiphilic nature, it is able to reach easily all cellular and subcellular compartments. The highest intracellular melatonin concentrations are found in mitochondria, raising the possibility of functional significance for this targeting with involvement in situ in mitochondrial activities. Mitochondria, the powerhouse of the cell, are considered to be the most important cellular organelles to contribute to degenerative processes mainly through respiratory chain dysfunction and formation of reactive oxygen species, leading to damage to mitochondrial proteins, lipids and DNA. Therefore, protecting mitochondria from oxidative damage could be an effective therapeutic strategy against cellular degenerative processes. Many of the beneficial effects of melatonin administration may depend on its effect on mitochondrial physiology. Cardiolipin, a phospholipid located at the level of inner mitochondrial membrane is known to be intimately involved in several mitochondrial bioenergetic processes as well as in mitochondrial-dependent steps of apoptosis. Alterations to cardiolipin structure, content and acyl chain composition have been associated with mitochondrial dysfunction in multiple tissues in several physiopathological situations and aging. Recently, melatonin was reported to protect the mitochondria from oxidative damage by preventing cardiolipin oxidation and this may explain, at least in part, the beneficial effect of this molecule in mitochondrial physiopathology. In this review, we discuss the role of melatonin in preventing mitochondrial dysfunction and disease.

Protective effect of melatonin upon neuropathology, striatal function, and memory ability after intracerebral hemorrhage in rats

Since free radicals play a role in the mechanisms of brain injury after hemorrhagic stroke, the effect of melatonin (a potent antioxidant and free-radical scavenger) on outcomes was investigated after intracerebral hemorrhage (ICH) in rats. ICH was induced by clostridial collagenase infusion into the right caudate putamen, and several time points and doses of melatonin were studied. Brain edema and neurological function at 24 h were unchanged in comparison with vehicle-treated groups, in spite of oxidative stress reductions. Repeated treatment with the lower dose of melatonin (5 mg/kg) given at 1 h and every 24 h thereafter for 3 days after ICH, led to normalization of striatal function and memory ability over the course of 8 weeks, and less brain atrophy 2 weeks later. These results suggest that melatonin is safe for use after ICH, reduces oxidative stress, provides brain protection, and could be used for future investigations of free radical mechanisms after cerebral hemorrhage.

Synergistic antitumor effect of melatonin with several chemotherapeutic drugs on human Ewing sarcoma cancer cells: potentiation of the extrinsic apoptotic pathway

Ewing sarcoma, the second most frequent bone cancer type, affects mainly adolescents, who have a survival of 50% 5 yr after diagnosis. Current treatments include a combination of surgery, radiotherapy and chemotherapy, which present potential serious side effects. Melatonin, a natural molecule without relevant side effects, has been previously shown to induce cytotoxicity in SK-N-MC cells, a Ewing sarcoma cell line. Here, we found that there is a synergy in the antitumor effect when melatonin (50 mum-1 mm) is combined with vincristine at the concentration of 5-10 nm or with ifosfamide at the range of 100 mum-1 mm. This synergism is due to the potentiation of cell death, particularly to the potentiation of apoptosis, i.e., mainly the extrinsic apoptotic pathway. There is a significant increase in the activation of caspase-3, -8, -9 and Bid when melatonin is combined with vincristine or ifosfamide compared to the individual treatments. Finally, there is also a potentiation of the early free radical production, likely dependent on the extrinsic apoptosis pathway activation, when the drugs are combined with melatonin. Other proteins which are related to this pathway including mitogen-activated protein kinase or protein kinase B/Akt are not involved in apoptosis induced by these agents separately or when combined. The results shown here together with the facts that: (i) no relevant side effects have been reported for melatonin and (ii) melatonin has a cytoprotective effect on noncancer cells, opens the door for a new approach in the treatment of the Ewing sarcoma family of tumors.

Melatonin inhibits the development of 2,4-dinitrofluorobenzene-induced atopic dermatitis-like skin lesions in NC/Nga mice

Atopic dermatitis (AD) is a common disease in children, and epicutaneous treatment with a chemical hapten such as 2,4-dinitrofluorobenzene (DNFB) evokes an AD-like reaction in NC/Nga mice under specific pathogen-free conditions. Melatonin (N-acetyl-5-methoxytryptamine) is synthesized by the pineal gland, has several different physiologic functions, which include seasonal reproduction control, immune system modulation, free radical scavenging, and inflammatory suppression. In the present study, we investigated whether melatonin suppresses DNFB-induced AD-like skin lesions in NC/Nga mice. The topical administration of melatonin to DNFB-treated NC/Nga mice was found to inhibit ear thickness increases and the skin lesions induced by DNFB. Furthermore, interleukin (IL)-4 and interferon (IFN)-gamma secretion by activated CD4(+) T cells from the draining lymph nodes of DNFB-treated NC/Nga mice were significantly inhibited by melatonin, and total IgE levels in serum were reduced. Our findings suggest that melatonin suppresses the development of AD-like dermatitis in DNFB-treated NC/Nga mice by reducing total IgE in serum, and IL-4 and IFN-gamma production by activated CD4(+) T cells.

A simple model for circadian timing by mammals

Circadian timing is structured in such a way as to receive information from the external and internal environments, and its function is the timing organization of the physiological and behavioral processes in a circadian pattern. In mammals, the circadian timing system consists of a group of structures, which includes the suprachiasmatic nucleus (SCN), the intergeniculate leaflet and the pineal gland. Neuron groups working as a biological pacemaker are found in the SCN, forming a biological master clock. We present here a simple model for the circadian timing system of mammals, which is able to reproduce two fundamental characteristics of biological rhythms: the endogenous generation of pulses and synchronization with the light-dark cycle. In this model, the biological pacemaker of the SCN was modeled as a set of 1000 homogeneously distributed coupled oscillators with long-range coupling forming a spherical lattice. The characteristics of the oscillator set were defined taking into account the Kuramoto's oscillator dynamics, but we used a new method for estimating the equilibrium order parameter. Simultaneous activities of the excitatory and inhibitory synapses on the elements of the circadian timing circuit at each instant were modeled by specific equations for synaptic events. All simulation programs were written in Fortran 77, compiled and run on PC DOS computers. Our model exhibited responses in agreement with physiological patterns. The values of output frequency of the oscillator system (maximal value of 3.9 Hz) were of the order of magnitude of the firing frequencies recorded in suprachiasmatic neurons of rodents in vivo and in vitro (from 1.8 to 5.4 Hz).

Melatonin alleviates memory deficits and neuronal degeneration induced by intracerebroventricular administration of streptozotocin in rats

In the present study the effect of melatonin on intracerebroventricularly administered streptozotocin (STZ)-induced neurodegeneration was investigated in rats. STZ (3mg/kg), administered twice with an interval of 48 h between the two doses, showed impairment in spatial memory tested by water maze test after 14 days of 1st dose. Administration of melatonin (2.5, 5.0 and 10mg/kg, i.p.) was started 1h prior to 1st dose of STZ and continued up to 14 days. Glutathione and malondialdehyde were used as biochemical markers of oxidative stress in different brain regions. Histopathological changes were examined by using hematoxylin and eosin stain. STZ administration caused significant decrease in glutathione and increase in malondialdehyde as compared to control and artificial Cerebrospinal Fluid treated rats indicating oxidative stress. Brain sections of STZ-treated rats showed increased vacuoles in the periventricular cortical area, damaged periventricular cells and damaged cells in the hippocampal CA4 region as compared to control and artificial Cerebrospinal Fluid treated groups. Melatonin treatment significantly attenuated the effect of STZ-induced oxidative stress and histopathological changes. The results indicate that melatonin is effective in providing protection against memory deficit, oxidative stress and neuronal damage induced by STZ.

Melatonin preserves longevity protein (sirtuin 1) expression in the hippocampus of total sleep-deprived rats

Sleep disorders cause cognitive dysfunction in which impaired neuronal plasticity in the hippocampus may underline the molecular mechanisms of this deficiency. As sirtuin 1 (SIRT1) plays an important role in maintaining metabolic homeostasis and neuronal plasticity, this study is aimed to determine whether melatonin exerts beneficial effects on preserving SIRT1 activation following total sleep deprivation (TSD). TSD was performed by disc on water method for five consecutive days. During this period, animals daily received melatonin at doses of 5, 25, 50 or 100 mg/kg. The cytochrome oxidase (COX) histochemistry, SIRT1 immunohistochemistry together with Morris water maze learning test were performed to examine the metabolic, neurochemical, as well as the behavioral changes in neuronal plasticity, respectively. The results indicate that in normal rats, numerous COX and SIRT1 positive-labeled neurons with strong staining intensities were found in hippocampal pyramidal and granular cell layers. Following TSD, both COX and SIRT1 reactivities were drastically decreased as revealed by reduced staining pattern and labeling frequency. Behavioral data corresponded well with morphological findings in which spatial memory test in water maze was significantly impaired after TSD. However, in rats receiving different doses of melatonin, both COX and SIRT1 expressions were successfully preserved. Considerably better performance on behavioral testing further strengthened the beneficial effects of melatonin. These findings suggest that melatonin may serve as a novel therapeutic strategy directed for preventing the memory deficits resulting from TSD, possibly by effectively preserving the metabolic function and neuronal plasticity engaged in maintaining cognitive activity.

You are only coming through in waves: wakefulness variability and assessment in patients with impaired consciousness

The vegetative state (VS) is defined as a condition of wakefulness without awareness. Being awake and being asleep are two behavioral and physiological manifestations of the daily cycles of vigilance and metabolism. International guidelines for the diagnosis of VS propose that a patient fulfills criteria for wakefulness if he/she exhibits cycles of eye closure and eye opening giving the impression of a preserved sleep-wake cycle. We argue that these criteria are insufficient and we suggest guidelines to address wakefulness in a more comprehensive manner in this complex and heterogeneous group of patients. Four factors underlying wakefulness, as well as their interactions, are considered: arousal/responsiveness, circadian rhythms, sleep cycle, and homeostasis. The first refers to the arousability and capacity to, consciously or not, respond to external stimuli. The second deals with the circadian clock as a synchronizer of physiological functions to environmental cyclic changes. The third evaluates general sleep patterns, while homeostasis refers to the capacity of the body to regulate its internal state and maintain a stable condition. We present examples of reflex responses, activity rhythms, and electroencephalographic (EEG) measurements from patients with disorders of consciousness (DOC) to illustrate these factors of wakefulness. If properly assessed, they would help in the evaluation of consciousness by informing when and in which context the patient is likely to exhibit maximal responsiveness. This evaluation has the potential to improve diagnosis and treatment and may also add prognostic value to the multimodal assessment in DOC.

The melatonin receptor MT1 is required for the differential regulatory actions of melatonin on neuronal 'clock' gene expression in striatal neurons in vitro

Through inhibitory G protein-coupled melatonin receptors, melatonin regulates intracellular signaling systems and also the transcriptional activity of certain genes. Clock genes are proposed as regulatory factors in forming dopamine-related behaviors and mood and melatonin has the ability to regulate these processes. Melatonin-mediated changes in clock gene expression have been reported in brain regions, including the striatum, that are crucial for the development of dopaminergic behaviors and mood. However, it is not known whether melatonin receptors present in striatum mediate these effects. Therefore, we investigated the role of the melatonin/melatonin receptor system on clock gene expression using a model of primary neuronal cultures prepared from striatum. We found that melatonin at the receptor affinity range (i.e., nm) affects the expression of the clock genes mPer1, mClock, mBmal1 and mNPAS2 (neuronal PAS domain protein 2) differentially in a pertussis toxin-sensitive manner: a decrease in Per1 and Clock, an increase in NPAS2 and no change in Bmal1 expression. Furthermore, mutating MT1 melatonin receptor (i.e., MT1 knockouts, MT1(-/-)) reversed melatonin-induced changes, indicating the involvement of MT1 receptor in the regulatory action of melatonin on neuronal clock gene expression. Therefore, by controlling clock gene expression we propose melatonin receptors (i.e., MT1) as novel therapeutic targets for the pathobiologies of dopamine-related behaviors and mood.