Melatonin Receptor Research Articles

Melatonin modulates the hypothalamic-pituitary neuroendocrine axis to regulate physiological color change in teleost fish.

Melatonin (MT) is a crucial neuroendocrine regulator of various physiological activities in vertebrates, especially in circadian or seasonal rhythm control. In the present study, the large yellow croaker (Larimichthys crocea), a marine bony fish with circadian body color change behavior, is chosen for functional investigation on teleost MT signaling systems that remain uncharacterized. All five melatonin receptors (LcMtnr1a1, LcMtnr1a2, LcMtnr1b1, LcMtnr1b2, and LcMtnr1c) were significantly activated by MT, triggering extracellular signal-regulated kinase 1/2 (ERK1/2) phosphorylation through different G protein coupling signaling pathways, with exclusive Gαi-dependency for LcMtnr1a2 and LcMtnr1c, and Gαq-dependency for two LcMtnr1b paralogs, whereas LcMtnr1a1 activated Gαi and Gαs dual-dependent signaling pathways. A comprehensive model of the MT signaling system in the hypothalamic-pituitary neuroendocrine axis was further constructed based on ligand-receptor interaction analysis using single-cell RNA-seq data, as well as spatial expression patterns of Mtnrs and related neuropeptides in central neuroendocrine tissues. A novel regulatory pathway of MT/melanin-concentrating hormone (MCH) and MT/(tachykinin precursor 1 (TAC1)+corticotropin-releasing hormone (CRH))/melanocyte-stimulating hormone (MSH) was discovered that functions in chromatophore mobilization and physiological color change and was further validated by pharmacological experiments. Together, our findings define multiple intracellular signaling pathways mediated by L. crocea melatonin receptors and provide the first in-depth evidence that uncover the upstream modulating roles of the MT signaling system in the hypothalamic-pituitary neuroendocrine axis of a marine teleost species, particularly in chromatophore mobilization and physiological color change.

The melatonin system is expressed in the ovine uterus: effect of the day of the oestrous cycle and undernutrition.

Melatonin influences female reproduction, but expression of the melatonin system has not been characterised in the ovine uterus. We aimed to determine whether synthesising enzymes (arylalkylamine N-acetyltransferase (AANAT) and N-acetylserotonin-O-methyltransferase (ASMT)), melatonin receptors 1 and 2 (MT1 and MT2), and catabolising enzymes (myeloperoxidase (MPO) and indoleamine 2,3-dioxygenase 1 and 2 (IDO1 and 2)), are expressed in the ovine uterus, and if they are influenced by the oestrous cycle (Experiment 1) or by undernutrition (Experiment 2). In Experiment 1, gene and protein expression was determined in sheep endometrium samples collected on days 0 (oestrus), 5, 10 and 14 of the oestrous cycle. In Experiment 2, we studied uterine samples from ewes fed either 1.5 or 0.5times their maintenance requirements. We have demonstrated the expression of AANAT and ASMT in the endometrium of sheep. AANAT and ASMT transcripts, and AANAT protein were more elevated at day 10, then decreased to day 14. A similar pattern was observed for MT2 , IDO1 , and MPO mRNA, which suggests that the endometrial melatonin system might be influenced by ovarian steroid hormones. Undernutrition increased AANAT mRNA expression, but seemed to decrease its protein expression, and increased MT2 and IDO2 transcripts, whereas ASMT expression was unaffected. The melatonin system is expressed in the ovine uterus and is affected by oestrous cycle and undernutrition. The results help explain the adverse effects of undernutrition on reproduction in sheep, and the success of exogenous melatonin treatments in improving reproductive outcomes.

PS-P02-1: MACHINE LEARNING PREDICTS MELATONIN TARGETS ON THE PSYCHOSOCIAL STRESS-SLEEP/CIRCADIAN-CARDIOMETABOLIC DISORDERS TRIAD

Objective: Melatonin may have a role in the pathophysiology of a set of three diseases categories that interact with each other, namely psychosocial stress disorders, sleep/circadian rhythm disturbances, and cardiometabolic diseases, forming a therapeutic target triad for melatonin (stress-sleep/circadian- cardiometabolic disorders triad). Establishing a relationship between the pharmacological target and disease has become a fundamental goal for scientists, as it is crucial for developing novel medicines or repurposing existing ones. We investigated the target prediction of melatonin for the stress-sleep/circadian- cardiometabolic disorders triad using machine learning predictive models. Design and Methods: The Open Targets Genetics, ChEMBL, PhenoDigm, PheWAS Catalog and Europe PMC databases were utilized to examine melatonin target tractability and prediction of the stress-sleep-cardiovascular triad. Diseases with association records for melatonin MT1, MT2 and MT3 receptors have been categorized into sleep, cardiovascular, diabetic pathology and psychosocial disorders discarding other pathologies. The collections of direct and indirect relationships were queried to generate tables containing the names of diseases, supporting data sources, and the number of evidences for each association and data source. Graphs were built by applying igraph library-based scripts and have been depicted applying the Gephi ForceAtlas algorithm. Results: To date, 144 phase I to IV trials for melatonin or agonists have been completed, and 78 phase 4 trials are ongoing or completed, for drugs with investigational or approved indications targeting melatonin receptors based on their proposed mode of action on stress-sleep/circadian- cardiometabolic disorders triad. The scientific evidence on the pathogenic linkages for melatonin within the stress-sleep- cardiometabolic disorders triad is identified. This study not only identified novel biologically plausible relationships that may justify further translational research for melatonin, but it also demonstrated an effective usage of data from several databases. Conclusion: Molecular biomarkers, 24-hour blood pressure, nocturnal blood pressure and heart rate, psychosocial markers, cardiometabolic risk scores, and multiple biomarker modeling are all referenced for this triad. Based on these findings, we propose combining outcome measures with biomarkers from different triad diseases when designing clinical trials for melatonin or agonists for a triad disorder.

Bioinformatic analysis of the coding region of the melatonin receptor 1b gene as a reliable DNA marker to resolve interspecific mammal phylogenetic relationships.

This research looks into the main DNA markers and the limits of their application in molecular phylogenetic analysis. Melatonin 1B (MTNR1B) receptor genes were analyzed from various biological sources. Based on the coding sequences of this gene, using the class Mammalia as example, phylogenetic reconstructions were made to study the potential of mtnr1b as a DNA marker for phylogenetic relationships investigating. The phylogenetic trees were constructed using NJ, ME and ML methods that establish the evolutionary relationships between different groups of mammals. The resulting topologies were generally in good agreement with topologies established on the basis of morphological and archaeological data as well as with other molecular markers. The present divergences provided a unique opportunity for evolutionary analysis. These results suggest that the coding sequence of the MTNR1B gene can be used as a marker to study the relationships of lower evolutionary levels (order, species) as well as to resolve deeper branches of the phylogenetic tree at the infraclass level.

Механизмы взаимодействия мелатонина c лимфоцитами

Melatonin is an indoleamine synthesized from the essential amino acid tryptophan. At the system level, it is produced mainly by the pineal gland, and at the local level, by most organs and tissues, including the gastrointestinal tract, liver, kidneys, lungs, skin, tissues of the reproductive system, and many others. The hormone regulates a wide range of biological reactions in health and diseases, and has a pronounced antioxidant, anti-inflammatory and antitumor activity. Along with this, melatonin is an effective regulator of the immune system, however, the data available to date on the problem are extremely contradictory, especially for the main effectors of adaptive immunity - T-lymphocytes. On the one hand, under physiological conditions or under immunodeficiency conditions, the effects of melatonin are usually stimulatory: it enhances the proliferative response of T- and B-lymphocytes, increases the production of Th1-cytokines, and inhibits apoptosis of lymphocytes induced by various stimuli. On the other hand, there are no fewer works demonstrating the immunosuppressive activity of melatonin, in particular, suppression of the production of pro-inflammatory cytokines. The resolution of these contradictions is the goal of this review. At the same time, the work focuses on two fundamental points. First, the main part of immunostimulating effects was obtained in experiments in vitro, while immunosuppressive effects were obtained in vivo, and since melatonin controls the synthesis of a number of other hormones of the hypothalamic-pituitary-adrenal and / or gonadal axes, many of which are effective immunomodulators themselves, it direct effects in vivo can be mediated and offset by other hormones. Second, lymphocytes express three high-affinity melatonin receptors: two membrane receptors, MT1 and MT2, and a nuclear one, RORα, as well as a number of low-specific targets, all with varying affinities for melatonin. Binding of different receptors apparently triggers different signaling mechanisms. Accordingly, physiological, pathological and pharmacological concentrations of melatonin can have different immunomodulating effects, and when evaluating the effect of melatonin on the immune system, it is important to correlate the hormone concentrations with the state of the receptor apparatus of the cells under study.

Mental disorders associated with acute COVID-19: clinical picture, therapy approaches

The purpose is to study the structure of clinical manifestations of mental disorders in the acute period of COVID-19 among patients, who were hospitalized with a new coronavirus infection and their relations with the severity of the immune response, to assess the efficacy and safety profile of the spectrum of used psychopharmacotherapy. A study was conducted of patients, hospitalized to the department of infectious diseases and repurposed for COVID-19 clinical departments with a diagnosis of COVID-19 (compliance with the criteria for ICD-10: U07.1) from September 2020 to March 2021. Study design: single center opened retrospective cohort study. The main group is consisted of 72 patients, average age - 71 [56.0; 81.0] years, the part of women - 64.0%. The control group (n=2221) was formed from those hospitalized in the same period with a diagnosis of U07.1 without mental disorders during the hospitalization period, average age 62 [51.0; 72.0] years, the part of women - 48.7%. Mental disorders were diagnosed in accordance to ICD-10 criteria, the following peripheral markers of inflammation, that were evaluated: neutrophils, lymphocytes, platelets, ESR, C-reactive protein, interleukin; also coagulogram indicators: APTT, fibrinogen, prothrombin time, D-dimers. In the following range of mental disorders were identified: a depressive episode (ICD-10 F32) by 31 patients, by 22 - a disorder of adaptive reactions (ICD-10 F43.2), by 5 - delirium not caused by alcohol or other psychoactive substances (ICD-10 F05), by 14 - mild cognitive impairment caused by damage and disfunction of the brain or somatic diseases (ICD-10 F06.7). In comparison with the control group, these patients showed a statistically significant (p<0.001) increasing the level of inflammatory markers (CRP, IL-6) and changes in the coagulogram. and anxiolytic drugs were used most often. Regarding psychopharmacotherapy, drugs from the group of atypical antipsychotics - quetiapine was prescribed in 44% patients in average dose 62.5 mg per day, and Melatonin receptor type 1 and 2 agonist and antagonists of serotonin 5-HT2C receptors: agomelatine was prescribed in 11% patients in average dose 25 mg per gay. The results of the study confirm the heterogeneity of the structure of mental disorders in the acute form of coronavirus infection, revealing the relations between the clinical picture and laboratory parameters of the immune response to systemic inflammation. Recommendations are given for the choice of psychopharmacotherapy, in conformity with the peculiarities of pharmacokinetics and interaction with somatotropic therapy.

Protective effects of melatonin receptor agonists on endotoxin-induced uveitis in rats.

Melatonin has an important role in regulating a variety of physiological functions of the body. We investigated the protective effects of Agomelatine (AGO) and Ramelteon (RAME) on Endotoxin-Induced Uveitis (EIU) in rats. 70 rats were randomly divided into fourteen groups. Healthy group normal saline, (IP), Uveitis group (200 μg/kg lipopolysaccharide (LPS), SC), DEX group (200 μg/kg LPS plus 1 mg/kg dexamethasone, IP), AGO20 group received 200 μg/kg LPS plus 20 mg/kg AGO, AGO40 group received 200 μg/kg LPS plus 40 mg/kg AGO, RAME2 group received 200 μg/kg LPS plus 2 mg/kg RAME, and group RAME4 received 200 μg/kg LPS plus 4 mg/kg RAME. Each group had two subgroups: the 3rd and 24th hr. The eye tissues were collected and investigated biomicroscopically (clinical manifestations and scoring, molecularly(qRT-PCR analyses of tumor necrosis factor-α (TNF-α), vascular endothelial growth factor (VEGF), and caspase 3 and caspase 9 mRNA expression), biochemically (Superoxide dismutase activity (SOD), Glutathione (GSH), and malondialdehyde levels (MDA)) and histopathologically (staining with Harris Hematoxylin and Eosin Y). Melatonin receptor agonist treatment reduced the clinical score count of ocular inflammation in the uveitic rats. TNF-α, VEGF, caspase 9, and caspase 3 levels markedly decreased in the uveitic rats. Melatonin receptor agonists significantly ameliorated fixed changes in GSH, SOD, and MDA levels. Melatonin receptor agonists also ameliorated histopathological injury in eye tissues associated with uveitis. Melatonin receptor agonists ameliorated the inflammatory response in EIU. These findings suggest that melatonin receptor agonists may represent a potential novel therapeutic drug for uveitis treatment.

Preventing and treating delirium in clinical settings for older adults.

Delirium is a serious consequence of many acute or worsening chronic medical conditions, a side effect of medications, and a precipitant of worsening functional and cognitive status in older adults. It is a syndrome characterized by fluctuations in cognition and impaired attention that develops over a short period of time in response to an underlying medical condition, a substance (prescribed, over the counter, or recreational), or substance withdrawal and can be multi-factorial. We present a narrative review of the literature on nonpharmacologic and pharmacologic approaches to prevention and treatment of delirium with a focus on older adults as a vulnerable population. Older adult patients are most at risk due to decreasing physiologic reserves, with delirium rates of up to 80% in critical care settings. Presentation of delirium can be hyperactive, hypoactive, or mixed, making identification and study challenging as patients with hypoactive delirium are less likely to come to attention in an inpatient or long-term care setting. Studies of delirium focus on prevention and treatment with nonpharmacological or medication interventions, with the preponderance of evidence favoring multi-component nonpharmacological approaches to prevention as the most effective. Though use of antipsychotic medication in delirium is common, existing evidence does not support routine use, showing no clear benefit in clinically significant outcome measures and with evidence of harm in some studies. We therefore suggest that antipsychotics be used to treat agitation, psychosis, and distress associated with delirium at the lowest effective doses and shortest possible duration and not be considered a treatment of delirium itself. Future studies may clarify the use of other agents, such as melatonin and melatonin receptor agonists, alpha-2 receptor agonists, and anti-epileptics.

Prophylactic Use of Ramelteon for Delirium in Hospitalized Patients: A Systematic Review and Meta-Analyses.

Small prospective studies, case reports, as well as some randomized placebo-controlled trials and previous meta-analyses have shown that ramelteon, a melatonin agonist, may reduce the risk of developing delirium. The goal of this systemic review and meta-analyses was to assess the current evidence supporting the use of ramelteon in delirium prevention by including data from larger (>100 subjects) and more recent trials since the most recent meta-analyses were published in 2019. There were no exclusions for trial size, age, ramelteon dose, length of treatment, or hospital setting. Medline, Embase, PsycINFO, EBM Reviews, Scopus, and Web of Science databases were queried using the search terms delirium (with subterms including prevention and control), ramelteon, Rozerem, or melatonin receptor agonists, for English-language publications until March 16, 2021. Randomized placebo-controlled trials of hospitalized subjects receiving ramelteon for delirium prevention were included. The primary outcome of interest was delirium incidence. Odds ratios of the risk of developing incident delirium and 95% confidence intervals were calculated using a random effects model. A total of 177 articles were identified by the literature search. Five studies (n=443, 53.7% male) met criteria for inclusion in the final meta-analyses. The meta-analyses of the randomized placebo-controlled trials revealed that ramelteon did not result in a reduction in the risk of incident delirium (n=443; odds ratio=0.49; 95% confidence interval=0.13-1.85). A moderate degree of heterogeneity was noted among the studies (I2=53%). Current evidence suggests that ramelteon is ineffective as a prophylactic drug in reducing the incidence of delirium in hospitalized patients.

Agomelatine: a potential novel approach for the treatment of memory disorder in neurodegenerative disease.

Agomelatine is a selective agonist of melatonin receptor 1A/melatonin receptor 1B (MT1/MT2) and antagonist of 5-hydroxytryptamine 2C receptors. It is used clinically to treat major depressive episodes in adults. The pro-chronobiological activity of agomelatine reconstructs sleep-wake rhythms and normalizes circadian disturbances via its agonistic effect of melatonin receptor 1A/melatonin receptor 1B, which work simultaneously to counteract depression and anxiety disorder. Moreover, by antagonizing neocortical postsynaptic 5-hydroxytryptamine 2C receptors, agomelatine enhances the release of dopamine and noradrenaline in the prefrontal cortex, increases the activity of dopamine and noradrenaline, and thereby reduces depression and anxiety disorder. The combination of these two effects means that agomelatine exhibits a unique pharmacological role in the treatment of depression, anxiety, and disturbance of the circadian rhythm. Emotion and sleep are closely related to memory and cognitive function. Memory disorder is defined as any forms of memory abnormality, which is typically evident in a broad range of neurodegenerative diseases, including Alzheimer's disease. Memory impairment and cognitive impairment are common symptoms of neurodegenerative and psychiatric diseases. Therefore, whether agomelatine can improve memory and cognitive behaviors if used for alleviating depression and circadian-rhythm sleep disorders has become a research "hotspot". This review presents the latest findings on the effects of agomelatine in the treatment of psychologic and circadian-rhythm sleep disorders in clinical trials and animal experiments. Our review evaluates recent studies on treatment of memory impairment and cognitive impairment in neurodegenerative and psychiatric diseases.

Genetic variation within the melatonin receptor 1C (MTNR1C) gene in the native chicken ‘Zo-ar’ of Mizoram, India

The study has been aimed to uncover the presence of polymorphism within the MTNR1C gene in native chicken population, ‘Zo-ar’ of the Mizoram state of India and to calculate the allelic and genotypic frequency to screen the variation present within the population with respect to the MTNR1C gene which is associated with various egg production traits in poultry. DNA extraction has been done with the help of blood samples collected from a total of 50 randomly chosen ‘Zo-ar’ chicken irrespective of age or sex from different regions of Mizoram. The polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) assay has been used for the detection of SNPs within the MTNR1C gene. Two genotypes AG (0.34) and GG (0.66) have been detected for the MTNR1C gene in the ‘Zo-ar’ chicken population while the AA (0.00) genotype was found to be completely absent in the present study. The G allele (0.83) was found to be predominantly present in the populations. Further, the population was found to be conforming to the Hardy-Weinberg Equilibrium with respect to the MTNR1C locus. From the present study the presence of variation within the MTNR1C locus was seen in the ‘Zo-ar’ chicken of Mizoram. This indicates the possibility of genetic improvement in egg production traits by using proper selection methods and formulating appropriate mating systems.

Remote ischemic preconditioning-induced late cardioprotection: possible role of melatonin-mitoKATP-H2S signaling pathway.

Remote ischemic preconditioning (RIPC) confers cardioprotection against ischemia reperfusion (IR) injury. However, the precise mechanisms involved in RIPC-induced cardioprotection are not fully explored. The present study was aimed to identify the role of melatonin in RIPC-induced late cardioprotective effects in rats and to explore the role of H2S, TNF-α and mitoKATP in melatonin-mediated effects in RIPC. Wistar rats were subjected to RIPC in which hind limb was subjected to four alternate cycles of ischemia and reperfusion of 5 min duration by using a neonatal blood pressure cuff. After 24 h of RIPC or ramelteon-induced pharmacological preconditioning, hearts were isolated and subjected to IR injury on the Langendorff apparatus. RIPC and ramelteon preconditioning protected the hearts from IR injury and it was assessed by a decrease in LDH-1, cTnT and increase in left ventricular developed pressure (LVDP). RIPC increased the melatonin levels (in plasma), H2S (in heart) and decreased TNF-α levels. The effects of RIPC were abolished in the presence of melatonin receptor blocker (luzindole), ganglionic blocker (hexamethonium) and mitochondrial KATP blocker (5-hydroxydecanoic acid). RIPC produce delayed cardioprotection against IR injury through the activation of neuronal pathway, which may increase the plasma melatonin levels to activate the cardioprotective signaling pathway involving the opening of mitochondrial KATP channels, decrease in TNF-α production and increase in H2S levels. Ramelteon-induced pharmacological preconditioning may also activate the cardioprotective signaling pathway involving the opening of mitochondrial KATP channels, decrease in TNF-α production and increase in H2S levels.

Identification of Melatonin Receptors Type C (MTNR1C) and Neuropeptide Y (NPY) Genes Related to Egg Production in Thai Indigenous Chickens

Identification of Melatonin Receptors Type C (MTNR1C) and Neuropeptide Y (NPY) Genes Related to Egg Production in Thai Indigenous Chickens

Melatonin influences the biological characteristics of keloid fibroblasts through the Erk and Smad signalling pathways.

Keloids are abnormal fibrous hyperplasias that are difficult to treat. Melatonin can be used to inhibit the development of certain fibrotic diseases but has never been used to treat keloids. We aimed to discover the effects and mechanisms of melatonin in keloid fibroblasts (KFs). Flow cytometry, CCK-8 assays, western blotting, wound-healing assays, transwell assays, collagen gel contraction assays and immunofluorescence assays were applied to demonstrate the effects and mechanisms of melatonin in fibroblasts derived from normal skin, hypertrophic scars and keloids. The therapeutic potential of the combination of melatonin and 5-fluorouracil (5-FU) was investigated in KFs. Melatonin significantly promoted cell apoptosis and inhibited cell proliferation, migration and invasion, contractile capability and collagen production in KFs. Further mechanistic studies demonstrated that melatonin could inhibit the cAMP/PKA/Erk and Smad pathways through the membrane receptor MT2 to alter the biological characteristics of KFs. Moreover, the combination of melatonin and 5-FU remarkably promoted cell apoptosis and inhibited cell migration and invasion, contractile capability and collagen production in KFs. Furthermore, 5-FU suppressed the phosphorylation of Akt, mTOR, Smad3 and Erk, and melatonin in combination with 5-FU markedly suppressed the activation of the Akt, Erk and Smad pathways. Collectively, melatonin may inhibit the Erk and Smad pathways through the membrane receptor MT2 to alter the cell functions of KFs, while combination with 5-FU could exert even more inhibitory effects in KFs through simultaneous suppression of multiple signalling pathways.

Association of Melatonin receptor 1A (MTNR1A) gene polymorphism with seasonal suppression of fertility in buffaloes

The polymorphism in Melatonin receptor 1A (MTNR1A) gene and its association with reproductive cyclicity (cyclic, n=51; non-cyclic, n=50) during summer season and age at first calving (&lt;3.5 years, n=38; &gt;3.5 years, n=60) was investigated in buffaloes subjected to blood sampling. Polymerase chain reaction (PCR) of genomic DNA was carried out using three primers viz. 824 bp (primer pair 1), 856 bp (primer pair 2) and 268 bp (primer pair 3) corresponding to exon-II of MTNR1A gene. Restriction fragment length polymorphism was performed using PCR products of primer pair 1 and 2. The digestion of PCR product of primer pair 1 with restriction enzymes viz. MnII, RsaI or Eco3II generated total restriction sites respectively as 14, 4 and 5. Based upon differential restriction sites, six genotypes revealed in buffaloes using MnII were MM-1 to MM-6, four genotypes using RsaI were RR-1 to RR-4, and four genotypes using Eco3II were EE-1 to EE-4. The digestion of PCR product of primer pair 2 with MnII, RsaI or Eco3II generated restriction sites respectively as 13, 5 and 6. Based upon differential restriction sites, six genotypes revealed using MnII were mm-1 to mm-6, five genotypes using RsaI were rr-1to rr-5, and three genotypes using Eco3II were ee-1 to ee-3. For primer pair 3, single stranded conformational polymorphism analysis exhibited 5 genotypes viz. AA, BB, AB, CC and DD. The results revealed that the buffaloes during summer had polymorphic genotypes for MTNR1A gene as buffaloes showing reproductive cyclicity had MM-3, MM-4, RR-2, EE-3, mm-2, mm-4, rr-3, ee-3, CC and DD genotypes, whereas their non-cyclic counterparts had MM-2, MM-6, EE-4, mm-3, mm-6, AA, BB and AB genotypes. However, no such differences were recorded with respect to age at first calving. In conclusion, polymorphic genotypes of MTNR1A gene may be considered as genetic markers to identify buffaloes with better reproductive potential during summer season.

Melatonin regulates dihydrotestosterone formation via its membrane receptor in the epididymal epithelial cells of sheep

Both melatonin and androgen, which affect sperm fertility, are the important factors in epididymis of male animal. In the present study, we confirmed that melatonin regulates the formation of dihydrotestosterone (DHT) in sheep epididymides. Here, we investigated the localization and the expression levels of melatonin keys synthases AANAT and HIOMT, membrane receptors MT1 and MT2, and nuclear receptor RORα in sheep epididymides and testes. We also cultured epididymal epithelial cells and treated them with different concentrations of melatonin (10−11-10−7 M) and luzindole (10−5 M) and 4P-PDOT (10−5 M) to investigate whether melatonin is involved in the regulation of DHT formation and whether these effects are mediated through its receptor pathways. The results showed that AANAT, HIOMT, MT1, MT2, and RORα were differentially expressed between sheep epididymides and testes. In addition, melatonin is involved in mediating the formation of DHT in epididymal epithelial cells, and its influence on DHT is at least partially regulated by the melatonin receptor pathway. Our findings showed that melatonin regulates the functions of the testes and epididymides through an autocrine mechanism and regulates the formation of androgen in sheep epididymides via the receptor pathway. These results provide a basis for further exploring the regulatory mechanisms of melatonin in animal reproduction.

Effects of melatonin on development and hormone secretion of sheep theca cells in vitro

Theca cells (TCs) play a unique role in the structure and function of the ovary. They are not only the structural basis of the follicle but also the androgen-secreting cells in female mammals, which can affect the normal development and atresia of the follicle. The results showed that melatonin receptor (MTR) MT1 and MT2 were expressed on sheep TCs. In the present study, the effects of different concentrations of MT at 0, 10−10, 10−8, 10−6 and 10−4 M/L on sheep TCs with regards to the antioxidant levels, proliferation, apoptosis and steroid hormone secretion were investigated. The results showed that in sheep TCs, all concentrations of MT significantly decreased reactive oxygen species (ROS) concentration and BAX expression; increased Cat, Sod1, and BCL-2 expression. The proliferation viability of TCs was significantly inhibited in all groups except for 10−10 M/L MT, and the expression of cyclin D1 and CDK4 was significantly reduced. MT significantly increased StAR expression and progesterone secretion in TCs, but there was no significant effect on androgen secretion and CYP11A1, CYP17A1 and 3β-HSD expression in all groups. MT-induced progesterone secretion was completely inhibited by Luzindole (a nonspecific MT1 and MT2 inhibitor) and partially inhibited by 4p-PDOT (specific MT2 inhibitor). MT-induced progesterone secretion can be inhibited by LY294002 (PI3K/AKT pathway inhibitor). This study indicated that MT inhibits apoptosis and proliferation of in vitro cultured sheep TCs, which has implications for slowing ovarian atresia and aging. MT activates the PI3K/Akt pathway to mediate the synthesis and secretion of progesterone by TCs. This study provides a basis for further exploration of the role of TCs on follicle development and ovarian steroid hormone secretion.

Melatonin upregulates BMAL1 to attenuate chronic sleep deprivation-related cognitive impairment by alleviating oxidative stress.

To investigate the mechanism underlying the regulatory effect of melatonin on chronic sleep deprivation-related cognitive impairment. Chronic sleep deprivation (CSD) model was established using the MMPM method. After the model was established, melatonin receptor agonist and inhibitor were given, respectively. Water maze was conducted to record the escape latency and the duration of crossing the platform of space exploration. The concentration of TNF-α, IL-6, MDA, and SOD was measured by ELISA. Immunofluorescence was used to determine the expression level of CD86 and CD206, while the mRNA expression of Bax, Bcl-2, P65, IκB, and BMAL1 was detected by qPCR. Western blotting assay was utilized to determine the protein expression of Bax, Bcl-2, P65, p-P65, IκB, p-I κB, and BMAL1. Compared with the control, the escape latency was greatly increased on the second and third day, accompanied by the increased expression of TNF-α, IL-6, MDA, and SOD in serum. Furthermore, dramatically upregulated Bax, Bcl-2, P65, IκB, and CD86 were observed in the model group, accompanied by the declined expression level of BMAL1 and CD206. Compared with the model group, the escape latency was declined, the concentration of TNF-α, IL-6, MDA, and SOD was decreased, the expression level of Bax, Bcl-2, P65, IκB, and CD86 was declined, and the level of BMAL1 and CD206 was promoted by the treatment of the melatonin agonist, while the opposite results were observed under the treatment of the melatonin inhibitor. Melatonin upregulates BMAL1 to attenuate chronic sleep deprivation-related cognitive impairment by alleviating oxidative stress.

Melatonin receptors and Per1 expression in the inferior olivary nucleus of the Sapajus apella monkey.

Melatonin is a transducer of photic environmental information and participates in the synchronization of various physiological and behavioral phenomena. Melatonin can act directly in several areas of the central nervous system through its membrane receptors coupled to G protein, called MT1 and MT2 receptors. In some structures, such as the retina, hypothalamus and pars tuberalis, the expression of both melatonin receptors shows circadian variations. Melatonin can act in the synchronization of the clock proteins rhythm in these areas. Using the immunohistochemistry technique, we detected the immunoexpression of the melatonin receptors and clock genes clock protein Per1 in the inferior olivary nucleus (ION) of the Sapajus apella monkey at specific times of the light-dark phase. The mapping performed by immunohistochemistry showed expressive immunoreactivity (IR) Per1 with predominance during daytime. Both melatonin receptors were expressed in the ION without a day/night difference. The presence of both melatonin receptors and the Per1 protein in the inferior olivary nucleus can indicate a functional role not only in physiological, as in sleep, anxiety, and circadian rhythm, but also a chronobiotic role in motor control mechanisms.

Melatonin as a Potential Approach to Anxiety Treatment.

Anxiety disorders are the most common mental diseases. Anxiety and the associated physical symptoms may disturb social and occupational life and increase the risk of somatic diseases. The pathophysiology of anxiety development is complex and involves alterations in stress hormone production, neurosignaling pathways or free radical production. The various manifestations of anxiety, its complex pathophysiological background and the side effects of available treatments underlie the quest for constantly seeking therapies for these conditions. Melatonin, an indolamine produced in the pineal gland and released into the blood on a nightly basis, has been demonstrated to exert anxiolytic action in animal experiments and different clinical conditions. This hormone influences a number of physiological actions either via specific melatonin receptors or by receptor-independent pleiotropic effects. The underlying pathomechanism of melatonin's benefit in anxiety may reside in its sympatholytic action, interaction with the renin-angiotensin and glucocorticoid systems, modulation of interneuronal signaling and its extraordinary antioxidant and radical scavenging nature. Of importance, the concentration of this indolamine is significantly higher in cerebrospinal fluid than in the blood. Thus, ensuring sufficient melatonin production by reducing light pollution, which suppresses melatonin levels, may represent an endogenous neuroprotective and anxiolytic treatment. Since melatonin is freely available, economically undemanding and has limited side effects, it may be considered an additional or alternative treatment for various conditions associated with anxiety.