Cell protective role of melatonin in the brain

Lower plasma melatonin levels in non-hypoxic premature newborns associated with neonatal pain

We analyzed plasma melatonin levels in different groups of preterm newborns without hypoxia and their relationship with several perinatal variables like gestational age or neonatal pain. Prospective cohort study of preterm newborns (PTNB) without perinatal hypoxia, Apgar > 6 at 5 min, and oxygen needs on the third day of life. We compared melatonin levels at day 3 of life in different groups of non-hypoxic preterm infants (Student's t-tests, Mann-Whitney U, and chi2) and analyzed the relationship of melatonin with GA, birth weight, neonatal pain (Premature Infant Pain Profile (PIPP) scale), caffeine treatment, parenteral nutrition, or the development of free radical diseases (correlation study, linear regression) and factors associated with moderate/intense pain and free radical diseases (logistic regression analysis). Sixty-one preterm infants with gestational age (GA) of 30.7 ± 2.0 weeks with no oxygen requirements at day 3 of life were studied with plasma melatonin levels of 33.8 ± 12.01 pg/ml. Preterm infants weighing < 1250 g at birth had lower plasma melatonin levels (p = 0.05). Preterm infants with moderate or severe pain (PPIPP > 5) have lower melatonin levels (p = 0.01), and being preterm with PIPP > 5 is associated with lower plasma melatonin levels (p = 0.03). Being very preterm (GA < 32 GS), having low weight for gestational age (LWGA), receiving caffeine treatment, or requiring parenteral nutrition did not modify melatonin levels in non-hypoxic preterm infants (p = NS). Melatonin on day 3 of life in non-hypoxic preterm infants is not associated with later development of free radical diseases (BPD, sepsis, ROP, HIV, NEC).

CONCLUSION

We observed that preterm infants with moderate to severe pain have lower melatonin levels. These findings are relevant because they reinforce the findings of other authors that melatonin supplementation decreases pain and oxidative stress in painful procedures in premature infants. Further studies are needed to evaluate whether melatonin could be used as an analgesic in painful procedures in preterm infants.

TRIAL REGISTRATION

Trial registration was not required since this was an observational study.

WHAT IS KNOWN

• Melatonin is a potent antioxidant and free radical scavenger in newborns under stress conditions: hypoxia, acidosis, hypotension, painful procedures, or parenteral nutrition. • Pain stimulates the production of melatonin. • Various studies conclude that melatonin administration decreases pain during the neonatal period.

WHAT IS NEW

• Non-hypoxic preterm infants with moderate to severe pain (PIPP>5) have lower levels of melatonin. • Administration of caffeine and treatment with parenteral nutrition do not modify melatonin levels in non-hypoxic preterm infants.

Melatonin: a ferroptosis inhibitor with potential therapeutic efficacy for the post-COVID-19 trajectory of accelerated brain aging and neurodegeneration

The unprecedented pandemic of COVID-19 swept millions of lives in a short period, yet its menace continues among its survivors in the form of post-COVID syndrome. An exponentially growing number of COVID-19 survivors suffer from cognitive impairment, with compelling evidence of a trajectory of accelerated aging and neurodegeneration. The novel and enigmatic nature of this yet-to-unfold pathology demands extensive research seeking answers for both the molecular underpinnings and potential therapeutic targets. Ferroptosis, an iron-dependent cell death, is a strongly proposed underlying mechanism in post-COVID-19 aging and neurodegeneration discourse. COVID-19 incites neuroinflammation, iron dysregulation, reactive oxygen species (ROS) accumulation, antioxidant system repression, renin-angiotensin system (RAS) disruption, and clock gene alteration. These events pave the way for ferroptosis, which shows its signature in COVID-19, premature aging, and neurodegenerative disorders. In the search for a treatment, melatonin shines as a promising ferroptosis inhibitor with its repeatedly reported safety and tolerability. According to various studies, melatonin has proven efficacy in attenuating the severity of certain COVID-19 manifestations, validating its reputation as an anti-viral compound. Melatonin has well-documented anti-aging properties and combating neurodegenerative-related pathologies. Melatonin can block the leading events of ferroptosis since it is an efficient anti-inflammatory, iron chelator, antioxidant, angiotensin II antagonist, and clock gene regulator. Therefore, we propose ferroptosis as the culprit behind the post-COVID-19 trajectory of aging and neurodegeneration and melatonin, a well-fitting ferroptosis inhibitor, as a potential treatment.

Neurometabolic alterations in children and adolescents with functional neurological disorder

OBJECTIVES

In vivo magnetic resonance spectroscopy (MRS) was used to investigate neurometabolic homeostasis in children with functional neurological disorder (FND) in three regions of interest: supplementary motor area (SMA), anterior default mode network (aDMN), and posterior default mode network (dDMN). Metabolites assessed included N-acetyl aspartate (NAA), a marker of neuron function; myo-inositol (mI), a glial-cell marker; choline (Cho), a membrane marker; glutamate plus glutamine (Glx), a marker of excitatory neurotransmission; γ-aminobutyric acid (GABA), a marker of inhibitor neurotransmission; and creatine (Cr), an energy marker. The relationship between excitatory (glutamate and glutamine) and inhibitory (GABA) neurotransmitter (E/I) balance was also examined.

METHODS

MRS data were acquired for 32 children with mixed FND (25 girls, 7 boys, aged 10.00 to 16.08 years) and 41 healthy controls of similar age using both short echo point-resolved spectroscopy (PRESS) and Mescher-Garwood point-resolved spectroscopy (MEGAPRESS) sequences in the three regions of interest.

RESULTS

In the SMA, children with FND had lower NAA/Cr, mI/Cr (trend level), and GABA/Cr ratios. In the aDMN, no group differences in metabolite ratios were found. In the pDMN, children with FND had lower NAA/Cr and mI/Cr (trend level) ratios. While no group differences in E/I balance were found (FND vs. controls), E/I balance in the aDMN was lower in children with functional seizures-a subgroup within the FND group. Pearson correlations found that increased arousal (indexed by higher heart rate) was associated with lower mI/Cr in the SMA and pDMN.

CONCLUSIONS

Our findings of multiple differences in neurometabolites in children with FND suggest dysfunction on multiple levels of the biological system: the neuron (lower NAA), the glial cell (lower mI), and inhibitory neurotransmission (lower GABA), as well as dysfunction in energy regulation in the subgroup with functional seizures.

Melatonin-related dysfunction in chronic restraint stress triggers sleep disorders in mice

Stress may trigger sleep disorders and are also risk factors for depression. The study explored the melatonin-related mechanisms of stress-associated sleep disorders on a mouse model of chronic stress by exploring the alteration in sleep architecture, melatonin, and related small molecule levels, transcription and expression of melatonin-related genes as well as proteins. Mice undergoing chronic restraint stress modeling for 28 days showed body weight loss and reduced locomotor activity. Sleep fragmentation, circadian rhythm disorders, and insomnia exhibited in CRS-treated mice formed sleep disorders. Tryptophan and 5-hydroxytryptamine levels were increased in the hypothalamus, while melatonin level was decreased. The transcription and expression of melatonin receptors were reduced, and circadian rhythm related genes were altered. Expression of downstream effectors to melatonin receptors was also affected. These results identified sleep disorders in a mice model of chronic stress. The alteration of melatonin-related pathways was shown to trigger sleep disorders.

EEG coherence and power spectra during REM sleep related to melatonin intake in mild-to-moderate Alzheimer's disease: a pilot study

It has been reported that melatonin diminishes rapid eye movement (REM) sleep latency in patients with Alzheimer's disease (AD). Pharmacological studies suggest that melatonin promotes prompt sleep installation through interaction with GABA receptors, and that it is associated with acute suppression of neural electrical activity. Nevertheless, melatonin's effects on electroencephalographic (EEG) activity related to REM sleep onset in AD patients have not been analyzed. Thus, in this pilot study we analyzed the effects of melatonin on EEG activity during the first episode of REM sleep in eight patients treated with 5-mg of fast-release melatonin.

During a single-blind, placebo-controlled study, polysomnographic recordings were obtained from frontal, central, temporal, and occipital scalp derivations. REM sleep latency, as well as the relative power (RP) and EEG coherences of six EEG bands, were compared between the placebo and melatonin conditions.

Results showed that melatonin intake in AD patients decreased REM sleep onset, and that this was associated with lower RP and coherence of the β and γ EEG bands.

The possibility that the inhibitory GABAergic pathways related to REM sleep generation are well-preserved in mild-to-moderate AD is discussed. We conclude that the short REM sleep onset related to melatonin intake in AD patients is associated with a significant decrease in both RP and EEG coherence, mainly in the fast frequencies.

Walnut (Juglans regia L.) Oligopeptide Effects on Enhancing Memory, Cognition and Improving Sleep Quality in Teenagers and Elderly People in a Randomized Double-Blind Controlled Trial

Walnut has been reported to have beneficial effects on improving cognitive performance. This randomized double-blind placebo-controlled clinical trial evaluates the clinical effectiveness and safety of walnut oligopeptide (WO) on memory enhancement, cognition, and sleep quality in teenagers and elderly people. Eighteen teenagers and 18 elderly people were, respectively, randomly allocated to placebo, low dosage (170 mg), and high dosage (340 mg) WO administration groups (n = 6 per group in each population). After 90 days of administration, the Wechsler Adult Intelligence Scale (WAIS) score was significantly increased and the global Pittsburgh Sleep Quality Index (PSQI) score was significantly decreased in the WO administration group. In addition, the average scores for test subjects of Chinese, Mathematics, and English examinations were significantly increased from the baseline for the teenagers in the WO administration group. Our results support the claim that WO has the potential to become a new option for nutritional intervention, to enhance the memory, cognitive ability, and sleep quality of teenagers and elderly people. This study was approved by the Institutional Review Board of the Shanghai Nutrition Society and registered at the Chinese Clinical Trial Registry ( http://www.chictr.org.cn ) with an ID number of ChiCTR1900028160.

Protective Effect of Melatonin Administration against SARS-CoV-2 Infection: A Systematic Review

Introduction: according to the World Health Organization (WHO), COVID-19 is an infectious disease caused by the SARS-CoV-2 virus, responsible for an increasing number of cases and deaths. From a preventive and therapeutic point of view, there are two concerns that affect institutions and healthcare professionals: global immunization (which is still far from being achieved) and the availability of drugs capable of preventing its consequences in the infected patient. In this sense, the role that melatonin can play is has been assessed in the recent literature. Justification and Objectives: the serious health, social and economic consequences of COVID-19 have forced an urgent search for preventive methods, such as vaccines, among others, and therapeutic methods that could be alternatives to the drugs currently used. In this sense, it must be accepted that one of the most recommended has been the administration of melatonin. The present study proposes to carry out a systematic review of its possible role in the treatment and/or prevention of COVID-19. Material and methods: a systematic review of the literature related to the prevention of COVID-19 through the administration of melatonin was carried out, following the sequence proposed by the Prisma Declaration regarding the identification and selection of documents, using the specialized health databases Trip Medical Database, Cochrane Library, PubMed, Medline Plus, BVS, Cuiden and generic databases such as Dialnet, Web of Science and Google Scholar for their retrieval. Appropriate inclusion and exclusion criteria are described for the articles assessed. The main limitation of the study has been the scarcity of works and the lack of defining a specific protocol in terms of dosage and administration schedule. Results: once the selection process was completed, and after an in-depth critical analysis, 197 papers were selected, and 40 of them were finally used. The most relevant results were: (1) melatonin prevents SARS-CoV-2 infection, (2) although much remains to be clarified, at high doses, it seems to have a coadjuvant therapeutic effect in the treatment of SARS-CoV-2 infection and (3) melatonin is effective against SARS-CoV-2 infection. Discussion: until group immunization is achieved in the population, it seems clear that we must continue to treat patients with SARS-CoV-2 infection, and, in the absence of a specific and effective antiviral therapy, it is advisable to continue researching and providing drugs that demonstrate validity based on the scientific evidence. In this regard, we believe that the available studies recommend the administration of melatonin for its anti-inflammatory, antioxidant, immunomodulatory, sleep-inducing, CD147, Mpro, p65 and MMP9 protein suppressing, nephrotoxicity-reducing and highly effective and safe effects. Conclusions: (1) melatonin has anti-inflammatory, antioxidant, immunomodulatory, and Mpro and MMP9 protein-inhibitory activity. (2) It has been shown to have a wide margin of safety. (3) The contributions reviewed make it an effective therapeutic alternative in the treatment of SARS-CoV-2 infection. (4) Further clinical trials are recommended to clearly define the administration protocol.

Melatonin Regulates the Neurotransmitter Secretion Disorder Induced by Caffeine Through the Microbiota-Gut-Brain Axis in Zebrafish (Danio rerio)

Melatonin has been widely used as a “probiotic agent” capable of producing strong neurotransmitter secretion regulatory effects, and the microbiota-gut-brain axis-related studies have also highlighted the role of the gut microbiota in neuromodulation. In the present study, a zebrafish neural hyperactivity model was established using caffeine induction to explore the regulatory effects of melatonin and probiotic on neurotransmitter secretion disorder in zebrafish. Disorders of brain neurotransmitter secretion (dopamine, γ-aminobutyric acid, and 5-hydroxytryptamine) caused by caffeine were improved after interference treatment with melatonin or probiotic. Shotgun metagenomic sequencing demonstrated that the melatonin-treated zebrafish gradually restored their normal intestinal microbiota and metabolic pathways. Germ-free (GF) zebrafish were used to verify the essential role of intestinal microbes in the regulation of neurotransmitter secretion. The results of the neurotransmitter and short-chain fatty acid determination revealed that the effect on the zebrafish in the GF group could not achieve that on the zebrafish in the melatonin group after adding the same dose of melatonin. The present research revealed the potential mode of action of melatonin through the microbiota-gut-brain axis to regulate the disruption of neurotransmitter secretion, supporting the future development of psychotropic drugs targeting the intestinal microbiota.

Microscopic Interactions of Melatonin, Serotonin and Tryptophan with Zwitterionic Phospholipid Membranes

The interactions at the atomic level between small molecules and the main components of cellular plasma membranes are crucial for elucidating the mechanisms allowing for the entrance of such small species inside the cell. We have performed molecular dynamics and metadynamics simulations of tryptophan, serotonin, and melatonin at the interface of zwitterionic phospholipid bilayers. In this work, we will review recent computer simulation developments and report microscopic properties, such as the area per lipid and thickness of the membranes, atomic radial distribution functions, angular orientations, and free energy landscapes of small molecule binding to the membrane. Cholesterol affects the behaviour of the small molecules, which are mainly buried in the interfacial regions. We have observed a competition between the binding of small molecules to phospholipids and cholesterol through lipidic hydrogen-bonds. Free energy barriers that are associated to translational and orientational changes of melatonin have been found to be between 10-20 kJ/mol for distances of 1 nm between melatonin and the center of the membrane. Corresponding barriers for tryptophan and serotonin that are obtained from reversible work methods are of the order of 10 kJ/mol and reveal strong hydrogen bonding between such species and specific phospholipid sites. The diffusion of tryptophan and melatonin is of the order of 10-7 cm2/s for the cholesterol-free and cholesterol-rich setups.

Insights into Potential Targets for Therapeutic Intervention in Epilepsy

Epilepsy is a chronic brain disease that affects approximately 65 million people worldwide. However, despite the continuous development of antiepileptic drugs, over 30% patients with epilepsy progress to drug-resistant epilepsy. For this reason, it is a high priority objective in preclinical research to find novel therapeutic targets and to develop effective drugs that prevent or reverse the molecular mechanisms underlying epilepsy progression. Among these potential therapeutic targets, we highlight currently available information involving signaling pathways (Wnt/β-catenin, Mammalian Target of Rapamycin (mTOR) signaling and zinc signaling), enzymes (carbonic anhydrase), proteins (erythropoietin, copine 6 and complement system), channels (Transient Receptor Potential Vanilloid Type 1 (TRPV1) channel) and receptors (galanin and melatonin receptors). All of them have demonstrated a certain degree of efficacy not only in controlling seizures but also in displaying neuroprotective activity and in modifying the progression of epilepsy. Although some research with these specific targets has been done in relation with epilepsy, they have not been fully explored as potential therapeutic targets that could help address the unsolved issue of drug-resistant epilepsy and develop new antiseizure therapies for the treatment of epilepsy.

Hypothermia Plus Melatonin in Asphyctic Newborns: A Randomized-Controlled Pilot Study

OBJECTIVES

To investigate the effect of adding melatonin to hypothermia treatment on neurodevelopmental outcomes in asphyctic newborns.

DESIGN

Pilot multicenter, randomized, controlled, double-blind clinical trial. Statistical comparison of results obtained in two intervention arms: hypothermia plus placebo and hypothermia plus melatonin.

SETTING

Level 3 neonatal ICU.

PATIENTS

Twenty-five newborns were recruited.

INTERVENTIONS

The hypothermia plus melatonin patients received a daily dose of IV melatonin, 5 mg per kg body weight, for 3 days. General laboratory variables were measured both at neonatal ICU admission and after intervention. All infants were studied with amplitude-integrated electroencephalography and brain MRI within the first week of life. The neurodevelopmental Bayley III test, the Gross Motor Function Classification System, and the Tardieu scale were applied at the ages of 6 and 18 months.

MEASUREMENTS AND MAIN RESULTS

Clinical characteristics, laboratory evaluations, MRI findings, and amplitude-integrated electroencephalography background did not differ between the treatment groups. The newborns in the hypothermia plus melatonin group achieved a significantly higher composite score for the cognitive section of the Bayley III test at 18 months old, with respect to the hypothermia plus placebo group (p = 0.05). There were no differences between the groups according to the Gross Motor Function Classification System and Tardieu motor assessment scales.

CONCLUSIONS

The early addition of IV melatonin to asphyctic neonates is feasible and may improve long-term neurodevelopment. To our knowledge, this is the first clinical trial to analyze the administration of IV melatonin as an adjuvant therapy to therapeutic hypothermia.

Cellular absorption of small molecules: free energy landscapes of melatonin binding at phospholipid membranes

Free energy calculations are essential to unveil mechanisms at the atomic scale such as binding of small solutes and their translocation across cell membranes, eventually producing cellular absorption. Melatonin regulates biological rhythms and is directly related to carcinogenesis and neurodegenerative disorders. Free energy landscapes obtained from well-tempered metadynamics simulations precisely describe the characteristics of melatonin binding to specific sites in the membrane and reveal the role of cholesterol in free energy barrier crossing. A specific molecular torsional angle and the distance between melatonin and the center of the membrane along the normal to the membrane Z-axis have been considered as suitable reaction coordinates. Free energy barriers between two particular orientations of the molecular structure (folded and extended) have been found to be of about 18 kJ/mol for z-distances of about 1–2 nm. The ability of cholesterol to expel melatonin out of the internal regions of the membrane towards the interface and the external solvent is explained from a free energy perspective. The calculations reported here offer detailed free energy landscapes of melatonin embedded in model cell membranes and reveal microscopic information on its transition between free energy minima, including the location of relevant transition states, and provide clues on the role of cholesterol in the cellular absorption of small molecules.

Melatonin effects on EEG activity during non-rapid eye movement sleep in mild-to-moderate Alzheimer´s disease: a pilot study

INTRODUCTION

There is evidence to suggest that melatonin diminishes non-rapid eye movement sleep (NREMS) latency in patients with Alzheimer´s disease (AD). However, melatonin's effects on cortical activity during NREMS in AD have not been studied. The objective of this research was to analyze the effects of melatonin on cortical activity during the stages of NREMS in 8 mild-to-moderate AD patients that received 5-mg of fast-release melatonin.

METHODS

During a single-blind, placebo-controlled crossover study, polysomnographic recordings were obtained from C3-A1, C4-A2, F7-T3, F8-T4, F3-F4 and O1-O2. Also, the relative power (RP) and EEG coherences of the delta, theta, alpha1, alpha2, beta1, beta2 and gamma bands were calculated during NREMS-1, NREMS-2 and NREMS-3. These sleep latencies and all EEG data were then compared between the placebo and melatonin conditions.

RESULTS

During NREMS-2, a significant RP increase was observed in the theta band of the left-central hemisphere. During NREMS-3, significant RP decreases in the beta bands were recorded in the right-central hemisphere, compared to the placebo group. After melatonin administration, significant decreases of EEG coherences in the beta2, beta1 and gamma bands were observed in the right hemisphere during NREMS-3.

DISCUSSION

We conclude that short NREMS onset related to melatonin intake in AD patients is associated with a significant RP increase in the theta band and a decrease in RP and EEG coherences in the beta and gamma bands during NREMS-3. These results suggest that the GABAergic pathways are preserved in mild-to-moderate AD.

Levels of Melatonin in Continuous Spikes and Waves During Sleep

Levels of melatonin have been reported before in children with epilepsy, but such has not been reported to date in those with continuous spikes and waves during sleep. The aim of the present study was to assess serum melatonin levels and melatonin circadian rhythm in patients with continuous spikes and waves during sleep and epilepsy. Serum melatonin was measured in 39 children stratified into 3 groups. Group 1 included 15 patients with continuous spikes and waves during sleep, group 2 included 12 epilepsy patients, and group 3 included 12 controls, respectively. Blood samples were taken from all participants at 1:00 am and 9:00 am and melatonin levels were measured using a quantitative enzyme-linked immunosorbent assay test. The 9:00 am melatonin levels of group 1 were significantly decreased and pair groups were compared. The P_a value (representing a comparison between groups 1 and 2) was .002, the P_b value (representing a comparison between groups 1 and 3) was .001, and the P_c value (representing a comparison between groups 2 and 3) was .86. These findings suggest that the 9:00 am melatonin levels were significantly decreased in the comparison of groups 2 and 3. Further detailed research is necessary to determine the factors leading to the rapid decline of morning melatonin levels of children with continuous spikes and waves during sleep.

Role of Melatonin in Aluminum-Related Neurodegenerative Disorders: a Review

Aluminum (Al), a potentially neurotoxic element, provokes various adverse effects on human health such as dialysis dementia, osteomalacia, and microcytic anemia. It has been also associated with serious neurodegenerative diseases such as Alzheimer's disease (AD), amyotrophic lateral sclerosis, and Parkinsonism dementia of Guam. The "aluminum hypothesis" of AD assumes that the metal complexes can potentiate the rate of aggregation of amyloid-β (Aβ), enhancing the toxicity of this peptide, and being able of contributing to the pathogenesis of AD. It has been supported by a number of analytical, epidemiological, and neurotoxicological studies. On the other hand, melatonin (Mel) is a potent direct free radical scavenger and indirect antioxidant, which acts increasing the activity of important related antioxidant enzymes, and preventing oxidative stress and cell death of neurons exposed to Aβ-induced neurotoxicity. Therefore, Mel might be useful in the treatment of AD by reducing the Aβ generation and by inhibiting mitochondrial cell death pathways. The present review on the role of Mel in Al-related neurodegenerative disorders concludes that the protective effects of this hormone, together with its low toxicity, support the administration of Mel as a potential supplement in the treatment of neurological disorders, in which oxidative stress is involved.

Melatonin Effects on EEG Activity During Sleep Onset in Mild-to-Moderate Alzheimer's Disease: A Pilot Study

There is evidence demonstrating that 5-mg of fast-release melatonin significantly reduces nocturnal sleep onset in patients with mild-to-moderate Alzheimer's disease (AD). However, the physiological mechanism that could promote sleep installation by melatonin in patients with AD is still poorly understood. The present pilot study was designed to analyze the effects of melatonin on cortical activity during the sleep onset period (SOP) in eight mild-to-moderate AD patients treated with 5-mg of fast-release melatonin. Electroencephalographic recordings were obtained from C3-A1, C4-A2, F7-T3, F8-T4, F3-F4, and O1-O2. The relative power (RP), interhemispheric, intrahemispheric, and fronto-posterior correlations of six electroencephalographic bands were calculated and compared between two conditions: placebo and melatonin. Results show that at F7-T3, F3-F4, and C3-A1, melatonin induced an increase of the RP of the delta band. Likewise, in F7-T3, melatonin induced a decrease of the RP in the alpha1 band. Similarly, results show a lower interhemispheric correlation between the F7-T3 and F8-T4 derivations in the alpha1 band compared to the placebo condition. We conclude that the short sleep onset related to melatonin intake in AD patients was associated with a lower RP of the alpha1, a higher RP of the delta band (mainly in the left hemisphere) and a decreased interhemispheric EEG coupling in the alpha1 band. The possible role of the GABAergic neurotransmission as well as of the cascade of neurochemical events that melatonin triggers on sleep onset are discussed.

Melatonin: A Review of Its Potential Functions and Effects on Dental Diseases

Melatonin is a hormone synthesised and secreted by the pineal gland and other organs. Its secretion, controlled by an endogenous circadian cycle, has been proven to exert immunological, anti-oxidant, and anti-inflammatory effects that can be beneficial in the treatment of certain dental diseases. This article is aimed at carrying out a review of the literature published about the use of melatonin in the dental field and summarising its potential effects. In this review article, an extensive search in different databases of scientific journals was performed with the objective of summarising all of the information published on melatonin use in dental diseases, focussing on periodontal diseases and dental implantology. Melatonin released in a natural way into the saliva, or added as an external treatment, may have important implications for dental disorders, such as periodontal disease, as well as in the osseointegration of dental implants, due to its anti-inflammatory and osseoconductive effects. Melatonin has demonstrated to have beneficial effects on dental pathologies, although further research is needed to understand the exact mechanisms of this molecule.

Evaluation of Plasma Melatonin Levels in Children With Afebrile and Febrile Seizures

BACKGROUND

Melatonin modulates central nervous system neuronal activity. We compared the melatonin levels of patients with febrile and afebrile seizures during and after seizure with those of healthy controls.

METHODS

We enrolled 59 individuals with afebrile and febrile seizures (mean age, 6.09 ± 4.46 years) and 28 age-, sex-, and weight-matched healthy children. Melatonin levels were measured near the time of a seizure (0 to 1 hour) and at 12 and 24 hours post-seizure, and control melatonin levels were measured from a single venous blood sample.

RESULTS

Plasma melatonin levels increased during seizures in the study group (P < 0.001). Post-seizure plasma melatonin levels were significantly lower in the study group than in the control group (P < 0.05). Plasma melatonin levels did not differ between patients with afebrile seizures who had and had not used antiepileptic drugs. Daytime (8 AM to 8 PM) and nighttime (8 PM to 8 AM) post-seizure melatonin levels were not significantly different.

CONCLUSIONS

Melatonin levels were lower in pediatric patients prone to seizures than in healthy children and increased during seizures. Further research is needed to test the role of melatonin in the pathophysiology and treatment of epilepsy.

The potential physiological crosstalk and interrelationship between two sovereign endogenous amines, melatonin and homocysteine

The antioxidant melatonin and the non-proteinogenic excitotoxic amino acid homocysteine (Hcy) are very distinct but related reciprocally to each other in their mode of action. The elevated Hcy level has been implicated in several disease pathologies ranging from cardio- and cerebro-vascular diseases to neurodegeneration owing largely to its free radical generating potency. Interestingly, melatonin administration potentially normalizes the elevated Hcy level, thereby protecting the cells from the undesired Hcy-induced excitotoxicity and cell death. However, the exact mechanism and between them remain obscure. Through literature survey we have found an indistinct but a vital link between melatonin and Hcy i.e., the existence of reciprocal regulation between them, and this aspect has been thoroughly described herein. In this review, we focus on all the possibilities of co-regulation of melatonin and Hcy at the level of their production and metabolism both in basal and in pathological conditions, and appraised the potential of melatonin in ameliorating homocysteinemia-induced cellular stresses. Also, we have summarized the differential mode of action of melatonin and Hcy on health and disease states.

Melatonin enhances L-DOPA therapeutic effects, helps to reduce its dose, and protects dopaminergic neurons in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced Parkinsonism in mice

L-3,4-dihydroxyphenylalanine (L-DOPA) reduces symptoms of Parkinson's disease (PD), but suffers from serious side effects on long-term use. Melatonin (10-30 mg/kg, 6 doses at 10 hr intervals) was investigated to potentiate L-DOPA therapeutic effects in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced parkinsonism in mice. Striatal tyrosine hydroxylase (TH) immunoreactivity, TH, and phosphorylated ser 40 TH (p-TH) protein levels were assayed on 7th day. Nigral TH-positive neurons stereology was conducted on serial sections 2.8 mm from bregma rostrally to 3.74 mm caudally. MPTP caused 39% and 58% decrease, respectively, in striatal fibers and TH protein levels, but 2.5-fold increase in p-TH levels. About 35% TH neurons were lost between 360 and 600 μm from 940 μm of the entire nigra analyzed, but no neurons were lost between 250 μm rostrally and 220 μm caudally. When L-DOPA in small doses (5-8 mg/kg) failed to affect MPTP-induced akinesia or catalepsy, co-administration of melatonin with L-DOPA attenuated these behaviors. Melatonin administration significantly attenuated MPTP-induced loss in striatal TH fibers (82%), TH (62%) and p-TH protein (100%) levels, and nigral neurons (87-100%). Melatonin failed to attenuate MPTP-induced striatal dopamine depletion. L-DOPA administration (5 mg/kg, once 40 min prior to sacrifice, p.o.) in MPTP- and melatonin-treated mice caused significant increase in striatal dopamine (31%), as compared to L-DOPA and MPTP-treated mice. This was equivalent to 8 mg/kg L-DOPA administration in parkinsonian mouse. Therefore, prolonged, effective use of L-DOPA in PD with lesser side effects could be achieved by treating with 60% lower doses of L-DOPA along with melatonin.

Extrapineal melatonin: sources, regulation, and potential functions

Endogenous melatonin is synthesized from tryptophan via 5-hydroxytryptamine. It is considered an indoleamine from a biochemical point of view because the melatonin molecule contains a substituted indolic ring with an amino group. The circadian production of melatonin by the pineal gland explains its chronobiotic influence on organismal activity, including the endocrine and non-endocrine rhythms. Other functions of melatonin, including its antioxidant and anti-inflammatory properties, its genomic effects, and its capacity to modulate mitochondrial homeostasis, are linked to the redox status of cells and tissues. With the aid of specific melatonin antibodies, the presence of melatonin has been detected in multiple extrapineal tissues including the brain, retina, lens, cochlea, Harderian gland, airway epithelium, skin, gastrointestinal tract, liver, kidney, thyroid, pancreas, thymus, spleen, immune system cells, carotid body, reproductive tract, and endothelial cells. In most of these tissues, the melatonin-synthesizing enzymes have been identified. Melatonin is present in essentially all biological fluids including cerebrospinal fluid, saliva, bile, synovial fluid, amniotic fluid, and breast milk. In several of these fluids, melatonin concentrations exceed those in the blood. The importance of the continual availability of melatonin at the cellular level is important for its physiological regulation of cell homeostasis, and may be relevant to its therapeutic applications. Because of this, it is essential to compile information related to its peripheral production and regulation of this ubiquitously acting indoleamine. Thus, this review emphasizes the presence of melatonin in extrapineal organs, tissues, and fluids of mammals including humans.

A double-blind, placebo-controlled intervention trial of 3 and 10 mg sublingual melatonin for post-concussion syndrome in youths (PLAYGAME): study protocol for a randomized controlled trial

Background

By the age of sixteen, one in five children will sustain a mild traumatic brain injury also known as concussion. Our research found that one in seven school children with mild traumatic brain injury suffer post-concussion syndrome symptoms for three months or longer. Post-concussion syndrome is associated with significant disability in the child and his/her family and yet there are no evidence-based medical treatments available. Melatonin has several potential mechanisms of action that could be useful following mild traumatic brain injury, including neuroprotective effects. The aim of this study is to determine if treatment with melatonin improves post-concussion syndrome in youths following mild traumatic brain injury. Our hypothesis is that treatment of post-concussion syndrome following mild traumatic brain injury with 3 or 10 mg of sublingual melatonin for 28 days will result in a decrease in post-concussion syndrome symptoms compared with placebo.

Methods/Design

Ninety-nine youths with mild traumatic brain injury, aged between 13 and 18 years, who are symptomatic at 30 days post-injury will be recruited. This study will be conducted as a randomized, double blind, placebo-controlled superiority trial of melatonin. Three parallel treatment groups will be examined with a 1:1:1 allocation: sublingual melatonin 3 mg, sublingual melatonin 10 mg, and sublingual placebo. Participants will receive treatment for 28 days. The primary outcome is a change on the Post-Concussion Symptom Inventory (Parent and Youth). The secondary outcomes will include neurobehavioral function, health-related quality of life and sleep. Neurophysiological and structural markers of change, using magnetic resonance imaging techniques and transcranial magnetic stimulation, will also be investigated.

Discussion

Melatonin is a safe and well-tolerated agent that has many biological properties that may be useful following a traumatic brain injury. This study will determine whether it is a useful treatment for children with post-concussion syndrome. Recruitment commenced on 4 December 2014.

Trial registration

This trial was registered on 6 June 2013 at ClinicalTrials.gov. Registration number: NCT01874847.

Analgesic and sedative effects of melatonin in temporomandibular disorders: a double-blind, randomized, parallel-group, placebo-controlled study

CONTEXT

The association between myofascial temporomandibular disorder (TMD) and nonrestorative sleep supports the investigation of therapies that can modulate the sleep/wake cycle. In this context, melatonin becomes an attractive treatment option for myofascial TMD pain.

OBJECTIVES

To investigate the effects of melatonin on pain (primary aim) and sleep (secondary aim) as compared with placebo in a double-blind, randomized, parallel-group trial.

METHODS

Thirty-two females, aged 20-40 years, with myofascial TMD pain were randomized into placebo or melatonin (5mg) treatment groups for a period of four weeks.

RESULTS

There was a significant interaction (time vs. group) for the main outcomes of pain scores as indexed by the visual analogue scale and pressure pain threshold (analysis of variance; P<0.05 for these analyses). Post hoc analysis showed that the treatment reduced pain scores by -44% (95% CI -57%, -26%) compared with placebo, and it also increased the pressure pain threshold by 39% (95% CI 14%, 54%). The use of analgesic doses significantly decreased with time (P<0.01). The daily analgesic doses decreased by -66% (95% CI -94%, -41%) when comparing the two groups. Additionally, melatonin improved sleep quality, but its effect on pain was independent of the effect on sleep quality.

CONCLUSION

This study provides additional evidence supporting the analgesic effects of melatonin on pain scores and analgesic consumption in patients with mild-to-moderate chronic myofascial TMD pain. Furthermore, melatonin improves sleep quality but its effect on pain appears to be independent of changes in sleep quality.

Correlations between behavioural and oxidative parameters in a rat quinolinic acid model of Huntington's disease: protective effect of melatonin

The present study was designed to examine the correlations between behavioural and oxidative parameters in a quinolinic acid model of Huntington's disease in rats. The protective effect of melatonin against the excitotoxicity induced by quinolinic acid was investigated. Rats were pre-treated with melatonin (5 or 20mg/kg) before injection of quinolinic acid (240nmol/site; 1μl) into their right corpora striata. The locomotor and exploratory activities as well as the circling behaviour were recorded. The elevated body swing test was also performed. After behavioural experiments, biochemical determinations were carried out. Melatonin partially protected against the increase of circling behaviour caused by quinolinic acid injection. No alteration was found in the number of crossings and rearings of animals treated with melatonin and/or quinolinic acid. Melatonin decreased the percentage of contralateral biased swings induced by quinolinic acid. Melatonin protected against the increase in reactive species and protein carbonyl levels as well as the inhibition of superoxide dismutase activity resulting from quinolinic acid injection. Melatonin was partially effective against the inhibition of striatal catalase activity and a decrease of non-protein thiol levels induced by quinolinic acid. Melatonin was not effective against the inhibition of Na(+), K(+) ATPase activity caused by quinolinic acid injection. There were significant correlations between circling behaviour and oxidative parameters. The antioxidant property of melatonin is involved, at least in part, in its neuroprotective effect. The results reinforce the idea that melatonin could be useful in overwhelming neurotoxicity caused by quinolinic acid, a rat model of Huntington's disease.

Melatonin: bone metabolism in oral cavity

Throughout life, bone tissue undergoes a continuous process of resorption and formation. Melatonin, with its antioxidant properties and its ability to detoxify free radicals, as suggested by Conconi et al. (2000) may interfere in the osteoclast function and thereby inhibit bone resorption, as suggested by Schroeder et al. (1981). Inhibition of bone resorption may be enhanced by a reaction of indoleamine in osteoclastogenesis. That it has been observed melatonin, at pharmacological doses, decrease bone mass resorption by suppressing through down regulation of the RANK-L, as suggested by Penarrocha Diago et al. (2005) and Steflik et al. (1994). These data point an osteogenic effect towards that may be of melatonin of clinical importance, as it could be used as a therapeutic agent in situations in which would be advantageous bone formation, such as in the treatment of fractures or osteoporosis or their use as, a bioactive surface on implant as suggested by Lissoni et al. (1991).

Melatonin utility in neonates and children

Melatonin (N-acetyl-5-methoxytryptamine) is an endogenously produced indoleamine secreted by the pineal gland and the secretion is suppressed by light. Melatonin is a highly effective antioxidant, free radical scavenger, and has anti-inflammatory effect. Plenty of evidence supports the utility of melatonin in adults for cancer, neurodegenerative disorders, and aging. In children and neonates, melatonin has been used widely, including for respiratory distress syndrome, bronchopulmonary dysplasia, periventricular leukomalacia (PVL), hypoxia-ischemia encephalopathy and sepsis. In addition, melatonin can be used in childhood sleep and seizure disorders, and in neonates and children receiving surgery. This review article discusses the utility of melatonin in neonates and children.

The interaction of melatonin and agmatine on pentylenetetrazole-induced seizure threshold in mice

Melatonin, the major hormone produced by the pineal gland, has a number of functions in mammals, for example, its function as an anticonvulsant. Agmatine, a biogenic amine formed by decarboxylation of L-arginine by arginine decarboxylase, also has anticonvulsant effects. This study investigated the effect of the interaction of melatonin and agmatine on seizure susceptibility in the mouse model of pentylenetetrazole (PTZ)-induced clonic seizures. Further, the researchers investigated the involvement of melatonin receptors in this interaction using luzindole, a ML(1/2) receptor antagonist and prazosin, a ML(3) receptor antagonist. Melatonin, at 40 and 80 mg/kg, and agmatine, at 10 and 20mg/kg, exerted anticonvulsant effects. Luzindole, at 1.25 and 2.5mg/kg, or prazosin, at 0.5mg/kg, did not change the seizure threshold as compared with that of vehicle-treated mice. The anticonvulsant effect of melatonin (40 and 80 mg/kg) was prevented by luzindole (2.5mg/kg) (P<0.001) but not prazosin (0.5mg/kg), indicating the possible involvement of ML(1/2) receptors in the anticonvulsant effect of melatonin. Agmatine (5mg/kg) significantly increased the anticonvulsant effect of both the noneffective dose (20mg/kg) (P<0.05) and the effective dose (80 mg/kg) (P<0.001) of melatonin. Luzindole (2.5mg/kg), but not prazosin (0.5mg/kg), decreased the anticonvulsant effect of agmatine (20mg/kg) (P<0.05). Luzindole (2.5mg/kg), but not prazosin (0.5mg/kg), also decreased the seizure threshold when agmatine (5mg/kg) was administered before melatonin (20mg/kg); the decrease was significant compared with that of the group that received only agmatine and melatonin (P<0.001). In conclusion, melatonin and agmatine exhibit an additive effect in decreasing pentylenetetrazole-induced seizure threshold in mice, probably through ML(1/2) receptors.

Melatonin in experimental seizures and epilepsy

Although melatonin is approved only for the treatment of jet-lag syndrome and some types of insomnia, clinical data suggest that it is effective in the adjunctive therapy of osteoporosis, cataract, sepsis, neurodegenerative diseases, hypertension, and even cancer. Melatonin also modulates the electrical activity of neurons by reducing glutamatergic and enhancing GABA-ergic neurotransmission. The indoleamine may also be metabolized to kynurenic acid, an endogenous anticonvulsant. Finally, the hormone and its metabolites act as free radical scavengers and antioxidants. The vast majority of experimental data indicates anticonvulsant properties of the hormone. Melatonin inhibited audiogenic and electrical seizures, as well as reduced convulsions induced by pentetrazole, pilocarpine, L-cysteine and kainate. Only a few studies have shown direct or indirect proconvulsant effects of melatonin. For instance, melatonin enhanced low Mg2+-induced epileptiform activity in the hippocampus, whereas melatonin antagonists delayed the onset of pilocarpine-induced seizures. However, the relatively high doses of melatonin required to inhibit experimental seizures can induce some undesired effects (e.g., cognitive and motor impairment and decreased body temperature). In humans, melatonin may attenuate seizures, and it is most effective in the treatment of juvenile intractable epilepsy. Its additional benefits include improved physical, emotional, cognitive, and social functions. On the other hand, melatonin has been shown to induce electroencephalographic abnormalities in patients with temporal lobe epilepsy and increase seizure activity in neurologically disabled children. The hormone showed very low toxicity in clinical practice. The reported adverse effects (nightmares, hypotension, and sleep disorders) were rare and mild. However, more placebo-controlled, double-blind randomized clinical trials are needed to establish the usefulness of melatonin in the adjunctive treatment of epilepsy.

Psychosocial dwarfism: psychopathological aspects and putative neuroendocrine markers

There exists an extensive terminology for defining the situation of children who, in varying circumstances, suffer from affective deprivation (AD), within an unsatisfactory family situation or in institutions. Nevertheless, the neuroendocrine mechanisms (if they exist) determining it have yet to be identified. Our objective was to determine if specific neuroendocrine markers, all of them previously implicated in affective disorders, could be modified, and in which sense, in affective deprivation syndrome of the child. For this purpose, we studied three separate groups of children: (1) control group (CG); (2) children suffering from AD; and (3) children with non-organic failure to thrive (NOFT). In every case, we studied the serum levels of melatonin, serotonin, β-endorphins and adrenocorticotropic hormone (ACTH); and kynurenine pathway tryptophan metabolites (both during the day and at night). Significantly, there was a conspicuous reduction in the levels of each of the neuroendocrine markers (melatonin, serotonin, β-endorphins and ACTH) in the group suffering from affective deficiency, a diminution which was even more noticeable in the group of patients presenting delayed growth. Furthermore, as also occurs in other affective disorders, there were corresponding modifications in the metabolisation of tryptophan. We report the existence of neuroendocrine mechanisms that are associated with the above-mentioned clinical manifestations in these patients, mechanisms that may underlie the close connection existing between AD syndrome and the cause of NOFT. These data suggest that the AD syndrome and NOFT comprise a single process, but one with a different evolutionary continuum of psychosocial dwarfism.

Melatonin administration after pilocarpine-induced status epilepticus: a new way to prevent or attenuate postlesion epilepsy?

OBJECTIVE

The goal of this study was to verify the effects of treatment with melatonin and N-acetylserotonin on the pilocarpine-induced epilepsy model.

METHODS

The animals were divided into four groups: (1) animals treated with saline (Saline); (2) animals that received pilocarpine and exhibited SE (SE); (3) animals that exhibited SE and were treated with N-acetylserotonin (30 minutes and 1, 2, 4, 6, 12, 24, 36, and 48 hours) after SE onset (SE+NAS); (4) animals that exhibited SE and were treated with melatonin at the same time the SE+NAS group (SE+MEL). Behavioral (latency to first seizure, frequency of seizures, and mortality) and histological (Nissl and neo-Timm) parameters were analyzed.

RESULTS

The animals treated with melatonin (SE+MEL) had a decreased number of spontaneous seizures during the chronic period (P<0.05), a reduction in mossy fiber sprouting, and less cell damage than the SE group. Animals treated with N-acetylserotonin did not exhibit any kind of significant change.

CONCLUSION

Melatonin exerts an important neuroprotective effect by attenuating SE-induced postlesion and promoting a decrease in the number of seizures in epileptic rats. This suggests, for the first time, that melatonin could be used co-therapeutically in treatment of patients exhibiting SE to minimize associated injuries in these situations.

Neurochemical evidence that lysine inhibits synaptic Na+,K+-ATPase activity and provokes oxidative damage in striatum of young rats in vivo

Lysine (Lys) accumulation in tissues and biological fluids is the biochemical hallmark of patients affected by familial hyperlysinemia (FH) and other inherited metabolic disorders. In the present study we investigated the effects of acute administration of Lys on relevant parameters of energy metabolism and oxidative stress in striatum of young rats. We verified that Lys in vivo intrastriatal injection did not change the citric acid cycle function and creatine kinase activity, but, in contrast, significantly inhibited synaptic Na(+),K(+)-ATPase activity in striatum prepared 2 and 12 h after injection. Moreover, Lys induced lipid peroxidation and diminished the concentrations of glutathione 2 h after injection. These effects were prevented by the antioxidant scavengers melatonin and the combination of α-tocopherol and ascorbic acid. Lys also inhibited glutathione peroxidase activity 12 h after injection. Therefore it is assumed that inhibition of synaptic Na(+),K(+)-ATPase and oxidative damage caused by brain Lys accumulation may possibly contribute to the neurological manifestations of FH and other neurometabolic conditions with high concentrations of this amino acid.

Scopoli's work in the field of mercurialism in light of today's knowledge: past and present perspectives

The Idrija Mercury Mine (1490-1994) appointed its first physician, Joannes Antonius Scopoli, in 1754. Most of his descriptions of mercurialism are still relevant today. This study highlights Scopoli's observations on the interaction between elemental mercury (Hg degrees ) and alcohol, on the appearance of lung impairment, insomnia, and depressive mood in mercurialism. This presentation is based on Scopoli's experiences presented in his book, De Hydrargyro Idriensi Tentamina (1761), current knowledge, and our own experience acquired through health monitoring of occupational Hg degrees exposure. Some studies have confirmed Scopoli's observation that alcohol enhances mercurialism and his hypothesis that exposure to high Hg degrees concentrations causes serious lung impairment. Neurobiological studies have highlighted the influence of Hg degrees on sleep disorder and depressive mood observed by Scopoli. Although today's knowledge provides new perspectives of Scopoli's work on mercurialism, his work is still very important and can be considered a part of occupational medicine heritage.

Potential use of melatonergic drugs in analgesia: mechanisms of action

Melatonin is a remarkable molecule with diverse physiological functions. Some of its effects are mediated by receptors while other, like cytoprotection, seem to depend on direct and indirect scavenging of free radicals not involving receptors. Among melatonin's many effects, its antinociceptive actions have attracted attention. When given orally, intraperitoneally, locally, intrathecally or through intracerebroventricular routes, melatonin exerts antinociceptive and antiallodynic actions in a variety of animal models. These effects have been demonstrated in animal models of acute pain like the tail-flick test, formalin test or endotoxin-induced hyperalgesia as well as in models of neuropathic pain like nerve ligation. Glutamate, gamma-aminobutyric acid, and particularly, opioid neurotransmission have been demonstrated to be involved in melatonin's analgesia. Results using melatonin receptor antagonists support the participation of melatonin receptors in melatonin's analgesia. However, discrepancies between the affinity of the receptors and the very high doses of melatonin needed to cause effects in vivo raise doubts about the uniqueness of that physiopathological interpretation. Indeed, melatonin could play a role in pain through several alternative mechanisms including free radicals scavenging or nitric oxide synthase inhibition. The use of melatonin analogs like the MT(1)/MT(2) agonist ramelteon, which lacks free radical scavenging activity, could be useful to unravel the mechanism of action of melatonin in analgesia. Melatonin has a promising role as an analgesic drug that could be used for alleviating pain associated with cancer, headache or surgical procedures.

Mitochondria, oxidative stress, and temporal lobe epilepsy

Mitochondrial oxidative stress and dysfunction are contributing factors to various neurological disorders. Recently, there has been increasing evidence supporting the association between mitochondrial oxidative stress and epilepsy. Although certain inherited epilepsies are associated with mitochondrial dysfunction, little is known about its role in acquired epilepsies such as temporal lobe epilepsy (TLE). Mitochondrial oxidative stress and dysfunction are emerging as key factors that not only result from seizures, but may also contribute to epileptogenesis. The occurrence of epilepsy increases with age, and mitochondrial oxidative stress is a leading mechanism of aging and age-related degenerative disease, suggesting a further involvement of mitochondrial dysfunction in seizure generation. Mitochondria have critical cellular functions that influence neuronal excitability including production of adenosine triphosphate (ATP), fatty acid oxidation, control of apoptosis and necrosis, regulation of amino acid cycling, neurotransmitter biosynthesis, and regulation of cytosolic Ca(2+) homeostasis. Mitochondria are the primary site of reactive oxygen species (ROS) production making them uniquely vulnerable to oxidative stress and damage which can further affect cellular macromolecule function, the ability of the electron transport chain to produce ATP, antioxidant defenses, mitochondrial DNA stability, and synaptic glutamate homeostasis. Oxidative damage to one or more of these cellular targets may affect neuronal excitability and increase seizure susceptibility. The specific targeting of mitochondrial oxidative stress, dysfunction, and bioenergetics with pharmacological and non-pharmacological treatments may be a novel avenue for attenuating epileptogenesis.

Melatonin stimulates osteointegration of dental implants

The aim of this study was to evaluate the effect of the topical application of melatonin on osteointegration of dental implants in Beagle dogs 14 days after their insertion. In preparation for subsequent insertion of dental implants, upper and lower premolars and molars were extracted from 12 Beagle dogs. Each mandible received cylindrical screw implants of 3.25 mm in diameter and 10 mm in length. The implants were randomly assigned to the mesial and distal sites on each side of the mandible. Prior to implanting, 1.2 mg lyophylized powdered melatonin was applied to one bone hole at each side of the mandible. None was applied at the control sites. Eight histological sections per implant were obtained for histomorphometric studies. After a 2-wk treatment period, melatonin significantly increased the perimeter of bone that was in direct contact with the treated implants (P < 0.0001), bone density (P < 0.0001), new bone formation (P < 0.0001) and inter-thread bone (P < 0.05) in comparison with control implants. Topical application of melatonin may act as a biomimetic agent in the placement of endo-osseous dental implants.

Melatonin enhances the anticonvulsant and proconvulsant effects of morphine in mice: Role for nitric oxide signaling pathway

Melatonin has different interactions with opioids including enhancing their analgesic effect and reversal of opioid tolerance and dependence. Opioids are known to exert dose-dependent anti- and proconvulsant effects in different experimental seizure paradigms. This study investigated the effect of melatonin on biphasic modulation of seizure susceptibility by morphine, in mouse model of pentylenetetrazole (PTZ)-induced clonic seizures. We further investigated the involvement of the nitric oxidergic pathway in this interaction, using a nitric oxide synthase inhibitor, NG-nitro-L-arginine-methyl-ester (L-NAME). Melatonin exerted anticonvulsant effect with doses as high as 40-80 mg/kg, but with a dose far bellow that amount (10 mg/kg), it potentiated both the anticonvulsant and proconvulsant effects of morphine on the PTZ-induced clonic seizures. Possible pharmacokinetic interaction of melatonin and morphine cannot be ruled out in the enhancement of two opposing effects of morphine on seizure threshold. L-NAME (1 mg/kg) reversed the anticonvulsant property of the combination of melatonin (10 mg/kg) plus morphine (0.5 mg/kg). Moreover, L-NAME (5 mg/kg) blocked the enhancing effect of melatonin (10 mg/kg) on proconvulsant activity of morphine (60 mg/kg). Our results indicate that co-administration of melatonin enhances both anti- and proconvulsant effects of morphine via a mechanism that may involve the nitric oxidergic pathway.

Melatonin enhances the rewarding properties of morphine: involvement of the nitric oxidergic pathway

Melatonin has different interactions with opioids including the enhancement of the analgesic effects of morphine and also reversal of tolerance and dependence to morphine. The present study assessed the effect of melatonin on morphine reward in mice using a conditioned place preference (CPP) paradigm. Our data showed that subcutaneous administration of morphine (1-7.5 mg/kg) significantly increased the time spent in the drug-paired compartment in a dose-dependent manner. Intraperitoneal (i.p.) administration of melatonin (1-40 mg/kg) alone did not induce either CPP or conditioned place aversion (CPA), while the combination of melatonin (5-20 mg/kg) and sub-effective dose of morphine (0.5 mg/kg) led to rewarding effect. We further investigated the involvement of the nitric oxidergic pathway in the enhancing effect of melatonin on morphine CPP, by a general nitric oxide synthase inhibitor, N(G)-nitro-L-arginine methyl ester (L-NAME). L-NAME (1 and 5 mg/kg, i.p.) alone or in combination with morphine (0.5 mg/kg) did not show any significant CPP or CPA. Co-administration of L-NAME (5 mg/kg) with an ineffective combination of melatonin (1 mg/kg) plus morphine (0.5 mg/kg) produced significant CPP that may imply the similarity of action of melatonin and L-NAME and involvement of the nitric oxidergic pathway in this regard. Our results indicate that pretreatment of animals with melatonin enhances the rewarding properties of morphine via a mechanism which may involve the nitric oxidergic pathway.