Evidence for feedback control of pineal melatonin secretion

MR Spectroscopy Assessment of Daily Variations of GABA Levels within the Parietal Lobe and Anterior Cingulate Gyrus Regions of Healthy Young Adults

BACKGROUND

The changes that occur in the gamma-aminobutyric acid (GABA) levels within specific brain regions throughout the day are less clear.

PURPOSE

To evaluate the daily fluctuations of GABA levels within the parietal lobe (PL) and anterior cingulate gyrus (ACC) regions and explore their association with melatonin (MT) levels, heart rate (HR), and blood pressure.

STUDY TYPE

Prospective.

SUBJECTS

26 healthy young adults (15 males and 11 females aged 22-27 years).

FIELD STRENGTH/SEQUENCE

3.0T, T1-weighted imaging, Mescher-Garwood point resolved spectroscopy (MEGA-PRESS) sequence.

ASSESSMENT

The acquired GABA signal contained the overlapping signals of macromolecules and homocarnosine, hence expressed as GABA+. The creatine (Cr) signal was applied as an endogenous reference. The GABA+, GABA+/Cr were measured at six different time points (1:00, 5:00, 9:00, 13:00, 17:00, and 21:00 hours) using MEGA-PRESS. The blood pressure, HR and sputum MT levels, were also acquired.

STATISTICAL TESTS

The one-way repeated-measures analysis of variance (ANOVA) was used to evaluate the GABA, blood pressure, HR, and MT levels throughout the day. A general linear model was used to find the correlation between GABA and blood pressure, HR, and MT. P < 0.05 was statistically significant.

RESULTS

Significant variations in GABA+/Cr and GABA+ levels were observed throughout the day within the PL region. The lowest levels were recorded at 9:00 hour (GABA+/Cr: 0.100 ± 0.003，GABA+:1.877 ± 0.051 i.u) and the highest levels were recorded at 21:00 hour (GABA+/Cr: 0.115 ± 0.003, GABA+:2.122 ± 0.052 i.u). The MT levels were positively correlated with GABA+/Cr (r = 0.301) and GABA+ (r = 0.312) within the ACC region.

DATA CONCLUSION

GABA+/Cr and GABA+ in ACC are positively correlated with MT. GABA levels in the PL have diurnal differences. These findings may indicate that the body's GABA level change in response to the light-dark cycle.

LEVEL OF EVIDENCE

1 TECHNICAL EFFICACY: Stage 2.

Assessment of sleep quality and its factors among clinicians working in critical care units and operation theaters at North West Ethiopia, 2022: a multicenter cross-sectional study

The quality of sleep has an effect on the health of clinicians and the quality of patient care. Maintaining cognitive function/mood, facilitation of glucose metabolism, and strengthening of the immune system are among the roles that adequate sleep may contribute. Poor sleep quality is multifactorial, and studies had shown inconsistencies in the factors that contribute to the development of this poor sleep quality. The prevalence of poor sleep quality among clinicians working in the critical care unit and operation theater in the study setting was not investigated yet.

OBJECTIVE

The objective of this study was conducted for the purpose of assessing the quality of sleep and associated factors among clinicians working in the critical care unit and operation theater.

METHODS

A cross-sectional study was conducted from 15 May to 15 June 2022. Data were collected using a self-administered questionnaire from 421 clinicians selected by simple random sampling techniques. Sleep quality was measured by the Pittsburg sleep quality index. The data were entered into Epi-data and exported to SPSS. Frequency and percentage were used for the descriptive analysis. Binary and multivariate logistic regression analysis were used to identify factors associated with poor quality of sleep. The strength of the association was measured with an OR within the 95% CI and P-value of <0.05.

RESULT

About half 220 (52.3%) of the study participants age between 25 and 30 year old and the majority 321 (76.2%) of them were males. The prevalence of poor sleeps quality was 81.5% (95% CI: 77.9-85.5). Working night shift (AOR: 3.37, 95% CI: 1.754-6.484), having depressive symptoms (AOR: 3.25, 95% CI: 1.485-7.147) and having no regular exercises (AOR: 0.299, 95% CI: 0.166-0.537) were predisposing factors for poor sleep quality.

CONCLUSION AND RECOMMENDATION

The prevalence of poor sleep quality among clinicians working in the ICU and operation room was high. Clinicians who had no regular exercise, who worked in night shift, and who had depressive symptoms were associated with poor quality of sleep. Clinicians should have an awareness on the symptoms of depression, implement sleep hygiene education programs and promoting regular exercise. The authors recommend healthcare policy makers for improving working schedules.

Effects of Duodenal 5-Hydroxytryptophan Perfusion on Melatonin Synthesis in GI Tract of Sheep

The purpose of this study is to investigate the potential effects of 5-hydroxytryptophan (5-HTP) duodenal perfusion on melatonin (MT) synthesis in the gastrointestinal (GI) tract of sheep. 5-hydroxytryptophan is a precursor in the melatonin synthetic pathway. The results showed that this method significantly increased melatonin production in the mucosa of all segments in GI tract including duodenum, jejunum, ileum, cecum and colon. The highest melatonin level was identified in the colon and this indicates that the microbiota located in the colon may also participate in the melatonin production. In addition, portion of the melatonin generated by the GI tract can pass the liver metabolism and enters the circulation via portal vein. The current study provides further evidence to support that GI tract is the major site for melatonin synthesis and the GI melatonin also contributes to the circulatory melatonin level since plasma melatonin concentrations in 5-HTP treated groups were significantly higher than those in the control group. In conclusion, the results show that 10–50 mg of 5-HTP flowing into the duodenum within 6 h effectively improve the production of melatonin in the GI tract and melatonin concentration in sheep blood circulation during the day.

El-Taieb M, N. Fares N, M. Fayed H, Toghan R, M. Ibrahim H. Men with idiopathic oligoasthenoteratozoospermia exhibit lower serum and seminal plasma melatonin levels: Comparative effect of night-light exposure with fertile males

Melatonin is a darkness hormone secreted by the pineal gland, which serves a role in idiopathic oligoasthenoteratozoospermia (iOAT). The present study aimed to evaluate the seminal plasma and serum melatonin levels of 50 patients with iOAT and 50 normal fertile controls and the effects of exposure to light at night on semen parameters. Semen analyses were performed according to the World Health Organization 2010 guidelines. Measurements of serum and seminal plasma melatonin, serum TSH, FT3, FT4, free testosterone, prolactin, FSH and LH were performed using ELISA. The overall results revealed that the serum and seminal plasma levels of melatonin were lower in patients with iOAT compared with the control subjects (P=0.0004 and 0.01, respectively). Patients with iOAT who were exposed to light at night exhibited lower serum and seminal plasma melatonin levels compared with those who were not exposed to light at night (P<0.0001 and 0.02, respectively). Additionally, similar significant differences were identified in control subjects exposed to light at night when compared to non-exposed controls. There was a significantly positive correlation between serum melatonin levels and sperm motility in the entire iOAT patient cohort (r=0.614; P<0.0001) and a significantly positive correlation between the serum and seminal plasma melatonin levels in the non-exposed iOAT patient subgroup (r=0.753; P<0.001). Thus, darkness and sleep at night may improve the semen parameters of patients with iOAT, as evidenced by the effects of light exposure at night on the serum and seminal plasma levels of melatonin and, consequently, on semen parameters.

Central regulation of breast cancer growth and metastasis

Cancer is a systemic disease. In order to fully understand it, we must take a holistic view on how cancer interacts with its host. The brain monitors and responds to natural and aberrant signals arriving from the periphery, particularly those of metabolic or immune origin. As has been well described, a hallmark of cancer is marked disruption of metabolic and inflammatory processes. Depending on the salience and timing of these inputs, the brain responds via neural and humoral routes to alter whole-body physiology. These responses have consequences for tumor growth and metastasis, directly influencing patient quality of life and subsequent mortality. Additionally, environmental inputs such as light, diet, and stress, can promote inappropriate neural activity that benefits cancer. Here, I discuss evidence for brain-tumor interactions, with special emphasis on subcortical neuromodulator neural populations, and potential ways of harnessing this cross-talk as a novel approach for cancer treatment.

Neuroendocrine Control of Sleep

Sleep is a phenomenon in animal behavior as enigmatic as it is ubiquitous, and one deeply tied to endocrine function. Though there are still many unanswered questions about the neurochemical basis of sleep and its functions, extensive interactions have been identified between sleep and the endocrine system, in both the endocrine system's effect on sleep and sleep's effect on the endocrine system. Unfortunately, until recent years, much research on sleep behavior largely disregarded its connections with the endocrine system. Use of both clinical studies and rodent models to investigate interactions between neuroendocrine function, including biological sex, and sleep therefore presents a promising area of further exploration. Further investigation of the neurobiological and neuroendocrine basis of sleep could have wide impact on a number of clinical and basic science fields. In this review, we summarize the state of basic sleep biology and its connections to the field of neuroendocrine biology, as well as suggest key future directions for the neuroendocrine regulation of sleep that may significantly impact new therapies for sleep disorders in women and men.

Melatonin receptor 1B -1193T>C polymorphism is associated with diurnal preference and sleep habits

BACKGROUND

Melatonin modulates the master circadian clock through the activation of G-protein-coupled receptors MT1 and MT2. It is presumed, therefore, that genetic variations in melatonin receptors can affect both sleep and circadian phase. We investigated whether the -1193T > C (rs4753426) polymorphism in the promoter of MT2 receptor gene (MTNR1B) is associated with diurnal preference and sleep habits. This polymorphism was previously associated with sunshine duration, suggesting a role in circadian entrainment.

METHODS

A total of 814 subjects who completed the Morningness-Eveningness and the Munich Chronotype questionnaires were genotyped for the selected polymorphism. Linear and multinomial regression were performed to test the interaction between gene variants and diurnal preference/sleep habits.

RESULTS

The -1193C variant was associated with the extreme morningness phenotype in a codominant model (C/C vs. T/T), recessive model (C/C + C/T vs. T/T) and alleles (C vs. T). A negative correlation was found between -1193C alleles and social jetlag scores. The frequency of -1193T allele was higher in the group that stay in bed more than 8 h/night compared to the group that stay in bed less than 8 h/night on weekends.

CONCLUSION

To the best of our knowledge, these data provide the first insights into the role of MTNR1B gene in the regulation of sleep, biological rhythms, and entrainment in humans.

Melatonin Administration Methods for Research in Mammals and Birds

Endocrine research in animals often entails exogenous hormone administration. Special issues arise when developing administration protocols for hormones with circadian and seasonal periodicity. This article reviews various methods for the exogenous administration of hormones with such periodicities by focusing on melatonin. We discuss that methodological variations across studies can affect experimental results. Melatonin administration techniques used in vertebrates includes infusion pumps, beeswax pellets, oral administration, injections, SILASTIC capsules, osmotic pumps, transdermal delivery, beads, and sponges.

Melatonin decreases neuronal excitability in a sub-population of dorsal root ganglion neurons

Melatonin, a powerful antioxidant, participates in the regulation of important physiological and pathological processes. We investigated the actions of melatonin on neuronal excitability of intact dorsal root ganglions (DRG) from rats using intracellular recording techniques in current clamps. Melatonin blocked the generation of action potentials in a concentration-dependent manner. Bath applied melatonin (1.0-1000.0 nM) hyperpolarized the resting membrane potential, and increased the input resistance and rheobase. Melatonin also altered the active electrophysiological properties of the action potential, amplitude and maximum descendant inclination, in a statistically significant way. In order to provide evidence on the mechanism of action of melatonin in the DRG, quantitative PCR (qPCR) was performed. Analyses were performed for melatonin membrane receptors, MT₁ and MT₂, and it was observed that the DRG expresses MT₁ receptors. In addition, we noted that the melatonin-induced effects were blocked in the presence of luzindole, a melatonin receptor antagonist. The minimal effective concentrations of melatonin (10.0 nM) and the blockade of effects caused by luzindole suggest that the effects of melatonin are hormonal, and are induced when it binds to MT₁ receptors.

Seasonal Reproduction in Vertebrates: Melatonin Synthesis, Binding, and Functionality Using Tinbergen's Four Questions

One of the many functions of melatonin in vertebrates is seasonal reproductive timing. Longer nights in winter correspond to an extended duration of melatonin secretion. The purpose of this review is to discuss melatonin synthesis, receptor subtypes, and function in the context of seasonality across vertebrates. We conclude with Tinbergen's Four Questions to create a comparative framework for future melatonin research in the context of seasonal reproduction.

Photoperiodic regulation of behavior: Peromyscus as a model system

Winter and summer present vastly different challenges to animals living outside of the tropics. To survive and reproduce, individuals must anticipate seasonal environmental changes and adjust physiology and behavior accordingly. Photoperiod (day length) offers a relatively 'noise free' environmental signal that non-tropical animals use to tell the time of year, and whether winter is approaching or receding. In some cases, photoperiodic signals may be fine-tuned by other proximate cues such as food availability or temperature. The pineal hormone, melatonin, is a primary physiological transducer of the photoperiodic signal. It tracks night length and provokes changes in physiology and behavior at appropriate times of the year. Because of their wide latitudinal distribution, Peromyscus has been well studied in the context of photoperiodic regulation of physiology and behavior. Here, we discuss how photoperiodic signals are transduced by pineal melatonin, how melatonin acts on target tissues, and subsequent consequences for behavior. Using a life-history paradigm involving trade-offs between the immune and reproductive systems, specific emphasis is placed on aggression, metabolism, and cognition. We discuss future directions including examining the effects of light pollution on photoperiodism, genetic manipulations to test the role of specific genes in the photoperiodic response, and using Peromyscus to test evolutionary theories of aging.

The Relationship between Seminal Melatonin with Sperm Parameters, DNA Fragmentation and Nuclear Maturity in Intra-Cytoplasmic Sperm Injection Candidates

Objective

Melatonin, the chief secretory product of the pineal gland, regulates dynamic physiological adaptations that occur in seasonally breeding mammals as a response to changes in daylight hours. Because of the presence of melatonin in semen and the mem- brane melatonin receptor in spermatozoa, the impact of melatonin on the regulation of male infertility is still questionable. The aim of this study was to determine the effects of endogenous melatonin on human semen parameters (sperm concentration, motility and normal morphology), DNA fragmentation (DF) and nuclear maturity.

Materials and Methods

In this clinical prospective study, semen samples from 75 infer- tile men were routinely analyzed and assessed for melatonin and total antioxidant capac- ity (TAC) levels using the enzyme-linked immunosorbent assay (ELISA) and colorimetric assay kits, respectively. DF was examined by the sperm chromatin dispersion (SCD) test. Acidic aniline blue staining was used to detect chromatin defects in the sperm nuclei.

Results

There was no significant correlation between seminal plasma melatonin and TAC with sperm parameters and nuclear maturity. However, we observed a positive significant correlation between DF and melatonin level (r=0.273, P<0.05).

Conclusion

Melatonin in seminal plasma is positively correlated with damaged sperm DNA of infertile patients. The mechanism of this phenomenon needs further study.

Neuroendocrine control of photoperiodic changes in immune function

Seasonal variation in immune function putatively maximizes survival and reproductive success. Day length (photoperiod) is the most potent signal for time of year. Animals typically organize breeding, growth, and behavior to adapt to spatial and temporal niches. Outside the tropics individuals monitor photoperiod to support adaptations favoring survival and reproductive success. Changes in day length allow anticipation of seasonal changes in temperature and food availability that are critical for reproductive success. Immune function is typically bolstered during winter, whereas reproduction and growth are favored during summer. We provide an overview of how photoperiod influences neuronal function and melatonin secretion, how melatonin acts directly and indirectly to govern seasonal changes in immune function, and the manner by which other neuroendocrine effectors such as glucocorticoids, prolactin, thyroid, and sex steroid hormones modulate seasonal variations in immune function. Potential future research avenues include commensal gut microbiota and light pollution influences on photoperiodic responses.

Synthetic melatoninergic ligands: achievements and prospects

Pineal hormone melatonin is widely used in the treatment of disorders of circadian rhythms. The presence of melatonin receptors in various animal tissues motivates the use of this hormone in some other diseases. For this reason, in recent years investigators continued the search for synthetic analogues of melatonin which are metabolically stable and selective to receptors. This review includes recent information about the most famous melatonin analogues, their structure, properties, and physiological features of the interaction with melatonin receptors.

Melatonin and its atheroprotective effects: a review

Atherosclerosis is a chronic vascular disease in which oxidative stress and inflammation are commonly implicated as major causative factors. Identification of novel strategies that contribute to plaque stabilization or inhibition represents a continuing challenge for the medical community. The evidence from the last decade highlights that melatonin influences the cardiovascular system, but its mechanisms of action have not been definitively clarified. Melatonin has atheroprotective effects by acting on different pathogenic signaling processes; these result from its direct free radical scavenger activity, its indirect antioxidant properties and its anti-inflammatory actions. In this review, we summarize the many pieces of the puzzle which identified molecular targets for prevention and therapy against the atherosclerotic pathogenic processes and we evaluate the data documenting that melatonin treatment has important actions that protect against atherosclerosis and atherosclerosis-related cardiovascular diseases.

The effects of exogenous melatonin and melatonin receptor blockade on aggression and estrogen-dependent gene expression in male California mice (Peromyscus californicus)

Photoperiodic regulation of aggression has been well established in several vertebrate species, with rodents demonstrating increased aggression in short day photoperiods as compared to long day photoperiods. Previous work suggests that estrogens regulate aggression via rapid nongenomic pathways in short days and act more slowly in long days, most likely via genomic pathways. The current study therefore examines the role of melatonin in mediating aggression and estrogen-dependent gene transcription. In Experiment 1, male California mice were housed under long day photoperiods and were treated with either 0.3 μg/g of melatonin, 40 mg/kg of the melatonin receptor antagonist luzindole, or vehicle for 10 days. We found that melatonin administration significantly increased aggression as compared to mice receiving vehicle, but this phenotype was not completely ameliorated by luzindole. In Experiment 2, male California mice were injected with either 1mg/kg of the aromatase inhibitor letrozole or vehicle, and oxytocin receptor (OTR), estrogen receptor alpha (ERα), and c-fos gene expression was examined in the bed nucleus of the stria terminalis (BNST) and medial preoptic area (MPOA). In the BNST, but not MPOA, OTR mRNA was significantly downregulated following letrozole administration, indicating that OTR is an estrogen-dependent gene in the BNST. In contrast, ERα was not estrogen dependent in either brain region. In the MPOA, OTR mRNA was inhibited by melatonin, and luzindole suppressed this effect. C-fos and ERα did not differ between treatments in any brain region examined. These results suggest that it is unlikely that melatonin facilitates aggression via broad spectrum regulation of estrogen-dependent gene expression. Instead, melatonin may act via regulation of other transcription factors such as extracellular signal regulated kinase.