Plasma Melatonin Research Articles

Impact of an extended light regimen imposed during nursery period on the performance and lipid metabolism of weanling pigs.

This study aimed to assess the impact of a prolonged photoperiod on the growth performance and lipid metabolism of weaned piglets. Twenty-four piglets weaned at 28 days of age were randomly dichotomized into two groups that were alternatively subjected to either long photoperiod (LP) group (16L:8D) or short photoperiod (SP) group (10L:14D) for 42days. Four replicates of three animals per replicates were used per experimental treatment. Our results demonstrated that prolonged photoperiod increased piglet body weight, average daily weight gain (ADG), backfat thickness (BF), backfat index during the nursery period, and increased ADG, average daily feed intake (ADFI), and decreased the F/G of piglets during the experiment days 29 to 42. Meanwhile, we observed LP piglets' plasma melatonin, growth hormone and serotonin levels were decreased at 14 d and 42 d compared to SP piglets. Moreover, up-regulated mRNA or protein expression of PPARγ and CEBPα, and lower mRNA or protein expression of MTR1, ATGL, HSL, PPARα, and CPT1α, were observed in back subcutaneous fat (BSF) of LP group compared with that of SP group. Significant increases were observed in the mRNA or protein contents of lipogenic genes, including C/EBPα, SREBP-1c, ACCα, and FAS, in the liver of LP piglets, whereas CPT1α and ACOX1 mRNA levels and PPARα and MTR1 protein expression were significantly down-regulated in LP group compared to SP group. Extended photoperiod also increased lipid content in longissimus dorsi muscle (LDM) that was associated with higher mRNA or protein levels of SREBP-1c, ACCα, FAS, Pref1, and LPL, decreased mRNA or protein contents of LeptinR, MTR1, HSL, and ACOX1. Together, these findings suggest that there is an advantage, in terms of growth performance and fat deposition, in imposing a prolonged light program (16-h light/day) on nursery piglets to alleviate the negative aspects of weaning stress.

Rising global temperatures and its impact on sleep behavior of male redheaded bunting (Emberiza bruniceps).

Anthropogenic global warming is one of the most pervasive threats to nature and biodiversity. The magnitude with which earths' temperature is rising is affecting every lifeform uniquely; however, the studies highlighting the impacts of global warming on avian sleep are scarce. To this end, the present study was aimed at analyzing the impact of global warming on sleep behavior of a nocturnal migrant, Emberiza bruniceps. For this purpose, the birds were divided into two groups (N = 15 each), subjected to high (35 ± 1°C) and low (19 ± 1°C) temperature schedule with concurrent exposure to 8L:16D (short day; SD) photoperiod followed by 13L:11D (long day; LD). The experiment continued till 7 cycles of zugunruhe (LD) in birds. The results reveal significant impact of temperature treatment on initiation and quality of zugunruhe. Temporal distribution of activity and rest varied according to the temperature provided. Focusing on rest and specifically on sleep of birds, high ambient temperatures resulted in greater sleep fragmentation (evident by increased awakenings during night), whereas low temperature created a sleep conducive environment (evident by abundance of back sleep). Besides postural differences, high temperature resulted in reduced sleep duration, sleep onset latency and circulating plasma melatonin levels in comparison with low temperature suggesting the negative impact of high temperature on different sleep attributes. Not only sleep, seasonal physiology of birds such as hyperphagia, gain in body mass, and fat stores showed significant reduction in high temperature condition. Besides behavioral and physiological alterations, high ambient temperature led to elevated expression of temperature sensitive (trpv4, trpm8, hspa8, and hsp70) genes. Enhanced expression of chrm3 (responsible for wakefulness) also affirms sleep fragmentation in response to high temperature. Thus, the study highlights the negative impact of high temperature on birds' sleep behavior and seasonal physiology.

Мелатонин и мужское бесплодие, вызванное окислительным стрессом

Among couples unable to conceive a child, infertility is explained by the male factor in about 50% of cases. The etiology of male infertility remains uncertain in 30-50% of patients. One of the frequent etiological factors of male infertility is oxidative stress, a statusin which an unbalance between the production of reactive oxygen species and the mechanisms of antioxidant protection. Today, the term «male oxidative stressinfertility» has been proposed as a new descriptor for infertile men with a combination of abnormalsperm characteristics and oxidative stress. Along with the use of traditional antioxidants, it is necessary to search for new moleculesto combat oxidative stressin infertile men. A promising strategy is to use melatonin, a hormone secreted by the pineal gland, as an antioxidant. The review examinesthe antioxidant effects of the melatonin metabolic cascade. The results ofstudies on the relationship between the level of melatonin in seminal plasma and male fertility are presented. New scientific data on the protective potential of melatonin against oxidative stress caused by various metabolic disorders, anticancer chemo- and radiation therapy and other pathogenetic conditions and negative effects are presented. The research on the prospects of using melatonin to protectspermatozoa from oxidative damage in the implementation of assisted reproductive technologiesis analyzed. The interim results ofstudies on the possibility of using melatonin as a dietary supplement in infertile men are summarized.

Comparative Pharmacokinetics of Sustained-Release versus Immediate-Release Melatonin Capsules in Fasting Healthy Adults: A Randomized, Open-Label, Cross-Over Study.

Background: Exogenous melatonin, a nutraceutical for maintaining a healthy sleep-wake cycle and managing sleep disorders, requires large, repeated doses due to its low bioavailability and short half-life. This necessitates the development of a sustained-release formulation with a longer half-life and sustained plasma concentration. Therefore, exogenous novel 5 mg sustained-release melatonin capsules (Melatonin-SR, test product) were formulated. Methods: This open-label cross-over study compared the pharmacokinetics (maximum concentration [Cmax], time to reach Cmax [Tmax], area under the curve [AUC], and elimination half-life [t1/2]) and the safety of Melatonin-SR with 5 mg immediate-release melatonin capsules (Melatonin-IR, reference product) after single-dose oral administration in healthy fasting adults. Results: Sixteen participants (aged 18-45 years) were randomized (1:1) to receive either Melatonin-SR or Melatonin-IR in two periods with a 7-day washout period. Melatonin-SR reported a lower Cmax (11,446.87 pg/mL) compared to Melatonin-IR (22,786.30 pg/mL). The mean Tmax of Melatonin-SR and Melatonin-IR was 1.26 h and 0.87 h, respectively. The mean t1/2 of Melatonin-SR (5.10 h) was prolonged by five-fold compared to Melatonin-IR (1.01 h). One adverse event (vomiting) was reported following the administration of the Melatonin-IR. Conclusions: Melatonin-SR resulted in higher and sustained plasma melatonin concentrations for an extended period and was well-tolerated. Hence, Melatonin-SR may be a promising nutraceutical for maintaining healthy sleep.

Melatonin Bioavailability After Oral Administration of a New Delayed-Release Form in Healthy Male Volunteers.

Two main types of galenic formulation, immediate release and prolonged release, have been developed to optimize melatonin bioavailability. We recently described the kinetic profile of a prolonged-release form generating a peak of plasma melatonin 1 h (Tmax) after intake, followed by a prolonged decay over time. We have developed a new oral form of melatonin with the aim of producing a melatonin peak several hours after intake. The objective is to investigate melatonin bioavailability after administration of this new delayed-release form (DR form). In this single-centre open-label study, 12 healthy male volunteers received one tablet of the DR form containing 1.9 mg melatonin, 10 mg zinc and 200 mg lemon balm extract (Melissa officinalisL aerial parts). Blood samples were collected for 12 h, beginning at 8:00 am. Plasma concentrations of melatonin and 6-sulfatoxymelatonin (6-SMT), the main hepatic melatonin metabolite, were determined by radioimmunoassay. A progressive increase in plasma melatonin concentrations was observed from 20 min and a peak about 3 h after intake (Cmax 740 ± 824 pg/mL; Tmax 179 ± 60min). Concentrations remained high between 140 and 220 min, the concentration remaining physiologically significant (over 100pg/mL) up to 7 h after intake. The DR form was well tolerated. The melatonin release profile was consistent with what was anticipated for the DR form. The DR form generated a 2 h delayed Tmax compared with a prolonged-release form previously evaluated. This suggests that the DR form is suitable for the treatment of certain sleep disorders such as short sleep duration or early awakening. Registration number: NCT05419466.

Significance of plasma melatonin as a diagnostic marker in full-term with late onset sepsis

Significance of plasma melatonin as a diagnostic marker in full-term with late onset sepsis

Participation of Ca2+-Calmodulin-Dependent Protein Kinase II in the Antidepressant-Like Effects of Melatonin.

Melatonin (N-acetyl-5-methoxytryptamine) is an indoleamine secreted by the pineal gland during the dark phase of the photoperiod. Its main function is the synchronization of different body rhythms with the dark-light cycle. Research on melatonin has significantly advanced since its discovery and we now know that it has considerable significance in various physiological processes, including immunity, aging, and reproduction. Moreover, in recent years evidence of the pharmacological possibilities of melatonin has increased. Indoleamine, on the other hand, has antidepressant-like effects in rodents, which may be mediated by the activation of calcium-calmodulin-dependent kinase II (CaMKII) and are also related to the regulation of neuroplasticity processes, including neurogenesis, synaptic maintenance, and long-term potentiation. Remarkably, patients with major depression show decreased levels of circulating melatonin in plasma. This review presents evidence of the antidepressant-like effects of melatonin in preclinical models and the participation of CaMKII in these actions. CaMKII's role in cognition and memory processes, which are altered in depressive states, are part of the review, and the effects of melatonin in these processes are also reviewed. Furthermore, participation of CaMKII on structural and synaptic plasticity and the effects of melatonin are also described. Finally, the advantages of using melatonin in combination with other antidepressants such as ketamine for neuroplasticity are described. Evidence supports that CaMKII is activated by melatonin and downstream melatonin receptors and may be the common effector in the synergistic effects of melatonin with other antidepressants. SIGNIFICANCE STATEMENT: This review compiled evidence supporting that melatonin causes antidepressant-like effects in mice through calmodulin kinase II stimulation of downstream melatonin receptors as well as the participation of this enzyme in neuroplasticity, memory, and cognition. Finally, we describe evidence about the effectiveness of antidepressant-like effects of melatonin in combination with ketamine.

Determination of Rhythmicity and Gestational Stage-Related Distribution of Blood Plasma Melatonin Concentrations in Donkey Mares.

The aim of this study is to obtain a more complete picture of blood plasma melatonin concentrations in the donkey mares. To this purpose, sampling and statistical processing were carried out in such a way that allowed the researchers to establish the annual and daily rhythms. Based on human observations, according to the hypothesis of the authors, the blood plasma melatonin concentration of pregnant individuals rises during the late gestational period, before parturition. To confirm this, the melatonin concentrations of pregnant and non-pregnant jennies were monitored and compared. In regard to the circannual rhythm, the significantly lowest midnight melatonin value (27.67 pg mL-1) was typical for the summer solstice. Under consideration of circadian changes, a significantly strongest melatonin production (45.16 pg mL-1) was observed on the night of the winter solstice (p < 0.001). Considering gestational age, the blood plasma melatonin concentration (around 38 pg mL-1) does not change as gestation progresses (p = 0.136). The results obtained in this studied population of the domestic ass usefully expand the little knowledge previously gathered about the development of the blood plasma melatonin concentrations of this species.

Concentrations of plasma estradiol, progesterone, melatonin, serotonin and nitric oxide in Tuj ewes after estrus syncronization in and out of breeding season

Concentrations of plasma estradiol, progesterone, melatonin, serotonin and nitric oxide in Tuj ewes after estrus syncronization in and out of breeding season

Dysregulation of circadian clock gene expression patterns in a treatment-resistant animal model of depression.

Circadian rhythm (CR) disturbances are among the most commonly observed symptoms during major depressive disorder, mostly in the form of disrupted sleeping patterns. However, several other measurable parameters, such as plasma hormone rhythms and differential expression of circadian clock genes (ccgs), are also present, often referred to as circadian phase markers. In the recent years, CR disturbances have been recognized as an essential aspect of depression; however, most of the known animal models of depression have yet to be evaluated for their eligibility to model CR disturbances. In this study, we investigate the potential of adrenocorticotropic hormone (ACTH)-treated animals as a disease model for research in CR disturbances in treatment-resistant depression. For this purpose, we evaluate the changes in several circadian phase markers, including plasma concentrations of corticosterone, ACTH, and melatonin, as well as gene expression patterns of 13 selected ccgs at 3 different time points, in both peripheral and central tissues. We observed no impact on plasma corticosterone and melatonin concentrations in the ACTH rats compared to vehicle. However, the expression pattern of several ccgs was affected in the ACTH rats compared to vehicle. In the hippocampus, 10 ccgs were affected by ACTH treatment, whereas in the adrenal glands, 5 ccgs were affected and in the prefrontal cortex, hypothalamus and liver 4 ccgs were regulated. In the blood, only 1 gene was affected. Individual tissues showed changes in different ccgs, but the expression of Bmal1, Per1, and Per2 were most generally affected. Collectively, the results presented here indicate that the ACTH animal model displays dysregulation of a number of phase markers suggesting the model may be appropriate for future studies into CR disturbances.

Low plasma melatonin levels negatively correlate with melasma severity

Background: Chronic exposure to ultraviolet light plays a role in the pathogenesis of melasma. Exposure to excessive sunlight leads to the formation of free radicals. As a result, the body responds by forming antioxidants such as melatonin, which is activated through the melatoninergic antioxidative system to fight oxidative stress. The relationship between melatonin and melasma is yet to be elucidated. This study aims to determine the correlation between melatonin and the severity of melasma. Methods: This analytical cross-sectional study involved 50 melasma subjects and 10 non-melasma subjects who met the inclusion criteria and were aged between 21-50 years at Prof. I.G.N.G. Ngoerah National General Hospital, Denpasar. The severity of melasma was measured by calculating the melasma area severity index (MASI) score and plasma melatonin levels were assessed using the ELISA method. Results: The median plasma melatonin level in the melasma subjects was lower (92.48 ng/ml) than in non-melasma subjects (436.35 ng/ml), with a p-value of Conclusion: Low plasma melatonin levels negatively-correlate with the severity of melasma.

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.

Disruption of central and peripheral circadian clocks and circadian controlled estrogen receptor rhythms in night shift nurses in working environments.

Chronic disruption of circadian rhythms by night shift work is associated with an increased breast cancer risk. However, little is known about the impact of night shift on peripheral circadian genes (CGs) and circadian-controlled genes (CCGs) associated with breast cancer. Hence, we assessed central clock markers (melatonin and cortisol) in plasma, and peripheral CGs (PER1, PER2, PER3, and BMAL1) and CCGs (ESR1 and ESR2) in peripheral blood mononuclear cells (PBMCs). In day shift nurses (n = 12), 24-h rhythms of cortisol and melatonin were aligned with day shift-oriented light/dark schedules. The mRNA expression of PER2, PER3, BMAL1, and ESR2 showed 24-h rhythms with peak values in the morning. In contrast, night shift nurses (n = 10) lost 24-h rhythmicity of cortisol with a suppressed morning surge but retained normal rhythmic patterns of melatonin, leading to misalignment between cortisol and melatonin. Moreover, night shift nurses showed disruption of rhythmic expressions of PER2, PER3, BMAL1, and ESR2 genes, resulting in an impaired inverse correlation between PER2 and BMAL1 compared to day shift nurses. The observed trends of disrupted circadian markers were recapitulated in additional day (n = 20) and night (n = 19) shift nurses by measurement at early night and midnight time points. Taken together, this study demonstrated the misalignment of cortisol and melatonin, associated disruption of PER2 and ESR2 circadian expressions, and internal misalignment in peripheral circadian network in night shift nurses. Morning plasma cortisol and PER2, BMAL1, and ESR2 expressions in PBMCs may therefore be useful biomarkers of circadian disruption in shift workers.

In Vitro Effects of Fentanyl on Aortic Viscoelasticity in a Rat Model of Melatonin Deficiency.

Melatonin influences arterial biomechanics, and its absence could cause remodeling of the arterial wall, leading to increased stiffness. Direct effects of fentanyl on the aortic wall have also been observed previously. This study aimed to evaluate in vitro the effects of fentanyl on aortic viscoelasticity in a rat model of melatonin deficiency and to test the hypothesis that melatonin deficiency leads to increased arterial wall stiffness. The viscoelasticity was estimated in strip preparations from pinealectomized (pin, melatonin deficiency) and sham-operated (sham, normal melatonin) adult rats using the forced oscillations method. In the untreated aortic wall pin, the viscoelasticity was not significantly altered. However, combined with 10-9 M fentanyl, the pin increased the natural frequency (f0) and modulus of elasticity (E') compared to the sham-operated. Independently, fentanyl treatment decreased f0 and E' compared separately to untreated sham and pin preparations. The effects of fentanyl were neither dose-dependent nor affected by naloxone, suggesting a non-opioid mechanism. Furthermore, an independent effect of naloxone was also detected in the normal rat aortic wall, resulting in reduced E'. Additional studies are needed that may improve the clinical decisions for pain management and anesthesia for certain patients with co-occurring chronic low levels of blood plasma melatonin and some diseases.

Sperm melatonin receptors, seminal plasma melatonin and semen freezability in goats

Goat bucks are seasonal breeders that show variation in sperm quality, endogenous melatonin (MLT), and presumably in the expression of MLT receptors on the sperm throughout the year, which may modify sperm freezability. The aim of this study was to determine whether sperm freezability is associated with (i) endogenous melatonin levels in seminal plasma and (ii) the expression of sperm plasma membrane melatonin receptors (MT1, MT2). To evaluate this, spermatozoa from seven Saanen goat bucks were cryopreserved throughout the year in Mexico using a standard freezing protocol. Seminal plasma MLT concentrations were determined by ELISA and the expression and localization of MT1 and MT2 were detected by immunocytochemistry and confirmed by western blotting. The recovery rate of progressive motility after thawing was higher in spring than autumn and winter; in contrast, the F pattern (CTC assay) was higher in winter than in the other seasons. A proportional increase in the AR pattern (CTC assay) was smaller in winter than in the other seasons and the proportion of sperm showing high plasma membrane fluidity was higher in spring than in summer and autumn. The seminal plasma MLT concentrations showed no significant interseasonal differences. The MT1 receptor was immunolocalised at the apical region of the sperm head, while MT2 was mainly localised in the neck. The relative expression of MLT receptors showed significant differences between summer and winter for all bands, except at 75 kDa of MT2. In conclusion, there was an association between the relative expression of MT1 and MT2 receptors throughout the year and sperm freezability in goat bucks in México. Post-thaw sperm quality is enhanced in semen samples collected during breeding season.

Levels of melatonin and some indicators of angiogenesis, antioxidant system and lipid peroxidation in blood plasma in women with uterine leiomyoma

Uterine leiomyoma is one of the most common gynaecological diseases, which often leads to loss of fertility. It is known that in this pathology, damage to the tissues of the uterus is accompanied by oxidative stress, and the mechanisms of its compensation play a decisive role in the process of myometrial regeneration, especially when performing organ-preserving operations. The aim of the study was to determine the levels of melatonin, reproductive hormones and state of angiogenesis, antioxidant system and lipid peroxidation in women of reproductive age who were diagnosed with uterine leiomyoma. Material and methods. 60 women of reproductive age with uterine leiomyoma (study group) were examined. The control group consisted of 20 healthy women of the same age group. Melatonin levels in women's blood were determined once, on an empty stomach, at 8 a.m.; the concentrations of estradiol and progesterone in the follicular phase of the menstrual cycle were also measured. The state of the angiogenesis system was studied by examining the levels of vascular endothelial growth factor (VEGF) and the content of the final metabolites of nitric oxide NO in blood plasma. The activity of the antioxidant system was assessed by blood plasma concentrations of reduced glutathione, glutathione peroxidase, and glutathione transferase. Indicators of lipid peroxidation were investigated by the content of malondialdehyde (MDA) in blood plasma and erythrocytes. Results. It was found that in the patients of the study group with leiomyoma, there was a significantly lower level of melatonin in blood plasma (111.1 ± 18.5 ng/mL) compared to the control group (153.5 ± 8.5 ng/mL), while the concentration of estradiol was almost three times higher (107.4 ± 25.3 pg/mL) compared to the control group (36.2 ± 3.2 pg/mL), and the concentration of progesterone was 1.9 times higher (2.1 ± 0.4 ng/mL compared to 1.1 ± 0.5 ng/mL in the control group). The level of VEGF in blood plasma in women with uterine leiomyoma was also higher (90.4 ± 23.6 pg/mL) compared to the control group (35.1 ± 8.3 pg/mL), as well as the concentration of final metabolites of nitric oxide, which reached 25.3 ± 5.9 pg/mL compared to 9.9 ± 3.9 pg/mL in the control group. The reduced glutathione level in the blood plasma of women with uterine leiomyoma was significantly lower (0.77 ± 0.13 µmol/L) compared to healthy women (1.02 ± 0.14 µmol/L) in the control group, while the concentrations of glutathione-S-transferase and glutathione peroxidase enzymes were higher (161.3 ± 22.3 ng/mL and 235.7 ± 35.9 ng/mL, respectively), whereas in the control group these indicators were 118.9 ± 18.0 ng/mL and 105.3 ± 41.2 ng/mL, respectively. The MDA content in women of the study group was higher, measuring 5.2 ± 0.8 nmol/L in plasma and 10.8 ± 1.1 nmol/L in erythrocytes compared to 2.3 ± 0.8 nmol/L and 5.3 ± 0.8 nmol/L in the control group, respectively. Conclusions. The levels of melatonin and reduced glutathione in the blood plasma of women with uterine leiomyoma were significantly lower, while the concentrations of estradiol, progesterone, glutathione-S-transferase, glutathione peroxidase, VEGF, final metabolites of nitric oxide, as well as the average MDA content in plasma and erythrocytes, were significantly higher compared to healthy women. In the study group, the relationship between the level of progesterone in blood plasma and the content of malondialdehyde in erythrocytes was described using a linear regression equation, which, as we suggest, indicates an activating effect of progesterone on oxidative stress mechanisms in the myometrium. In our opinion, oxidative stress in uterine leiomyoma occurs due to inadequate activity of the antioxidant system, an integral part of which is melatonin, leading to enhanced angiogenesis against the background of estrogen-induced myometrial proliferation.

Immune-pineal-ocular axis in amphibians: unveiling a novel connection?

Melatonin is a hormone known as an endogenous temporal marker signaling the dark phase of the day. Although the eyes seem to be the main site of melatonin production in amphibians, little information is available about the natural variation in the ocular melatonin levels and its modulation following immune stimulation. We investigated the daily variation of plasma and ocular melatonin levels in bullfrogs (Lithobates catesbeianus) and their modulation following an immune stimulation with lipopolysaccharide (LPS) in yellow cururu toads (Rhinella icterica). For the daily variation, bullfrogs were bled and then euthanized for eye collection every 3h over 24h to determine plasma and ocular melatonin levels. We found a positive correlation between ocular and plasma melatonin levels, with maximum values at night (22h) for both plasma and the eyes. For immune stimulation, yellow cururu toads received an intraperitoneal injection of LPS or saline solution during the day (10h) or at night (22h). Two hours after injection, toads were bled and euthanized for eye collection to obtain plasma and ocular melatonin levels. In addition, the liver and bone marrow were collected to investigate local melatonin modulation. Our results demonstrate that retina light-controlled rhythmic melatonin production is suppressed while liver and bone marrow melatonin levels increase during the inflammatory assemblage in anurans. Interestingly, the LPS injection decreased only ocular melatonin levels, reinforcing the central role of the eyes (i.e., retina) as an essential organ of melatonin production, and a similar role to the pineal gland during the inflammatory response in amphibians. Together, these results point to a possible immune-pineal-ocular axis in amphibians, yet to be fully described in this group.

Changes in Behavior and Diel Melatonin Secretion Toward Estivation in Western Sand Lance, Ammodytes japonicus (Uranoscopiformes, Ammodytidae).

Western sand lance, Ammodytes japonicus, is known to have an estivation period, in which they cease feeding and stay in the sand from early summer to late autumn, followed by gonadal maturation. During the feeding period prior to estivation, they swim in daytime and spend the night in the sand. Before they start swimming, they show a typical behavior of head-exposing from the sand, which is likely to be related to foraging and predation avoidance. Our previous study revealed that melatonin regulates such diel behavior of this species. To elucidate the mechanisms of behavioral regulation throughout the life cycle of this sand lance, the present study examined the changes in behavior and melatonin secretion toward the estivation period. Both head-exposing and swimming behaviors were frequently observed at the transition period toward estivation. On the other hand, occurrence of these behaviors was suppressed just before entering estivation. Subsequently, it was found that plasma melatonin concentration was about three times higher at night than in daytime in the non-estivation period, while it was retained at high levels throughout the day in the estivation period. These results indicate that diurnal swimming behavior of sand lance from the feeding to estivation periods is associated with the daily cycle of melatonin secretion.

Melatonin alleviates endoplasmic reticulum stress to improve ovarian function by regulating the mTOR pathway in aged laying hens

Granular cell apoptosis is a key factor leading to follicular atresia and decreased laying rate in aged laying hens. Endoplasmic reticulum stress (ERS) induced cell apoptosis is a new type of apoptosis pathway. Previous studies have shown that the ERS pathway is involved in the regulation of follicular development and atresia, and can be regulated by mTOR. Melatonin (MEL) can protect the normal development of follicles, but the precise mechanism by which MEL regulates follicular development is not yet clear. So, we investigated the potential relationship between MEL and ERS and mTOR signaling pathway in vivo through intraperitoneal injection of MEL in aged laying hens. The results show that the laying rate, ovarian follicle number, plasma MEL, E2, LH, FSH concentrations, as well as the mRNA expression of mTOR signaling-associated genes TSC1, TSC2, mTOR, 4E-BP1, and S6K in old later-period chicken control (Old-CN) group was significantly decreased (P < 0.01). In contrast, the ERS-related of plasma and granular cell layer mRNA expression of Grp78, CHOP, and Caspase-3 was significantly increased (P < 0.01). While both of the effects were reversed by MEL. Then, aging granulosa cells were treated with MEL in vitro, followed by RNA seq analysis, and it was found that 259 and 322 genes were upregulated and downregulated. After performing GO enrichment analysis, it was found that DEGs significantly contribute to the biological processes including cell growth and apoptosis. Using pathway enrichment analysis, we found significant overrepresentation of cellular processes related to mTOR signaling and endoplasmic reticulum (ER) stress, involving genes such as GRB10, SGK1, PRKCA, RPS6KA2, RAF1, PIK3R3, FOXO1, DERL3, HMOX1, TLR7, VAMP7 and INSIG2. The obtained results of RT-PCR showed consistency with the RNA-Seq data. In summary, the underlined results revealed that MEL has significantly contributed to follicular development via activating the mTOR signaling pathway-related genes and alleviating ERS-related genes in laying hens. The current study provides a theoretical background for enhancing the egg-laying capability of hens and also providing a basis for elucidating the molecular mechanism of follicular selection.

Effect of exogenous melatonin implant on post-thaw semen quality of buffalo bulls.

Melatonin is an intracellular antioxidant of sperm membrane that protects the cells from lipid peroxidation. Yet, its role as an antioxidant on semen quality of buffalo bulls is still obscure. The present study was undertaken to assess the effect of exogenous melatonin implant (18 mg/50 kg bodyweight) on post-thaw sperm characteristics, oxidative stress, endocrinological profiles and fertility of buffalo bulls. Six apparently healthy breeding Murrah buffalo bulls were randomly selected at bull farm, Guru Angad Dev Veterinary and Animal Sciences University for the present study and divided into two groups viz. control (n = 3) and melatonin implanted group (n = 3). A total of 120 ejaculates were collected from bulls of both groups (n = 60 each) throughout the study period. Most beneficial effects of melatonin implants were observed during post-implantation period. The percentages of post-thaw sperm total and progressive motility, viability and mitochondrial membrane potential were higher (p < .05) in melatonin implanted buffalo bulls compared to controls during post-implantation period. Following melatonin implantation, MDA production in post-thaw semen was lower (p < .05) in melatonin implanted group than in control group. Plasma melatonin and testosterone concentrations were higher (p < .05) in buffalo bulls implanted with melatonin as compared to their control counterparts. No differences (p > .05) in plasma LH concentrations were observed in both groups. First service pregnancy rate was 43.3% using semen of melatonin implanted bulls and 30.0% with semen of controls (p > .05). Thus, melatonin was able to protect sperm membrane against oxidative damage and improve post-thaw semen quality, thereby resulting in higher fertilizing potential of spermatozoa.