Melatonin receptor subtypes Mel1a and Mel1c but not Mel1b are associated with monochromatic light-induced B-lymphocyte proliferation in broilers

Immunoregulatory properties of melatonin in the humoral immune system: A narrative review

Melatonin is the major product both synthesized and secreted by the pineal gland during the night period and it is the principal chronobiotic hormone that regulates the circadian rhythms and seasonal changes in vertebrate biology. Moreover, melatonin shows both a broad distribution along the phylogenetically distant organisms and a high functional versatility. At the present time, a significant amount of experimental evidence has been reported in scientific literature and has clearly shown a functional relationship between the endocrine, nervous, and immune systems. The biochemistry basis of the functional communication between these systems is the utilization of a common chemicals signals. In this framework, at present melatonin is considered to be a relevant member of the so-called neuro-endocrine-immunological network. Thus, both in vivo and in vitro investigations conducted in both experimental animals and humans, have clearly documented that melatonin has an important immunomodulatory role. However, most of the published results refer to information on T lymphocytes, i.e., cell-mediated immunity. On the contrary, fewer studies have been carried out on B lymphocytes, the cells responsible for the so-called humoral immunity. In this review, we have focused on the biological role of melatonin in the humoral immunity. More precisely, we report the actions of melatonin on B lymphocytes biology and on the production of different types of antibodies.

Melatonin in animal husbandry: functions and applications

Melatonin (N-acetyl-5-methoxytryptamine) is an essential small molecule with diverse biological functions. It plays several key roles, including regulating the secretion of reproductive hormones and the reproductive cycle, enhancing the functionality of reproductive organs, improving the quality of sperm and eggs, and mitigating oxidative stress in the reproductive system. Melatonin effectively inhibits and scavenges excess free radicals while activating the antioxidant enzyme system and reduces the production of inflammatory factors and alleviates tissue damage caused by inflammation by regulating inflammatory pathways. Additionally, melatonin contributes to repairing the intestinal barrier and regulating the gut microbiota, thereby reducing bacterial and toxin permeation. The use of melatonin as an endogenous hormone in animal husbandry has garnered considerable attention because of its positive effects on animal production performance, reproductive outcomes, stress adaptation, disease treatment, and environmental sustainability. This review explores the characteristics and biological functions of melatonin, along with its current applications in animal production. Our findings may serve as a reference for the use of melatonin in animal farming and future developmental directions.

Influence of Different Light Spectra on Melatonin Synthesis by the Pineal Gland and Influence on the Immune System in Chickens

It is well known that the pineal gland in birds influences behavioural and physiological functions, including those of the immune system. The purpose of this research is to examine the endocrine-immune correlations between melatonin and immune system activity. Through a description of the immune-pineal axis, we formulated the objective to determine and describe: the development of the pineal gland; how light influences secretory activity; and how melatonin influences the activity of primary and secondary lymphoid organs. The pineal gland has the ability to turn light information into an endocrine signal suitable for the immune system via the membrane receptors Mel1a, Mel1b, and Mel1c, as well as the nuclear receptors RORα, RORβ, and RORγ. We can state the following findings: green monochromatic light (560 nm) increased serum melatonin levels and promoted a stronger humoral and cellular immune response by proliferating B and T lymphocytes; the combination of green and blue monochromatic light (560-480 nm) ameliorated the inflammatory response and protected lymphoid organs from oxidative stress; and red monochromatic light (660 nm) maintained the inflammatory response and promoted the growth of pathogenic bacteria. Melatonin can be considered a potent antioxidant and immunomodulator and is a critical element in the coordination between external light stimulation and the body's internal response.

Prolonging photoperiod promotes testosterone synthesis of Leydig cells by directly targeting local melatonin system in rooster testes

The study investigated the effects of prolonging photoperiod on the synthesis of testosterone and melatonin in roosters, and the effect of melatonin on testosterone synthesis in rooster Leydig cells as well as its molecular mechanisms. We randomly divided one hundred and twenty 20-week-old roosters into three groups and provided 6, 12.5 and 16 h light, respectively. The results showed that prolonging photoperiod promoted testosterone synthesis, decreased melatonin production, and inhibited the expression of melatonin membrane receptors MEL1A, MEL1B, MEL1C, and aralkylamine n-acetyltransferase (AANAT) in rooster testes. Subsequently, rooster Leydig cells were isolated and treated with 0, 0.1, 1, 10, and 100 ng/mL melatonin for 36 h. The results suggested that melatonin inhibited testosterone synthesis in rooster Leydig cells, and silencing MEL1A and MEL1B relieved the inhibition of melatonin on testosterone synthesis. Additionally, melatonin reduced the intracellular cyclic adenosine monophosphate (cAMP) level and the phosphorylation level of cAMP-response element binding protein (CREB), and CREB overexpression alleviated the inhibition of melatonin on testosterone synthesis. Furthermore, pretreatment with cAMP activator forskolin or protein kinase A (PKA) activator 8-bromo-cAMP blocked the inhibition of melatonin on CREB phosphorylation and testosterone synthesis. These results indicated that prolonging photoperiod promoted testosterone synthesis associated with the decrease in melatonin production and membrane receptors and biosynthetic enzyme of melatonin in rooster testes, and melatonin inhibited testosterone synthesis of rooster Leydig cells by inhibiting the cAMP/PKA/CREB pathway via MEL1A and MEL1B. This may be evidence that prolonging photoperiod could promote testosterone synthesis through the inhibition of the local melatonin pathway in rooster testes.

Melatonin mediates monochromatic light-induced expression of somatostatin in the hypothalamus and pituitary of chicks

Melatonin (MEL) plays an important role in regulating growth and development of organisms and the cellular metabolism. This study was conducted to explore the role of MEL in mediating monochromatic light-induced secretion of somatostatin (SST) in the hypothalamus and pituitary in chicks. Pinealectomy models of newly hatched broilers were exposed to white (WL), red (RL), green (GL), and blue (BL) lights. The results showed that SST immunoreactive neurons and fibers were distributed in the hypothalamus. SST and SST receptor 2 (SSTR2) mRNA and protein levels in the hypothalamus and pituitary were higher in chicks exposed to RL than in chicks exposed to GL and BL. However, after pinealectomy, the mRNA and protein levels of SST and SSTR2 in the hypothalamus and pituitary in the different light groups were increased, and the differences between the groups disapeared. The expression trend of SSTR5 mRNA in the pituitary was the idential to that of SSTR2 mRNA in the pituitary. In vitro, exogenous SST inhibited growth hormone (GH) secretion, and selective antogonists of SSTR2 and SSTR5 promoted GH secretion. Selective antogonists of the melatonin receptor 1b (Mel1b) and Mel1c increased the relative concentrations of SST in the adenohypophysis cells. These results indicated that monochromatic light affects the expression of SST in chick hypothalamus and pituitary. MEL, via Mel1b and Mel1c, decreased SST secretion under GL, which was associated with the inhibition of SST, SSTR2, and SSTR5 in adenohypophysis cells.

Effects of Monochromatic Lighting During Incubation and Vaccination on the Splenic Transcriptome Profiles of Chicken

Lighting is a crucial environmental variable in poultry operations, but illumination during incubation is relatively understudied. The ability to stimulate development or immune performance using in ovo lighting is a promising approach for improving poultry health and welfare. This study investigated how monochromatic green light during incubation and vaccination method and timing affected chicken splenic gene expression patterns. We performed this study with 1,728 Hy-Line white layer eggs incubated under two light treatments during incubation: continuous dark and continuous green monochromatic light, over the entire incubation period. Half the eggs in each light treatment received in ovo vaccination, applied on embryonic day 18 (ED18). The remaining half were vaccinated by spraying on hatch day. After hatching, the light treatments followed the industry-standard lighting regimens. The study had six treatment groups with light-dark pairs for non-vaccinated, in ovo vaccinated, and post-hatch vaccinated. We assessed splenic gene expression at ED18 and at 7 days post-hatch (PH) in all the treatments. We isolated and sequenced 24 mRNA libraries on the Illumina platform, followed by bioinformatics and differential gene expression analyses. RNAseq analysis showed between 62 and 6,755 differentially expressed genes (DEGs) between comparisons, with the most prominent differences observed between ED and PH samples, followed by comparisons between vaccination methods. In contrast, light vs. dark treatments at ED showed limited effects on transcriptomic profiles. However, we observed a synergistic effect of lighting during incubation on post-hatch vaccination responses, with differentially expressed genes (DEGs) unique to the light treatment showing stimulation of cell proliferation with significance for immune activity (inferred from gene ontology terms). Gene ontology and pathway analysis indicated biological processes like cellular component organization or biogenesis, rhythmic process, developmental process, response to stimulus, and immune system processes were explained by the DEGs. While lighting is an important source of circadian stimulation, other controlled studies are required to clarify whether in ovo circadian entrainment plays a role in modulating immune responses.

Melatonin mediates monochromatic light-induced proliferation of T/B lymphocytes in the spleen via the membrane receptor or nuclear receptor

Our studies found that melatonin mediates the monochromatic light–induced lymphocyte proliferation in chickens. However, melatonin receptor subtypes contain membrane receptor (Mel1a/Mel1b/Mel1c) and nuclear receptor (Retinoic acid receptor–related orphan receptor [ROR] α/RORβ/RORγ) and are characteristic with cell specificity. This study compared receptor pathway of melatonin, which mediated the monochromatic light–induced T/B lymphocyte proliferations in chickens. Newly hatched chicks were randomly divided into white light, red light, green light (GL), and blue light groups. Green light promoted the membrane receptor expression in the spleen but decreased the nuclear receptor level compared with that of red light. These changes were accompanied by increase of T/B lymphocyte proliferation and plasma melatonin level under GL. Pinealectomy reversed aforementioned changes and resulted in no differences among the light-treated groups. Supplementation of exogenous melatonin enhanced GL-induced T/B lymphocyte proliferation in the spleen but was reversed by Mel1c antagonist prazosin and RORα agonist SR1078 and enhanced by RORα antagonist SR3335. However, Mel1b antagonist 4P-PDOT and RORγ antagonist GSK increased the stimulation effect of melatonin on GL-induced T lymphocyte proliferation but no effect on the B-lymphocyte proliferation. These results indicate that melatonin promotes the GL-induced T lymphocyte proliferation through Mel1b, Mel1c, and RORα/RORγ; however, the Mel1a, Mel1c, and RORα may be involved in the B lymphocyte proliferation.

Melatonin Promotes the Proliferation of Chicken Sertoli Cells by Activating the ERK/Inhibin Alpha Subunit Signaling Pathway

Melatonin influences physiological processes such as promoting proliferation and regulating cell development and function, and its effects on chicken Sertoli cells are unknown. Therefore, we investigated the effects of melatonin on cell proliferation and its underlying mechanisms in chicken Sertoli cells. Chicken Sertoli cells were exposed to varying melatonin concentrations (1, 10, 100, and 1000 nM), and the melatonin-induced effects on cell proliferation were measured by Cell Counting Kit 8 (CCK-8), 5-ethynyl-2'-deoxyuridine (EdU), real-time qPCR, and western blotting. We found that 1000 nM melatonin significantly (p < 0.05) promoted cell proliferation in chicken Sertoli cells. Furthermore, melatonin significantly (p < 0.05) increased the expression of inhibin alpha subunit (INHA), and the silencing of INHA reversed the melatonin-induced effects on Sertoli cell proliferation. We also found that melatonin activates the extracellular-regulated protein kinase (ERK) signaling pathway. To explore the role of the ERK signaling pathway in melatonin-induced cell proliferation, PD98059 (an inhibitor of EKR1/2) was used to pre-treat chicken Sertoli cells. The melatonin-induced proliferation of chicken Sertoli cells was reversed by PD98059, with decreased cell viability, weakened cell proliferation, and down-regulated expression of the proliferating cell nuclear antigen (PCNA), cyclin D1 (CCND1) and INHA. In summary, our results indicate that melatonin promotes the proliferation of chicken Sertoli cells by activating the ERK/inhibin alpha subunit signaling pathway.

Melatonin mediates mucosal immune cells, microbial metabolism, and rhythm crosstalk: A therapeutic target to reduce intestinal inflammation

Nowadays, melatonin, previously considered only as a pharmaceutical product for rhythm regulation and sleep aiding, has shown its potential as a co-adjuvant treatment in intestinal diseases, however, its mechanism is still not very clear. A firm connection between melatonin at a physiologically relevant concentration and the gut microbiota and inflammation has recently established. Herein, we summarize their crosstalk and focus on four novelties. First, how melatonin is synthesized and degraded in the gut and exerts potentially diverse phenotypic effects through its diverse metabolites. Second, how melatonin mediates the activation and proliferation of intestinal mucosal immune cells with paracrine and autocrine properties. By modulating T/B cells, mast cells, macrophages and dendritic cells, melatonin immunomodulatory involved in regulating T-cell differentiation, intervening T/B cell interaction and attenuating the production of pro-inflammatory factors, achieving its antioxidant action via specific receptors. Third, how melatonin exerts antimicrobial action and modulates microbial components, such as lipopolysaccharide, amyloid-β peptides via nuclear factor κ-light-chain-enhancer of activated B cells (NF-κB) or signal transducers and activators of transcription (STAT1) pathway to modulate intestinal immune function in immune-pineal axis. The last, how melatonin mediates the effect of intestinal bacterial activity signals on the body rhythm system through the NF-κB pathway and influences the mucosal epithelium oscillation via clock gene expression. These processes are achieved at mitochondrial and nuclear levels to control the host immune cell development. Considering unclear mechanisms and undiscovered actions of melatonin in gut-microbiome-immune axis, it's time to reveal them and provide new insight for the outlook of melatonin as a potential therapeutic target in the treatment and management of intestinal diseases.

Melatonin Receptor Mel1b- and Mel1c-mediated Green Light Induced the Secretion of Growth Hormone in Anterior Pituitary of Chicks

Previous studies have found that melatonin was related to the growth and development in avian. Therefore, the newly hatched broilers were exposed to colors of light to establish a model of pinealectomy and explored the mechanism of pineal melatonin promoting growth hormone (GH) secretion. The results showed that green light (GL) promoted the levels of GH, pituitary-specific transcription factor-1 (Pit-1) genes and proteins in pituitary. Moreover, the mRNA and protein levels of melatonin receptor subtypes Mel1b and Mel1c in the pituitary in GL were higher than other monochromatic light groups. After pinealectomy, the expression of Pit-1, GH, Mel1b and Mel1c in pituitary decreased. In vitro, exogenous melatonin promoted the level of Pit-1 mRNA and the secretion of GH in anterior pituitary cells. However, when melatonin was added with exogenous selective Mel1b antagonist (4-phenyl-2-propionamideotetralin) and selective Mel1c antagonist (prazosin), the level of Pit-1 mRNA and the GH secretion decreased. When selective Mel1b and Mel1c antagonists were added simultaneously, the decrease in Pit-1 mRNA and GH secretion was more significant. These results indicated that pineal melatonin promotes the expression of Pit-1 under GL by binding to melatonin receptor subtypes Mel1b and Mel1c in the pituitary, thereby increasing GH secretion and promoting the growth.

Natural Selection Footprints Among African Chicken Breeds and Village Ecotypes

Natural selection is likely a major factor in shaping genomic variation of the African indigenous rural chicken, driving the development of genetic footprints. Selection footprints are expected to be associated with adaptation to locally prevailing environmental stressors, which may include diverse factors as high altitude, disease resistance, poor nutrition, oxidative and heat stresses. To determine the existence of a selection footprint, 268 birds were randomly sampled from three indigenous ecotypes from East Africa (Rwanda and Uganda) and North Africa (Baladi), and two registered Egyptian breeds (Dandarawi and Fayoumi). Samples were genotyped using the chicken Affymetrix 600K Axiom^® Array. A total of 494,332 SNPs were utilized in the downstream analysis after implementing quality control measures. The intra-population runs of homozygosity (ROH) that occurred in >50% of individuals of an ecotype or in >75% of a breed were studied. To identify inter-population differentiation due to genetic structure, F_ST was calculated for North- vs. East-African populations and Baladi and Fayoumi vs. Dandarawi for overlapping windows (500 kb with a step-size of 250 kb). The ROH and F_ST mapping detected several selective sweeps on different autosomes. Results reflected selection footprints of the environmental stresses, breed behavior, and management. Intra-population ROH of the Egyptian chickens showed selection footprints bearing genes for adaptation to heat, solar radiation, ion transport and immunity. The high-altitude-adapted East-African populations' ROH showed a selection signature with genes for angiogenesis, oxygen-heme binding and transport. The neuroglobin gene (GO:0019825 and GO:0015671) was detected on a Chromosome 5 ROH of Rwanda-Uganda ecotypes. The sodium-dependent noradrenaline transporter, SLC6A2 on a Chromosome 11 ROH in Fayoumi breed may reflect its active behavior. Inter-population F_ST among Egyptian populations reflected genetic mechanisms for the Fayoumi resistance to Newcastle Disease Virus (NDV), while F_ST between Egyptian and Rwanda-Uganda populations indicated the Secreted frizzled related protein 2, SFRP2, (GO:0009314) on Chromosome 4, that contributes to melanogenic activity and most likely enhances the Dandarawi chicken adaptation to high-intensity of solar radiation in Southern Egypt. These results enhance our understanding of the natural selection forces role in shaping genomic structure for adaptation to the stressful African conditions.

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.

Physiological crosstalk between the AC/PKA and PLC/PKC pathways modulates melatonin-mediated, monochromatic-light-induced proliferation of T-lymphocytes in chickens

Previous study has demonstrated that melatonin plays a critical role in monochromatic-light-induced lymphocyte proliferation in response to T cell mitogen concanavalin A (ConA). However, its intracellular mechanism is still unclear. In this study, we investigate the intracellular signal pathways of melatonin receptor-mediated T-lymphocyte proliferation in the spleens of chicks exposed to different light wavelengths. Results showed that green light enhanced T-lymphocyte proliferation by 2.46-6.83% and increased splenic mRNA and protein expressions of melatonin receptor subtypes (Mel1a, Mel1b and Mel1c) by 16.05-40.43% compared with the white, red and blue light groups. However, pinealectomy resulted in a decrease in T-lymphocyte proliferation and melatonin receptor expression with no statistically significant differences between the different light groups. In vitro experiments showed that the Mel1b selective antagonist 4P-PDOT, the Mel1c selective antagonist prazosin and the mitogen-activated protein kinase kinase-1 (MEK-1) inhibitor PD98059 suppressed both melatonin-induced lymphocyte proliferation in response to ConA and melatonin- and ConA-stimulated extracellular signal-regulated kinase 1/2 (ERK1/2) activity but that the Mel1a/Mel1b non-selective antagonist luzindole did not. In addition, pretreatment with forskolin (FSK, the adenylyl cyclase activator), H89 (the PKA inhibitor), U73122 (the PLC inhibitor) or Go6983 (the broad spectrum PKC inhibitor) markedly attenuated melatonin- and ConA-stimulated T-lymphocyte proliferation and ERK1/2 activity. These results demonstrate that melatonin mediates green-light-induced T-lymphocyte proliferation via the Mel1b and Mel1c receptors by triggering crosstalk between the cAMP/PKA and PLC/PKC signal pathways followed by ERK1/2 activation.

Green light inhibits GnRH-I expression by stimulating the melatonin-GnIH pathway in the chick brain

To study the mechanism by which monochromatic light affects gonadotrophin-releasing hormone (GnRH) expression in chicken hypothalamus, a total of 192 newly-hatched chicks were divided into intact, sham-operated and pinealectomy groups and exposed to white (WL), red (RL), green (GL) and blue (BL) lights using a light-emitting diode system for 2 weeks. In the GL intact group, the mRNA and protein levels of GnRH-I in the hypothalamus, the mean cell area and mean cell optical density (OD) of GnRH-I-immunoreactive (-ir) cells of the nucleus commissurae pallii were decreased by 13.2%-34.5%, 5.7%-39.1% and 9.9%-17.3% compared to those in the chicks exposed to the WL, RL and BL, respectively. GL decreased these factors related to GnRH-I expression and the effect of GL was not observed in pinealectomised birds. However, the mRNA and protein levels of hypothalamic gonadotrophin-inhibitory hormone (GnIH) and GnIH receptor (GnIHR), the mean cell area and mean cell OD of the GnIH-ir cells of the paraventricularis magnocellularis, and the plasma melatonin concentration in the chicks exposed to GL were increased by 18.6%-49.2%, 21.1%-60.0% and 8.6%-30.6% compared to the WL, RL and BL intact groups, respectively. The plasma melatonin concentration showed a negative correlation with GnRH-I protein and a positive correlation with GnIH and GnIHR proteins. Protein expression of both GnRH-I and GnIHR showed a negative correlation in the hypothalamus. After pinealectomy, GnRH-I expression increased, whereas plasma melatonin concentration, GnIH and GnIHR expression decreased, and there were no significant differences among the WL, RL, GL and BL groups. Double-labelled immunofluorescence showed that GnIH axon terminals were near GnRH-I neurones, some GnRH-I neurones coexpressed with GnIHR and GnIH neurones coexpressed with melatonin receptor subtype quinone reductase 2. These results demonstrate that green light inhibits GnRH-I expression by increasing melatonin secretion and stimulating melatonin receptor-GnIH-GnIH receptor pathway in the chick brain.

Effect of Monochromatic Light on Expression of Estrogen Receptor (ER) and Progesterone Receptor (PR) in Ovarian Follicles of Chicken

Artificial illumination is widely used in modern poultry houses and different wavelengths of light affect poultry production and behaviour. In this study, we measure mRNA and protein abundance of estrogen receptors (ERs) and progesterone receptors (PRs) in order to investigate the effect of monochromatic light on egg production traits and gonadal hormone function in chicken ovarian follicles. Five hundred and fifty-two 19-wk-old laying hens were exposed to three monochromatic lights: red (RL; 660 nm), green (GL; 560 nm), blue (BL; 480 nm) and control cool white (400–760 nm) light with an LED (light-emitting diode). There were 4 identical light-controlled rooms (n = 138) each containing 3 replicate pens (46 birds per pen). Water was supplied ad libitum and daily rations were determined according to the nutrient suggestions for poultry. Results showed that under BL conditions there was an increase in the total number of eggs at 300 days of age and egg-laying rate during the peak laying period. The BL and GL extended the duration of the peak laying period. Plasma melatonin was lowest in birds reared under BL. Plasma estradiol was elevated in the GL-exposed laying hens, and GL and BL increased progesterone at 28 wk of age. In the granulosa layers of the fifth largest preovulatory follicle (F5), the third largest preovulatory follicle (F3) and the largest preovulatory follicle (F1), ERα mRNA was increased by BL and GL. Treatment with BL increased ERβ mRNA in granulosa layers of F5, F3 and F1, while GL increased ERβ mRNA in F5 and F3. There was a corresponding increase in abundance of the proteins in the granulosa layers of F5, with an increase in PR-B, generated via an alternative splice site, relative to PR-A. Treatment with BL also increased expression of PR mRNA in all of the granulosa layers of follicles, while treatment with GL increased expression of PR mRNA in granulosa layers of SYF(small yellow follicle), F5 and F1. These results indicate that blue and green monochromatic lights promote egg production traits via stimulating gonadal hormone secretion and up-regulating expression of ERs and PRs. Changes in PR-B protein suggest that this form of the progesterone receptor is predominant for progesterone action in the granulosa layers of preovulatory follicles in chickens during light stimulation.

Developmental changes of melatonin receptor expression in the spleen of the chicken, Gallus domesticus

Melatonin plays an essential role in development and immunoregulation of the avian spleen through its receptors; however, the variations in the expression of the melatonin receptor subtypes in the developing avian spleen are still unclear. The objective of the present study was not only to investigate the distribution patterns and development changes of the expression of the melatonin receptor subtypes (Mel1a, Mel1b and Mel1c) in the chicken spleen but also to identify the correlation between the plasma melatonin concentration and the expression of the melatonin receptor subtypes. The immunohistochemical results indicated that Mel1a was mainly distributed in the red pulp and capillaries, Mel1b was predominantly distributed in the periarterial lymphatic sheath (PALS) and splenic nodule, and Mel1c was widely located in the red pulp, PALS and splenic nodule. From P0 to P21, the mRNA and protein expressions of Mel1a, Mel1b and Mel1c in the spleen were increased (P<0.05); however, a slight increase in the expression of the three melatonin receptor subtypes was observed after P21 (P>0.05). Furthermore, the mRNA levels of Mel1b and Mel1c between P0 and P14 raised more quickly than Mel1a. The plasma melatonin concentration increased in an age-dependent manner in the chicken from P0 to P42 (P<0.05), and this increasing change was linear after P14 (P<0.05). The melatonin level in the plasma is strongly correlated with the protein expressions of Mel1a (r=0.938, P=0.005), Mel1b (r=0.912, P=0.011), and Mel1c (r=0.906, P=0.012) in the chicken spleen. These results suggest the existence of age-related and region-specific changes in the expression of the melatonin receptor subtypes within the spleen of the chicken, and this characteristic pattern may be involved in the development and functional maturation of the avian spleen.

Restraint stress alters immune parameters and induces oxidative stress in the mouse uterus during embryo implantation

The influence of stress on embryo implantation is not well understood. Prior studies have focused on later gestational stages and the long-term impact of stress on immune function. The objective of this study is to investigate the effects of restraint stress on the immune parameters and the oxidative states of the uterus during implantation. In this study, pregnant CD1 mice were subjected to restraint stress (4 h/d) on embryonic day 1 (E1) and sacrificed on E3, E5, and E7. Maternal plasma corticosterone (CORT) secretion and implantation sites in the uterus were examined. The uterine (excluding embryos) homogenate and uterine lymphocytes were collected to examine oxidative stress states and associated immune parameters. The results demonstrated that restraint stress increased maternal plasma CORT secretion and reduced the number of implantation sites by 15.3% on E5 and by 26.1% on E7. Moreover, restraint stress decreased the density of uterine natural killer (uNK) cells in the endometrium by 22.1-47.9% and increased the density of mast cells in the myometrium by 55.6-76.9%. Restraint stress remarkably decreased the CD3(+)CD4(+) T/CD3(+)CD8(+) T cell ratio (by 26.2-28.9%) and attenuated uterine lymphocyte proliferation and secretion of cytokines. In addition, restraint stress threatened the intracellular equilibrium between oxidants and antioxidants, resulting in decreased glutathione peroxidase (GSH-PX) (32.2% and 45.7%), superoxide dismutase (SOD) (15.5% and 26.1%), and total antioxidant capacity (T-AOC) (18.4% and 18.2%) activities and increased malondialdehyde (MDA) (34.4% and 43.0%) contents on E5 and E7. In conclusion, these findings demonstrate that restraint stress causes abnormal implantation and negatively impacts immune parameters in association with oxidative stress in mice.

The melatonin analog 5-MCA-NAT increases endogenous dopamine levels by binding NRH:quinone reductase enzyme in the developing chick retina

NRH:quinone reductase (QR2) is present in the retinas of embryonic and post-hatched (PH) chicks. 5-Methoxycarbonylamino-N-acetyltryptamine (5-MCA-NAT) is a QR2 ligand that increases cAMP levels in developing retinas, but it does not affect cAMP levels in CHO-QR2 cells. The dopamine quinone reductase activity of QR2 retrieves dopamine, which increases cAMP levels in developing retinas. The objective of the present study was to investigate whether 5-MCA-NAT increases endogenous dopamine levels in retinas from chick embryos and post-hatched chicks. Endogenous dopamine was measured by enzyme-linked immunosorbent assay (ELISA). 5-MCA-NAT increased retinal endogenous dopamine levels at all developmental stages studied and in PH chicks (-logEC50=11.62±0.34 M). This effect was inhibited by non-selective antagonists of receptors and melatonin binding sites N-acetyl-2-benzyltryptamine (luzindole, 5 μM), but it was not inhibited by the Mel1b melatonin receptor antagonist 4-phenyl-2-propionamidotetralin (4-P-PDOT, 10 nM). The QR2 cosubstrate, N-methyl-dihydronicotinamide (NMH) (-logEC50=6.74±0.26 M), increased endogenous dopamine levels in controls and in retinas stimulated with 5-MCA-NAT (3 nM). The QR2 inhibitor benzo[e]pyrene inhibited endogenous dopamine levels in both control (-logIC50=7.4±0.28 M) and NMH-stimulated (at 100 nM and 1 μM benzo[e]pyrene concentrations) retinas. Theoretical studies using Molegro Virtual Docking software corroborated these experimental results. We conclude that 5-MCA-NAT increases the level of endogenous dopamine via QR2. We suggest that this enzyme triggers double reduction of the dopamine quinone, recovering dopamine in retinal development.