Intraperitoneal Injection Of Melatonin Research Articles

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.

Melatonin protects photoreceptor cells against ferroptosis in dry AMD disorder by inhibiting GSK-3B/Fyn-dependent Nrf2 nuclear translocation

BackgroundFerroptosis is a type of non-apoptotic cell death that relies on iron ions and reactive oxygen species to induce lipid peroxidation. This study aimed to determine whether ferroptosis exists in the pathogenesis of dry age-related macular degeneration (AMD) and to confirm that melatonin (MLT) suppresses the photoreceptor cell ferroptosis signaling pathway. MethodsWe exposed 661W cells to sodium iodate (NaIO3) in vitro and treated them with different concentrations of MLT. In vivo, C57BL/6 mice were given a single caudal vein injection of NaIO3, followed by an intraperitoneal injection of MLT, and eyeballs were taken for subsequent trials. ResultsWe found that NaIO3 could induce photoreceptor cell death and lipid peroxide accumulation, and result in changes in the expression of ferroptosis-related factors and iron maintenance proteins, which were treated by MLT. We further demonstrated that MLT can block Fyn-dependent Nrf2 nuclear translocation by suppressing the GSK-3β signaling pathway. In addition, the therapeutic effect of MLT was significantly inhibited when Nrf2 was silenced. ConclusionsOur findings provide a novel insight that NaIO3 induces photoreceptor cell ferroptosis in dry AMD and suggest that MLT has therapeutic effects by suppressing GSK-3β/Fyn-dependent Nrf2 nuclear translocation.

Melatonin alleviates early brain injury by inhibiting the NRF2-mediated ferroptosis pathway after subarachnoid hemorrhage

Ferroptosis is a novel form of cell death that plays a critical role in the pathological and physiological processes of early brain injury following subarachnoid hemorrhage. Melatonin, as the most potent endogenous antioxidant, has shown strong protective effects against pathological changes following subarachnoid hemorrhage, but its impact on ferroptosis induced by subarachnoid hemorrhage remains unexplored. In our study, we established a subarachnoid hemorrhage model in male SD rats. We found that subarachnoid hemorrhage induced changes in ferroptosis-related indicators such as lipid peroxidation and iron metabolism, while intraperitoneal injection of melatonin (40 mg/kg) effectively ameliorated these changes to a certain degree. Moreover, in a subset of rats with subarachnoid hemorrhage who received pre-treatment via intravenous injection of the melatonin receptor antagonist Luzindole (1 mg/kg) and 4P-PDOT (1 mg/kg), we found that the protective effect of melatonin against subarachnoid hemorrhage includes inhibition of lipid peroxidation and reduction of iron accumulation depended on melatonin receptor 1B (MT2). Furthermore, our study demonstrated that melatonin inhibited neuronal ferroptosis by activating the NRF2 signaling pathway, as evidenced by in vivo inhibition of NRF2. In summary, melatonin acts through MT2 and activates NRF2 and downstream genes such as HO-1/NQO1 to inhibit ferroptosis in subarachnoid hemorrhage-induced neuronal injury, thereby improving neurological function in rats. These results suggest that melatonin is a promising therapeutic target for subarachnoid hemorrhage.

Effects of exogenous melatonin on body mass and thermogenesis in red-backed vole (Eothenomys miletus) between Kunming and Dali regions.

Melatonin (MEL) is an indole hormone synthesized and secreted by the pineal gland at night, which is involved in the regulation of body mass and thermogenesis in small mammals. To test the effects of exogenous MEL on body mass and thermogenic ability in two different red-backed vole (Eothenomys miletus) populations from two different regions (Kunming [KM] and Dali [DL]) with different annual variation in climatic variables, such as temperature, sunshine and rainfall. we traced the changes of energy balance in E. miletus from KMand DL, which were placed at 25 ± 1°C with photoperiod of 12 L:12 D, intraperitoneal injection of MEL was performed daily for 28 days. The results showed that body mass and food intake were significantly decreased, while resting metabolic rate (RMR) and nonshivering thermogenesis (NST) were significantly increased after MEL injection; Contents of total protein, mitochondrial protein, the activities of cytochrome C oxidase (COX) and α-glycerophosphate oxidase (α-PGO) in liver and brown adipose tissue (BAT) were enhanced; the activity of thyroxin 5'-deiodinase (T4 5'-DII) and uncoupling protein 1 (UCP1) in BAT were also increased. Serum leptin, triiodothyronine (T3 ) levels and T3 /T4 ratio were significantly increased, thyroxine (T4 ) levels was significantly decreased. Moreover, body mass and food intake in E. miletus from KM were higher than those from DL, but RMR and NST were lower than those from DL. Changes of body mass, food intake and thermogenic activity of KM were higher than those of DL when exposed to injection of MEL, indicating that E. miletus in KM were more sensitive to MEL. Furthermore, MEL was involved in the regulation of body mass and thermogenesis in E. miletus between KM and DL.

Melatonin alleviates PTSD-like behaviors and restores serum GABA and cortisol levels in mice.

Melatonin is an endogenous hormone which modulates sleep-wake cycles. Previous studies have found a close correlation between melatonin and post-traumatic stress disorder (PTSD), a trauma- and stress-related psychiatric disorder with symptoms of sleep disturbance. However, it is still unclear if melatonin can have a therapeutic effect on PTSD. This study aimed to investigate the effects of melatonin on foot shocks induced PTSD-like behaviors and abnormal neuroendocrine levels in mice. As compared to no-shock controls, PTSD-like mice spent significantly more time freezing and displayed less rearing in a contextual fear test, spent significantly less time in and had fewer entries into open arms in an elevated maze test, and spent significantly less time in and had fewer entries into a light box in a light-dark transition task. In addition, serum GABA and cortisol levels were both found to be significantly decreased, whereas epinephrine levels were significantly increased in the PTSD-like mice. Our results showed that intraperitoneal injections of melatonin (2 mM, but not 0.2 nor 20 mM, 0.1 ml/day for two consecutive weeks) alleviated PTSD-like behaviors and restored serum GABA and cortisol levels. Further, it was found that melatonin receptor 1/2 antagonist luzindole significantly blocked the beneficial effects of melatonin for PTSD-like behaviors and serum GABA and cortisol levels, whereas melatonin receptor 2 antagonist 4-P-PDOT slightly blocked these effects. These results indicate that melatonin has a potential therapeutic effect on PTSD-like symptoms in mice, and melatonin receptor 1 mediated the effect.

Melatonin Prevents Chondrocyte Matrix Degradation in Rats with Experimentally Induced Osteoarthritis by Inhibiting Nuclear Factor-κB via SIRT1.

Osteoarthritis (OA) is a common degenerative joint disease characterized by an imbalance of cartilage extracellular matrix (ECM) breakdown and anabolism. Melatonin (MT) is one of the hormones secreted by the pineal gland of the brain and has anti-inflammatory, antioxidant, and anti-aging functions. To explore the role of MT in rats, we established an OA model in rats by anterior cruciate ligament transection (ACLT). Safranin O-fast green staining showed that intraperitoneal injection of MT (30 mg/kg) could alleviate the degeneration of articular cartilage in ACLT rats. Immunohistochemical (IHC) analysis found that MT could up-regulate the expression levels of collagen type II and Aggrecan and inhibit the expression levels of matrix metalloproteinase-3 (MMP-3), matrix metalloproteinase-13 (MMP-13), and ADAM metallopeptidase with thrombospondin type 1 motif 4 (ADAMTS-4) in ACLT rats. To elucidate the mechanism of MT in protecting the ECM in inflammatory factor-induced rat chondrocytes, we conducted in vitro experiments by co-culturing MT with a culture medium. Western blot (WB) showed that MT could promote the expression levels of transforming growth factor-beta 1 (TGF-β1)/SMAD family member 2 (Smad2) and sirtuin 2-related enzyme 1 (SIRT1) and inhibit the expression of levels of phosphorylated nuclear factor of kappa light polypeptide gene enhancer in B-cells inhibi-tor (p-p65) and phosphorylated IκB kinase-α (p-IκBα). In addition, WB and real-time PCR (qRT-PCR) results showed that MT could inhibit the expression levels of MMP-3, MMP-13, ADAMTS-4, inducible nitric oxide synthase (iNOS), and cyclooxygenase-2 (COX-2) in chondrocytes induced by interleukin-1β (IL-1β), and up-regulate the expression of chondroprotective protein type II collagen. We found that in vivo, MT treatment protected articular cartilage in the rat ACLT model. In IL-1β-induced rat chondrocytes, MT could reduce chondrocyte matrix degradation by up-regulating nuclear factor-kB (NF-κB) signaling pathway-dependent expression of SIRT1 and protecting chondrocyte by activating the TGF-β1/Smad2 pathway.

Melatonin attenuates spatial learning and memory dysfunction in developing rats by suppressing isoflurane-induced endoplasmic reticulum stress via the SIRT1/Mfn2/PERK signaling pathway

Use of the inhalation anesthetic isoflurane may increase the risk of cognitive deficiency and neurotoxicity after birth. A growing body of evidence suggests that melatonin is an effective treatment for various types of oxidative stress damage and neurodegenerative disease. In this study, we aimed to examine the effects of melatonin on isoflurane-induced endoplasmic reticulum (ER) stress, spatial learning and memory impairment during development. The rats were grouped according to whether the rats were exposed to isoflurane or a control gas and whether they were administered melatonin or phosphate buffered saline (PBS). We administered isoflurane to 7-day-old Sprague–Dawley rat pups with intraperitoneal injections of melatonin (20 mg/kg) 15 min before and 3 h after the initiation of anesthesia. Twelve hours after isoflurane anesthesia, rats were randomly selected from each group and sacrificed. The hippocampal tissue and serum were collected to determine the levels of SIRT1, Mfn2, PERK, and other proteins or cytokines related to ER stress, apoptosis, and neuroinflammation. Subsequently, all remaining rats were assessed for spatial learning and memory deficiency 31 days after birth using the Morris water maze test. We found that melatonin attenuated isoflurane-induced ER stress and neuroapoptosis in the hippocampus and decreased the level of neuroinflammatory markers in the serum of newborn rats, resulting in improved spatial learning and memory. In addition, the neuroprotective effect of melatonin was weakened after the SIRT1/Mfn2/PERK signaling pathway was suppressed by lentivirus transfection. Therefore, our findings demonstrate that melatonin ameliorates spatial learning and memory impairment after isoflurane exposure, and these beneficial effects are associated with a reduction in ER stress, neuroapoptosis, and neuroinflammation via the SIRT1/Mfn2/PERK signaling pathway.

Melatonin prevents experimental central serous chorioretinopathy in rats.

Central serous chorioretinopathy (CSC) is a vision-threatening disease with no validated treatment and unclear pathogenesis. It is characterized by dilation and leakage of choroidal vasculature, resulting in the accumulation of subretinal fluid, and serous detachment of the neurosensory retina. Numerous studies have demonstrated that melatonin had multiple protective effects against endothelial dysfunction, vascular inflammation, and blood-retinal barrier (BRB) breakdown. However, the effect of melatonin on CSC, and its exact pathogenesis, is not well understood thus far. In this study, an experimental model was established by intravitreal injection of aldosterone in rats, which mimicked the features of CSC. Our results found that melatonin administration in advance significantly inhibited aldosterone-induced choroidal thickening and vasodilation by reducing the expression of calcium-activated potassium channel KCa2.3, and attenuated tortuosity of choroid vessels. Moreover, melatonin protected the BRB integrity and prevented the decrease in tight junction protein (ZO-1, occludin, and claudin-1) levels in the rat model induced by aldosterone. Additionally, the data also showed that intraperitoneal injection of melatonin in advance inhibited aldosterone-induced macrophage/microglia infiltration, and remarkably diminished the levels of inflammatory cytokines (interleukin-6 [IL-6], IL-1β, and cyclooxygenase-2), chemokines (chemokine C-C motif ligand 3, and C-X-C motif ligand 1), and matrix metalloproteinases (MMP-2and MMP-9). Luzindole, as the nonselective MT1 and MT2 antagonist, and 4-phenyl-2-propionamidotetraline, as the selective MT2 antagonist, neutralized the melatonin-induced inhibition of choroidal thickening and choroidal vasodilation, indicating that melatonin might exert the effects via binding to its receptors. Furthermore, the IL-17A/nuclear factor-κB signaling pathway was activated by intravitreal administration of aldosterone, while it was suppressed in melatonin-treated in advance rat eyes. This study indicates that melatonin could serve as a promising safe therapeutic strategy for CSC patients.

The anti-inflammatory and analgesic effects of intraperitoneal melatonin after spinal nerve ligation are mediated by inhibition of the NF-κB/NLRP3 inflammasome signaling pathway

ObjectiveTo explore the potential analgesic effect of melatonin and its underlying molecular mechanisms in a neuropathic pain model induced by spinal nerve ligation (SNL). MethodsThe experimental animals were divided into different groups including sham, vehicle, melatonin (MT) treatment, caspase-1 inhibitor (VX-765) treatment and MT2 antagonist (4P-PDOT) treatment. On the first three successive postoperative days, rats were intraperitoneally administered with MT, VX-765 or combination of MT and 4P-PDOT. Hyperalgesic behavior after SNL was evaluated using the paw withdrawal threshold (PWT). We then assessed expression of tumor necrosis factor-α (TNF-α), IL-18, interleukin-1β (IL-1β), NLRP3 inflammasome components, and nuclear factor-κB (NF-κB) activation using enzyme-linked immunosorbent assay kits (ELISA), real-time PCR, immunohistochemistry, and western blot, respectively, in spinal cord horn tissues extracted on postoperative day 7. ResultsThe results showed that melatonin treatment alleviated SNL-induced allodynia. We observed an SNL-induced upregulation of TNF-α, IL-18, IL-1β, NLRP3, ASC, cleaved caspase-1, and NF-κB in the lumbar spinal cord horn of rats, which was significantly attenuated by intraperitoneal injection of melatonin or VX-765. Additionally, co-treatment of melatonin and 4P-PDOT abrogated the analgesic and anti-inflammatory effect of melatonin. ConclusionMelatonin had potent analgesic and anti-inflammatory effects in SNL-induced neuropathic pain via NF-κB/NLRP3 inflammasome signaling pathway. Our results therefore suggested that this pathway could represent a novel therapeutic target for the management of neuropathic pain.

Pathogenetically oriented approach to prevention of retinopathy of prematurity (experimental study)

To study the influence mechanism of melatonin and its analogues on the development of EROP at the preclinical stage of the pathological process to substantiate new approaches to prevention of ROP. The study included 42 Wistar rat pups (84 eyes) divided into 6 groups: control group, experimental group (rat pups with EROP), experimental groups who underwent injections of melatonin and its analogues K-148, AL-3, K-096. The pups were euthanized on day 7 (4-5 pups from each group at each study period), binocular enucleation was performed, and the content of hypoxia-induced factor1α (HIF-1α) and VEGF-A was determined in retinal samples. The intraperitoneal injections of melatonin and its analogs led to a significant decrease in the level of HIF-1α and VEGF-A in the retina of the rat pups of the experimental group until the beginning of pathological vasoproliferation. Melatonin and its analogues are able to prevent the development of EROP by reducing the level of angiogenic factors in the retina of rat pups at the stage of existing avascular zones, which allows for them to be considered as a new promising approach to preventing the development of ROP.

Melatonin attenuates choroidal neovascularization by regulating macrophage/microglia polarization via inhibition of RhoA/ROCK signaling pathway.

Choroidal neovascularization (CNV) is an important characteristic of advanced wet age-related macular degeneration (AMD) and leads to severe visual impairment among elderly patients. Previous studies have demonstrated that melatonin induces several biological effects related to antioxidation, anti-inflammation, and anti-angiogenesis. However, the role of melatonin in CNV, and its underlying mechanisms, has not been investigated thus far. In this study, we found that melatonin administration significantly reduced the scale and volume of CNV lesions, suppressed vascular leakage, and inhibited the capacity of vascular proliferation in the laser-induced mouse CNV model. Additionally, the results also show that the melatonin-treated retinal microglia in the laser-induced mice exhibited enhanced expression of M1-type markers, such as iNOS, CCL-3, CCL-5, and TNF-α, as well as decreased production of M2-type markers, such as Arg-1, Fizz-1, IL-10, YM-1, and CD206, indicating that melatonin switched the macrophage/microglia polarization from pro-angiogenic M2 phenotype to anti-angiogenic M1 phenotype. Furthermore, the RhoA/ROCK signaling pathway was activated during CNV formation, yet was suppressed after an intraperitoneal injection of melatonin. In conclusion, melatonin attenuated CNV, reduced vascular leakage, and inhibited vascular proliferation by switching the macrophage/microglia polarization from M2 phenotype to M1 phenotype via inhibition of RhoA/ROCK signaling pathway in CNV. This suggests that melatonin could be a novel agent for the treatment of AMD.

SIRT1 Mediates Melatonin's Effects on Microglial Activation in Hypoxia: In Vitro and In Vivo Evidence.

Melatonin exerts direct neuroprotection against cerebral hypoxic damage, but the mechanisms of its action on microglia have been less characterized. Using both in vitro and in vivo models of hypoxia, we here focused on the role played by silent mating type information regulation 2 homolog 1 (SIRT1) in melatonin’s effects on microglia. Viability of rat primary microglia or microglial BV2 cells and SH-SY5Y neurons was significantly reduced after chemical hypoxia with CoCl2 (250 μM for 24 h). Melatonin (1 μM) significantly attenuated CoCl2 toxicity on microglia, an effect prevented by selective SIRT1 inhibitor EX527 (5 μM) and AMP-activated protein kinase (AMPK) inhibitor BML-275 (2 μM). CoCl2 did not modify SIRT1 expression, but prevented nuclear localization, while melatonin appeared to restore it. CoCl2 induced nuclear localization of hypoxia-inducible factor-1α (HIF-1α) and nuclear factor-kappa B (NF-kB), an effect contrasted by melatonin in an EX527-dependent fashion. Treatment of microglia with melatonin attenuated potentiation of neurotoxicity. Common carotid occlusion was performed in p7 rats, followed by intraperitoneal injection of melatonin (10 mg/kg). After 24 h, the number of Iba1+ microglia in the hippocampus of hypoxic rats was significantly increased, an effect not prevented by melatonin. At this time, SIRT1 was only detectable in the amoeboid, Iba1+ microglial population selectively localized in the corpus callosum. In these cells, nuclear localization of SIRT1 was significantly lower in hypoxic animals, an effect prevented by melatonin. NF-kB showed an opposite expression pattern, where nuclear localization in Iba1+ cells was significantly higher in hypoxic, but not in melatonin-treated animals. Our findings provide new evidence for a direct effect of melatonin on hypoxic microglia through SIRT1, which appears as a potential pharmacological target against hypoxic-derived neuronal damage.

Effect of Melatonin on the Expression of VEGF-A and on the Degeneration of Follicle Reserve in Rat Ovary.

To analyze the effects of melatonin on vascular endothelial growth factor A (VEGF-A) expression and follicle reserve in rat ovary. A total of 45 female Wistar rats were used in the present study. Rats were divided into three groups: group 1 (control), group 2 (vehicle), and group 3 (melatonin). Rats in the melatonin group were treated with an intraperitoneal injection of melatonin at a dose of 50 mg/kg/day for 56 days. We investigated VEGF-A expression in rat ovary in all the groups using Western blot and reverse transcription-polymerase chain reaction. Histopathological parameters were evaluated using light microscopy. The number of atretic follicles was significantly lower in the melatonin treatment rats than in the control rats (p<0.05); however, the number of antral follicles was significantly higher in the former (p<0.05). Additionally, we observed a weak immunoblot stain in the melatonin group for VEGF-A protein. Interestingly, melatonin treatment induced a significant decrease in VEGF-A expression in the ovary of group 3 rats (p<0.05), whereas no such difference was observed between group 1 and group 2 rats (p>0.05). The present study demonstrates that the protective effect of melatonin on the degeneration of follicles in rat ovary is reduced by decreasing the VEGF-A expression. These results suggest that melatonin is effective against follicular atresia and preserves antral follicles, thus, offering a therapeutic advantage in clinical use.

Radioprotective effect of melatonin on expression of Cdkn1a and Rad50 genes in rat peripheral blood.

Ionizing radiation is a critical threat to biomolecules, especially DNA. Various combinatorial compounds have been studied to protect this biomolecule. Melatonin has been reported as a direct and indirect free radical scavenger, but in this study, we explored the effect of melatonin on assisting in DNA repair by expression of Cdkn1a and Rad50; both of these genes are involved in DNA repair signaling, induced by radiation in rat peripheral blood. Rats were irradiated with single whole-body linear accelerator X-ray radiation doses of 2 and 8 Gy with or without melatonin (100 mg/kg body weight) pretreatments. The rats were randomly divided into nine groups and given an intraperitoneal injection of melatonin or the same volume of vehicle alone 1 h before radiation. Blood samples were taken 8, 24, and 48 h postradiation to measure gene expression of Cdkn1a and Rad50 using quantitative reverse transcription polymerase chain reaction technique. Melatonin pretreatment increased the expression of Cdkn1a and Rad50 in 8 and 24 h postradiations (2 and 8 Gy) (P < 0.05), and there was no significant difference in 48 h postradiation compared to the radiation-only and vehicle plus radiation (2 and 8 Gy) groups. Based on our results, pretreatment with melatonin (100 mg/kg) may ameliorates injurious effects of 2 and 8 Gy ionization radiation by increasing the expression level of Cdkn1a and Rad50 in rat peripheral blood and assist in DNA double-strand breaks repair, especially during the early postradiation.

Динамика ноцицептивной чувствительности крыс после введения мелатонина в норме и при длительном стрессорном воздействии

Цель - изучение динамики ноцицептивной чувствительности крыс в разные временные периоды после внутрибрюшинного введения мелатонина (10 мг/кг) в условиях нормы и при однократной длительной стрессорной нагрузке на модели 24-ч иммобилизации. Результаты. Установлено, что введение мелатонина приводит к усилению перцептуального компонента ноцицепции животных, выраженность которого возрастает на протяжении 8 сут. наблюдений. На 3-и - 5-е сут. у этих особей выявлено возрастание порога вокализации в ответ на электрокожное раздражение, что иллюстрирует ослабление эмоционального компонента болевой чувствительности. Стрессорное воздействие сопровождалось снижением латентного периода реакции отведения хвоста при светотермальном раздражении, что наблюдалось сразу, а также через 1, 2 и 3 сут. после окончания стрессорного воздействия. В этих условиях увеличение порога вокализации крыс при электрокожной стимуляции обнаружено сразу после стрессорной нагрузки. Указанные изменения характеризуют усиление перцептуального компонента ноцицепции - формирование гипералгезии, но подавление эмоционального восприятия болевого раздражения на ранних стадиях постстрессорного периода. Показано, что экзогенный мелатонин не предупреждает развитие гипералгезии после 24-ч иммобилизации, однако подавляет эмоциональный компонент ноцицептивной чувствительности животных в отдаленный период после длительного стрессорного воздействия (4-е и 7-е сут.). Заключение. Применение мелатонина в целях коррекции измененной болевой чувствительности, при отрицательных эмоциогенных нагрузках, необходимо проводить с учетом временной стадии постстрессорного периода, а также принимая во внимание необходимость воздействия на перцептуальный или эмоциональный компонент ноцицепции. The dynamics of nociceptive sensitivity in rats was studied in various periods after intraperitoneal injection of melatonin (10 mg/kg) under normal conditions and during long-term stress exposure on the model of 24-h immobilization. Administration of melatonin was shown to enhance the perceptual component of nociception, whose degree progressively increased over 8 days of observations. The vocalization threshold of these specimens in response to electrocutaneous stimulation was elevated on days 3-5, which illustrates suppression of the emotional component of nociceptive sensitivity. Stress exposure in animals was accompanied by a decrease in the tail-flick latency during light-heat stimulation. It was observed immediately and 1, 2, and 3 days after termination of the stress procedure. An increase in the vocalization threshold of rats was found immediately after stress. These changes illustrate an enhancement of the perceptual component of nociception (hyperalgesia), but suppression of the emotional evaluation of pain stimulation at the early stage of the post-stress period. Exogenous melatonin did not prevent the development of hyperalgesia after 24-h restraint stress. However, melatonin inhibited the emotional component of nociceptive sensitivity in animals during the late period after long-term stress exposure (days 4 and 7). We conclude that the use of melatonin for correction of changes in nociceptive sensitivity due to negative emotiogenic factors should be performed taking into account the stage of the post-stress period and necessity to affect the perceptual or emotional component of nociception.

Possible promoting effects of melatonin, leptin and alcar on regeneration of the sciatic nerve

Peripheral nerve injury is a widespread and disabling condition that can impair the individual’s daily life. Studies involving medications that may positively affect peripheral nerve regeneration are rare. The aim of this study was to investigate new treatments after peripheral nerve injury using various neuroprotectants, melatonin, alcar and leptin, in the regenerative process in an experimental rat model. Wistar albino rats were randomly divided into eight groups containing equal number of animals. Intraperitoneal injection of melatonin (50mg/kg, for 21days), leptin (1mg/kg, for 21days) and acetyl-l-carnitine (50mg/kg, for six weeks) was performed postoperatively. Histological and electromyographical assessments of the regenerated nerves were performed 12 weeks after surgery. Stereological analysis was performed to estimate myelinated and unmyelinated axon numbers, surface area, myelin thickness and the myelin thickness/axon diameter ratio for each group. The results showed that only alcar has a beneficial effect on the regeneration of unmyelinated axons. Neither melatonin and leptin nor alcar were observed to have any therapeutic effect on the regeneration of myelinated axons. Alcar therapy has a positive effect on the regeneration of unmyelinated fiber in the sciatic nerve. However, the same effect was not observed in myelinated nerve fibers after intraperitoneal application of melatonin and leptin.

Participation of melatonin in regulation of blood oxygen-transport function in oxidative stress induced by injection of lipopolisaccharide

The contribution of melatonin to the regulatoin of the blood oxygen transport function was studied during oxidative stress induced by a triple injection of lipopolysaccharide (at a dose of 5 mg/kg) in conditions of erythropoietin and gasetransmitters (nitrogen monoxide, hydrogen sulfide) action. In the experimental groups, intraperitoneal injections of melatonin (5 mg/kg), erythropoietin (1000 U/kg), hydrogen sulfide donor (NaHS 5 mg/kg), and L-arginine (100 mg/kg), were performed. The use of melatonin alone or in combination with erythropoietin, sodium hydrosulfide or L-arginine led to a decrease in lipid peroxidation products and an increase in the antioxidant protection. Melatonin, during lipopolysaccharide administration, caused changes of blood oxygen transport function: blood oxygen saturation increased, hemoglobin oxygen affinity increased. The modifying effect of melatonin on the blood oxygen transport function in combination with erythropoietin and gastransmitters did not exceed the effect of melatonin alone.

Modulation of Radiation-induced Base Excision Repair Pathway Gene Expression by Melatonin.

Objective:Approximately 70% of all cancer patients receive radiotherapy. Although radiotherapy is effective in killing cancer cells, it has adverse effects on normal cells as well. Melatonin (MLT) as a potent antioxidant and anti-inflammatory agent has been proposed to stimulate DNA repair capacity. We investigated the capability of MLT in the modification of radiation-induced DNA damage in rat peripheral blood cells.Materials and Methods:In this experimental study, male rats (n = 162) were divided into 27 groups (n = 6 in each group) including: irradiation only, vehicle only, vehicle with irradiation, 100 mg/kg MLT alone, 100 mg/kg MLT plus irradiation in 3 different time points, and control. Subsequently, they were irradiated with a single whole-body X-ray radiation dose of 2 and 8 Gy at a dose rate of 200 MU/min. Rats were given an intraperitoneal injection of MLT or the same volume of vehicle alone 1 h prior to irradiation. Blood samples were also taken 8, 24, and 48 h postirradiation, in order to measure the 8-oxoguanine glycosylase1 (Ogg1), Apex1, and Xrcc1 expression using quantitative real-time-polymerase chain reaction.Results:Exposing to the ionizing radiation resulted in downregulation of Ogg1, Apex1, and Xrcc1 gene expression. The most obvious suppression was observed in 8 h after exposure. Pretreatments with MLT were able to upregulate these genes when compared to the irradiation-only and vehicle plus irradiation groups (P < 0.05) in all time points.Conclusion:Our results suggested that MLT in mentioned dose may result in modulation of Ogg1, Apex1, and Xrcc1 gene expression in peripheral blood cells to reduce X-ray irradiation-induced DNA damage. Therefore, administration of MLT may increase the normal tissue tolerance to radiation through enhancing the cell DNA repair capacity. We believed that MLT could play a radiation toxicity reduction role in patients who have undergone radiation treatment as a part of cancer radiotherapy.

Influence of melatonin on IL-1Ra gene and IL-1 expression in rats with liver ischemia reperfusion injury.

The aim of the present study was to explore the influence of melatonin (MT) on rats with liver ischemia reperfusion injury (IRI) and its mechanism. A total of 66 male Sprague-Dawley rats were randomly divided into 3 groups: i) Normal control group, ii) ischemia reperfusion group (IR group) and iii) melatonin treatment group (MT group). Rats in the MT group were administered an intraperitoneal injection of MT (10 mg/kg, 1 ml) at 70 and 35 min before ischemia, early reperfusion, and 1 and 2 h after reperfusion, respectively. Blood was removed at the normal time-point (prior to any processes), 35 min before ischemia, 2, 4, 8 and 24 h after reperfusion. Subsequently the rats were sacrificed. The pathological changes of liver tissues, interleukin-1 receptor antagonist (IL-1Ra) gene and IL-1 expression levels were detected. There were no evident differences between the immediate reperfusion and 2 h IR group and MT group. The liver structure injury of the 4, 8 and 24 h MT groups were improved to various differences compared to the corresponding IR group; liver IL-1β of the MT group at 35 min after ischemia, and 2, 4, 8 and 24 h after reperfusion was evidently lower than that of the IR group (P<0.05); IL-1Ra mRNA expression in the 2 h MT group was higher compared to the 2 h IR group by 4.85-fold; and IL-1Ra mRNA expression in the 4 h MT group was higher compared to the 4 h IR group by 9.34-fold. Differences between two groups at other time-points were <2-fold. In conclusion, MT can upregulate IL-1Ra gene expression by reducing generation of IL-1 thus reducing IRI.

Reduction of Endogenous Melatonin Accelerates Cognitive Decline in Mice in a Simulated Occupational Formaldehyde Exposure Environment

Individuals afflicted with occupational formaldehyde (FA) exposure often suffer from abnormal behaviors such as aggression, depression, anxiety, sleep disorders, and in particular, cognitive impairments. Coincidentally, clinical patients with melatonin (MT) deficiency also complain of cognitive problems associated with the above mental disorders. Whether and how FA affects endogenous MT metabolism and induces cognitive decline need to be elucidated. To mimic occupational FA exposure environment, 16 healthy adult male mice were exposed to gaseous FA (3 mg/m3) for 7 consecutive days. Results showed that FA exposure impaired spatial memory associated with hippocampal neuronal death. Biochemical analysis revealed that FA exposure elicited an intensive oxidative stress by reducing systemic glutathione levels, in particular, decreasing brain MT concentrations. Inversely, intraperitoneal injection of MT markedly attenuated FA-induced hippocampal neuronal death, restored brain MT levels, and reversed memory decline. At tissue levels, injection of FA into the hippocampus distinctly reduced brain MT concentrations. Furthermore, at cellular and molecular levels, we found that FA directly inactivated MT in vitro and in vivo. These findings suggest that MT supplementation contributes to the rescue of cognitive decline, and may alleviate mental disorders in the occupational FA-exposed human populations.