Short-term effectiveness of transcranial direct current stimulation in the nociceptive behavior of neuropathic pain rats in development.

Neuropathic pain (NP) is caused by a lesion that triggers pain chronification and central sensitization and it can develop in a different manner, dependent of age. Recent studies have demonstrated the efficacy of transcranial direct current stimulation (tDCS) for treating NP. Then, we aimed to investigate the effects of tDCS and BDNF levels in neuropathic pain rats in development, with 30 days old in the beginning of experiments. Eight-five male Wistar rats were subjected to chronic constriction injury. After establishment of NP, bimodal tDCS was applied to the rats for eight consecutive days, for 20 minutes each session. Subsequently, nociceptive behavior was assessed at baseline, 14 days after surgery, 1 day and 7 days after the end of tDCS. The rats were sacrificed 8 days after the last session of tDCS. An increase in the nociceptive threshold was observed in rats in development 1 day after the end of tDCS (short-term effect), but this effect was not maintained 7 days after the end of tDCS (long-term effect). Furthermore, brain derived neurotrophic factor (BDNF) levels were analyzed in the frontal cortex, spinal cord and serum using ELISA assays. The neuropathic pain model showed an effect of BDNF in the spinal cord of rats in development. There were no effects of BNDF levels of pain or tDCS in the frontal cortex or serum. In conclusion, tDCS is an effective technique to relieve nociceptive behavior at a short-term effect in neuropathic pain rats in development, and BDNF levels were not altered at long-term effect.

Evidence of Anti-Inflammatory Effect of Transcranial Direct Current Stimulation in a CFA-Induced Chronic Inflammatory Pain Model in Wistar Rats.

INTRODUCTION: Given that chronic inflammatory pain is highly prevalent worldwide, it is important to study new techniques to treat or relieve this type of pain. The present study evaluated the effect of transcranial direct current stimulation (tDCS) in rats submitted to a chronic inflammatory model by nociceptive response, biomarker levels (brain-derived neurotrophic factor [BDNF] and interleukin [IL]-6 and IL-10), and by histological parameters. METHODS: Sixty-day-old male Wistar rats were used in this study and randomized by weight into 6 major groups: total control, control + sham-tDCS, control + active tDCS, total CFA, CFA + sham-tDCS, and CFA + active tDCS. After inflammatory pain was established, the animals were submitted to the treatment protocol for 8 consecutive days, according to the experimental group. The nociceptive tests (von Frey and hot plate) were assessed, and euthanasia by decapitation occurred at day 8 after the end of tDCS treatment, and the blood serum and central nervous structures were collected for BDNF and IL measurements. All experiments and procedures were approved by the Institutional Committee for Animal Care and Use (UFPel #4538). RESULTS: The tDCS treatment showed a complete reversal of the mechanical allodynia induced by the pain model 24 h and 8 days after the last tDCS session, and there was partial reversal of the thermal hyperalgesia at all time points. Serum BDNF levels were decreased in CFA + sham-tDCS and CFA + tDCS groups compared to the control + tDCS group. The control group submitted to tDCS exhibited an increase in serum IL-6 levels in relation to the other groups. In addition, there was a significant decrease in IL-10 striatum levels in control + tDCS, CFA, and CFA + sham-tDCS groups in relation to the control group, with a partial tDCS effect on the CFA pain model. Local histology demonstrated tDCS effects in decreasing lymphocytic infiltration and neovascularization and tissue regeneration in animals exposed to CFA. CONCLUSION: tDCS was able to reverse the mechanical allodynia and decrease thermal hyperalgesia and local inflammation in a chronic inflammatory pain model, with a modest effect on striatum IL-10 levels. As such, we suggest that analgesic tDCS mechanisms may be related to tissue repair by modulating the local inflammatory process.

Static Magnetic Stimulation Induces Changes in the Oxidative Status and Cell Viability Parameters in a Primary Culture Model of Astrocytes.

Astrocytes play an important role in the central nervous system function and may contribute to brain plasticity response during static magnetic fields (SMF) brain therapy. However, most studies evaluate SMF stimulation in brain plasticity while few studies evaluate the consequences of SMF at the cellular level. Thus, we here evaluate the effects of SMF at 305 mT (medium-intensity) in a primary culture of healthy/normal cortical astrocytes obtained from neonatal (1 to 2-day-old) Wistar rats. After reaching confluence, cells were daily subjected to SMF stimulation for 5 min, 15 min, 30 min, and 40 min during 7 consecutive days. Oxidative stress parameters, cell cycle, cell viability, and mitochondrial function were analyzed. The antioxidant capacity was reduced in groups stimulated for 5 and 40 min. Although no difference was observed in the enzymatic activity of superoxide dismutase and catalase or the total thiol content, lipid peroxidation was increased in all stimulated groups. The cell cycle was changed after 40 min of SMF stimulation while 15, 30, and 40 min led cells to death by necrosis. Mitochondrial function was reduced after SMF stimulation, although imaging analysis did not reveal substantial changes in the mitochondrial network. Results mainly revealed that SMF compromised healthy astrocytes' oxidative status and viability. This finding reveals how important is to understand the SMF stimulation at the cellular level since this therapeutic approach has been largely used against neurological and psychiatric diseases.

Carnosic acid depends on glutathione to promote mitochondrial protection in methylglyoxal-exposed SH-SY5Y cells.

Methylglyoxal (MG) is an endogenously produced toxicant that induces mitochondrial dysfunction leading to impaired redox biology homeostasis, bioenergetics collapse, and cell death in mammalian cells. However, MG toxicity is particularly relevant to neurons and glia given their chemical and metabolic characteristics. Here, we have investigated whether a pretreatment with carnosic acid (CA) would be able to promote mitochondrial protection in human neuroblastoma SH-SY5Y cells exposed to MG. We found that a pretreatment with CA at 1 µM for 12 h prevented the MG-induced lipid peroxidation and protein carbonylation and nitration in the membranes of mitochondria obtained from the SH-SY5Y cells. CA also prevented the MG-elicited Complexes I and V dysfunction, adenosine triphosphate (ATP) levels decline, and loss of mitochondrial membrane potential (MMP). Moreover, CA also reduced the mitochondrial production of the radical anion superoxide (O2-•) in the MG-challenged cells. We found that CA upregulated the synthesis of glutathione (GSH) by increasing the activity of the γ-glutamylcysteine ligase (γ-GCL). Inhibition of the GSH synthesis by buthionine sulfoximine (BSO) abolished the CA-induced mitochondrial protection. Besides, inhibition of the phosphoinositide 3-kinase (PI3K)/Akt signaling pathway, as well as silencing of the transcription factor nuclear factor erythroid 2-related factor 2 (Nrf2), suppressed the CA-stimulated protection and the synthesis of GSH. Thus, CA promoted mitochondrial protection by a PI3K/Akt/Nrf2/γ-GCL/GSH axis in MG-treated SH-SY5Y cells.

Mitochondrial Protection and Anti-inflammatory Effects Induced by Emodin in the Human Neuroblastoma SH-SY5Y Cells Exposed to Hydrogen Peroxide: Involvement of the AMPK/Nrf2 Signaling Pathway.

Emodin (EM; 1,3,8-trihydroxy-6-methylanthracene-9,10-dione; C15H10O5) is an anthraquinone and exerts cytoprotective effects, as observed in both in vitro and in vivo experimental models. Mitochondrial dysfunction induced by reactive species plays a central role in the onset and progression of different human diseases. Thus, we have tested here whether a pretreatment (for 4 h) with EM (at 40 µM) would be able to promote mitochondrial protection in the human neuroblastoma SH-SY5Y cells exposed to the pro-oxidant agent hydrogen peroxide (H2O2). We found that the pretreatment with EM suppressed the effects of H2O2 on the activity of the mitochondrial complexes I and V, as well as on the production of adenosine triphosphate (ATP) and on the mitochondrial membrane potential (MMP). EM also prevented the H2O2-induced collapse in the tricarboxylic acid cycle (TCA) function. An anti-inflammatory role for EM was also observed in this experimental model, since this anthraquinone decreased the secretion of interleukin-1ß (IL-1ß) and tumor necrosis factor-α (TNF-α) by the H2O2-challenged cells. Inhibition of the adenosine monophosphate-activated protein kinase (AMPK) or silencing of the transcription factor nuclear factor erythroid 2-related factor 2 (Nrf2) abolished the protection induced by EM in the H2O2-treated cells. Therefore, EM prevented the H2O2-induced mitochondrial dysfunction and pro-inflammatory state in the SH-SY5Y cells by an AMPK/Nrf2-dependent manner.

Promotion of Mitochondrial Protection by Emodin in Methylglyoxal-Treated Human Neuroblastoma SH-SY5Y Cells: Involvement of the AMPK/Nrf2/HO-1 Axis.

Mitochondrial dysfunction is part of the mechanism of several human diseases. This negative circumstance may be induced by certain toxicants, as methylglyoxal (MG). MG is a reactive dicarbonyl presenting both endogenous and exogenous sources and is also able to induce protein cross-linking and glycation. Emodin (EM; 1,3,8-trihydroxy-6-methylanthracene-9,10-dione; C15H10O5) is a cytoprotective agent. Nonetheless, it was not previously demonstrated whether EM would be able to promote mitochondrial protection in cells challenged with MG. Therefore, we investigated here whether and how EM would prevent the MG-induced mitochondrial collapse in the human neuroblastoma SH-SY5Y cells. We found that a pretreatment (for 4 h) with EM at 40 µM prevented the MG-induced mitochondrial dysfunction (i.e., decreased activity of the complexes I and V, reduced adenosine triphosphate levels, and loss of mitochondrial membrane potential) in the SH-SY5Y cells. EM also prevented the redox impairment induced by MG in mitochondrial membranes. Inhibiting the adenosine monophosphate-activated protein kinase (AMPK) or silencing of the nuclear factor erythroid 2-related factor 2 (Nrf2), transcription factor abolished the EM-induced protection. Inhibition of heme oxygenase-1 (HO-1) also blocked the EM-induced mitochondrial protection. Therefore, EM protected the mitochondria by a mechanism dependent on the AMPK/Nrf2/HO-1 signaling pathway in MG-challenged SH-SY5Y cells.

Butaphosphan Effects on Glucose Metabolism Involve Insulin Signaling and Depends on Nutritional Plan.

Butaphosphan is an organic phosphorus compound used in several species for the prevention of rapid catabolic states, however, the mechanism of action remains unclear. This study aimed at determining the effects of butaphosphan on energy metabolism of mice receiving a normal or hypercaloric diet (HCD) and submitted or not to food restriction. Two experiments were conducted: (1) during nine weeks, animals were fed with HCD (n = 28) ad libitum, and at the 10th week, were submitted to food restriction and received butaphosphan (n = 14) or saline injections (n = 14) (twice a day, for seven days) and; (2) during nine weeks, animals were fed with a control diet (n = 14) or HCD (n = 14) ad libitum, and at the 10th week, all animals were submitted to food restriction and received butaphosphan or saline injections (twice a day, for seven days). In food restriction, butaphosphan preserved epididymal white adipose tissue (WAT) mass, increased glucose, NEFA, and the HOMA index. In mice fed HCD and submitted to food restriction, the butaphosphan preserved epididymal WAT mass. Control diet influences on PI3K, GCK, and Irs1 mRNA expression. In conclusion, butaphosphan increased blood glucose and reduced fat mobilization in overweight mice submitted to caloric restriction, and these effects are influenced by diet.

Mitochondrial Protection Promoted by the Coffee Diterpene Kahweol in Methylglyoxal-Treated Human Neuroblastoma SH-SY5Y Cells.

The coffee diterpene kahweol (KW; C20H26O3) is a cytoprotective agent exhibiting potent antioxidant actions, as demonstrated in several experimental models. In spite of the efforts to elucidate exactly how KW promotes cytoprotection, it was not previously examined whether KW would be able to protect mitochondria of human cells undergoing redox stress. In the present work, we have treated the human neuroblastoma SH-SY5Y cell line with KW at 0.1-10 µM for 12 h prior to a challenge with methylglyoxal (MG), a reactive dicarbonyl that impairs mitochondrial function. We have found that KW at 10 µM suppressed the loss of mitochondrial membrane potential (MMP) and the bioenergetics decline (including decreased activity of the mitochondrial complexes I and V and reduced production of adenosine triphosphate, ATP) in the MG-treated SH-SY5Y cells. KW also prevented the MG-elicited generation of reactive oxygen and nitrogen species (ROS and RNS, respectively) in the SH-SY5Y cells. In this regard, KW exerted an antioxidant effect on the membranes of mitochondria obtained from the MG-treated cells. The mitochondria-related effects induced by KW were blocked by inhibition of the phosphoinositide 3-kinase (PI3K)/Akt or of the p38 mitogen-activated protein kinase (MAPK) signaling pathways. Moreover, silencing of the transcription factor nuclear factor E2-related factor 2 (Nrf2) suppressed the mitochondrial protection promoted by KW in the MG-challenged cells. Therefore, KW protected mitochondria by a mechanism associated with the PI3K/Akt and p38 MAPK/Nrf2 signaling pathways.

The effects of kahweol, a diterpene present in coffee, on the mitochondria of the human neuroblastoma SH-SY5Y cells exposed to hydrogen peroxide.

The oxidative phosphorylation (OXPHOS) system located in the mitochondria is the main source of adenosine triphosphate (ATP) in mammals. The mitochondria are also the main site of reactive oxygen species (ROS) production in those cells. Disruption of the mitochondrial redox biology has been seen in the onset and progression of neurodegenerative diseases. In this regard, we have tested here whether kahweol (KW; C20H26O3), a diterpene present in coffee, would be able to promote mitochondrial protection in the human neuroblastoma SH-SY5Y cells exposed to hydrogen peroxide (H2O2). A pretreatment (for 12 h) with KW (at 10 µM) decreased the impact of H2O2 (at 300 µM) on the levels of oxidative stress markers in the mitochondrial membranes, as well as reduced the production of ROS by the organelles. KW pretreatment also suppressed the effects of H2O2 on the activity of components of the OXPHOS. The KW-induced mitochondria-related effects were blocked by inhibition of the phosphoinositide 3-kinase/Akt (PI3K/Akt) and p38 mitogen-activated protein kinase (MAPK) signaling pathways. Furthermore, silencing of the transcription factor nuclear factor erythroid 2-related factor 2 (Nrf2) and inhibition of the heme oxygenase-1 (HO-1) enzyme abrogated the KW-induced protective effects on the mitochondria. Therefore, KW promoted mitochondrial protection by the PI3K/Akt and p38 MAPK/Nrf2/HO-1 axis in H2O2-challenged SH-SY5Y cells.

Tanshinone I Induces Mitochondrial Protection by a Mechanism Involving the Nrf2/GSH Axis in the Human Neuroblastoma SH-SY5Y Cells Exposed to Methylglyoxal.

Methylglyoxal (MG) is a dicarbonyl molecule exhibiting high reactivity and is a major responsible for glycation in human cells. Accumulation of MG is seen in certain diseases, including metabolic disturbances and neurodegeneration. Among other effects, MG promotes mitochondrial dysfunction, leading to bioenergetic decline and redox impairment in virtually any nucleated human cells. The detoxification of MG is dependent on the availability of reduced glutathione (GSH), a major antioxidant that is also utilized in phase II detoxification reactions. The synthesis of GSH is mainly controlled by the transcription factor nuclear factor (erythroid-derived 2)-like 2 (Nrf2). The activation of Nrf2 is stimulated by several reactive compounds, including natural molecules produced by plants. Tanshinone I (T-I) is obtained from Salvia miltiorrhiza Bunge and exerts potent cytoprotective actions in different cell types. Thus, we have investigated here whether and how T-I would be able to protect mitochondria of the human neuroblastoma SH-SY5Y cell line exposed to MG. The cells were pretreated with T-I at 2.5 µM for 2 h before the challenge with MG at 500 µM. T-I significantly attenuated the MG-induced loss of cell viability, bioenergetic decline, and redox impairment in SH-SY5Y cells. The inhibition of the GSH synthesis by buthionine sulfoximine (BSO) at 100 µM suppressed the mitochondrial protection promoted by T-I. The silencing of Nrf2 by small interfering RNA (siRNA) abrogated the synthesis of GSH and the mitochondrial protection stimulated by T-I in SH-SY5Y cells. Therefore, T-I induced mitochondrial protection by a mechanism involving the Nrf2/GSH axis in MG-challenged SH-SY5Y cells.

Carnosic Acid Induces Anti-Inflammatory Effects in Paraquat-Treated SH-SY5Y Cells Through a Mechanism Involving a Crosstalk Between the Nrf2/HO-1 Axis and NF-κB.

Carnosic acid (CA) is a phenolic diterpene obtained from Rosmarinus officinalis L. and has demonstrated cytoprotective properties in several experimental models. CA exerts antioxidant effects by upregulating the transcription factor nuclear factor erythroid 2-related factor 2 (Nrf2), which controls the expression of antioxidant and phase II detoxification enzymes. Heme oxygenase-1 (HO-1) expression is modulated by Nrf2 and has been demonstrated as part of the mechanism underlying the CA-induced cytoprotection. Nonetheless, it remains to be studied whether and how HO-1 would mediate CA-elicited anti-inflammatory effects. Therefore, we have investigated here whether and how CA would prevent paraquat (PQ)-induced inflammation-related alterations in human neuroblastoma SH-SY5Y cells. SH-SY5Y cells were pretreated for 12 h with CA at 1 µM before exposure to PQ for further 24 h. CA suppressed the PQ-induced alterations on the levels of interleukin-1ß (IL-1ß), tumor necrosis factor-α (TNF-α), and cyclooxygenase-2 (COX-2) through a mechanism involving the activation of the Nrf2/HO-1 axis. Furthermore, we observed a crosstalk between the Nrf2/HO-1 signaling pathway and the activation of the nuclear factor-κB (NF-κB) transcription factor, since administration of ZnPP IX (specific inhibitor of HO-1) or Nrf2 knockdown using small interfering RNA (siRNA) abolished the anti-inflammatory effects induced by CA. Moreover, administration of SN50 (specific inhibitor of NF-κB) inhibited the PQ-induced inflammation-related effects in SH-SY5Y cells. Therefore, CA exerted anti-inflammatory effects in SH-SY5Y cells through an Nrf2/HO-1 axis-dependent manner associated with downregulation of NF-κB.

Tanshinone I Attenuates the Effects of a Challenge with H2O2 on the Functions of Tricarboxylic Acid Cycle and Respiratory Chain in SH-SY5Y Cells.

Tanshinone I (T-I; C18H12O3) is a cytoprotective molecule. T-I has been viewed as an antioxidant and anti-inflammatory agent exerting neuroprotective actions in several experimental models. Nonetheless, the mechanisms underlying the beneficial effects of T-I in mammalian cells are not completely understood yet. Mitochondrial dysfunction has been associated with several neurodegenerative diseases which remain uncured. Therefore, there is increasing interest in compounds that may be used in the prevention or treatment of those pathologies. Since T-I presents an antioxidant capacity, we investigated here whether and how this compound would prevent mitochondrial impairment in SH-SY5Y cells exposed to hydrogen peroxide (H2O2), which has been involved in the triggering of deleterious effects in several experimental models mimicking neurodegenerative processes. We found that a pretreatment with T-I at 2.5 µM for 2 h suppressed the pro-oxidant effects of H2O2 on mitochondrial membranes. Furthermore, T-I prevented the H2O2-elicited inhibition of the tricarboxylic acid (TCA) cycle enzymes (aconitase, α-ketoglutarate dehydrogenase, and succinate dehydrogenase) and of the mitochondrial complexes I and V. T-I also abrogated the mitochondrial depolarization and the mitochondrial failure to produce ATP in cells exposed to H2O2. T-I upregulated the levels of reduced glutathione (GSH) in the mitochondria of SH-SY5Y cells. T-I induced mitochondrial protection, at least in part, by activating the nuclear factor erythroid 2-related factor 2 (Nrf2), because silencing of Nrf2 by using small interference RNA (SiRNA) blocked these effects. Therefore, T-I afforded mitochondrial protection (involving both redox and bioenergetics-related aspects) against H2O2 through the activation of Nrf2.

Resveratrol Regulates the Quiescence-Like Induction of Activated Stellate Cells by Modulating the PPARγ/SIRT1 Ratio.

The activation of hepatic stellate cell (HSC), from a quiescent cell featuring cytoplasmic lipid droplets to a proliferative myofibroblast, plays an important role in liver fibrosis development. The GRX line is an activated HSC model that can be induced by all-trans-retinol to accumulate lipid droplets. Resveratrol is known for activating Sirtuin1 (SIRT1), a NAD(+)-dependent deacetylase that suppresses the activity of peroxisome proliferator-activated receptor gamma (PPARγ), an important adipogenic transcription factor involved in the quiescence maintenance of HSC. We evaluated the effects of 0.1 µM of resveratrol in retinol-induced GRX quiescence by investigating the interference of SIRT1 and PPARγ on cell lipogenesis. GRX lipid accumulation was evaluated through Oil-red O staining, triacylglycerides quantification, and [(14)C] acetate incorporation into lipids. mRNA expression and protein content of SIRT1 and PPARγ were measured by RT-PCR and immunoblotting, respectively. Resveratrol-mediated SIRT1 stimuli did not induce lipogenesis and reduced the retinol-mediated fat-storing capacity in GRX. In order to support our results, we established a cell culture model of transgenic super expression of PPARγ in GRX cells (GRXPγ). Resveratrol reduced lipid droplets accumulation in GRXPγ cells. These results suggest that the PPARγ/SIRT1 ratio plays an important role in the fate of HSC. Thus, whenever the PPARγ activity is greater than SIRT1 activity the lipogenesis is enabled.

Melatonin analgesia is associated with improvement of the descending endogenous pain-modulating system in fibromyalgia: a phase II, randomized, double-dummy, controlled trial.

BACKGROUND: Central disinhibition is a mechanism involved in the physiopathology of fibromyalgia. Melatonin can improve sleep quality, pain and pain threshold. We hypothesized that treatment with melatonin alone or in combination with amitriptyline would be superior to amitriptyline alone in modifying the endogenous pain-modulating system (PMS) as quantified by conditional pain modulation (CPM), and this change in CPM could be associated with serum brain-derived neurotrophic factor (BDNF). We also tested whether melatonin improves the clinical symptoms of pain, pain threshold and sleep quality. METHODS: Sixty-three females, aged 18 to 65, were randomized to receive bedtime amitriptyline (25 mg) (n = 21), melatonin (10 mg) (n = 21) or melatonin (10 mg) + amitriptyline (25 mg) (n = 21) for a period of six weeks. The descending PMS was assessed with the CPM-TASK. It was assessed the pain score on the Visual Analog Scale (VAS 0-100 mm), the score on Fibromyalgia Impact Questionnaire (FIQ), heat pain threshold (HPT), sleep quality and BDNF serum. Delta values (post- minus pre-treatment) were used to compare the treatment effect. The outcomes variables were collected before, one and six weeks after initiating treatment. RESULTS: Melatonin alone or in combination with amitriptyline reduced significantly pain on the VAS compared with amitriptyline alone (P < 0.01). The delta values on the VAS scores were-12.85 (19.93),-17.37 (18.69) and-20.93 (12.23) in the amitriptyline, melatonin and melatonin+amitriptyline groups, respectively. Melatonin alone and in combination increased the inhibitory PMS as assessed by the Numerical Pain Scale [NPS(0-10)] reduction during the CPM-TASK:-2.4 (2.04) melatonin + amitriptyline,-2.65 (1.68) melatonin, and-1.04 (2.06) amitriptyline, (P < 0.05). Melatonin + amitriptyline treated displayed better results than melatonin and amitriptyline alone in terms of FIQ and PPT improvement (P < 0.05, fort both). CONCLUSION: Melatonin increased the inhibitory endogenous pain-modulating system as assessed by the reduction on NPS(0-10) during the CPM-TASK. Melatonin alone or associated with amitriptyline was better than amitriptyline alone in improving pain on the VAS, whereas its association with amitriptyline produced only marginal additional clinical effects on FIQ and PPT. TRIAL REGISTRATION: Current controlled trail is registered at clinical trials.gov upon under number NCT02041455. Registered January 16, 2014.

Melatonin treatment entrains the rest-activity circadian rhythm in rats with chronic inflammation.

We assessed the therapeutic effect of exogenous melatonin (MEL), dexamethasone (DEXA), and a combination of both on nociceptive response induced by chronic inflammation and on the rest-activity circadian rhythm in rats. A total of 64 animals were randomly divided into eight groups of eight rats each: one control group and seven groups with complete Freund's adjuvant-inflamed animals (CFA; injection into the footpad). One of the CFA-inflamed groups did not receive any treatment; the other six were treated with melatonin (MEL), dexamethasone (DEXA), melatonin plus dexamethasone (MELDEXA), and their respective vehicles. Fifteen days after CFA injection, animals were treated with intraperitoneal injection of MEL (50 mg/kg) or its vehicle (8% ethanol in saline), DEXA (0.25 mg/kg) or its vehicle (saline), and MEL plus DEXA or their vehicles, for 8 days. The von Frey test was performed 24 h after the last administration of each treatment regimen. Hind paw thickness was measured using a pachymeter during the treatment days. The degree of swelling and histological findings were analyzed. All treated groups significantly reduced the severity of inflammation when compared with their vehicles (repeated-measures analysis of variance [ANOVA], p < 0.05 for all analyses). Inflamed animals treated with dexamethasone alone or associated with melatonin showed marked inhibition of histological findings. On the other hand, the group treated with melatonin remained with moderate inflammation. The CFA group showed a decrease in the mean rest-activity circadian rhythm, determined by the number of touch-detections per hour during water intake in comparison with the control group; only the group treated with melatonin showed a synchronized rest-activity rhythm. At the end of treatment, a significant increase was observed in hind paw withdrawal threshold on the von Frey test in the treated groups (one-way ANOVA, p < 0.05 for all). Our findings showed that melatonin (50 mg/kg) has strong chronobiotic and antinociceptive effects, but only mild anti-inflammatory effects. This evidence supports the hypothesis that melatonin can induce phase advance and circadian rhythm synchronization in rats with chronic inflammation.

Efficacy of melatonin in the treatment of endometriosis: a phase II, randomized, double-blind, placebo-controlled trial.

Endometriosis-associated chronic pelvic pain (EACPP) presents with an intense inflammatory reaction. Melatonin has emerged as an important analgesic, antioxidant, and antiinflammatory agent. This trial investigates the effects of melatonin compared with a placebo on EACPP, brain-derived neurotrophic factor (BDNF) level, and sleep quality. Forty females, aged 18 to 45 years, were randomized into the placebo (n = 20) or melatonin (10 mg) (n = 20) treatment groups for a period of 8 weeks. There was a significant interaction (time vs group) regarding the main outcomes of the pain scores as indexed by the visual analogue scale on daily pain, dysmenorrhea, dysuria, and dyschezia (analysis of variance, P < 0.01 for all analyses). Post hoc analysis showed that compared with placebo, the treatment reduced daily pain scores by 39.80% (95% confidence interval [CI] 12.88-43.01%) and dysmenorrhea by 38.01% (95% CI 15.96-49.15%). Melatonin improved sleep quality, reduced the risk of using an analgesic by 80%, and reduced BNDF levels independently of its effect on pain. This study provides additional evidence regarding the analgesic effects of melatonin on EACPP and melatonin's ability to improve sleep quality. Additionally, the study revealed that melatonin modulates the secretion of BDNF and pain through distinct mechanisms.

BDNF as an effect modifier for gender effects on pain thresholds in healthy subjects.

BDNF is an important marker of neuronal plasticity. It has also been associated with pain processing. Increased BDNF levels are observed in chronic pain syndromes. In order to understand the role of BDNF associated with other factors such as gender on experimental pain we aimed to determine whether experimental heat or pressure pain threshold is correlated with brain derived neurotrophic factor (BDNF) level, gender and age. Heat pain threshold and pressure pain threshold were measured in 49 healthy volunteers (27 females). The multivariate linear regression models (on heat and pressure pain thresholds) revealed a significant effect of gender (p=0.001 for both models), serum BDNF (p<0.004 for both models) and interaction between BDNF and gender (<0.001 for both models). In fact, when adjusting for BDNF levels and age, heat and pressure pain thresholds were significantly reduced in women as compared to men (p<0.001 for both models). These effects were not observed when gender was analyzed alone. These finding suggests that experimental heat and pressure pain threshold is gender-related and BDNF dependent. In fact BDNF has a facilitatory effect on pain threshold in females but has an opposite effect in males; supporting the notion that BDNF is an effect modifier of the gender effects on pain threshold in healthy subjects.

Neurobiological effects of transcranial direct current stimulation: a review.

Transcranial Direct Current Stimulation (tDCS) is a non-invasive brain stimulation technique that is affordable and easy to operate compared to other neuromodulation techniques. Anodal stimulation increases cortical excitability, while the cathodal stimulation decreases it. Although tDCS is a promising treatment approach for chronic pain as well as for neuropsychiatric diseases and other neurological disorders, several complex neurobiological mechanisms that are not well understood are involved in its effect. The purpose of this systematic review is to summarize the current knowledge regarding the neurobiological mechanisms involved in the effects of tDCS. The initial search resulted in 171 articles. After applying inclusion and exclusion criteria, we screened 32 full-text articles to extract findings about the neurobiology of tDCS effects including investigation of cortical excitability parameters. Overall, these findings show that tDCS involves a cascade of events at the cellular and molecular levels. Moreover, tDCS is associated with glutamatergic, GABAergic, dopaminergic, serotonergic, and cholinergic activity modulation. Though these studies provide important advancements toward the understanding of mechanisms underlying tDCS effects, further studies are needed to integrate these mechanisms as to optimize clinical development of tDCS.