Transcranial Direct Current Stimulation (tDCS) Promotes state-dependent Effects on Neuroinflammatory and Behavioral Parameters in rats Chronically Exposed to Stress and a Hyper-Palatable Diet.

Chronic stress is a common condition affecting health, often associated with unhealthy eating habits. Transcranial direct current stimulation (tDCS) has been proposed to address these issues. Thus, this research investigated the effects of tDCS on biometric, behavioral, and neurochemical parameters in chronically stressed rats fed a hyper-palatable cafeteria diet (CAFD). The study lasted 8 weeks, with CAFD exposure and/or chronic restraint stress model (CRS - 1 h/day, 5 days/week, for 7 weeks) started concurrently. tDCS or sham sessions were applied between days 42 and 49 (0.5 mA, 20 min/day). CAFD increased body weight, caloric consumption, adiposity, and liver weight. It also altered central parameters, reducing anxiety and cortical levels of IL-10 and BDNF. In turn, the CRS resulted in increased adrenals in rats with standard diet (SD), and anxiety-like and anhedonic behaviors in rats with CAFD. tDCS provided neurochemical shifts in CAFD-fed stressed rats increasing central levels of TNF-α and IL-10, while in stressed rats SD-fed induced a decrease in the adrenals weight, relative visceral adiposity, and serum NPY levels. These data demonstrated the anxiolytic effect of CAFD and anxiogenic effect of stress in CAFD-fed animals. In addition, tDCS promoted state-dependent effects on neuroinflammatory and behavioral parameters in rats chronically exposed to stress and a hyper-palatable diet. These findings provide primary evidence for additional mechanistic and preclinical studies of the tDCS technique for stress-related eating disorders, envisioning clinical applicability.

Single exercise stress reduces central neurotrophins levels and adenosine A1 and A2 receptors expression, but does not revert opioid-induced hyperalgesia in rats.

BACKGROUND: This study assessed the effects of an acute stress model upon the long-term hyperalgesia induced by repeated morphine administration in neonatal rats. We also evaluated neurotrophins and cytokines levels; expressions of adenosine and acetylcholine receptors, and acetylcholinesterase enzyme at the spinal cord. MATERIAL AND METHODS: Male Wistar rats were subjected to morphine or saline administration from P8 to P14. Thermal hyperalgesia and mechanical hyperesthesia were assessed using the hot plate (HP) and von Frey (vF) tests, respectively, at postnatal day P30 and P60. After baseline measurements, rats were subjected to a single exercise session, as an acute stress model, at P30 or P60. We measured the levels of BDNF and NGF, interleukin-6, and IL-10 in the cerebral cortex and the brainstem; and the expression levels of adenosine and muscarinic receptors, as well as acetylcholinesterase (AChE) enzyme at the spinal cord. RESULTS: A stress exercise session was not able to revert the morphine-induced hyperalgesia. The morphine and exercise association in rats induced a decrease in the neurotrophins brainstem levels, and A1 , A2A , A2B receptors expression in the spinal cord, and an increase in the IL-6 cortical levels. The exercise reduced M2 receptors expression in the spinal cord of naive rats, while morphine prevented this effect. CONCLUSIONS: Single session of exercise does not revert hyperalgesia induced by morphine in rats; however, morphine plus exercise modulate neurotrophins, IL-6 central levels, and expression of adenosine receptors.

Maternal deprivation alters nociceptive response in a gender-dependent manner in rats.

The present study aimed at investigating both the early and long-term effects of maternal deprivation as well as gender on neuromotor reflexes, anxiety behavior and thermal nociceptive responses. A total of 64 Wistar rats pups (32 males, 32 females) were utilized and were deprived of their mother for 3 h/daily, from postnatal day 1 (P1) until P10. Successively, animals were divided into 2 groups: control group (C) - pups no subjected to intervention; and the maternal-deprived group (MD): pups subjected to maternal deprivation. The neuromotor reflexes were evaluated through the righting reflex and negative geotaxis tests; the exploratory behavior by open field test (OFT); the anxiety-like behavior by elevated plus-maze test (EPM); the thermal nociceptive responses byhot plate (HP) and tail-flick (TFL) tests. All the animals subjected to maternal deprivation showed a delayed reflex response at P8 in the negative geotaxis test. In contrast, the OFT at P20 identified an effect of gender on the outer crossings and grooming as well as an interaction between gender and maternal deprivation on latency. Additionally, effect of maternal deprivation in the open and closed arms as well as gender effect in the protected head-dipping (PHD) and non-protected head-dipping (NPHD) were observed at P20 (EPM). In contrast, there were a gender effect on latency and an interaction between gender and maternal deprivation on rearing at P42. Moreover, in nociceptive tests was observed an analgesic effect induced by maternal deprivation; however, in the TFL test, only deprived females showed this effect. Surprisingly, only control animals presented an ontogeny nociceptive effect in the HP testat P21 and P43, which may be related to an increase in the inhibitory nociceptive pathways throughout life. In this way, we suggest maternal deprivation to be able to anticipate the maturation of the inhibitory nociceptive pathway. In conclusion, maternal deprivation induced a delayed reflex response at P8 and altered the anxiety and nociceptive behaviors according to the time after exposure to this stressor, in a gender-specific manner.

Increased Oxidative Parameters and Decreased Cytokine Levels in an Animal Model of Attention-Deficit/Hyperactivity Disorder.

Attention-deficit/hyperactivity disorder (ADHD) is a highly heterogeneous disorder characterized by impairing levels of hyperactivity, impulsivity and inattention. Oxidative and inflammatory parameters have been recognized among its multiple predisposing pathways, and clinical studies indicate that ADHD patients have increased oxidative stress. In this study, we aimed to evaluate oxidative (DCFH oxidation, glutathione levels, glutathione peroxidase, catalase and superoxide dismutase activities) and inflammatory (TNF-α, IL-1ß and IL-10) parameters in the most widely accepted animal model of ADHD, the spontaneously hypertensive rats (SHR). Prefrontal cortex, cortex (remaining regions), striatum and hippocampus of adult male SHR and Wistar Kyoto rats were studied. SHR presented increased reactive oxygen species (ROS) production in the cortex, striatum and hippocampus. In SHR, glutathione peroxidase activity was decreased in the prefrontal cortex and hippocampus. TNF-α levels were reduced in the prefrontal cortex, cortex (remaining regions), hippocampus and striatum of SHR. Besides, IL-1ß and IL-10 levels were decreased in the cortex of the ADHD model. Results indicate that SHR presented an oxidative profile that is characterized by an increase in ROS production without an effective antioxidant counterbalance. In addition, this strain showed a decrease in cytokine levels, mainly TNF-α, indicating a basal deficit. These results may present a new approach to the cognitive disturbances seen in the SHR.

Melatonin Alters the Mechanical and Thermal Hyperalgesia Induced by Orofacial Pain Model in Rats.

Melatonin is a neuroendocrine hormone that presents a wide range of physiological functions including regulating circadian rhythms and sleep, enhancing immune function, sleep improvement, and antioxidant effects. In addition, melatonin has received special attention in pain treatment since it is effective and presents few adverse effects. In this study, we evaluated the effect of acute dose of melatonin upon hyperalgesia induced by complete Freund's adjuvant in a chronic orofacial pain model in Sprague-Dawley rats. Nociceptive behavior was assessed by facial Von Frey and the hot plate tests at baseline and thereafter 30, 60, and 120 min, 24 h, and 7 days after melatonin treatment. We demonstrated that acute melatonin administration alters mechanical and thermal hyperalgesia induced by an orofacial pain model (TMD), highlighting that the melatonin effect upon mechanical hyperalgesia remained until 7 days after its administration. Besides, we observed specific tissue profiles of neuroimmunomodulators linked to pain conditions and/or melatonin effect (brain-derived neurotrophic factor, nerve growth factor, and interleukins 6 and 10) in the brainstem levels, and its effects were state-dependent of the baseline of these animals.

Obesity and Hyperlipidemia Modulate Alveolar Bone Loss in Wistar Rats.

BACKGROUND: A positive association between obesity-associated metabolic disorders (e.g., hyperlipidemia and diabetes) and periodontitis has been demonstrated in the literature. This study evaluates the role of cafeteria diet-induced obesity/hyperlipidemia (CAF) on alveolar bone loss (ABL) in rats. METHODS: Sixty male Wistar rats were randomly divided in four groups: control, periodontitis (PERIO), obesity/hyperlipidemia (CAF), and obesity/hyperlipidemia plus periodontitis (CAF+PERIO). Groups CAF and CAF+PERIO were exposed to a high-fat, hypercaloric diet. At week 12, periodontal disease was induced in groups PERIO and CAF+PERIO by ligatures in the upper second molar. The contralateral tooth was considered the intragroup control. Body weight and Lee index were evaluated weekly during the experiment. Serum glucose and cholesterol/triglycerides in the liver were evaluated, and percentage of ABL was measured by microcomputed tomography. Serum tumor necrosis factor (TNF)-α and interleukin (IL)-1ß were evaluated by enzyme-linked immunosorbent assay at week 17. RESULTS: Body weight, Lee index, and cholesterol/triglycerides in the liver increased in groups exposed to the cafeteria diet. Groups PERIO and CAF+PERIO exhibited a significantly higher ABL compared to control and CAF groups. The presence of obesity and hyperlipidemia significantly increased ABL in the CAF+PERIO group compared to the PERIO group (53.60 ± 3.44 versus 42.78 ± 7.27, respectively) in the sides with ligature. Groups exposed to CAF exhibited higher ABL in the sides without ligature. No differences were observed among groups for IL-1ß and TNF-α. CONCLUSION: Obesity and hyperlipidemia modulate the host response to challenges in the periodontium, increasing the expression of periodontal breakdown.

Hypercaloric diet modulates effects of chronic stress: a behavioral and biometric study on rats.

Obesity is a chronic disease that has been associated with chronic stress and hypercaloric diet (HD) consumption. Increased ingestion of food containing sugar and fat ingredients (comfort food) is proposed to "compensate" chronic stress effects. However, this eating habit may increase body fat depositions leading to obesity. This study evaluated behavioral/physiological parameters seeking to establish whether there is an association between the effects of HD intake and stress, and to test the hypothesis that the development of anxious behavior and obesity during chronic stress periods depends on the type of diet. Sixty-day-old male Wistar rats (n = 100) were divided into four groups: standard chow, hypercaloric diet, chronic stress/standard chow and chronic stress/hypercaloric diet. Chronic stress was induced by restraint stress exposure for 1 h/day, for 80 d. At the end of this period, rat behavior was evaluated using open-field and plus-maze tests. The results showed that HD alone increased weight gain and adipose deposition in subcutaneous and mesenteric areas. However, stress reduced weight gain and adipose tissue in these areas. HD also increased naso-anal length and concurrent stress prevented this. Behavioral data indicated that stress increased anxiety-like behaviors and comfort food reduced these anxiogenic effects; locomotor activity increased in rats fed with HD. Furthermore, HD decreased corticosterone levels and stress increased adrenal weight. The data indicate that when rats are given HD and experience chronic stress this association reduces the pro-obesogenic effects of HD, and decreases adrenocortical activity.

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.

Spinal cord brain-derived neurotrophic factor levels increase after dexamethasone treatment in male rats with chronic inflammation.

Dexamethasone is widely used in the therapy of chronic inflammatory diseases for its pain-modulating effects. The objective of this study was to evaluate the effect of dexamethasone on nociception and local inflammation, and the levels of brain-derived neurotrophic factor (BDNF) in the spinal cord in male rats with chronic inflammation induced by complete Freund's adjuvant (CFA). Rats were randomly divided into a control group (not manipulated) and 2 CFA-induced chronic inflammation groups (in the 15th post-CFA injection): 1 injected with vehicle (saline solution) and 1 received dexamethasone (0.25 mg/kg) for 8 days. The hot-plate and electronic von Frey tests were performed 24 h after the end of treatment. BDNF spinal cord levels were determined by enzyme-linked immunosorbent assay (ELISA). The level of inflammation in the tibiotarsal joint (the ankle region) was evaluated histologically at the end of treatment. Dexamethasone produced significantly increased latency in the hot-plate test (one-way ANOVA, p < 0.05) and withdrawal threshold in the electronic von Frey test (p < 0.005). The dexamethasone group showed increased spinal cord BDNF levels compared to the other groups (one-way ANOVA p, < 0.05). Histological analysis showed a local inflammatory response only in animals treated with vehicle, which demonstrated that the dexamethasone treatment decreased the inflammatory process. Our findings corroborate the antinociceptive and anti-inflammatory properties of dexamethasone. In addition, we showed that the dexamethasone treatment increased BDNF levels in the spinal cord; its pain- modulating effects can be attributed to this effect.

After-effects of consecutive sessions of transcranial direct current stimulation (tDCS) in a rat model of chronic inflammation.

Transcranial direct current stimulation (tDCS) induces cortical excitability changes in animals and humans that can last beyond the duration of stimulation. Preliminary evidence suggests that tDCS may have an analgesic effect; however, the timing of these effects, especially when associated with consecutive sessions of stimulation in a controlled animal experiment setting, has yet to be fully explored. To evaluate the effects of tDCS in inflammatory chronic pain origin immediately and 24 h after the last treatment session, complete Freund's adjuvant (CFA) was injected (100 µl) in the right footpad to induce inflammation. On the 15th day after CFA injection, rats were divided into two groups: tDCS (n = 9) and sham (n = 9). The tDCS was applied for 8 days. The hot plate and Von Frey tests were applied immediately and 24 h after the last tDCS session. Eight 20-min sessions of 500 µA anodal tDCS resulted in antinociceptive effects as assessed by the hot plate test immediately (P = 0.04) and 24 h after the last tDCS session (P = 0.006), for the active tDCS group only. There was increased withdrawal latency in the Von Frey test at 24 h after the last session (P = 0.01). Our findings confirm the hypothesis that tDCS induces significant, long-lasting, neuroplastic effects and expands these findings to a chronic pain model of peripheral inflammation, thus supporting the exploration of this technique in conditions associated with chronic pain and peripheral inflammation, such as osteoarthritis.