Tail-flick Latency Research Articles

Nigella sativa oil on chronic constrictive injury (CCI) induced neuropathic pain of sciatic nerve in Wistar rats

Background: Various adverse effects have been reported with conventional treatments of neuropathic pain. Nigella sativa (N. sativa), a medicinal herb, has been shown to possess several beneficiary effects. Objective: To assess the effects of N. sativa oil on neuropathic pain and ATP sensitive potassium channel (KATP) in Wistar rats. Methods: This experimental study was conducted on 120 Wistar rats (200±50gm). On the basis of treatments, all rats were grouped into Group I [normal control (NC) normal saline (NS) 5 ml/kg]; Group II [sham control (SC) {sham surgery + NS}], Group III [CCI control (CCIC) {Chronic constriction injury to sciatic nerve (CCI) + NS}]; Group IV [N. sativa oil experimental (NSOexp) {CCI + N.sativa (400 mg/kg)}], Group V [Glibenclamide experimental (Gliexp) {CCI + N. sativa (400 mg/kg) + glibenclamide (15 mg/kg)}] groups. Both the NSO and NS were administered orally once daily for consecutive 21 days and single dose of glibenclamide was given intraperitoneally on the day of experiment, to the respective rats. Then on the basis of neuropathic pain evaluation tests, all the groups were subdivided into ‘a’ [for sciatic functional index (SFI) in walking track analysis], ‘b’ [for tail flick latency (TFL) in cold tail immersion test], ‘c’ [for paw withdrawal threshold (PWT) in von Frey test], and ‘d’ (for rection time in hot plate test). The statistical analysis was done by one way ANOVA followed by Bonferroni post hoc test. Results: In this study, significantly (pd”0.001) higher SFI, TFL, PWT and reaction time were found in NSO exp rats when compared to those of CCIC rats. In addition, there were significant (pd”0.001) differences in the above-mentioned variables between rats of NSO exp group and Gliexp group. Conclusion: From the present study it might be concluded that, N. sativa prevents worsening of neuropathic pain in Wistar rats by blocking KATP channel. J Bangladesh Soc Physiol 2023;18(1): 35-45

Mirtazapine Improves Locomotor Activity and Attenuates Neuropathic Pain Following Spinal Cord Injury in Rats via Neuroinflammation Modulation.

Neuroinflammation-related locomotor deficits and neuropathic pain are expected outcomes of spinal cord injury (SCI). The atypical antidepressant mirtazapine has exhibited potential neuroprotective and anti-inflammatory effects. This research aims to investigate the impacts of mirtazapine on post-SCI neuropathic pain and locomotor recovery, with a particular focus on neuroinflammation. The study utilized 30 male Wistar rats divided into five groups: Sham, SCI with vehicle treatment, and SCI administered with mirtazapine (3, 10, and 30mg/kg/day,ip, for one week). Locomotor activity was assessed using the Basso, Beattie, and Bresnahan (BBB) scale. Mechanical, thermal, and cold allodynia were assessed using von-Frey filaments, tail flick latency, and the acetone test, respectively. ELISA was utilized to measure cytokines, while Western blotting was used to determine TRPV1 channel, 5-HT2A receptor, NLRP3, and iNOS expression. Histopathological analyses were also examined, including hematoxylin and eosin (H&E) and Luxol fast blue (LFB) staining. Mirtazapine (10 and 30mg/kg/day) significantly improved locomotor recovery according to BBB score. It attenuated mechanical, thermal, and cold allodynia post-SCI. Moreover, it decreased pro-inflammatory cytokines TNF-α, IL-1β, IL-6, and IL-18, while increasing anti-inflammatory cytokine IL-4 and IL-10. Furthermore, it downregulated iNOS, NLRP3, and TRPV1 expression and upregulated the 5-HT2A receptor. H&E and LFB staining further revealed attenuated tissue damage and decreased demyelination. Our findings suggest that mirtazapine can alleviate neuropathic pain and reinforce locomotor recovery post-SCI by modulating neuroinflammatory responses, NLRP3, iNOS, TRPV1 channel, and 5-HT2A receptor expression.

The restraint stress-induced antinociceptive effects decreased by antagonism of both orexin receptors within the CA1 region of the hippocampus

Studies have indicated that stress-related symptoms can lead to hormonal and neural changes, affecting the pain threshold and nociceptive behaviors. The precise role of orexin receptors (OX1r and OX2r) in stress-induced analgesia (SIA) remains an inquiry yet to be comprehensively elucidated. The current investigation aimed to assess the impact of acute immobilization restraint stress on pain-related behavioral responses after administering antagonists targeting OX1r and OX2r in a rat model using the tail-flick test. After a period of five to seven days post-stereotaxic surgery in CA1, the baseline tail-flick latency (TFL) was recorded for each animal. Subsequently, rats were unilaterally administered varying doses of the OX1r antagonist (SB334867; 1, 3, 10, and 30 nmol), the OX2r antagonist (TCS OX2 29; 1, 3, 10, and 30 nmol), or a vehicle (0.5 μl solution containing 12% DMSO) through an implanted cannula. Following a 5-min interval, the animals were subjected to a restraint stress (RS) lasting for 3 h. The tail-flick test was conducted after the stress exposure, and the TFLs were assessed at 60-min intervals. The findings of this study revealed that RS elicits antinociceptive responses in the tail-flick test. Microinjection of OX1r and OX2r antagonists into the CA1 attenuated RS-induced analgesia during the tail-flick test. Furthermore, the results underscored the preeminent role of OX2 receptors in modulating SIA. In conclusion, the orexin system localized within the hippocampal CA1 region may, in part, contribute to the manifestation of SIA in the context of acute pain.

Benzofuran Iboga-Analogs Modulate Nociception and Inflammation in an Acute Mouse Pain Model.

Pain management following acute injury or post-operative procedures is highly necessary for proper recovery and quality of life. Opioids and non-steroidal anti-inflammatory drugs (NSAIDS) have been used for this purpose, but opioids cause addiction and withdrawal symptoms whereas NSAIDS have several systemic toxicities. Derivatives of the naturally occurring iboga alkaloids have previously shown promising behavior in anti-addiction of morphine by virtue of their interaction with opioid receptors. On this frontier, four benzofuran analogs of the iboga family have been synthesized and their analgesic effects have been studied in formalin induced acute pain model in male Swiss albino mice at 30 mg/kg of body weight dose administered intraperitoneally. The antioxidant, anti-inflammatory and neuro-modulatory effects of the analogs were analyzed. Reversal of tail flick latency, restricted locomotion and anxiogenic behavior were observed in iboga alcohol, primary amide and secondary amide. Local neuroinflammatory mediators' substance P, calcitonin gene related peptide, cyclooxygenase-2 and p65 were significantly decreased whereas the depletion of brain derived neurotrophic factor and glia derived neurotrophic factor was overturned on iboga analog treatment. Behavioral patterns after oral administration of the best analog were also analyzed. Taken together, these results show that the iboga family of alkaloid has huge potential in pain management.

A Buffered Local Anesthetic Without Epinephrine: Development, Characterization, and In Vivo Efficacy and Toxicity Analysis.

Lidocaine hydrochloride (HCl) 2% with 1:100,000 epinephrine (LW/E) is widely used to prevent pain during dental procedures and has been associated with injection sting, jittering effects, slow onset, and a bitter aftertaste. Since LW/E's introduction in 1948, no significant modifications have been proposed. This study aims to design and characterize an improved dental lidocaine HCl injectable formulation without epinephrine (LW/O/E) via buffers, sweeteners, and amino acids. LW/O/E injections were prepared with pH and osmolality values of 6.5-7.0 and 590-610 mOsm/kg. Using the electronic tongue (ETongue), the LW/O/E injectable formulations were characterized for viscosity, injectability, and taste analysis. The results were compared with the LW/E control. In vivo efficacy and anesthetic duration of the samples were measured through radiant heat tail-flick latency (RHTFL) and hot plate (HP) tests and local toxicity was assessed after a single intra-oral injection in Sprague Dawley rats (SDR). The viscosity and injectability values of the LW/O/E samples were found to be comparable to the LW/E injection. ETongue taste analysis showed an improvement in bitterness reduction of the LW/O/E samples compared to the LW/E formulation. Toxicity studies of samples in SDR showed minor and transient signs of erythema/eschar and edema. Anesthetic duration via RHTFL and HP paw withdrawal latency time in SDR were found to be comparable for the LW/O/E Sample 3A and the LW/E injection (p < 0.05). In conclusion, the buffered, higher osmolality and reduced bitterness developed LW/O/E formulation (Sample 3A) could be considered a promising alternative to the LW/E formulation for dental use.

Analgesic activity of new ligands of the NMDA receptor complex

BACKGROUND: The activation of spinal cord NMDA receptors is a key factor in the pathogenesis of acute and chronic pain. Therefore, the use of existing NMDA antagonists in analgesic schemes and the development of new compounds targeting the NMDA receptor complex are gaining attention. New ligands of the glutamate NMDA receptor complex are derivatives of imidazole-4,5-dicarboxylic acid. The conformational rigidity of the molecules of imidazole-4,5-dicarboxylic acid derivatives allows for increased selectivity of interaction and reduced side effects. AIM: This study aimed to investigate the analgesic effect of new ligands of the glutamate NMDA receptor complex, which are derivatives of imidazole-4,5-dicarboxylic acid, in rats using the tail-flick test and the formalin test. MATERIALS AND METHODS: The analgesic activity of the compounds was examined in a model of acute somatic (thermal) pain in the tail-flick test and model of somatic pain induced by algogens in the formalin test. The tested compounds (IEM-303 and IEM-2044) were administered intraperitoneally at doses of 5, 10, 15, and 20 mg/kg. Мetamizole was used as the comparison drug. RESULTS: The experiments demonstrated a significant dose-dependent analgesic effect of the tested compounds on the experimental models of acute pain at doses of 5–20 mg/kg. The tail-flick latency increased by 1.4–1.7 times in the IEM-2044 and IEM-303 groups compared with the value in the control group. CONCLUSIONS: The analgesic activity of the tested compounds at 10–20 mg/kg doses was comparable to that of metamizole, indicating the prospect of developing these agents and further searching for effective and safe analgesics in this pharmacological class.

The additive effect between bupropion and citicoline upon induction of anti-nociceptive effect in nerve-ligated mice

ABSTRACT Objectives Bupropion is an atypical antidepressant that shows robust efficacy in the regulation of neuropathic pain. Citicoline is a dietary supplement which is used as a neuroprotective agent for central nervous system (CNS) disorders. The probable interaction between bupropion and citicoline on neuropathic pain was assessed in male mice. Methods Neuropathic pain was induced by sciatic nerve ligation. Neuropathic pain was examined in nerve-ligated mice using tail-flick and hot-plate tests. Results The results indicated that intraperitoneal (i.p.) administration of citicoline (50 and 100 mg/kg) induced an anti-nociceptive effect in nerve-ligated animals. Similarly, i.p. injection of bupropion (2.5 and 5 mg/kg) induced anti-nociceptive effects in nerve-ligated mice. Co-administration of different doses of bupropion (2.5 and 5 mg/kg) along with a low dose of citicoline (25 mg/kg) caused an anti-nociceptive effect by enhancement of tail-flick and hot plate latencies. Interestingly, there is an additive effect between bupropion and citicoline upon the induction of the anti-nociceptive effect. Conclusions Based on these results, it can be concluded that there is an interaction between bupropion and citicoline upon induction of an anti-nociceptive effect in nerve-ligated mice.

Restraint stress-induced antinociceptive effects in acute pain: Involvement of orexinergic system in the nucleus accumbens

The complicated relevance between stress and pain has been identified. Neurotransmitters and neuropeptides of various brain areas play a role in this communication. Pain inhibitory response is known as stress-induced analgesia (SIA). The studies demonstrated that the nucleus accumbens (NAc) is critical in modulating pain. As a neuropeptide, orexin is crucially involved in initiating behavioral and physiological responses to threatening and unfeeling stimuli. However, the role of the orexin receptors of the NAc area after exposure to restraint stress (RS) as acute physical stress in the modulation of acute pain is unclear. One hundered twenty adult male albino Wistar rats (230–250 g) were used. Animals were unilaterally implanted with cannulae above the NAc. The SB334867 and TCS OX2 29 were used as antagonists for OX1r and OX2r, respectively. Different doses of the antagonists (1, 3, 10, and 30 nmol/0.5 µl DMSO) were microinjected intra-NAc five minutes before exposure to RS (3 hours). Then, the tail-flick test as a model of acute pain was performed, and the nociceptive threshold (Tail-flick latency; TFL) was measured in 60-minute time set intervals. According to this study's findings, the antinociceptive effects of RS in the tail-flick test were blocked during intra-NAc administration of SB334867 or TCS OX2 29. The RS as acute stress increased TFL and deceased pain-like behavior responses. The 50 % effective dose values of the OX1r and OX2r antagonists were 12.82 and 21.64 nmol, respectively. The result demonstrated contribution of the OX1r into the NAc was more remarkable than that of the OX2r on antinociceptive responses induced by the RS. Besides, in the absence of RS, the TFL was attenuated. The current study’s data indicated that OX1r and OX2r into the NAc induced pain modulation responses during RS in acute pain. In conclusion, the findings revealed the involvement of intra-NAc orexin receptors in improving SIA.

Tropine exacerbates the ventilatory depressant actions of fentanyl in freely-moving rats.

Our lab is investigating the efficacy profiles of tropine analogs against opioid-induced respiratory depression. The companion manuscript reports that the cell-permeant tropeine, tropine ester (Ibutropin), produces a rapid and sustained reversal of the deleterious actions of fentanyl on breathing, alveolar-arterial (A-a) gradient (i.e., index of alveolar gas exchange), and arterial blood-gas (ABG) chemistry in freely-moving male Sprague Dawley rats, while not compromising fentanyl analgesia. We report here that in contrast to Ibutropin, the injection of the parent molecule, tropine (200μmol/kg, IV), worsens the adverse actions of fentanyl (75μg/kg, IV) on ventilatory parameters (e.g., frequency of breathing, tidal volume, minute ventilation, peak inspiratory and expiratory flows, and inspiratory and expiratory drives), A-a gradient, ABG chemistry (e.g., pH, pCO2, pO2, and sO2), and sedation (i.e., the righting reflex), while not affecting fentanyl antinociception (i.e., the tail-flick latency) in freely-moving male Sprague Dawley rats. These data suggest that tropine augments opioid receptor-induced signaling events that mediate the actions of fentanyl on breathing and alveolar gas exchange. The opposite effects of Ibutropin and tropine may result from the ability of Ibutropin to readily enter peripheral and central cells. Of direct relevance is that tropine, resulting from the hydrolysis of Ibutropin, would combat the Ibutropin-induced reversal of the adverse effects of fentanyl. Because numerous drug classes, such as cocaine, atropine, and neuromuscular blocking drugs contain a tropine moiety, it is possible that their hydrolysis to tropine has unexpected/unintended consequences. Indeed, others have found that tropine exerts the same behavioral profile as cocaine upon central administration. Together, these data add valuable information about the pharmacological properties of tropine.

The additive effect between citalopram and muscimol upon induction of antinociceptive effect in male mice

Previous investigations have revealed the role of GABAergic and serotonergic systems in the modulation of pain behavior. This research aimed to examine the effects of intracerebroventricular (i.c.v.) infusion of GABAA receptor agonist and antagonist as well as citalopram on pain behavior in male mice. For i.c.v. microinjection, a guide cannula was surgically implanted in the left lateral ventricle of male mice. Pain behavior was evaluated using a tail-flick test. Tail flick latency was measured in each experimental group of mice every 15 min (for 60 min). I.c.v. microinjection of muscimol (0.5 and 1 µg/mouse; GABAA receptor agonist) into the left lateral ventricle dose-dependently induced an antinociceptive effect. On the other hand, i.c.v. infusion of bicuculline (1 µg/mouse; GABAA receptor antagonist) induced a hyperalgesia response. Moreover, intraperitoneally (i.p.) administration of citalopram (8 mg/kg) produced an antinociceptive effect. Co-treatment of citalopram (8 mg/kg) along with muscimol (0.25 µg/mouse) or bicuculline (0.25 µg/mouse) potentiated the antinociceptive effect produced by citalopram. We found an additive antinociceptive effect of citalopram and muscimol in male mice. In conclusion, our results suggested an interaction between citalopram and GABAergic agents on the modulation of pain behavior in male mice.

Neuroprotective Potential of Hygrophila auriculata Targeting Oxidative Stress-Mediated Deficits in Streptozotocin-Induced Sciatic Nerve Injury

Abstract Objective Diabetic neuropathy, a microvascular complication of diabetes, affects 50% of individuals. Addressing this challenge is challenging due to its poorly understood origin and existing therapeutic approaches. This study used a methanolic extract from Hygrophila auriculata (MEHA) to treat oxidative stress-induced sciatic nerve injury in diabetic rats. Materials and Methods A study was conducted to assess the nociceptive reflex after a single streptozotocin (STZ) (45 mg/kg intraperitoneal.) injection. The rats were divided into six groups (n = 6 rats per group). Group I nondiabetic (ND) rats received oral gavage of 1% carboxymethyl cellulose (CMC). The diabetic rats in groups II to VI were given 1% CMC, 100, 200, and 400 mg/kg of MEHA, and 180 mg/kg of metformin (MET). The freshly prepared 1% (w/v) CMC suspension of both MEHA and MET was administered over a 4-week period, commencing from the 28th day through the 56th day post-STZ injection. The impact of STZ-induced sciatic nerve injury was analyzed through the estimation of serum glucose and glycohemoglobin levels, paw withdrawal and tail-flick latencies, oxidative stress markers, and neural histoarchitecture. Results Diabetic (STZ) control group II showed significantly altered serum glucose and glycohemoglobin levels, a reduced paw withdrawal threshold, and reduced paw withdrawal and tail-flick latencies in contrast to ND group I. Furthermore, increased oxidative stress in the sciatic nerve correlates with a reduced nociceptive threshold and disrupted neural histoarchitecture in diabetic rats. These behavioral, biochemical, and molecular changes were markedly and dose-dependently reduced by MEHA and MET treatments. Conclusion The antioxidant efficacy of MEHA modulated oxidative stress in STZ-sensitized diabetic rats and corrected neuropathic pain by attenuating hyperglycemia.

ANALGESIC ACTIVITY OF ETHANOLIC EXTRACT OF PORTIERIA HORNEMANNII (LYNGBYE) P. C. SILVA IN MANDAPAM, RAMANADHAPURAM, TAMIL NADU, INDIA

Objective: The present study intends to detect the analgesic activity of the ethanolic extract of Portieria hornemannii collected from Mandapam, Ramanathapuram district, Tamil Nadu, India. Methods: Diclofenac sodium (100 mg/kg) was the standard. The analgesic activity of P. hornemannii was predicted on intact rats by tail flick latency in the Tail Immersion Method. The various concentrations of the ethanolic extracts were used as 200 mg/kg and 400 mg/kg, considering the body weight of mice. The control group received a typical saline solution. Results: The present study shows that the doses (200 mg/kg and 400 mg/kg body weight of mice) of the ethanolic extracts of P. hornemannii have brought out the analgesic activity. Conclusion: The conclusion of the study is that the ethanolic extracts of P. hornemannii Silva at 400 mg/kg showed more effect than the 200 mg/kg ethanolic extract.

Effects of Crocin on Brain Neurotrophins, Cognition, Balance and Pain in Toxic-Induced Demyelination Model

Objective: The purpose of this study was to investigate the effects of Crocin on brain neuroterophins, cognition, sensory and motor dysfunction and compare to fingolimod effects in toxic-induced demyelination with Ethidium Bromide (EB) in female Wistar rats. Methods: Animals were assigned in to 8 groups; Sham, Sham operated (ShOp), Experimental Autoimmune Encephalomyelitis (EAE), crocin treated (Cr5,10,20 mg/kg), Vehicle, Fingolompd (Fing) and fingolimod + crocin (Cr+Fing). Demyelination was induced by single dose injection of 10 μl of EB 0.1% into the fourth ventricle of the brain. Crocin and fingolimod were administered for 21 days, daily, oral gavage. BDNF, NGF1, tail flake latency, balance and behavioral variables were sampled and analyzed by paired t-test and ANOVA test with repeated post hoc measurements. Results: The results showed that crocin improves all studied factors, but remarkable improvements were observed in dosage of 10 mg/kg. Crocin (10mg/kg) and fingolimod (1mg/kg) significantly improved cognition variables in open field test, sensory and motor nerve conduction velocity, tail flick latency and clinical scores (p&lt;005). In addition, applying of crocin co-administered with fingolimod led to significant increases in all assessed factors, greater than crocin or fingolimod intervention alone (α≤0.001). Conclusion: Based on the current findings, crocin can improve the level of brain neurotrophins, exploratory behavior, balance and pain after toxin-demyelination as close as fingolimod results.

Inhibition of spinal BRD4 alleviates pyroptosis and M1 microglia polarization via STING-IRF3 pathway in morphine-tolerant rats

BackgroundMorphine tolerance has been a challenging medical issue. Neuroinflammation is considered as a critical mechanism for the development of morphine tolerance. Bromodomain-containing protein 4 (BRD4), a key regulator in cell damage and inflammation, participates in the development of chronic pain. However, whether BRD4 is involved in morphine tolerance and the underlying mechanisms remain unknown. MethodsThe morphine-tolerant rat model was established by intrathecal administration of morphine twice daily for 7 days. Behavior test was assessed by a tail-flick latency test. The roles of BRD4, pyroptosis, microglia polarization and related signaling pathways in morphine tolerance were elucidated by Western blot, real-time quantitative polymerase chain reaction, and immunofluorescence. ResultsRepeated morphine administration upregulated BRD4 level, induced pyroptosis, and promoted microglia M1-polarization in spinal cord, accompanied by the release of proinflammatory cytokines, such as TNF-α and IL-1β. JQ-1, a BRD4 antagonist, alleviated the development of morphine tolerance, diminished pyroptosis and induced the switch of microglia from M1 to M2 phenotype. Mechanistically, stimulator of interferon gene (STING)- interferon regulatory factor 3 (IRF3) pathway was activated and the protective effect of JQ-1 against morphine tolerance was at least partially mediated by inhibition of STING-IRF3 pathway. ConclusionThis study demonstrated for the first time that spinal BRD4 contributes to pyroptosis and switch of microglia polarization via STING-IRF3 signaling pathway during the development of morphine tolerance, which extend the understanding of the neuroinflammation mechanism of morphine tolerance and provide an alternative strategy for the precaution against of this medical condition.

Intra-accumbal orexinergic system contributes to the stress-induced antinociceptive behaviors in the animal model of acute pain in rats.

Stress and pain are interleaved at numerous levels - influencing each other. Stress can increase the nociception threshold in animals, long-known as stress-induced analgesia (SIA). Orexin is known as a neuropeptide that modulates pain. The effect of stress on the mesolimbic system in the modulation of pain is known. The role of the intra-accumbal orexin receptors in the modulation of acute pain by forced swim stress (FSS) is unclear. In this study, 117 adult male albino Wistar rats (270-300 g) were used. The animals were unilaterally implanted with cannulae above the NAc. The antagonist of the orexin-1 receptor (OX1r), SB334867, and antagonist of the orexin-2 receptor (OX2r), TCS OX2 29, were microinjected into the NAc in different doses (1, 3, 10, and 30 nmol/0.5 µl DMSO) before exposure to FSS for a 6-min period. The tail-flick test was carried out as an assay nociception of acute pain, and the nociceptive threshold [tail-flick latency (TFL)] was measured for 60-minute. The findings demonstrated that exposure to acute stress could remarkably increase the TFLs and antinociceptive responses. Moreover, intra-accumbal microinjection of SB334867 or TCS OX2 29 blocked the antinociceptive effect of stress in the tail-flick test. The contribution of orexin receptors was almost equally modulating SIA. The present study's findings suggest that OX1r and OX2r within the NAc modulate stress-induced antinociceptive responses. The intra-accumbal microinjection of orexin receptors antagonists declares inducing antinociceptive responses by FSS in acute pain. Proposedly, intra-accumbla orexinergic receptors have a role in the development of SIA.

Chronic restraint stress induces abnormal behaviors in pain sensitivity and cognitive function in mice: the role of Keap1/Nrf2 pathway

Stress is a series of physical and psychological responses to external and internal environmental stimuli. Growing studies have demonstrated the detrimental impacts of acute restraint stress (ARS) and chronic restraint stress (CRS) on animal behavior. However, the related pathogenesis and therapeutic mechanisms remain unclear. Hence, the present study aimed to examine whether unfolded protein response (UPR) and Kelch-like ECH-associated protein 1 (Keap1)-nuclear factor erythroid 2 related factor 2 (Nrf2) pathway are associated with ARS- and CRS- induced abnormal behaviors of pain sensitivity and cognitive function. We here used four behavioral tests to evaluate pain sensitivity and cognitive function in ARS and CRS mice. CRS markedly decreased Paw Withdrawal Mechanical Threshold (PWMT) and Tail-flick Latency (TFL) scores, whereas ARS altered TFL but had no effect on PWMT scores. Additionally, CRS, but not ARS, significantly changed behaviors in nest building behavior and MWMT. Intriguingly, the expression of Keap1 and Nrf2 protein were decreased in the spinal cord and hippocampus in CRS mice, but not in ARS mice. Moreover, neither the ARS nor the CRS groups significantly differed from the control group in terms of endoplasmic reticulum stress (ERS). Taken together, this study demonstrated that CRS could induce abnormal pain sensitivity and cognitive function probably via Keap1/Nrf2 pathway in spinal cord and hippocampus. It is therefore likely that effective intervention of Keap1/Nrf2 pathway may contribute to preventing and treating hyperalgesia and cognitive dysfunction in CRS.

Ayahuasca and its major component harmine promote antinociceptive effects in mouse models of acute and chronic pain

Ethnopharmacological relevanceAyahuasca (AYA) is a psychedelic brew used in religious ceremonies. It is broadly used as a sacred medicine for treating several ailments, including pain of various origins. Aim of the studyTo investigate the antinociceptive effects of AYA and its mechanisms in preclinical models of acute and chronic pain in mice, in particular during experimental neuropathy. Materials and methodsThe antinociceptive effects of AYA administered orally were assessed in the following models of pain: formalin test, Complete Freund's Adjuvant (CFA)-induced inflammation, tail flick test, and partial sciatic nerve ligation model of neuropathic pain. Antagonism assays and Fos immunohistochemistry in the brain were performed. AYA-induced toxicity was investigated. AYA was chemically characterized. The antinociceptive effect of harmine, the major component present in AYA, was investigated. ResultsAYA (24–3000 μL/kg) dose-dependently reduced formalin-induced pain-like behaviors and CFA-induced mechanical allodynia but did not affect CFA-induced paw edema or tail flick latency. During experimental neuropathy, single treatments with AYA (24–3000 μL/kg) reduced mechanical allodynia; daily treatments once or twice a day for 14 days promoted consistent and sustained antinociception. The antinociceptive effect of AYA (600 μL/kg) was reverted by bicuculline (1 mg/kg) and methysergide (5 mg/kg), but not by naloxone (5 mg/kg), phaclofen (2 mg/kg), and rimonabant (10 mg/kg), suggesting the roles of GABAA and serotonergic receptors. AYA increased Fos expression in the ventrolateral periaqueductal gray and nucleus raphe magnus after 1 h, but not after 6 h or 14 days of daily treatments. AYA (600 μL/kg) twice a day for 14 days did not alter mice's motor function, spontaneous locomotion, body weight, food and water intake, hematological, biochemical, and histopathological parameters. Harmine (3.5 mg/kg) promoted consistent antinociception during experimental neuropathy. ConclusionsAYA promotes consistent antinociceptive effects in different mouse models of pain without inducing detectable toxic effects. Harmine is at least partially accountable for the antinociceptive properties of AYA.

Small G-Protein Rheb Gates Mammalian Target of Rapamycin Signaling to Regulate Morphine Tolerance in Mice.

Analgesic tolerance due to long-term use of morphine remains a challenge for pain management. Morphine acts on μ-opioid receptors and downstream of the phosphatidylinositol 3-kinase signaling pathway to activate the mammalian target of rapamycin (mTOR) pathway. Rheb is an important regulator of growth and cell-cycle progression in the central nervous system owing to its critical role in the activation of mTOR. The hypothesis was that signaling via the GTP-binding protein Rheb in the dorsal horn of the spinal cord is involved in morphine-induced tolerance. Male and female wild-type C57BL/6J mice or transgenic mice (6 to 8 weeks old) were injected intrathecally with saline or morphine twice daily at 12-h intervals for 5 consecutive days to establish a tolerance model. Analgesia was assessed 60 min later using the tail-flick assay. After 5 days, the spine was harvested for Western blot or immunofluorescence analysis. Chronic morphine administration resulted in the upregulation of spinal Rheb by 4.27 ± 0.195-fold (P = 0.0036, n = 6), in turn activating mTOR by targeting rapamycin complex 1 (mTORC1). Genetic overexpression of Rheb impaired morphine analgesia, resulting in a tail-flick latency of 4.65 ± 1.10 s (P < 0.0001, n = 7) in Rheb knock-in mice compared to 10 s in control mice (10 ± 0 s). Additionally, Rheb overexpression in spinal excitatory neurons led to mTORC1 signaling overactivation. Genetic knockout of Rheb or inhibition of mTORC1 signaling by rapamycin potentiated morphine-induced tolerance (maximum possible effect, 52.60 ± 9.56% in the morphine + rapamycin group vs. 16.60 ± 8.54% in the morphine group; P < 0.0001). Moreover, activation of endogenous adenosine 5'-monophosphate-activated protein kinase inhibited Rheb upregulation and retarded the development of morphine-dependent tolerance (maximum possible effect, 39.51 ± 7.40% in morphine + metformin group vs. 15.58 ± 5.79% in morphine group; P < 0.0001). This study suggests spinal Rheb as a key molecular factor for regulating mammalian target of rapamycin signaling.

Green preparation, charetrization, in vitro/in vivo safety assessment and in vivo pain management of nortriptyline HCl loaded in niosome (norosome) manufactured by ecofriendly green method

Pain is an unfavorable feeling that is generally triggered by endogenous or exogenous harmful stimulation and has a strong emotional impact. The objective of this experimentation was to increase the cutaneous absorption of nortriptyline HCl (NOR) encapsulated in a niosome (norosomes) produced by an ultrasonic approach for the management of antinociceptive and anti-inflammatory disorders. Exploring the implications of the cholesterol:surfactant ratio on norosome compositions, the study revealed that increasing cholesterol significantly enlarged the norosome diameter from 66.84 ± 5.70 to 293.06 ± 36.54 nm (p < 0.05). More research revealed that changes in the cholesterol:surfactant ratio could influence the surface charge (19.27 ± 0.89 to 16.30 ± 0.78 mV) and entrapment efficiency (EE%) (7.90 ± 1.59 to 87.44 ± 2.11%) (p < 0.05). The amorphous nature of NOR in the niosome was shown by solid-state research. The dermal absorption study revealed that NOR was present at larger levels in dermal layers (41.79 ± 2.38%) and the receiver area (28.67 ± 1.33%) for norosome gel than for NOR-Carbopol gel. The norosomal’s cell safety was 84%, and the MTT study indicated a reduction in norosome cytotoxicity. The skin irritation analysis conducted on Wistar rats showed that the niosome component used did not cause irritation to the skin. Eventually, in comparison to the control group, norosome formulation demonstrated significant antinociceptive and anti-inflammatory (246.16 ± 53.60 s) actions in the late stage formalin test, tail-flick latency (5.18 ± 0.18 s), and hot plate latency (12.57 ± 1.78 s) (p < 0.05). These findings suggest that niosomes have the potential to enhance the effectiveness of NOR as an antinociceptive and anti-inflammatory agent by improving drug delivery to the targeted site.

Rubia cordifolia L. Attenuates Diabetic Neuropathy by Inhibiting Apoptosis and Oxidative Stress in Rats.

Diabetic neuropathy is a debilitating manifestation of long-term diabetes mellitus. The present study explored the effects of the roots of Rubia cordifolia L. (R. cordifolia L.) in the Wistar rat model for diabetic neuropathy and possible neuroprotective, antidiabetic, and analgesic mechanisms underlying this effect. Rats were divided into five experimental groups. An amount of 0.25% carboxy methyl cellulose (CMC) in saline and streptozotocin (STZ) (60 mg/kg) was given to group 1 and group 2, respectively. Group 3 was treated with STZ and glibenclamide simultaneously while groups 4 and 5 were simultaneously treated with STZ and hydroalcoholic extract of the root of R. cordifolia, respectively. Hot plate and cold allodynias were used to evaluate the pain threshold. The antioxidant effects of R. cordifolia were assessed by measuring Thiobarbituric acid reactive substances (TBARS), reduced glutathione (GSH), catalase (CAT), and superoxide dismutase (SOD). At the end of the study, sciatic nerve and brain tissues were collected for histopathological study. Bcl-2 proteins, cleaved caspase-3, and Bax were assessed through the Western blot method. R. cordifolia significantly attenuated paw withdrawal and tail flick latency in diabetic neuropathic rats. R. cordifolia significantly (p < 0.01) improved the levels of oxidative stress. It was found to decrease blood glucose levels and to increase animal weight in R. cordifolia-treated groups. Treatment with R. cordifolia suppressed the cleaved caspase-3 and reduced the Bax:Bcl2 ratio in sciatic nerve and brain tissue compared to the diabetic group. Histopathological analysis also revealed a marked improvement in architecture and loss of axons in brain and sciatic nerve tissues at a higher dose of R. cordifolia (400 mg/kg). R. cordifolia attenuated diabetic neuropathy through its antidiabetic and analgesic properties by ameliorating apoptosis and oxidative stress.