Tail-flick Latency Research Articles

Teneligliptin Exerts Antinociceptive Effects in Rat Model of Partial Sciatic Nerve Transection Induced Neuropathic Pain.

Neuropathic pain (NP), is a chronic pain resulting from nerve injury, with limited treatment options. Teneligliptin (TEN) is a dipeptidyl peptidase-4 inhibitor (DPP-4i) approved to treat type 2 diabetes. DPP-4is prevent the degradation of the incretin hormone glucagon-like peptide 1 (GLP-1) and prolong its circulation. Apart from glycemic control, GLP-1 is known to have antinociceptive and anti-inflammatory effects. Herein, we investigated the antinociceptive properties of TEN on acute pain, and partial sciatic nerve transection (PSNT)-induced NP in Wistar rats. Seven days post PSNT, allodynia and hyperalgesia were confirmed as NP, and intrathecal (i.t) catheters were implanted and connected to an osmotic pump for the vehicle (1 μL/h) or TEN (5 μg/1 μL/h) or TEN (5 μg) + GLP-1R antagonist Exendin-3 (9–39) amide (EXE) 0.1 μg/1 μL/h infusion. The tail-flick response, mechanical allodynia, and thermal hyperalgesia were measured for 7 more days. On day 14, the dorsal horn was harvested and used for Western blotting and immunofluorescence assays. The results showed that TEN had mild antinociceptive effects against acute pain but remarkable analgesic effects against NP. Furthermore, co-infusion of GLP-1R antagonist EXE with TEN partially reversed allodynia but not tail-flick latency. Immunofluorescence examination of the spinal cord revealed that TEN decreased the immunoreactivity of glial fibrillary acidic protein (GFAP). Taken together, our findings suggest that TEN is efficient in attenuation of PSNT-induced NP. Hence, the pleiotropic effects of TEN open a new avenue for NP management.

Dopamine receptors in the anterior cingulate cortex implicate in nicotine enhanced morphine analgesia.

It is well known that the anterior cingulate cortex (ACC) plays an important role in acute pain perception. In the present study, we aimed to investigate the possible involvement of the ACC dopamine D1 and D2 receptors in nicotine plus morphine-induced analgesia. The ACC's of adult male Wistar rats were bilaterally cannulated bystereotaxic instrument and the tail-flick test was used to measure the thermal pain threshold. The results indicated that subcutaneous (s.c.) injection of nicotine (0.3mg/kg) potentiated the analgesic response of intraperitoneal (i.p.) administration of morphine (3mg/kg). Systemic administration of the same doses of nicotine or morphine alone had no effect on tail-flick latency. Intra-ACC administration of apomorphine (0.3-0.9μg/rat), the non-selective D1/D2 receptors agonist, plus ineffective doses of nicotine (0.1mg/kg, s.c.) plus morphine (3mg/kg, i.p) induced analgesia in rats. In addition, the analgesia induced with co-administration of nicotine and morphine was inhibited via intra-ACC administration of SCH23390 (0.5-1μg/rat) or sulpiride (0.5-2μg/rat), the selective antagonists of D1 or D2 receptors, respectively. The intra-ACC microinjection of the same doses of drugs alone had no effect on tail-flick latency. Cubic interpolation analysis also confirmed that activation or inactivation of the ACC D1 and D2 receptors by different doses of drugs can modulate the nicotine-morphine analgesic response. The findings suggest that the ACC has an important role in acute thermal pain perception and modulates the analgesia induced by nicotine plus morphine via dopaminergic receptors.

Electrophysiological Study on the Influence of the Morphine Microiontophoresis on Firing Activity of Neurons in Nuclei Related to Acupuncture Analgesia

Background and Aim: Many nuclei such as periaqueductal central gray (PAG), raphe magnus nucleus (RMG) and gigantocellular reticular nucleus (Gi) are related in acupuncture analgesia. The aim of this study is to find the analgesic characteristics when dorsolateral periaqueductal gray (DLPAG), ventrolateral periaqueductal gray (VLPAG), RMG and Gi were individually stimulated in rat. Methods: Wistar rats (200~230g) were used in experiments. Rats were put in a small plastic box except the tail when the tail of a rat was stimulated by using radiant heat, tail flick latency (TFL), threshold of the painful response on account of the radiant heat was determined. The stimulus experiments were performed 3 to 5 days after inserting the electrodes. The current intensity for microiontophoresis is 30nA and time is 20s. Results: When DLPAG was locally stimulated in rats, the analgesia gradually appeared. Its characteristics resembled those of electroacupuncture at ST36 point. And then the analgesic effect appeared only in the period when VLPAG, RMG and Gi were individually stimulated in rats, but didn’t appear after cessation of stimulation. The rates of the excited neurons in the VLPAG, RMG and Gi were increased by microiontophoresis of morphine. Conclusion: There are mechanisms inhibiting the painful impulse in input of spinal cord by influence of endogenous morphine-type substance affecting neurons in VLPAG, RMG, and Gi among the mechanisms of electroacupuncture analgesia on ST36 point.

Synergistic effect between imipramine and citicoline upon induction of analgesic and antidepressant effects in mice

Imipramine is a tricyclic antidepressant (TCA) drug that is sometimes used to treat neuropathic pain. Citicoline is a dietary supplement that has been used as a neuroprotective agent for neurological disorders. Probable interaction between imipramine and citicoline on pain and depression behaviors was examined in mice using a tail-flick test, open field test (OFT), forced swimming test (FST), and tail suspension test (TST). The results indicated that the intraperitoneal (i.p.) administration of citicoline (50 mg/kg) induced analgesic and antidepressant-like behaviors in mice. Similarly, i.p. injection of imipramine (5 mg/kg) induced dose-dependent anti-nociceptive and anti-depressive effects. Co-administration of different doses of imipramine (1.25, 2.5, and 5 mg/kg) along with an ineffective dose of citicoline (6.25 mg/kg) increased tail-flick latency and decreased immobility time in the FST, suggesting an analgesic and antidepressant-like behaviors. Interestingly, there is a synergistic effect between imipramine and citicoline upon the induction of analgesic and antidepressant effects. All doses of the drugs had no significant effect on the locomotor activity. Based on these results, it can be concluded that the administration of citicoline (as an adjuvant drug) in combination with imipramine increased the efficacy of TCA drugs for modulation of pain and depression behaviors.

Effects of Spirulina platensis on neuropathic pain in Wistar rats

Background: In treatment of neuropathic pain, conventional analgesics showed various adverse effects. Spirulina platensis (Sp), a medicinal herb, shown to possess several beneficiary biological activities including analgesic, anti-inflammatory and anti-ulcerogenic potential. Objectives: To assess the effect of Sp on neuropathic pain in Wistar rats and also to assess the involvement of ATP sensitive potassium channel (KATP) as its possible underlying mechanism of action. Methods: For this experimental study 120 Wistar rats of both sexes (200±50 gm body weight) were grouped into control [normal saline (NS) 5 ml/kg/day], sham control [sham surgery + NS], CCI control [Chronic constriction injury to sciatic nerve (CCI) + NS], Sp experimental [CCI + Sp 400 mg/kg/day], Gli experimental [CCI + Sp (400 ml/kg/day) + glibenclamide (15 mg/kg)] groups. Sp and NS were administered orally once daily for consecutive 21 days and single dose of glibenclamide was given intraperitoneally. Then again on the basis of neuropathic pain evaluation tests, all the groups were subdivided into ‘a’ (for walking track analysis), ‘b’ (for cold tail immersion test), ‘c’ (for von Frey test), ‘d’ (for hot plate test). The statistical analysis was done by one-way ANOVA followed by Bonferroni post hoc test, where P£0.05 was considered as statistically significant. Results: In this study, Sp showed significantly (P£0.001) higher sciatic functional index, tail flick latency, paw withdrawal threshold and reaction time in Sp experimental rats compared to those of CCI control rats. In addition, there were significant (P£0.001) differences in the above-mentioned variables between rats of Sp experimental group and Gli experimental group. Conclusion: From the present study it could be concluded that, Spirulina platensis prevents the development of neuropathic pain in Wistar rats through opening of KATP channel. J Bngladesh Soc Physiol 2021;16(1): 1-10

Activation of spinal PDGFRβ in microglia promotes neuronal autophagy via p38 MAPK pathway in morphine-tolerant rats.

The adverse side effects of opioids, especially antinociceptive tolerance, limit their clinical application. A recent study reported that platelet-derived growth factor receptor β (PDGFRβ) blockage selectively inhibited morphine tolerance. Autophagy has been reported to contribute to the cellular and behavioral responses to morphine. However, little is known about the relationship between PDGFRβ and autophagy in the mechanisms of morphine tolerance. In this study, rats were intrathecally administered with morphine twice daily for 7days to induce antinociceptive tolerance, which was evaluated using a tail-flick latency test. By administration autophagy inhibitor 3-Methyladenine, PDGFRβ inhibitor imatinib, p38 mitogen-activated protein kinase (MAPK) inhibitor SB203580 hydrochloride and minocycline hydrochloride, western blot, immunofluorescence, and transmission electron microscopy techniques were used to elucidate the roles of PDGFRβ, autophagy, and related signaling pathways in morphine tolerance. This study demonstrated for the first time that spinal PDGFRβ in microglia promotes autophagy in gamma-aminobutyric acid (GABA) interneurons through activating p38 MAPK pathway during the development of morphine tolerance, which suggest a potential strategy for preventing the development of morphine tolerance clinically, thereby improving the use of opioids in pain management.

Loss of Nociceptin/Orphanin FQ peptide receptor protects against traumatic brain injury (TBI)‐induced deficits in male and female rats

Introduction : Traumatic brain injury (TBI) is a leading cause of death and disability in the United States and often chronically affects mental and physical health and overall quality of life. We previously reported that acute treatment of blast TBI with a Nociceptin/OrphaninFQ (N/OFQ) peptide receptor (NOP) antagonist improved vestibulomotor deficits in male rats, corresponding to TBI-induced increases in NOP and its endogenous neuropeptide N/OFQ. The goal of this study is to determine whether the absence of NOP protects against neurological and behavioral sequelae of TBI in male and female KO rats compared to WT. Methods Male and female Wistar NOP receptor knockout (NOP KO) and wildtype (WT) rats received either a sham craniotomy, mild TBI (mTBI) or moderate TBI (ModTBI) controlled cortical impact (CCI) to the left cerebral hemisphere. Injury severity and recovery were assessed using modified neurological severity score (mNSS) on days 1 and 8 post-TBI. Vestibulomotor function was determined using the rotarod. Nociceptive sensitivity to mechanical and thermal stimuli were determined by measuring hind paw withdrawal threshold (PWT) to plastic filaments and by measuring tail flick latency (TFL) from radiant heat, respectively, prior to injury (baseline) and on days 2, 4, and 7 post-TBI. The presence of anxiety-like symptoms was assessed using the elevated plus maze (EPM) on day 7 post-TBI. Data were analyzed by two-way ANOVA with or without repeated measures (as appropriate). Results Rats of both genotypes and sexes showed complete neurological recovery (mNSS<1) following mTBI, and partial recovery following ModTBI by day 8. Mild and ModTBI produced significant vestibular deficits in rat rotarod performance on days 1-8 post-TBI in WT male (n=7-8). In WT females (n=8), ModTBI produced vestibular deficits on days 1-7, whereas mTBI only produced vestibular deficits on days 1-4. Interestingly, neither male (n=5-6) nor female (n=3) mTBI NOP KO rats exhibited vestibulomotor deficits. ModTBI caused significant vestibular deficits only on day 1 post-TBI in male and female NOP KO rats. Rotarod performance in WT females was significantly worse than KO females on days 2-4 post TBI following moderate injury (*p<0.05), and on days 4-7 following mild injury (*p<0.05). WT males (n=7-8) and females (n=8) exhibited thermal hyperalgesia and mechanical allodynia throughout the study, with little difference between mild and moderate TBI groups. KO males (n=3) developed no thermal hyperalgesia after either mild or ModTBI. Only ModTBI rats developed mechanical allodynia, and it lasted throughout the study. KO females (n=3) showed both thermal and mechanical hypersensitivity on day 2 and only mechanical hypersensitivity on day 4. No differences in anxiety-like behaviors were found between any of the groups. Conclusion The N/OFQ-NOP system contributes to vestibular deficits and hyperalgesia associated with TBI; the absence of NOP protects against TBI-induced vestibulomotor deficits and nociceptive hypersensitivity.

Glutathione ethyl ester reverses the deleterious effects of fentanyl on ventilation and arterial blood-gas chemistry while prolonging fentanyl-induced analgesia

There is an urgent need to develop novel compounds that prevent the deleterious effects of opioids such as fentanyl on minute ventilation while, if possible, preserving the analgesic actions of the opioids. We report that L-glutathione ethyl ester (GSHee) may be such a novel compound. In this study, we measured tail flick latency (TFL), arterial blood gas (ABG) chemistry, Alveolar-arterial gradient, and ventilatory parameters by whole body plethysmography to determine the responses elicited by bolus injections of fentanyl (75 μg/kg, IV) in male adult Sprague–Dawley rats that had received a bolus injection of GSHee (100 μmol/kg, IV) 15 min previously. GSHee given alone had minimal effects on TFL, ABG chemistry and A-a gradient whereas it elicited changes in some ventilatory parameters such as an increase in breathing frequency. In vehicle-treated rats, fentanyl elicited (1) an increase in TFL, (2) decreases in pH, pO2 and sO2 and increases in pCO2 (all indicative of ventilatory depression), (3) an increase in Alveolar-arterial gradient (indicative of a mismatch in ventilation-perfusion in the lungs), and (4) changes in ventilatory parameters such as a reduction in tidal volume, that were indicative of pronounced ventilatory depression. In GSHee-pretreated rats, fentanyl elicited a more prolonged analgesia, relatively minor changes in ABG chemistry and Alveolar-arterial gradient, and a substantially milder depression of ventilation. GSHee may represent an effective member of a novel class of thiolester drugs that are able to prevent the ventilatory depressant effects elicited by powerful opioids such as fentanyl and their deleterious effects on gas-exchange in the lungs without compromising opioid analgesia.

Hydrogen enriched saline alleviates morphine tolerance via inhibiting neuroinflammation, GLT-1, GS nitration and NMDA receptor trafficking and functioning in the spinal cord of rats

The development and maintenance of morphine tolerance showed association with neuroinflammation and dysfunction of central glutamatergic system (such as nitration of glutamate transporter). Recent evidence indicated that hydrogen could reduce the levels of neuroinflammation and oxidative stress, but its role in morphine tolerance has not been studied. The rats were intrathecally administered with morphine (10 μg/10 μL each time, twice/day for 5 days). Hydrogen enriched saline (HS) or saline was given intraperitoneally at 1, 3 and 10 mL/kg for 10 min before each dose of morphine administration. The tail-flick latency, mechanical threshold and thermal latency were assessed one day (baseline) before and daily for up to 5 days during morphine injection. The pro-inflammatory cytokine expressions [tumor necrosis factor-alpha (TNF-α), interleukin-1β (IL-1β), IL-6)] (by western blotting), astrocyte activation (by immunofluorescence and western blotting), and nitration of glutamate transporter-1 (GLT-1) and glutamine synthetase (GS) (by immunoprecipitation), membrane and total expression of N-methyl-d-aspartic acid (NMDA) receptor NR1 and NR2B subunits were carried out in the spinal dorsal horns. Chronic morphine administration induced antinociceptive tolerance, and together led to increased TNF-α, IL-1β and IL-6 expression, astrocyte activation, GLT-1 and GS nitration, increased membrane and total NR1, NR2B expression. Injection of HS attenuated morphine tolerance in a dose-dependent manner, decreased proinflammatory cytokine expression, inhibited astrocyte activation, decreased GLT-1 and GS nitration, and inhibited membrane trafficking of NMDA receptor. Our result showed that hydrogen pretreatment prevented morphine tolerance by reducing neuroinflammation, GLT-1, GS nitration, NMDA receptor trafficking in the spinal dorsal horn. Pretreatment with hydrogen might be considered as a novel therapeutic strategy for the prevention of morphine tolerance.

Synthesis and Assessment of Fused β-Carboline Derivatives as Kappa Opioid Receptor Agonists.

The synthesis of 5-formyl-6-aryl-6H-indolo[3,2,1-de][1,5] naphthyridine-2-carboxylates by reaction between 1-formyl-9H-β-carbolines and cinnamaldehydes in the presence of pyrrolidine in water with microwave irradiation is described. Pharmacophoric modification of the formyl group offered several new fused β-carboline derivatives, which were investigated for their κ-opioid receptor (KOR) agonistic activity. Two compounds 4 a and 4 c produced appreciable agonist activity on KOR with EC50 values of 46±19 and 134±9 nM, respectively. Moreover, compound-induced KOR signaling studies suggested both compounds to be extremely G-protein-biased agonists. The analgesic effect of 4 a was validated by the increase in tail flick latency in mice in a time-dependent manner, which was completely blocked by the KOR-selective antagonist norBNI. Moreover, unlike U50488, an unbiased full KOR agonist, 4 a did not induce sedation. The docking of 4 a with the human KOR was studied to rationalize the result.

Maternal Morphine Exposure and Post-Weaning Social Isolation Impair Memory and Ventral Striatum Dopamine System in Male Offspring: Is an Enriched Environment Beneficial?

Maternal opioids abuse has some deleterious consequences on next generations. Besides, children’s rearing conditions can affect the behavioral states and brain plasticity in their later life. In the present study, we investigated the effects of maternal morphine (MOR) treatment and post-weaning rearing conditions on memory, pain threshold, and the ventral striatum dopaminergic activity in male offspring. Female Wistar rats were treated twice daily either with escalating doses of MOR or with normal saline (NS) one week before mating, during pregnancy and lactation. After weaning, the male pups were assigned to six groups and then raised for an 8-week period under three different conditions: standard (STD), isolated (ISO) or enriched environment (EE). The behavioral tests, including passive avoidance task, novel object recognition, and tail-flick test, were also performed. Moreover, the ventral striatum dopamine’s content (DA), mRNA expressions of dopamine receptor 1(D1R) and dopamine receptor 2 (D2R), and dopamine transporter (DAT) were evaluated. The obtained data showed that maternal MOR exposure and post-weaning social isolation could dramatically impair memory in offspring, while EE could reverse these adverse outcomes. Moreover, results of tail flick latency indicated the increased pain threshold in EE animals. At molecular level, maternal MOR injections and social isolation reduced DA levels and altered expressions of D1R, D2R, and DAT within the ventral striatum of these male offspring. However, post-weaning EE partially buffered these changes. Our finding signified the effects of maternal MOR exposure and social isolation on the behaviors and neurochemistry of brain in next generation, and it also provided evidence on reversibility of these alterations following EE.

Antinociceptive and anti-inflammatory activities of Copaifera pubiflora Benth oleoresin and its major metabolite ent-hardwickiic acid

Ethnopharmacological relevanceCopaifera species folkloric names are “copaíbas, copaibeiras, copaívas or oil stick”, which are widely used in Brazilian folk medicine. Among all ethnopharmacological applications described for Copaifera spp oleoresins, their anti-inflammatory effect stands out. However, the knowledge of anti-inflammatory and antinociceptive properties of Copaifera pubiflora Benth is scarce. Aim of the studyTo investigate the cytotoxic, anti-inflammatory, and antinociceptive activities of C. pubiflora oleoresin (CPO), and its major compound ent-hardwickiic acid (HA). Material and methodsThe phosphatase assay was used to evaluate the cytotoxicity of CPO and HA in three different cell lines. CPO and HA doses of 1, 3, and 10 mg/kg were employed in the biological assays. The assessment of motor activity was performed using open-field and rotarod tests. Anti-inflammatory activity of CPO and HA was assessed through luciferase assay, measurement of INF-γ, IL-1β, IL-6, IL-10, and TNF-α in a multi-spot system with the immortalized cell line THP-1, zymosan-induced arthritis, and carrageenan-induced paw edema. Acetic acid-induced abdominal writhing and formalin tests were undertaken to evaluate the antinociceptive potential of CPO and HA. In addition, the evaluation using carrageenan was performed to investigate the effect of CPO in pain intensity to a mechanical stimulus (mechanical hyperalgesia), using the von Frey filaments. A tail-flick test was used to evaluate possible central CPO and HA actions. ResultsIn the cytotoxicity evaluation, CPO and HA were not cytotoxic to the cell lines tested. CPO and HA (10 mg/kg) did not affect animals' locomotor capacity in both open-field and rotarod tests. In the luciferase assay, CPO and HA significantly reduced luciferase activity (p < 0.05). This reduction indicates a decrease in NF-κB activity. HA and CPO decreased INF-γ, IL-1β, IL-6, IL-10, and TNF-α at 24 and 72 h in the multi-spot system. In zymosan-induced arthritis, CPO and HA decreased the number of neutrophils in the joint of arthritic mice and the number of total leukocytes (p < 0.05). In experimental arthritis HA significantly decreased joint swelling (p < 0.05). CPO and HA also increased the mechanical threshold during experimental arthritis. HA and CPO significantly inhibited the carrageenan-induced paw edema, being the doses of 10 mg/kg the most effective, registering maximum inhibitions of 58 ± 8% and 76 ± 6% respectively, p < 0.05. CPO and HA reduced the nociceptive behavior in both phases of formalin at all tested doses. The highest doses tested displayed inhibitions of 87 ± 1% and 72 ± 4%, respectively, p < 0.001, in the first phase, and 87 ± 1% and 81 ± 2%, respectively, p < 0.001, in the second phase. Oral treatment of CPO and HA (1, 3, 10 mg/kg) significantly reduced the nociceptive response in acetic acid-induced abdominal writhings, and the 10 mg/kg dose was the most effective with maximum inhibitions of 86 ± 2% and 82 ± 1%, respectively, p < 0.001. Both HA and CPO significantly decreased the intensity of mechanical inflammatory hyper-nociception on carrageenan-induced hyperalgesia at all tested doses, and 10 mg/kg was the most effective dose with maximum inhibitions of 73 ± 5% and 74 ± 7%, respectively, p < 0.05.CPO increased the tail-flick latencies in mice, and concomitant administration of naloxone partially reduced its effect. ConclusionsCPO and HA may inhibit the production of inflammatory cytokines by suppressing the NF-κB signaling pathway, resulting in anti-inflammatory and antinociceptive activities.

Involvement of opioidergic and GABAergic systems in the anti-nociceptive activity of the methanolic extract of Cuscuta Epithymum Murr. in mice

Ethnopharmacological relevanceCuscuta epithymum Murr. (CE) is a parasitic plant used as a traditional medicine to treat various diseases such as muscle and joint pains and headache different parts of the world, Europe in the north, Asia in the east. Aim of the studyIn this study, we aimed to investigate the anti-nociceptive effect of the methanolic extract of the aerial parts of CE and its probable mechanism(s) in mice. Materials and methodsThe anti-nociceptive activity of different doses of CE methanolic extract (2.5, 5, 10, 25, 50 and 100 mg/kg, i.p.) was assessed using tail flick, formalin and writhing tests. Morphine (5 mg/kg, s.c.) was used as positive control drug. The possible mechanisms were evaluated by using naloxone (4 mg/kg, i.p.), ondansetron (4 mg/kg, i.p.), picrotoxin (0.6 mg/kg, i.p.) and MK-801 (0.03 mg/kg, i.p.). ResultsGC-MS analysis indicated that one of the main components of CE extract was terpenoid compounds. The CE extract (25–100 mg/kg), like morphine, reduced tail flick latency and nociceptive response in both phases of the formalin test. We also observed that the extract significantly decreased the number of abdominal contractions dose-dependently from 5 to 100 mg/kg. The results of tail flick and the first phase of formalin test proved that unlike ondansetron and MK-801, naloxone and picotroxin were able to reverse the anti-nociceptive effect of CE extract. ConclusionOur observations showed the anti-nociceptive potential of the CE extract, which may be mediated by opioidergic and GABAergic systems.

Pharmacological evaluation of processed Cannabis leaves as a non sedative analgesic: The novel approach

Background: Ayurvedic pharmacopoeia records vivid indications of Cannabis (Bhanga) including its analgesic, sedative and intoxicant actions. For inhibition of intoxication, Ayurveda recommends certain processing (Shodhana) techniques for Cannabis. The present study is planned to evaluate the analgesic potential and sedative effects of water washed (Jalaprakshalana)–processed Cannabis sativa leaves through pharmacological experimentation. Methods: Wistar strain albino rats weighing 200 ± 20 g and Swiss albino mice (25–35 g) of either sex were used in the study. Pharmacologically validated models were used to evaluate the analgesic effects (by formalin test and tail flick method) and neuromuscular coordination by rotarod experiment. water-washed–processed Cannabis leaves powder (test drug [TD]) was administered at dose of 22.5 and 45 mg/kg for rat and mouse, respectively, against reference standard morphine sulfate (MS) 5 mg/kg and the results were evaluated statistically. Results: TD at 22.5 and 45 mg/kg showed significant decrease in paw licking response at early phase in formalin test. TD at 22.5 mg/kg showed significant increase in tail flick latency after 3 h, and in 45 mg/kg dose, it was significant up to 4 h. In rotarod experiment, TD did not show any decrease in latency of fall-off time after 1 and 3 h. Conclusion: Water-washed processed Cannabis leaves powder possesses significant analgesic effect at 22.5 mg/kg (250 mg human dose) and 45 mg/kg (500 mg human dose) comparable to MS 5 mg while nonsignificant effect in neuromuscular in-coordination, thus devoid of sedative effect.

The Anti-nociceptive Effect of Ellagic Acid in Streptozotocin-induced Hyperglycemic Rats by Oxidative Stress Involvement.

Introduction:Hyperalgesia is among the current complications of diabetes mellitus; oxidative stress and inflammation were influential in its development. As an herbal component, Ellagic Acid (EA) has some biological activities, including antioxidant and anti-inflammatory effects. This study was designed to evaluate the possible beneficial effect of EA on hypernociception in Streptozotocin (STZ)-induced hyperglycemic rats.Methods:Forty-eight male Wistar rats were divided into the control (receiving vehicle), hyperglycemic, EA (25 mg/kg)-treated control, EA (50 mg/kg)-treated control, EA (25 mg/kg)-treated hyperglycemic, and EA (50 mg/kg)-treated hyperglycemic groups. Hyperglycemia was induced by a single Intraperitoneal (IP) injection of STZ (60 mg/Kg). EA was administered daily by oral gavage for four weeks. The nociceptive response was assessed using Tail-Flick (TF) and Hot-Plate (HP) tests. Also, oxidative stress markers, including Malondialdehyde (MDA), Total Oxidant Status (TOS), and Total Antioxidant Capacity (TAC) in the serum, were evaluated.Results:Hyperglycemic animals were found with significant changes, including a reduction in TF and HP latencies, an elevation in serum MDA level and TOS, and a decrease in serum TAC compared with controls. The treatment of hyperglycemic rats with EA facilitated the reduction of TF latency at the dose of 25 mg/kg and HP latency at 50 mg/kg. Furthermore, EA significantly increased TAC and decreased MDA level at a 50 mg/kg dose and reduced TOS at both doses in the serum of hyperglycemic animals. No significant alterations were found in the parameters studied in EA-treated normal rats.Conclusion:These results displayed the antinociceptive effect of EA in hyperglycemic rats via attenuating oxidative stress. Therefore, EA appears to be a promising agent for managing. Hyperglycemic hypernociception.HighlightsHyperalgesia is among the current complications of diabetes mellitus.Oxidative stress and inflammation were influential in its development.EA has some biological activities, including antioxidant and anti-inflammatory effects.Plain Language SummaryDN is among the most common chronic complications of diabetes among diabetic patients. DPN is mainly characterized by pain perception alterations, increased sensitivity to mild painful stimuli (hyperalgesia), and abnormal pain sensitivity to stimuli. On the other hand, hyperglycemia by induction of multiple changes, such as fatty acid metabolism abnormalities plays a crucial role in developing DN. Oxidative stress and inflammation are involved in the pathogenesis of DPN. The lack of efficacy and various adverse effects of the current medications for DNP, therefore, new therapeutic candidates are continuously required to improve DNP. Several studies reported the antinociceptive activity of EA in different animal models of pain, such as formalin. Since oxidative stress is involved in diabetic hyperalgesia, compounds with antioxidant properties are good candidates for DN management. Therefore, this research aimed to determine the possible effectiveness of EA and evaluate some oxidative stress-related mechanisms.

Harmaline potentiates morphine-induced antinociception via affecting the ventral hippocampal GABA-A receptors in mice

Morphine is one of the most effective medications for treatment of pain, but its side effects limit its use. Therefore, identification of new strategies that can enhance morphine-induced antinociception and/or reduce its side effects will help to develop therapeutic approaches for pain relief. Considering antinociceptive efficacy of harmaline and also highlighted the important role of GABA-A receptors in the pain perception, this research aimed to determine whether the ventral hippocampal (vHip) GABA-A receptors are involved in the possible harmaline-induced enhancement of morphine antinociception. To achieve this, vHip regions of adult male mice were bilaterally cannulated and pain sensitivity was measured in a tail-flick apparatus. Intraperitoneally administration of morphine (0, 2, 4 and 6 mg/kg) or harmaline (0, 1.25, 5 and 10 mg/kg) increased the percentage of maximal possible effect (%MPE) and induced antinociception. Interestingly, co-administration of sub-effective doses of harmaline (5 mg/kg) and morphine (2 mg/kg) induced antinociception. Intra-vHip microinjection of muscimol (0, 200 and 300 ng/mice), a GABA-A receptor agonist, enhanced the anti-nociceptive effects of harmaline (2.5 mg/kg)+morphine (2 mg/kg) combination. Microinjection of the same doses of muscimol into the vHip by itself did not alter tail-flick latency. Intra-vHip microinjection of bicuculline (100 ng/mouse), a GABA-A receptor antagonist, did not cause a significant change in MPE%. Bicuculline (60 and 100 ng/mouse, intra-vHip) was administered with the harmaline (5 mg/kg)+morphine (2 mg/kg), and inhibited the potentiating effect of harmaline on morphine response. These findings favor the notion that GABAergic mechanisms in the vHip facilitate harmaline-induced potentiation of morphine response in the tail-flick test in part through GABA-A receptors. These findings shall provide insights and strategies into the development of pain suppressing drugs.

The amino-terminal heptapeptide of the algesic substance P provides analgesic effect in relieving chronic neuropathic pain

Of painful conditions, somatic pain of acute nociceptive origin can be effectively managed clinically, while neuropathic pain of chronic neuropathy origin is difficult to control. For molecules involved in pain sensation, substance P (SP) is algesic, exacerbating painful sensation, while its amino-terminal fragment, heptapeptide SP(1-7), confers biological activities different from its full-length parent neuropeptide precursor. We previously demonstrated SP(1-7) interaction with pain processing to alleviate chronic pain. Here we evaluated SP(1-7) and its C-terminal amidated analogue SP(1-7)amide, together with SP and opioid agonist DAMGO. We tested mouse behaviors of both acute somatic pain in tail-flick latency assay, and neuropathic pain in sciatic nerve injury model of chronic constriction injury (CCI). DAMGO produced dose-dependent analgesia for somatic pain as expected, so did both SP(1-7) and its analogue SP(1-7)amide, while SP yielded the opposite effect of algesia, in a phenomenon we termed ‘contrintus’, meaning ‘opposite from within’ to denote that two peptides of the same origin (SP and its metabolic fragment SP(1-7)) produced opposite effects. In CCI model, DAMGO showed a general reduction in allodynia sensitivity for both nerve-injured and normal paws, without selective effect for neuropathic pain, consistent with clinical observation that opioids are less effective for chronic neuropathic pain. On the other hand, both SP(1-7) and SP(1-7)amide displayed dose-dependent anti-allodynia effect that is selective for neuropathic pain. These findings suggest that SP(1-7) and its analogue may be useful for developing pharmaceuticals to treat neuropathic pain.

Influence of forced treadmill and voluntary wheel running on the sensitivity of gastric mucosa to ulcerogenic stimuli in male rats.

Physical activity is crucial for maintaining health. Here we investigated the preconditioning effects of exercise on the vulnerability of gastric mucosa to ulcerogenic action of indomethacin (IM, 35 mg/kg, s.c.) or cold-restraint stressor (CR, 3 h, 10°C) in male rats. Single or repeated (5 days) training was used either voluntarily (2 h/day, wheel running) or in a forced way (treadmill). The intensity of the later was either "moderate" (9 m/min, 15 min) or "intensive" (15 m/min, 30 min). All protocols were confirmed by elevated plasma corticosterone and increased tail flick latencies (analgesia). IM-induced ulceration was attenuated by single intensive forced exercise, repeated voluntary and moderate forced exercise. On the contrary, single 2 h voluntary session aggravated the IM-induced ulceration. The ulcerogenic effect of CR was aggravated by single and repeated voluntary and single intensive forced exercise, while repeated moderate forced running was gastroprotective. Single moderate forced running did not influence the ulcerogenic effect of both agents. The results suggest that physical training might have both beneficial and harmful effects on the vulnerability of gastric mucosa to ulcerogenic stimuli depending on the nature of ulcerogenic stimulus as well as the intensity of running and its duration.

Transplantation of neural stem cells encapsulated in hydrogels improve functional recovery in a cauda equina lesion model.

This study explored the therapeutic effects of transplantation of neural stem cells (NSCs) encapsulated in hydrogels in a cauda equina lesion model. NSCs were isolated from neonatal dorsal root ganglion (nDRG) and cultured in three-dimensional porous hydrogel scaffolds. Immunohistochemistry, transmission electron microscopy and TUNEL assay were performed to detect the differentiation capability, ultrastructural and pathological changes, and apoptosis of NSCs. Furthermore, the functional recovery of sensorimotor reflexes was determined using the tail-flick test. NSCs derived from DRG were able to proliferate to form neurospheres and mainly differentiate into oligodendrocytes in the three-dimensional hydrogel culture system. After transplantation of NSCs encapsulated in hydrogels, NSCs differentiated into oligodendrocytes, neurons or astrocytes in vivo. Moreover, NSCs engrafted on the hydrogels decreased apoptosis and alleviated the ultrastructural and pathological changes of injured cauda equina. Behavioral analysis showed that transplanted hydrogel-encapsulated NSCs decreased the tail-flick latency and showed a neuroprotective role on injured cauda equina. Our results indicate transplantation of hydrogel-encapsulated NSCs promotes stem cell differentiation into oligodendrocytes, neurons or astrocytes and contributes to the functional recovery of injured cauda equina, suggesting that NSCs encapsulated in hydrogels may be applied for the treatment of cauda equina injury.

Effects of gestational and breastfeeding caffeine exposure in adenosine A1 agonist-induced antinociception of infant rats.

Caffeine is extensively consumed as a psychostimulant drug, acting on A1 and A2A adenosine receptors blockade. Chronic exposure to caffeine during gestation and breast-feeding may be involved in infant rat's behavioral and biochemical alterations. Our goal was to evaluate the effect of chronic caffeine exposure during gestation and breast-feeding in the functionality of adenosine A1 receptors in infant rats at P14. NTPDase and 5'-nucleotidase activities were also evaluated. Mating of adult female Wistar rats was confirmed by presence of sperm in vaginal smears. Rats were divided into three groups on the first day of pregnancy: (1) control: tap water, (2) caffeine: 0.3g/L until P14, and (3) washout caffeine: caffeine was changed to tap water at P7. Evaluation of nociceptive response was performed at P14 using hot plate (HP) and tail-flick latency (TFL) tests. A1 receptor involvement was assessed using caffeine agonist (CPA) and antagonist (DPCPX). Enzymatic activities assays were conducted in the spinal cord. Gestational and breastfeeding exposure to caffeine (caffeine and washout groups) did not induce significant alterations in thermal nociceptive thresholds (HP and TF tests). Both caffeine groups did not show analgesic response induced by CPA when compared to the control group at P14, indicating chronic exposure to caffeine in the aforementioned periods inhibits the antinociceptive effects of the systemic A1 receptor agonist administration. No effect was observed upon ectonucleotidase activities. Our results demonstrate that chronic caffeine exposure in gestational and breastfeeding alters A1-mediated analgesic response in rats.