Tail-flick Test Research Articles

The Influence of Diabetic Peripheral Neuropathy on the Duration of Sciatic Nerve Block with 1.3% Liposomal Bupivacaine and 0.25% Bupivacaine Hydrochloride in a Mouse Model.

Little is known regarding the pharmacological properties of extended-release local anesthetics in the setting of diabetic peripheral neuropathy. We investigated and compared the duration of sciatic nerve block following administration of clinically relevant concentrations of liposomal bupivacaine (LB) and bupivacaine hydrochloride (BH) in diabetic mice with peripheral neuropathy. In this prospective, randomized, and double-blind study, twenty-four female C57BL/6J-OlaHsd mice were assigned to a streptozotocin-induced type 1 diabetes group and a control group without diabetes. The presence of peripheral neuropathy was established by assessing the duration of thermal latency of the plantar and tail-flick tests, following which both groups were subdivided into two subgroups in which 35 mg/kg of 1.31% LB and 7 mg/kg of 0.25% BH were respectively administered for sciatic nerve block. The average sensory block duration with BH was 106 min and 117.1 min in the control and diabetic groups, respectively. With LB, the average sensory block duration was 118 min in the control mice, while in mice with diabetic peripheral neuropathy, the average block duration was significantly longer and above the 270 min limit set in our study. Accordingly, sensory block duration was longer with LB compared to BH, and diabetic peripheral neuropathy significantly increased sciatic nerve block duration with LB.

Exploring pharmacological inhibition of Gq/11 as an analgesic strategy.

Misuse of opioids has greatly affected our society. One potential solution is to develop analgesics that act at targets other than opioid receptors. These can be used either as stand-alone therapeutics or to improve the safety profile of opioid drugs. Previous research showed that activation of Gq/11 proteins by G-protein coupled receptors has pro-nociceptive properties, suggesting that blockade of Gq/11 signalling could be beneficial for pain control. The aim of this study was to test this hypothesis pharmacologically by using potent and selective Gq/11 inhibitor YM-254890. We used a series of behavioural assays to evaluate the acute responses of mice to painful thermal stimulation while administering YM-254890 alone and in combination with morphine. We then used electrophysiological recordings to evaluate the effects of YM-254890 on the excitability of dorsal root ganglion (DRG) nociceptor neurons. We found that systemic administration of YM-254890 produced anti-nociceptive effects and also augmented morphine analgesia in both hotplate and tail flick paradigms. However, it also caused substantial inhibition of locomotion, which may limit its therapeutic utility. To circumvent these issues, we explored the local administration of YM-254890. Intrathecal injections of YM-254890 produced lasting analgesia in a tail flick test and greatly augmented the anti-nociceptive effects of morphine without any significant effects on locomotor behaviour. Electrophysiological studies showed that YM-254890 reduced the excitability of DRG nociceptors and augmented their opioid-induced inhibition. These findings indicate that pharmacological inhibition of Gq/11 could be explored as an analgesic strategy.

Neuroprotective Potential of Intranasally Delivered Sulforaphane-Loaded Iron Oxide Nanoparticles Against Cisplatin-Induced Neurotoxicity

Cisplatin (CIS) is a platinum-based chemotherapeutic drug that is widely used to treat cancer. However, its therapeutic efficiency is limited due to its potential to provoke neurotoxicity. Sulforaphane (SF) is a natural phytochemical that demonstrated several protective activities. Iron oxide nanoparticles (Fe3O4-NPs) could be used as drug carriers. This study aimed to explore the nanotoxic influence of SF-loaded within Fe3O4-NPs (N.SF), and to compare the neuroprotective potential of both N.SF and SF against CIS-induced neurotoxicity. N.SF or SF was administrated intranasally for 5 days before and 3 days after a single dose of CIS (12 mg/kg/week, i.p.) on the 6th day. Neuromuscular coordination was assessed using hanging wire and tail-flick tests. Acetylcholinesterase (AChE) activities and markers of oxidative stress were measured in the brain. In addition, the brain iron (Fe) content was estimated. CIS significantly induced a significant increase in AChE activities and lipid peroxides, and a significant decrement in glutathione (GSH) and nitric oxide (NO) contents. CIS elicited impaired neuromuscular function and thermal hyperalgesia. CIS-induced brains displayed a significant reduction in Fe content. Histopathological examination of different brain regions supported the biochemical and behavioral results. Contradict, treatment of CIS-rats with either N.SF or SF significantly decreased AChE activity, mitigated oxidative stress, and ameliorated the behavioral outcome. The histopathological features supported our results. Collectively, N.SF demonstrated superior neuroprotective activities on the behavioral, biochemical, and histopathological (striatum and cerebral cortex) aspects. N.SF could be regarded as a promising “pre-clinical” neuroprotective agent. Furthermore, this study confirmed the safe toxicological profile of Fe3O4-NPs.

Roxadustat alleviates nitroglycerin-induced migraine in mice by regulating HIF-1α/NF-κB/inflammation pathway.

Sensitization of central pain and inflammatory pathways play essential roles in migraine, a primary neurobiological headache disorder. Since hypoxia-inducible factor-1α (HIF-1α) is implicated in neuroprotection and inflammation inhibition, herein we investigated the role of HIF-1α in migraine. A chronic migraine model was established in mice by repeated injection of nitroglycerin (10 mg/kg, i.p.) every other day for 5 total injections. In the prevention and acute experiments, roxadustat, a HIF-1α stabilizer, was orally administered starting before or after nitroglycerin injection, respectively. Pressure application measurement, and tail flick and light-aversive behaviour tests were performed to determine the pressure pain threshold, thermal nociceptive sensitivity and migraine-related light sensitivity. At the end of experiments, mouse serum samples and brain tissues were collected for analyses. We showed that roxadustat administration significantly attenuated nitroglycerin-induced basal hypersensitivity and acute hyperalgesia by improving central sensitization. Roxadustat administration also decreased inflammatory cytokine levels in serum and trigeminal nucleus caudalis (TNC) through NF-κB pathway. Consistent with the in vivo results showing that roxadustat inhibited microglia activation, roxadustat (2, 10, and 20 μM) dose-dependently reduced ROS generation and inflammation in LPS-stimulated BV-2 cells, a mouse microglia cell line, by inhibiting HIF-1α/NF-κB pathway. Taken together, this study demonstrates that roxadustat administration ameliorates migraine-like behaviours and inhibits central pain sensitization in nitroglycerin-injected mice, which is mainly mediated by HIF-1α/NF-κB/inflammation pathway, suggesting the potential of HIF-1α activators as therapeutics for migraine.

CB1 receptor signalling mediates cannabidiol-induced panicolytic-like effects and defensive antinociception impairment in mice threatened by Bothrops jararaca lancehead pit vipers.

Cannabis sativa-derived substances such as cannabidiol (CBD) have attracted increasing clinical interest and consist in a new perspective for treating some neurological and psychiatric diseases. The aim of this work was to investigate the effect of acute treatment with CBD on panic-like defensive responses displayed by mice threatened by the venomous snake Bothrops jararaca. Mice were habituated in the enriched polygonal arena for snake panic test. After recording the baseline responses of the tail-flick test, the prey were pretreated with intraperitoneal (i.p.) administrations of the endocannabinoid type 1 receptor (CB1) antagonist AM251 (selective cannabinoid 1 receptor antagonist with an IC50 of 8 nM) at different doses, which were followed after 10 min by i.p. treatment with CBD (3 mg/kg). Thirty minutes after treatment with CBD, mice were subjected to confrontations by B. jararaca for 5 min, and the following defensive responses were recorded: risk assessment, oriented escape behaviour, inhibitory avoidance and prey-versus-snake interactions. Immediately after the escape behaviour was exhibited, the tail-flick latencies were recorded every 5 min for 30 min. Mice threatened by snakes displayed several anti-predatory defensive and innate fear-induced antinociception responses in comparison to the control. CBD significantly decreased the risk assessment and escape responses, with a consequent decrease in defensive antinociception. The CBD panicolytic effect was reversed by i.p. treatment with AM251. These findings suggest that the anti-aversive effect of CBD depends at least in part on the recruitment of CB1 receptors.

GPR171 activation regulates morphine tolerance but not withdrawal in a test-dependent manner in mice.

A newly deorphanized G protein-coupled receptor, GPR171, is found to be highly expressed within the periaqueductal gray, a pain-modulating region in the brain. Our recent research has shown that a GPR171 agonist increases morphine antinociception in male mice and opioid signaling in vitro. The objective of this study was to evaluate the effects of combination treatment in females as well as whether chronic treatment can be used without exacerbating morphine-induced tolerance and withdrawal in female and male mice. Our results demonstrate that activation of GPR171 with an agonist attenuates morphine tolerance in both female and male mice on the tail-flick test, but not the hotplate test. Importantly, the GPR171 agonist in combination with morphine does not exacerbate morphine-induced tolerance and withdrawal during long-term morphine treatment. Taken together, these data suggest that the GPR171 agonist may be combined with morphine to maintain antinociception while reducing the dose of morphine and therefore reducing side effects and abuse liability. The outcome of this study is clearly an important step toward understanding the functional interactions between opioid receptors and GPR171 and developing safer therapeutics for long-term pain management.

Pharmacological evaluation of analgesic, anti-inflammatory and anti-pyretic activities of amaranthus spinosus stem.

The herbal medicines have stood the test of time for their safety, efficacy, lesser side effects, cultured and traditional acceptability. Natural plant-based product are promising for the drug discovery and they still continue to play a significant role in future drug development programs. Practitioners of herbal medicine generally use unpurified plant extracts containing several different constituents. The extracts of the plant (Stem) was evaluated for the different pharmacological activities. The need for safer and effective analgesic (Acetic Acid Induced Writhing Test, Eddy’s Hot Plate, Tail Flick Test) anti-inflammatory (Rat hind paw edema test) and antipyretic agents and the lack of enough scientific data to support the claims made in ancient literature prompted the present study. Key words: Analgesic, Anti-pyretic and Anti-inflammatory, Plant Amaranthus spinosus

The N-methyl-D-aspartate receptor antagonist ketamin exerts analgesic effects via modulation of the nitric oxide pathway.

Ketamine, an NMDA receptor antagonist, has been approved to have analgesic effects. It is known that nitric oxide pathway is involved in antinociception but with dual effects. In this study, we investigated the role of nitric oxide in ketamine-induced analgesia. Ketamine was administered to mice acute and chronically with/without nitric oxide synthase (NOS) inhibitors. Experimental models of nociception pain, including hot plate, tail flick, and formalin tests, were performed. Western blot was used to measure levels of nitric oxide synthase enzymes in the brain. Ketamine doses of 0.03 and 0.3 mg/kg had significant analgesic effects (p < 0.01). High-dose chronic ketamine could induce analgesia in later phases of the treatment in tail flick test (p < 0.01). Pretreatment with various NOS inhibitors decreased the analgesic effect. In western blot analysis, the expression of NOS proteins was decreased. Low-dose ketamine is effective in analgesia induction. The expression of nNOS and iNOS proteins is dependent on the inhibition of the NMDA/NO pathway.

Preparation and Optimization of an Ultraflexible Liposomal Gel for Lidocaine Transdermal Delivery.

The pain caused by lidocaine injections into the face prior to facial plastic surgeries intended to remove growths or tumorous lesions has been reported by many patients to be the worst part of these procedures. However, the lidocaine gels and creams currently on the market do not deliver an equal or better local anesthetic effect to replace these injections. To develop an alternative to the painful local anesthetic injection, we prepared ultraflexible liposomes using soy phosphatidylcholine, lidocaine, and different amounts of sodium cholate, a surfactant. The prepared ultraflexible liposomes (UFLs) were examined for particle size, zeta potential, cytotoxicity, and in vitro release. By using a carbomer as a gelling agent, the prepared UFL lidocaine gels were evaluated for their penetration ability in a Franz diffusion cell, using Strat-M membranes. The formulation achieving the highest amount of penetrated lidocaine was chosen for further pH, viscosity, and stability tests. The local anesthetic efficacy of the formulation was investigated by an in vivo tail-flick test in rats. Our findings suggested that this topical gel formulated with ultraflexible liposomal lidocaine has enhanced skin permeation ability, as well as an improved local analgesic effect from the lidocaine.

Anti-inflammatory, antinociceptive effects and involvement of opioid receptors in the antinociceptive activity of Eugenia uniflora leaves obtained with water, ethanol, and propylene glycol mixture

Ethnopharmacological relevanceEugenia uniflora (Myrtaceae) is a species native to Brazil and has a traditional use in the treatment of inflammation. Aim of the studyTo evaluate the anti-inflammatory and antinociceptive effects, and the involvement of opioid receptors in the antinociceptive activity of extract and fractions from Eugenia uniflora leaves. Materials and methodsTLC and HPLC were used to characterize the spray-dried extract (SDE) and fractions. In the in vivo assays, Swiss (Mus musculus) mice were used. Carrageenan-induced hind-paw edema and carrageenan-induced peritonitis models were used to determine the anti-inflammatory effect of the extract (50, 100, or 200 mg/kg). Acetic acid-induced writhing, tail-flick, and formalin tests were used to determine the antinociceptive effect of the extract (50, 100, or 200 mg/kg). The aqueous (AqF) and ethyl acetate (EAF) fractions (6.25, 12.5, and 25 mg/kg) were then combined with naloxone to evaluate the involvement of opioid receptors in the antinociceptive activity. ResultsIn this work, the TLC and HPLC analysis evidenced the enrichment of EAF, which higher concentration of gallic acid (5.29 ± 0.0004 %w/w), and ellagic acid (1.28 ± 0.0002 %w/w) and mainly myricitrin (8.64 ± 0.0002 %w/w). The extract decreased the number of total leukocytes and neutrophils in the peritoneal cavity (p < 0.05), at doses of 100 and 200 mg/kg and showed significant inhibition in the increase of paw edema volume (p < 0.05). The treatment per oral route (doses of 50, 100, and 200 mg/kg) significantly reduced the nociceptive response in acetic acid-induced abdominal writhing (p < 0.05). The effect of the extract on the tail-flick test showed a significant increase in latency time of animals treated at doses of 200 and 100 mg/kg (p < 0.05). The extract and ethyl acetate fraction reduced the nociceptive effect in both phases of formalin at all tested doses. The naloxone reversed the antinociceptive effect of EAF, suggesting that opioid receptors are involved in mediating the antinociceptive activity of EAF of E. uniflora in the formalin test. ConclusionThe current study demonstrates the anti-inflammatory and analgesic activities of water: ethanol: propylene glycol spray-dried extract from E. uniflora leaves using in vivo pharmacological models in mice. Our findings suggest that spray-dried extract and ethyl acetate fraction exhibit peripheral and central antinociceptive activity with the involvement of opioid receptors that may be related to the presence of flavonoids, mainly myricitrin.

Analgesic Effects of Vilazodone, Indatraline, and Talsupram in a Rat Model of Neuropathic Pain.

Drugs that inhibit the reuptake of serotonin, norepinephrine, and/or dopamine are widely used for treating depressive disorders and have emerged as effective drugs for neuropathic pain. They have no substantial anti-nociceptive effects but are considered, with gabapentin/pregabalin, first-line drugs for neuropathic pain. In this study, three different antidepressant agents were used in different doses to investigate their anti-hyperalgesic effects in rat models of neuropathic pain using hot plate and tail flick methods. They have different mechanisms of action; vilazodone hydrochloride is a selective serotonin inhibitor and a 5-HT1A partial agonist; talsupram hydrochloride is a selective noradrenaline inhibitor, and it has a high affinity for noradrenaline transporter (NET), whereas indatraline hydrochloride is a triple reuptake inhibitor that inhibits transporters for 5-HT (SERT), dopamine (DAT), and NET. All the drugs used in the experiment were found to have an anti-hyperalgesic effect in both tests compared to the sham group. When anti-hyperalgesic effects of the three agents were compared to each other, it was found that talsupram hydrochloride was significantly more effective than the two other drugs in hot plate test. However, there was no statistically significant difference in the tail flick test. Indatraline hydrochloride was more effective than vilazodone hydrochloride at the same doses in the tail flick test. Our data suggest that three drugs are effective analgesics in rat models of neuropathic pain and inhibition of noradrenaline reuptake represents the cornerstone of analgesic mechanisms of effective antidepressants.

The Impact of Increase in the Vertical Dimension of Occlusion on Nociception in Rats - A Preliminary Report

Abstract Since the change in vertical dimension of occlusion (VDO) is extremely important in prosthetic dentistry, the aim of the study was to examine the effect of VDO increase on nociception parameters in rodent experimental model. The study was performed on seven experimental groups (6 animals per group) on male Wistaralbino rats: sham; 0.6/3, 0.9/3, and 1.2/3 groups where VDO was increased by 0.6, 0.9, and 1.2 mm (respectively), for three days; 0.6/20, 0.9/20, and 1.2/20 groups where VDO was increased by 0.6, 0.9, and 1.2 mm (respectively), for twenty days. The VDO raising protocols were performed as follows: on a day 1, following anaesthesia, a two-phase impression was taken with addition silicones; on a day 3, the cementing process for both maxillary incisors and inside crowns preparation was performed, and cementing zirconium crowns, manufactured using CAD-CAM technology, were applied. The behavioural testing (the tail flick and hot plate test) was performed on day 3 and 20. The results obtained in the tail flick test suggest that the raise in VDO in the early phase induced increased sensitivity to pain in a stepwise manner, while this hyperalgesic effect was diminished in a timedependent manner. The stepwise increase in VDO also resulted in significant decline in the pain tolerance with the higher VDO (0.9 and 1.2 mm) in the hot plate test that persisted after twenty days in 1.2/20 group. It seems that VDO elevation is sufficient to produce hyperalgesic effect in this experimental model, which may be attenuated in time-dependent manner.

Basolateral amygdala cannabinoid CB1 receptors mediate the antinociceptive activity of harmaline in adolescent male mice

Evidence suggests a clear role for the amygdala endocannabinoid system in pain processing. Harmaline has been also known as the main nociceptive agent extracted from the Peganum harmala plant. In this study, the role of basolateral amygdala (BLA) cannabinoid CB1 receptors in pain sensitivity of harmaline-treated mice were assessed using tail-flick and hot plate methods in adolescent male NMRI mice. Intraperitoneal administration of two higher doses of harmaline (6 and 8 mg/kg) increased tail-flick latency, suggesting an antinociceptive activity. The same result was observed for the higher dose of harmaline in the hot plate test. Intra-BLA microinjection of CB1 receptor agonist ACPA (1 and 1.5 ng/mouse) or (1.5 ng/mouse) enhanced the ineffective dose-response of harmaline on pain threshold in the tail-flick or hot plate tests, respectively. Microinjection of two higher doses of CB1 receptor antagonist AM251 (0.5 and 1 ng/mouse) attenuated the antinociceptive activity of harmaline (8 ng/mouse) in both tail-flick and hot plate tests. Meanwhile, ACPA and AM251 did not alter latency to withdraw from the noxious stimulus in both tests, by themselves. It should be noted that the analgesic dose of the drugs alone or in combination did not affect locomotor activity. The obtained results highlight that BLA CB1 receptors mediate the antinociceptive activity of harmaline.

The Human SCN9A R185H Point Mutation Induces Pain Hypersensitivity and Spontaneous Pain in Mice.

The voltage-gated sodium channel Nav1.7 is encoded by SCN9A gene and plays a critical role in pain sensitivity. Several SCN9A gain-of-function (GOF) mutations have been found in patients with small fiber neuropathy (SFN) having chronic pain, including the R185H mutation. However, for most of these variants, their involvement in pain phenotype still needs to be experimentally elucidated. In order to delineate the impact of R185H mutation on pain sensitivity, we have established the Scn9aR185H mutant mouse model using the CRISPR/Cas9 technology. The Scn9aR185H mutant mice show no cellular alteration in the dorsal root ganglia (DRG) containing cell bodies of sensory neurons and no alteration of growth or global health state. Heterozygous and homozygous animals of both sexes were investigated for pain sensitivity. The mutant mice were more sensitive than the wild-type mice in the tail flick and hot plate tests, acetone, and von Frey tests for sensitivity to heat, cold, and touch, respectively, although with sexual dimorphic effects. The newly developed bioinformatic pipeline, Gdaphen is based on general linear model (GLM) and random forest (RF) classifiers as well as a multifactor analysis of mixed data and shows the qualitative and quantitative variables contributing the most to the pain phenotype. Using Gdaphen, tail flick, Hargreaves, hot plate, acetone, cold plate, and von Frey tests, sex and genotype were found to be contributing most to the pain phenotype. Importantly, the mutant animals displayed spontaneous pain as assessed in the conditioned place preference (CPP) assay. Altogether, our results indicate that Scn9aR185H mice show a pain phenotype, suggesting that the SCN9AR185H mutation identified in patients with SFN having chronic pain contributes to their symptoms. Therefore, we provide genetic evidence for the fact that this mutation in Nav1.7 channel plays an important role in nociception and in the pain experienced by patients with SFN who have this mutation. These findings should aid in exploring further pain treatments based on the Nav1.7 channel.

Protective effect of naringin against oxaliplatin-induced peripheral neuropathy in rats: A behavioral and molecular study.

Oxaliplatin (OXL) is a chemotherapeutic drug used for metastatic and other types of cancer, but it causes peripheral neuropathy as a dose-limiting side effect. Herein, we used the rat model of OXL-induced peripheral neuropathy to demonstrate the protective effects of naringin (NRG) in this neuropathy. In this study, rats were injected with OXL (4 mg/kg, body weight, i.p.) in 5% glucose solution 30 min after oral administration of NRG (50 and 100 mg/kg, body weight) on the 1st, 2nd, 5th, and 6th days. OXL caused sensory and motor neuropathy (as revealed by the hot plate, tail flick, rota-rod, and cold hyperalgesia tests) in the sciatic nerve of rats. Coadministration of oral NRG alleviated OXL-induced sensory and motor neuropathy. Levels of superoxide dismutase, catalase, glutathione peroxidase, nuclear factor erythroid 2-related factor 2, Heme oxygenase-1, nuclear factor-κ B, tumor necrosis factor-α, interleukin-1β, Bax, Bcl-2, caspase-3, paraoxonase, mitogen-activated protein kinase 14, neuronal nitric oxide synthase(nNOS), acetylcholinesterase, and arginase 2 in the sciatic nerve tissues were assessed by real-time polymerase chain reaction. Moreover, the protein levels of caspase-3, Bax, Bcl-2, intercellular adhesion molecules-1, glial fibrillary acidic protein, and nNOS were examined by Western blot analysis. NRG treatment significantly improved all the above-mentioned parameters and reduced OXL-induced oxidative stress, inflammation, and apoptosis in the sciatic nerve tissue. In conclusion, this study demonstrated that NRG significantly attenuated OXL-induced peripheral neuropathy and might be considered as a new protective agent to prevent the OXL-induced peripheral neuropathy.

ViphyllinTM, a Standardized Black Pepper Extract Exerts Antihyperglycemic Effect and Improves Sciatic Nerve Conduction in High Fat Diet/Streptozotocin-Induced Diabetic Model Rats.

PurposeResearch on plant-based formulations has drawn considerable attention in the management of diabetic neuropathy (DN) for having lesser side effects than the synthetic counterparts. Here, we have investigated for the first time the therapeutic effects of a standardized Piper nigrum L., (black pepper) seed extract, ViphyllinTM in mitigating hyperglycemia and neuropathic pain of type 2 diabetes model rats.MethodsType 2 diabetes was induced in male Wistar rats using high fat diet and a single dose of streptozotocin (60 mg/kg i.p.). The diabetic rats were orally administered with Viphyllin containing not less than 30% β-caryophyllene (BCP), at 25 mg, 50 mg and 100 mg/kg/day doses for 6 weeks. Changes in body weight, fasting blood glucose (FBG), glucose tolerance, and blood biochemical parameters were measured. The nociceptive response to thermal stimulus (tail flick test) and sciatic nerve conduction velocity (NCV) were recorded at the end of study.ResultsViphyllin treatment markedly improved the body weight and glucose tolerance in diabetic rats. Also, the extract could significantly reduce the diabetes-induced elevation in FBG, liver and kidney indices. Further, Viphyllin dose-dependently increased the nociception latency in tail flick test compared to untreated diabetic rats (p<0.05). Viphyllin at 100 mg/kg significantly increased the NCV (44.12±1.91*** m/s vs diabetic control 25.80±1.88 m/s). The antioxidant enzyme activities in sciatic nerve tissue were considerably increased in Viphyllin-treated groups compared to diabetic control. A 6-week treatment with Viphyllin markedly reversed the pathological manifestations of diabetes in vital organs such as liver, kidney and pancreas.ConclusionThe study concludes that Viphyllin exerts antidiabetic effects and improves nerve conduction to mitigate neuropathic pain.

Agmatine prevents development of tolerance to anti-nociceptive effect of ethanol in mice.

Drug tolerance is directly correlated with drug abuse and physical dependence. The development of tolerance is manifested as the decline in pharmacological responses of drugs following repeated administration of the constant dose. The present study evaluated the effect of agmatine in ethanol-induced anti-nociception and tolerance in the tail-flick assay in mice. In an acute protocol, ethanol (1 and 2g/kg, i.p. [intraperitoneally]) and agmatine (20 and 40 μg/mouse, i.c.v. [intracerebroventricularly]) produced significant analgesic effects in mice, as was evident from the increased baseline tail-flick latency when tested 20 minutes after their administration. Agmatine in a per se non-effective dose (5 μg/mouse, i.c.v.), L-arginine (40 μg/mouse, i.c.v.), and arcaine (25 μg/mouse, i.c.v.) significantly potentiated the anti-nociceptive effect of ethanol. Blood ethanol analysis showed no significant differences in blood ethanol concentration between ethanol/saline- and ethanol/agmatine-treated mice, suggesting that the effects of agmatine were not due to any possible effects on the pharmacokinetics of ethanol. In a separate study, mice were injected with ethanol (2g/kg, i.p., 12%) or saline (1mL/kg, i.p.) once daily for 9 days. On days 1, 3, 5, 7, and 9 of the experiment, they were subjected to the tail-flick test. Agmatine (5-20 μg/mouse, i.c.v.), L-arginine (40 μg/mouse, i.c.v.), arcaine (25 μg/mouse, i.c.v.), aCSF (2 μL/mouse, i.c.v.), or saline (1mL/kg, i.p.) was administered daily prior to the first daily ethanol or saline injections, and reaction latencies were determined in the tail-flick assay. Injections of agmatine, L-arginine, and arcaine prevented the development of tolerance to ethanol-induced analgesia. Given that agmatine and its endogenous modulation can prevent tolerance to the anti-nociceptive effects of ethanol, these data suggest it as a possible new therapeutic strategy for the treatment of alcohol use disorder and associated complications.

Superiority of microemulsion-based hydrogel for non-steroidal anti-inflammatory drug transdermal delivery: a comparative safety and anti-nociceptive efficacy study

Non-steroidal anti-inflammatory drugs (NSAIDs) represent the foundation of pain management caused by inflammatory disorders. Nevertheless, their oral administration induces several side effects exemplified by gastric ulceration, thus, delivering NSAIDs via skin has become an attractive alternative. Herein, microemulsion-based hydrogel (MBH), proliposomal, and cubosomal gels were fabricated, loaded with diclofenac, and physicochemically characterized. The size, charge, surface morphology, and the state of diclofenac within the reconstituted gels were also addressed. The ex-vivo permeation study using Franz cells was performed via the rat abdominal skin. The formulations were assessed in-vivo on mice skin for their irritation effect and their anti-nociceptive efficacy through tail-flick test. Biosafety study of the optimal gel was also pointed out. The gels and their dispersion forms displayed accepted physicochemical properties. Diclofenac was released in a prolonged manner from the prepared gels. MBH revealed a significantly higher skin permeation and the foremost results regarding in-vivo assessment where no skin irritation or altered histopathological features were observed. MBH further induced a significant anti-nociceptive effect during the tail-flick test with a lower tendency to evoke systemic toxicity. Therefore, limonene-containing microemulsion hydrogel is a promising lipid-based vehicle to treat pain with superior safety and therapeutic efficacy.

Comparison of Analgesic Effect of Rosmarinic Acid With Piroxicam in Mice

Introduction: Nonsteroidal anti-inflammatory drugs (NSAIDs) are one of the most widely used drugs in the treatment of pain and inflammation. Although, their side effects i.e.; gastrointestinal and renal adverse effects, limit the use of these drugs. Therefore, investigating new compounds with higher efficacy and fewer side effects is considerable issue. In this study, the analgesic activity of rosmarinic acid at different doses was compared with piroxicam (known standard NSAID).Methods: To evaluate the analgesic effects of rosmarinic acid, two well-known methods, Hot plate, and Tail-flick, were used. The experiments were performed in 10 groups (6 male mice per group) including the experimental groups (rosmarinic acid), the positive control group (piroxicam), and the negative control group (normal saline). All administrations were through intraperitoneal injection. The obtained data were analyzed separately by SPSS software and an independent student t test.Results: Rosmarinic acid at doses of 10 mg/kg and higher had significant analgesic effects compared with the control group, 30 minutes after injection in both hot plate and tail flick tests (P &lt; 0.05). Concomitant injection of 50 mg/kg of rosmarinic acid with 15 mg/kg of piroxicam produced significant painkiller effects when compared with the dose of 15 mg/kg piroxicam injection alone.Conclusion: Rosmarinic acid was able to exert analgesic effects in pharmacological tests in a dose-dependent manner. Concomitant use of rosmarinic acid and piroxicam may lead to synergic pain relief, especially in acute and severe pain in patients, reducing the therapeutic dose of piroxicam and subsequently, its side effects.

Contribution Of Opioid Receptors To Antinociception Produced By ß‐Caryophyllene

Despite decades of research examining the biological mechanisms of pain, few new treatments have been developed. Cannabis has been used for centuries to treat pain, and previous evidence indicates that non‐∆9‐tetrahydrocannabinol and non‐cannabidiol constituents of Cannabis can produce pain relief in animal models. The Cannabis‐related terpene ß‐caryophyllene (BCP) produces pain relief in various pain tests with varying degrees of efficacy; however, the pharmacological mechanism underlying this pain relief is unclear. Previous studies by other groups have demonstrated that BCP produces antinociception via cannabinoid and opioid mechanisms following local administration into the hindpaw. As such, we hypothesized that BCP produces analgesia via opioid mechanisms following systemic administration. To test this hypothesis, we administered varying doses of BCP and evaluated their antinociceptive effects on the hot plate and tail‐flick tests in adult male Sprague‐Dawley rats. The hot plate test identifies pain relief mediated by supraspinal mechanisms. The tail‐flick test identifies pain relief mediated by spinal mechanisms. One intraperitoneal injection of 30 mg/kg BCP produced antinociception on the hot plate test and the tail‐flick test approximately 15 minutes after injection. Vehicle and doses of 3 mg/kg and 10 mg/kg were ineffective at producing pain relief on the hot plate and tail‐flick tests. In order to test the contribution of opioid receptors, a subset of rats received a 30 min pretreatment of the opioid receptor antagonist naltrexone. The effect of naltrexone on BCP‐induced antinociception varied depending on both dose and time. These results indicate that low doses of BCP may effectively alleviate acute pain and that BCP‐induced antinociception may be mediated, in part, by opioid receptors. Further studies are needed to fully understand the relationship between BCP and opioid receptors to determine their therapeutic potential.