Repeated administration of orexin into the thalamic paraventricular nucleus inhibits the development of morphine-induced analgesia

Background: Hypothalamic neuropeptides, orexins, play pivotal roles in nociception and pain modulation. Objective: In this study, we investigated the effect of the administration of orexin into the paraventricular nucleus (PVT) on the development of morphine-induced analgesia in rats. Method. Male Wistar rats weighing 250-300 g received subcutaneous (s.c.) chronic morphine (6, 16, 26, 36, 46, 56 and 66 mg/kg, 2 ml/kg) at an interval of 24 hours for 7 days. Animals were divided into two experimental groups in which the orexin (100 μM, 200 nl) and its vehicle were microinjected into the PVT nucleus for 7 days before each morphine injection. Then, the formalin test was performed for the assessment of pain-related behaviors. Results: The results demonstrated that the rats pretreated by intra-PVT orexin exhibited higher pain-related behaviors than the morphine-treated group. The analgesic effects of morphine were significantly lower in orexin plus morphine-treated rats than the vehicle plus morphine-treated ones. Conclusion: Our findings suggested that the animals receiving the prolonged intra-PVT application of orexin before morphine injection demonstrated a significant increase in the development of nociceptive behaviors in all phases. Therefore, the present study highlighted a new area of the brain involved in the effect of orexin on analgesia induced by morphine.

A Novel Multitarget Mu- and Delta-Opioid Receptors Agonist HAGD Has Peripherally Restrictive Potent Analgesia with Less Side Effects in Mice and Minimal Impact on Human Sperm Motility

ObjectivePain is a common clinical symptom. Although a variety of opioid analgesics have been developed, the side effects including negative impact on human sperm motility still hinder their application. Aim of this study is to develop a novel opioid analgesic, a multitarget peptide HAGD (H-Tyr-D-AIa-GIy-Phe-NH2) which has less side effects and minimal impact on sperm motility.MethodsThe peripheral antinociceptive effects of HAGD were appraised in a series of preclinical mice pain models, including the tail-flick test, carrageenan-induced inflammatory pain, acetic acid-induced writhing test and formalin test. In conditioned place preference experiment, open field test, gastrointestinal transit test and rotarod test, the side effects of HAGD in mice were assessed. The impacts of HAGD on sperm motility in vitro were investigated.ResultsHAGD produced equipotent antinociception compared with morphine. HAGD was stronger in terms of analgesia intensity in chemical stimulation pain of formalin test phase I. The antinociception was mediated by mu- and delta-opioid receptors. HAGD didn’t induce conditioned place preference and hyperlocomotion, but morphine did. Both HAGD and morphine had no impacts on motor coordination. HAGD had a limited side effect in gastrointestinal transit, while morphine inhibited gastrointestinal transit to a greater extent. However, HAGD had minimal impact on human sperm motility, whereas morphine declined sperm motility at concentrations of 1 × 10-7 mol/l and 1 × 10-8 mol/l at 3.5 h of incubation.Conclusion HAGD may be a better candidate for future development of novel multitarget opioid analgesics with less side effects and minimal impact on human sperm motility.

Citral inhibits the nociception in the rat formalin test: Effect of metformin and blockers of opioid receptor and the NO-cGMP-K+ channel pathway

The objective of the present study was to scrutinize the effect of nitric oxide (NO), cGMP, potassium channel blockers and metformin on the citral-produced peripheral antinociception. The rat paw 1% formalin test was used to assess nociception and antinociception. Rats were treated with local peripheral administration of citral (10-100 µg/paw). The antinociception of citral (100 µg/paw) was evaluated with and without the local pretreatment of naloxone, NG-L-nitro-arginine methyl ester (L-NAME, a NO synthesis inhibitor), 1H-(1,2,4)-oxadiazolo(4,2-a)quinoxalin-1-one (ODQ, a soluble guanylyl cyclase inhibitor), metformin, opioid receptors antagonists, and K+ channel blockers. Injection of citral in the rat paw significantly decreased the nociceptive effect of formalin administration during the two phases of the test. Local pretreatment of the paws with L-NAME and ODQ did not reduced the citral-induced antinociception. Glipizide or glibenclamide (Kir6.1-2; ATP-sensitive K+ channel blockers), tetraethylammonium or 4-aminopyridine (KV; voltage-gated K+ channel blockers) or charybdotoxin (KCa1.1; big conductance calcium-activated K+ channel blocker) or apamin (KCa2.1-3; small conductance Ca2+-activated K+ channel antagonist), or metformin, but not the opioid antagonists, reduced the antinociception of citral. Citral produced peripheral antinociception during both phases of the formalin test. These effects were due to the activation of K+ channels and a biguanide-dependent mechanism.

The effect of maternal exposure to titanium dioxide nanoparticles on the pain response in offspring mice using formalin test

This study was conducted to evaluate the effect of maternal exposure to TiO2 nanoparticles on the pain response in offspring mice. 30 female mice with a mean ± SD weight of 30 ± 5 g were randomly divided into three groups: the control group (group 1) received only the basal diet; the sham group (group 2) received saline plus as a carrier (100 μL/mice) subcutaneously on days 3, 7, 10, and 14 post-mating; and the test group (group 3) received 100 μL/mice TNPs subcutaneously on days 3, 7, 10, and 14 post-mating. Offspring were divided into 6 groups 21 days after birth and underwent formalin test. Blood samples were taken to evaluate possible oxidative changes in total antioxidant capacity (TAC) and malondialdehyde (MDA). Exposure to TNPs significantly ( p < 0.05) decreased pain perception. Except for a significant difference between the sham group and the control group, MDA and TAC were not significantly different among the studied groups. Injection of TNPs to pregnant mice would affect the pain perception in their offspring. This may be attributable to the ability of these particles to pass through the placenta to produce free radicals.

Anti-inflammatory secondary metabolites from Scrophularia kotschyana

The species belonging to Scrophularia genus grow mainly in Irano-Turanian and Mediterranean regions and have been used as folk remedy for inflammatory-related diseases since ancient times. The present study was aimed to evaluate the anti-inflammatory activity of the extracts of Scrophularia kotschyana as well as the isolated compounds. The aerial parts and the roots of the plant were separately extracted with methanol. Anti-inflammatory activities of both extracts were evaluated with formalin test in mice. As the methanolic extract of the aerial parts significantly ( p < .05) inhibited inflammation, it was then submitted to successive solvent extractions with n-hexane, dichloromethane, ethyl acetate and n-butanol to yield subextracts. Anti-inflammatory activities of the subextracts were evaluated within the same test system. Among the subextracts tested, the n-butanol subextract produced a significant ( p < .05) anti-inflammatory activity at all doses (5, 10, and 30 mg/kg, ip.). Sequential chromatographic separation of the n-butanol subextract yielded 8-O-acetyl-4′- O-( E)- p-coumaroylharpagide, 8- O-acetyl-4′- O-( Z)- p-coumaroylharpagide, β-sitosterol 3- O-β-glucopyranoside, apigenin 7- O-β-glucopyranoside, apigenin 7- O-rutinoside, luteolin 7- O-β-glucopyranoside and luteolin 7- O-rutinoside. The anti-inflammatory activities of the isolates were evaluated at 5 mg/kg dose. Luteolin 7- O-β-glucopyranoside and apigenin 7- O-rutinoside caused a significant ( p < .05) inhibition of oedema formation.

Baccharis trimera aqueous extract modulates inflammation and nociception in mice

Background The aerial parts of Baccharis trimera (Less.) are frequently used as a tea to treat several diseases. Therefore, the aim of this study was to identify the constituents of an aqueous extract of B. trimera, focusing on their antioxidant, anti-inflammation, and antinociception activities and properties. For that, the researchers performed in vivo assays using the formalin test and Freund’s Complete Adjuvant (FCA) to measure the acute and chronic inflammatory pain in mice. Moreover, the myeloperoxidase enzyme (MPO) was analyzed in the subcutaneous tissue after the FCA injection, together with the counting of lymphocytes in the peripheral blood of the mice. Results The qualitative phytochemical analysis indicated the presence of flavonoids and saponins in the B. trimera aqueous extract. The high-performance liquid chromatography (HPLC) analyses showed the presence of phenolic compounds, such as chlorogenic acid, ellagic acid, rosmarinic acid, as well as flavonoids, such as rutin, quercetin, and luteolin. The DPPH assay was used in order to measure the antioxidant activity of the aqueous extract of B. trimera and this showed an IC50 of 118.18 ± 1.02 μg/mg. The data from the formalin test demonstrated that a single dose of the aqueous extract of B. trimera was not able to decrease the nociceptive behavior during the neurogenic phase, at any of the tested doses (20, 40, or 80 mg/kg p.o.). However, during the inflammatory phase of this test, the aqueous extract of B. trimera at 80 mg/kg (p.o.) significantly decreased the nociceptive behavior, showing more effectiveness when compared to the other tested doses (p < 0.05). Importantly, in the chronic inflammatory model on the 5th day of treatment, the aqueous extract of B. trimera (80 mg/kg p.o.) significantly reduced mechanical allodynia (p < 0.01), heat thermal hyperalgesia (p < 0.001), and paw edema (p < 0.05). There were no changes in the MPO activity, but the data exhibited an equivalent decrease in the number of lymphocytes in the blood of the mice that were treated with B. trimera (80 mg.kg− 1 p.o.) and diclofenac sodium. Conclusion Taken together, the present data reinforces the potential of the B. trimera aqueous extract as an anti-inflammatory and analgesic compound.

The Effect of Fluoxetine and Ibuprofen on BCG-Induced Alteration in Pain Sensitivity in Mice

Clinical observations recognized the co-existence and interactions of pain and depression a long time, ago. The aim of this work was to study the effect of ibuprofen and fluoxetine on BCGinduced depressive-like behaviour, on formalin-induced pain, as well as on mechanical allodynia after planter incision in mice. BCG induced a depressive behaviour that was seen in the forced swim test (FST) and the tail suspension test (TST). It also induced a decrease in pain-related behaviour in the formalin test, and an increase in the baseline in mechanical allodynia test compared to the control group. Fluoxetine (80 mg/L of drinking water) showed a significant decrease in the immobility time in the FST and TST and enhanced pain related behaviour in formalin test in the BCG-inoculated group. However, it did not affect the increase in the pain threshold in the planter incision allodynia model. Adding ibuprofen to drinking water (0.2 g/L of drinking water), reversed the depressive like behaviour induced by BCG and enhanced pain-related behaviour in formalin test, in both the total pain-related behaviour and phase 2. It also prevented the increase in the base line induced by BCG. On the other hand, the incisional pain model was not affected by BCG inoculation except at the 2-hour time point, where it showed hypoalgesia, as well.