Involvement Of Opioid Receptors Research Articles

A targeted CRISPR-Cas9 mediated F0 screen identifies genes involved in establishment of the enteric nervous system.

The vertebrate enteric nervous system (ENS) is a crucial network of enteric neurons and glia resident within the entire gastrointestinal tract (GI). Overseeing essential GI functions such as gut motility and water balance, the ENS serves as a pivotal bidirectional link in the gut-brain axis. During early development, the ENS is primarily derived from enteric neural crest cells (ENCCs). Disruptions to ENCC development, as seen in conditions like Hirschsprung disease (HSCR), lead to the absence of ENS in the GI, particularly in the colon. In this study, using zebrafish, we devised an in vivo F0 CRISPR-based screen employing a robust, rapid pipeline integrating single-cell RNA sequencing, CRISPR reverse genetics, and high-content imaging. Our findings unveil various genes, including those encoding opioid receptors, as possible regulators of ENS establishment. In addition, we present evidence that suggests opioid receptor involvement in the neurochemical coding of the larval ENS. In summary, our work presents a novel, efficient CRISPR screen targeting ENS development, facilitating the discovery of previously unknown genes, and increasing knowledge of nervous system construction.

Pharmacological potential of 4-dimethylamino chalcone against acute and neuropathic pain in mice.

This work investigated the acute antinociceptive effect of a synthetic chalcone, 4-dimethylamino chalcone (DMAC), as well as its effects on vincristine-induced peripheral neuropathy (VIPN) in mice. The inhibitory activity of myeloperoxidase was assessed by measuring HOCl formation. Formalin and hot plate tests were used to study the acute antinociceptive effect of DMAC. VIPN was induced through the administration of vincristine sulphate (0.1mg/kg, i.p., 14 days). Then, DMSO, DMAC (10 or 30mg/kg; i.p.), or pregabalin (10mg/kg, i.p.) were administered for 14 consecutive days. Thermal hyperalgesia and mechanical allodynia were evaluated before and after VIPN induction and on days 1, 3, 7, and 14 of treatment. Neurodegeneration and neuroinflammation were assessed through immunohistochemistry for NF200, iNOS, and arginase-1 within the sciatic nerve. DMAC inhibited myeloperoxidase activity in vitro and presented an acute antinociceptive effect in both formalin and hot plate tests, with the involvement of muscarinic and opioid receptors. Treatment with 30mg/kg of DMAC significantly attenuated thermal hyperalgesia and mechanical allodynia and prevented macrophage proinflammatory polarisation in VIPN mice. Our results show that DMAC, acting through different mechanisms, effectively attenuates VIPN.

Neurocomputational involvement of dopamine and opioid receptors in perceived loss of control

Neurocomputational involvement of dopamine and opioid receptors in perceived loss of control

Ghrelin mechanisms of food reward. Part 2. Interaction of ghrelin with hormones, neuropeptides and other endogenous ligands

The hunger hormone, ghrelin, is produced not only in response to food deprivation, but is also released during various types of stress. In recent years, the rise in ghrelin levels has come to be seen as an essential component of the stress response. The review is devoted to ghrelin-dependent mechanisms providing reciprocal interaction between the hypothalamuspituitaryadrenal cortex axis and the dopaminergic reward system. Direct and feedback links between the stress-realizing system of the paraventricular nucleus, the neural networks of the lateral hypothalamus and the arcuate nucleus (which form the centers of hunger/satiation), and the mesolimbic reward system are considered. The role of peripheral satiety hormones and glucocorticoids in the regulation of motivation and reinforcement is discussed, as well as the involvement of endogenous opioid and endocannabinoid receptors in the learning of dopaminergic neurons in the ventral tegmental area and the hippocampus.

TOFİSOPAM’IN OPİOİDERJİK SİSTEM ARACILIKLI ANTİNOSİSEPTİF ETKİNLİĞİ

Objective: In this study, it was aimed to investigate the antinociceptive activity potential of Tofisopam and to elucidate the possible involvement of opioid system in this effect.Material and Method: The antinociceptive efficacy potential of Tofisopam (25 and 50 mg/kg) was evaluated by hot-plate and acetic acid-induced writhing tests; while possible effects of this drug on the motor coordination of mice were evaluated with the Rota-rod tests.Result and Discussion: Tofisopam at a dose of 50 mg/kg significantly prolonged the reaction times of mice in hot-plate tests and reduced the number of writhing behaviors in writhing tests. These findings indicated that Tofisopam has antinociceptive activity mediated by central and peripheral mechanisms. Tofisopam did not change the motor activities of mice. Pre-administration of naloxone to investigate the possible involvement of opioid receptors in the antinociceptive effect abolished the antinociceptive activity of Tofisopam. To elucidate the opioid receptor subtypes mediating the effect, mechanistic studies were carried out with naloxonazine (μ-opioid receptor blocker), naltrindole (δ-opioid receptor blocker) and nor-binaltorphimine (ҡ-opioid receptor blocker). All agents antagonized the antinociceptive effect of Tofisopam. Obtained findings revealed that Tofisopam at a dose of 50 mg/kg have antinociceptive activity mediated by μ-, δ- and ҡ-oipiod receptors.

Synthesis and Investigation of the Analgesic Potential of Enantiomerically Pure Schiff Bases: A Mechanistic Approach.

Schiff bases are a class of organic compounds with azomethine moiety, exhibiting a wide range of biological potentials. In this research, six chiral Schiff bases, three ‘S’ series (H1–H3) and three ‘R’ series (H4–H6), were synthesized. The reaction was neat, which means without a solvent, and occurred at room temperature with a high product yield. The synthesized compounds were evaluated for analgesic potential in vivo at doses of 12.5 and 25 mg/kg using acetic-acid-induced writhing assay, formalin test, tail immersion and hot plate models, followed by investigating the possible involvement of opioid receptors. The compounds H2 and H3 significantly (*** p < 0.001) reduced the writhing frequency, and H3 and H5 significantly (*** p < 0.001) reduced pain in both phases of the formalin test. The compounds H2 and H5 significantly (*** p < 0.001) increased latency at 90 min in tail immersion, while H2 significantly (*** p < 0.001) increased latency at 90 min in the hot plate test. The ‘S’ series Schiff bases, H1–H3, were found more potent than the ‘R’ series compounds, H4–H6. The possible involvement of opioid receptors was also surveyed utilizing naloxone in tail immersion and hot plate models, investigating the involvement of opioid receptors. The synthesized compounds could be used as alternative analgesic agents subjected to further evaluation in other animal models to confirm the observed biological potential.

Opioidergic and nitrergic systems mediate the anticonvulsant effect of mefloquine and chloroquine on seizures induced by pentylenetetrazol and maximal electroshock in mice.

This study was designed to investigate the involvement of opioidergic/nitrergic systems in the anticonvulsant effect of mefloquine, compared with chloroquine, in mice. Seizures were induced by pentylenetetrazol and maximal electroshock. Mice were randomly subjected to receive mefloquine or chloroquine thirty minutes in advance. The role of opioidergic/nitrergic systems was shown by co‑administration of pharmacological intervention and nitrite levels measurement in mice hippocampi. Results indicated that mefloquine (40 mg/kg) and chloroquine (5 mg/kg) significantly decreased the occurrence of tonic hindlimb extension. Also, mefloquine 120 mg/kg and chloroquine 5 mg/kg significantly increased seizure latency and decreased mortality rate. Mefloquine decreased seizure frequency too. Besides, mefloquine (20 mg/kg) and chloroquine (5, 10 mg/kg) significantly increased seizure threshold. Interestingly, L‑NAME, 7‑NI and naltrexone pre‑treatment reversed the anticonvulsant effects of both mefloquine (20 mg/kg) and chloroquine (5 mg/kg). Moreover, co‑administration of minimal‑effective doses of morphine with mefloquine/chloroquine (both 1 mg/kg) potentiated anticonvulsant effects, which was reversed by naltrexone and endorsed the involvement of opioid receptors. Also, nitrite levels in mice hippocampi remarkably increased after treatment with both mefloquine (20 mg/kg) and chloroquine (5 mg/kg). To conclude, mefloquine could protect the central nervous system against seizures in PTZ/MES‑induced models through opioidergic/nitrergic pathways, with similarity to chloroquine effects.

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.

Mechanisms of liver-soothing and mind-regulating acupuncture mediating opioid receptor participated in the treatment of migraine

To observe the effect of "Shugan Tiaoshen"(liver-soothing and mind-regulating) acupuncture on behavior reactions, opioid receptor expressions in the anterior cingulate cortex tissue and inflammatory factors in the serum in migraine rats, in order to explore its mechanism underlying improvement of migraine. In the first part of this study, forty male Wistar rats were randomized into control, model, routine acupuncture and "Shugan Tiaoshen" acupuncture groups (n=10/group), and in the second part, other 40 more male Wistar rats were randomized into low, medium and high dosage of blocker of μopioid receptor (OPRM）CTOP5 and PBS groups (n=10/group, for validating the involvement of opioid receptor in the effect of "Shugan Tiaoshen"). The migraine model was established by subcutaneous injection of glyceryl trinitrate. Routine acupuncture was applied to "Baihui" (GV20) and bilateral"Fengchi" (GB20), and "Shugan Tiaoshen" acupuncture applied to GV20, and bila-teral GB20, "Neiguan" (PC6) and "Taichong" (LR3), with the needles retained for 30 min. Behavior responses (head scratching, tail biting, cage climbing and number of going there and back) were scaled. Serum IL-1β, IL-6 and TNF-α were detected by ELISA, and the expression levels of opioid receptor μ, δ and κ (OPRM, OPRD, OPRK) mRNAs and proteins in the anterior cingulate cortex were detected by fluorescence quantitative PCR and Western blot separately. In the second part of this study, CTOP solution (5μL at concentrations of 20μg/μL,10μg/μL and 5μg/μL) or PBS was injected into the bilateral rostral portions of anterior cingulate cortex 30 min before every "Shugan Tiaoshen" acupuncture intervention, followed by observing the behavioral changes and assaying the contents of serum IL-1β, IL-6 and TNF-α. After modeling, the behavioral score, serum IL-1β, IL-6 and TNF-α contents were significantly increased in the model group relevant to the control group (P<0.05), and the beha-vioral score had no significant difference among the model and two acupuncture groups before intervention (P>0.05). Whereas the expression levels of OPRM, OPRD and OPRK mRNAs and proteins had a slight increase in the model group (P>0.05). After the intervention, the behavioral score, serum IL-1β, IL-6 and TNF-α contents were significantly decreased and the expression levels of OPRM, OPRD and OPRK mRNAs (2.150, 1.066 and 0.805 folds in the "Shugan Tiaoshen" group) and proteins (2.273, 0.901 and 0.893 folds in the "Shugan Tiaoshen" group) notably up-regulated in both "Shugan Tiaoshen" and routine acupuncture groups relevant to the model group (P<0.01, P<0.05), showing that the biggest up-regulation of mRNA expression was OPRM. Comparison between two acupuncture groups showed that the behavioral score, and serum IL-1β, IL-6 and TNF-α contents were significantly lower, and the expression levels of OPRM, OPRD and OPRK mRNAs and proteins obviously higher in the "Shugan Tiaoshen" group than those in the routine acupuncture group (P<0.01,P<0.05). Results of the second part of this study showed that after injection of antagonist CTOP of OPRM, the therapeutic effect of "Shugan Tiaoshen" acupuncture was weakened in the reduction of behavioral score and serum IL-1β, IL-6 and TNF-α contents, being minimal, moderate and maximum in the high, medium and low dose of antagonist relevant to PBS in sequence (P<0.05, P<0.01). "Shugan Tiaoshen" acupuncture can mitigate pain in migraine rats, which may be associated with its function in up-regulating the expressions of opioid receptors (especially OPRM), and in inhibiting inflammatory reaction in the anterior cingulate cortex.

Mitragynine Reverses Paclitaxel Chemotherapy‐Induced Peripheral Neuropathy and is Mediated via Opioid Receptor Involvement

Chemotherapy‐induced peripheral neuropathy (CIPN) is a problematic side effect in patients receiving chemotherapeutic cancer treatments. Clinical use of approved analgesic drugs often does not adequately control the pathological pain arising from CIPN and does not account for potential abuse with opioid therapeutics. Mitragyna speciosa (kratom) contains the alkaloid mitragynine, which exhibits analgesic properties. However, the underlying pharmacological mechanisms that underlie these analgesic properties are complex and not completely understood. Male and female C57bl/6 mice received 8 mg/kg intraperitoneal injections of paclitaxel, a taxane class chemotherapeutic, every other day over the course of 7 days. To confirm the development of CIPN, the von Frey assay was utilized to determine the onset mechanical allodynia, which arises when a previously non‐painful stimulus is perceived as painful. Intraperitoneal mitragynine and the prototypical opioid agonist morphine both dose‐relatedly reversed CIPN‐induced mechanical allodynia. Effective doses (ED)50 were as follows – morphine: 7.02 (6.56 – 7.51) mg/kg, mitragynine: 109.80 (104.27 – 115.62) mg/kg. Pretreatment with the opioid antagonist naltrexone 0.032 mg/kg, intraperitoneally produced a rightward shift in both morphine and mitragynine dose‐response curves. Effective doses (ED)50 were as follows – naltrexone + morphine: 27.93 (24.84 – 31.40), naltrexone + mitragynine: 245.41 (211.76 – 284.39), resulting in a 3.98 and 2.24 fold shift of dose response curves, respectively. Here we show that mitragynine reverses mechanical allodynia associated with paclitaxel CIPN. We also show that opioid receptors mediate such activity, though additional data suggest a role for adrenergic and serotonin receptors as well. Mitragynine may be an effective analgesic treatment option for patients experiencing painful CIPN.

Biological and Molecular Docking Evaluation of a Benzylisothiocyanate Semisynthetic Derivative From Moringa oleifera in a Pre-clinical Study of Temporomandibular Joint Pain.

ObjectiveMoringa oleifera possesses multiple biological effects and the 4-[(4′-O-acetyl-α-L- rhamnosyloxy) benzyl] isothiocyanate accounts for them. Based on the original isothiocyanate molecule we obtained a semisynthetic derivative, named 4-[(2′,3′,4′-O-triacetyl-α-L-rhamnosyloxy) N-benzyl] hydrazine carbothioamide (MC-H) which was safe and effective in a temporomandibular joint (TMJ) inflammatory hypernociception in rats. Therefore, considering that there is still a gap in the knowledge concerning the mechanisms of action through which the MC-H effects are mediated, this study aimed to investigate the involvement of the adhesion molecules (ICAM-1, CD55), the pathways heme oxygenase-1 (HO-1) and NO/cGMP/PKG/K+ATP, and the central opioid receptors in the efficacy of the MC-H in a pre-clinical study of TMJ pain.MethodsMolecular docking studies were performed to test the binding performance of MC-H against the ten targets of interest (ICAM-1, CD55, HO-1, iNOS, soluble cGMP, cGMP-dependent protein kinase (PKG), K+ATP channel, mu (μ), kappa (κ), and delta (δ) opioid receptors). In in vivo studies, male Wistar rats were treated with MC-H 1 μg/kg before TMJ formalin injection and nociception was evaluated. Periarticular tissues were removed to assess ICAM-1 and CD55 protein levels by Western blotting. To investigate the role of HO-1 and NO/cGMP/PKG/K+ATP pathways, the inhibitors ZnPP-IX, aminoguanidine, ODQ, KT5823, or glibenclamide were used. To study the involvement of opioid receptors, rats were pre-treated (15 min) with an intrathecal injection of non-selective inhibitor naloxone or with CTOP, naltrindole, or norbinaltorphimine.ResultsAll interactions presented acceptable binding energy values (below −6.0 kcal/mol) which suggest MC-H might strongly bind to its molecular targets. MC-H reduced the protein levels of ICAM-1 and CD55 in periarticular tissues. ZnPP-IX, naloxone, CTOP, and naltrindole reversed the antinociceptive effect of MC-H.ConclusionMC-H demonstrated antinociceptive and anti-inflammatory effects peripherally by the activation of the HO-1 pathway, as well as through inhibition of the protein levels of adhesion molecules, and centrally by μ and δ opioid receptors.

The Role of Transient Receptor Potential A1 and G Protein-Coupled Receptor 39 in Zinc-Mediated Acute and Chronic Itch in Mice.

Itching is a common symptom of many skin or systemic diseases and has a negative impact on the quality of life. Zinc, one of the most important trace elements in an organism, plays an important role in the regulation of pain. Whether and how zinc regulates itching is largely unclear. Herein, we explored the role of Zn2+ in the regulation of acute and chronic itch in mice. It is found that intradermal injection (i.d.) of Zn2+ dose-dependently induced acute itch and transient receptor potential A1 (TRPA1) participated in Zn2+-induced acute itch in mice. Moreover, the pharmacological analysis showed the involvement of histamine, mast cells, opioid receptors, and capsaicin-sensitive C-fibers in Zn2+-induced acute itch in mice. Systemic administration of Zn2+ chelators, such as N,N,N′,N′-Tetrakis(2-pyridylmethyl)ethylenediamine (TPEN), pyrithione, and clioquinol were able to attenuate both acute itch and dry skin-induced chronic itch in mice. Quantitative polymerase chain reaction (Q-PCR) analysis showed that the messenger RNA (mRNA) expression levels of zinc transporters (ZIPs and ZnTs) significantly changed in the dorsal root ganglia (DRG) under dry skin-induced chronic itch condition in mice. Activation of extracellular signal-regulated kinase (ERK) pathway was induced in the DRG and skin by the administration of zinc or under dry skin condition, which was inhibited by systemic administration of Zn2+ chelators. Finally, we found that the expression of GPR39 (a zinc-sensing GPCR) was significantly upregulated in the dry skin mice model and involved in the pathogenesis of chronic itch. Together, these results indicated that the TRPA1/GPR39/ERK axis mediated the zinc-induced itch and, thus, targeting zinc signaling may be a promising strategy for anti-itch therapy.

Anti-nociceptive and anti-inflammatory activities of the essential oil isolated from Cupressus arizonica Greene fruits.

BackgroundCupressus arizonica Greene is a coniferous tree with great importance in fragrance and pharmaceutical industries. Essential oils from C. arizonica (EC) have shown potential antioxidant, and anti-microbial activities. This study aimed at investigating the anti-nociceptive and anti-inflammatory effects/mechanisms of EC.MethodsThe EC was evaluated for anti-nociceptive and anti-inflammatory activities on male Wistar rats using a formalin test and carrageenan-induced paw edema, respectively. Also, we pre-treated some of the animals with naloxone and flumazenil in the formalin test to find out the possible contributions of opioid and benzodiazepine receptors to EC anti-nociceptive effects. Finally, gas chromatography/mass spectrometry (GC/MS) analysis was used to identify the EC’s constituents.ResultsEC in intraperitoneal doses of 0.5 and 1 g/kg significantly decrease the nociceptive responses in both early and late phases of the formalin test. From a mechanistic point of view, flumazenil administration 20 minutes before the most effective dose of EC (1 g/kg) showed a meaningful reduction in the associated anti-nociceptive responses during the early and late phases of the formalin test. Naloxone also reduced the anti-nociceptive role of EC in the late phase. Furthermore, EC at the doses of 1, 0.5, and 0.25 g/kg significantly reduced paw edema from 0.5 hours after carrageenan injection to 4 hours. GC/MS analysis showed that isolated EC is a monoterpene-rich oil with the major presence of α-pinene (71.92%), myrcene (6.37%), δ-3-carene (4.68%), β-pinene (3.71%), and limonene (3.34%).ConclusionsEC showed potent anti-nociceptive and anti-inflammatory activities with the relative involvement of opioid and benzodiazepine receptors.

Tannic acid is a gastroprotective that regulates inflammation and oxidative stress

This study investigated the gastroprotective effect of TA against gastric ulcer in mice, and its possible mechanisms of action. The effects were investigated in a model of ethanol and ethanol/HCl induced ulcers, and physical barrier test. Quantification of oxidative stress mediators and inflammatory cytokines in gastric tissue was performed. The involvement of sulfhydryl compounds (-SH), nitric oxide (NO), prostaglandin E2 (PGE2), potassium channels (K +ATP) and opioid receptors in gastroprotection were investigated. Oral treatment with TA at a dose of 50 mg/kg resulted in 97.96% and 94.20% (reduction in gastric injury) of gastroprotection, against injuries caused by ethanol and ethanol/HCL, respectively, in addition to having a systematic effect. TA promotes increased levels of superoxide dismutase (SOD), catalase (CAT) and reduced glutathione (GSH), as well as reduced levels of malondialdehyde (MDA) reaction to thiobarbituric acid and myeloperoxidase (MPO). In addition, there was reduction in levels of tumor necrosis factor alpha (TNF-α) and interleukins (IL) IL-1β and IL-6 and increased IL-10. The gastroprotective activity of TA involved K +ATP channels and the production of –SH, NO and PGE2, demonstrating multiple mechanisms of action. The results of the present study suggest that TA may be a gastroprotective agent counteracting oxidative and inflammatory stress.

Kappa opioid receptor modulation of endometriosis pain in mice

The kappa opioid receptor is a constituent of the endogenous opioid analgesia system widely expressed in somatosensory nervous pathways and also in endometrial tissues. This work investigates the possible involvement of kappa opioid receptor on the nociceptive, behavioral and histopathological manifestations of endometriosis in a murine model. Female mice receiving endometrial implants develop a persistent mechanical hypersensitivity in the pelvic area that is stronger during the estrus phase of the estrous cycle. The kappa opioid receptor agonist U50,488H produces a dose-dependent relief of this mechanical hypersensitivity, regardless of the cycle phase. Repeated exposure to a low dose of U50,488H (1 mg/kg/day s.c. for one month) provides sustained relief of mechanical hypersensitivity, without tolerance development or sedative side effects. Interestingly, this treatment also inhibits a decreased rearing behavior associated with spontaneous pain or discomfort in endometriosis mice. This KOR-mediated pain relief does not prevent the anxiety-like behavior or the cognitive impairment exhibited by endometriosis mice, and the growth of endometriotic cysts is also unaltered. These data provide evidence of strong pain-relieving properties of kappa opioid receptor stimulation in female mice with endometriosis pain. The persistence of affective and cognitive manifestations suggests that these comorbidities are independent of pelvic pain and simultaneous treatment of these comorbidities may be necessary for successful management of endometriosis.

Anti-Neuropathic Pain Activity of Ageratum conyzoides L due to the Essential Oil Components.

Neuropathic pain is one of the contributors to the global burdens of illness. At present many patients do not achieve satisfactory pain relief even with synthetic painkillers. Taking this into consideration, it is necessary to search for natural product-derived alternative treatment with confirmed safety and efficacy. Ageratum conyzoides L is a plant often used as an analgesic in Indonesia, however, anti-neuropathic pain activity of this plant is still unknown. To determine the anti-neuropathic pain activity of the essential oil and non-essential oil component (distillation residue) of A. conyzoides L. We conducted the separation of the essential oil component from other secondary metabolites through steam distillation. Both components were tested for anti-neuropathic pain activity using chronic constriction injury animal models with thermal hyperalgesia and allodynia tests. The animals were divided into 7 test groups, namely normal, sham, negative, positive (pregabalin at 0.195 mg/20 g BW of mice), essential oil component (100 mg/kg BW), and non-essential oil component (100 mg/kg BW). Naloxone was tested against the most potent anti-neuropathic pain component (essential oil or non-essential oil) to investigate the involvement of opioid receptors. The GC-MS of the essential oil component indicated the presence of 60 compounds. Meanwhile, non-essential oil components include alkaloid, flavonoid, polyphenol, quinone, steroid, and triterpenoid. This non-essential oil component contained a total flavonoid equivalent to 248.89 ppm quercetin. The anti-neuropathic pain activity test showed significantly higher activity of the essential oil component compared to the non-essential oil component and negative groups (p<0.05). Furthermore, the essential oil component showed equal activity to pregabalin (p>0.05). However, this activity was abolished by naloxone, indicating the involvement of the opioid receptor in the action of the essential oil component. The essential oil component of A. conyzoides L is a potential novel substance for use as anti-neuropathic pain.

Central and peripheral pain intervention by Ophiorrhizarugosa leaves: Potential underlying mechanisms and insight into the role of pain modulators

Ethnopharmacological relevanceOphiorrhiza rugosa var. prostrata is a traditional medicinal plant used by the indigenous and local tribes (Chakma, Marma and Tanchangya) of Bangladesh for the management of chest pain, body ache, and earache. However, the knowledge of anti-nociceptive and anti-inflammatory potentials of this plant is scarce. Aim of the studyTherefore, we scrutinized the anti-nociceptive and anti-inflammatory properties of O. rugosa leaves along with its possible mechanism(s) of action using chemical and heat-induced pain models. Methods and materialsO. rugosa was extracted using 100% ethanol (EEOR) followed by exploring phytochemicals and assessing acute toxicity. To determine anti-nociceptive potentials, chemical-induced (acetic acid and formalin) and heat-induced (hot plate and tail immersion) nociceptive models were followed. To investigate the possible involvement of opioid receptors during formalin, hot plate, and tail immersion tests, naltrexone was administered whereas methylene blue and glibenclamide were used to explore cGMP involvement and ATP-sensitive K+ channel pathways, respectively. Moreover, the anti-inflammatory potential was assessed using the carrageenan-induced paw edema test model. Motor behaviours of EEOR were assessed by the open-field test. Finally, bioactive constituents (identified by GC-MS) from O. rugosa were subjected to molecular docking and ADME/t analysis to evaluate its potency and safety. ResultsDuring chemical-induced and heat-induced pain models, EEOR exhibited significant and effective nociception suppression at all experimental doses (200 and 400 mg/kg). Also, the administration of naltrexone corroborated the association of opioid receptors with the anti-nociceptive activity by EEOR. Similarly, cGMP and ATP-sensitive K+ channel pathways were also found to be involved in the anti-nociceptive mechanism. Furthermore, significant and dose-dependent inhibition of inflammation induced by carrageenan was recorded for EEOR. Both doses of EEOR did not affect the animal's locomotor capacity in the open-field test. Besides, in silico test identified the key compounds (loliolide, harman, squalene, vitamin E, and gamma-sitosterol) that inhibited some particular receptors regarding pain and inflammation. ConclusionThis research exposes central and peripheral pain intervention as well as anti-inflammatory activity of O. rugosa. Also, the identified compounds from this plant support its activities by effectively inhibiting anti-nociceptive and anti-inflammatory receptors. Overall, these outcomes valorize the ethnomedicinal efficacy of O. rugosa in managing various painful conditions.

Analgesic effects of cuminic alcohol (4-isopropylbenzyl alcohol), a monocyclic terpenoid, in animal models of nociceptive and neuropathic pain: Role of opioid receptors, L-arginine/NO/cGMP pathway, and inflammatory cytokines

Cuminic alcohol (4-isopropylbenzyl alcohol; 4-IPBA) is a monocyclic terpenoid found in the analgesic medicinal plants Cuminum cyminum and Bunium persicum. The current study assessed the analgesic effects of 4-IPBA in different animal models of pain. Hot plate, formalin, and acetic acid tests were used to evaluate nociceptive pain in mice. The involvement of opioid receptors and the L-arginine/NO/cGMP/K+ channel pathway in 4-IPBA effects were investigated. Allodynia and hyperalgesia were assessed following peripheral neuropathy induced by chronic constriction of the sciatic nerve in rats. The spinal levels of inflammatory cytokines were measured using the ELISA method. The drugs and compounds were administered intraperitoneally. The results showed that 4-IPBA (200 and 400 mg/kg) significantly prolonged the hot plate latency. This effect was antagonized by naloxone (2 mg/kg). 4-IPBA (25–100 mg/kg) also significantly attenuated formalin- and acetic acid-induced nociceptive pain. L-arginine (200 mg/kg), sodium nitroprusside (0.25 mg/kg), and sildenafil (0.5 mg/kg) reversed while L-NAME (30 mg/kg) and methylene blue (20 mg/kg) potentiated the antinociceptive effects of 4-IPBA in the writhing test. Glibenclamide (10 mg/kg) and tetraethylammonium chloride (4 mg/kg) did not have any influence on the 4-IPBA effect. Furthermore, 4-IPBA (6.25–25 mg/kg) significantly relieved mechanical allodynia, cold allodynia, and hyperalgesia in rats. The concentrations of TNF-α and IL-1β in the spinal cord of rats were decreased by 4-IPBA. No evidence of 4-IPBA-induced toxicity was found in behavioral or histopathological examinations. These results demonstrate that 4-IPBA attenuates nociceptive and neuropathic pain through the involvement of opioid receptors, the L-arginine/NO/cGMP pathway, and anti-inflammatory functions.

Involvement of Peripheral Opioid Receptors in the Realization of Food Motivation Into Eating Behavior.

The involvement of peripheral opioid receptors in the mechanisms of eating behavior is still unclear. The aim of this work was to study the role of peripheral, predominantly gastric mu and delta opioid receptors in the realization of food motivation in conditions of different energy costs for eating behavior. Experiments were performed under a between-sessions progressive ratio schedule of reinforcement in food-deprived rats. The level of food motivation was calculated using a self-developed method. Food intake, motor activity, and metabolic rate were recorded in fed and hungry animals. Results showed that intragastric administration of the mu opioid receptor agonist DAMGO led to an increase in the level of food motivation in the light variant of operant feeding behaviors. Food consumption did not change. At high costs for feeding behavior, the administration of DAMGO did not alter food motivation; however, food consumption and motor activity were reduced. Intragastric administration of the delta opioid receptor agonist DADLE did not lead to changes in the level of food motivation and physical activity, but inhibition of feeding behavior was observed in all reinforcement schedules. Three regulatory pathways of eating behavior in difficult food conditions by peripheral, predominantly gastric opioid receptors are hypothesized: environmental-inhibitory afferentations and suppression of the realization of food motivation into behavior; homeostatic-inhibitory action on food motivation; and rewarding-suppression of the anticipatory reinforcement.

Effects of intrathecal and intracerebroventricular microinjection of kaempferol on pain: possible mechanisms of action.

Background and purpose:Kaempferol (KM), a flavonoid, has an anti-inflammatory and anticancer effect and prevents many metabolic diseases. Nonetheless, very few studies have been done on the antinociceptive effects of KM. This research aimed at assessing the involvement of opioids, gamma-aminobutyric acid (GABA) receptors, and inflammatory mediators in the antinociceptive effects of KM in male Wistar rats.Experimental approach:The intracerebroventricular and/or intrathecal administration of the compounds was done for examining their central impacts on the thermal and chemical pain by the tail-flick and formalin paw tests. For assessing the role of opioid and GABA receptors in the possible antinociceptive effects of KM, several antagonists were used. Also, a rotarod test was carried out for assessing motor performance.Findings/Results:The intracerebroventricular and/or intrathecal microinjections of KM (40 μg/rat) had partially antinociceptive effects in the tail-flick test in rats (P < 0.05). In the formalin paw model, the intrathecal microinjection of KM had antinociceptive effects in phase 1 (20 and 40 μg/rat; P < 0.05 and P < 0.01, respectively) and phase 2 (20 and 40 μg/rat; P < 0.01 and P < 0.001, respectively). Using naloxonazine and/or bicuculline approved the involvement of opioid and GABA receptors in the central antinociceptive effects of KM, respectively. Moreover, KM reduced the expression levels of caspase 6, interleukin-1β, tumor necrosis factor-α, and interleukin-6. The antinociceptive effects of KM were not linked to variations in the locomotor activity.Conclusion and implications:It can be concluded that KM has remarkable antinociceptive effects at a spinal level, which is associated with the presence of the inflammatory state. These impacts were undetectable following injections in the lateral ventricle. The possible mechanisms of KM antinociception are possibly linked to various modulatory pathways, including opioid and GABA receptors.