Involvement of opioid receptors in the oxytocin-induced antinociception in the central nervous system of rats

Recent studies showed that oxytocin and opioid peptides play important roles in pain modulation at different levels in the central nervous system. The present study was performed to explore whether opioid system is involved in the oxytocin-induced antinociception in the brain of rats. The results showed that: (1) intracerebroventricular injection of oxytocin induced dose-dependent increases in hindpaw withdrawal latencies (HWL) to noxious thermal and mechanical stimulation in rats. (2) The antinociceptive effect of oxytocin was attenuated dose-dependently by intracerebroventricular injection of naloxone, indicating an involvement of opioid system in the oxytocin-induced antinociception. (3) It is interesting that the antinociceptive effect of oxytocin was attenuated by subsequent intracerebroventricular injection of the μ-opioid antagonist β-funaltrexamine (β-FNA) and the κ-opioid antagonist nor-binaltorphimine (nor-BNI), but not the δ-opioid antagonist naltrindole. The results indicate that oxytocin plays an antinociceptive role in the brain of rats; μ- and κ-opioid receptors, not δ-receptors, are involved in the oxytocin-induced antinociception in the central nervous system of rats.     

Study on the molecular mechanism of antinociception induced by ghrelin in acute pain in mice

Ghrelin has been identified as the endogenous ligand for the GHS-R1α (growth hormone secretagogue receptor 1 alpha). Our previous experiments have indicated that ghrelin (i.c.v.) induces antinociceptive effects in acute pain in mice, and the effects were mediated through the central opioid receptors and GHS-R1α. However, which opioid receptor (OR) mediates the antinociceptive effects and the molecular mechanisms are also needed to be further explored. In the present study, the antinociceptive effects of ghrelin (i.c.v.) could be fully antagonized by δ-opioid receptor antagonist NTI. Furthermore, the mRNA and protein levels of δ-opioid peptide PENK and δ-opioid receptor OPRD were increased after i.c.v injection of ghrelin. Thus, it showed that the antinociception of ghrelin was correlated with the GHS-R1α and δ-opioid receptors. To explore which receptor was firstly activated by ghrelin, GHS-R1α antagonist [D-Lys³]-GHRP-6 was co-injection (i.c.v.) with deltorphin II (selective δ-opioid receptor agonist). Finally, the antinociception induced by deltorphin II wasn’t blocked by the co-injection (i.c.v.) of [D-Lys³]-GHRP-6, indicating that the GHS-R1α isn’t on the backward position of δ-opioid receptor. The results suggested that i.c.v. injection of ghrelin initially activated the GHS-R1α, which in turn increased the release of endogenous PENK to activation of OPRD to produce antinociception.     

Antinociceptive effects of [D-Ala2]deltorphin II, a highly selective delta agonist in vivo

The present study has characterized the antinociceptive actions of [D-Ala2]deltorphin II following intracerebroventricular (i.c.v.) administration in the mouse tail-flick test. [D-Ala2]deltorphin II produced dose- and time-related antinociception, with maximal effects at +10 min and significant antinociception which lasted for 40-60 min. [D-Ala2]deltorphin II was 13-fold more potent than i.c.v. [D-Pen2, D-Pen5]enkephalin (DPDPE), a second highly selective delta agonist, and approximately equipotent with i.c.v. morphine in producing antinociception. The antinociceptive effects of i.c.v. [D-Ala2]deltorphin II and DPDPE, but not those of morphine, were antagonized by the selective delta antagonist, ICI 174,864. In contrast, pretreatment with the non-equilibrium mu antagonist, beta-funaltrexamine blocked morphine antinociception, but failed to antagonize [D-Ala2]deltorphin II and DPDPE antinociception. These data indicate that [D-Ala2]deltorphin II produced its antinociceptive effects at a supraspinal delta receptor. [D-Ala2]deltorphin II appears to be the most appropriate delta opioid agonist currently available for studies in vivo and support the involvement of delta receptors in supraspinal antinociception.     

Involvement of spinal release of α-neo-endorphin on the antinociceptive effect of TAPA

The antinociceptive effect of i.t.-administered Tyr-d-Arg-Phe-β-Ala (TAPA), an N-terminal tetrapeptide analog of dermorphin, was characterized in ddY mice. In the mouse tail-flick test, TAPA administered i.t. produced a potent antinociception. The antinociception induced by TAPA was significantly attenuated by i.t. pretreatment with the κ-opioid receptor antagonist nor-binaltorphimine, as well as by the μ-opioid receptor antagonist β-funaltrexamine and the μ₁-opioid receptor antagonist naloxonazine. TAPA-induced antinociception was also significantly suppressed by co-administration of the μ₁-opioid receptor antagonist Tyr-d-Pro-Phe-Phe-NH₂ (d-Pro²-endomorphin-2) but not by co-administration of the μ₂-opioid receptor antagonists Tyr-d-Pro-Trp-Phe-NH₂ (d-Pro²-endomorphin-1) and Tyr-d-Pro-Trp-Gly-NH₂ (d-Pro²-Tyr-W-MIF-1). In CXBK mice whose μ₁-opioid receptors were naturally reduced, the antinociceptive effect of TAPA was markedly suppressed compared to the parental strain C57BL/6ByJ mice. Moreover, the antinociception induced by TAPA was significantly attenuated by i.t. pretreatment with antiserum against the endogenous κ-opioid peptide α-neo-endorphin but not antisera against other endogenous opioid peptides. In prodynorphin-deficient mice, the antinociceptive effect of TAPA was significantly reduced compared to wild-type mice. These results suggest that the spinal antinociception induced by TAPA is mediated in part through the release of α-neo-endorphin in the spinal cord via activation of spinal μ₁-opioid receptors.     

Synergistic analgesic effects between neuronostatin and morphine at the supraspinal level

Neuronostatin, a 13-amino acid peptide, is encoded in the somatostatin pro-hormone. I.c.v. administration of neuronostatin produces a significant antinociceptive effect in the mouse tail-flick test, which is mediated by endogenous opioid receptor. However, the direct functional interaction between morphine and neuronostatin has not been characterized. In the present study, effect of neuronostatin on morphine analgesia was investigated in the tail-flick test. Our findings showed that i.c.v. administration of neuronostatin (0.3 nmol/mouse i.c.v.) significantly enhanced the antinociceptive effect of morphine (2.5, 5 or 10 μg/kg) at the supraspinal level. Results of antagonism experiments suggested that the synergistic analgesia induced by morphine and neuronostatin was mediated by μ- and к-opioid receptors not δ-opioid receptor. In conclusion, there may be a cascade amplification phenomenon when morphine and neuronostatin were co-administered in acute pain model. The above results provide evidence for the potential use of neuronostatin in combination with morphine to control pain and addiction.     

The effect of the leucopyrokinin analogue: [2-8]-leucopyrokinin on central opioid receptors in rats

The antinociceptive effect of intracerebroventricular injections of [2–8]-leucopyrokinin (LPK), a truncated leucopyrokinin analogue, was determined in rats, by means of a tail immersion test. We found a significant antinociceptive effect of three i.c.v. doses of [2–8]-LPK: 1, 5 and 10 nmol. Pre-treating animals with naloxone hydrochloride (1 mg/kg i.p.) completely blocked the effect of two high doses of [2–8]-LPK. To determine the sub-types of opioid receptors involved in [2–8]-leucopyrokinin-induced analgesia we injected specific blockers of μ-, δ- and κ-receptors namely, β-funaltrexamine hydrochloride, naltrindole hydrochloride and nor-binaltorphimine dihydrochloride, respectively, prior to [2–8]-leucopyrokinin at equimolar doses. We conclude that the antinociceptive effect of [2–8]-leucopyrokinin is mediated mainly by central μ- and δ-opioid receptors.     

Antinociceptive effect of chrysin in diabetic neuropathy and formalin-induced pain models

ABSTRACT

Chrysin, a natural flavonoid, is the main ingredient of many medicinal plants, which shows potent pharmacological properties. In the present study, the antinociceptive effects of chrysin were examined in ICR mice. Chrysin orally administered at the doses of from 10 to 100?mg/kg exerted the reductions of formalin-induced pain behaviors observed during the second phase in the formalin test in a dose-dependent manner. In addition, the antinociceptive effect of chrysin was further characterized in streptozotocin-induced diabetic neuropathy model. Oral administration chrysin caused reversals of decreased pain threshold observed in diabetic-induced peripheral neuropathy model. Intraperitoneally (i.p.) pretreatment with naloxone (a classic opioid receptor antagonist), but not yohimbine (an antagonist of α2-adrenergic receptors) or methysergide (an antagonist of serotonergic receptors), effectively reversed chrysin-induced antinociceptive effect in the formalin test. Moreover, chrysin caused a reduction of formalin-induced up-regulated spinal p-CREB level, which was also reversed by i.t. pretreated naloxone. Finally, chrysin also suppressed the increase of the spinal p-CREB level induced by diabetic neuropathy. Our results suggest that chrysin shows an antinociceptive property in formalin-induced pain and diabetic neuropathy models. In addition, spinal opioid receptors and CREB protein appear to mediate chrysin-induced antinociception in the formalin-induced pain model.     

The oral administration of trans-caryophyllene attenuates acute and chronic pain in mice

Trans-caryophyllene is a sesquiterpene present in many medicinal plants’ essential oils, such as Ocimum gratissimum and Cannabis sativa. In this study, we evaluated the antinociceptive activity of trans-caryophyllene in murine models of acute and chronic pain and the involvement of trans-caryophyllene in the opioid and endocannabinoid systems. Acute pain was determined using the hot plate test (thermal nociception) and the formalin test (inflammatory pain). The chronic constriction injury (CCI) of the sciatic nerve induced hypernociception was measured by the hot plate and von Frey tests. To elucidate the mechanism of action, mice were pre-treated with naloxone or AM630 30 min before the trans-caryophyllene treatment. Afterwards, thermal nociception was evaluated. The levels of IL-1β were measured in CCI-mice by ELISA. Trans-caryophyllene administration significantly minimized the pain in both the acute and chronic pain models. The antinociceptive effect observed during the hot plate test was reversed by naloxone and AM630, indicating the participation of both the opioid and endocannabinoid system. Trans-caryophyllene treatment also decreased the IL-1β levels. These results demonstrate that trans-caryophyllene reduced both acute and chronic pain in mice, which may be mediated through the opioid and endocannabinoid systems.     

Central administration of neuronostatin induces antinociception in mice

Neuronostatin, a recently discovered endogenous bioactive peptide, was encoded by pro-mRNA of somatostatin that contributes to modulation of nociception. However, nociceptive effect of neuronostatin is still not fully known. The aim of this study was to evaluate effect of neuronostatin on nociception and elucidate its possible mechanism of action. Intracerebroventricular (i.c.v.) administration of neuronostatin (0.3, 3, 6, 12 nmol/mouse) produced a dose- and time-related antinociceptive effect in the tail immersion assay in mice, an acute pain model. The antinociceptive effect of neuronostatin was significantly antagonized by naloxone, and was strongly inhibited by co-injection with β-funaltrexamine or nor-binaltorphimine, but not by naltrindole. Also, melanocortin 3/4 receptor antagonist, SHU9119, completely blocked the effect of neuronostatin. These data indicated the involvement of both μ- and κ-opioid receptors and central melanocortin system in the analgesic response induced by neuronostatin. In addition, neuronostatin (6 nmol, i.c.v.) increased c-Fos protein expression in the periaqueductal gray (PAG) and the nucleus raphe magnus (NRM) that have a pivotal role in regulating descending pain pathways. Taken together, this study is the first to reveal that neuronostatin produces antinociceptive effect via opioid and central melanocortin systems, which is associated with an increase in neuronal activity the PAG and NRM.     

Induction of c-fos mRNA Expression in Rat Striatum by Neuroleptic Drugs

The effect of selective dopamine D2 receptor-acting drugs on striatal c-fos mRNA expression in the rat has been investigated by Northern hybridization and autoradiography to determine a possible role for c-fos in the initiation of adaptive changes in D2 receptor number by neuroleptic drugs. The neuroleptic drug haloperidol, a D2 receptor antagonist, was found to produce a rapid and transient induction of c-fos mRNA expression as compared with the expression in animals treated with saline. This induction by haloperidol was found to be dose dependent and D2 receptor mediated, inasmuch as a D2 agonist completely reversed the induction and the inactive isomer of the neuroleptic butaclamol, which does not produce an increase in D2 receptors, had no effect on c-fos mRNA expression. From these data, it can be concluded that c-fos expression in striatum is under dopamine D2 receptor-mediated inhibitory control. It is suggested that c-fos may play a role in the initiation of the increase in D2 receptor number produced by chronic neuroleptic drug treatment.     

Crotalphine, a novel potent analgesic peptide from the venom of the South American rattlesnake Crotalus durissus terrificus

We have shown that the venom of the South American rattlesnake Crotalus durissus terrificus induces a long-lasting antinociceptive effect mediated by activation of kappa- and delta-opioid receptors. Despite being mediated by opioid receptors, prolonged treatment with the crotalid venom does not cause the development of peripheral tolerance or abstinence symptoms upon withdrawal. In the present study, we have isolated and chemically characterized a novel and potent antinociceptive peptide responsible for the oral opioid activity of this crotalid venom. The amino acid sequence of this peptide, designated crotalphine, was determined by mass spectrometry and corroborated by solid-phase synthesis to be 相似文献   

Gastroprotective potential of risperidone, an atypical antipsychotic, against stress and pyloric ligation induced gastric lesions

Risperidone has been used in some stress disorders and may be potentially protective against stress-induced gastric lesions. Thus, the aim of the present study is to investigate, whether risperidone, a D(2) receptor and 5-HT(2A) receptor antagonist, would be able to result in gastroprotective effect in stress-induced lesions and also explore the possible mechanism of action behind its gastroprotective activity. Gastroprotective activity of risperidone was evaluated both by single treatment and 21 days repeated (0.03, 0.1, 0.3 and 1mg/kg, p.o.) treatment in the cold restraint stress (CRS) model and 21 days repeated treatment in the pyloric ligation (PL) model and compared with that of sulpiride (D(2) receptor antagonist) and ketanserin (5-HT(2) receptor antagonist) as standard. Histopathological assessment was done to evaluate the gastroprotective activity of risperidone in CRS model. The roles of nitric oxide (NO), sulfhydryl (SH) group, ATP-sensitive K(+) channels (K(ATP) channels) and prostaglandins (PGs) in the gastroprotective effect of risperidone against CRS were also investigated. PGE(2), hexosamine as a marker of mucus barrier and microvascular permeability were also estimated. Results show that repeated treatment of risperidone, sulpiride and ketanserin exhibited a gastroprotective effect against CRS-induced lesions while single administration of risperidone was found to be ineffective. Moreover, repeated treatment of risperidone and ketanserin was found to be ineffective in case of PL in contrast to sulpiride. Risperidone pretreatment reverses the stress induced alteration in hexosamine, PGE(2) and microvascular permeability. Pretreatment with l-NAME, NEM, glibenclamide and indomethacin reversed the gastroprotective effect of risperidone. The results suggest that risperidone has significant gastroprotective effects in CRS-induced gastric lesions models, which appears to be mediated by endogenous NO, SH, PGs and K(ATP) channel opening.     

Antinociceptive interactions of opioid delta receptor agonists with morphine in mice: supra- and sub-additivity.

In this study, the antinociceptive interactions of fixed ratio combinations of intracerebroventricularly (i.c.v.) given morphine and subantinociceptive doses of the delta agonists, [D-Pen2, D-Pen5]enkephalin (DPDPE), [D-Ala2, Glu4]deltorphin (DELT) or [Met5]enkephalin (MET) were examined using the mouse warm water tail flick test. When morphine was coadministered with DPDPE or DELT in a 4:1 and 9:1 mixture, respectively, a synergistic antinociceptive effect was observed. In contrast, when morphine was coadministered with MET in a 1:2 fixed ratio mixture, a subadditive interaction occurred. These results demonstrate both positive and negative modulatory interactions of delta agonists with morphine in an antinociceptive endpoint and that these interactions can be either supra- or subadditive. The data support the concept of a functional interaction between opioid mu and delta receptors and a potential regulatory role for the endogenous ligands of the opioid delta receptor.     

Novel glycosylated endomorphin-2 analog produces potent centrally-mediated antinociception in mice after peripheral administration

We report the synthesis and pharmacological characterization of a novel glycosylated analog of a potent and selective endogenous μ-opioid receptor (MOP) agonist, endomorphin-2 (Tyr-Pro-Phe-Phe-NH₂, EM-2), obtained by the introduction in position 3 of the tyrosine residue possessing the glucose moiety attached to the phenolic function via a β-glycosidic bond. The improved blood–brain barrier permeability and enhanced antinociceptive effect of the novel glycosylated analog suggest that it may be a promising template for design of potent analgesics. Furthermore, the described methodology may be useful for increasing the bioavailability and delivery of opioid peptides to the CNS.     

D2-dopamine receptor and alpha2-adrenoreceptor-mediated analgesic response of quercetin

Quercetin, a bioflavonoid (100-300 mg/kg) produced dose dependent increase in tail-flick latency, the analgesic effect being sensitive to reversal by naloxone (1 mg/kg). Prior treatment with haloperidol (1 mg/kg), D1/D2 receptor antagonist haloperidol, sulpiride (50 mg/kg), a selective D2 receptor antagonist, yohimbine (5 mg/kg), a alpha2-adrenoreceptor antagonist but not by SCH 23390 a, selective D1 receptor antagonist blocked this response. Apomorphine (1 mg/kg) a mixed D1/D2 dopamine receptor agonist, and quinpirole (0.5 mg/kg), a selective D2 receptor agonist also produced antinociception, that was reversed by haloperidol (1 mg/kg), sulpiride (50 mg/kg), but not by yohimbine (5 mg/kg). The antinociceptive action of quercetin (200 mg/kg) was potentiated by D2 agonist quinpirole (0.2 mg/kg). Dopamine D1 receptor agonist SKF38393 (10 and 15 mg/kg) failed to alter the antinociceptive effect of quercetin (200 mg/kg). Quercetin (200 mg/kg) reversed reserpine (2 mg/kg-4 hr) induced hyperalgesia, which was reversed by sulpiride but not by yohimbine. Thus, a role of dopamine D2 and alpha2-adrenoreceptors is postulated in the antinociceptive action of quercetin.     

Supraspinal antinociceptive effect of apelin-13 in a mouse visceral pain model

Apelin, as the endogenous ligand of the APJ receptor, is a novel identified neuropeptide whose biological functions are not fully understood. APJ receptor mRNA was found in several brain regions related to descending control system of pain, such as amygdala, hypothalamus and dorsal raphe nucleus (DRN). The present study was designed to determine whether supraspinal apelin-13 may produce antinociceptive effect observed in the acetic acid-induced writhing test, a model of visceral pain. Apelin-13 not only significantly produced preemptive antinociception at the dose of 0.3, 0.5, 1 and 3μg/mouse when injected intracerebroventricularly (i.c.v.) before acetic acid, but also significantly induced antinociception at a dose of 0.5, 1 and 3μg/mouse when injected i.c.v. after acetic acid. And i.c.v. apelin-13 did not influence 30-min locomotor activity counts in mice. Intrathecal (i.t.) administration of apelin-13 (1 and 3μg/mouse) significantly decreased the number of writhes, however, intraperitoneal (i.p.) injection of apelin-13 (10-100μg/mouse) had no effect on the number of writhes in the writhing test. The specific APJ receptor antagonist apelin-13(F13A), no-specific opioid receptor antagonist naloxone and μ-opioid receptor antagonist β-funaltrexamine hydrochloride (β-FNA) could significantly antagonize the antinociceptive effect of i.c.v. apelin-13, suggesting APJ receptor and μ-opioid receptor are involved in this process. Central low dose of apelin-13 (0.3μg/mouse, i.c.v.) could significantly potentiate the analgesic potencies of modest and even relatively ineffective doses of morphine administrated at supraspinal level. This enhanced antinociceptive effect was reversed by naloxone, suggesting that the potentiated analgesic response is mediated by opioid-responsive neurons.     

Antinociception induced by beta-lactotensin,a neurotensin agonist peptide derived from beta-lactoglobulin,is mediated by NT2 and D1 receptors

In this study, we examined the antinociceptive effect of beta-lactotensin, a neurotensin agonist that has been isolated from the chymotrypsin digest of beta-lactoglobulin as an ileum-contracting peptide. Beta-lactotensin showed naloxone-insensitive antinociceptive activity by the tail-pinch test after i.c.v. (200 nmol/mouse) or s.c. (300 mg/kg) administration in ddY mice. Tolerance was not developed to antinociception induced by beta-lactotensin after repeated s.c. administration for 5 days. The antinociceptive activity of beta-lactotensin was blocked by treatment with the neurotensin NT2 receptor antisense ODN, while treatment with the NT1 receptor antisense ODN had no effect. The antinociceptive activity was also blocked by a dopamine D1 receptor antagonist, SCH23390 (1 microg/mouse, i.c.v.), while a D2 receptor antagonist, raclopride (0.5 microg/mouse, i.c.v.), did not block the activity. These results indicate that the antinociceptive activity of beta-lactotensin is mediated by NT2 and D1 receptors.     

Antinociceptive effect of topiramate in models of acute pain and diabetic neuropathy in rodents

This study assesses the antinociceptive effect induced by different dosages of topiramate (TP), an anticonvulsant drug that is orally administered in models of neuropathic pain and acute pain in rats and mice, respectively. Orally administered TP (80 mg/Kg) in mice causes antinociception in the first and second phases of a formalin test, while in doses of 20 and 40 mg/Kg it was only effective in the second phase. TP (80 mg/Kg, p.o) also exhibited antinociceptive action in the hot plate test, however, it did not have an effect in the capsaicin test in mice, nor in the model of neuropathic pain in diabetic rats. The antinociceptive effect caused by TP (80 mg/Kg, p.o) in the formalin test was reversed by prior treatment with naloxone (opioid antagonist), but not with glibenclamide (antagonist of the potassium channel), ondansetron (antagonist of the serotonin 5HT3 receptor) or cyproheptadine (antagonist of the serotonin 5HT2A receptor).The data show that TP has an important antinociceptive effect in the models of nociception induced by chemical (formalin) or thermal (hot plate) stimuli, and that the opioid system plays a part in the antinociceptive effect, as shown by formalin.     

CY 208-243: a unique combination of atypical opioid antinociception and D1 dopaminomimetic properties

Here we describe the potent antinociceptive action of the indolophenanthridine, CY 208-243, which has high affinities to the dopamine D1 binding and the opioid sites as well as to the 5-HT1A site. The antinociceptive action was comparable to that of morphine in most, but not all models of nociception, nevertheless, basic differences exist in its overall profile. Antagonism of CY 208-243's antinociceptive action was only possible with either high doses of naloxone or not at all and no cross-tolerance with morphine in CY 208-243 tolerant rats occurred. The biochemical basis for dependence liability may be absent and no opioid activity was observed in cultured hippocampal cells. Physical dependence did not occur after programmed administration in the rhesus monkey, nor did CY 208-243 cause respiratory depression in the rat (rather a stimulation). Lack of generalization in fentanyl-trained rats strongly suggests that CY 208-243 lacks opioid-like subjective cues. The coexistence of D1 dopaminergic and atypical opioid agonist properties represents a unique pharmacodynamic combination which is not shared with any other analgesic, and may provide safe and innovative pain therapy.