Involvement of δ-and μ-opioid receptors in the delayed cerebral ischemic tolerance induced by repeated electroacupuncture preconditioning in rats

Background Preconditioning with repeated electroacupuncture （EA） could mimic ischemic preconditioning to induce cerebral ischemic tolerance in rats. The present study was designed to investigate whether mu（μ）-, delta（δ）- or kappa（κ）-opioid receptors are involved in the neuroprotecUon induced by repeated EA preconditioning. Methods The rats were pretreated with naltrindole （NTI）, nor-binaltorphimine （nor-BNI） or D-Phe-Cys-Tyr-D- Trp-Om-Thr-Pen-Thr-NH2 （CTOP）, which is a highly selective δ-, κ- or μ-opioid receptor antagonist respectively, before each EA preconditioning （30 minutes per day, 5 days）. Twenty-four hours after the last EA treatment, the middle cerebral artery occlusion （MCAO） was induced for 120 minutes. The brain infarct volume was determined with 2,3,5-tdphenyltetrazolium chloride staining at 24 hours after MCAO and compared with that in rats which only received EA preconditioning. In another experiment, the met-enkephalin-like immunoreactivity in rat brain was investigated by immunohistochemistry in both EA preconditioning and control rats. Results The EA preconditioning reduced brain infarct volume compared with the control rats （P=-0.000）. Administration of both NTI and CTOP attenuated the brain infarct volume reduction induced by EA preconditioning, presenting with larger infarct volume than that in the EA preconditioning rats （P〈0.001）. But nor-BNI administration did not block the infarct volume reduction induced by EA preconditioning, presenting with smaller infarct volume than the control group rats （P=-0.000）. The number of met-enkephalin-like immunoreactivity positive neurons in the EA preconditioning rats was more than that of the control rats （P=-0.000）. Conclusion Repeated EA preconditioning stimulates the release of enkephalins, which may bind 5- and p-opioid receptors to induce the tolerance against focal cerebral ischemia.

Interaction and regulatory functions of μ- and δ-opioid receptors in nociceptive afferent neurons

μ-opioid receptor （MOR） agonists such as morphine are powerful analgesics used for pain therapy. However, the use of these drugs is limited by their side-effects, which include antinociceptive tolerance and dependence. Earlier studies reported that MOR analgesic tolerance is reduced by blockade of 5-opioid receptors （DORs） that interact with MORs. Recent studies show that the MOR/DOR interaction in nociceptive afferent neurons in the dorsal root ganglion may contribute to morphine analgesic tolerance. Further analysis of the mechanisms for regulating the trafficking of receptors, ion channels and signaling molecules in nociceptive afferent neurons would help to understand the nociceptive mechanisms and improve pain therapy.

A non-opioid pathway for dynorphin-caused spinal cord injury in rats

Intrathecal injection of dynorphin into rats via subarachnoid catheter induces damage to spinal cord tissue and motor function. Injection of the kappa opioid receptor antagonist nor-binaltorphine, or the excitatory amino acid N-methyl-D-aspartate receptor antagonist MK-801 into rats alleviated the pathological changes of dynorphin-caused spinal cord tissue injury and reduced the acid phosphatase activity in the spinal cord. The experimental findings indicate that there are opioid and non-opioid pathways for dynorphin-induced spinal cord injury, and that the non-opioid receptor pathway may be mediated by the excitatory amino acid N-methyl-D-aspartate receptor.

Subtype of Opioid Receptor in Airway SmoothMuscle and the Role of the Receptor in Asthmatic Attacks

In order to elucidate the behavior of opioid receptor in the airway smooth muscle (ASM) and potential role of the receptor in asthmatic attacks electrical field stimulation (EFS) was used to evaluate the effects of different narcotics and naloxine (Nal) on isolated rabbit ASM and biochemical methods were used to assay the influences of morphine (Mor) and pethidine(Pet) on the activities of adenylcyclase (AAC) and phosphodiesterase(APDE) in homogenate derived from rabbit ASM.Nal was used to treat the bronchospasm during anesthesia. It shows that Mor increased the rabbit ASM contraction and Nal reversed this effect, while Nal itself did not affect ASM. Fentanyl(Fen) decreased the contraction and Pet not only decreased the contraction but relaxed the ASM. Mor decreased the AAC in the rabbit ASM but didn't affect the APDE in the rabbit ASM. Pet had no influence on both the AAC and the APDE. Nal effectively relieved the bronchospasm which failed to the traditional treatment during anesthsia. These indicate that the opioid receptor in the ASM is a new subtype one.Mor exhibits satuable binding the subtype receptor and exerts strong agonistic activity to induce bronchospasm, while Nal antagonizes this effect. Yet Fen and Pet don's bind this subtype receptor. Endogenous opioid-like peptides may also bind this subtype receptor. In patients with airway hyperreactivity (PAHR) Mor is contraindicated, Fen and Pet may be used. and the latter may be the best choice.Asthma or bronchospasm may be treated with Nal.

Corelation Between Single Nucleotide Polymorphisms in Mu Opioid Receptor Exon 2 and Stereotypic Behaviour in Sows

Three breeds of sows were observed to investigate the relationship between Single Nucleotide Polymorphisms（SNPs） in Mu Opioid Receptor（MOR）and stereotypic behaviour,such as,sham-chewing,bar biting and standing still in order to better understand the mechanism of stereotypic development of the animals in restrained conditions.MOR exon 2 partial sequences were amplified to analyze single nucleotide polymorphisms by PCR-SSCP.One SNP,a silence mutant was found.A significant difference （P〈0.01）was found in the frequency of genotypes in these 3 breeds where only the BB genotype,which was identical to that published in GenBank,was found in the Duroc breed,while no AA genotype was found in Landrace,3 genotypes AA,BB and AB were found in Yorkshire.The result also indicated that the individuals with AA and AB genotypes tended to be more active in sham-chewing than those with the BB genotype（P〈0.05）.The overall results of this study suggested that sham-chewing of sows may be subjected to both genetic control and environmental conditions,but activity level was more likely to be affected by their environment.We can putatively draw the conclusion that MOR gene has effect on the sham-chewing behavioral traits of sow.

MODULATION OF A δ－AND C－FIBER EVOKED RESPONSES OF NOCICEPTIVE NEURONS IN THE SUPERFICIAL AND THE DEEPER DORSAL HORN OF THE ME

The present study was designed to investigate the effects of intravenously administered agonists and antagonists at μ(DAMGO, naloxone,)δ1 (DPDPE,BNTX)andδ2(DELT, NTB)opioid receptors on the Aδ-and C-fiber evoked responses of nociceptive neurons in the superficial and the deeper dorsal horn of the rat medulla.Extracellular single unit recording were made from 70 nociceptive neurons(28 NS,42 WDR) in the superficial dorsal horn and 37 nociceptive neurons(4 NS,33 WDR)in the deeper dorsal horn.All these neurons had an ipsilateral orofacial mechanoreceptive field and majority of these neurons had no spontaneous activity. The latencies for the C fiber evoked responses ranged from 34～105 msec whereas for Aδfiber-evoked responses it ranged from 3～22msec. A clear separation was observed between early and late responses of evoked by Cand Aδ-fiber.Application of DPDPE,DELT and DAMGO produced inhibitory effects on the Aδ-and C-fiber evoked responses of nociceptive neurons in the superficial and thedeeper dorsal horn.By comparison,the inhibition was more pronounced on the C-fiber evoked response than on the Aδ-fiber evoked response,and DAMGO produced a stronger inhibitory action than both DELT and DPDPE. Additionally,DPDPE produced facilitation, or inhibition followed by facilitation on the Aδ-and C-response and the effect had longer latency and longer time course.DPDPE also induced completely oppsite effects on the Aδ-and C-fiber evoked responses.Although the facilitation was observed,the effect was not dose-dependent. Application of BNTX (0.4～1mg/kg),a δ1 receptor antagonist,produced antagonism of DPDPE in 88%(7/8) neurons. Application of the doses (0.7～1mg/kg) of BTB,δ2-receptor antagonist,resulted in antagonism of both DELT and DPDPE. The inhibition of DELT on Aδ-response was antagonized by doses (0.3～1mg/kg)of NTB in 100% (14/14)neurons while the antagonism on C-response was in 79%(11/14) neurons.The effect produced by DPDPE was antagonized by the doses (0.7～1mg/kg) of NTB in 100%(4/4) neurons. However,a smaller dose of NTB(0.3mg/kg)which and antagonize the effect of DELT,did not antagonize the effect of DPEPE in 100%(4/4) neurons. The inhibitory action of DAMGO on Aδ-and C-fiber evoked responses was completely antagonized by naloxone(0. 2mg/kg) in 100% (6/6) neurons. These results suggest that:①μ-and δ-opioid receptors play an important role in modulating Aδ-and Cfiber evoked responses of nociceptive neurons in the superficial and the deeper dorsal horn of the rat medulla; ② The inhibitory action produced by DPDPE, DELT and DAMGO was more pronounced on the C-fiber evoked excitation and indicates that the agonists produce more predominant inhibition on the responses of dorsal horn neurons to noxious stimuli; ③ activation of either δ1-orδ2-opioid receptors produces inhibitory actions on Aδ- and C-response of nociceptive neurons in the superficial and the deeper dorsal horn of the medullal;DPDPE and DELT act at different δ-opioid receptor subtypes in the rat rnedulla; ⑤i.v.-administered NTB can distinguish δ-opioid receptor subtypes in a limited dose range.When administered i. v., 0. 3mg/kg of NTB is selective for δ2-opioid receptor.

Involvement of Opioid Peptides in the Analgesic Effect of Spinal Cord Stimulation in a Rat Model of Neuropathic Pain

Spinal cord stimulation(SCS)-induced analgesia was characterized,and its underlying mechanisms were examined in a spared nerve injury model of neuropathic pain in rats.The analgesic effect of SCS with moderate mechanical hypersensitivity was increased with increasing stimulation intensity between the 20%and 80%motor thresholds.Various frequencies(2,15,50,100,10000 Hz,and 2/100 Hz dense-dispersed)of SCS were similarly effective.SCS-induced analgesia was maintained without tolerance within 24 h of continuous stimulation.SCS at 2 Hz significantly increased methionine enkephalin content in the cerebrospinal fluid.The analgesic effect of 2 Hz was abolished byμorκopioid receptor antagonist.The effect of 100 Hz was prevented by aκantagonist,and that of 10 kHz was blocked by any of theμ,δ,orκreceptor antagonists,suggesting that the analgesic effect of SCS at different frequencies is mediated by different endorphins and opioid receptors.

Far infrared-emitting ceramics decrease Freund's adjuvant-induced inflammatory hyperalgesia in mice through cytokine modulation and activation of peripheral inhibitory neuroreceptors

Objective： The present study aimed to evaluate the analgesic and anti-inflammatory effects of far infrared-emitting ceramics （cFIRs） in a model of persistent inflammatory hyperalgesia and to elucidate the possible mechanisms of these effects. Methods： Mice were injected with complete Freund＇s adjuvant （CFA） and treated with cFIRs via place- ment on a pad impregnated with cFIRs on the bottom of the housing unit for different periods of time. Mice underwent mechanical hyperalgesia and edema assessments, and tumor necrosis factor-α （TNF-α）, interleukin-1β （IL-1β） and IL-10 levels were measured. Twenty-four hours after CFA injection and 30 min before cFIR treatment, mice were pretreated with a nonselective adenosinergic antagonist, caffeine, the selective adenosine receptor A antagonist, 1,3-dipropyl-8-cyclopentylxanthine （DPCPX）, the selective cannabinoid receptor type 1 antagonist, AM281, the selective cannabinoid receptor type 2 antagonist, AM630, or the nonselective opioid receptor antagonist, naloxone, and mechanical hyperalge- sia was assessed. Results： cFIRs statistically （P 〈 0.05） decreased CFA-induced mechanical hyperalgesia （82.86 ±5.21）% in control group vs （56.67±9.54）% in cFIR group） and edema （（1699.0 ± 77.8） gm in control group vs （988.7±107.6） gm in cFIR group）, cFIRs statistically （P 〈 0.05） reduced TNF-α （0.478± 0.072） pg/mg of protein in control group vs （0.273 ±0.055） pg/mg of protein in cFIR group） and IL-113 （（95.81 ± 3.95） pg/mg of protein in control group vs （80.61 ±4.71）pg/mg of protein in cFIR group） levels and statistically （P〈 0.05） increased IL-10 （（18.32 ±0.78） pg/mg of protein in control group vs （25.89 ±1.23） pg/mg of protein in cFIR group） levels in post-CFA-injected paws. Peripheral pre-administration of inhibitory neuroreceptor antagonists （caffeine, DPCPX, AM281, AM630 and naloxone） prevented the analgesic effects of cF1Rs （P 〈 0.05）.Conclusion： These data provide additional support for the use of cFIRs in the treatment of painful inflam- matory conditions and contribute to our understanding of the neurobiological mechanisms of the ther- apeutic effects of cFIRs.

Electroacupuncture Attenuates Surgical Stress-Induced Reduction of T Lymphocytes through Modulation of Peripheral Opioid System

Objective:To investigate the action mechanisms of electroacupuncture(EA)on postoperative immunosuppression.Methods:Male C57 BL/6 mice(5–7 weeks old)were randomly divided into:the sham injury group,the surgical trauma stressed group,the EA group[surgery+2/100 Hz EA at Neiguan(PC 6)],and the EA+Nal(surgery+EA+intraperitoneal injection of naloxone).Abdominal surgical trauma stress mice model was established.EA was performed on bilateral PC 6 acupoints by an EA apparatus(2/100 Hz)for 20 min once a day for 3 days.The m RNA expressions of MOR,DOR,and KOR in thymus and L3-5 dorsal root ganglions(DRG)were determined by quantitative real-time polymerase chain reaction(q RT-PCR)and the protein expressions of MOR,DOR,and KOR in thymus were measured by Western blot.Flow cytometry assay was used to detect the levels of T lymphocyte subtypes in the peripheral blood.Results:Surgical trauma induced decreased the m RNA expression level of MOR in both thymus(P<0.01)and L3-L5 DRGs(P<0.05).Moreover,EA treatment not only significantly attenuated the MOR protein and m RNA expression in the thymus(both P<0.05),but also markedly increased expression of DOR and KOR opioid receptor in thymus(P<0.01).However,the m RNA expressions of opioid receptors were not regulated by EA in the DRG(all P>0.05).Furthermore,T lymphocyte population of CD3^+ and CD4^+ was decreased in the peripheral blood after surgical trauma(both P<0.01).EA treatment can significantly elevate the population of CD3^+(P<0.01),CD4^+(P<0.05)and CD8^+T cells(P<0.01).Intraperitoneal injection of the non-selective opioid receptor antagonist naloxone blocked the up-regulation of T lymphocytes by EA.Conclusion:EA may improve postoperative immunosuppression through the peripheral opioid system.

Enantiospecific Synthesis of All Four Stereoisomers of Novel Bicyclic Arylacetamides as κ-Opioid Agonists

Conformationally constrained bicyclic derivatives of the potent and selective κ-opioid receptor agonist 2-(3,4-dichlorophenyl)-N-methyl-N- [(1S)-1-phenyl-2- (1-pyrrolidinyl)-ethyl] acetam^ide (3, ICI-199, 441) were designed to explore the effect of the conformational restriction and stereochemistry of the pharmacophoric ethylenediamine incorporated into the pyrrolidine on the affinity and κ-selectivity. A facile enantiospecific synthetic route was established to afford all four stereoisomers starting from readily available amino acids through mild cyclization and amide formation.

Kigelia africana Fruit:Constituents,Bioactivity, and Reflection on Composition Disparities

Objective: Kigelia africana, a tropical tree, which has long been used in African traditional medicine. The objective of the current study has been identifying the constituents of K. africana and verifying its utilities in traditional medicine. Materials and Methods: The methanol extract of K. africana fruits was subjected to chromatographic fractionation utilizing different techniques. The methanol extract together with the isolated compounds were tested for their bioactivities in a series of cell-based assays. Results: The current work led to isolation and characterization of nine constituents including iridoid glycosides, phenylpropanoid derivatives, and a eucommiol derivative. The hexanes extract caused inhibition of the opportunistic yeast; Cryptococcus neoformans Pinh. The chloroform extract exhibited substantial antileishmanial activity of Leishmania donovani. Verminoside(1) showed weak inhibition of the CB1, CB2, and Kappa opioid receptors. Compound 4 exhibited weak inhibition of the Kappa and Mu opioid receptors. The hexanes and the chloroform extracts of K. africana exhibited inhibitory activity against the pathogenic parasite Trypanosoma brucei. The ethyl acetate extract showed the same activity. Conclusions: This is the first report on the isolation of coniferyl 4-0-(3-D-glucopyranoside(7), a eucommiol derivative(crescentin IV)(6), and 6-feruloylcatalpol(4) from the genus Kigelia. It is also the first report on the separation of ajugol(2), catalpol(3), and specioside(5) from the fruits of K. africana. Revision of the^1 H and ^(13)C-NMR spectra of 6-feruloylcatalop(4) and 6-p-hydroxycinnamoylcatalpol(5, specioside) is described. Further, the results of the in vitro assays corroborate the traditional utility of this plant in medicine.

Cardioprotective effects of morphine on rat heart suffering from ischemia and reperfusion

Objective To investigate the cardioprotective effects of morphine on ischemic reperfused rat heart in vitro and its mechanism Methods The isolated rat heart was perfused in a Langendorff apparatus Infarct myocardium was determined by TTC Coronary flow (CF), heart rate (HR), left ventricular pressure (LVP), the first derivative of ventricular pressure (LVP/dtmax) and infarct size after ischemia and reperfusion in rat heart given 0.3 μmol/L morphine were observed The effects of naloxone and glibenclamide on the cardioprotection of morphine were also measured Results After ischemia and reperfusion, CF, HR, LVP and LVP/dtmax of isolated rat hearts decreased significantly ( P <0 01) After morphine preconditioning, HR, LVP and LVP/dtmax increased ( P <0 01) and infarct size was reduced significantly ( P <0 01), while no significant change in CF ( P >0 05) The cardioprotective effects of morphine were abolished by naloxone or glibenclamide completely Conclusions Morphine can reduce ischemia reperfusion injuries in isolated rat heart The cardioprotective effects of morphine are mediated by a local opioid receptor K ATP channel linked mechanism in rat hearts

Effects of remifentanil on intracellular Ca^2＋ and its transients induced by electrical stimulation and caffeine in rat ventricular myocytes

Background Preconditioning with remifentanil confers cardioprotection. Since Ca^2＋ overload is a precipitating factor of injury, we determined the effects of remefentanil on intracellular Ca^2＋ （[Ca^2＋]i） and its transients induced by electrical stimulation and caffeine, which reflects Ca^2＋ handling by Ca^2＋ handling proteins, in rat ventricular myocytes. Methods Freshly isolated adult male Sprague-Dawley rat myocytes were loaded with Fura-2/AM and [Ca]i was determined by spectrofluorometry. Remifentanil at 0.1-1000 μg/L was administered. Ten minutes after administration, either 0.2 Hz electrical stimulation was applied or 10 mmol/L caffeine was added. The [Ca^2＋]i, and the amplitude, time resting and 50% decay （t50） of both transients induced by electrical stimulation （E[Ca^2＋]i） and caffeine （C[Ca^2＋]i） were determined. Results Remifentanil （0.1-1000.0 μg/L） decreased the [Ca^2＋]i in a dose-dependent manner. It also decreased the amplitude of both transients dose-dependently. Furthermore, it increased the time to peak and tso of both transients dose-dependently. Conclusion Remifentanil reduced the [Ca^2＋]i and suppressed the transients induced by electrical stimulation and caffeine in rat ventricular myocytes.

Intrathecal administration of neuronostatin induces an antinociceptive effect in a mouse visceral pain model

Neuronostatin(NST)is a peptide encoded by the somatostatin gene that serves important physiological functions in diverse tissues.Previous studies have shown that intracerebroventricular administration of NST induces antinociceptive effects and hyperalgesic effects as determined by the tail immersion assay and formalin test,respectively.In the present study,we aimed to evaluate the effects of intrathecal(i.t.)injection of NST on nociception in a model of visceral pain,and determine possible mechanisms of action in mice.NST(1,3,6,or 12 nmol)was administered to mice,leading to a dose-dependent antinociceptive effect as determined by the acetic acid-induced writhing test in mice.NST(1 nmol)also enhanced the antinociceptive effect of morphine(2.5 and 5μg/kg)in the spine.Naloxone andβ-funaltrexamine hydrochloride significantly antagonized the antinociceptive effect of NST.The expression of G-protein-coupled receptor 107(GPR107)protein and the phosphorylation of PKA at Thr197 were increased after i.t.administration of NST,suggesting that theμ-opioid receptor and GPR107/PKA signaling pathway are involved in the analgesic response.In conclusion,i.t.injection of NST may potentially be used as a new approach in the mediation of visceral pain.