Effects Of Opioid Agonists Research Articles

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Anesthesiology's Journal CME is open to all readers. Members of the American Society of Anesthesiologists (ASA) enjoy a preferred rate for their subscription. However, Journal CME is not limited to ASA members or Journal subscribers. To take part in Journal CME, complete the following steps:The American Society of Anesthesiologists is accredited by the Accreditation Council for Continuing Medical Education to provide continuing medical education for physicians.The American Society of Anesthesiologists designates this educational activity for a maximum of 1 AMA PRA Category 1 Credit(s) ™. Physicians should only claim credit commensurate with the extent of their participation in the activity.Purpose: The focus of Anesthesiology Journal CME is to educate readers on current developments in the science and clinical practice of anesthesiology.Target Audience: Anesthesiology Journal CME is designed for physicians involved with anesthesiology education, clinical practice, and research.Editor-in-Chief: James C. Eisenach, M.D., has no relevant financial relationships to disclose.CME Editors: Leslie C. Jameson, M.D., and Richard P. Dutton, M.D., M.B.A., have no relevant financial relationships to disclose.ASA Staff: Employees involved in planning have no relevant financial relationships to disclose.All tests and requests for credit must be submitted through the Anesthesiology CME website at www.asahq.org/journal-cme. Participants should claim credit in 15-minute increments, for a maximum of 1 AMA PRA Category 1 Credit(s) ™ per journal article.Two payment options are available:ASA Member Non-memberAnnual Fee $60 $120Per Issue $10 $20Payment may be made using Visa or MasterCard.Please direct any questions about Journal CME to:Joyce CanselorEducation Coordinator, CME(847) 268-9185j.canselor@asahq.orgRead the article by Dahan et al . entitled “Incidence, reversal, and prevention of opioid-induced respiratory depression” on page 226 of this issue.After completing this activity, the learner will understand the effects of opioid agonists on the central nervous system, be able to recognize and treat respiratory depression caused by opioid agonists, and understand the risks and benefits of naloxone administration.Authors: Albert Dahan, M.D., Ph.D., returned a disclosure form indicating that he received funded research from Gruenenthal GmbH Aachen, Mundipharma Cambridge UK, Eurocept NL, and Abbott Netherlands, and other material support from Aspect MS Int. Leon Aarts, M.D., Ph.D., and Terry W. Smith, Ph.D., returned disclosure forms indicating that they have no financial interest in or affiliation with any commercial supporter or providers of any commercial services discussed in this educational material.Registration and submission of answers must be completed by January 31, 2013.

Estradiol: A key biological substrate mediating the response to cocaine in female rats

A consistent finding in drug abuse research is that males and females show differences in their response to drugs of abuse. In women, increased plasma estradiol is associated with increased vulnerability to the psychostimulant and reinforcing effects of drugs of abuse. Our laboratory has focused on the role of estradiol in modulating the response to cocaine. We have seen that ovariectomy increases the locomotor response to a single cocaine injection, whereas estradiol exacerbates the locomotor response to repeated cocaine administration. Cocaine-induced sensitization of brain activity, as measured by fMRI, is also dependent on plasma estradiol. Moreover, we observed that although all ovariectomized rats show conditioned place preference to cocaine, it is more robust in ovariectomized rats with estradiol. Opioid receptors are enriched in brain regions associated with pleasure and reward. We find that in females, the effectiveness of kappa opioid agonists in decreasing the locomotor response to repeated cocaine varies with plasma estradiol. We also find that estradiol regulates the density of mu opioid receptors in brains areas associated with reward. These data hint that in females, estradiol modulates the behavioral effects of cocaine by regulating mu and kappa opioid signaling in mesocorticolimbic brain structures. Identifying the mechanisms that mediate differences in vulnerability to drugs of abuse may lead to effective therapeutic strategies for the treatment and prevention of addiction and relapse. We encourage health practitioners treating persons addicted to drugs to consider gender differences in response to particular pharmacotherapies, as well the sex steroid milieu of the patient.

Magnesium ions and opioid agonists in vincristine-induced neuropathy

Neuropathic pain is difficult to treat. Classic analgesics (i.e., opioid receptor agonists) usually possess low activity. Therefore other agents such as antidepressants, anticonvulsants, and corticosteroids are used. It is commonly known that NMDA antagonists increase analgesic activity of opioids. Unfortunately, clinical use of NMDA antagonists is limited because of the relatively frequent occurrence of adverse effects e.g., memory impairment, psychomimetic effects, ataxia and motor in-coordination. Magnesium ions (Mg2+) are NMDA receptor blockers in physiological conditions. Therefore, in this study the effect of opioid receptor agonists and the influence of Mg2+ on the action of opioid agonists in vincristine-induced hyperalgesia were examined. Opioid agonists such as morphine (5mg/kg, ip), and fentanyl (0.0625mg/kg, ip), as well as the partial agonist buprenorphine (0.075mg/kg, ip) administered alone on 5 consecutives days did not modify the hyperalgesia in vincristine rats. In contrast, pretreatment with a low dose of magnesium sulfate (30mg/kg, ip) resulted in a progressive increase of the analgesic action of all three investigated opioids. After discontinuation of drug administration, the effect persisted for several days.

Excitatory and inhibitory effects of opioid agonists on respiratory motor output produced by isolated brainstems from adult turtles (Trachemys)

To determine how central opioid receptor activation alters turtle breathing, respiratory-related hypoglossal (XII) motor bursts were recorded from isolated adult turtle brainstems during 60 min bath applications of agonists for delta- (DOR), kappa- (KOR), or nociceptin/orphanin (NOR) receptors. DADLE (DOR agonist) abolished XII burst frequency at 0.3-0.5 microM. DPDPE (DOR agonist) increased frequency by 40-44% at 0.01-0.1 microM and decreased frequency by 88+/-8% at 1.0 microM. U-50488 and U-59693 (KOR agonists) decreased frequency by 65-68% at 100 and 50 microM, respectively. Orphanin (NOR agonist) decreased frequency by 31-51% at 1.0-2.0 microM during the first 30 min period. Orphanin (0.5 and 2.0 microM) increased bursts/episode. Although morphine (10 microM) abolished frequency in nearly all brainstems, subsequent co-application of phenylephrine (alpha(1)-adrenergic agonist, 20-100 microM) with morphine restored activity to 16-78% of baseline frequency. Thus, DOR, KOR, and NOR activation regulates frequency and NOR activation regulates episodicity, while alpha(1)-adrenergic receptor activation reverses opioid-induced respiratory depression in turtles.

Bioequivalence Criteria for Transdermal Fentanyl Generics

With the increasing appearance of transdermal fentanyl generics since 2004 when patent protection of the reference Duragesic expired, opportunities to switch between different generics have arisen. Transdermal fentanyl is subject to bioequivalence regulation because only approximately 92% of the dose is absorbed as a result of the need to maintain a diffusion gradient from plaster to skin. Considering the high potency of fentanyl and the potential dangerous adverse effects of full mu opioid receptor agonists, we assessed evidence suggesting a revision of the confidence limits of bioequivalence of 80-125%. A few cases have been reported where a prescribed ascension in transdermal fentanyl dosing triggered respiratory depression. Values of concentration that produce a 50% effective response for decreasing the ventilatory volume lie within the plasma concentration range of 1.4-2.5 ng/mL during transdermal fentanyl analgesia. However, an exchange of the reference with a generic with higher bioavailability would trigger respiratory depression only in extreme situations and is clinically supported by only a single case report. Experimental or clinical evidence is required to provide the necessary database for final judgement of bioequivalent limits of fentanyl generics. At present, the evidence is not sufficient to advise other bioequivalence criteria than those previously applied to transdermal fentanyl.

Spotlight on Buprenorphine/Naloxone in the Treatment of Opioid Dependence†

Buprenorphine/naloxone (Suboxone) comprises the partial micro-opioid receptor agonist buprenorphine in combination with the opioid antagonist naloxone in a 4 : 1 ratio. When buprenorphine/naloxone is taken sublingually as prescribed, the naloxone exerts no clinically significant effect, leaving the opioid agonist effects of buprenorphine to predominate. However, when buprenorphine/naloxone is parenterally administered in patients physically dependent on full agonist opioids, the opioid antagonism of naloxone causes withdrawal effects, thus reducing the abuse potential of the drug combination. Buprenorphine/naloxone is an effective maintenance therapy for opioid dependence and has generally similar efficacy to methadone, although more data are needed. Less frequent dispensing of buprenorphine/naloxone (e.g. thrice weekly) does not appear to compromise efficacy and can improve patient satisfaction. Buprenorphine/naloxone is more effective than clonidine as a medically supervised withdrawal therapy. Moreover, buprenorphine/naloxone is a generally well tolerated medically supervised withdrawal and maintenance treatment. Thus, sublingual buprenorphine/naloxone is a valuable pharmacotherapy for the treatment of opioid dependence.

Effects of Anesthetics on Cancer Recurrence

TO THE EDITOR: We read with great interest the recent article by Weckermann et al on the perioperative activation of disseminated tumor cells in bone marrow of patients with prostate cancer. The authors postulate “unknown perioperatively acting triggers that stimulate outgrowth of DTCs” (disseminated tumor cells). Recent clinical and laboratory data suggest that anesthetic technique may play a role in tumor dissemination and recurrence. This issue has been highlighted in the anesthesia literature in a recent article of the Anesthesia Patient Safety Foundation Newsletter, which reviews the clinical and laboratory data for such an effect. In a retrospective study of prostate cancer, there was a significant difference in the rate of tumor recurrence contingent on the type of anesthesia used. A small retrospective study in breast cancer had similar findings. A large, multicenter, prospective, randomized trial investigating the influence of type of anesthesia on breast cancer recurrence is currently underway. In addition to the clinical studies, there is also an evolving basic science literature suggesting that opiates affect tumor growth. Both we and Gupta et al have shown that clinically relevant concentrations of opiates can cause endothelial cell proliferation and migration in vitro. The proangiogenic effect of mu opioid agonists seems to be the result of reciprocal transactivation of the vascular endothelial growth factor receptor. We have also demonstrated that mu opioids induce a defect in barrier function, potentially allowing penetration of tumor cells. The effects of mu agonists on both angiogenesis and barrier function are reversed by tertiary opiate antagonists or by methylnaltrexone, a peripherally acting mu opioid receptor antagonist approved in the United States to treat opioid-induced constipation in patients with advanced illness receiving palliative care when response to laxatives has not been sufficient. If these laboratory studies are confirmed clinically, then the selection of anesthetic technique used during the operative procedure and the possible use of peripheral mu opioid receptor antagonists in the perioperative period may be of potential importance. It would be particularly interesting if the authors were able to review the perioperative records of their patients to see which drugs were administered and what anesthetic techniques were used. We commend the authors for their diligent work and believe that their observations deserve additional investigation.

Nanoelectrospray with ion-trap mass spectrometry for the determination of beta-casomorphins in derived milk products

beta-Casomorphins (b-CMs) are bioactive peptides derived from casein with opioid agonist effects similar to morphine. The use of electrospray (ESI) with quadrupole ion-trap mass spectrometry (QIT-MS) for these compounds in two matrices, cheese and milk, was examined. It was compared to a liquid chromatography (LC) coupled to mass spectrometry (LC–MS), and a “soft” ionisation technique, NanoMate, with selected ion monitoring (SIM), which are unreliable for the determination of trace casomorphins in derived milk products. b-CM mass fragmentation pathways were done for the four most common b-CMs: β-casomorphin (1-5) bovine (b-CM-5), β-casomorphin (1-7) bovine (b-CM-7), [D-Ala2, D-Pro4,Tyr5]-β-casomorphin (1-5) amide (b-CM-10) and β-casomorphin (1-5) amide [D-Ala2,Hyp4,Tyr5] (b-CM-11). The major product ions obtained in QIT-MS were used to construct fragmentation pathways for b-CMs. The different collision energies using automated nanoelectrospray ion source NanoMate and conventional LC in QIT-MS were studied. Calibration data for b-CMs, using spiked milk or cheese samples (10 g or 10 mL), were: NanoMate/MS (25–1000 μg/L), r 2 = 0.998; NanoMate/MS 2 (5–1000 μg/L), r 2 = 0.9992; NanoMate/MS 3 (2.5–1000 μg/L), r 2 = 0.9998. Reproducibility data (% RSD, N = 5) for NanoMate/MS n mode ranged between 2.0 at 500 μg/L and 7.0 at 10 μg/L.

Yohimbine prevents the effect of morphine on the redox status of neuroblastoma×glioma NG108-15 cells

The alpha(2)-adrenoceptor antagonist yohimbine is known to interact with the effects of opioid receptor agonists in vivo, and thus could modulate the action of morphine-like analgesics. The focus of the present work was to further study these interactions in a cell culture endowed with opioid and alpha(2)-adrenoceptors in order to know if they could happen at the cellular level. In a first step, incubation with morphine (10microM) or the delta opioid agonist DPDPE (1microM) for 6h was shown to decrease the reduction of (4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium (MTT) by NG108-15 neuroblastomaxglioma hybrid cells in a naloxone-sensitive manner, thus showing that the opioids affect the redox status of the cells in a delta receptor-mediated way. Further experiments with 2-24h incubation periods were subsequently performed with morphine 0.1microM, 10microM and 1mM and several tests to confirm the effects on metabolism (MTT, Alamar Blue tests) to examine the potential toxic consequences (neutral red test, trypan blue exclusion assay, LDH test, caspase 3/7 activity) and to study the potential effect of yohimbine on morphine toxicity. These studies confirmed that incubation with morphine (0.1microM and 10microM) affected to a similar extent the redox status of the cells, an effect that did not translated into significant cell death and was transient since completely disappeared after 24h of incubation. Morphine 1mM was much more toxic than the lower concentrations. Yohimbine effectively prevented the effects of the lower concentrations of morphine when added to the incubation medium at 10microM, a concentration devoid of significant toxicity. It seems that the exposure to pharmacologically relevant concentrations of morphine gives rise to short-term metabolic alterations of NG108-15 cells mediated by delta receptors and also sensitive to alpha(2)-adrenoceptor blockade; therefore, the interactions previously described in vivo between opioid and alpha(2)-adrenoceptor ligands do not necessarily require the presence of functional neuronal networks and they could happen at the cellular level.

Pharmacological characterization of the nociceptin/orphanin FQ receptor non peptide antagonist Compound 24

Compound 24, 1-benzyl-N-{3-[spiroisobenzofuran-1(3H),4′-piperidin-1-yl]propyl} pyrrolidine-2-carboxamide was recently identified as a nociceptin/orphanin FQ (N/OFQ) peptide receptor (NOP) ligand. In this study, the in vitro and in vivo pharmacological profiles of Compound 24 were investigated. In vitro studies were performed measuring receptor and [35S]GTPγS binding and calcium mobilization in cells expressing the recombinant NOP receptor as well as using N/OFQ sensitive tissues. In vivo studies were conducted using the tail withdrawal assay in mice. Compound 24 produced a concentration-dependent displacement of [3H]N/OFQ binding to CHOhNOP cell membranes showing high affinity (pKi 9.62) and selectivity (1000 fold) over classical opioid receptors. Compound 24 antagonized with high potency the following in vitro effects of N/OFQ: stimulation of [35S]GTPγS binding in CHOhNOP cell membranes (pA2 9.98), calcium mobilization in CHOhNOP cells expressing the Gαqi5 chimeric protein (pKB 8.73), inhibition of electrically evoked twitches in the mouse (pA2 8.44) and rat (pKB 8.28) vas deferens, and in the guinea pig ileum (pKB 9.12). In electrically stimulated tissues, Compound 24 up to 1 µM did not modify the effects of classical opioid receptor agonists. Finally in vivo, in the mouse tail withdrawal assay, Compound 24 at 10 mg/kg antagonized the pronociceptive and antinociceptive effects of 1 nmol N/OFQ given supraspinally and spinally, respectively. Under the same experimental conditions Compound 24 did not affect the antinociceptive action of 3 nmol endomorphin-1 injected intrathecally. The present study demonstrated that Compound 24 is a pure, competitive, and highly potent non-peptide NOP receptor selective antagonist.

New therapeutic principles for adverse effects on upper and lower gastrointestinal tract in patients treated with opioid analgesics

Recent large scale surveys document that patients on opioid analgesics suffer adverse effects from increased tone in sphincters of both the upper and lower part of the gastrointestinal tract, decreased secretions into and increased absorption of fluids out of the bowel. These adverse effects often cause patients to discontinue opioid analgesics. Also patients treated with opioids for acute pain after surgery and in the intensive care units suffer gastrointestinal adverse effects. Constipation is the most common adverse effect of opioids. Most patients self-medicate with over-the-counter laxatives but suffer unpredictable responses and bothersome adverse effects of laxatives. Potent prescription laxatives may further adversely impact quality of life of chronic pain patients. Opioid-induced dysfunctions of the upper gastrointestinal tract are often misinterpreted by health care providers, and they are not relieved by laxatives. Two therapeutic developments make specific and effective prophylaxis and treatment possible: (1) Peripherally acting opioid antagonists that do not cross the blood brain barrier (methylnaltrexone and alvimopan), and (2) the opioid antagonist naloxone added to an opioid agonist in prolonged-release oral formulations (tilidin or oxycodone). Orally administered prolonged-release naloxone is almost completely eliminated during the first-pass through the liver and will therefore not reach opioid receptors in the central nervous system. These drugs relieve both upper and lower gastrointestinal adverse effects of opioid agonists, although their effects on constipation have been the focus of most clinical studies. These new pharmacological principles promise improved management of pain with opioids both for acute and chronic pain conditions.

Buprenorphine/Naloxone

Buprenorphine/naloxone (Suboxone) comprises the partial mu-opioid receptor agonist buprenorphine in combination with the opioid antagonist naloxone in a 4 : 1 ratio. When buprenorphine/naloxone is taken sublingually as prescribed, the naloxone exerts no clinically significant effect, leaving the opioid agonist effects of buprenorphine to predominate. However, when buprenorphine/naloxone is parenterally administered in patients physically dependent on full agonist opioids, the opioid antagonism of naloxone causes withdrawal effects, thus reducing the abuse potential of the drug combination. Buprenorphine/naloxone is an effective maintenance therapy for opioid dependence and has generally similar efficacy to methadone, although more data are needed. Less frequent dispensing of buprenorphine/naloxone (e.g. thrice weekly) does not appear to compromise efficacy and can improve patient satisfaction. Buprenorphine/naloxone is more effective than clonidine as a medically-supervised withdrawal therapy. Moreover, buprenorphine/naloxone is a generally well tolerated medically-supervised withdrawal and maintenance treatment. Thus, sublingual buprenorphine/naloxone is a valuable pharmacotherapy for the treatment of opioid dependence.

Activation of δ-Opioid Receptors Reduces Excitatory Input to Putative Gustatory Cells Within the Nucleus of the Solitary Tract

The rostral nucleus of the solitary tract (NST) is the first central relay in the gustatory pathway and plays a key role in processing and modulation of gustatory information. Here, we investigated the effects of opioid receptor agonists and antagonists on synaptic responses of the gustatory parabrachial nuclei (PbN)-projecting neurons in the rostral NST to electrical stimulation of the solitary tract (ST) using whole cell recordings in the hamster brain stem slices. ST-evoked excitatory postsynaptic currents (EPSCs) were significantly reduced by met-enkephalin (MetE) in a concentration-dependent fashion and this effect was eliminated by naltrexone hydrochloride, a nonselective opioid receptor antagonist. Bath application of naltrindole hydrochloride, a selective delta-opioid receptor antagonist, eliminated MetE-induced reduction of EPSCs, whereas CTOP, a selective mu-opioid receptor antagonist had no effect, indicating that delta-opioid receptors are involved in the reduction of ST-evoked EPSCs induced by MetE. SNC80, a selective delta-opioid receptor agonist, mimicked the effect of MetE. The SNC80-induced reduction of ST-evoked EPSCs was eliminated by 7-benzylidenenaltrexone, a selective delta1-opioid receptor antagonist but not by naltriben mesylate, a selective delta2-opioid receptor antagonist, indicating that delta1-opioid receptors mediate the reduction of ST-evoked EPSCs induced by SNC80. Single-cell reverse transcriptase-polymerase chain reaction analysis revealed the presence of delta1-opioid receptor mRNA in cells that responded to SNC80 with a reduction in ST-evoked EPSCs. Moreover, Western blot analysis demonstrated the presence of 40-kDa delta-opioid receptor proteins in the rostral NST tissue. These results suggest that postsynaptic delta1-opioid receptors are involved in opioid-induced reduction of ST-evoked EPSCs of PbN-projecting rostral NST cells.

Role of delta opioid efficacy as a determinant of mu/delta opioid interactions in rhesus monkeys

Delta opioid agonists can selectively enhance the antinociceptive effects of mu opioid agonists without enhancing some other, potentially undesirable mu agonist effects. However, the degree of delta receptor efficacy required to produce this profile of interactions is unknown. To address this issue, the present study examined interactions produced by the mu agonist fentanyl and the intermediate-efficacy delta opioid MSF61 in rhesus monkeys. For comparison, interactions were also examined between fentanyl and the relatively high-efficacy delta agonist SNC243A and the delta antagonist naltrindole, which has negligible efficacy at delta receptors. Two different behavioral procedures were used: (a) a warm-water tail-withdrawal assay of thermal nociception, and (b) an assay of schedule-controlled responding for food reinforcement. Drug interactions within each procedure were evaluated using dose-addition analysis to compare experimental results with expected additivity. Drug interactions across procedures were evaluated using dose–ratio analysis to assess relative potencies to produce antinociception vs. response-rate suppression. As expected, dose-addition analysis found that fentanyl/SNC243A interactions were superadditive in the assay of antinociception but additive in the assay of schedule-controlled responding. Conversely, fentanyl/MSF61 interactions were generally additive in both procedures, and fentanyl/naltrindole interactions were additive or subadditive in both procedures. Dose–ratio analysis found that fentanyl alone produced antinociception and rate suppression with similar potencies. Some fentanyl/SNC243A mixtures produced antinociception with up to 4-fold greater potency than rate-suppression. However, fentanyl/MSF61 and fentanyl/naltrindole mixtures produced antinociception with lower potency than rate suppression. These results suggest that relatively high delta receptor efficacy is required for mu/delta antinociceptive synergy.

Nociceptin produces antinociception after spinal administration in amphibians

Nociceptin, also known as orphanin FQ, is a opioid -like neuropeptide that mediates its effects at the nociceptin receptor, a member of the G protein-coupled receptor superfamily. In mammals, nociceptin produces analgesia after spinal administration, however the role of nociceptin and nociceptin receptors in the modulation of noxious stimuli in non-mammalian species has not been examined. In an amphibian pain model using the acetic acid test with Rana pipiens, nociceptin and nociceptin 1–13 amide produced dose-dependent antinociception (1–100 nmol), blocked by the nociceptin antagonist, [Nphe 1]-nociceptin 1–13 amide (30 nmol), but not the opioid antagonist, naltrexone (100 nmol/g, s.c.). Conversely, the antinociceptive effects of mu, delta, and kappa opioid receptor agonists were not blocked by the nociceptin antagonist. Nociceptin and nociceptin 1–13 amide were the least potent of the opioid agonists tested. These studies demonstrate that spinal nociceptin receptors and not opioid receptors mediate the antinociceptive effect of nociceptin. Considered with previous findings, these behavioral data supports a role for nociceptin inhibition of spinal nociception in amphibians and perhaps all vertebrates.

Opioids as triggers for metabolic depression in the frog, Cyclorana alboguttata

Many species of Australian arid zone frogs survive the dry winter months by burrowing underground and entering a state of metabolic depression known as aestivation. While in aestivation these frogs can survive months to years in the absence of food and water, yet the endogenous mechanisms involved in initiation and maintenance of metabolic depression remain poorly understood. The aim of this study was to investigate the potential role of opioids in initiating a metabolic depression in the aestivating frog, Cyclorana alboguttata. To do this we took a two fold approach. First, the presence of opioid receptors was confirmed using PCR and degenerate primers designed from known opioid receptor sequences. Secondly, we used closed box respirometry to measure the direct effects of opioid agonists on tissue metabolic rate. The delta opioid DADLE was found to decrease oxygen consumption of liver and muscle slices by 20% and 25%, respectively, compared to control slices, whereas the kappa opioid Dynorphin A and the mu opioid Morphiceptin had no effect on tissue metabolic rate. This is the first time that opioids have been shown to directly affect metabolic rate in an aestivating species, indicating that endogenous opioids may play an important role in initiating a metabolic depression. Copyright © 2008 Published by Elsevier Inc.

Differential effects of opioid agonists on G protein expression in CHO cells expressing cloned human opioid receptors

Recent evidence indicates that agonist ligands of G protein coupled receptors (GPCR) can activate different signaling systems. Such “agonist-directed” signaling also occurs with opioid receptors. Previous work from our laboratory showed that chronic morphine, but not DAMGO, up-regulates the expression of Gα12 and that both morphine and DAMGO decreased Gαi3 expression in CHO cells expressing the cloned human mu opioid receptor. In this study, we tested the hypothesis that chronic opioid regulation of G protein expression is agonist-directed. Following a 20 h treatment of CHO cells expressing the cloned human mu (hMOR-CHO), delta (hDOR-CHO) or kappa (hKOR-CHO) opioid receptors with various opioid agonists, we determined the expression level of Gα12 and Gαi3 by Western blots. Among five mu agonists (morphine, etorphine, DADLE, DAMGO, herkinorin) tested with hMOR-CHO cells, only chronic morphine and etorphine up-regulated Gα12 expression. All five mu agonists decreased Gαi3 expression. Among six delta agonists (SNC80, DPDPE, deltorphin-1, morphine, DADLE, etorphine) tested with hDOR-CHO cells, all six agonists down-regulated Gαi3 expression or moderately up-regulated Gα12 expression. Among five kappa agonists, ((−)-ethylketocyclazocine, salvinorin A, U69,593, etorphine, (−)-U50,488) tested with hKOR-CHO cells, only chronic (−)-U50,488 and (−)-EKC up-regulated Gα12 expression. All kappa agonists decreased Gαi3 expression. These data demonstrate that chronic opioid agonist regulation of G protein expression depends not only on the agonist tested, but also on the type of opioid receptor expressed in a common cellular host, providing additional evidence for agonist-directed signaling.

Strategy to Eliminate Pethidine Use in Hospitals

Strategy to Eliminate Pethidine Use in Hospitals

Interactions between Δ9-tetrahydrocannabinol and μ opioid receptor agonists in rhesus monkeys: discrimination and antinociception

Opioid receptor agonists can enhance some effects of cannabinoid receptor agonists, and cannabinoid receptor agonists can enhance some effects of opioid receptor agonists; however, the generality of these interactions is not established. This study examined interactions between the discriminative stimulus and antinociceptive effects of mu opioid receptor agonists and Delta(9)-tetrahydrocannabinol (THC) in rhesus monkeys. Neither heroin nor morphine (intravenous (i.v.) or subcutaneous (s.c.)) altered the discriminative stimulus effects of THC in monkeys (n = 5) discriminating 0.1 mg/kg THC i.v. In contrast, THC (s.c.) markedly attenuated the discriminative stimulus effect of morphine and heroin in nondependent monkeys (n = 4) discriminating 1.78 mg/kg morphine s.c. Doses of THC that attenuated the discriminative stimulus effects of morphine in nondependent monkeys failed to modify the discriminative stimulus effects of morphine in morphine-dependent (5.6 mg/kg/12 h) monkeys (n = 4) discriminating 0.0178 mg/kg naltrexone s.c. THC also failed to modify the discriminative stimulus effects of naltrexone in morphine-dependent monkeys or the effects of midazolam in monkeys (n = 4) discriminating 0.32 mg/kg midazolam s.c. Doses of THC (s.c.) that attenuated the discriminative stimulus effects of morphine in nondependent monkeys enhanced the antinociceptive effects of morphine (s.c.) in nondependent monkeys. While mu receptor agonists did not alter the discriminative stimulus effects of THC, THC altered the effects of mu receptor agonists in a context-dependent manner. That the same doses of THC enhance, attenuate, or do not affect morphine, depending on the condition, suggests that attenuation of morphine by THC can result from perceptual masking rather than common pharmacodynamic mechanisms or pharmacokinetic interactions.

Activation of kappa opioid receptors decreases synaptic transmission and inhibits long-term potentiation in the basolateral amygdala of the mouse

Background The amygdala plays an important role in the processing of chronic pain and pain memory formation. Particularly, it is involved in the emotional and affective components of the pain circuitry. The role of kappa opioid receptors in these pain conditions is only partly known. The present study investigates the effect of kappa receptor activation on synaptic transmission and synaptic plasticity in the amygdala. Methods Electrophysiological in vitro experiments were carried out in brain slices of male C57BL/6JOlaHsd mice. The effect of the kappa opioid receptor agonist U50,488H (5 μM) and the selective kappa opioid receptor antagonist nor-BNI (3 μM) on field potential (FP) amplitude and the induction of long-term potentiation (LTP) in the basolateral amygdala (BLA) was examined. Results High frequency stimulation (HFS) of afferents in the lateral amygdala with two trains of 100 pulses at 50 Hz increased the FP amplitudes to 119 ± 2% (mean ± SEM; n = 6) in the BLA. U50,488H decreased synaptic transmission (baseline: 100 ± 0.5%; U50,488H: 86.3 ± 2.4%; n = 6) and blocked the induction of LTP (U50,488H: 100 ± 4.1%; HFS: 102.6 ± 7%; n = 6). The effect on synaptic transmission and on LTP was completely reversed or prevented by application of nor-BNI, which itself had no effect on synaptic transmission or the induction of LTP. Conclusion Kappa opioid receptor activation decreases synaptic transmission and inhibits the induction of LTP in the BLA of the mouse. These findings may be associated with the effects of kappa opioid agonists in chronic pain and pain memory formation.