Development Of Opiate Tolerance Research Articles

Anti-opioid Effects of RFRP-3 on Magnocellular Neuron Activity in Morphine-naïve and Morphine-treated Female Rats.

Neuropeptide FF receptors (NPFFR1 and NPFFR2) have been proposed to possess anti-opioid properties, and be involved in the development of opiate tolerance and dependence. However, there is no evidence to date supporting such opioid effects at the cellular level in vivo. Using in vivo electrophysiological recordings from vasopressin and oxytocin neurons in the supraoptic nucleus, we aimed to determine the effects of NPFFRs on opiate inhibition, tolerance, and dependence at a cellular level. Both vasopressin and oxytocin neurons are acutely inhibited by opioids and develop opiate tolerance. Oxytocin neurons also develop cellular opiate dependence and undergo withdrawal hyperexcitation upon cessation of opiate administration. Here, the classical μ-opioid receptor agonist, morphine robustly inhibited the spontaneous firing rate of vasopressin and oxytocin neurons, and this inhibition was attenuated by pretreatment with the NPFFR1 agonist, RFamide-related peptide-3. In rats infused with morphine for 6 d, vasopressin neurons were unresponsive to morphine, indicating the development of cellular tolerance, but pretreatment with the NPFFR antagonist, GJ14, restored acute morphine inhibition. In morphine-infused rats, RFamide related peptide-3 did not induce withdrawal excitation in oxytocin neurons and GJ14 did not reverse naloxone-precipitated withdrawal excitation. This is the first evidence of anti-opioid effects of the NPFFR system at a cellular level in vivo. Our results suggest that the anti-opioid properties of the NPFFR system reduce morphine sensitivity during tolerance but that it is not involved in dependence.

NPYFa, A Chimeric Peptide of Met-Enkephalin, and NPFF Induces Tolerance-Free Analgesia.

Methionine-enkephalin-Arg-Phe is an endogenous amphiactive analgesic peptide. Neuropeptide FF, on the other hand, is reported for its role in opioid modulation and tolerance development. Based on these reports, in the present study we designed a chimeric peptide NPYFa (YGGFMKKKPQRFamide), having the Met-enkephalin (opioid) and PQRFamide sequence of neuropeptide FF, which can then target both the opioid and neuropeptide FF receptors. We hypothesized that the chimeric peptide so designed would have both analgesic properties and further aid in understanding of the role of neuropeptide FF in the development of opiate tolerance. Our studies indicated that NPYFa induced an early onset, potent, dose-dependent and prolonged antinociception. Additionally, antagonists (MOR, KOR, and DOR) pretreatment studies determined a KOR-mediated antinociception activity of the ligand. Further, in vitro binding studies using the Eu-GTP-γS binding assay on cell lines expressing opioid and NPFF receptors showed binding to both the opioid and neuropeptide FF receptors suggesting a multiple receptor binding character of NPYFa. Moreover, chronic (6 days) treatment with NPYFa exhibited an absence of tolerance development subsequent to its analgesia. The current study proposes NPYFa as a potent, long-acting antinociceptor lacking tolerance development as well as a probe to study opioid analgesia and the associated complex mechanisms of tolerance development.

Editorial: Monitoring endogenous GPCRs: lessons for drug design.

Editorial: Monitoring endogenous GPCRs: lessons for drug design.

P.6.d.012 Pregabalin and topiramate regulate behavioural and brain gene transcription changes induced by cannabinoid withdrawal

Opiate addiction is a chronic medical disorder characterized by drug tolerance and dependence, behavioral sensitization, vulnerability to compulsive relapse, and high mortality. In laboratory animals, the potential effect of opiate drugs to induce cell death by apoptosis is a controversial topic. This postmortem human brain study examined the status of the extrinsic and intrinsic apoptotic pathways in the prefrontal cortex of a large group of well-characterized heroin or methadone abusers. In these subjects (n=36), the immunocontent of apoptosis-1 protein (Fas) death receptor did not differ from that in age-, gender-, and postmortem delay-matched controls. In contrast, Fas-associated protein with death domain (FADD), the mediator of the death signal, was significantly decreased in the same brain samples (all addicts: 30%, n=36; short-term abuse (ST): 31%, n=15; long-term abuse (LT): 29%, n=21). The initiator caspase-8 was not altered, but FLIPL (Fas-associated protein with death domain-like interleukin-1β-converting enzyme-inhibitory protein), a dominant inhibitor of caspase-8, was increased in LT addicts (19%). In the intrinsic pathway, the pro-apoptotic mitochondrial proteins Bax (Bcl-2-associated X protein) and AIF (apoptosis-inducing factor) remained unchanged, but cytochrome c was decreased (all addicts: 25%; ST: 31%; LT: 20%) and anti-apoptotic B-cell leukemia 2 (Bcl-2) increased in LT addicts (24%). The content of executioner caspase-3 and the pattern of cleavage of the nuclear enzyme poly-(ADP-ribose)-polymerase-1 (PARP-1) were similar in opiate addicts and control subjects. Taken together, the data revealed that the extrinsic and intrinsic canonical apoptotic pathways are not abnormally activated in the prefrontal cortex of opiate abusers. Instead, the chronic modulation of some of their components (downregulation of FADD and cytochrome c; upregulation of FLIPL and Bcl-2) suggests the induction of non-apoptotic actions by opiate drugs related to phenomena of synaptic plasticity in the brain. These neurochemical adaptations could play a major role in the development of opiate tolerance, sensitization and relapse in human addicts.

Role of the delta -opioid receptor in the regulation of mu -opioid receptor function during morphine tolerance

Morphine tolerance involves numerous and complex mechanisms. The heterodimerization of mu and delta opioid receptors put forward recently is one of the important mechanisms which cause the development of opiate tolerance. Once transported to the membrane of neural cells, delta opioid receptors (DOR) combine with mu opioid receptors (MOR) to form MOR-DOR heterodimers,leading to the formation of new signaling pathway. This novel mechanism plays the critical role of DOR in the development of morphine tolerance. This review summarizes the regulation of DOR on MOR function during morphine tolerance in light of the recent findings about the regulation of DOR membrane transport and the new complex: MOR-DOR heterodimer. Key words: Morphine tolerance; MOR-DOR heterodimerization; MOR gene knockout; β-arrestin; Signaling regulation

Regulation of the extrinsic and intrinsic apoptotic pathways in the prefrontal cortex of short- and long-term human opiate abusers

Opiate addiction is a chronic medical disorder characterized by drug tolerance and dependence, behavioral sensitization, vulnerability to compulsive relapse, and high mortality. In laboratory animals, the potential effect of opiate drugs to induce cell death by apoptosis is a controversial topic. This postmortem human brain study examined the status of the extrinsic and intrinsic apoptotic pathways in the prefrontal cortex of a large group of well-characterized heroin or methadone abusers. In these subjects ( n=36), the immunocontent of apoptosis-1 protein (Fas) death receptor did not differ from that in age-, gender-, and postmortem delay-matched controls. In contrast, Fas-associated protein with death domain (FADD), the mediator of the death signal, was significantly decreased in the same brain samples (all addicts: 30%, n=36; short-term abuse (ST): 31%, n=15; long-term abuse (LT): 29%, n=21). The initiator caspase-8 was not altered, but FLIP L (Fas-associated protein with death domain-like interleukin-1β-converting enzyme-inhibitory protein), a dominant inhibitor of caspase-8, was increased in LT addicts (19%). In the intrinsic pathway, the pro-apoptotic mitochondrial proteins Bax (Bcl-2-associated X protein) and AIF (apoptosis-inducing factor) remained unchanged, but cytochrome c was decreased (all addicts: 25%; ST: 31%; LT: 20%) and anti-apoptotic B-cell leukemia 2 (Bcl-2) increased in LT addicts (24%). The content of executioner caspase-3 and the pattern of cleavage of the nuclear enzyme poly-(ADP-ribose)-polymerase-1 (PARP-1) were similar in opiate addicts and control subjects. Taken together, the data revealed that the extrinsic and intrinsic canonical apoptotic pathways are not abnormally activated in the prefrontal cortex of opiate abusers. Instead, the chronic modulation of some of their components (downregulation of FADD and cytochrome c; upregulation of FLIP L and Bcl-2) suggests the induction of non-apoptotic actions by opiate drugs related to phenomena of synaptic plasticity in the brain. These neurochemical adaptations could play a major role in the development of opiate tolerance, sensitization and relapse in human addicts.

When it comes to opiates, just say NO

Repeated use of opiate analgesic drugs such as morphine for the relief of chronic pain may result in the development of opiate tolerance and dependence, leading to a narrowing of the drug's therapeutic index and increased side effects. Previous preclinical work has shown that interruption of a signaling cascade involving the N-methyl-D-aspartate receptor and NO prevents morphine tolerance. In this issue of the JCI, Muscoli and colleagues extend our understanding of the role of NO in tolerance by demonstrating that, in mice, tolerance to chronic morphine administration is associated with NO conversion to peroxynitrite, which accumulates and nitrates tyrosine moieties within various proteins in the spinal cord (see the related article beginning on page 3530). This and other data suggest that peroxynitrite plays a role in opiate tolerance and that regulation of peroxynitrite may be utilized for the management of opiate-induced tolerance.

Chronic morphine treatment alters expression of N-methyl-D-aspartate receptor subunits in the extended amygdala

The nucleus accumbens (NAcc) and central amygdala (CeA) are parts of the extended amygdala, a complex that plays a key role in drug abuse and dependence. Our previous studies showed that opiates and ethanol alter glutamatergic transmission in these regions. N-methyl-D-aspartate (NMDA) receptors are key components of glutamatergic transmission likely involved in the development of opiate tolerance and dependence. In this study we examined the effects of chronic morphine administration on gene and protein expression of three major NMDA receptors subunits (NR1, NR2A, and NR2B) in NAcc and CeA. Real-time PCR showed no differences in mRNA levels of any of the subunits in the whole NAcc between naïve and morphine-dependent rats. However, at the protein level, immunoblotting revealed that chronic morphine significantly increased levels of NR1 and NR2B subunits. In contrast to the case for NAcc, in CeA we found an increased mRNA level for the NR1 subunit only but unchanged protein levels of all three subunits in morphine-dependent rats. The altered expressions of NMDA receptor subunits, especially in NAcc, of morphine-dependent rats may represent a neuroadaptation to chronic morphine and suggest a mechanism for the changes of glutamatergic transmission found in the extended amygdala in dependent rats. In addition, our results indicate a region-specific response of NMDA receptor subunits to chronic morphine administration at the gene and protein levels.

Modeling the onset of drug dependence: A consideration of the requirement for protein synthesis

It has been proposed, with some supporting evidence, that development of opiate tolerance and dependence requires protein synthesis. However, a quantitative, biologically based model within which to analyse and support the data has been lacking. Utilizing such a framework or model, we recently compared the time course of onset of opiate dependence in laboratory animals, with the mathematical time course of general changes in protein levels. Not only did the time course of onset of dependence parallel the time course of increasing levels of a protein, but also the half-life of the putative protein required by the model was very similar to those of many brain proteins. In this study, we have more extensively tested the model by producing and examining a much more detailed and surprisingly complex time course of the onset of dependence. Applying the protein synthesis time course model to the data suggested the presence of two distinct components of dependence, an early transient component and a later long-lasting component. These components appear to correspond to acute and chronic dependence, respectively. The protein synthesis hypothesis more readily applies to the chronic dependence portion. Because consideration of the model can generate components that correspond to accepted and well-known components of dependence, both the utility of the model as well as the hypothesis that opiate dependence at least partially requires protein synthesis are supported. It is also possible that individual components of the withdrawal syndrome have individual and unique rate limiting mechanisms. In any case, time course analysis may be helpful in revealing underlying mechanisms of change.

Interleukin-1 antagonizes morphine analgesia and underlies morphine tolerance

Pain sensitivity reflects a balance between pain facilitatory and inhibitory systems. To characterize the relationships between these systems we examined the interactions between the analgesic effects of morphine and the anti-analgesic effects of the pro-inflammatory cytokine interleukin-1 (IL-1). We report that administration of a neutral dose of IL-1β abolished morphine analgesia in mice, whereas acute or chronic blockade of IL-1 signaling by various IL-1 blockers (IL-1 receptor antagonist (IL-1ra), α-melanocyte-stimulating hormone, or IL-1 tri-peptide antagonist) significantly prolonged and potentiated morphine analgesia. Morphine-induced analgesia was also extended in strains of mice genetically impaired in IL-1 signaling (mice with transgenic over-expression of IL-1 receptor antagonist, deletion of the IL-1 receptor type I, or deletion of the IL-1 receptor accessory protein). The finding that IL-1 produces a marked anti-analgesic effect, suggests that it may also be involved in the development of opiate tolerance. Indeed, genetic or pharmacological blockade of IL-1 signaling prevented the development of tolerance following repeated morphine administration. Moreover, acute administration of IL-1ra in wild type mice, either immediately following the cessation of acute morphine analgesia, or following the development of chronic morphine tolerance, re-instated the analgesia, suggesting that blockade of the IL-1 system unmasks the analgesic effect of morphine. These findings suggest that morphine produces an IL-1-mediated homeostatic response, which serves to limit the duration and extent of morphine analgesia and which underlies the development of tolerance.

Metabotropic glutamate receptors and opiate analgesia: Therapeutic implications

Morphine acts at μ-opioid receptors within the brain and spinal cord to induce analgesia. However, tolerance and dependence are potentially undesirable side effects encountered with repeated opiate administration. Opiate withdrawal, the physical correlate of dependence, is involved in the negative reinforcement of opiate addiction. Recently, blockers of ionotropic subtypes of glutamate receptors have been suggested to have therapeutical potential for opiate withdrawal. Fundytus and Coderre have also shown that antagonism of metabotropic glutamate receptors (mGluRs) and δ-opioid receptors can separately alleviate the behavioral symptoms of withdrawal. They propose that mGluRs and δ-opioid receptors share intermediates and products of the same second messenger pathways as μ-opioid receptors, thereby enhancing the desensitization of this receptor. Thus, mGluRs appear to be involved in the development of opiate tolerance and dependence and may provide a key target for adjunct therapy with opiate analgesia.

Influence of antineoplastic drugs on morphine analgesia and on morphine tolerance

The possible influence of cisplatin, methotrexate, adriamycin and vincristine on thermal pain threshold, morphine analgesia and development of morphine tolerance was investigated in mice. In the hot-plate test, the nociceptive threshold was not affected by acute or repeated administration of any of the antineoplastic drugs used. The analgesic activity of morphine was significantly reduced by pretreatment with cisplatin, intraperitoneally (i.p.) injected at the dose of 2 mg/kg. In contrast, methotrexate, subcutaneously (s.c.) injected at the dose of 1 and 5 mg/kg, adriamycin (1 and 3 mg/kg s.c.), vincristine (0.25 and 0.5 mg/kg i.p.) and a lower dose of cisplatin (1 mg/kg i.p.) had no effect. The development of tolerance to morphine analgesia was delayed by adriamycin but was not influenced by the other antineoplastic drugs used. These data show that, of the four antineoplastic agents used in this study, cisplatin may interfere in the mechanism of action of morphine, and that adriamycin may delay the development of opiate tolerance.

Effects of chronic morphine administration on mu opioid receptor- stimulated [35S]GTPgammaS autoradiography in rat brain

Chronic opiate administration results in the development of tolerance and dependence, but the regulation of mu opioid receptor function during this process is not clearly understood. To localize changes in mu opioid receptor-coupled G-protein activity in various brain regions after chronic morphine treatment, the present study examined mu opioid agonist-stimulated [35S]GTPgammaS binding to brain sections by in vitro autoradiography. Rats were treated for 12 d with increasing doses (10-320mg . kg-1 . d-1) of morphine. Control rats were injected with either saline or a single acute injection of morphine (20 mg/kg). mu opioid-stimulated [35S]GTPgammaS binding was measured by autoradiography of brain sections in the presence and absence of the mu opioid-selective agonist DAMGO. In rats injected with a single acute dose of morphine, no significant changes were detected in basal or agonist-stimulated [35S]GTPgammaS binding in any region. In sections from chronic morphine-treated rats, however, DAMGO-stimulated [35S]GTPgammaS binding was reduced significantly compared with control rats in the following brain-stem nuclei: dorsal raphe nucleus, locus coeruleus, lateral and medial parabrachial nuclei, and commissural nucleus tractus solitarius. No significant changes were observed in several other brain regions, including the nucleus accumbens, amygdala, thalamus, and substantia nigra. These data indicate that chronic morphine administration results in reductions in mu opioid activation of G-proteins in specific brainstem nuclei involved in physiological homeostasis and autonomic function, which may have implications in the development of opiate tolerance and physical dependence.

The development of morphine tolerance and dependence is associated with translocation of protein kinase C

The development of tolerance to the analgesic effects of morphine as well as morphine dependence were greatly reduced by co-administration with morphine of GM1 ganglioside, a substance reported to block the translocation of protein kinase C (PKC) from cytosol to membrane of neurons. Rats made tolerant to intrathecal administration of morphine showed increased membrane-bound PKC in the superficial layers (laminae I and II) of the spinal cord dorsal horn but not in deeper layers. This increase was prevented by co-administration with morphine of GM1 ganglioside. These results indicate that the translocation and activation of PKC may be a critical step in the development of opiate tolerance and dependence. Modulation of PKC translocation and activation may prove useful for the management of pain and opiate addiction.

The CCK-B receptor antagonist Cl 988 reverses tolerance to morphine in rats.

The ability of the selective cholecystokinin-B (CCK-B) receptor antagonist Cl 988 to reverse tolerance to morphine's antinociceptive effect was investigated with the hot-plate test in Sprague-Dawley rats. Tolerance was induced by subcutaneous (s.c.) injection of 10 mg kg-1 morphine twice daily for four days. On the fifth day rats were administered CI 988 (10 mg kg-1) or saline plus 5 mg kg-1 morphine s.c. Significant antinociception was observed in the group that received the CCK-B antagonist plus morphine, whereas the saline plus morphine group exhibited total tolerance. These results suggest that upregulation of the endogenous CCK system during repeated morphine administration may have an important role in the development of opiate tolerance.

Modulation by chronic morphine administration of single-stranded cAMP response element (ssCRE) binding proteins in the mouse cerebellum

The development of opiate tolerance and dependence are thought to be associated with gene expression. Our previous studies have shown that the binding activity of nuclear factors to a single-stranded oligo-DNA containing cAMP response element (ssCRE) is altered by long term treatment with morphine in cultured neuronal cells. In the present experiments, the effects of acute and chronic treatments with morphine on the binding of nuclear proteins to single- and double-stranded oligo-DNAs of the cAMP response element were studied in the mouse brains by using gel shift assay. The activity of single-stranded CRE binding proteins (ssCRE-BP) was decreased by chronic morphine treatment to about 40% of control in the cerebellum. The effect of chronic morphine treatment on the binding activity persisted for at least 2 weeks after morphine withdrawal. The activity of double-stranded CRE binding proteins was also detected in the cerebellum, but it was insensitive to the morphine treatment. The activity of ssCRE-BP was also decreased by acute morphine treatment in 5 h, but it returned to control level in 24 h. These data suggest that the change of ssCRE-BP can be involved in the development of tolerance and dependence.

Opioid antagonists up-regulate prodynorphin gene expression in rat brain

Neurochemical alterations in opioid receptor function and post-transductional events have been demonstrated to occur during the development of opiate tolerance (1). In addition, it has been recently shown that chronic opiate agonists, acting on μ, κ and δ receptors, induce a down-regulation of the biosynthesis of the endogenous opioid system in rat brain (2,3). In order to better understand the mechanisms underlying this phenomenon, the present study was carried out to investigate the effect of chronic intracerebroventricular (icv) exposure to selective opioid antagonists: the preferential μ naltrexone (NTX), the selective κ norbinaltorphimine (nor-BNI) and the selective μ naltrindole (NTI), on opioid gene expression in rat brain

Inhibition of opiate tolerance by non-competitive N- d-aspartate receptor antagonists

Our laboratory and others have previously reported that the non-competitive N-methyl- d-aspartate (NMDA) receptor antagonist, MK-801, interferes with the development of tolerance to the analgesic effects of morphine. The present studies were performed in order to further characterize the role of NMDA receptors in opiate tolerance. The results demonstrate that opiate tolerance is inhibited rapidly, and at low doses, by four different non-competitive NMDA receptor antagonists (MK-801, ketamine, dextrorphan and phencyclidine), suggesting that this inhibition results from blockade of NMDA receptors rather than from the ‘side-effect’ of a particular drug. The NMDA antagonists were found to inhibit the development but not the expression of opiate tolerance; i.e. they were able to prevent but not reverse tolerance. Finally, the results suggest that NMDA receptor antagonists do not interfere with associative tolerance; instead it appears that these drugs may specifically inhibit non-associative tolerance. It thus appears that NMDA receptors may have a fundamental role in the development of opiate tolerance, and that non-competitive NMDA receptor antagonists may be effective adjuncts to opiates in the treatment of chronic pain.

Signal Transduction of Opiate Receptors in Spinal Cord Cells

AbstractThe spinal cord plays an important role in opiate-induced analgesia and in the development of opiate tolerance. We have shown that the majority of the opiate receptors in the spinal cord (> 70%) are of the K type. We have also demonstrated that cocultures consisting of neurons of spinal cord and dorsal root ganglia express primarily the K type of opiate receptors. Using these cocultures, we found that activation of k-opiate receptors leads to inhibition of the basal-and forskolin-stimulated adenylate cyclase, as well as to the inhibition of the activity of voltage-dependent Ca2+ channels. In addition, activation of the k-opiate receptor led to stimulation of the phosphatidylinositol turnover in these cells. All these opiate-induced activities could be blocked by opiate antagonists, as well as by pretreatment of the cells with pertussis toxin, demonstrating the involvement of authentic opiate receptors and pertussis toxin-sensitive GTP-binding protein(s) in the transduction pathways. We found that ...

Cholecystokinin Antianalgesia: Safety Cues Abolish Morphine Analgesia

Environmental stimuli that signal the occurrence of aversive or dangerous events activate endogenous opiate analgesia systems. Signals for safety (the nonoccurrence of aversive events) produce the opposite and inhibit environmentally produced analgesia. Stimuli that signal safety are now shown to abolish the analgesic effect of morphine, even when morphine is applied directly to spinal cord. Further, this antiopiate effect occurs because the environmental stimulus leads to release of the neuropeptide cholecystokinin in the spinal cord. This process may contribute to the regulation of pain and the development of opiate tolerance.