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Marwari S, Kowalski C, Martemyanov KA. Exploring pharmacological inhibition of G q/11 as an analgesic strategy. Br J Pharmacol 2022; 179:5196-5208. [PMID: 35900909 PMCID: PMC9633401 DOI: 10.1111/bph.15935] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2022] [Revised: 07/06/2022] [Accepted: 07/14/2022] [Indexed: 01/05/2023] Open
Abstract
BACKGROUND AND PURPOSE Misuse of opioids has greatly affected our society. One potential solution is to develop analgesics that act at targets other than opioid receptors. These can be used either as stand-alone therapeutics or to improve the safety profile of opioid drugs. Previous research showed that activation of Gq/11 proteins by G-protein coupled receptors has pro-nociceptive properties, suggesting that blockade of Gq/11 signalling could be beneficial for pain control. The aim of this study was to test this hypothesis pharmacologically by using potent and selective Gq/11 inhibitor YM-254890. EXPERIMENTAL APPROACH We used a series of behavioural assays to evaluate the acute responses of mice to painful thermal stimulation while administering YM-254890 alone and in combination with morphine. We then used electrophysiological recordings to evaluate the effects of YM-254890 on the excitability of dorsal root ganglion (DRG) nociceptor neurons. KEY RESULTS We found that systemic administration of YM-254890 produced anti-nociceptive effects and also augmented morphine analgesia in both hotplate and tail flick paradigms. However, it also caused substantial inhibition of locomotion, which may limit its therapeutic utility. To circumvent these issues, we explored the local administration of YM-254890. Intrathecal injections of YM-254890 produced lasting analgesia in a tail flick test and greatly augmented the anti-nociceptive effects of morphine without any significant effects on locomotor behaviour. Electrophysiological studies showed that YM-254890 reduced the excitability of DRG nociceptors and augmented their opioid-induced inhibition. CONCLUSION AND IMPLICATIONS These findings indicate that pharmacological inhibition of Gq/11 could be explored as an analgesic strategy.
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Affiliation(s)
- Subhi Marwari
- Department of NeuroscienceThe Scripps Research InstituteJupiterFloridaUSA
| | - Cody Kowalski
- Department of NeuroscienceThe Scripps Research InstituteJupiterFloridaUSA
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GRKs as Key Modulators of Opioid Receptor Function. Cells 2020; 9:cells9112400. [PMID: 33147802 PMCID: PMC7692057 DOI: 10.3390/cells9112400] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2020] [Revised: 10/21/2020] [Accepted: 10/28/2020] [Indexed: 12/21/2022] Open
Abstract
Understanding the link between agonist-induced phosphorylation of the mu-opioid receptor (MOR) and the associated physiological effects is critical for the development of novel analgesic drugs and is particularly important for understanding the mechanisms responsible for opioid-induced tolerance and addiction. The family of G protein receptor kinases (GRKs) play a pivotal role in such processes, mediating phosphorylation of residues at the C-tail of opioid receptors. Numerous strategies, such as phosphosite specific antibodies and mass spectrometry have allowed the detection of phosphorylated residues and the use of mutant knock-in mice have shed light on the role of GRK regulation in opioid receptor physiology. Here we review our current understanding on the role of GRKs in the actions of opioid receptors, with a particular focus on the MOR, the target of most commonly used opioid analgesics such as morphine or fentanyl.
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Abdolrazaghnejad A, Banaie M, Tavakoli N, Safdari M, Rajabpour-Sanati A. Pain Management in the Emergency Department: a Review Article on Options and Methods. ADVANCED JOURNAL OF EMERGENCY MEDICINE 2018; 2:e45. [PMID: 31172108 PMCID: PMC6548151 DOI: 10.22114/ajem.v0i0.93] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
CONTEXT The aim of this review is to recognizing different methods of analgesia for emergency medicine physicians (EMPs) allows them to have various pain relief methods to reduce pain and to be able to use it according to the patient's condition and to improve the quality of their services. EVIDENCE ACQUISITION In this review article, the search engines and scientific databases of Google Scholar, Science Direct, PubMed, Medline, Scopus, and Cochrane for emergency pain management methods were reviewed. Among the findings, high quality articles were eventually selected from 2000 to 2018, and after reviewing them, we have conducted a comprehensive comparison of the usual methods of pain control in the emergency department (ED). RESULTS For better understanding, the results are reported in to separate subheadings including "Parenteral agents" and "Regional blocks". Non-opioids analgesics such as nonsteroidal anti-inflammatory drugs (NSAIDs) and acetaminophen are commonly used in the treatment of acute pain. However, the relief of acute moderate to severe pain usually requires opioid agents. Considering the side effects of systemic drugs and the restrictions on the use of analgesics, especially opioids, regional blocks of pain as part of a multimodal analgesic strategy can be helpful. CONCLUSION This study was designed to investigate and identify the disadvantages and advantages of using each drug to be able to make the right choices in different clinical situations for patients while paying attention to the limitations of the use of these analgesic drugs.
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Affiliation(s)
- Ali Abdolrazaghnejad
- Department of Emergency Medicine, Sina Hospital, Tehran University of Medical Sciences, Tehran, Iran
| | - Mohsen Banaie
- Department of Emergency Medicine, Sina Hospital, Tehran University of Medical Sciences, Tehran, Iran
| | - Nader Tavakoli
- Trauma and Injury research center, Iran university of medical sciences, Tehran, Iran
| | - Mohammad Safdari
- Department of Neurosurgery, Khatam-Al-Anbia Hospital, Zahedan University of Medical Sciences, Zahedan, Iran
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Jacob JC, Sakakibara K, Mischel RA, Henderson G, Dewey WL, Akbarali HI. Ethanol Reversal of Oxycodone Tolerance in Dorsal Root Ganglia Neurons. Mol Pharmacol 2018; 93:417-426. [PMID: 29467238 DOI: 10.1124/mol.117.110775] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2017] [Accepted: 02/08/2018] [Indexed: 01/23/2023] Open
Abstract
Oxycodone is a semisynthetic opioid compound that is widely prescribed, used, and abused today, and has a well-established role in shaping the current opioid epidemic. Previously, we have shown that tolerance develops to the antinociceptive and respiratory depressive effects of oxycodone in mice, and that a moderate dose of acute ethanol or a protein kinase C (PKC) inhibitor reversed that tolerance. To investigate further if tolerance was occurring through neuronal mechanisms, our aims for this study were to assess the effects of acute and prolonged oxycodone in isolated dorsal root ganglia (DRG) neurons and to determine if this tolerance was reversed by either ethanol or a PKC inhibitor. We found that an acute exposure to 3 μM oxycodone reduced neuronal excitability, as measured by increased threshold potentials and reduced action potential amplitude, without eliciting measurable changes in resting membrane potential. Exposure to 10 μM oxycodone for 18-24 hours prevented oxycodone's effect on neuronal excitability, indicative of tolerance development. The development of opioid tolerance was mitigated in DRG neurons from β-arrestin 2 knockout mice. Oxycodone tolerance was reversed in isolated DRG neurons by the acute application of either ethanol (20 mM) or the PKC inhibitor, bisindolylmaleimide XI hydrochloride (Bis XI), when a challenge of 3 µM oxycodone significantly reduced neuronal excitability following prolonged exposure. Through these studies, we concluded that oxycodone acutely reduced neuronal excitability, tolerance developed to this effect, and reversal of that tolerance occurred at the level of a single neuron, suggesting that reversal of oxycodone tolerance by either ethanol or Bis XI involves cellular mechanisms.
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Affiliation(s)
- Joanna C Jacob
- Department of Pharmacology and Toxicology, Virginia Commonwealth University, Richmond, Virginia (J.C.J., K.S., R.A.M., W.L.D., H.I.A.); and School of Physiology, Pharmacology and Neuroscience, University of Bristol, Bristol, United Kingdom (G.H.)
| | - Kensuke Sakakibara
- Department of Pharmacology and Toxicology, Virginia Commonwealth University, Richmond, Virginia (J.C.J., K.S., R.A.M., W.L.D., H.I.A.); and School of Physiology, Pharmacology and Neuroscience, University of Bristol, Bristol, United Kingdom (G.H.)
| | - Ryan A Mischel
- Department of Pharmacology and Toxicology, Virginia Commonwealth University, Richmond, Virginia (J.C.J., K.S., R.A.M., W.L.D., H.I.A.); and School of Physiology, Pharmacology and Neuroscience, University of Bristol, Bristol, United Kingdom (G.H.)
| | - Graeme Henderson
- Department of Pharmacology and Toxicology, Virginia Commonwealth University, Richmond, Virginia (J.C.J., K.S., R.A.M., W.L.D., H.I.A.); and School of Physiology, Pharmacology and Neuroscience, University of Bristol, Bristol, United Kingdom (G.H.)
| | - William L Dewey
- Department of Pharmacology and Toxicology, Virginia Commonwealth University, Richmond, Virginia (J.C.J., K.S., R.A.M., W.L.D., H.I.A.); and School of Physiology, Pharmacology and Neuroscience, University of Bristol, Bristol, United Kingdom (G.H.)
| | - Hamid I Akbarali
- Department of Pharmacology and Toxicology, Virginia Commonwealth University, Richmond, Virginia (J.C.J., K.S., R.A.M., W.L.D., H.I.A.); and School of Physiology, Pharmacology and Neuroscience, University of Bristol, Bristol, United Kingdom (G.H.)
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Posa L, Accarie A, Noble F, Marie N. Methadone Reverses Analgesic Tolerance Induced by Morphine Pretreatment. Int J Neuropsychopharmacol 2016; 19:pyv108. [PMID: 26390873 PMCID: PMC4966270 DOI: 10.1093/ijnp/pyv108] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/16/2015] [Accepted: 09/11/2015] [Indexed: 11/14/2022] Open
Abstract
BACKGROUND Opiates such as morphine are the most powerful analgesics, but their protracted use is restrained by the development of tolerance to analgesic effects. Recent works suggest that tolerance to morphine might be due to its inability to promote mu opioid receptor endocytosis, and the co-injection of morphine with a mu opioid receptor internalizing agonist like [D-Ala(2),N-Me-Phe(4),Gly-ol(5)]enkephalin reduces tolerance to morphine. So far, no studies have been conducted to evaluate the ability of methadone to reduce morphine tolerance in morphine-pretreated animals, a treatment sequence that could be encountered in opiate rotation protocol. We investigated the ability of methadone (a mu opioid receptor internalizing agonist used in therapy) to reverse morphine tolerance and the associated cellular mechanisms in the periaqueductal gray matter, a region involved in pain control. METHODS We measured analgesic response following a challenge dose of morphine in the hot plate test and investigated regulation of mu opioid receptor (coupling and endocytosis) and some cellular mechanisms involved in tolerance such as adenylate cyclase superactivation and changes in N-methyl-d-aspartate receptor subunits expression and phosphorylation state. RESULTS A chronic treatment with morphine promoted tolerance to its analgesic effects and was associated with a lack of mu opioid receptor endocytosis, adenylate cyclase overshoot, NR2A and NR2B downregulation, and phosphorylation of NR1. We reported that a methadone treatment in morphine-treated mice reversed morphine tolerance to analgesia by promoting mu opioid receptor endocytosis and blocking cellular mechanisms of tolerance. CONCLUSIONS Our data might lead to rational strategies to tackle opiate tolerance in the frame of opiate rotation.
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Affiliation(s)
- Luca Posa
- Centre National de la Recherche Scientifique, Unité Mixte de Recherche, Paris, France; Institut national de la santé et de la recherche médicale, Paris, France; Université Paris Descartes, Laboratoire de Neuropsychopharmacologie des Addictions, Paris, France
| | - Alison Accarie
- Centre National de la Recherche Scientifique, Unité Mixte de Recherche, Paris, France; Institut national de la santé et de la recherche médicale, Paris, France; Université Paris Descartes, Laboratoire de Neuropsychopharmacologie des Addictions, Paris, France
| | - Florence Noble
- Centre National de la Recherche Scientifique, Unité Mixte de Recherche, Paris, France; Institut national de la santé et de la recherche médicale, Paris, France; Université Paris Descartes, Laboratoire de Neuropsychopharmacologie des Addictions, Paris, France.
| | - Nicolas Marie
- Centre National de la Recherche Scientifique, Unité Mixte de Recherche, Paris, France; Institut national de la santé et de la recherche médicale, Paris, France; Université Paris Descartes, Laboratoire de Neuropsychopharmacologie des Addictions, Paris, France
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Kibaly C, Loh H, Law PY. A Mechanistic Approach to the Development of Gene Therapy for Chronic Pain. INTERNATIONAL REVIEW OF CELL AND MOLECULAR BIOLOGY 2016; 327:89-161. [DOI: 10.1016/bs.ircmb.2016.06.002] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
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Allouche S, Noble F, Marie N. Opioid receptor desensitization: mechanisms and its link to tolerance. Front Pharmacol 2014; 5:280. [PMID: 25566076 PMCID: PMC4270172 DOI: 10.3389/fphar.2014.00280] [Citation(s) in RCA: 101] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2014] [Accepted: 12/02/2014] [Indexed: 02/04/2023] Open
Abstract
Opioid receptors (OR) are part of the class A of G-protein coupled receptors and the target of the opiates, the most powerful analgesic molecules used in clinic. During a protracted use, a tolerance to analgesic effect develops resulting in a reduction of the effectiveness. So understanding mechanisms of tolerance is a great challenge and may help to find new strategies to tackle this side effect. This review will summarize receptor-related mechanisms that could underlie tolerance especially receptor desensitization. We will focus on the latest data obtained on molecular mechanisms involved in opioid receptor desensitization: phosphorylation, receptor uncoupling, internalization, and post-endocytic fate of the receptor.
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Affiliation(s)
- Stéphane Allouche
- Laboratoire de Signalisation, Électrophysiologie et Imagerie des Lésions D'ischémie-Reperfusion Myocardique, Université de Caen, UPRES EA 4650, IFR 146 ICORE Caen, France
| | - Florence Noble
- Centre National de la Recherche Scientifique, ERL 3649 Paris, France ; Institut National de la Santé et de la Recherche Médicale, UMR-S 1124 Paris, France ; Université Paris Descartes, Neuroplasticité et Thérapies des Addictions Paris, France
| | - Nicolas Marie
- Centre National de la Recherche Scientifique, ERL 3649 Paris, France ; Institut National de la Santé et de la Recherche Médicale, UMR-S 1124 Paris, France ; Université Paris Descartes, Neuroplasticité et Thérapies des Addictions Paris, France
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Nagi K, Pineyro G. Kir3 channel signaling complexes: focus on opioid receptor signaling. Front Cell Neurosci 2014; 8:186. [PMID: 25071446 PMCID: PMC4085882 DOI: 10.3389/fncel.2014.00186] [Citation(s) in RCA: 49] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2014] [Accepted: 06/18/2014] [Indexed: 12/03/2022] Open
Abstract
Opioids are among the most effective drugs to treat severe pain. They produce their analgesic actions by specifically activating opioid receptors located along the pain perception pathway where they inhibit the flow of nociceptive information. This inhibition is partly accomplished by activation of hyperpolarizing G protein-coupled inwardly-rectifying potassium (GIRK or Kir3) channels. Kir3 channels control cellular excitability in the central nervous system and in the heart and, because of their ubiquitous distribution, they mediate the effects of a large range of hormones and neurotransmitters which, upon activation of corresponding G protein-coupled receptors (GPCRs) lead to channel opening. Here we analyze GPCR signaling via these effectors in reference to precoupling and collision models. Existing knowledge on signaling bias is discussed in relation to these models as a means of developing strategies to produce novel opioid analgesics with an improved side effects profile.
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Affiliation(s)
- Karim Nagi
- Département de Pharmacologie, Faculté de Médecine, Université de Montréal Montreal, QC, Canada ; Centre de Recherche du CHU Sainte-Justine Montréal, QC, Canada
| | - Graciela Pineyro
- Département de Pharmacologie, Faculté de Médecine, Université de Montréal Montreal, QC, Canada ; Centre de Recherche du CHU Sainte-Justine Montréal, QC, Canada ; Département de Psychiatrie, Faculté de Médecine, Université de Montréal Montréal, QC, Canada
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Lin HY, Law PY, Loh HH. Activation of protein kinase C (PKC)α or PKCε as an approach to increase morphine tolerance in respiratory depression and lethal overdose. J Pharmacol Exp Ther 2012; 341:115-25. [PMID: 22228806 DOI: 10.1124/jpet.111.188235] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Long-term use of opioids is hindered by respiratory depression and the possibility for fatal overdose in drug abusers. This is attributed to higher levels of tolerance that develops against antinociception than to respiratory depression. Identifying important mechanisms that would increase morphine respiratory depression and overdose tolerance could lead to the safer use of opioids. Because protein kinase C (PKC) activity mediates the development and maintenance of morphine antinociceptive tolerance, we hypothesized that activating PKCα or PKCε at the pre-Bötzinger complex (preBötC) can increase morphine tolerance in respiration and overdose. Laser microdissection and quantitative reverse transcriptase-polymerase chain reaction were used to compare the relative mRNA abundances of PKCα, γ, and ε between ventrolateral periaqueductal gray (vlPAG) and preBötC. To test whether PKCα or ε could enhance morphine tolerance in respiratory depression and overdose, lentivirus carrying the wild type, constitutively activated mutants, and small interference RNA against PKCα or ε was stereotaxically injected into the preBötC. Expression of constitutively active PKC (CAPKC) α or ε, but not wild-type PKC (WTPKC) α or ε, at the preBötC allowed rats to develop tolerance to morphine respiratory depression. In terms of lethality, expression of WTPKCε, CAPKCα, or CAPKCε at preBötC increased morphine tolerance to lethal overdose. CAPKCε-expressing rats developed the highest level of respiratory depression tolerance. Furthermore, when CAPKCε lentivirus was injected into the vlPAG, rats were able to develop significant antinociceptive tolerance at low doses of morphine that normally do not cause tolerance. The approach of increasing morphine respiratory depression and lethality tolerance by increasing PKCα or ε activity at preBötC could be used to make opioids safer for long-term use.
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Affiliation(s)
- Hong-Yiou Lin
- Department of Pharmacology, University of Minnesota, 6-120 Jackson Hall, 321 Church St. S.E., Minneapolis, MN 55455-0217, USA.
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Kobayashi H, Iwata M, Mitani H, Yamada T, Nakagome K, Kaneko K. Valproic acid improves the tolerance for the stress in learned helplessness rats. Neurosci Res 2012; 72:355-63. [PMID: 22240171 DOI: 10.1016/j.neures.2011.12.009] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2011] [Revised: 12/01/2011] [Accepted: 12/14/2011] [Indexed: 01/16/2023]
Abstract
In this study, we investigated whether previously stressed rats with learned helplessness (LH) paradigm could recover from depressive-like behavior four weeks after the exposure, and also whether chronic treatment with valproic acid (VPA) could prevent behavioral despair due to the second stress on days 54 in these animals. Four weeks after induction of LH, we confirmed behavioral remission in the previously stressed rats. Two-way analysis of variance (ANOVA) performed with two factors, pretreatment (LH or Control) and drug (VPA or Saline), revealed a significant main effect of the drug on immobility time in forced swimming test. Post hoc test showed a shorter immobility time in the LH+VPA group than in the LH+Saline group. Immunohistochemical study of synapsin I showed a significant effect of drug by pretreatment interaction on immunoreactivity of synapsin I in the hippocampus: its expression levels in the regions were higher in the LH+VPA group than in the LH+Saline group. These results suggest that VPA could prevent the reappearance of stress-induced depressive-like behaviors in the rats recovering from prior stress, and that the drug-induced presynaptic changes in the expression of synapsin I in the hippocampus of LH animals might be related to improved tolerance toward the stress.
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Affiliation(s)
- H Kobayashi
- Division of Neuropsychiatry, Department of Brain and Neuroscience, Tottori University Faculty of Medicine, 36-1 Nishi-cho, Yonago 683-8504, Japan.
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Opioid Receptor Trafficking and Signaling: What Happens After Opioid Receptor Activation? Cell Mol Neurobiol 2011; 32:167-84. [DOI: 10.1007/s10571-011-9755-5] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2011] [Accepted: 09/04/2011] [Indexed: 01/14/2023]
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12
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Bedini A, Baiula M, Carbonari G, Spampinato S. Transcription factor REST negatively influences the protein kinase C-dependent up-regulation of human mu-opioid receptor gene transcription. Neurochem Int 2009; 56:308-17. [PMID: 19913583 DOI: 10.1016/j.neuint.2009.10.014] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2009] [Revised: 10/20/2009] [Accepted: 10/29/2009] [Indexed: 11/15/2022]
Abstract
Mu-opioid receptor expression increases during neurogenesis, regulates the survival of maturing neurons and is implicated in ischemia-induced neuronal death. The repressor element 1 silencing transcription factor (REST), a regulator of a subset of genes in differentiating and post-mitotic neurons, is involved in its transcriptional repression. Extracellular signaling molecules and mechanisms that control the human mu-opioid receptor (hMOR) gene transcription are not clearly understood. We examined the role of protein kinase C (PKC) on hMOR transcription in a model of neuronal cells and in the context of the potential influence of REST. In native SH-SY5Y neuroblastoma cells, PKC activation with phorbol 12-myristate 13-acetate (PMA, 16 nM, 24h) down-regulated hMOR transcription and concomitantly elevated the REST binding activity to repressor element 1 of the hMOR promoter. In contrast, PMA activated hMOR gene transcription when REST expression was knocked down by an antisense strategy or by retinoic acid-induced cell differentiation. PMA acts through a PKC-dependent pathway requiring downstream MAP kinases and the transcription factor AP-1. In a series of hMOR-luciferase promoter/reporter constructs transfected into SH-SY5Y cells and PC12 cells, PMA up-regulated hMOR transcription in PC12 cells lacking REST, and in SH-SY5Y cells either transfected with constructs deficient in the REST DNA binding element or when REST was down-regulated in retinoic acid-differentiated cells. These findings help explain how hMOR transcription is regulated and may clarify its contribution to epigenetic modifications and reprogramming of differentiated neuronal cells exposed to PKC-activating agents.
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Affiliation(s)
- Andrea Bedini
- Department of Pharmacology, University of Bologna, Bologna, Italy
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Effect of Chronic Administration of Morphine on the Gene Expression Level of Sodium-Dependent Vitamin C Transporters in Rat Hippocampus and Lumbar Spinal Cord. J Mol Neurosci 2009; 38:236-42. [DOI: 10.1007/s12031-009-9203-x] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2008] [Accepted: 04/13/2009] [Indexed: 10/20/2022]
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Chu J, Zheng H, Loh HH, Law PY. Morphine-induced mu-opioid receptor rapid desensitization is independent of receptor phosphorylation and beta-arrestins. Cell Signal 2008; 20:1616-24. [PMID: 18558479 DOI: 10.1016/j.cellsig.2008.05.004] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2008] [Accepted: 05/12/2008] [Indexed: 10/22/2022]
Abstract
Receptor desensitization involving receptor phosphorylation and subsequent betaArrestin (betaArr) recruitment has been implicated in the tolerance development mediated by mu-opioid receptor (OPRM1). However, the roles of receptor phosphorylation and betaArr on morphine-induced OPRM1 desensitization remain to be demonstrated. Using OPRM1-induced intracellular Ca(2+) ([Ca(2+)](i))release to monitor receptor activation, as predicted, [D-Ala(2), N-Me-Phe(4), Gly(5)-ol]-enkephalin (DAMGO), induced OPRM1 desensitization in a receptor phosphorylation- and betaArr-dependent manner. The DAMGO-induced OPRM1 desensitization was attenuated significantly when phosphorylation deficient OPRM1 mutants or Mouse Embryonic Fibroblast (MEF) cells from betaArr1 and 2 knockout mice were used in the studies. Specifically, DAMGO-induced desensitization was blunted in HEK293 cells expressing the OPRM1S375A mutant and was eliminated in MEF cells isolated from betaArr2 knockout mice expressing the wild type OPRM1. However, although morphine also could induce a rapid desensitization on [Ca(2+)](i) release to a greater extent than that of DAMGO and could induce the phosphorylation of Ser(375) residue, morphine-induced desensitization was not influenced by mutating the phosphorylation sites or in MEF cells lacking betaArr1 and 2. Hence, morphine could induce OPRM1 desensitization via pathway independent of betaArr, thus suggesting the in vivo tolerance development to morphine can occur in the absence of betaArr.
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Affiliation(s)
- Ji Chu
- Department of Pharmacology, Medical School, University of Minnesota, Minneapolis, MN 55455-0217, USA.
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Gabra BH, Bailey CP, Kelly E, Smith FL, Henderson G, Dewey WL. Pre-treatment with a PKC or PKA inhibitor prevents the development of morphine tolerance but not physical dependence in mice. Brain Res 2008; 1217:70-7. [PMID: 18501877 DOI: 10.1016/j.brainres.2008.04.036] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2008] [Revised: 04/16/2008] [Accepted: 04/18/2008] [Indexed: 12/11/2022]
Abstract
We previously demonstrated that intracerebroventricular (i.c.v.) administration of protein kinase C (PKC) or protein kinase A (PKA) inhibitors reversed morphine antinociceptive tolerance in 3-day morphine-pelleted mice. The present study aimed at evaluating whether pre-treating mice with a PKC or PKA inhibitor prior to pellet implantation would prevent the development of morphine tolerance and physical dependence. Antinociception was assessed using the warm-water tail immersion test and physical dependence was evaluated by quantifying/scoring naloxone-precipitated withdrawal signs. While drug-naïve mice pelleted with a 75 mg morphine pellet for 3 days developed a 5.8-fold tolerance to morphine antinociception, mice pre-treated i.c.v. with the PKC inhibitors bisindolylmaleimide I, Go-7874 or Go-6976, or with the myristoylated PKA inhibitor, PKI-(14-22)-amide failed to develop any tolerance to morphine antinociception. Experiments were also conducted to determine whether morphine-pelleted mice were physically dependent when pre-treated with PKC or PKA inhibitors. The same inhibitor doses that prevented morphine tolerance were evaluated in other mice injected s.c. with naloxone and tested for precipitated withdrawal. The pre-treatment with PKC or PKA inhibitors failed to attenuate or block the signs of morphine withdrawal including jumping, wet-dog shakes, rearing, forepaw tremor, increased locomotion, grooming, diarrhea, tachypnea and ptosis. These data suggest that elevations in the activity of PKC and PKA in the brain are critical to the development of morphine tolerance. However, it appears that tolerance can be dissociated from physical dependence, indicating a role for PKC and PKA to affect antinociception but not those signs mediated through the complex physiological processes of withdrawal.
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Affiliation(s)
- Bichoy H Gabra
- Department of Pharmacology and Toxicology, Virginia Commonwealth University Medical Center, Richmond, VA 23298, USA
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mGluR5 antagonists that block calcium mobilization in vitro also reverse (S)-3,5-DHPG-induced hyperalgesia and morphine antinociceptive tolerance in vivo. Brain Res 2007; 1187:58-66. [PMID: 18022146 DOI: 10.1016/j.brainres.2007.10.007] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2007] [Revised: 09/22/2007] [Accepted: 10/01/2007] [Indexed: 11/22/2022]
Abstract
The present study comparatively evaluated the potency of a series of new phenylethyl[1,2,4]methyltriazines which are analogues of the classical metabotropic glutamate (mGlu) receptor subtype 5 (mGluR5) antagonist 2-methyl-6-(phenylethynyl)pyridine (MPEP) in blocking hyperalgesia induced by the group I mGlu receptor agonist (S)-3,5-DHPG as well as in reversing morphine antinociceptive tolerance in mice. Hyperalgesia was assessed in mice using the tail immersion test. Intrathecal (i.t.) pre-treatment with the test compounds 5-methyl-3-phenylethynyl-[1,2,4]triazine (RTI-4229-707), 5-methyl-3-(4-phenoxy-phenylethynyl-[1,2,4]triazine (RTI-4229-766), and 3-(3-methylphenylethynyl)-5-methyl-[1,2,4]triazine (RTI-4229-787) resulted in a dose-dependent blockade of (S)-3,5-DHPG-induced hyperalgesia. The inhibitory dose-50 (ID(50)) values were 0.49, 0.72 and 0.44 nmol/mouse, for RTI-4229-707, RTI-4229-766 and RTI-4229-787, respectively, compared to 18.63 nmol/mouse for MPEP. The other two compounds tested 3-(2,5-dimethylphenylethynyl)-5-methyl[1,2,4]triazine (RTI-4229-785) and 3-(2-methylphenylethynyl)-5-methyl[1,2,4]triazine (RTI-4229-828) were totally inactive. Morphine tolerance was induced in mice by implanting a 75 mg morphine pellet and assessing morphine-induced antinociception 72-h later. The morphine-pelleted mice showed a 5.5-fold tolerance to the antinociceptive effect of acute morphine compared to placebo-pelleted mice in the tail immersion test. Intracerebroventricular (i.c.v.) administration of the three active mGluR5 antagonists dose-dependently reversed morphine antinociceptive tolerance. The ID(50) values were 57.7, 25.8 and 64.3 nmol/mouse, for RTI-4229-707, RTI-4229-766 and RTI-4229-787, respectively, compared to 1050 nmol/mouse for MPEP. Similar to the hyperalgesia study, test compounds RTI-4229-785 and RTI-4229-828 were totally inactive in reversing morphine tolerance. These results are in agreement with our previous study in which we demonstrated that the same active mGluR5 antagonists blocked glutamate-mediated mobilization of internal calcium in a selective mGluR5 in vitro efficacy assay.
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Ferrero AJ, Cereseto M, Sifonios LL, Reinés A, Peixoto E, Rubio MC, Wikinski S. Cytoskeleton of hippocampal neurons as a target for valproic acid in an experimental model of depression. Prog Neuropsychopharmacol Biol Psychiatry 2007; 31:1419-28. [PMID: 17683840 DOI: 10.1016/j.pnpbp.2007.06.014] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/13/2006] [Revised: 06/16/2007] [Accepted: 06/19/2007] [Indexed: 10/23/2022]
Abstract
BACKGROUND Atrophy of pyramidal hippocampal neurons and of the entire hippocampus has been reported in experimental models of depression and in depressive patients respectively. We investigated the efficacy of valproic acid (VPA) for reversing a depressive-like behaviour and a cytoskeletal alteration in the hippocampus, the loss of the light neurofilament subunit (NF-L). METHODS Depressive-like behaviour was induced by inescapable stress. Animals were divided into four groups: two to assess the response to 21 days of treatment with 200 mg/kg (I.P.) of valproic acid, and two in which the treatment was interrupted and the effects of VPA were evaluated 90 days later. Depressive-like behaviour was evaluated by the quantification of escape movements in a swimming test. NF-L was quantified by immunohistochemistry in dentate gyrus and CA3 of hippocampus. RESULTS VPA corrected the depressive-like behaviour and reversed the diminution of NF-L in the hippocampus. Ninety days after the end of the treatment, and in contrast to the results previously obtained with fluoxetine, no recurrence of the depressive-like behaviour was observed. CONCLUSIONS Despite interruption of the treatment, a long-lasting effect of VPA was observed. A possible relationship between the effect on NF-L and the prevention of depressive-like behaviour recurrence could be suggested.
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Affiliation(s)
- Alejandro J Ferrero
- Instituto de Investigaciones Farmacológicas (ININFA-UBA/CONICET), (1113) Buenos Aires, Argentina
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18
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Matsushita Y, Ishikawa M, Abe K, Utsunomiya I, Chikuma T, Hojo H, Hoshi K, Quock RM, Taguchi K. Involvement of the protein kinase Cγ isoform in development of tolerance to nitrous oxide–induced antinociception in mice. Neuroscience 2007; 148:541-7. [PMID: 17681696 DOI: 10.1016/j.neuroscience.2007.06.019] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2007] [Revised: 06/11/2007] [Accepted: 06/18/2007] [Indexed: 11/23/2022]
Abstract
Prolonged exposure to nitrous oxide (N2O) results in development of acute tolerance to its antinociceptive effect. Cross-tolerance to N2O-induced antinociception is also observed in morphine-tolerant animals. Despite increasing evidence of tolerance development to N2O-induced antinociception, the details of the mechanisms that underlie this tolerance remain unknown. The present study was conducted to investigate the involvement of brain protein kinase C (PKC) isoform in these two types of tolerance to N2O-induced antinociception in mice. Prolonged exposure (41 min in total, including 30 min pre-exposure and 11 min of antinociceptive testing) to 70% N2O produced a reduction in N2O-induced antinociception, indicating development of acute tolerance. The prolonged exposure to 70% N2O caused an activation of PKCgamma isoform in the brain, but not the PKCepsilon isoform. Pretreatment with a PKCgamma-antisense oligonucleotide but not the corresponding mismatch oligonucleotide (i.c.v.) prevented the development of acute tolerance to N2O-induced antinociception. Chronic morphine treatment (10 mg/kg, s.c., b.i.d. for 5 days) resulted in development of tolerance to morphine-induced antinociception and cross-tolerance to N2O-induced antinociception. The development of tolerance to morphine and cross-tolerance to N2O were both inhibited by pretreatment with PKC inhibitor, chelerythrine (1 nmol, i.c.v.). Morphine-tolerant mice showed an activation of PKC within the brain, which was suppressed by pretreatment with chelerythrine (1 nmol, i.c.v.). Thus, activation of brain PKC, in particular, the PKCgamma isoform, appears to play an important role in the development of both acute tolerance and cross-tolerance to N2O-induced antinociception in mice.
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Affiliation(s)
- Y Matsushita
- Department of Pharmacotherapeutics, Showa Pharmaceutical University, PO Box 3-3165, Higashitamagawagakuen, Tokyo 194-8543, Japan
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Newton PM, Kim JA, McGeehan AJ, Paredes JP, Chu K, Wallace MJ, Roberts AJ, Hodge CW, Messing RO. Increased response to morphine in mice lacking protein kinase C epsilon. GENES, BRAIN, AND BEHAVIOR 2007; 6:329-38. [PMID: 16899053 PMCID: PMC4264050 DOI: 10.1111/j.1601-183x.2006.00261.x] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
The protein kinase C (PKC) family of serine-threonine kinases has been implicated in behavioral responses to opiates, but little is known about the individual PKC isozymes involved. Here, we show that mice lacking PKCepsilon have increased sensitivity to the rewarding effects of morphine, revealed as the expression of place preference and intravenous self-administration at very low doses of morphine that do not evoke place preference or self-administration in wild-type mice. The PKCepsilon null mice also show prolonged maintenance of morphine place preference in response to repeated testing when compared with wild-type mice. The supraspinal analgesic effects of morphine are enhanced in PKCepsilon null mice, and the development of tolerance to the spinal analgesic effects of morphine is delayed. The density of mu-opioid receptors and their coupling to G-proteins are normal. These studies identify PKCepsilon as a key regulator of opiate sensitivity in mice.
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Affiliation(s)
- P. M. Newton
- Ernest Gallo Clinic and Research Center, Department of Neurology, University of California, San Francisco, Emeryville, CA
| | - J. A. Kim
- Ernest Gallo Clinic and Research Center, Department of Neurology, University of California, San Francisco, Emeryville, CA
| | - A. J. McGeehan
- Ernest Gallo Clinic and Research Center, Department of Neurology, University of California, San Francisco, Emeryville, CA
| | - J. P. Paredes
- Ernest Gallo Clinic and Research Center, Department of Neurology, University of California, San Francisco, Emeryville, CA
| | - K. Chu
- Molecular and Integrative Neurosciences Department, The Scripps Research Institute, La Jolla, CA
| | - M. J. Wallace
- Ernest Gallo Clinic and Research Center, Department of Neurology, University of California, San Francisco, Emeryville, CA
| | - A. J. Roberts
- Molecular and Integrative Neurosciences Department, The Scripps Research Institute, La Jolla, CA
| | - C. W. Hodge
- Bowles Center for Alcohol Studies, Departments of Psychiatry and Pharmacology, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA
| | - R. O. Messing
- Ernest Gallo Clinic and Research Center, Department of Neurology, University of California, San Francisco, Emeryville, CA
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Gabra BH, Bailey CP, Kelly E, Sanders AV, Henderson G, Smith FL, Dewey WL. Evidence for an important role of protein phosphatases in the mechanism of morphine tolerance. Brain Res 2007; 1159:86-93. [PMID: 17582387 PMCID: PMC3736353 DOI: 10.1016/j.brainres.2007.05.017] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2007] [Revised: 05/10/2007] [Accepted: 05/14/2007] [Indexed: 11/17/2022]
Abstract
Acute morphine antinociception has been shown to be blocked by very low picogram doses of okadaic acid indicating that inhibition of protein phosphatase PP2A allows for increases in phosphorylation to inhibit antinociception. Comparative studies in morphine tolerant animals have not been reported. In the present study, we showed a significant increase in the total phosphatase activity in the periaqueductal gray matter (PAG) from morphine-pelleted versus placebo-pelleted mice, 72-h after pellet implantation. This supports our hypothesis that phosphatase activity is increased in tolerance as a compensatory mechanism for the increase in kinase activity during the development of tolerance. We also demonstrated that i.c.v. administration of the phosphatase inhibitor okadaic acid (3 pmol/mouse; a dose tested to be inert in placebo-pelleted mice) enhanced the level of morphine antinociceptive tolerance assessed by the tail immersion test, 72-h following pellet implantation. This was supported by the fact that the same treatment with okadaic acid blocked the increase in phosphatase activity in PAG of morphine tolerant mice indicating that selective inhibition of PP2A contributes to enhanced levels of morphine tolerance. We have previously reported that PKC or PKA inhibitors reversed morphine antinociceptive tolerance in mice. The current study shows that i.c.v. administration of the PKC inhibitors bisindolylmaleimide I or Go6976 reversed the enhanced level of morphine tolerance induced by okadaic acid treatment to the same level of tolerance observed in non-okadaic acid-treated tolerant mice. However, the PKA inhibitor PKI-(14-22)-amide only partially reversed the enhancement of morphine tolerance induced by okadaic acid. Our data suggest an important role for the balance between kinases and phosphatases in modulating tolerance levels. Further studies will be directed towards a better understanding of the role of different phosphatase isoforms in morphine tolerance.
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Affiliation(s)
- Bichoy H. Gabra
- Department of Pharmacology and Toxicology, Virginia Commonwealth University Medical Center, Richmond, VA 23298 USA
| | - Chris P. Bailey
- Department of Pharmacology, University of Bristol, Bristol BS8 1TD, UK
| | - Eamonn Kelly
- Department of Pharmacology, University of Bristol, Bristol BS8 1TD, UK
| | - Amanda V. Sanders
- Department of Pharmacology and Toxicology, Virginia Commonwealth University Medical Center, Richmond, VA 23298 USA
| | - Graeme Henderson
- Department of Pharmacology, University of Bristol, Bristol BS8 1TD, UK
| | - Forrest L. Smith
- Department of Pharmaceutical Sciences, Harding University College of Pharmacy, Searcy, AR 72149 USA
| | - William L. Dewey
- Department of Pharmacology and Toxicology, Virginia Commonwealth University Medical Center, Richmond, VA 23298 USA
- Author for correspondence: William L. Dewey, Ph.D., Department of Pharmacology and Toxicology, Virginia Commonwealth University Medical Center, P.O. Box 980613, Richmond, VA 23298-0524, Office: 804-827-0375, Fax: 804-827-1548,
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Bailey CP, Smith FL, Kelly E, Dewey WL, Henderson G. How important is protein kinase C in μ-opioid receptor desensitization and morphine tolerance? Trends Pharmacol Sci 2006; 27:558-65. [PMID: 17000011 DOI: 10.1016/j.tips.2006.09.006] [Citation(s) in RCA: 78] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2006] [Revised: 08/21/2006] [Accepted: 09/12/2006] [Indexed: 11/30/2022]
Abstract
The repeated administration of opiate drugs such as morphine results in the development of tolerance to their analgesic, rewarding (euphoric) and respiratory-depressant effects; thus, to obtain the same level of response with subsequent administrations, a greater dose must be used. Tolerance can limit the clinical efficacy of opiate drugs and enhance the social problems that are inherent in recreational opioid abuse. Surprisingly, the mechanism (or mechanisms) underlying the development of morphine tolerance remains controversial. Here, we propose that protein kinase C could have a crucial role in the desensitization of mu-opioid receptors by morphine and that this cellular process could contribute to the development and maintenance of morphine tolerance in vivo.
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Affiliation(s)
- Chris P Bailey
- Department of Pharmacology, University of Bristol, Bristol BS8 1TD, UK
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22
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Ishikawa M, Matsushita Y, Abe K, Utsunomiya I, Hoshi K, Quock RM, Taguchi K. Involvement of brain protein kinase C in nitrous oxide-induced antinociception in mice. Neuroscience 2006; 140:227-33. [PMID: 16533570 DOI: 10.1016/j.neuroscience.2006.02.001] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2005] [Revised: 12/23/2005] [Accepted: 02/01/2006] [Indexed: 11/22/2022]
Abstract
Exposure of mice to the anesthetic gas nitrous oxide (N(2)O) produces a marked antinociceptive effect. Protein kinase C is a key regulatory enzyme that may be targeted by general anesthetics. However, a relationship between N(2)O-induced antinociception and protein kinase C has yet to be established. The present study was conducted to identify whether protein kinase C might influence N(2)O-induced antinociception in mice. Regular exposure (11 min) to N(2)O produced concentration-dependent antinociception in mice, as determined using the abdominal constriction test. N(2)O-induced antinociception was attenuated by i.c.v. pretreatment with phorbol 12,13-dibutyrate, a protein kinase C activator. This phorbol 12,13-dibutyrate antagonism of N(2)O-induced antinociception was reversed by i.c.v. pretreatment with calphostin C, a protein kinase C inhibitor. Long-term exposure (41 min in total, including 30 min prior to, and 11 min of analgesic testing) to 70% N(2)O produced reduced analgesic effects, compared with regular exposure to 70% N(2)O, thus indicating acute tolerance to N(2)O-induced antinociception. However, mice pretreated with calphostin C, chelerythrine, which is another protein kinase C inhibitor, and phorbol 12,13-dibutyrate, did not develop acute tolerance. Regarding activation of protein kinase C, regular exposure to 70% N(2)O did not increase protein kinase C within the membrane fraction of brain tissue, as determined by immunoblot analysis, but long-term exposure to 70% N(2)O did. The i.c.v. pretreatment with calphostin C and phorbol 12,13-dibutyrate prevented the increase in protein kinase C observed with long-term exposure to 70% N(2)O. These results suggest that brain protein kinase C negatively regulates the antinociceptive effect of N(2)O, and that activation of brain protein kinase C is related to the development of acute tolerance to N(2)O-induced antinociception in mice.
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Affiliation(s)
- M Ishikawa
- Department of Pharmacotherapeutics, Showa Pharmaceutical University, P.O. Box 3-3165, Higashitamagawagakuen, Tokyo 194-8543, Japan
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Abstract
This paper is the 27th consecutive installment of the annual review of research concerning the endogenous opioid system, now spanning over 30 years of research. It summarizes papers published during 2004 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior, and the roles of these opioid peptides and receptors in pain and analgesia; stress and social status; tolerance and dependence; learning and memory; eating and drinking; alcohol and drugs of abuse; sexual activity and hormones, pregnancy, development and endocrinology; mental illness and mood; seizures and neurologic disorders; electrical-related activity and neurophysiology; general activity and locomotion; gastrointestinal, renal and hepatic functions; cardiovascular responses; respiration and thermoregulation; and immunological responses.
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Affiliation(s)
- Richard J Bodnar
- Department of Psychology and Neuropsychology Doctoral Sub-Program, Queens College, City University of New York, Flushing, NY 11367, USA.
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Laferrière A, Colin-Durand J, Moss IR. Ontogeny of respiratory sensitivity and tolerance to the mu-opioid agonist fentanyl in rat. BRAIN RESEARCH. DEVELOPMENTAL BRAIN RESEARCH 2005; 156:210-7. [PMID: 16099308 DOI: 10.1016/j.devbrainres.2005.03.002] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/22/2004] [Revised: 03/01/2005] [Accepted: 03/03/2005] [Indexed: 11/18/2022]
Abstract
Whereas developmental changes in analgesic sensitivity and tolerance to the mu-opioid agonist fentanyl have been reported, knowledge of respiratory responses to that drug is lacking. Using 7- and 14-day-old (P7, P14) and adult conscious rats, we first established, using whole body plethysmography, the fentanyl dose that decreased minute ventilation by 50% (ED50) at each age. ED50 increased with postnatal age (40, 60 and 120 microg/kg sc, respectively), indicating a high sensitivity to fentanyl in the youngest rats that decreased with maturation. In separate rat groups of the 3 ages, we injected each ED50 dose, once a day, for several consecutive days, until tolerance was established. Tolerance was defined as a reduction in respiratory depression from 50% to 75% of baseline. All age groups reached tolerance in minute ventilation, respiratory frequency, tidal volume and instantaneous flow (equivalent to respiratory drive). The P14 rat pups attained tolerance more rapidly (at 2.6 days) than did either the younger (5.1 days) or the adult rats (4.4 days). These results indicate that respiratory sensitivity and tolerance to fentanyl in rat vary in a distinct manner during maturation.
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Affiliation(s)
- Andrè Laferrière
- Developmental Respiratory Laboratory, Montreal Children's Hospital Research Institute, Montreal, QC, Canada H3H 1P3
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