title: cAMP-mediated mechanisms for pain sensitization during opioid withdrawal.
abstract: Chronic opioid-induced drug dependence and withdrawal syndrome after opioid cessation remain a severe obstacle in clinical treatment of chronic pain and opioid drug addiction. One of the key symptoms during opioid withdrawal is a state of sensitized pain. The most significant molecular adaptation induced by chronic opioids in the brain is upregulation of the cAMP-signaling pathway. Although the cAMP system is known to have multiple effects on central neuron functions, how its upregulation mediates behavioral opioid dependence and withdrawal-induced pain in vivo remains unclear. In this study, we demonstrate that withdrawal from chronic morphine significantly upregulates the mRNA level of adenylyl cyclase (AC) VI and VIII isoforms and immunoreactivity of ACV/VI in the nucleus raphe magnus (NRM), a brainstem site critically involved in opioid modulation of pain. In cellular studies of NRM neurons containing mu-opioid receptors, we show that morphine withdrawal significantly increases glutamate synaptic transmission via a presynaptic mechanism mediated by an upregulated cAMP pathway. Morphine withdrawal also enhances the hyperpolarization-activated current in these neurons by increased intracellular cAMP. Both of the withdrawal-induced cAMP actions increase the excitability of these mu-receptor-containing neurons, which are thought to facilitate spinal pain transmission. Furthermore, in morphine-dependent rats in vivo, blocking the cAMP pathway significantly reduces withdrawal-induced pain sensitization. These results illustrate neurobiological mechanisms for the cAMP-mediated withdrawal pain and provide potential therapeutic targets for the treatment of opioid dependence and withdrawal-related problems.
authors.affiliation: Department of Anesthesiology, The University of Texas-M.D. Anderson Cancer Center, Houston, Texas 77030, USA.
authors.forename: Bihua
authors.initials: B
authors.lastname: Bie
authors.forename: Yi
authors.initials: Y
authors.lastname: Peng
authors.forename: Yong
authors.initials: Y
authors.lastname: Zhang
authors.forename: Zhizhong Z
authors.initials: ZZ
authors.lastname: Pan
mesh_terms: D015763:2-Amino-5-phosphonovalerate / Q000494:pharmacology; D018750:6-Cyano-7-nitroquinoxaline-2,3-dione / Q000494:pharmacology; D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000494:pharmacology; D000262:Adenylyl Cyclases / Q000235:genetics / Q000378:metabolism; D000818:Animals; D000831:Animals, Newborn; D001522:Behavior, Animal; D015153:Blotting, Western / Q000379:methods; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000502:physiology*; D004307:Dose-Response Relationship, Radiation; D004334:Drug Administration Schedule; D004347:Drug Interactions; D004558:Electric Stimulation / Q000379:methods; D004791:Enzyme Inhibitors / Q000494:pharmacology; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects / Q000502:physiology / Q000528:radiation effects; D005786:Gene Expression Regulation / Q000187:drug effects / Q000502:physiology; D007097:Imines / Q000494:pharmacology; D066298:In Vitro Techniques; D007546:Isoquinolines / Q000494:pharmacology; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology / Q000528:radiation effects; D008845:Microinjections / Q000379:methods; D009020:Morphine / Q000008:administration & dosage; D009270:Naloxone / Q000494:pharmacology; D009292:Narcotic Antagonists / Q000494:pharmacology; D009294:Narcotics / Q000008:administration & dosage; D009293:Opioid-Related Disorders / Q000209:etiology / Q000503:physiopathology*; D010088:Oxidoreductases / Q000235:genetics / Q000378:metabolism; D010146:Pain / Q000378:metabolism / Q000503:physiopathology*; D010147:Pain Measurement / Q000379:methods; D018408:Patch-Clamp Techniques / Q000379:methods; D011743:Pyrimidines / Q000494:pharmacology; D012333:RNA, Messenger / Q000096:biosynthesis; D011903:Raphe Nuclei / Q000187:drug effects / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D020133:Reverse Transcriptase Polymerase Chain Reaction / Q000379:methods; D013449:Sulfonamides / Q000494:pharmacology
chemical_list: D004791:Enzyme Inhibitors; D018691:Excitatory Amino Acid Antagonists; D007097:Imines; D007546:Isoquinolines; D009292:Narcotic Antagonists; D009294:Narcotics; D011743:Pyrimidines; D012333:RNA, Messenger; D013449:Sulfonamides; C082246:ICI D2788; D005576:Colforsin; D015124:8-Bromo Cyclic Adenosine Monophosphate; D009270:Naloxone; D018750:6-Cyano-7-nitroquinoxaline-2,3-dione; D015763:2-Amino-5-phosphonovalerate; D009020:Morphine; C014925:RMI 12330A; D000242:Cyclic AMP; D010088:Oxidoreductases; C038370:isopenicillin N synthetase; D000262:Adenylyl Cyclases; C118292:adenylyl cyclase 8; C063509:N-(2-(4-bromocinnamylamino)ethyl)-5-isoquinolinesulfonamide