title: Chronic morphine exposure increases the phosphorylation of MAP kinases and the transcription factor CREB in dorsal root ganglion neurons: an in vitro and in vivo study.
abstract: Tolerance to opiates reduces their effectiveness in the treatment of severe pain. Although the mechanisms are unclear, overactivity of pro-nociceptive systems has been proposed to contribute to this phenomenon. We have reported that the development of morphine tolerance significantly increased calcitonin-gene-related-peptide-like immunoreactivity (CGRP-IR) in primary sensory afferents of the spinal dorsal horn, suggesting that changes in pain-related neuropeptides in the dorsal root ganglion (DRG) neurons may be involved (Menard et al., 1996, J. Neurosci., 16, 2342-2351). Recently, we have shown that repeated morphine treatments induced increases in CGRP- and substance P (SP)-IR in cultured DRG, mimicking the in vivo effects (Ma et al., 2000, Neuroscience, 99, 529-539). In this study, we investigated the intracellular signal transduction pathways possibly involved in morphine-induced increases in CGRP- and SP-IR in DRG neurons. Repeated morphine exposure (10-20 microm) for 6 days increased the number of neurons expressing phosphorylated (p) mitogen-activated protein (MAP) kinases, including the extracellular signal-regulated kinase (pERK), c-jun N-terminal kinase (pJNK) and P38 (pP38 MAPK). The number of neurons expressing phosphorylated cAMP responsive element binding protein (pCREB) was also markedly increased in morphine-exposed cultured DRG neurons. pERK-, pP38-, pJNK- and pCREB-IR were colocalized with CGRP-IR in cultured DRG neurons. Naloxone effectively blocked these actions of morphine, whereas a selective MEK1 inhibitor, PD98059, inhibited the morphine-induced increase in the phosphorylation of ERK and CREB, and the expression of CGRP and SP. Moreover, in morphine-tolerant rats, the number of pCREB-, CGRP- and SP-IR neurons in the lumbar DRG was also significantly increased. These in vitro and in vivo data suggest that the phosphorylation of MAP kinases and CREB plays a role in the morphine-induced increase in spinal CGRP and SP levels in primary sensory afferents, contributing to the development of tolerance to opioid-induced analgesia.
authors.affiliation: Douglas Hospital Research Centre, McGill University, Montreal, Quebec, Canada H4H 1R3.
authors.forename: W
authors.initials: W
authors.lastname: Ma
authors.forename: W H
authors.initials: WH
authors.lastname: Zheng
authors.forename: K
authors.initials: K
authors.lastname: Powell
authors.forename: K
authors.initials: K
authors.lastname: Jhamandas
authors.forename: R
authors.initials: R
authors.lastname: Quirion
mesh_terms: D000818:Animals; D015740:Calcitonin Gene-Related Peptide / Q000187:drug effects / Q000378:metabolism; D002452:Cell Count; D002478:Cells, Cultured / Q000187:drug effects / Q000378:metabolism; D017362:Cyclic AMP Response Element-Binding Protein / Q000187:drug effects* / Q000378:metabolism; D004334:Drug Administration Schedule; D004361:Drug Tolerance / Q000502:physiology*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005419:Flavonoids / Q000494:pharmacology; D005455:Fluorescent Antibody Technique; D005727:Ganglia, Spinal / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D048031:JNK Mitogen-Activated Protein Kinases; D048369:MAP Kinase Kinase 1; D020935:MAP Kinase Signaling System / Q000187:drug effects* / Q000502:physiology; D008297:Male; D020929:Mitogen-Activated Protein Kinase Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D020928:Mitogen-Activated Protein Kinases / Q000187:drug effects / Q000378:metabolism; D009020:Morphine / Q000494:pharmacology*; D009292:Narcotic Antagonists / Q000494:pharmacology; D009475:Neurons, Afferent / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D010146:Pain / Q000188:drug therapy* / Q000378:metabolism / Q000503:physiopathology; D010766:Phosphorylation / Q000187:drug effects; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D013373:Substance P / Q000187:drug effects / Q000502:physiology; D048051:p38 Mitogen-Activated Protein Kinases
chemical_list: D017362:Cyclic AMP Response Element-Binding Protein; D004791:Enzyme Inhibitors; D005419:Flavonoids; D009292:Narcotic Antagonists; D013373:Substance P; D009020:Morphine; D017346:Protein Serine-Threonine Kinases; D048031:JNK Mitogen-Activated Protein Kinases; D020928:Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases; D048369:MAP Kinase Kinase 1; D020929:Mitogen-Activated Protein Kinase Kinases; D015740:Calcitonin Gene-Related Peptide; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one