Abstract
Morphine is one of the analgesics used most to treat chronic pain, although its long-term administration produces tolerance and dependence through neuronal plasticity. The ability of morphine to regulate neuron differentiation in vivo has been reported. However, the detailed mechanisms have not yet been elucidated because of the inability to separate maternal influences from embryonic events. Using zebrafish embryos as the model, we demonstrate that morphine decreases miR-133b expression, hence increasing the expression of its target, Pitx3, a transcription factor that activates tyrosine hydroxylase and dopamine transporter. Using a specific morpholino to knock down the zebrafish μ-opioid receptor (zfMOR) in the embryos and selective mitogen-activated protein kinase inhibitors, we demonstrate that the morphine-induced miR-133b decrease in zebrafish embryos is mediated by zfMOR activation of extracellular signal-regulated kinase 1/2. A parallel morphine-induced down-regulation of miR-133b was observed in the immature but not in mature rat hippocampal neurons. Our results indicate for the first time that zebrafish embryos express a functional μ-opioid receptor and that zebrafish serves as an excellent model to investigate the roles of microRNA in neuronal development affected by long-term morphine exposure.
Footnotes
This work was funded by the Spanish Ministry of Education and Science [Grant SAF2007-61581]; the Regional Government of Castilla y Leon [Grant SA0800A5]; and by the National Institutes of Health National Institute on Drug Abuse [Grants DA007339, DA011806].
Article, publication date, and citation information can be found at http://molpharm.aspetjournals.org.
doi:10.1124/mol.110.066837.
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ABBREVIATIONS:
- MOR
- μ-opioid receptor
- DOR
- δ-opioid receptor
- zfMOR
- zebrafish μ-opioid receptor
- zfDOR
- zebrafish δ-opioid receptor
- NAc
- nucleus accumbens
- miRNA
- microRNA
- miR
- microRNA
- CNS
- central nervous system
- hpf
- hours after fertilization
- TH
- tyrosine hydroxylase
- DAT
- dopamine transporter
- UTR
- untranslated region
- MO
- morpholino
- MAPK
- mitogen-activated protein kinase
- JNK
- Jun N-terminal kinase
- ERK
- extracellular signal-regulated kinase
- MEK
- mitogen-activated protein kinase kinase
- Pitx3
- paired-like homeodomain transcription factor 3
- SB203580
- 4-(4-fluorophenyl)-2-(4-methylsulfinylphenyl)-5-(4-pyridyl)1H-imidazole
- PD98059
- 2′-amino-3′-methoxyflavone
- U0126
- 1,4-diamino-2,3-dicyano-1,4-bis(methylthio)butadiene
- qRT-PCR
- quantitative real-time-polymerase chain reaction.
- Received June 9, 2010.
- Accepted August 17, 2010.
- Copyright © 2010 The American Society for Pharmacology and Experimental Therapeutics
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