Differential effects of acute and repeated morphine treatment on κ-opioid receptor mRNA levels in mesocorticolimbic system.
BACKGROUND
Morphine induces adaptive changes in gene expression throughout the reward circuitry of the brain. Here, we investigated the acute and chronic effects of morphine on mRNA levels of κ-opioid receptor in the rat mesocorticolimbic system.


METHODS
Three groups of rats received ip injection of saline, acute morphine (8.0 mg/kg) and repeated morphine (8.0 mg/kg, once daily for 5 consecutive days) and the κ-receptor mRNA expression was examined using real-time quantitative PCR method.


RESULTS
We found that κ-receptor mRNA in medial prefrontal cortex (mPFC) increased after acute and repeated morphine treatment. However, the mRNA levels in nucleus accumbens (NAc) and ventral tegmental area (VTA) were upregulated after acute morphine treatment and returned to basal levels after repeated morphine treatment.


CONCLUSIONS
These results suggest that morphine dependence was associated with regionally specific changes in mRNA levels of κ-opioid receptor in mesocorticolimbic system.
Beijing Institute of Pharmacology and Toxicology, 27 Taiping Road, Beijing 100850, People's Republic of China.
Gang
G
Yu
Hui
H
Yan
Ze-Hui
ZH
Gong
D000701:Analgesics, Opioid / Q000008:administration & dosage / Q000494:pharmacology*; D000818:Animals; D004305:Dose-Response Relationship, Drug; D004334:Drug Administration Schedule; D008297:Male; D009020:Morphine / Q000008:administration & dosage / Q000494:pharmacology*; D009021:Morphine Dependence / Q000378:metabolism; D009714:Nucleus Accumbens / Q000187:drug effects* / Q000378:metabolism; D017397:Prefrontal Cortex / Q000187:drug effects* / Q000378:metabolism; D012333:RNA, Messenger / Q000096:biosynthesis*; D051381:Rats; D017208:Rats, Wistar; D017473:Receptors, Opioid, kappa / Q000096:biosynthesis*; D015854:Up-Regulation; D017557:Ventral Tegmental Area / Q000187:drug effects* / Q000378:metabolism
D000701:Analgesics, Opioid; D012333:RNA, Messenger; D017473:Receptors, Opioid, kappa; D009020:Morphine