Effects of acute and repeated morphine treatment on κ-opioid receptor protein levels in mesocorticolimbic system.
BACKGROUND
Our previous study demonstrated that acute and repeated morphine treatment differentially regulated κ-opioid receptor mRNA levels in the rat mesocorticolimbic system. Here, we further investigated the effects of morphine on protein levels of κ-opioid receptor in this reward-related circuitry.


METHODS
Three groups of rats received intraperitoneal 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 protein expression was examined by Western blot analysis.


RESULTS
We found that acute morphine treatment did not affect the κ-receptor protein levels in medial prefrontal cortex (mPFC), nucleus accumbens (NAc) and ventral tegmental area (VTA). However, repeated morphine treatment downregulated the κ-receptor protein levels in mPFC and VTA, while there was no significant change in NAc.


CONCLUSIONS
These results, along with those reported previously, suggested that morphine dependence may be associated with regionally specific changes in κ-opioid receptor expression in mesocorticolimbic system.
Beijing Institute of Pharmacology and Toxicology , Beijing , People's Republic of China.
Gang
G
Yu
Hui
H
Yan
Ze-Hui
ZH
Gong
D000818:Animals; D005786:Gene Expression Regulation / Q000187:drug effects; D006801:Humans; D009020:Morphine / Q000008:administration & dosage*; D017397:Prefrontal Cortex / Q000187:drug effects; D012333:RNA, Messenger / Q000187:drug effects*; D051381:Rats; D017473:Receptors, Opioid, kappa / Q000096:biosynthesis*; D017557:Ventral Tegmental Area / Q000187:drug effects
D012333:RNA, Messenger; D017473:Receptors, Opioid, kappa; D009020:Morphine