Repeated peripheral electrical stimulations suppress both morphine-induced CPP and reinstatement of extinguished CPP in rats: accelerated expression of PPE and PPD mRNA in NAc implicated.
Previous studies have shown that peripheral electrical stimulation (PES) can suppress morphine-induced conditioned place preference (CPP) and the reinstatement of extinguished CPP in the rat. The present study was performed to elucidate if preproenkephalin (PPE) and preprodynorphin (PPD) mRNAs in the nucleus accumbens (NAc) play a role in this event. Rats were trained with morphine for 4 days to establish CPP paradigm. They were then given 15-min test once a day for eight consecutive days for extinction trial. Twenty-four hours after the 8th session of extinction trials, rats were given peripheral electrical stimulation (PES) at 2 or 100 Hz once a day for 3 days, then a morphine-priming injection at a dose of 1, 2, or 4 mg/kg to reinstate the extinguished CPP. At the end of the experiment, PPE and PPD mRNA levels in the nucleus acccumbens (NAc) were determined by the semiquantitative RT-PCR technique. The results showed that PES at 2- and 100-Hz administered 30 min a day for 3 days suppressed both the expression of morphine-induced CPP and the reinstatement of extinguished CPP. PES at 2 Hz increased preproenkephalin (PPE) mRNA levels, whereas PES of 100 Hz that of preprodynorphin (PPD) mRNA levels in the NAc. These findings suggest that enkephalin and dynorphin in NAc may play important roles in the mechanisms underlying the inhibitory effect of PES on the expression and reinstatement of morphine-induced CPP in rats.
Shi
Xiang-Dang
XD
Neuroscience Research Institute, Key laboratory for Neuroscience, Peking University, the Ministry of Education, 38 Xueyuan Road, Beijing 100083, PR China.
Wang
Gui-Bin
GB
Ma
Yao-Ying
YY
Ren
Wei
W
Luo
Fei
F
Cui
Cai-Lian
CL
Han
Ji-Sheng
JS
D000704:Analysis of Variance; D000818:Animals; D001522:Behavior, Animal; D003216:Conditioning, Operant / Q000187:drug effects / Q000502:physiology / Q000528:radiation effects*; D004305:Dose-Response Relationship, Drug; D004307:Dose-Response Relationship, Radiation; D004399:Dynorphins / Q000235:genetics / Q000378:metabolism*; D004558:Electric Stimulation; D004745:Enkephalins / Q000235:genetics / Q000378:metabolism*; D005108:Extinction, Psychological / Q000528:radiation effects*; D005786:Gene Expression Regulation / Q000528:radiation effects*; D006614:Hindlimb / Q000294:innervation / Q000528:radiation effects; D008297:Male; D009020:Morphine / Q000494:pharmacology; D009043:Motor Activity / Q000187:drug effects / Q000528:radiation effects; D009294:Narcotics / Q000494:pharmacology; D009714:Nucleus Accumbens / Q000528:radiation effects*; D011498:Protein Precursors / Q000235:genetics / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D020133:Reverse Transcriptase Polymerase Chain Reaction / Q000379:methods; D013997:Time Factors
D004745:Enkephalins; D009294:Narcotics; D011498:Protein Precursors; D012333:RNA, Messenger; C036448:pre-prodynorphin; D004399:Dynorphins; D009020:Morphine; C033660:preproenkephalin