Differential regulation of μ-opioid receptor mRNA in the nucleus accumbens shell and core accompanying amphetamine behavioral sensitization

• Published in: Brain research. Molecular brain research. 1999-05, Vol.69 (1), p.1-9
• Main Authors: Vecchiola, Andrea, Collyer, Phillip, Figueroa, Roberto, Labarca, Rodrigo, Bustos, Gonzalo, Magendzo, Karin
• Format: Article
• Language: English
• Subjects: Amphetamine - pharmacology; Amphetamine behavioral sensitization; Animals; Antisense Elements (Genetics); Behavior, Animal - drug effects; Brain Chemistry - drug effects; Brain Chemistry - genetics; Central Nervous System Stimulants - pharmacology; Corpus Striatum - chemistry; Corpus Striatum - physiology; Gene Expression Regulation - drug effects; In Situ Hybridization; Locomotion - drug effects; Male; Non-radioactive in situ hybridization; Nucleus Accumbens - chemistry; Nucleus Accumbens - physiology; Nucleus accumbens shell; Rats; Rats, Sprague-Dawley; Receptors, Opioid, mu - genetics; RNA, Messenger - metabolism; Striatum; μ-Opioid receptor mRNA
• ISSN: 0169-328X; 1872-6941
• DOI: 10.1016/S0169-328X(99)00044-3

Repeated amphetamine (AMPH) administration results in behavioral sensitization. To investigate the participation of the opioid system in this phenomenon, we examined the effects of acute and repeated AMPH administration on μ-opioid receptor (MOR) mRNA levels in the nucleus accumbens (NAc) and striatum (STR) of rats, by quantitative non-radioactive in situ hybridization. Five injections of d-AMPH (1.5 mg kg −1, i.p., once every other day), resulted in a sensitization response profile and a significant down-regulation of MOR mRNA levels in the NAc shell, whereas no change was observed in MOR mRNA levels in the NAc core compared to the saline controls. Conversely, MOR mRNA levels were up-regulated in the rostral STR of AMPH-sensitized rats compared to saline controls. No changes in MOR mRNA levels were observed after acute AMPH treatment in any of the brain regions studied. These results suggest that the opioid system participates in the neurobiological underpinnings of behavioral sensitization and that opioid receptor (OR) expression in the STR and NAc shell and core is differentially modulated by repeated AMPH exposure.