Browsing by Author "Magendzo, K"

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    Differential regulation of μ-opioid receptor mRNA in the nucleus accumbens shell and core accompanying amphetamine behavioral sensitization
    (1999) Vecchiola, A; Collyer, P; Figueroa, R; Labarca, R; Bustos, G; Magendzo, K
    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 mu-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 PAh IPH (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. (C) 1999 Elsevier Science B.V. All rights reserved.
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    Expression of amphetamine-induced behavioral sensitization after short- and long-term withdrawal periods
    (2003) Magendzo, K; Bustos, G
    Repeated amphetamine administration results in behavioral sensitization, an enduring behavioral transformation expressed after short and long periods of withdrawal. To investigate the participation of the opioid system in amphetamine-induced behavioral sensitization, we studied the effect of naloxone, an opioid receptor antagonist, on the expression of behavioral sensitization tested after short- (2 days) and long-term (14 days) withdrawal periods. In addition, using quantitative competitive RT-PCR, we examined the levels of mu-opioid receptor (MOR) and delta-opioid receptor (DOR) mRNA in the nucleus accumbens shell (NAcSh) and ventral tegmental area (VTA) of behaviorally sensitized rats, at these two withdrawal times. This study showed that whereas naloxone did not modify the expression of behavioral sensitization tested after 2 days of withdrawal, it completely blocked the expression when tested after 14 days of withdrawal. DOR and MOR mRNA levels were not modified in the NAcSh of rats expressing behavioral sensitization after 2 or 14 days of withdrawal. Conversely, DOR and MOR mRNA levels were elevated in the VTA of animals expressing behavioral sensitization after 2 days of withdrawal. However, whereas DOR mRNA returned to control levels, MOR mRNA levels remained elevated in animals expressing behavioral sensitization after 14 days of withdrawal. These results indicate a striking difference between the role played by opioid receptors in the expression of amphetamine-induced behavioral sensitization, when tested after short- or long-term withdrawal periods. In addition, our results support the notion that repeated amphetamine-induced changes in opioid receptor expression may contribute to the perpetuation of psychostimulant abuse and/or relapse.