| Summary: | 碩士 === 長庚大學 === 生物醫學研究所 === 105 === Methamphetamine (METH) is a widely abused addictive drug. Repeated exposure to addictive drugs can readily induce drug tolerance, dependence, craving, and behavioral sensitization, in parallel to altered neural plasticity. METH-induced increase in release of dopamine in the striatum (including, nucleus accumbens, NAc) could cause neurological and morphological changes in the central nervous system. Previous studies had shown that dopamine D2 receptor downstream signaling PI3K/Akt/GSK3 altered significantly in amphetamine sensitized animals that linked with aberrant behaviors. Consequently, previous study also revealed that Akt-dependent mTOR signaling altered in abused drug-induced behavioral sensitization, but the role of mTOR in METH-induced behavioral sensitization remained unclear. Thus, in this study, we treated animals with continuous injections of methamphetamine (METH) for continuous eight days to induce characteristic behavioral sensitization, afterwards monitored mammalian target of rapamycin (mTOR) downstream factors -p70S6K and S6 during the development of behavioral sensitization. Current results showed that phosphorylation and total amount of p70S6K protein did not up-regulate in the ventral striatum along with behavioral sensitization. However, the phosphorylation of p70S6K substrate S6 (Ser235/236) protein increased in the ventral striatum of sensitized mice, reaching a peak level at 6 days of METH administration. In addition, we tested if mTOR would play a role during the expression of METH sensitization, animals were treated with mTOR inhibitor, rapamycin during withdrawal period. The results showed that injection of low-dose METH at withdrawal day 7 significantly suppressed the behavioral sensitization. To further substantiate the role of mTOR in neuroplasitcity of behaviorally sensitized mice, we observed if there is changes in amount of dendritic spines in the nucleus accumbens (both shell and core, as well as dorsal striatum) in METH-sensitized mice via Golgi stain. The results confirmed previous reports that mTOR did play an important role in regulating the neural plasticity, as numbers of dendritic spine in the NAc and striatum were both reduced after treatment of rapamycin. Finally, to pinpoint the role of mTOR in designated brain area, we applied LV-shRNA to knockdown mTOR as well as mTOR complex 1 (mTORC1)-related components -raptor and PRAS40, using Cre-loxp recombination technique followed by behavioral sensitization evaluation. The experiments are currently under investigation.
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