Addiction liability and depressive phenotype in NPFFR2 transgenic mice

• Main Authors: Ching Yao Yang, 楊景堯
• Other Authors: J. C. Chen
• Format: Others
• Published: 2012
• Online Access: http://ndltd.ncl.edu.tw/handle/34052881871503436360

碩士 === 長庚大學 === 生物醫學研究所 === 100 === Neuropeptide FF (NPFF, F-L-F-Q-P-Q-R-F-NH2) was originally isolated from bovine brain in 1985, using antiserum against the molluscan peptide FMRF-amide. There are two types of NPFF receptors, i.e. NPFFR1 and NPFFR2, which are G protein couple receptors, and NPFF receptor type 2 bears high binding affinity towards NPFF. In the present study, we produced NPFFR2 over-expressed mice under the control of NSE promoter to explore the physiological functions of NPFF-NPFFR2, a presumed anti-opioid system. In the pioneer study, we proved that NPFFR2 Tg mice process lower threshold towards thermal and mechanical algesic stimulation. On the other hand, NPFF was reported to suppress morphine-induced behavioral sensitization and enhanced dopamine metabolism in the nucleus accumbens (NAc). Brain NPFF system has also been linked with affective disorders, such as depression and anxiety. Hence, we first performed a series of behavioral tests to fully characterize the behavioral and biochemical phenotypes of NPFFR2 Tg mice. Locomotor activity was monitored for determining morphine and methamphetamine behavioral sensitization. Forced-swimming and tail-suspension tests were used to characterize anxiety and depressive behaviors. Results show that NPFFR2 Tg mice process normal response to locomotor activity as well as morphine- and methamphetamine-induced behavioral sensitization. On the other hand, NPFFR2 Tg mice have a tendency towards depression. In addition, we also performed morphine-conditioned place preference (CPP) to both groups of mice since CPP was designed to evaluate drug rewarding, but there was no obvious difference between wt and NPFFR2 Tg mice. To correlate with cellular mechanism, a set of animals were sacrificed, distinct brain area dissected then subjected to HPLC-ECD analyses for monoamine quantification. Results show that levels of 5-HT reduced in various serotonergic projecting area, however amounts of TH, phospho-TH, 5-HT1A receptor, SERT and TPH by western blot were similar between Tg and wt mice. Since depressive behavior and 5-HT reduction could link with adult hippocampus neurogenesis in the subgranular zone (SGZ), we traced stem cell proliferation up to neurogenesis stage via BrdU labeling and specific markers by immunohistological stain. Results show that SGZ stem cells proliferation reduced significantly in the NPFFR2 Tg mice but neurogenesis remained similar as compared to wt control. Finally, since NPFFR2 mice display depression liability, we treated Tg mice with antidepressant, fluoxetine (FLX) for either acute or chronic (28 days) systemic administration. The results show that acute FLX treatment decreased significantly the depressive behavior. On the other hand, FLX treatment for 28 days resulted in enhanced hippocampal neurogenesis in both wt and NPFFR2 Tg mice. Overall, we conclude NPFFR2 Tg mice exert normal basal locomotor activity as well as response to morphine- and methamphetamine-induced behavioral sensitization. However, NPFFR2 Tg mice appear to process depressive behavior, possibly due to brain 5-HT defect and reduced hippocampal stem cell proliferation.