反复注射吗啡使大鼠脑内前强啡肽原mRNA和κ受体mRNA表达增强

REPEATED MORPHINE INJECTION INCREASED PREPRODYNORPHIN mRNA AND κ RECEPTOR mRNA EXPRESSION IN RAT BRAIN

为探讨急性吗啡耐受的分子机制，本研究观察了急性吗啡耐受对大鼠脑内与奖赏系统有关核团中前脑啡肽原、前强啡肽原和κ受体基因表达的影响。２４只雄性Ｗｉｓｔａｒ大鼠连续注射６次硫酸吗啡（６．２５ｍｇ／ｋｇ）或等体积生理盐水（１ｍｌ／ｋｇ），每两次注射间期为２ｈ。在最后一次注射后３０ｍｉｎ，断头取检测样品：全脑（除去皮层，小脑和低位脑干）、伏核、尾壳核、黑质。用灵敏的液相杂交ＲＮＡ酶保护分析法检测ｍＲＮＡ水平（ｐｇｍＲＮＡ／μｇ总ＲＮＡ）。结果显示：大鼠急性吗啡耐受时中枢神经系统强啡肽和κ受体基因ｍＲＮＡ增加（即基因表达增强），但不影响脑啡肽基因表达。以上结果提示强啡肽－κ受体系统可能参与了急性吗啡耐受的形成。此外，尾壳核前强啡肽基因表达增强、黑质κ受体表达减弱，提示多次吗啡注射影响了脑内与奖赏系统有关核团中强啡肽－κ受体系统基因的表达。

The Purpose of this study was to determine the effect of repeated morphine administration on opioid peptides and kappa receptor gene mRNA levels in specific brain regions related with rewarding and aversive properties. Male Wistar rats were given 6 consecutive subcutaneous injection of morphine sulfate (6.25 mg/ kg) or normal saline (1 ml/ kg) at 2 hour intervals. Thirty min after final injection, the whole brain (except cortex, cerebellum and lower brain stem) and regions of interest were dissected. Using a quantitative solution hybridization protection assay for mRNA levels (pg mRNA/ μg total RNA ), we detected: 1. the concentration of preprodynorphin for morphine treated vs normal saline control group in the whole brain 1.34 ±0.06 vs 0.82±0.14(ANOVA, P<0.01), in nucleus accumbens 8.41±1.39 vs 10.28±0.67 (P=0.26) and in caudate putamen 7.88±0.50 vs 6.23±0.38 (P<0.05); 2. the concentration of preproenkephalin for morphine treated vs normal saline control group in the whole brain 8.33± 0.51 vs 8.84±1.37 (P=0.73), in nucleus accumbens 18.62±1.96 vs 20.37±2.23 (P=0.58) and in caudate putamen 37.07±2.81 vs 29.62±3.09 (P=0.11); 3. the concentration of kappa receptor for the 2 groups in the whole brain 0.70±0.07 vs 0.47±0.02 (P<0.01), in caudate putamen 1.51±0.19 vs 1.76±0.34 (P=0.54) and in substantia nigra 0.36±0.07 vs 0.66±0.11 (P=0.05, marginally significant). The data first indicated that brain dynorphin κ receptor system may be involved in the development of acute morphine tolerance, and that repeated morphine injection may effect dynorphine κ system in brain nuclei associated with rewarding and aversion.