Zhao T J, Chiu T H, Rosenberg H C
Department of Pharmacology, Medical College of Ohio, Toledo 43699.
Mol Pharmacol. 1994 Apr;45(4):657-63.
Previous studies showed that chronic benzodiazepine administration in rats affected the gamma-aminobutyric acid (GABA)A/benzodiazepine receptor. The present experiment investigated the effects of chronic flurazepam treatment on the mRNA levels for alpha 1, alpha 5, gamma 2, and gamma 2L (an alternatively spliced product of the gamma 2 gene) subunits of the GABAA/benzodiazepine receptor in rat cerebral cortex, cerebellum, and hippocampus. Rats were treated with flurazepam for 2 or 4 weeks, and the mRNA levels were measured while rats were still receiving drug or 48 hr after 4-week flurazepam treatment had been stopped. The level of alpha 5 mRNA was also measured in other rats 4 hr after a single injection of flurazepam or diazepam. The levels of mRNAs were analyzed by Northern blotting using digoxigenin-labeled oligonucleotide probes. Compared with the pair-handled controls, the levels of gamma 2 subunit mRNA in cortex and hippocampus were not changed after flurazepam treatment for 2 weeks. However, with rats treated with flurazepam for 4 weeks the levels of gamma 2 subunit mRNA were significantly reduced in cortex (31%) and hippocampus (39%) but not in cerebellum. The values returned to control levels by 48 hr after termination of the treatment. The regional distribution and time course of reduced gamma 2 levels matched the decrease in benzodiazepine binding produced by the same chronic flurazepam treatment. The amounts of alpha 5 mRNA were reduced in cortex (23%) and hippocampus (18%) 4 hr after a single dose of flurazepam but not diazepam. The levels of alpha 5 mRNA remained reduced in cerebral cortex and hippocampus (about 50%) after 2 weeks but returned to control after 4 weeks of chronic treatment with flurazepam. No change in alpha 1 or gamma 2L subunit mRNAs was observed in any of the three brain regions examined after 4 weeks of flurazepam treatment. These results suggest that benzodiazepine receptor down-regulation after chronic benzodiazepine treatment may be related to the reduced expression of gamma 2 subunit mRNA, and they also suggest differential temporal and regional regulation of alpha 5 and gamma 2 subunit mRNAs in rat brain.
先前的研究表明，对大鼠长期给予苯二氮䓬会影响γ-氨基丁酸（GABA）A/苯二氮䓬受体。本实验研究了长期使用氟西泮治疗对大鼠大脑皮层、小脑和海马体中GABAA/苯二氮䓬受体的α1、α5、γ2和γ2L（γ2基因的一种可变剪接产物）亚基mRNA水平的影响。给大鼠使用氟西泮治疗2周或4周，在大鼠仍在接受药物治疗时或在4周氟西泮治疗停止后48小时测量mRNA水平。还在单次注射氟西泮或地西泮后4小时测量其他大鼠的α5 mRNA水平。使用地高辛标记的寡核苷酸探针通过Northern印迹法分析mRNA水平。与配对处理的对照组相比，氟西泮治疗2周后，皮层和海马体中γ2亚基mRNA水平没有变化。然而，氟西泮治疗4周的大鼠，皮层（31%）和海马体（39%）中γ2亚基mRNA水平显著降低，但小脑中未降低。治疗终止后48小时，这些值恢复到对照水平。γ2水平降低的区域分布和时间进程与相同的长期氟西泮治疗所产生的苯二氮䓬结合减少相匹配。单次给予氟西泮而非地西泮后4小时，皮层（23%）和海马体（18%）中的α5 mRNA量减少。氟西泮长期治疗2周后，大脑皮层和海马体中的α5 mRNA水平仍降低（约50%），但4周后恢复到对照水平。氟西泮治疗4周后，在所检查的三个脑区中均未观察到α1或γ2L亚基mRNA的变化。这些结果表明，长期苯二氮䓬治疗后苯二氮䓬受体下调可能与γ2亚基mRNA表达降低有关，并且它们还表明大鼠脑中α5和γ2亚基mRNA存在不同的时间和区域调节。
