GABAA receptor γ2 subunit knockdown mice have enhanced anxiety-like behaviour but unaltered hypnotic response to benzodiazepines -: art. no. 30
GABAA receptor γ2 subunit knockdown mice have enhanced anxiety-like behaviour but unaltered hypnotic response to benzodiazepines -: art. no. 30
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DOI：
10.1186/1471-2202-6-30
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发表时间：
2005-04-25
期刊：
影响因子：
2.4
通讯作者：
Homanics, GE
中科院分区：
文献类型：
--
作者：
Chandra, D;Korpi, ER;Homanics, GE
背景：γ-氨基丁酸A型受体(GABA(A)-Rs)是哺乳动物大脑中的主要抑制性受体，受包括苯二氮卓类和麻醉药在内的多种镇静/催眠药物的调节。关于特定的GABA(A)-Rs亚基在行为和体内药物反应中的重要性，人们还没有完全了解。伽马2亚单位在整个大脑中高度表达。全球伽马2基因敲除小鼠对安定的催眠作用不敏感，并在围产期死亡。杂合的伽马2基因敲除小鼠是可以存活的，并且有更多的焦虑样行为。为了进一步研究伽马2亚单位在行为学和整体动物药物作用中的作用，我们利用基因打靶技术建立了一种新的伽马2基因表达减弱的小鼠系，即伽马2基因敲除小鼠。结果：通过在伽马2基因内含子8中插入新霉素抗性盒，建立了伽马2基因敲除小鼠。平均而言，与对照组相比，基因敲除小鼠的Gamma 2亚单位mRNA减少了65%；然而，这些小鼠的Gamma 2基因表达变化很大，从正常的10%到95%不等。免疫组织化学研究表明，伽马2蛋白水平也有不同程度的降低。在冰冻脑切片上使用放射自显影进行的药理学研究表明，与对照组相比，突变小鼠的苯二氮卓类位点配体Ro15-4513的结合减少。在行为学上，基因敲除小鼠在高架加迷宫和强迫新奇探索测试中表现出增强的焦虑样行为。令人惊讶的是，突变小鼠对催眠剂量的苯二氮卓类位点配体安定、咪达唑仑和唑吡坦以及乙醇和戊巴比妥的反应没有改变。结论：1)在伽马2基因内含子8中插入新霉素抗性基因可以可变地减少伽马2的含量，2)减弱伽马2的表达可增加焦虑样行为，但不会导致对苯二氮卓类配体的催眠反应的差异。这表明，减少突触抑制可以导致焦虑样行为增加的表型。相反，尽管GABA(A)-R靶点大幅减少，正常的药物效应仍然可以保持。
Background: Gamma-aminobutyric acid type A receptors (GABA(A)-Rs)are the major inhibitory receptors in the mammalian brain and are modulated by a number of sedative/hypnotic drugs including benzodiazepines and anesthetics. The significance of specific GABA(A)-Rs subunits with respect to behavior and in vivo drug responses is incompletely understood. The gamma 2 subunit is highly expressed throughout the brain. Global gamma 2 knockout mice are insensitive to the hypnotic effects of diazepam and die perinatally. Heterozygous gamma 2 global knockout mice are viable and have increased anxiety-like behaviors. To further investigate the role of the gamma 2 subunit in behavior and whole animal drug action, we used gene targeting to create a novel mouse line with attenuated gamma 2 expression, i.e., gamma 2 knockdown mice.Results: Knockdown mice were created by inserting a neomycin resistance cassette into intron 8 of the gamma 2 gene. Knockdown mice, on average, showed a 65% reduction of gamma 2 subunit mRNA compared to controls; however gamma 2 gene expression was highly variable in these mice, ranging from 10-95% of normal. Immunohistochemical studies demonstrated that gamma 2 protein levels were also variably reduced. Pharmacological studies using autoradiography on frozen brain sections demonstrated that binding of the benzodiazepine site ligand Ro15-4513 was decreased in mutant mice compared to controls. Behaviorally, knockdown mice displayed enhanced anxiety-like behaviors on the elevated plus maze and forced novelty exploration tests. Surprisingly, mutant mice had an unaltered response to hypnotic doses of the benzodiazepine site ligands diazepam, midazolam and zolpidem as well as ethanol and pentobarbital. Lastly, we demonstrated that the g2 knockdown mouse line can be used to create gamma 2 global knockout mice by crossing to a general deleter cre- expressing mouse line.Conclusion: We conclude that: 1) insertion of a neomycin resistance gene into intron 8 of the gamma 2 gene variably reduced the amount of gamma 2, and that 2) attenuated expression of gamma 2 increased anxiety- like behaviors but did not lead to differences in the hypnotic response to benzodiazepine site ligands. This suggests that reduced synaptic inhibition can lead to a phenotype of increased anxiety- like behavior. In contrast, normal drug effects can be maintained despite a dramatic reduction in GABA(A)-R targets.