Thompson C L, Tehrani M H, Barnes E M, Stephenson F A
Department of Pharmaceutical and Biological Chemistry, School of Pharmacy, University of London, 29/39 Brunswick Square, London, WC1N 1AX, UK.
Brain Res Mol Brain Res. 1998 Oct 1;60(2):282-90. doi: 10.1016/s0169-328x(98)00205-8.
The cerebellar granule cells of the spontaneous recessive mutant mouse strain, stargazer (stg/stg), fail to express brain-derived neurotrophic factor mRNA. This deficit is exclusive to these neurons and is believed to underlie the motor irregularities displayed by stg/stg, though the molecular basis for their phenotype has still to be resolved. Brain-derived neurotrophic factor has been shown to play a role in the postnatal maturation of cerebellar granule cells. Differentiation of these neurons, postnatally, is characterised by a switch in their GABAA receptor subunit expression profile. Notably, the GABAA receptor alpha6 subunit, which is specific to these neurons, becomes detectable at postnatal days 10-14 (P10-14). To determine whether cerebellar GABAA receptor expression has been compromised in stg/stg mice, the expression levels of GABAA receptor alpha1, alpha6, beta2 and beta3 subunits were compared between stg/stg mice and the appropriate wild-type background strain, C57BL/6J (+/+). By quantitative immunoblotting, it was found that the expression of the alpha6 and beta3 subunits was 23+/-8% and 38+/-12% (mean+/-S.E.M., n=6) of control (+/+) levels, respectively. In contrast, the expression of the alpha1 and beta2 subunits was not significantly different from controls, being 116+/-11% and 87+/-24% (mean+/-S.E.M., n=6) of +/+ levels, respectively. Total specific [3H]Ro15-4513 binding activity detected in cerebellar membranes prepared from stg/stg was not significantly different from +/+ mice. However, the benzodiazepine agonist-insensitive subtype of [3H]Ro15-4513 binding activity, a pharmacological motif of alpha6 subunit-containing GABAA receptors, was lower in stg/stg mice relative to the +/+ strain which correlated with the lowered level of alpha6 subunit expression. Thus, we have identified an abnormality in the GABAA receptor profile of stg/stg mutant mice that might underpin its irregular phenotype.
自发隐性突变小鼠品系“凝视者”（stargazer，stg/stg）的小脑颗粒细胞无法表达脑源性神经营养因子mRNA。这种缺陷仅存在于这些神经元中，被认为是stg/stg小鼠表现出运动不规律的基础，尽管其表型的分子基础仍有待解决。脑源性神经营养因子已被证明在小脑颗粒细胞的出生后成熟过程中发挥作用。这些神经元在出生后的分化特征是其GABAA受体亚基表达谱的转变。值得注意的是，这些神经元特有的GABAA受体α6亚基在出生后第10 - 14天（P10 - 14）开始可检测到。为了确定stg/stg小鼠的小脑GABAA受体表达是否受损，比较了stg/stg小鼠与相应野生型背景品系C57BL/6J（+/+）中GABAA受体α1、α6、β2和β3亚基的表达水平。通过定量免疫印迹法发现，α6和β3亚基的表达分别为对照（+/+）水平的23±8%和38±12%（平均值±标准误，n = 6）。相比之下，α1和β2亚基的表达与对照无显著差异，分别为+/+水平的116±11%和87±24%（平均值±标准误，n = 6）。在从stg/stg小鼠制备的小脑膜中检测到的总特异性[3H]Ro15 - 4513结合活性与+/+小鼠无显著差异。然而，[3H]Ro15 - 4513结合活性中对苯二氮䓬激动剂不敏感的亚型，即含α6亚基的GABAA受体的药理学特征，在stg/stg小鼠中相对于+/+品系较低，这与α6亚基表达水平降低相关。因此，我们在stg/stg突变小鼠的GABAA受体谱中发现了一种异常，这可能是其不规律表型的基础。
