Huntsman M M, Isackson P J, Jones E G
Department of Anatomy and Neurobiology, University of California, Irvine 92717.
J Neurosci. 1994 Apr;14(4):2236-59. doi: 10.1523/JNEUROSCI.14-04-02236.1994.
Seven monkey-specific GABAA receptor subunit cDNAs were isolated and cloned; radioactive cDNA and cRNA probes derived from them were used for Northern blot analysis and in situ hybridization histochemistry of the primary visual cortex (area 17), with comparative observations on other cortical areas. cDNAs corresponding to alpha 1, alpha 2, alpha 4, alpha 5, beta 1, beta 2, and gamma 2 GABAA receptor subunits were isolated and had sequences unique to the monkey but recognized mRNAs of distinct molecular weights consistent with those reported in other species. mRNAs for the alpha 1, beta 2, and gamma 2 subunits were expressed at much higher levels in area 17 than in motor, somatosensory, or temporal association cortex, possibly reflecting the greater density of GABA cells and synapses in area 17. In areas 17 and 18, each of the seven subunit mRNAs showed individually distinct patterns of laminar distribution. alpha 1, beta 2, and gamma 2 subunit mRNAs, which are thought to form the basis of receptors with the full range of classical GABAA receptor properties in the adult, were particularly enriched in layers II-III, IVC, and VI of area 17, following patterns of receptor distribution previously demonstrated by radioligand binding and immunocytochemistry. alpha 2, alpha 4, alpha 5, and beta 1 transcripts had quite different localization patterns that did not match the antoradiographic or immunocytochemical receptor localization patterns. alpha 2 and alpha 5 subunit mRNAs, which are thought to be the subunits mainly expressed in development, were enriched in layer VI and the underlying white matter, possibly reflecting the involvement of receptors formed from alpha 2 and alpha 5 polypeptides in trophic interactions in the cortical subplate zone during development of the cerebral cortex. Following 8-21 d periods of monocular deprivation induced by intravitreal injection of TTX, levels of alpha 1, beta 2, and gamma 2 subunit mRNAs were substantially reduced in deprived ocular dominance columns of layer IVC in area 17. The effect was greatest for the alpha 1 subunit; for both alpha 1 and gamma 2 subunit mRNAs, it extended into deprived rows of cytochrome oxidase-identified periodicities in other layers. Apart from the alpha 5 subunit mRNA, which showed reduced levels in layer VI, the other subunit mRNAs were unaffected by monocular deprivation. These results demonstrate the heterogeneity of GABAA receptor subunit expression in a complex, multilaminar cortical area. They suggest that receptors with different functional properties may be assembled from different combinations of subunit polypeptides in different layers and show that subunit expression is differentially regulated under activity-dependent conditions.
七个猴特异性GABAA受体亚基cDNA被分离和克隆；从它们衍生的放射性cDNA和cRNA探针用于初级视皮层（17区）的Northern印迹分析和原位杂交组织化学，并对其他皮层区域进行了比较观察。分离出了与α1、α2、α4、α5、β1、β2和γ2 GABAA受体亚基相对应的cDNA，其序列是猴所特有的，但能识别与其他物种报道的分子量不同的mRNA。α1、β^2和γ2亚基的mRNA在17区的表达水平远高于运动、躯体感觉或颞叶联合皮层，这可能反映了17区GABA能细胞和突触的密度更高。在17区和18区，七个亚基mRNA各自呈现出独特的层状分布模式。α1、β2和γ2亚基mRNA，被认为是构成成年后具有全套经典GABAA受体特性的受体的基础，在17区的II-III层、IVC层和VI层中特别富集，遵循先前通过放射性配体结合和免疫细胞化学所证明的受体分布模式。α2、α4、α5和β1转录本具有截然不同的定位模式，与放射自显影或免疫细胞化学受体定位模式不匹配。α2和α5亚基mRNA，被认为是主要在发育过程中表达的亚基，在VI层和下层白质中富集，这可能反映了在大脑皮层发育期间，由α2和α5多肽形成的受体参与了皮层下板区的营养相互作用。在玻璃体内注射TTX诱导的8-21天单眼剥夺期后，17区IVC层被剥夺的眼优势柱中α1、β2和γ2亚基mRNA的水平显著降低。对α1亚基的影响最大；对于α1和γ2亚基mRNA，这种影响延伸到其他层中由细胞色素氧化酶确定的周期性的被剥夺行。除了α5亚基mRNA在VI层中水平降低外，其他亚基mRNA不受单眼剥夺的影响。这些结果证明了在一个复杂的多层皮层区域中GABAA受体亚基表达的异质性。它们表明具有不同功能特性的受体可能由不同层中不同亚基多肽的组合组装而成，并表明亚基表达在活动依赖的条件下受到差异调节。
