De Biasi S, Vitellaro-Zuccarello L, Brecha N C
Department of General Physiology and Biochemistry, University of Milan, Italy.
Neuroscience. 1998 Apr;83(3):815-28. doi: 10.1016/s0306-4522(97)00414-4.
GABA plasma membrane transporters mediate GABA uptake into presynaptic terminals and surrounding glial processes and thus play a key role in shaping the time course and spatial extent of GABA's action. In the present study we have investigated the cellular and subcellular localization of two GABA transporters (1 and 3) in the rat thalamus using affinity-purified polyclonal antibodies. GABA transporter-1 and -3 immunoreactivity, detected with immunoperoxidase and immunofluorescence methods, is present throughout the thalamus in small punctate structures scattered in the neuropil among unlabelled neuronal perikarya. Labelling for GABA transporter-3 is always more intense than that for GABA transporter-1. Astrocytic processes, identified by their immunoreactivity for glial fibrillary acidic protein, express both GABA transporters. Ultrastructural investigations confirm that GABA transporter-1 and -3 labelling is restricted to astrocytes. Labelled astrocytes are adjacent to terminals making either symmetric or asymmetric synaptic contacts, and are close to neuronal profiles that do not form synaptic contacts in the plane of the section. In double-labelled thin sections some GABA transporter-1- or -3-positive astrocytic processes, detected with immunoperoxidase labelling, surround GABA-positive terminals, detected with antibodies to GABA and immunogold labelling. These findings demonstrate that in rat thalamus the GABA uptake system mediated by GABA transporter-1 and -3 is localized exclusively to astrocytes near the synapses and in the neuropil, and absent from GABAergic terminals. Astrocytes play therefore an important role in mediating GABA transmission in the thalamus, compared to cortical regions.
γ-氨基丁酸（GABA）质膜转运体介导GABA摄取到突触前终末和周围的胶质细胞突起中，因此在塑造GABA作用的时间进程和空间范围方面发挥关键作用。在本研究中，我们使用亲和纯化的多克隆抗体研究了大鼠丘脑中两种GABA转运体（1和3）的细胞和亚细胞定位。通过免疫过氧化物酶和免疫荧光方法检测到的GABA转运体-1和-3免疫反应性存在于整个丘脑中，呈小的点状结构，散布在未标记神经元胞体之间的神经毡中。GABA转运体-3的标记总是比GABA转运体-1的标记更强。通过其对胶质纤维酸性蛋白的免疫反应性鉴定的星形胶质细胞突起表达两种GABA转运体。超微结构研究证实，GABA转运体-1和-3的标记仅限于星形胶质细胞。标记的星形胶质细胞与形成对称或不对称突触接触的终末相邻，并且靠近在切片平面中不形成突触接触的神经元轮廓。在双重标记的薄切片中，一些用免疫过氧化物酶标记检测到的GABA转运体-1或-3阳性星形胶质细胞突起围绕着用GABA抗体和免疫金标记检测到的GABA阳性终末。这些发现表明，在大鼠丘脑中，由GABA转运体-1和-3介导的GABA摄取系统仅定位于突触附近和神经毡中的星形胶质细胞，而在GABA能终末中不存在。因此，与皮质区域相比，星形胶质细胞在介导丘脑中的GABA传递中起重要作用。
