Nyíri G, Freund T F, Somogyi P
Institute of Experimental Medicine, Hungarian Academy of Sciences, Budapest, PO Box 67, H-1450 Hungary.
Eur J Neurosci. 2001 Feb;13(3):428-42. doi: 10.1046/j.1460-9568.2001.01407.x.
Pyramidal cells, expressing at least 14 subunits of the heteropentameric GABA(A) receptor, receive GABAergic input on their soma and proximal dendrites from basket cells, activating GABA(A) receptors and containing either parvalbumin or cholecystokinin and vasoactive intestinal polypeptide. The properties of GABA(A) receptors are determined by the subunit composition, and synaptic receptor content governs the effect of the presynaptic neuron. Using a quantitative electron microscopic immunogold technique, we tested whether the synapses formed by the two types of basket cell show a difference in the subunit composition of GABA(A) receptors. Terminals of one of the basket cells were identified by antibodies to parvalbumin. Synapses made by parvalbumin-negative terminals showed five times more immunoreactivity for the alpha(2) subunit than synapses made by parvalbumin-positive basket cells, whose synapses were frequently immunonegative. This difference is likely to be due to specific GABA(A) receptor alpha subunit composition, because neither synaptic size nor immunoreactivity for the beta(2/3) subunits, indicating total receptor content, was different in these two synapse populations. Synapses established by axo-axonic cells on axon initial segments showed an intermediate number of immunoparticles for the alpha(2) subunit compared to those made by basket cells but, due to their smaller size, the density of the alpha(2) subunit immunoreactivity was higher in synapses on the axon. Because the two basket cell types innervate the same domain of the pyramidal cell, the results indicate that pyramidal cells have mechanisms to target GABA(A) receptors, under presynaptic influence, preferentially to distinct synapses. The two basket cell types act via partially distinct GABA(A) receptor populations.
锥体细胞表达至少14种异五聚体GABA(A)受体亚基，其胞体和近端树突接受来自篮状细胞的GABA能输入，激活GABA(A)受体，篮状细胞含有小白蛋白或胆囊收缩素以及血管活性肠肽。GABA(A)受体的特性由亚基组成决定，突触受体含量决定突触前神经元的作用。我们使用定量电子显微镜免疫金技术，测试了两种类型篮状细胞形成的突触在GABA(A)受体亚基组成上是否存在差异。其中一种篮状细胞的终末通过抗小白蛋白抗体进行鉴定。小白蛋白阴性终末形成的突触对α(2)亚基的免疫反应性比小白蛋白阳性篮状细胞形成的突触高五倍，后者的突触通常免疫阴性。这种差异可能是由于特定的GABA(A)受体α亚基组成，因为这两种突触群体中，突触大小以及对β(2/3)亚基的免疫反应性（表明总受体含量）均无差异。轴-轴突细胞在轴突起始段形成的突触，其α(2)亚基的免疫颗粒数量介于篮状细胞形成的突触之间，但由于其尺寸较小，轴突上突触中α(2)亚基免疫反应性的密度更高。由于两种篮状细胞类型支配锥体细胞的同一区域，结果表明锥体细胞具有在突触前影响下将GABA(A)受体优先靶向不同突触的机制。两种篮状细胞类型通过部分不同的GABA(A)受体群体发挥作用。
