Fletcher E L, Wässle H
Max-Planck-Institut für Hirnforschung, D-60528 Frankfurt am Main, Germany.
J Comp Neurol. 1999 Oct 11;413(1):155-67. doi: 10.1002/(sici)1096-9861(19991011)413:1<155::aid-cne11>3.0.co;2-6.
gamma-Aminobutyric acid (GABA), is a main source of inhibitory modulation of the rod pathway in the mammalian retina. The authors previously showed that rod bipolar cells express at least three types of ionotropic GABA receptors. Here, the authors sought to determine which neurons are the presynaptic partners at these synapses in the rabbit retina. Indoleamine-accumulating amacrine cells (IACs) were immunolabeled with an antiserum against serotonin (5HT) in vertical sections and wholemounts of rabbit retinae that had been preloaded with 5HT. The tissue was double labeled for the rho subunits of the GABA(C) receptor or the alpha3 subunit of the GABA(A) receptor. Punctate immunofluorescence was observed for both receptor subunits and was found to coincide with the dendrites and varicosities of IACs. The localization of rho subunits was examined at the ultrastructural level by using postembedding techniques on slam-frozen, cryosubstituted tissue. Double labeling at the electron microscopic level revealed that 5HT-immunoreactive processes were presynaptic to rod bipolar cells through GABA(C) receptors. Intracellular injection of the two morphologic subclasses of IAC amacrine cells, S1 and S2, with Lucifer yellow followed by immunolabeling for the alpha3 or rho subunits revealed that varicosities on the dendrites of both cell types were in register with alpha3- and rho-immunoreactive puncta. Taken together, these results suggest that IACs are presynaptic to rod bipolar cells through GABA(C) receptors and possibly through GABA(A) receptors.
γ-氨基丁酸（GABA）是哺乳动物视网膜中视杆通路抑制性调节的主要来源。作者之前表明视杆双极细胞表达至少三种离子型GABA受体。在此，作者试图确定在兔视网膜中这些突触的突触前伙伴是哪些神经元。在预先用5-羟色胺（5HT）预加载的兔视网膜垂直切片和整装片中，用抗血清对吲哚胺积聚无长突细胞（IACs）进行5-羟色胺（5HT）免疫标记。对组织进行GABA(C)受体的rho亚基或GABA(A)受体的α3亚基的双重标记。观察到两种受体亚基均有斑点状免疫荧光，且发现其与IACs的树突和曲张体相符。通过对快速冷冻、冷冻置换组织采用包埋后技术，在超微结构水平上检查rho亚基的定位。电子显微镜水平的双重标记显示，5HT免疫反应性过程通过GABA(C)受体与视杆双极细胞形成突触前联系。用荧光黄对IAC无长突细胞的两种形态学亚类S1和S2进行细胞内注射，随后对α3或rho亚基进行免疫标记，结果显示两种细胞类型树突上的曲张体与α3和rho免疫反应性斑点对齐。综上所述，这些结果表明IACs通过GABA(C)受体，可能还通过GABA(A)受体与视杆双极细胞形成突触前联系。
