Vaughn J E, Famiglietti E V, Barber R P, Saito K, Roberts E, Ribak C E
J Comp Neurol. 1981 Mar 20;197(1):113-27. doi: 10.1002/cne.901970109.
GABAergic neurons have been identified in light and electron microscopic preparations of rat retina by an immunocytochemical localization of the GABA-synthesizing enzyme, glutamic acid decarboxylase (GAD). GAD-positive neuronal somata are found only in the inner and middle parts of the inner nuclear layer, and GAD-positive neuronal terminals are observed exclusively within the inner plexiform layer (IPL) and the outermost part of the ganglion cell layer. Dense aggregations of GAD-positive terminals alternate with less dense zones to form a lamination of the IPL. GAD-positive terminals contain pleomorphic synaptic vesicles and are the presynaptic elements of conventional synapses onto bipolar and amacrine cell processes, as well as onto the somata and dendrites of ganglion cells. In addition, GAD-positive terminals are postsynaptic to unstained bipolar terminals and are components of synaptic dyads where they occasionally appear to form reciprocal synapses with the bipolar terminals, and serial with unstained amacrine processes. Probable synaptic contacts between adjacent GAD-positive terminals also have been observed. Most of the synaptic input to GAD-positive terminals comes from bipolar cells, while the small remaining input mainly comes from other GAD-positive terminals. The synaptic output to GAD-positive terminals is greatest to bipolar cells, followed in decreasing order by GAD-negative amacrine cells, ganglion cells, and other GAD-positive cells. The total synaptic output of GAD-positive cells appears to be more than twice as great as the total input of these cells. The location of GAD-positive somata, the distribution of GAD-positive terminals, and the synaptic relationships formed by these terminals all indicate that amacrine cells are the only GABAergic neurons in rat retina. Our observations also indicate that not all amacrines are GABAergic and suggest that GABAergic neurons may be limited to a narrow field subclass of amacrine cell. The findings concerning the synaptic connections of GABAergic amacrines suggest that such cells are the first link in several divergent pathways from bipolar to ganglion cells and that they probably serve more than one function since they feed synaptic activity forward directly upon ganglion cells as well as back upon bipolar cells.
通过对γ-氨基丁酸（GABA）合成酶谷氨酸脱羧酶（GAD）进行免疫细胞化学定位，已在大鼠视网膜的光学显微镜和电子显微镜标本中鉴定出GABA能神经元。GAD阳性神经元胞体仅见于内核层的内侧和中间部分，而GAD阳性神经元终末仅在内网状层（IPL）和神经节细胞层的最外层被观察到。GAD阳性终末的密集聚集与较稀疏区域交替出现，形成IPL的分层。GAD阳性终末含有多形性突触小泡，是常规突触的突触前成分，这些突触作用于双极细胞和无长突细胞的突起，以及神经节细胞的胞体和树突。此外，GAD阳性终末是未染色双极终末的突触后成分，并且是突触双联的组成部分，在突触双联中它们偶尔似乎与双极终末形成相互突触，并与未染色的无长突细胞突起形成串联突触。相邻GAD阳性终末之间可能的突触接触也已被观察到。GAD阳性终末的大部分突触输入来自双极细胞，而其余少量输入主要来自其他GAD阳性终末。GAD阳性终末的突触输出最大的是双极细胞，其次按递减顺序是GAD阴性无长突细胞、神经节细胞和其他GAD阳性细胞。GAD阳性细胞的总突触输出似乎是这些细胞总输入的两倍多。GAD阳性胞体的位置、GAD阳性终末的分布以及这些终末形成的突触关系均表明无长突细胞是大鼠视网膜中唯一的GABA能神经元。我们的观察结果还表明，并非所有无长突细胞都是GABA能的，并提示GABA能神经元可能仅限于无长突细胞的一个狭窄的亚类。关于GABA能无长突细胞突触连接的研究结果表明，这类细胞是从双极细胞到神经节细胞的几条发散通路中的第一个环节，并且它们可能具有多种功能，因为它们既将突触活动直接向前传递给神经节细胞，又反馈给双极细胞。
