哺乳动物视网膜中的无长突神经元包含具有不同性质和功能的多种细胞类型,其用于整合和调节呈现给输出神经元的信号。它们中的大多数使用甘氨酸或GABA作为抑制性神经递质,并表达甘氨酸转运蛋白1(GlyT1)或谷氨酸脱羧酶(GAD67)和GABA转运蛋白(GAT1和GAT3),分别作为甘氨酸能或GABA能标记物。我们在这里报道了一个新的无长碱神经元亚群,GABA能和甘氨酸能标志物,在来自野生型C57BL/6J小鼠和两个转基因品系的视网膜中。在甘氨酸转运蛋白2控制下表达eGFP的转基因系的视网膜切片中,eGFP表达仅在抑制性无长突神经元的细胞体和树突中发现,鉴定出它们对突触素1A的免疫反应性。所有的甘氨酸能和大部分的GABA能无能神经元都含有eGFP;其中,8-10%的GlyT1阳性神经元也用GAD67、GAT1或GAT3标记。这些发现在来自野生型和在GAD67启动子和两种不同的抗GlyT1抗体下表达eGFP的小鼠品系的视网膜中得到证实。显示存在具有双重表型的亚群。此外,在两个小鼠品系上的eGFP阳性树突被发现与GlyR亚基和支架蛋白gephyrin在内丛状层的几个区域并列,证明了这些神经元的甘氨酸能特性。这种双重表型也在原代视网膜培养物中得到证实,其中分离的神经元对GlyT1和GAD67或GAT1/3呈阳性。总之,这些数据提供了双重抑制亚群的令人信服的证据,甘氨酸能/GABA能无长突神经元。两种神经递质的共同释放可能有助于在突触过度兴奋下加强对神经节细胞的抑制。
The amacrine neurons in the mammalian retina comprise a large variety of cell types with distinct properties and functions that serve to integrate and modulate signals presented to output neurons. The majority of them use either glycine or GABA as inhibitory neurotransmitters and express the glycine transporter 1 (GlyT1) or glutamic acid decarboxylase (GAD67) and GABA transporters (GAT1 and GAT3), as a
glycinergic or GABAergic marker respectively. We report here a novel subpopulation of amacrine neurons expressing both, GABAergic and
glycinergic markers, in retinas from wild-type C57BL/6J mice and two transgenic lines. In retinal sections from the transgenic line expressing eGFP under the control of the glycine transporter 2, eGFP expression was exclusively found in cell bodies and dendrites of inhibitory amacrine neurons, identified for their immunoreactivity to syntaxin 1A. All of the
glycinergic and a large portion of the GABAergic amacrine neurons contained eGFP; of these, 8-10% of GlyT1 positive neurons were also labeled either with GAD67, GAT1 or GAT3. These findings were confirmed in retinas from a wild-type and a mouse line expressing eGFP under the GAD67 promoter and two different anti-GlyT1 antibodies, showing the presence of a subpopulation with a dual phenotype. Moreover, eGFP-positive dendrites on both mouse lines were found juxtaposed to GlyR subunits and the scaffold protein gephyrin in several areas of the inner plexiform layer, demonstrating the
glycinergic character of these neurons. This dual phenotype was also demonstrated in primary retina cultures, in which isolated neurons were positive for GlyT1 and GAD67 or GAT1/3. Altogether, these data provide compelling evidence of a subpopulation of dual inhibitory,
glycinergic/GABAergic amacrine neurons. The co-release of both neurotransmitters may serve to strengthen the inhibition on ganglion cells under synaptic hyperexcitability.