THE DOPAMINERGIC AMACRINE CELL
THE DOPAMINERGIC AMACRINE CELL
复制标题
DOI：
10.1002/cne.903010310
复制
发表时间：
1990-11-15
影响因子：
2.5
通讯作者：
DACEY, DM
中科院分区：
文献类型：
--
作者：
DACEY, DM
用辣根过氧化物酶(HRP)细胞内注射的方法，在猕猴视网膜内观察到多巴胺能无长突细胞类型的详细形态。这种细胞类型是通过它的大胞体在体外用荧光染料丫啶橙染色的全视网膜制备而被识别的。HRP-Fill显示一棵大的、稀疏的分枝、多刺的树突和大量极细的轴突，这些突起来自胞体和近端的树突。轴突状突起点缀着明显的静脉曲张，在树突树外可追踪到长达3毫米。然而，轴突的真实长度大于3 mm，因为在到达终点之前，HRP反应产物一直在减少。树突和轴突均在靠近内网状层外缘的位置呈狭层状分布，但少数情况下单个轴突投射到外核层和外丛状层。充满HRP的长春瑞林似乎相当于对酪氨酸羟化酶(TH)有强烈免疫反应的神经元亚群。TH免疫反应细胞显示出几乎相同的胞体大小和树突野大小范围，相同的树突分支和刺状形态，并从胞体和近端的树突中产生明显的轴突。为了更直接地测试这种对应关系，向大的吖啶染色的细胞注射荧光黄，随后使用二氨基联胺作为染色试剂处理视网膜以检测TH免疫反应。在所有病例中，荧光黄注射的细胞也显示出强烈的TH免疫反应。因此，使用TH无长突细胞的空间密度来计算树突树和HRP填充细胞的轴突成分的复盖率。轴突状突起的覆盖系数至少为300，约为树突区的100倍。这种巨大的重叠可以直接在TH免疫反应的视网膜整体上观察到，它是一个致密的细小静脉曲张突起的神经丛。然而，TH神经丛的密度大于从充满HRP的轴突的长度(1-3 mm)预测的密度，这表明轴突的实际长度约为4-5 mm。多巴胺能无长突的双重形态，再加上前人对已发现的多巴胺能突触的研究，表明轴突上的突触是突触输出的主要来源，刺状树突是锥体双极细胞和其他无长突细胞突触输入的主要接受者。硬骨鱼中罕见的轴突延伸到外丛状层，以及目前对硬骨鱼中多巴胺能网状细胞的形态的了解，支持这样的假设，即多巴胺能无长突细胞和网状细胞代表单一的细胞类型，其中轴突的投射模式在物种之间存在数量差异。
The detailed morphology of the dopaminergic amacrine cell type has been characterized in the macaque monkey retina by intracellular injection of horseradish peroxidase (HRP). This cell type was recognized by its large soma in an in vitro, wholemount preparation of the retina stained with the fluorescent dye, acridine orange. HRP-fills revealed a large, sparsely branching, spiny dendritic tree and a number of extremely thin, axon-like processes that arose from the soma and proximal dendrites. The axon-like processes were studded with distinct varicosities and were traced for up to 3 mm beyond the dendritic tree. The true lengths of the axon-like processes were greater than 3 mm, however, because the HRP reactionproduct consistently diminished before an endpoint was reached. Both the dendrites and the axon-like processes were narrowly stratified close to the outer border of the inner plexiform layer, although in a few cases single axon-like processes projected into the outer nuclear and outer plexiform layers. The HRP-filled amacrines appeared equivalent to a subpopulation of neurons that are intensely immunoreactive for tyrosine hydroxylase (TH). TH-immunoreactive cells showed a nearly identical soma size and dendritic field size range, the same pattern of dendritic branching and spiny morphology, and also gave rise to distinct axon-like processes from both the soma and proximal dendrites. To test this correspondence more directly, the large acridine stained cells were injected with Lucifer Yellow and the retina was subsequently processed for TH immunoreactivity using diaminobenzidine as the chromagen. In all cases Lucifer Yellow injected cells also showed intense TH immunoreactivity. Spatial densities of the TH amacrine cells were therefore used to calculate coverage factors for the dendritic trees and for the axon-like components of the HRP-filled cells. The axon-like processes showed a coverage factor of at least 300, about 100 times that of the dendritic field. This great overlap could be directly observed in TH-immunoreacted retinal wholemounts as a dense plexus of fine, varicose processes. The density of the TH plexus is greater than the density predicted from the lengths (1-3 mm) of the HRP-filled axon-like processes however, and suggests that the axon-like processes have an actual length of about 4-5 mm. The dual morphology of the dopaminergic amacrine, coupled with the previous studies of identified dopaminergic synapses, suggests the hypothesis that the varicosities on the axon-like processes are the major source of synaptic output, and that the spiny dendrites are the major recipients of synaptic input from cone bipolar cells and other amacrine cells. The rare extension of the axon-like processes into the outer plexiform layer, and current understanding of the morphology of dopaminergic interplexiform cells in teleost fish, supports the hypothesis that the dopaminergic amacrine and interplexiform cells represent a single cell type in which there is quantitative variation across species in the projection pattern of the axon-like processes.