Department of Molecular, Cellular, and Developmental Biology, and Neuroscience Research Institute, University of California at Santa Barbara, Santa Barbara, California 93106, USA.
J Neurosci. 2010 Feb 3;30(5):1677-85. doi: 10.1523/JNEUROSCI.5153-09.2010.
To establish dendritic arbors that integrate properly into a neural circuit, neurons must rely on cues from the local environment. The neurons presynaptic to these arbors, the afferents, are one potential source of these cues, but the particular dendritic features they regulate remain unclear. Retinal bipolar cells can be classified by the type of photoreceptor, cone or rod, forming synaptic contacts with their dendrites, suggesting a potential role of these afferents in shaping the bipolar cell dendritic arbor. In the present investigation, the role of photoreceptors in directing the differentiation of bipolar cells has been studied using two genetically modified "coneless" and "conefull" mice. Single cone (Type 7/CB4a) and rod bipolar cells were labeled with DiI to reveal the entire dendritic arbor and subsequently analyzed for several morphological features. For both cone and rod bipolar cells, the dendritic field area, number of dendritic terminals, and stratification of terminals in the outer plexiform layer were comparable among coneless, conefull, and wild-type retinas, and the overall morphological appearance of each type of cell was essentially conserved, indicating an independence from afferent specification. The presence of normal afferents was, however, found to be critical for the proper spatial distribution of dendritic terminals, exhibiting a clustered distribution for the cone bipolar cells and a dispersed distribution for the rod bipolar cells. These results demonstrate a selectivity in the afferent dependency of bipolar cell differentiation, their basic morphogenetic plan commanded cell intrinsically, and their fine terminal connectivity directed by the afferents themselves.
为了使树突分支正常整合到神经网络中，神经元必须依赖于来自局部环境的线索。这些树突分支的前突触神经元，即传入神经元，是这些线索的一个潜在来源，但它们调节的特定树突特征仍不清楚。视网膜双极细胞可以根据光感受器的类型（视锥或视杆）进行分类，与它们的树突形成突触接触，这表明这些传入神经元在塑造双极细胞树突分支方面可能发挥作用。在本研究中，使用两种遗传修饰的“无锥”和“全锥”小鼠研究了光感受器在指导双极细胞分化中的作用。用 DiI 标记单锥（Type 7/CB4a）和视杆双极细胞，以揭示整个树突分支，并随后对几个形态特征进行分析。对于视锥和视杆双极细胞，无锥、全锥和野生型视网膜的树突场面积、树突末梢数量和外丛状层末梢的分层情况相当，每种细胞的整体形态外观基本保持不变，表明其不受传入神经元的特异性影响。然而，研究发现，正常传入神经元的存在对于树突末梢的适当空间分布是至关重要的，视锥双极细胞的末梢表现出簇状分布，而视杆双极细胞的末梢则表现出分散分布。这些结果表明双极细胞分化的传入神经元依赖性具有选择性，其基本形态发生计划由细胞自身决定，而末梢的精细连接则由传入神经元自身指导。
