Raven Mary A, Orton Noelle C, Nassar Hadi, Williams Gary A, Stell William K, Jacobs Gerald H, Bech-Hansen N Torben, Reese Benjamin E
Neuroscience Research Institute, University of California, Santa Barbara 93106-5060, USA.
J Comp Neurol. 2008 Feb 10;506(5):745-58. doi: 10.1002/cne.21526.
The dendritic patterning of retinal horizontal cells has been shown to be specified by the cone photoreceptor afferents. The present investigation has addressed whether this specification is due to visually dependent synaptic transmission in the outer plexiform layer or to some other early, pre-visual, neural activity. Individually labeled horizontal cells from dark-reared mice, as well as from mice carrying a mutation in the Cacna1f gene, which encodes the pore-forming calcium channel subunit Ca(v)1.4, were assessed for various morphological features. The dark-reared mice showed no alteration in any of these features, despite showing a compromised maximal voltage response in the electroretinograms. The retinas of Cacna1f mutant mice, by contrast, showed conspicuous morphological changes that mimicked the effects observed previously in coneless transgenic mice. These changes were present as early as postnatal day 10, when the shape and density of the cone pedicles appeared normal. Ultrastructurally, however, the pedicles at this early stage, as well as in maturity, lacked synaptic ribbons and the invaginations associated with postsynaptic processes. These results suggest a role for this calcium channel subunit in ribbon assembly in addition to its role in modulating calcium influx and glutamate release. Together, they suggest a complex cascade of interactions between developing cone pedicles and horizontal cell dendrites involving early spontaneous activity, dendritic attraction, ribbon assembly, and pedicle invagination.
视网膜水平细胞的树突形态已被证明由视锥光感受器传入信号所决定。本研究探讨了这种决定作用是由于外网状层中视觉依赖的突触传递，还是由于其他一些早期的、视觉前的神经活动。对来自暗饲养小鼠以及携带编码孔形成钙通道亚基Ca(v)1.4的Cacna1f基因突变小鼠的单个标记水平细胞进行了各种形态学特征评估。尽管暗饲养小鼠的视网膜电图中最大电压反应受损，但这些小鼠在任何这些特征上均未显示出改变。相比之下，Cacna1f突变小鼠的视网膜显示出明显的形态学变化，这些变化与先前在无视锥转基因小鼠中观察到的效应相似。这些变化早在出生后第10天就已出现，此时视锥小足的形状和密度看起来正常。然而，在超微结构上，这个早期阶段以及成熟阶段的小足都缺乏突触带以及与突触后过程相关的内陷。这些结果表明，除了其在调节钙内流和谷氨酸释放中的作用外，该钙通道亚基在突触带组装中也发挥作用。总之，它们表明发育中的视锥小足和水平细胞树突之间存在复杂的相互作用级联，涉及早期自发活动、树突吸引、突触带组装和小足内陷。
