Bodnarenko S R, Chalupa L M
Department of Psychology, University of California, Davis 95616-0657.
Nature. 1993 Jul 8;364(6433):144-6. doi: 10.1038/364144a0.
A fundamental attribute of the vertebrate visual system is the segregation of ON and OFF pathways signalling increments and decrements of light. In the mature retina, dendrites of ON- and OFF-centre retinal ganglion cells (RGCs) stratify in different sublaminae of the inner plexiform layer (IPL), and are differentially innervated by two types of bipolar cells which depolarize and hyperpolarize on exposure to light. This stratification of ON and OFF RGCs is achieved by the gradual restriction of their dendrites which ramify throughout the IPL early in development. The factors underlying this regressive event are unknown. Dendritic stratification occurs around the time that bipolar cells form synapses in the IPL, which raises the possibility that synaptic activity is involved in this process. Here we test this hypothesis by treating the developing cat retina with the glutamate analogue 2-amino-4-phosphonobutyric acid (APB), which hyperpolarizes ON cone bipolar and rod bipolar cells, thereby preventing their release of glutamate. We report that intraocular injection of APB during the period when dendritic stratification normally occurs prevents the formation of structurally segregated ON and OFF retinal pathways. These results provide evidence that glutamate-mediated afferent activity regulates the remodelling of RGC dendrites during development.
脊椎动物视觉系统的一个基本特征是ON通路和OFF通路的分离，它们分别传导光强度的增加和减少信号。在成熟的视网膜中，ON中心和OFF中心视网膜神经节细胞（RGC）的树突在内网状层（IPL）的不同亚层中分层，并且由两种在受到光照时去极化和超极化的双极细胞进行不同的神经支配。ON和OFF RGC的这种分层是通过它们的树突在发育早期在整个IPL中分支，然后逐渐受限来实现的。导致这一退行性事件的因素尚不清楚。树突分层发生在双极细胞在IPL中形成突触的时期左右，这增加了突触活动参与这一过程的可能性。在这里，我们通过用谷氨酸类似物2-氨基-4-膦酰丁酸（APB）处理发育中的猫视网膜来检验这一假设，APB可使ON锥双极细胞和杆双极细胞超极化，从而阻止它们释放谷氨酸。我们报告说，在树突分层正常发生的时期，眼内注射APB会阻止结构上分离的ON和OFF视网膜通路的形成。这些结果提供了证据，表明谷氨酸介导的传入活动在发育过程中调节RGC树突的重塑。
