Light and dark adaptation in the primate retina

视觉系统对巨大范围的环境光照保持反应，这种适应完全在视网膜内完成。虽然一些敏感性的变化是由视杆细胞和视锥细胞本身介导的，但视网膜上的其他神经元也对适应做出了重要贡献。多巴胺将是第一个拨款期的重点，因为它被认为在光适应中起着关键作用，改变化学和电突触的强度，使视网膜在背景光强度增加时保持对对比度的敏感。作为哺乳动物多巴胺能神经元的主要靶点，所有的无毛细胞都被多巴胺和光刺激解耦。然而，哺乳动物视网膜中的多巴胺对光线的其他影响以及多巴胺在黑暗适应中扮演的角色（如果有的话）仍然不确定。去年，人们首次描述了多巴胺能神经元的膜特性，并在体外发现它们可以自发地激发动作电位。另外两个令人惊讶的新发现是，在完全黑暗的情况下，所有的无突细胞都被分离，多巴胺从视网膜释放出来。这些数据导致了一种假设，即多巴胺能神经元在完全黑暗的环境中自发活动，在暗背景下被强直抑制，在明亮的背景下同时接受兴奋性和抑制性输入。所提出的实验的目标是使用计算机模型更严格地检验这一假设的要素。很明显，多巴胺能视网膜神经元在人类视觉中起着重要作用，因为多巴胺能神经元退化的帕金森病患者和服用阻断多巴胺受体的抗精神病药物的患者的视网膜电图异常。这些实验的结果可能也适用于中枢神经系统其他部位的多巴胺能神经元。例如，多巴胺对电偶联的影响是在视网膜中发现的，后来发现也发生在大脑中。

The visual system remains responsive over an enormous range of ambient illumination, and this adaptation is accomplished entirely within the retina. While some of these changes in sensitivity are mediated by the rods and cones, themselves, there are also important contributions to adaptation from the other neurons in the retina. Dopamine will be the focus in the first grant period because it is thought to play a critical role in light adaptation, changing the strength of chemical and electrical synapses so that the retina remains sensitive to contrast as the intensity of the background light increases. The major targets of the dopaminergic neurons in mammals, All amacrine cells are known to be uncoupled both by dopamine and b photopic light stimulation. However, it is still uncertain which other effects of light are attributable to dopamine in mammalian retinas and what role, if any, dopamine plays in dark adaptation. Last year, the membrane properties of dopaminergic neurons were described for the first time, and they were found to fire action potentials spontaneously in vitro. Two other surprising, new findings were that, in total darkness, All amacrine cells are uncoupled and dopamine is released from the retina. These data led to the hypothesis that dopaminergic neurons are spontaneously active in total darkness, tonically inhibited in scotopic backgrounds and receive both excitatory and inhibitory input in brighter background. The goal of the proposed experiments is to test elements of this hypothesis more rigorously using computer models. It is clear that dopaminergic retinal neurons pla an important role in human vision since the electroretinogram is abnormal in patients with Parkinson's disease, in which dopaminergic neurons degenerate, and in patients taking neuroleptic drugs that block dopamine receptors. The results of these experiments may also be applicable to dopaminergic neurons elsewhere in the Central nervous system. For example, the effect of dopamine on electrical coupling was discovered in the retina and later found to occur in the brain, as well.