Neuromodulators and Signaling Cascades in Retina

描述(申请人提供)：感光细胞是视觉系统的主要感觉神经元。除了受光调节外，光感受器生理的某些方面还受神经调节剂的控制，如多巴胺、腺苷、生长抑素和一氧化氮。支持这些物质在光感受器细胞功能中发挥作用的大部分数据本质上是药理学的，从非哺乳动物脊椎动物获得，关于涉及的信号机制还有很多需要了解。我们在小鼠身上的初步数据导致了这样的假设，即多巴胺作用于多巴胺D4受体，通过钙依赖的腺酰环化酶调节，以及通过调节连接光暴露与抑制cAMP形成的信号级联元件的基因表达，在调节光感受器细胞的cAMP代谢中发挥主要作用。初步数据还表明，多巴胺在小鼠视网膜对变化的光照的适应性反应中发挥主要作用，可能是通过cAMP依赖的机制。目前的目标是验证这些假说，从而阐明多巴胺在光和暗适应过程中对光感受器基因表达和视网膜功能产生影响的信号机制。以小鼠视网膜为实验模型，我们将检验以下假设的预测：(1)光感受器细胞上的多巴胺D4受体调节光暴露与抑制cAMP合成的信号通路的一个或多个组成部分的基因表达。(2)多巴胺D4受体缺陷小鼠光感受器cAMP调节功能障碍改变了光感受器基因表达谱和关键基因产物的翻译后修饰。(3)多巴胺和光通过降低钙/钙调蛋白刺激的腺苷环化酶的活性来降低光感受器cAMP水平。(4)在多巴胺D4受体缺陷小鼠中，钙/钙调素刺激的腺苷酸环化酶(S)的表达减少，导致光和暗适应的异常。这些实验的结果将大大加深我们对多巴胺和cAMP如何调制光感受器功能，特别是光和暗适应的理解。

DESCRIPTION (provided by applicant): Photoreceptor cells are the primary sensory neurons of the visual system. In addition to being regulated by light, aspects of photoreceptor physiology are subject to control by neuromodulators, such as dopamine, adenosine, somatostatin, and nitric oxide. Much of the data supporting a role for these substances in photoreceptor cell function is pharmacological in nature, obtained from non-mammalian vertebrates, and much remains to be learned about the signaling mechanisms involved. Our preliminary data in mouse led to the hypothesis that dopamine, acting on dopamine D4 receptors, plays a major role in regulating cAMP metabolism in photoreceptor cells by Ca 2+ -dependent regulation of adenylyl cyclase and by regulating gene expression for components of the signaling cascade that links light exposure to inhibition of cAMP formation. Preliminary data also show that dopamine plays a major role in adaptive responses of mouse retina to changing illumination, possibly through a cAMP-dependent mechanism. The present goal is to test these hypotheses and to thereby elucidate the signaling mechanisms whereby dopamine produces it's effects on photoreceptor gene expression and retinal function during light- and dark-adaptation. Using mouse retina as an experimental model, we will test the following predictions of hypotheses: (1) Dopamine D4 receptors on photoreceptor cells regulate gene expression of one or more components of the signaling pathway that couples light-exposure to suppression of cAMP synthesis. (2) Dysfunctional cAMP regulation in photoreceptors of dopamine D4 receptor deficient mice alters photoreceptor gene expression profiles and posttranslational modification of key gene products, such as phosducin. (3) Dopamine and light decrease photoreceptor cAMP levels by reducing the activity of Ca 2+ / calmodutin-stimulated adenylyl cyclases. (4) Decreased expression of Ca 2+ / calmodulin-stimulated adenylyl cyclase(s) leads to the abnormalities of light and dark adaptation seen in dopamine D4 receptor deficient mice. The results of these experiments will significantly enhance our understanding of how dopamine and cAMP modulate photoreceptor function, especially light- and dark-adaptation.