Neurobiology and Development (UPR3294), Institute of Neurobiology Alfred Fessard, CNRS Gif-sur-Yvette, France.
Front Neuroanat. 2011 Mar 29;5:21. doi: 10.3389/fnana.2011.00021. eCollection 2011.
Dopamine (DA) neurotransmission in the central nervous system (CNS) is found throughout chordates, and its emergence predates the divergence of chordates. Many of the molecular components of DA systems, such as biosynthetic enzymes, transporters, and receptors, are shared with those of other monoamine systems, suggesting the common origin of these systems. In the mammalian CNS, the DA neurotransmitter systems are diversified and serve for visual and olfactory perception, sensory-motor programming, motivation, memory, emotion, and endocrine regulations. Some of the functions are conserved among different vertebrate groups, while others are not, and this is reflected in the anatomical aspects of DA systems in the forebrain and midbrain. Recent findings concerning a second tyrosine hydroxylase gene (TH2) revealed new populations of DA-synthesizing cells, as evidenced in the periventricular hypothalamic zones of teleost fish. It is likely that the ancestor of vertebrates possessed TH2 DA-synthesizing cells, and the TH2 gene has been lost secondarily in placental mammals. All the vertebrates possess DA cells in the olfactory bulb, retina, and in the diencephalon. Midbrain DA cells are abundant in amniotes while absent in some groups, e.g., teleosts. Studies of protochordate DA cells suggest that the diencephalic DA cells were present before the divergence of the chordate lineage. In contrast, the midbrain cell populations have probably emerged in the vertebrate lineage following the development of the midbrain-hindbrain boundary. The functional flexibility of the DA systems, and the evolvability provided by duplication of the corresponding genes permitted a large diversification of these systems. These features were instrumental in the adaptation of brain functions to the very variable way of life of vertebrates.
中枢神经系统（CNS）中的多巴胺（DA）神经传递存在于脊索动物中，其出现早于脊索动物的分化。许多 DA 系统的分子组成部分，如生物合成酶、转运体和受体，与其他单胺系统的组成部分共享，这表明这些系统具有共同的起源。在哺乳动物的 CNS 中，DA 神经递质系统多样化，用于视觉和嗅觉感知、感觉运动编程、动机、记忆、情感和内分泌调节。其中一些功能在不同的脊椎动物群体中是保守的，而另一些则不是，这反映在大脑前区和中脑的 DA 系统的解剖学方面。最近关于第二个酪氨酸羟化酶基因（TH2）的发现揭示了新的 DA 合成细胞群体，这在硬骨鱼的室周下丘脑区得到了证实。很可能脊椎动物的祖先是具有 TH2 DA 合成细胞的，而 TH2 基因在胎盘哺乳动物中已经发生了二次丢失。所有的脊椎动物都在嗅球、视网膜和间脑中有 DA 细胞。中脑 DA 细胞在羊膜动物中很丰富，而在一些群体中如硬骨鱼中则不存在。对原索动物 DA 细胞的研究表明，在脊索动物谱系分化之前，间脑的 DA 细胞就已经存在。相比之下，中脑细胞群体可能是在脊椎动物谱系中，随着中脑后脑边界的发育而出现的。DA 系统的功能灵活性以及相应基因的复制提供的可进化性，使得这些系统得到了极大的多样化。这些特征对于大脑功能适应脊椎动物非常多样化的生活方式至关重要。
