?脊椎动物和果蝇大脑都有所谓的视觉地图。这些视觉地图是由百万个神经细胞组成的，为了使成年动物能正常看见，在发育过程中这些神经细胞需要正确地组装。一般认为，视觉地图的复杂性就象其他大脑区域一样，不仅仅按照遗传学编程，而且需要大脑神经元或者神经细胞的活性。
??出版在当前生物学杂志上的最新研究，Baylor医学院发育生物学主任Dr. Hugo Bellen实验室Drs. P. Robin Hiesinger， R. Grace Zhai及其同事发现，在黑腹果蝇(Drosophila melanogaster)视觉地图形成中不需要神经元活性，黑腹果蝇是全世界实验室使用的果蝇的最普通的形式。
??“脊椎动物视觉系统形成有一个遗传组分，”Bellen说，他也是Howard Hughes医学研究所一名调查者，“脊椎动物的神经元是天生就具有的，按遗传学方式编入大脑的某一区域。接下来的是精炼视觉地图神经元活性的动态状态。相反，果蝇视觉系统似乎完全是硬接入，仅仅依靠遗传输入。”
??Bellen说：“昆虫和脊椎动物大脑最明显的区别就是神经元的大小和数目的不同，果蝇比脊椎动物有更少的神经元可能可以解释这个发现，因此果蝇视觉系统仅仅依靠遗传组分。”
??Bellen解释说：“脊椎动物的复杂性是因为数百万个神经元的挑战必须开通十亿个精确的联接。你必须先研究一个重大的局部解剖学地图，然后神经元精炼这个地图。”
??这项研究有一个没有解决的争论，即脑波可以遗传编程的程度。
??Bellen说：“当我们根据人脑复杂性来解释这些结果时，我们必须非常小心，然而，果蝇少数基因是如何编程十亿个突触的联接是非常惊人的。”
英文原文：
?Hard-wiring the fruit fly's visual system
Both vertebrate and fruit fly have so-called visual maps in the brain that represent the world they see. These visual maps consist of millions of nerve cell contacts that need to be wired correctly during development in order for the adult animal to see normally. It is generally thought that the complexity of visual maps, like other brain regions, cannot only be genetically programmed but requires activity by neurons or nerve cells in the brain.
In a new study published in the journal Current Biology, Drs. P. Robin Hiesinger, R. Grace Zhai and co-workers in the laboratory of Dr. Hugo Bellen, director of the Program in Developmental Biology at Baylor College of Medicine, found that this neuronal activity is not required for the formation of the visual map in Drosophila melanogaster, the most common form of fruit fly used in laboratories around the world.
"There is a genetic component (to formation of the vertebrate visual system)," said Bellen, who is also a Howard Hughes Medical Institute investigator. "The neurons in vertebrates are born and are genetically programmed to project into a certain brain region. This is followed by a dynamic phase where neuronal activity refines the visual map. In contrast, in flies the system seems to be completely hard-wired and only rely on genetic inputs."
"The most obvious difference between the insect and vertebrate brain is their size and the number of neurons and connections that need to be made. A possible explanation for the findings is that the fruit fly has many fewer neurons than vertebrates, and the system can therefore just rely on the genetic components in flies," said Bellen.
"In vertebrates, complexity is added because of the challenge of millions of neurons having to make billions of precise connections. You have to work with a gross topological map first, and neuronal activity refines this map later," he said.
The study adds to an ongoing debate about the extent to which brain wiring can be genetically programmed.
"We have to be careful when we interpret these results in light of the complexity of the human brain," said Bellen.
However, he said, "It is astonishing though how only a few thousand genes can program billions of synaptic connections."
Others who participated in this research include Drs. Yi Zhou, Tong-Wey Koh, Sunil Q. Mehta, Karen L. Schulze, Yu Cao and Patrik Verstreken, all of BCM; Thomas R. Clandin of Stanford University; Karl-Friedrich Fischbach of the University of Freiburg in Germany; and Ian A. Meinertzhagen at Dalhousie University in Halifax, Nova Scotia. Hiesinger, who is first author, is now with The University of Texas Southwestern Medical Center in Dallas.
Funding for this research comes from the Howard Hughes Medical Institute, the National Institutes of Health and the Deutsche Forschungsgemeinschaft.
