有一种小鼠不知道害怕。更准确地说，它对于讨厌的气味不能产生先天性的行为反应，而这种反应正常情况下可以保护小鼠不去吃腐烂的食物或避开某种捕食者的气味。在这种小鼠中，其嗅觉上皮的一个区域(鼻腔内一个对气味敏感的上皮组织)中的嗅觉神经元，已经被白喉毒素基因的定向表达除掉了。虽然没有先天的厌恶行为，但该小鼠却能探测和辨别讨厌的气味，并且可以条件性地作出厌恶反应。这些结果表明，同免疫系统一样，小鼠的嗅觉系统也具有“硬件连接的”、通过遗传程序编码的神经回路，它们与后天获得的、与先天系统联系在一起的适应性回路是并行的。
原始出处:
Nature 450, 503-508 (22 November 2007) | doi:10.1038/nature06281; Received 3 August 2007; Accepted 14 September 2007; Published online 7 November 2007
Innate versus learned odour processing in the mouse olfactory bulb
Ko Kobayakawa1,6, Reiko Kobayakawa1,6, Hideyuki Matsumoto2, Yuichiro Oka1, Takeshi Imai1, Masahito Ikawa3, Masaru Okabe3, Toshio Ikeda4, Shigeyoshi Itohara4, Takefumi Kikusui5, Kensaku Mori2 & Hitoshi Sakano1
Department of Biophysics and Biochemistry, Graduate School of Science, The University of Tokyo, Tokyo 113-0032, Japan
Department of Physiology, Graduate School of Medicine, The University of Tokyo, Tokyo 113-0033, Japan
Research Institute for Microbial Diseases, The Osaka University, Osaka 565-0871, Japan
Laboratory for Behavioral Genetics, Brain Science Institute, RIKEN, Saitama 351-0198, Japan
Laboratory of Veterinary Ethology, The University of Tokyo, Tokyo 113-8657, Japan
These authors contributed equally to this work.
Correspondence to: Hitoshi Sakano1 Correspondence and requests for materials should be addressed to H.S. (Email: sakano@mail.ecc.u-tokyo.ac.jp).
Abstract
The mammalian olfactory system mediates various responses, including aversive behaviours to spoiled foods and fear responses to predator odours. In the olfactory bulb, each glomerulus represents a single species of odorant receptor. Because a single odorant can interact with several different receptor species, the odour information received in the olfactory epithelium is converted to a topographical map of multiple glomeruli activated in distinct areas in the olfactory bulb. To study how the odour map is interpreted in the brain, we generated mutant mice in which olfactory sensory neurons in a specific area of the olfactory epithelium are ablated by targeted expression of the diphtheria toxin gene. Here we show that, in dorsal-zone-depleted mice, the dorsal domain of the olfactory bulb was devoid of glomerular structures, although second-order neurons were present in the vacant areas. The mutant mice lacked innate responses to aversive odorants, even though they were capable of detecting them and could be conditioned for aversion with the remaining glomeruli. These results indicate that, in mice, aversive information is received in the olfactory bulb by separate sets of glomeruli, those dedicated for innate and those for learned responses.
