PNAS：寄生虫可消除老鼠对猫的恐惧
北京时间4月4日消息，据“生活科学”网站报道，老鼠通常对猫尿有恐惧感。对于那些从未见过猫科动物的啮齿类动物来说这种恐惧感仍然存在。然而，当它们感染了一种脑部寄生虫——弓形虫之后，这种恐惧感却消失了。
这一现象已被科学家熟知，然而最新研究发现弓形虫能够像手术刀般精确的消除老鼠对猫尿的恐惧，但是却不影响其他的恐惧感。斯坦福大学神经学家阿贾伊-维亚斯表示，这一发现有助于科学家研究“恐惧是怎样产生的”，以及人类如何更好的处理恐惧感。
据了解，弓形虫的主要宿主是猫类。在其他大量温血动物的体内都能发现这种寄生虫的身影，美国超过一半的人口也都有不同程度的感染。曾有研究显示，弓形虫对人类行为的改变足以对人类文明造成彻底的影响。
弓形虫在猫科动物体内进行有性繁殖，而在其它生物体内则进行无性繁殖。弓形虫主要感染大脑，维亚斯表示：“这种寄生虫能够劫持心智。”维亚斯及其同事此次研究显示了弓形虫是通过什么方式改变老鼠大脑的，这一成果发表在4月2日的《美国科学院院刊》网络版上。
部分英文原文：
Published online before print April 2, 2007
Proc. Natl. Acad. Sci. USA, 10.1073/pnas.0608310104
Neuroscience
Behavioral changes induced by Toxoplasma infection of rodents are highly specific to aversion of cat odors
( behavioral manipulation | fear | parasites | predator )
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*Department of Biological Sciences, Stanford University, Stanford, CA 94305; and Department of Microbiology and Immunology and Departments of Neurology and Neurological Sciences and of Neurosurgery, Stanford University School of Medicine, Stanford, CA 94305
Edited by Bruce S. McEwen, The Rockefeller University, New York, NY, and approved February 14, 2007 (received for review September 21, 2006)
The protozoan parasite Toxoplasma gondii blocks the innate aversion of rats for cat urine, instead producing an attraction to the pheromone; this may increase the likelihood of a cat predating a rat. This is thought to reflect adaptive, behavioral manipulation by Toxoplasma in that the parasite, although capable of infecting rats, reproduces sexually only in the gut of the cat. The "behavioral manipulation" hypothesis postulates that a parasite will specifically manipulate host behaviors essential for enhancing its own transmission. However, the neural circuits implicated in innate fear, anxiety, and learned fear all overlap considerably, raising the possibility that Toxoplasma may disrupt all of these nonspecifically. We investigated these conflicting predictions. In mice and rats, latent Toxoplasma infection converted the aversion to feline odors into attraction. Such loss of fear is remarkably specific, because infection did not diminish learned fear, anxiety-like behavior, olfaction, or nonaversive learning. These effects are associated with a tendency for parasite cysts to be more abundant in amygdalar structures than those found in other regions of the brain. By closely examining other types of behavioral patterns that were predicted to be altered we show that the behavioral effect of chronic Toxoplasma infection is highly specific. Overall, this study provides a strong argument in support of the behavioral manipulation hypothesis. Proximate mechanisms of such behavioral manipulations remain unknown, although a subtle tropism on part of the parasite remains a potent possibility.
Author contributions: A.V., S.-K.K., J.C.B., and R.M.S. designed research; A.V., S.-K.K., and N.G. performed research; A.V. and S.-K.K. contributed new reagents/analytic tools; A.V. and N.G. analyzed data; and A.V., S.-K.K., J.C.B., and R.M.S. wrote the paper.
英文全文链接：www.pnas.org/cgi/content/full/0608310104/DC1
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