北京時(shí)間4月4日消息，據(jù)“生活科學(xué)”網(wǎng)站報(bào)道,，老鼠通常對(duì)貓尿有恐懼感,。對(duì)于那些從未見過貓科動(dòng)物的嚙齒類動(dòng)物來說這種恐懼感仍然存在。然而,，當(dāng)它們感染了一種腦部寄生蟲——弓形蟲之后,，這種恐懼感卻消失了。
這一現(xiàn)象已被科學(xué)家熟知,，然而最新研究發(fā)現(xiàn)弓形蟲能夠像手術(shù)刀般精確的消除老鼠對(duì)貓尿的恐懼,，但是卻不影響其他的恐懼感。斯坦福大學(xué)神經(jīng)學(xué)家阿賈伊-維亞斯表示,，這一發(fā)現(xiàn)有助于科學(xué)家研究“恐懼是怎樣產(chǎn)生的”,，以及人類如何更好的處理恐懼感。
據(jù)了解,，弓形蟲的主要宿主是貓類,。在其他大量溫血?jiǎng)游锏捏w內(nèi)都能發(fā)現(xiàn)這種寄生蟲的身影,，美國(guó)超過一半的人口也都有不同程度的感染。曾有研究顯示,，弓形蟲對(duì)人類行為的改變足以對(duì)人類文明造成徹底的影響,。
弓形蟲在貓科動(dòng)物體內(nèi)進(jìn)行有性繁殖，而在其它生物體內(nèi)則進(jìn)行無性繁殖,。弓形蟲主要感染大腦,，維亞斯表示：“這種寄生蟲能夠劫持心智。”維亞斯及其同事此次研究顯示了弓形蟲是通過什么方式改變老鼠大腦的,，這一成果發(fā)表在4月2日的《美國(guó)科學(xué)院院刊》網(wǎng)絡(luò)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 )
Ajai Vyas *, Seon-Kyeong Kim , Nicholas Giacomini *, John C. Boothroyd , and Robert M. Sapolsky *
*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.
