小鼠是研究人类疾病的重要模式动物之一，其基因组与人类基因组的相似性达到90%以上。一般认为，人类与小鼠在疾病发生的机理上基本相似，而两者在炎症响应基因表达谱方面也可以部分对应。 可是，在2013年初，美加两国多位科学家以“炎症和宿主损伤响应大型合作研究计划”（ the Inflammation and Host Response to Injury, Large Scale Collaborative Research Program ）的名义，在《美国国家科学院院报》（PNAS）上发表论文称，小鼠模型在基因组响应上极少模拟人类炎性疾病 。 该文指出，尽管源自不同病因的急性炎症在人体中所导致的基因组响应十分相似，但小鼠模型中的基因组响应却与人体中的基因组响应很不相同。当人体中基因表达出现明显变化时，小鼠中的相应基因却呈随机性改变，相关系数仅为0-0.1，即完全不相关。因此，作者建议在人类炎性疾病的转化医学研究中应该更看重人体实验结果，而不是依据小鼠实验。 Genomic responses in mouse models poorly mimic human inflammatory diseases Abstract A cornerstone of modern biomedical research is the use of mouse models to explore basic pathophysiological mechanisms, evaluate new therapeutic approaches, and make go or no-go decisions to carry new drug candidates forward into clinical trials. Systematic studies evaluating how well murine models mimic human inflammatory diseases are nonexistent. Here, we show that, although acute inflammatory stresses from different etiologies result in highly similar genomic responses in humans, the responses in corresponding mouse models correlate poorly with the human conditions and also, one another. Among genes changed significantly in humans, the murine orthologs are close to random in matching their human counterparts (e.g., R 2 between 0.0 and 0.1). In addition to improvements in the current animal model systems, our study supports higher priority for translational medical research to focus on the more complex human conditions rather than relying on mouse models to study human inflammatory diseases. 当这篇文章发表后，在科学界尤其是生物医学界引起巨大反响。《纽约时报》甚至一反常态地发表了足以耸人听闻的看法：“在错误的导向之下，宝贵的时间与无数的资金就这样被白白地浪费掉了”。更有甚者，学者们在使用小鼠疾病模型时提心吊胆，学生们则不知道没了小鼠他们如何完成毕业论文。相反，争取动物权益人士从此掌握了一个极具说服力的话柄。 然而，在本周刚刚出版的PNAS上，两位日本科学家发表最新论文，有力地反驳了美加科学家的观点，其论文题目更是针锋相对：小鼠模型在基因组响应上极大模拟人类炎性疾病 。仅仅一字之差（poorly vs greatly），小鼠作为模式动物的命运几乎阴阳两隔，而造成这种“冰火两重天”的原因竟然仅仅是统计学方法的不同！ 日本学者完全使用美加学者的转录组数据，但只是计算表达水平有显著差异的基因，结果求出人体数据与小鼠模型数据之间的相关系数在0.43-0.68之间，变化幅度为77%-93%，而且许多代谢途径的调节模式基本相同。因此，作者得出了完全相反的结论：小鼠可以用作人类炎性疾病模型动物！ Genomic responses in mouse models greatly mimic human inflammatory diseases Significance The role of mouse models in biomedical research was recently challenged by a report that genomic responses in mouse models poorly mimic human inflammatory diseases. Here we reevaluated the same gene expression datasets used in the previous study by focusing on genes whose expression levels were significantly changed in both humans and mice. Contrary to the previous findings, the gene expression patterns in the mouse models showed extraordinarily significant correlations with those of the human conditions. Moreover, many pathways were commonly regulated by multiple conditions in humans and mice. These findings demonstrate that gene expression patterns in mouse models closely recapitulate those in human inflammatory conditions and strongly argue for the utility of mice as animal models of human disorders. Abstract The use of mice as animal models has long been considered essential in modern biomedical research, but the role of mouse models in research was challenged by a recent report that genomic responses in mouse models poorly mimic human inflammatory diseases. Here we reevaluated the same gene expression datasets used in the previous study by focusing on genes whose expression levels were significantly changed in both humans and mice. Contrary to the previous findings, the gene expression levels in the mouse models showed extraordinarily significant correlations with those of the human conditions (Spearman’s rank correlation coefficient: 0.43–0.68; genes changed in the same direction: 77–93%; P = 6.5 × 10 −11 to 1.2 × 10 −35 ). Moreover, meta-analysis of those datasets revealed a number of pathways/biogroups commonly regulated by multiple conditions in humans and mice. These findings demonstrate that gene expression patterns in mouse models closely recapitulate those in human inflammatory conditions and strongly argue for the utility of mice as animal models of human disorders. 实际上，在这篇反驳文章发表之前，美国本土就有科学家对“小鼠不适合作为人类炎性疾病模型”的说法提出质疑，其要点集中在单一品系小鼠与遗传多样性人体之间进行比较的合理性上。同时，也指出了其方法学上的不足： 首先，采样时间不同。人体白细胞是在损伤后一年收集，而小鼠白细胞则在损伤后一周收集。未能使用平行信息，说基因组响应不相似就不准确。其次，探针敏感性不同，数据却同等对待。第三，计算错误。相关系数R可以是负数，相关系数的平方R2怎能是负数呢？最后，无重复验证。只使用芯片数据，未使用定量PCR与Western杂交数据。 Concerns over interspecies transcriptional comparisons in mice and humans after trauma We have read with interest the study by Seok et al. ( 1 ) describing transcriptional responses of the immune systems of humans and mice. The authors perform Affymetrix GeneChip-based microarray assays on blood samples collected from blunt trauma, burn, and endotoxemia patients and mouse models of these pathologies. They report little correlation between human and murine genomic responses. Furthermore, the authors assert that mouse models of human disease are of questionable value due to the low biological similarity they observed. This paper raises some legitimate issues regarding mouse vs. human differential and temporal responses at a gross whole blood level to biological perturbations occurring in other tissues. However, we are concerned that the failure to examine more than a single immune-polarized mouse strain, the lack of correction for differentially abundant cell types, and the use of data analysis approaches that did not consider these factors in an additive fashion strongly limit the conclusions that can be drawn from the data. We question the value of broad comparisons between genetically diverse patients and a single strain of mice. Male C57BL/6 inbred mice, which were used exclusively, have minimal genetic variation and are predisposed to Th1-mediated immune responses ( 2 ). Inclusion of additional mouse strains should have been considered in the study design to avoid pseudoreplication ( 3 ). Therefore, genetic background is the more appropriate unit of replication and not the individual patient or mouse. Differences between human and mouse responses to traumas are likely exaggerated when time course data are used in aggregate rather than comparing biologically analogous time intervals and individual cell populations. Mouse and human leukocyte populations differ; thus, the majority of observed effects could be attributed to differential cell population margination or cell death rather than pathway-specific alterations of otherwise constant levels of different cell types. The authors apparently compared expression data from total blood leukocytes collected up to 1 y after injury in human patients vs. only 1 wk in murine models. Although it is certainly true that recovery rates between humans and mice differ, it is inaccurate to suggest that the genomic responses are dissimilar when parallel information is not used. An additional issue is that data were analyzed without consideration of potential error resulting from variations in sensitivity among different probe sets for genes on the microarrays, which may have led to overestimation of expression divergence between species ( 4 , 5 ). Further, although negative R values can indicate an inverse correlation, the coefficient of determination, R 2 , cannot be negative (see figures 3 and 4 and table 1 in ref. 1 ). Finally, validation of expression levels using complementary methods (e.g., quantitative PCR or Western blotting) was not presented. We believe these concerns must be addressed before broad conclusions can be drawn from the data. The current conclusions are especially troubling in light of the attention given to this study by the popular media. Although concerns exist regarding the utility of animal models in translating basic research to successful clinical treatments, we believe the current conclusions drawn from this manuscript are of questionable validity. 针对这个书面质疑，原作者一一进行了解答。对于单一小鼠品系的选择，考虑了三点因素：一是C57B/6是最常用的；二是其他品系对脂多糖有抗性；三是结果跟别人相似或一致。对于取样时间，认为小鼠基因恢复比人体疾病基因恢复明显不同，依时比较比单一比较更严格，其实他们进行了多种形式的比较，包括变化的方向性与程度、变化的响应时间与恢复时间、时间依存模式。关于技术及统计学问题，回答是不是进行原始数据比较，而是对变化数据进行比较，而对R2的解释已列在图表中。最后，原作者强调，他们并非否定所有小鼠模型，但只是认为小鼠作为炎性疾病模型不合适。 Reply to Osterburg et al.: To study human inflammatory diseases in humans Osterburg et al. ( 1 ) raise questions from our recent publication ( 2 ). First, in our program, a single mouse strain, C57B/6, was selected because it has been the most commonly used in the field for decades. Furthermore, all strains of mice are remarkably resistant to LPS relative to humans. If anything, C57B/6 mice are less resistant and therefore potentially closer to the human response than many other mouse strains ( 3 ). Last, figure 4 and table 1 of ref. 2 show that our results are consistent with those of other independent mouse studies and not specific to strain, model, or investigator. Osterburg et al. ( 1 ) question whether the choice of time intervals was appropriate. Gene recoveries in mouse models differ markedly compared with those in complex human diseases. In general, time course comparisons are much more rigorous than single time point or cross-sectional studies in capturing the similarities and differences in the gene changes between humans and mice ( 4 ). We performed the time course comparison and compared multiple characteristics of the response in humans and mice, including directionality and maximum magnitude of the changes (figures 1, 4, and S1 and table 1 of ref. 2 ), the response time and recovery time of the changes (figures 2 B and S5 of ref. 2 ), and time course patterns (figures 2 A , S6, and S7 of ref. 2 ). For both species, the gene response time occurred within the first 6–12 h (figure S5 of ref. 2 ). Regarding the technical and statistical issues raised by Osterburg et al., instead of comparing the raw expression values from the microarrays between human and mouse, the comparisons were performed on the changes of expression values between disease conditions and controls within each species, where the same array platform was used for each of the species. The annotation of – R 2 was explained in the figure 3 legend and table 1 of ref. 2 . The myriad of ways that mice differ from humans including the different time intervals and the fact that mouse and human leukocyte cell populations differ raise the important question as to whether it is appropriate to try to adjust the model system to more closely compare similar features. To try to adjust or somehow correct for the mouse–human differences either in cell number, time course, or in any other way would introduce artifact. In our study, for example, had we adjusted the leukocyte populations, the genomics would not have reflected the in vivo condition. Our article provides data for what most investigators already know from their experiences: current mouse models poorly reflect human inflammatory diseases. We are not damning all mouse models. Rather, we propose that the scientific community raise the bar to require model systems to more accurately reproduce the molecular features of human inflammatory disease and we should reprioritize our infrastructure, resources, tools, and methodologies to study human inflammatory diseases in humans. 个人感觉，从大的方面来说，仅仅依据转录组数据就得出小鼠不适合用作人类炎性疾病模型的结论是值得商榷的；从小的方面来说，基因芯片数据未得到定量PCR和Western杂交数据支持显然是不充分的。尽管这样的学术争论可能还会持续下去，但依据“唯一”数据得出“非凡”结论的做法肯定是不严谨的。 有意思的是， PNAS把两种完全相反的意见呈现出来让众人评判，毫不忌讳自己可能发表了至少一篇错误的论文。我认为这是良性的学术争论，科学的相对真理正是在这种理性思辨中逐渐逼近绝对真理的。 蓝色的蒙古高原 （降央卓玛原唱，曾庆平翻唱） 出差在外，酒店录制，音效不佳，敬请海涵！
今天无聊看了些咨询，不过倒是读了一个挺有意思的文章，是 Nature Feb 10 Title：Functional identification of an aggression locus in the mouse hypothalamus。 大意说的是小鼠负责攻击性和交配的神经元可能是部分重叠，但又有distinct subpopulation。“Neurons activated during attack are inhibited during mating, suggesting a potential neural substrate for competition between these opponent social behaviors.” 引申一下就是说对小鼠来说性可能会化解暴力，这在人类身上也可能适用。 当时大学不知道是上什么课的时候听到了美国的这么一句话- Make love not war .说的是美国60年代反文化运动的时候，年轻人对老美针对越战提出的看法。现在看看，真是简洁，给力，生动，具体。想想现在埃及的局势，虽然还没有说到战争的地步，不过也是乱的一团糟，不知道穆巴拉克如果看到nature这篇文章，想到Make love not war，我觉得如果他以这个作为宣传口号的话，有可能还会对局势有一些缓解（如果真是这样那一切就简单了）。 说到埃及，早上看同学分享的奥巴马关于埃及的演讲，他用的是“The spirit of peaceful protest and the perseverance that the Egypt people have shown can serve as a powful wind at the back of this change. The united state will continue to be a friend and a partner to Egypt. We stand ready for whatever assistance necessary. And ask for to pursue a credible transition to democracy.”（不一定听得全对）也就是和平过渡，但每天CNN上面报到的死亡人数，似乎告诉我情况并不太平。 政治太复杂，这个是我和我们楼里一个老美（真挺老的）聊天的时候最后达成的共识。 首先各种因素牵涉其中，局外人很难分清什么才是真正的动机，甚至局内人可能也会因为事件的复杂以及各种机遇的出现而变更最初的想法，并且最终获利。 其次作为大众，获得信息的渠道是在是太有限了，CNN已经是投机倒把，BBC还算是在追求unbias的媒体，twitter虽然真实但是太零散，很容易让一个疯狂转载了1万次的状态放大了真实的情况。 还有，现在信息量太大，各个媒体为了追求自身利益而采取“修辞手段”，“独特视角”来诠释同一个问题，很容易让人产生迷惑，到底事情的真相是什么呢？很难知道。Wikileaks就是一个典型。 所以有的时候觉得搞科研还是挺幸福的。同样是对问题的好奇，政治你需要太多的人脉，资金，精力才可以介入，而科学主要需有一个好的实验室，和一个爱思考的大脑，就不妨碍你的信马由缰。相比生物，限制更少的还要算是数学和计算机，只要一个PC，同时身在中国，就可以任意发挥了（羡慕你们）。可惜已经选了生物这个不归路，只能这样走下去。希望未来还能有好奇心，开心点把科研搞好。 对文章感兴趣的同学可以看： Nature doi:10.1038/nature09736 Functional identification of an aggression locus in the mouse hypothalamus Dayu Lin1, 2 Maureen P. Boyle3 Piotr Dollar4 Hyosang Lee1 E. S. Lein3 Pietro Perona4 David J. Anderson1, 2 Electrical stimulation of certain hypothalamic regions in cats and rodents can elicit attack behaviour, but the exact location of relevant cells within these regions, their requirement for naturally occurring aggression and their relationship to mating circuits have not been clear. Genetic methods for neural circuit manipulation in mice provide a potentially powerful approach to this problem, but brain-stimulation-evoked aggression has never been demonstrated in this species. Here we show that optogenetic, but not electrical, stimulation of neurons in the ventromedial hypothalamus, ventrolateral subdivision (VMHvl) causes male mice to attack both females and inanimate objects, as well as males. Pharmacogenetic silencing of VMHvl reversibly inhibits inter-male aggression. Immediate early gene analysis and single unit recordings from VMHvl during social interactions reveal overlapping but distinct neuronal subpopulations involved in fighting and mating. Neurons activated during attack are inhibited during mating, suggesting a potential neural substrate for competition between these opponent social behaviours.
Rats and mice: what's the difference? What do the terms rat and mouse mean? Differences between Norway rats and house mice How can I tell rats and mice apart? Quiz: rat or mouse? History and evolution of the Norway rat and the house mouse Common ancestry of the Norway rat and house mouse Brief history of the house mouse Brief history of the Norway rat and black rat Are rat-mouse hybrids possible? Mouse-killing behavior in rats: muricide What do the terms rat and mouse mean? Rat and mouse are actually not scientific classifications. These words are common names for rodents that look alike to the casual eye. Rat is used to describe medium-sized rodents with long thin tails. There are many species of rodent that are called rats -- kangaroo rats, cotton rats, Norway rats, black rats, African pouched rats, naked mole rats, wood rats, pack rats, Polynesian rats, and many others. These different rodent species may not be closely related to each other at all! Mouse is used to describe tiny, sparrow-sized rodents with long thin tails. As with rats, there are many species of rodents called mice which may or may not be closely related to each other: house mice, field mice, deer mice, smoky mice, spiny mice, and dormice are all called mice. So, which rats and mice are you talking about? Generally, people are referring to the domestic or pest rats and mice, which means Norway rats ( Rattus norvegicus ), black rats ( Rattus rattus ), and house mice ( Mus musculus ). Differences between Norway rats and house mice Norway rats and house mice belong to different species. A species is a group of related individuals or populations which are potentially capable of interbreeding and producing fertile offspring. So Norway rats and house mice belong to different species and cannot interbreed . Humans and orangutangs, chipmunks and red squirrels, bottlenosed dolphins and killer whales, all belong to different species. Norway rats and house mice are related, however. They descend from a common ancestor that lived millions of years ago -- how long ago is currently under debate, with estimates ranging from 8 to 41 million years ago. That estimate will probably become more precise over time. The descendants of that common ancestor diverged into different species, among which are Norway rats and house mice. Norway rats and house mice now have many genetic, reproductive, developmental, morphological and anatomical differences. The list below is not exhaustive, but for those with a casual interest it should get you started: Genetic differnces : Norway rats have 22 chromosome pairs, house mice have 20 (see Levan 1991). Norway rats have 2.75 million base pairs while mice have 2.6 million (humans have 2.9). About 90% of rat genes have counterparts in the mouse and human genomes (Rat Genome Sequencing Consortium 2004). See Burt et al. 1999, Grutzner et al. 1999, and Watanabe et al . 1999 for more. Growth differences: In general, Norway rats develop more slowly than house mice. For example, Norway rat gestation is slightly longer (21-24 days) than house mouse gestation (19-20 days). Norway rats lactate for about 3 weeks, house mice for 2 weeks. Both species are born naked and blind, but Norway rats open their eyes at 6 days, they are fully furred at 15 days. House mice open their eyes at 3 days, have fur at 10 days (etc.). Anatomical differences: Norway rats have 6 pairs of nipples, house mice have 5 pairs. Morphological differences: Norway rats are larger, heavier and longer than house mice (Norway rat: 350-650 grams, 9-11 inch bodies and 7-9 inch tails; house mice: 30-90 grams, 3-4 inch bodies and 3-4 inch tails). Correlated with this larger size, Norway rat body parts are larger than those of the house mouse -- rats have larger ears, feet etc. The heads of Norway rats are heavy, blunt and chunky, house mouse heads are small and sharply triangular with pointed muzzles. Note, however, that Norway rats have smaller ears relative to their heads than house mice. Sign differences: Due to their larger body size, rat feces are larger than mouse feces (also see differences in rat and mouse sign from a pest management perspective). Life-size drawing of mouse and rat feces. How can I tell Norway rats and house mice apart? Adult rats and mice Adult mice are much smaller than adult rats (Fig. 1). Adult mice weigh about 30 grams, and fancy mice tip the scales at about 50 grams. Adult mice have bodies that are 3-4 inches long with 3-4 inch tails. Adult rats are far heavier and longer: they can weigh ten times as much, averaging 350-450 grams for females and 450-650 for males (with an overall range of 200-800 grams). They have 9-11 inch long bodies and 7-9 inch tails ( ref ). Figure 1. Drawing showing the relative size of rats and mice Young rats vs. adult mice Young, weaned rats are still larger than adult mice, weighing around 100 grams at six weeks. However, to the casual observer, very young rats and adult mice can be difficult to tell apart. Here's what to look for: baby rats will have more juvenile proportions than adult rodents. Their heads and feet will be large relative to their bodies, their faces will be stubby and blunt with wide noses. Adult mice, on the other hand, will have adult proportions: a small, triangular head with a small nose and little delicate feet as compared to the body. In addition, mouse ears are very large relative to their heads, rat ears are smaller relative to their heads. Rats also have thicker tails than mice. Feature Baby Rat Adult Mouse Head short, stubby, broad, large relative to body small, triangular, small relative to body Muzzle large and blunt with wide muzzle narrow with sharp muzzle Ears ears are small relative to the head ears are large relative to the head Tail thick thin Tail/body ratio Tail shorter than body Tail same length/longer than body Feet Large relative to body, especially the hind feet Small relative to body Weight around 100 grams at 6 weeks, 200 grams at 8 weeks 30-50 grams 6 week old rat Adult mouse Quiz: Rat or Mouse? Take this quiz to test your ability to tell photos of rats and mice apart. History and evolution of the Norway rat and the house mouse Common ancestry of the Norway rat and house mouse True rodents first appear in the fossil record at the end of the Paleocene and earliest Eocene in Asia and North America, about 54 million years ago. They are widely considered to have originated in Asia (Meng et al. 1994). These original rodents were themselves descended from rodent-like ancestors called anagalids, which also gave rise to the Lagomorpha, or rabbit group. Murids ( Muridae ), the family that gave rise to present-day Norway rats, house mice, hamsters, voles, and gerbils, first appeared during the late Eocene (around 34 million years ago). Modern murids had evolved by the Miocene (23.8-5 mya) and radiated during the Pliocene (5.3-1.8 mya) (for more, see Introduction to the Rodentia ). The Norway rat and the house mouse had a common murine rodent ancestor. How long ago that common ancestor lived is a matter of debate, however. The fossil record indicates that the most recent common ancestor of Norway rats and house mice lived about 8-14 million years ago (Jacobs and Pilbeam, 1980). Geneticists, however, estimated that their most recent common ancestor lived about 41 million years ago (Kumar and Hedges, 1998). Brief history of house mice The ancestors of the house mouse ( Mus musculus ) lived in the steppes of present-day Pakistan. Ten thousand years ago, at the end of the last ice age, neolithic farmers moved from the Fertile Crescent into the steppes of Pakistan, and these small rodents found a delightful new source of food and shelter. When humans migrated away from the steppes to colonize other areas, mice went along as stowaways in the humans' carts and later, their ships. House mice arrived in the new world in the 16th century, arriving with explorers and colonists. Mice went everywhere with humans, living in and around their houses, a human-dependent association called commensalism . Today, commensal house mice live in and around human dwellings on every continent, in every climate. Today, commensal house mice are divided into four subspecies: M. musculus bactrianus are the descendants of the original, ancestral house mice first encountered by our neolithic ancestors. They live in India, Pakistan and Afghanistan. M. musculus castaneus lives in Southeast Asia. M. musculus musculus lives in Russia and western China, and M. musculus domesticus lives in Europe, from whence it traveled to the Americas, Australia, New Zealand, and Africa with the colonists. Domestication : Domestic mice originated from stocks captured in China, Japan and Europe and developed into fancy mice. These fancy mice were found in pet shops in the 20th century, and were developed into laboratory mouse strains. Fancy mice are primarily descended from M. musculus domesticus , with a little admixture of the other three subspecies. As such, domestic mice do not represent one of the single subspecies, but are a mixture of all four. ( Silver, 1995 ). Brief history of Norway and black rats See separate article, History of the Norway rat . Are rat-mouse hybrids possible? See separate articles, are rat-mouse hybrids possible? and the hybridization page. Mouse-killing behavior in rats: muricide Rats can, and do, kill mice, a behavior known as muricide . Muricide is a form of predatory behavior: rats hunt, kill and eat mice. How common is muricide? Karli (1956) found that about 70% of wild rats and 12% of domestic laboratory rats kill mice. Male and female rats are equally likely to kill mice. Similarly, Galef (1970) found that 67% to 77% of captive born wild rats kill mice. Description of muricide Muricide is a stereotyped behavior, performed in much the same way each time: the rat chases the mouse around the cage and bites it using its sharp front incisors, usually aiming for the mouse's head, neck, or upper back. The first bite is frequently fatal, but the mouse may delay the rat's attacks by defending itself (by rearing up and boxing with its front paws or laying on its back). Eventually, however, the rat delivers a fatal bite. Mouse-killing behavior is very rapid, lasting only a few seconds (Hsuchou et al. 2002). The preferred area to bite is the back: out of 671 mice killed by rats, 89% were bitten on the spinal cord (specifically: 65% neck, 13% thoracic, 11% lumbar). Only 7% were bitten on the belly and 4% were bitten on the head (Karli 1956). Do rats eat the mice they kill? Karli (1956) found that all mouse-killing rats (wild or domestic) consumed part of the mice they killed. Specifically, out of 683 mice killed by rats, after 7 hours 25% of the mice had been entirely eviscerated (brain, thoracic and abdominal viscera), 67% had been partially eviscerated, and only 8% had not been eaten. Wild rats tended to start eating at the spot where they had bitten the mouse, which is usually the neck. They gradually opened the thorax and consumed the thoracic viscera, then proceeded to the liver. In contrast, domestic rats went right to the brain, opening the skull and consuming all or part of the brain, no matter what killing method had been used (Karli 1956). Exogenous and endogenous influences Mouse-killing is a complex behavior involving several neurotransmitter systems (Miachon et al . 1997, Onodera et al. 1981, Tadano et al. 1997, Ueda et al. 1999, Vergnes and Kempf 1982, Yamamoto et al. 1982), neural systems (Hull and Homan 1975, Spector et al. 1972) and hormonal systems (Miachon et al. 1995; Rastegar et al. 1993). Mouse-killing is also affected by by rearing (Garbanati et al. 1983), environmental conditions (Garbanti et al. 1983, Giammanco et al. 1990), social conditions (Eisenstein and Terwilliger 1984), diet (Bac et al. 2002, Onodera et al. 1981), learning (Tingstrom and Thorne 1978). Rats are more likely to kill mice at night than during the day (Russel and Singer 1983). Mouse-killing is affected by hunger , too: rats kill mice more when they are hungry (Malik 1975) and at times when they are normally inclined to eat food (Russel et al. 1985). Rats may start killing mice when they are starving, but stop when they are given plenty of food (Karli 1956). Familiarity with mice also plays a role: rats reared with mice tend not to kill mice as adults. Specifically, Galef (1970) found that 67-77% of captive born wild rats kill mice. However, if captive born wild rats are raised with a mouse from weaning to age 3 months, none of them kill the mice they're familiar with. When presented with an unfamiliar mouse, only 7% of the mouse-reared rats killed it. Response of mice to rats Rat odor is stressful to mice and has an effect on their behavior and reproduction. In fact, rat odor is sometimes used as a predator odor to study anxiety and antipredator behavior in mice. Specifically, domestic and wild-stock mice who are exposed to a conscious or anesthetized rat tend to flee, and if prevented from fleeing, they show defensive or attack behavior (Griebel et al. 1995, Blanchard et al. 1998). Mice housed in the same room as rats tend to be more stressed than mice housed without rats (Calvo-Torrent et al. 1999). Mice who can smell rat urine take ten times longer to start eating a treat than mice who cannot (Merali et al 2003). Mice who were exposed to rat urine for just a few minutes startle more afterwards, even up to two days after the rat urine exposure (Hebb et al. 2003). Pregnant mice exposed to rat urine produce fewer litters than mice who were not exposed (de Catanzaro 1988). http://www.ratbehavior.org/RatsMice.htm
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