The Rise of the Mouse

By Neuroskeptic | September 21, 2010 2:45 pm

Everyone knows that scientists experiment on rats, and guinea-pigs. That’s why we have “lab rats” and why, if you’re trying out something new, you’re a “human guinea-pig”.

But this is all out of date. Nowadays, mice are the most popular lab animals. Here’s a graph showing the number of scientific papers published each year, mentioning each kind of critter (data gathered with this script):

Rats were on top until about 10 years ago, when mice overtook them. Why? No-one wants to study mice if they can help it: they are horrible to work with compared to rats, and rats are more similar to humans physiologically. This is why rats were more popular for a long time. (Contrary to popular belief, guinea pigs were never used all that much, and they’ve become even less popular with the rise of mice.)

Non-scientists tend to think of rats as just big mice. They’re not: mice are less intelligent, harder to handle (they bite… a lot), and they smell bad. The fact that they’re smaller makes surgery, and even simple stuff like taking blood samples, much harder. On the plus side, you can fit more of them in any given space, making them cheaper, but that’s about it.

So why did mice suddenly claim the crown? One word – knockout. Mice are the only mammal in which it’s easy to perform genetic knockout, i.e. eliminating the function of a single gene. It’s extremely difficult in rats, because, for reasons no-one really understands, it is harder to get rat stem cells to grow in vitro.

Knockout mice were “invented” in 1989, and the inexorable rise in the number of mouse papers began a few years later. Recently, there have been reports that knockout rats may now be easy; whether this will lead to a rat renaissance remains to be seen.

Knockouts have revolutionized biology, because they make it easy to investigate what each gene does. Just knock it out, and see what’s wrong with your mouse. This is why there are mouse models of so many genetic diseases, while rat and monkey models are only available for a few disorders.

CATEGORIZED UNDER: animals, genes, graphs, history, science
  • computingintelligence

    To be fair, for all their drawbacks mice are cuter than rats. The standard white lab rat is somewhat creepy looking with its intense red eyes, but that look miniaturized still retains an adorable cuteness… at least until you get bitten.

  • strawberry shortcake

    It's cruel. Can't they invent an e-mice? use their freggin brain, make algorithms to predict genome sequences. Rip the Big Bang and expel that energy towards saving the human condition from perpetrating crimes against species. Lab furries is just irresponsible science.. so medieval how do they sleep at night? Tut tut! Shame!

  • strawberry shortcake

    Stop discriminating against rats. Who knows what heinous abuse you committed for the mice to bite you. Poor thing. Science is cruel.

  • Mike Lisieski

    @Strawberry. Wow.

    @computingintelligence – We use hooded rats in the lab I work at, and I definitely like them more than mice (I've kept both rats and mice as pets, too, and prefer the rats.) They smell less, they're easier to handle, and they're easier to perform surgical and other procedures on because they're bigger. I also think rats end up being cuter (behaviorally, that is) because they're generally more calm while being handled, so it's easier and more fun to interact with them.

    As far as I have seen, guinea pigs were popular for harvesting tissue to work on in some physiology and pharmacology experiments, but otherwise have been relatively little used. I don't know why they survive in the popular lexicon as the prototypical lab animal.

  • Anonymous

    Hu! Hu!
    Welcome to the new whacko.
    How long will he last?

  • Neuroskeptic

    Well I have never banned a commentator. I'm not sure you can with Blogger. So if anyone doesn't last, it's their own choice.

  • Anonymous

    So if anyone doesn't last, it's their own choice.

    Yes, this is what I meant, like veri

  • Jason Goldman

    Awesome post. Ignore the crazies :-)

  • mint leaves

    Anon, can you please stop smelling me? I'm not a mice you science fruitcake, learn to control your pheremone detectors. How long must I snorkel undercover online? You're cruel.

  • Anonymous

    @sock puppet

    No touching, not even smelling, could you be prudish?
    Neuro blogs aren't a safe place for you, they will NOT cure you, on the very contrary…

  • Allison

    Hm, the interesting parts of that graph, for me at least, are around 1970 (where use of rabbits drops off) and 2000 (when mice finally overtake rats). I'm just a neuroscience young'un looking for my first job as a research assistant in a neuro lab, so while I'm comfortable guessing that 2000 is around when genetic knockouts became practical and inexpensive enough for lots of labs to create/acquire (I'd actually be curious to see a graph comparing the number of papers that mention genetic knockouts in their methods with those that mention mice), I have no idea why rabbits would have been just as popular as mice back in the day.

  • Neuroskeptic

    Allison: I was surprised by the rabbit line too. But according to this site:

    “The rabbit has been used in a wide variety of research studies in genetics, nutrition, toxicology, physiology, immunology, and reproduction. Classically the rabbit has been utilized in human medicine to determine pregnancy in women by injecting the serum from the patient into the rabbit and thereby inducing ovulation in the doe. The pharmaceutical industry uses the rabbit widely to test toxic effects of cosmetics and pharmaceutical in their evaluation for new drugs (greatly on the decline now) and the rabbit is the standard animal for pyogen testing of all solutions for human medical use. The rabbit is also widely used by the research community for the production of antibodies and antiserums. Due to its large size, it can be of great benefit in the production of fairly large amounts of these materials.”

  • pj

    I think the rat-knockout has to give a little resurgence for the good old lab rat because most sophisticated behavioural paradigms in neuroscience (that don't involve monkeys) are based on the rat – there's years of research that can be drawn on.

    For the last decade or so people have tried quite hard to get mice to do analogues of the rat tasks (and, to a fair extent, failed at this) so there's surely at least a good few papers in just reproducing many of the original mouse knockout studies in rats using the behavioural paradigm they were trying to emulate in the first place.

    And one more vote for rats are cuter than mice – maybe not if you just look at them in a cage, but if you have to handle them and work with them rats win hands down.

  • ex-hedgehog freak

    They're not: mice are less intelligent, harder to handle (they bite… a lot)

    Dude, seriously, I would much rather get bitten by a mouse than a rat. I did some work with rats once, just because we could get more material for protein data than we could from mice. Those things scared the bejeezus outta me. Those eyes, boy, those eyes. There was more intelligence in one rat's eyes than in the entire room of mice…

    Try holding a rat in one hand and tell me how often you lose a finger. And let's face it, who doesn't mind a mouse chewing on your finger? Like they could ever break the skin. They looked cute while they did it, too. If nothing else it stopped them peeing all over my hands!

  • pj

    “Try holding a rat in one hand and tell me how often you lose a finger”

    Pah – real men work with ferrets, they're a serious lab animal, when they bite you know about it.

  • Neuroskeptic

    It's interesting that, with the rise of mice, rats actually went into recession for a few years (which is especially notable because of the continuing growth in the # of papers on all topics) – suggesting that people switched from rats to mice.

    But rats made a comeback. I suspect this is because of the growth of neuroscience over the past 10 years.

    I can't think of many scientific reasons (as opposed to I-like-rats-better reasons) to prefer rats over mice for stuff other than neuroscience/behaviour, although I may be wrong.

  • peanut muffin

    Anon, I'm not your sock puppet. I suggest you swap the sadistic friction for lube like everybody else.

  • Anonymous

    I wasn't talking to “peanut muffin”.
    Are you prey to some devilish fantasies?

  • veri

    I'm starting to suspect you might. Your heckling of me is unnatural. In the name of Jesus Christ I command you to leave.

  • Anonymous

    In the name of Jesus Christ I command you to leave.

    I am afraid I can't do that, I'll get bad marks for that and be yelled at by the boss.
    Plus I am trying to be the employee of the month!



No brain. No gain.

About Neuroskeptic

Neuroskeptic is a British neuroscientist who takes a skeptical look at his own field, and beyond. His blog offers a look at the latest developments in neuroscience, psychiatry and psychology through a critical lens.


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