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Posted Dec 11 2009 5:12pm
Last summer, I participated in an internship at the pharm/tox department at my university; and when the summer ended, I was asked to stay on for a few more months. One of the projects going on in my lab is trying to determine whether there is any connection between circadian rhythm and diabetes. Today, when I went to the lab, one of the experiments was ending for the forty-two mice in three groups: One, a control group; another, given fructose water during the night (when mice are active); and a third, given fructose water during the day (when mice are normally asleep). Mice on a high-sugar diet are good models for diabetes.

Naturally, mice like sugar water (don't we all?) and will disrupt their usual sleep-wake cycle to access it, which means they're eating when they would normally be asleep, which is of course the point of the project. What, exactly, happens when mice get high-sugar midnight (midday?) snacks?

At the end of almost every experiment, the mice are euthanized, and their tissues collected. It's amazing how much data you can get from a single mouse. I've spent hours on a fifteen-minute recording of mouse EKG (the electrical activity in the heart), or counting the bright pixels (by computer, thank goodness) in a photograph taken of a slide with a mouse heart section, stained for various substances of interest. I've done a lot of statistical work, too, which I find amusing because I've taken exactly one undergraduate statistics class and they still trust me with it (!). I've dug through hours or days of recordings taken with implanted telemetry equipment--tiny transmitters surgically implanted in a lab mouse, which can transmit things like heart rate, body temperature, movements, and blood pressure to a computer across the room.

It's odd, looking at a single mouse, just how much information you can get from such a tiny creature; while the mouse, of course, is totally oblivious to it all.

When I first was told we were working with animal research, I was also given a course in how to humanely handle lab animals. Every experiment has to be written down exactly, in advance, with everything that is done to the animals, every drug, every surgery (if any), how they'll be housed, etc., and has to be reviewed by a committee which checks that we're using the fewest animals possible with the least distress possible; then we're checked, periodically, to be sure we're following the protocol. Any changes have to be approved; and the animals are regularly checked by the institutional vet. Apparently, you can get in really big trouble for deviating from the protocol, and can even lose your grant or get kicked off the program. To me--animal lover here!--that was really reassuring. I'm aware of the necessity for animals in research; there are things you can do with living creatures that you'll never manage with tissue cultures. But that doesn't mean I can't care about the animals' welfare.

So... today, the experiment ended, and forty-one mice had to be killed. (Forty-two is around the minimum necessary to detect an effect of the size we were expecting; one mouse died before the end of the experiment, not surprisingly since mice are not so long-lived, so there were forty-one left.) We do call it "killing"--in the protocol, of course, it's "euthanasia", but I have a feeling these scientific types don't like euphemisms any more than I do. It's the second time I've done tissue collection; and I didn't like it this time any more than I did the last. Nobody else did, either. It's a tiring, picky job; and while nobody bonds with lab mice, nobody likes killing them. You get used to it, sure; but if you ever like it, I question your sanity.

The whole operation was set up in assembly-line fashion, eight of us in a small room with stainless-steel counters and a lot of equipment. The mice, still in their cages, were brought on carts; and another cart of microcentrifuge tubes waited for the blood and tissues.

Like many labs, we kill our mice by decapitation. The apparatus looks much like what you'd expect, a V-shaped guillotine; the operator simply takes the mouse by the scruff of the neck and presses the lever to remove the head at the base of the skull. For a mouse, I cannot imagine this causes much pain (a great deal less, I would suspect, than my cats inflict on the mice they catch). As I've heard it, a human has maybe ten seconds of consciousness after the heart is no longer pumping blood to the brain; for a mouse, with a much faster heartbeat (600-700 beats per minute, as opposed to 70), the time to death is less than a second. After the mouse is dead, the body is passed down the line, where it is snipped open with scissors, high-school frog-dissection fashion, and the various organs are removed, ready for analysis. Some parts are fixed in formaldehyde, others, frozen in dry ice. The blood is put into tubes prepared with heparin (to stop coagulation).

I had the job of weighing hearts and kidneys, recording the weights on a clipboard. With mice, everything is tiny; and everything has to be done gently. The hearts, submerged in a buffer solution to stop the tissue damage, still beat after being taken from the body (the heart has its own electrical system, and will beat for some time after the brain is dead). The scale I was using measures weights to a thousandth of a gram; most mouse hearts weigh about .15 grams, and the scale has to be so sensitive that breathing on it can change the measurement.

A mouse heart is maybe the size of a small pea, deep red in color. It's too small to see details without a magnifying glass; the ends of the arteries and veins still attached look like bits of string. The heart has to be picked up with tweezers because clumsy human fingers are simply too big. Mouse kidneys are the size of kidney beans, and look exactly like kidney beans; if you squint at a bisected kidney, you can just barely see the structures. The brains are white and wrinkled, but look very simple compared to the human brain (which I have also had the privilege of studying). When the organs are sectioned for staining, they should be whole and undamaged; having worked with organs that weren't whole and undamaged, I am always a little paranoid of causing damage. Every sample gets its own microcentrifuge tube, and each tube gets its own label.

To keep ourselves from accidentally skewing the experiment, we kill the mice in random order. My list shows only the mouse ID; never the group the mouse belongs to. It's important not to know which group the mouse belongs to simply because, if you knew, you might subconsciously affect the results. Your own brain can really play tricks on you if you aren't careful.

Killing forty-one mice takes hours, even with eight people to help. The small room gets uncomfortably warm with so many people in it; and we are in protective lab coats, which makes it even warmer. The room smells strongly of mouse, with an undertone of blood. Standing up for that long without walking around makes our legs tired. We don't talk much; most of the conversation consists of things like, "Thirty-two. Right kidney," and, "Where's the PBS?" and, "Number sixteen. You guys ready?" The biohazard sharps box and the bag for everything else fill up as we work through the mice. At least we are only in a biosafety level 2 lab; it would be much worse if we had to do all this in more than just the basic protective gear we're wearing.

In the end, I ended up staying late to finish helping one of the grad students centrifuge the blood and dole out plasma into more little tubes, ready for testing. Maybe this batch of mice will tell us something interesting; with so many people who have diabetes and so many scientists studying it, contributing our little part to the body of human knowledge may mean that someone out there will arrive at a breakthrough that much sooner. But I've done this only twice so far, and while it's fascinating to see the inside of a mouse, right now I wouldn't mind not doing it again for a good long while.
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