Back To Those Knockout Mice

I can write about knockout mice—that means mice genetically engineered to lack individual genes, I mentioned them a few days ago days ago in a post about ADHD—pretty much endlessly I'll try to keep this from turning into the Knockout Mouse Blog, but I chanced on a study by researchers at Vanderbilt University that has some more counter-intuitive results that are worth recounting.

Norepinephrine, is a hormone and neurotransmitter that is associated with anxiety and anger—and also with attention, and protection from depression. In the Vanderbilt study, mice were bred to lack the norepinephrine transporter, meaning they had a persistently high level of the hormone in their brain and nervous system.

This had two very different, and essentially opposite, effects. On the one hand, when placed in a stressful environment, the mice had lower heart rate and blood pressure than ordinary mice. They functioned well under stress—to a point. But they also had an extreme reaction to shock, with their heart rate shooting up dramatically, the equivalent of panic in humans. This makes a lot of sense. The operation of norepinephrine is complex. One thing that it does is vary the frequency and amplitude of signals in the brain, making some signals stronger and others weaker—you can imagine it as working a little like the dials on a higher end stereo.

What I find especially compelling here is how useful this kind of study is in modeling human behavior. Just as a malfunction in the dopamine transporter may be associated with hyperactivity and attention problems, so we can see patterns in the norepinephrine transporter deficient mice eerily reminiscent of those that we see in humans—surprisingly complicated patterns. Sometimes the very same people who seem to do well in real world stressful environments will have mysterious panic attacks, or choke under pressure. What looks like a confusing and hard to explain set behaviors can get traced back to a change in a single gene that affects levels of a single molecule in the body.