I think you've all got it wrong.
Why use rats?
What have they done but unintentionally spread disease and eat our stocks from an urge to survive?
We should be using Criminals!
People whom are of little to no use to society,and who would die either in dreadful circumstances by their nature, or quite boring ones cooped up in prison.
There are large portions of humanity just scquealing to be used for science.
Of extreme interest would be Criminals sentenced to death in the more strict countries.
After all, wouldn't you take the bargin, and dedicate the rest of your (tragically) short life to science, hope of reanimation?
After all, one can only suffer one death penalty, afterwards he is a free man, should the experiments be sucessful.