Were the lab rats chemically altered so that they exhibited these symptoms, or were they selectively bred? In other words, did the neurologists select the most mellow rats and breed them together to produce the (for lack of a better word) lethargic rats?

I think this is absolutely horrible, regardless. I am curious to know what they found out since its already been done, but at the same time I am crazy about animal rights and I can't stand to hear about animal testing in labs. I won't go into that, though.