Has there ever been evidence of schizophrenia, bipolar disorder and such problems observed in the animal world, including apes, our closest relatives ?
What methods worked for these animals ? With animal studies, you can pretty much rule out the placebo effect, which makes the results more reliable.
(I know, you have a crazy cat, but I'm talking about a properly diagnosed case of an animal with a mental disease)
What makes you think you can rule out the placebo effect in animal studies? That sounds like a completely fallacious assumption.