Depression in shelter cats is common. Especially when they're confined to cages. Older cats who have been with their humans for a long time and are forced live in a shelter don't do well. That's why whenever I pull a cat from the Humane Society, I always look for ones that have been there a long time. I just wish people who owned pets made provisions for them in their final wishes. It would make their pets lives alot more fulfilled, and keep the crowding at shelters to a minimum (for what it's worth).