Do dogs suffer from depression as such?

It rather depends how you define depression - in the case of dogs, boredom is a common cause of what we might regard as depression. Someone acquires a puppy and then goes out to work, leaving it on its own through the day. Not surprisingly, the young dog soon becomes bored, and to occupy itself, it starts to chew up furnishings, or scratches at the door. It is also likely to soil its surroundings.
depressed dog
The owner then blames their pet, and so begins a problem that is ultimately likely to result in the dog becoming nervous, withdrawn and shy with people, if it is constantly scolded and receives no encouragement. Winning back its confidence by this stage will be very difficult.