What’s the purpose of a distinct pleasure chemical and a “compulsion” chemical, evolutionarily? Wouldn’t a pleasurable response already compel you to repeat the action?
I would not say there is a pleasure chemical, more that it is a contentment chemical. It is more of a signal that the situation is so good that there is no point in trying to improve it.
In a sense they are antagonists. The compulsion is driving you to do something, perhaps anything, and will eventually drive you into the ground from stress. The other will drive you to do nothing, even if it means that you waste away from lack of water and nutrients.
I can't see any way of defining pleasure, in an objective way, without it being part of motivation. "Reinforce the recently followed decision paths" sort of thing.
Then it's semantics, if that's true, and dopamine may as well be "pleasure". For what it's worth the expert's explanation of how cocaine "compels" you to do work didn't sound intuitive. The common understanding is that it alleviates your brain's need for "pleasure" so you can focus on long term goals instead of short term goals (distractions). It's intuitive because it's analogous to satisfying one's pressing immediate needs so that one can do other higher level stuff.
