My understanding is that normally, a neurotransmitter binds to a receptor and then that ligand-receptor complex gets absorbed into the cell and either degraded or recycled. So does the same thing happen when the ligand is not the endogenous neurotransmitter, but instead an "artificial" antagonist -- like, say, bupropion bound to a nicotinic receptor?
When a neurotransmitter, like serotonin, binds to it's specific receptor, the ligand-receptor complex is not phagocytosed. Picture the human cell membrane and think of the serotonin receptor like a long piece of rope that has been wound up, but is embedded inside the cell membrane forever. After the serotonin binds, the structure of the receptor changes, causing lots of steps to start (like a domino effect) where molecules are released from the inner aspect of the receptor, thus carrying the message into the nucleus.