Thia actually is not true,
Caffeine, along with the other thioxanthenes, enter the cells and bind to the 2nd messenger systems responsible for conveying messages from the receptors to the nucleus, thereby altering the message. Caffeine doesn't actually bind to or block any receptor, unlike nicotine say.
Also, increasing the amounts of dopamine in the brain may help with the symptoms of Parkinson's disease, but not prevent it. It may also induce Schizophrenia like symptoms, as witnessed in Amphetamine users.