Another forty years went by before Arvid Carlsson discovered dopamine—specifically, low concentrations of dopamine—in the brains of people with Parkinson’s disease. Carlsson was interested in three neurotransmitters: noradrenaline, serotonin, and dopamine. He particularly wanted to know which of these was involved in drug-induced Parkinson’s. Reserpine, a drug that was used to treat high blood pressure, had been found to cause symptoms of Parkinson’s in people and in animals.
