It took exactly 150 years since James Parkinson's description in 1817 of the illness bearing his name until the development of effective
therapy for this disorder, namely, the introduction of high-dosage
levodopa by George Cotzias in 1967. During the first 50 years, no effective
therapy was available, but neurologists reported using different agents, including metals. Then, around 1867, Charcot found
solanaceous alkaloids to be somewhat helpful, and these became the accepted and popular
therapy for the next 75 years. When basic scientists discovered that these
alkaloids had central
antimuscarinic activity,
pharmaceutical chemists developed synthetic chemical agents that were equally effective, with possibly less adverse effects, and around 1950 these
synthetic drugs became the standard medical
therapy for
Parkinson's disease (PD). The link between
dopamine and PD did not take place until 1957, 140 years after Parkinson's Essay. The clue came from research on
reserpine, a
drug derived from the Rauwolfia plant that caused a
sedative effect, now recognized as a
drug-induced parkinsonian state. Initial investigations revealed that
reserpine caused the release and depletion of
serotonin stores in the brain. With that knowledge, Arvid Carlsson, a young pharmacologist in Sweden, decided to explore the possibility that
reserpine might also affect brain
catecholamines. In his now famous, elegant, and simple experiment, he showed that injecting
l-dopa, the precursor of
catecholamines, alleviated the
reserpine-induced parkinsonian state in animals, whereas the precursor of
serotonin failed to do so. Carlsson then developed a highly sensitive assay to measure
dopamine, and his lab found that
dopamine is selectively present in high concentrations in the striatum and that administered
l-dopa could restore the
dopamine depleted by
reserpine. Carlsson postulated that all these findings implicate
dopamine in
motor disorders. Oleh Hornykiewicz, a young pharmacologist in Vienna, on being aware of the regional localization of brain
dopamine, decided to measure it in the brains of people who had PD and
postencephalitic parkinsonism. In 1960, he reported finding markedly depleted
dopamine in the striatum in these conditions. Immediately after, Hornykiewicz teamed up with the geriatrician, Walther Birkmayer, to inject small doses of
l-dopa intravenously (IV) into PD patients. They found benefit and pursued this treatment, but the gastrointestinal side effects limited the dosage, and many neurologists were doubtful that the effects from
l-dopa were any better than those with
antimuscarinic agents. A number of neurologists tested such low doses of IV
l-dopa and even higher oral dosages, but without showing any dramatic benefit, not better than the
antimuscarinics. Some of these studies were small, controlled trials. This general lack of efficacy with
l-dopa prevailed, and neurologists were discouraged about
l-dopa until 1967, when George C. Cotzias, a neuropharmacologist in New York, reported his results. He thought that PD may be result from the loss of
neuromelanin in the substantia nigra, and he decided to try to replenish the depleted
neuromelanin. Among the agents he tried was dl-
dopa. He wisely began with low oral doses and increased the dosage slowly and steadily, thereby limiting the gastrointestinal complication. He also treated his patients for a long duration, months in a government-supported hospital. In the accompanying videotape of an interview Cotzias gave in 1970, he describes much of his success to be able to observe his patients over months while building up the dosage very slowly and observe for signs of toxicity. When higher doses, usually over 12 g/day, were reached, dramatic antiparkinsonian effects were observed, and a revolutionary new treatment for PD was established.