Arvid Carlsson, Paul Greengard and Eric Kandel will share the $ 915,000 prize for their pioneering discoveries concerning a way brain cells send messages to each other, according to the award citation.
These discoveries have been crucial for an understanding of the normal function of the brain. In addition, they laid the groundwork for developing the standard treatment for Parkinson's disease and contributed to the development a class of antidepressants that includes Prozac, the Nobel Assembly at Karolinska Institute said.
Carlsson, 77, is with the University of Goteborg in Sweden; Greengard, 74, is with Rockefeller University in New York; and Kandel, 70, is an Austrian-born U.S. citizen with Columbia University in New York.
The medicine prize was the first announced in a week of awards.
The winners of the prizes for physics and chemistry will be announced Tuesday and for economics, the only one not established in Nobel's will, on Wednesday in Stockholm.
The awards culminate Friday with the coveted peace prize, to be announced in Oslo, Norway. The date for the literature prize, also announced in Stockholm, has not yet been set.
Carlssson said he was thrilled to learn Monday morning that he had won.
"What shall I say, you get glad of course, overwhelmed so to speak," he said in an interview with Swedish radio.
Carlsson's studies during the late 1950s led to the discovery of the drug L-dopa used to treat Parkinson's disease which is still the most important treatment for the disease, the committee said.
His research also increased understanding of other drugs, especially antipsychotic drugs used against schizophrenia.
"The discoveries of Arvid Carlsson have had great importance for the treatment of depression, which is one of our most common diseases," the citation said. "He has contributed strongly to the development of selective serotonin uptake blockers, a new generation of antidepressive drugs."
Greengard was cited for his discovery of how dopamine and other chemical messengers shuttle messages between brain cells.
Kandel was honored for his research on the biology of memory, showing the importance of changes in the synapse, a tiny gap between brain cells where messages are transmitted.
Kandel's research laid the foundation for understanding memory loss, said Lars Olson, a member of the Nobel committee.
"We now understand more about memory because of Kandel. We regard this as just the beginning in understanding memory," Olson told The Associated Press.
This year's award for medicine was bumped to the first aannouncement after the academy failed to reach a decision last week on the literature prize, usually the first announced.
The Swedish Academy, whih traditionally keeps the date of the literature prize secret until a couple days before it announces the winner, has not set a time yet, but it is always a Thursday, usually in October.
The suspense for the literature award was heightened last week when the academy failed to reach a decision.
Alfred Nobel, the Swedish industrialist and inventor of dynamite, left only vague guidelines in his will establishing the prizes. The selection committees deliberate in strict secrecy.
The only public hints available are for the peace prize. The five-member awards committee never reveals the candidates, but sometimes those making the nominations announce their favorites.
This year they include President Clinton and former President Jimmy Carter for wide-ranging peace efforts, as well as former U.S. Sen. George Mitchell for his efforts to resolve conflict in Northern Ireland.
Other reported nominees are former Finnish President Martti Ahtisaari and former Russian Prime Minister Viktor Chernomyrdin for their Balkan peace efforts; South Korean President Kim Dae-jung for promoting good relations in Asia; and a town, northern Albania's Kukes, for accepting 150,000 refugees during the Kosovo conflict.
The literature and peace laureates are usually the most visible, but the adjective "Nobel winner" often also bring scientists more attention from outside their laboratories.
As for the first announcement, Nobel's direction that a prize be awarded to the person who made "the most important discovery within the domain of physiology or medicine" is interpreted by a committee of 50 professors from the world-renowned Karolinska Institute in the Swedish capital.
The Nobel Assembly at Karolinska invites nominations from previous recipients, professors of medicine and other professionals worldwide before whittling down its choices in the fall, as do the other selection committees.
Last year's winner was Dr. Guenter Blobel, 64, a German native and U.S. citizen who discovered how proteins find their rightful places in cells - a process that goes awry in diseases like cystic fibrosis and plays a key role in the manufacture of some medicines.
The awards always are presented Dec. 10, the anniversary of Nobel's death in 1896.
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