Two Americans and a Swede won the Nobel Prize in medicine Monday for discoveries about how brain cells communicate - research that laid the groundwork for Prozac and other drugs for depression and Parkinson's disease.
Arvid Carlsson, Paul Greengard and Eric Kandel will share the $915,000 prize for pioneering work that could lead to new treatments for schizophrenia, Alzheimer's disease, addiction and other mental disorders.
''The payoffs are potentially enormous,'' said Dr. Stephen Hyman, director of the National Institute of Mental Health.
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 at Columbia University in New York.
The awards were announced in Stockholm, Sweden.
They illuminated a key type of communication - called ''slow synaptic transmission'' - in which chemical messengers carry signals from one brain cell to another. The work has been crucial for understanding how the brain works and how diseases can arise when the system goes wrong.
The three winners worked largely independently.
Carlsson was honored for work in the late 1950s that showed a substance called dopamine is a key messenger between brain cells. He realized the implication for Parkinson's disease, which was later shown to result from a dopamine deficiency in part of the brain.
The work helped lead to development of a drug, L-dopa, to compensate for the missing dopamine. The drug is now standard treatment.
Carlsson's research also shed light on how other medications work, especially antipsychotic drugs used against schizophrenia.
The Nobel committee said Carlsson's work strongly contributed to the development of a class of antidepressants, including Prozac, that prolong the action of serotonin, another chemical messenger.
''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.
Greengard was honored for showing how brain cells react to the arrival of dopamine and other chemical messengers.
Kandel's work focused on the biology of learning and memory. It demonstrated that changes at synapses - the places where chemical messengers pass between brain cells - are crucial in forming memories.
Tim Bliss, head of neuroscience at the National Institute for Medical Research in London, said Kandel's work - ongoing since the 1960s - could lead to new treatments for Alzheimer's and other conditions involving memory loss.
''It's a very major piece of work and he's been an outstanding leader in the field for many years,'' Bliss said. ''He identified the physical embodiment of learning and memory in the brain.''
Kandel himself cautioned that ''there's an enormous distance between the kind of work I do and a clinical payoff.''
Last year's winner of the Nobel for medicine 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 winners of the prizes for physics and chemistry will be announced Tuesday, with the economics prize on Wednesday and the peace prize on Friday. No date has been set for the literature prize.
The awards are presented Dec. 10, the anniversary of Alfred Nobel's death in 1896. The Swedish industrialist and inventor of dynamite established the prizes in his will.
Kandel said he found out he had won the prize before dawn Monday when his wife, Denise, handed him the phone and said, ''Stockholm is calling.''
Asked if he had decided how to spend his share of the prize money, Kandel said: ''I don't have any specific plans, but Denise has lots of them.''
On the Net:
Nobel Prize site: http://www.nobel.se