Noting that the movement difficulties of his rabbits were similar to those of people with Parkinson’s disease, Dr. Carlsson proposed that the illness was related to a loss of dopamine. Other scientists confirmed that dopamine is depleted in people with Parkinson’s disease, a degenerative condition that causes tremors and rigidity, and L-dopa soon became the standard treatment for the illness.

Dr. Carlsson shared the 2000 Nobel Prize in Physiology or Medicine with two American researchers, Dr. Eric Kandel and Paul Greengard, who made their own discoveries about the transmission of chemical signals in the brain. In awarding the Nobel, the Karolinska Institute of Sweden said the contributions of the three scientists were “crucial for an understanding of the normal function of the brain” and for how signal disturbances could “give rise to neurological and psychiatric disorders.”

Arvid Carlsson was born on Jan. 25, 1923, in Uppsala, Sweden, one of four siblings in “an academic middle-class family,” he wrote in an autobiographical sketch for the Nobel committee. He grew up in the Swedish city of Lund, where his family moved after his father joined the University of Lund faculty as a history professor.

“My mother had passed a master-of-arts examination and my father a Ph.D. degree at the University of Uppsala,” Dr. Carlsson wrote. “My mother had a keen interest in research throughout her life but gave priority to raising her children and to assisting her husband in his research. However, when her husband died at the age of 76 she, then 71 years old, started to devote herself entirely to her favorite area of research, that is the legal status of women in the Middle Ages in Sweden. She published a couple of books and a number of articles on this subject in Swedish, which rendered her an honorary Ph.D. degree at the University of Uppsala several years later.”

His family had a “strong orientation toward the humanities,” Dr. Carlsson wrote. His older brother and sister followed his father into the humanities, but Dr. Carlsson, in an act of youthful rebellion, chose to study medicine, a field he saw as more useful than the arts.