Dr. Levi-Montalcini, widely regarded as one of the most influential scientists of her generation, died at 103. (Riccardo De Luca/AP)

Rita Levi-Montalcini, a Nobel Prize-winning neuroscientist who began her seminal research on cell development while dodging bombs and fleeing Nazi persecution during World War II, died Dec. 30 at her home in Rome. She was 103.

Gianni Alemanno, the city’s mayor, announced her death in a statement to international media. The cause was not disclosed.

Dr. Levi-Montalcini was widely regarded as one of the most influential scientists of her generation, and her accomplishments were particularly notable because of the handicaps and obstacles faced in science by women throughout the world when she began her career.

Her rise to the highest reaches of scientific achievement was made even more difficult because she embarked on her career under the fascist regime of Benito Mussolini, who expelled her and her fellow Jews from the Italian academic world.

She shared the 1986 Nobel Prize in medicine for her discovery of a substance known as the nerve growth factor, a naturally occurring protein that helps spark the growth of nerve cells. She launched that groundbreaking research in a makeshift bedroom laboratory during the war and deepened it in the 1950s at Washington University in St. Louis, where she worked alongside her co-Nobelist, the American biochemist Stanley Cohen.

In essence, Dr. Levi-Montalcini’s discovery helped explain how embryonic nerve cells grow into a fully developed nervous system and, more broadly, how a damaged nervous system might be repaired. Cohen was credited with the identification of the epidermal growth factor, a similar substance that helps regulate the growth of skin and other cells.

Together, those advances “opened new fields of widespread importance to basic science,” the Nobel Assembly at the Karolinska Institute declared in awarding the prize to the two scientists. The nerve growth factor is considered a foundation for modern research into treatment of Alzheimer’s disease and has also influenced research on cancer, Parkinson’s disease and muscular dystrophy.

Writing in the journal Science in 2000, Dr. Levi-Montalcini attributed her success to “the absence of psychological complexes, tenacity in following the path I reputed to be right, and the habit of underestimating obstacles.”

Rita Levi-Montalcini was born April 22, 1909, in the northern Italian city of Turin. Her mother, Adele Montalcini, was a painter; her father, Adamo Levi, was an engineer and subscribed to the then-prevailing view that women were best suited to the domestic life.

“It was he,” Dr. Levi-Montalcini wrote in an autobiography, “who had a decisive influence on the course of my life, both by transmitting to me a part of his genes and eliciting my admiration for his tenacity, energy and ingenuity; and, at the same time, by provoking my silent disapproval of other aspects of his personality and behavior.”

She discovered her affinity for science in her early 20s and gravitated toward medical research because she had lost a beloved governess to cancer. Dr. Levi-Montalcini received a medical degree in 1936 from the University of Turin, where her classmates included the future Nobel laureates Salvador Luria and Renato Dulbecco.

Dr. Levi-Montalcini began her career as an assistant to her professor, the eminent Italian neuroscientist Giuseppe Levi (no relation). In 1938, the fascist government handed down the anti-Semitic racial laws. She soon set up a laboratory in her home, reserving much of her bedroom to house the chicks she used in her experiments.

“The instruments, glassware, and chemical reagents necessary for my project were the same as my 19th-century predecessors had,” she wrote in the Science article. “I would bicycle to neighboring farms to buy fertilized chicken eggs (‘for my babies,’ I explained to the farmers, ‘because they were more nutritious’).”

Food was so hard to come by, Time magazine reported, that Dr. Levi-Montalcini sometimes made the leftover yolks into omelets.

When the bombardments of Turin became too fierce, she and her family fled to the highlands outside the city and then to Florence, where they eluded fascist persecution by assuming false identities. At the end of the war, Dr. Levi-Montalcini did medical work among war refugees.

In 1947, she received an invitation from Viktor Hamburger, a German-born embryologist whose writings had sparked the idea for her bedroom laboratory experiments. He asked her to join him at Washington University for a months-long fellowship. She became a full professor and stayed for three decades, holding dual Italian-American citizenship.

Dr. Levi-Montalcini also established an institute for the study of cell biology in Italy, where she was recognized about a decade ago as a senator-for-life. Her American honors included the prestigious Lasker Award for basic medical research in 1986 and a National Medal of Science in 1987.

Her autobiography, “In Praise of Imperfection,” was released in 1988. She explained in the book why she decided not to marry or have children.

“My experience in childhood and adolescence of the subordinate role played by the female in a society run entirely by men,” she wrote, “had convinced me that I was not cut out to be a wife.”

She had no immediate survivors.

After hearing that she had won the Nobel Prize, Dr. Levi-Montalcini remarked to an interviewer that the award was “a great honor.”

“Still,” she added, “there is no great a thrill as the moment of discovery.’’