Rita Levi-Montalcini

In 1952, working in Viktor Hamburger's laboratory in St. Louis, Levi-Montalcini showed that mouse tumours transplanted into chick embryos make sensory and sympathetic nerves grow without direct contact, and concluded that the tumours release a diffusible nerve growth-promoting factor. She developed the culture assay used to measure it and, with the biochemist Stanley Cohen, who joined the group in 1953 and purified it, discovered nerve growth factor (NGF), which the Nobel Assembly describes as one of the first of many growth-regulating signal substances to be discovered and characterized.

She and Cohen shared the 1986 Nobel Prize in Physiology or Medicine for their discoveries of growth factors, the same year they received the Lasker Foundation's Basic Medical Research Award. The Nobel Assembly said the discoveries opened new fields in basic science and that all research groups that later found new growth factors had followed in the tracks of Levi-Montalcini and Cohen.

Her embryology work indicated that developing nerve cells depend on their target tissues. In Turin in the early 1940s she found that after limb removal nerve cells formed and then died, she extended this with Hamburger in 1949, and in 1960 she and Barbara Booker showed that an antiserum to NGF destroyed most of the sympathetic nervous system in newborn mice. The Nobel Assembly describes the resulting picture, in which excess nerve cells are produced and only those that reach a target producing NGF survive, an idea known as the neurotrophic hypothesis.

In Turin in the early 1940s, in a small laboratory she had set up in her bedroom, with a makeshift incubator, instruments made from sewing needles and fertilised eggs bought from farms, Levi-Montalcini repeated Viktor Hamburger's experiments in which a limb bud is removed from a chick embryo. Examining the embryos over a range of time intervals, she saw that the nerve cells first multiplied and then died, and she concluded that the missing limb had withheld a factor needed to maintain the cells rather than one that made them form, a different reading from Hamburger's.

This is consistent with testing a published conclusion against finer-grained data and following the data to a different explanation. Analytical Rigour

In 1952, after injecting tumour extracts into chick embryos failed to reproduce the nerve growth that grafted mouse tumours produced, Levi-Montalcini flew to Rio de Janeiro with two tumour-bearing mice in her handbag to work in Hertha Meyer's tissue-culture laboratory, because her own facilities lacked that capacity. After several negative results, chick nerve tissue cultured next to a tumour fragment without touching it put out a dense halo of nerve fibres within about ten hours.

This is consistent with finding the means for an experiment elsewhere when her own laboratory lacked them. Resourcefulness

In 1946 Viktor Hamburger, who had read her wartime papers on limb removal in chick embryos, invited Levi-Montalcini to Washington University in St. Louis for a semester so that they could reconcile their differing findings. She arrived in 1947, the semester became about thirty years, and the 1949 paper by Hamburger and Levi-Montalcini and the later nerve growth factor work followed from it.

This is consistent with resolving a disagreement over the same data through joint experiments with the researcher who held the competing interpretation. Collaboration