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#36754
Complete Passage Discussion
In this passage, the author discusses some of the specific research that led to Rita Levi-Montalcini’s
Nobel Prize winning discovery of NGF, or “Nerve Growth Factor,” and the broad ramifications of this
and subsequent discoveries regarding neurotrophic factors.
Paragraph 1 Overview
The author begins this passage with an introduction to the concept of neurotrophic factors: Chemicals
which regulate the survival of nerve cells in animals. The first of these agents, known as NGF, was
discovered in the 1950’s by Rita Levi-Montalcini, who in 1986 shared the Nobel Prize for this discovery.
Paragraph 2 Overview
In the second paragraph, the author takes us back in time, to the mid-1940’s, at which point Levi-
Montalcini had hypothesized that many of a developing organism’s immature nerve cells are normally
programmed to die. She did research to confirm this study, and in 1949 found that embryos produce
many more nerve cells than are needed, and that the number of cells adjusts downward to suit the
tissue’s necessity.
A later phase of the research dealt with chick embryos, whose nerve development could be stimulated
with tumor implantation. Rita’s hypothesis was that this stimulation is caused by a chemical produced
by the tumors. The technique of tissue culture, which grows cells outside an organism, was used to
investigate and then prove her hypothesis. Further research identified the tumor substance responsible for
the observed effects, and Levi-Montalcini called it NGF, which stands for “nerve growth factor.”
Paragraph 3 Overview
The author begins the third paragraph by pointing out that NGF was the first of many cell-growth factors
found in animals. Levi-Montalcini’s work, supplemented by later research, led to the determination that
NGF is present in many tissues and fluids, and in heavy concentrations in some organs. This growth
factor appears to be supplied by muscle cells, by organs over which nerve impulses will be transmitted,
or sometimes by cells that are interspersed with the nerve tissues. The cells affected by NGF, generally
those outside the brain and spinal cord, die if NGF is absent, or if anti-NGF antibodies are present.
Passage Summary
Paragraph One: Introduce the chemical NGF, its function, and its Nobel Prize winning discoverer.
Paragraph Two: Provide specific background on the hypotheses and research that lead to the discovery of
NGF.
Paragraph Three: Provide further information about subsequent research which shed light on sources of
NGF within an organism.
In this passage, the author discusses some of the specific research that led to Rita Levi-Montalcini’s
Nobel Prize winning discovery of NGF, or “Nerve Growth Factor,” and the broad ramifications of this
and subsequent discoveries regarding neurotrophic factors.
Paragraph 1 Overview
The author begins this passage with an introduction to the concept of neurotrophic factors: Chemicals
which regulate the survival of nerve cells in animals. The first of these agents, known as NGF, was
discovered in the 1950’s by Rita Levi-Montalcini, who in 1986 shared the Nobel Prize for this discovery.
Paragraph 2 Overview
In the second paragraph, the author takes us back in time, to the mid-1940’s, at which point Levi-
Montalcini had hypothesized that many of a developing organism’s immature nerve cells are normally
programmed to die. She did research to confirm this study, and in 1949 found that embryos produce
many more nerve cells than are needed, and that the number of cells adjusts downward to suit the
tissue’s necessity.
A later phase of the research dealt with chick embryos, whose nerve development could be stimulated
with tumor implantation. Rita’s hypothesis was that this stimulation is caused by a chemical produced
by the tumors. The technique of tissue culture, which grows cells outside an organism, was used to
investigate and then prove her hypothesis. Further research identified the tumor substance responsible for
the observed effects, and Levi-Montalcini called it NGF, which stands for “nerve growth factor.”
Paragraph 3 Overview
The author begins the third paragraph by pointing out that NGF was the first of many cell-growth factors
found in animals. Levi-Montalcini’s work, supplemented by later research, led to the determination that
NGF is present in many tissues and fluids, and in heavy concentrations in some organs. This growth
factor appears to be supplied by muscle cells, by organs over which nerve impulses will be transmitted,
or sometimes by cells that are interspersed with the nerve tissues. The cells affected by NGF, generally
those outside the brain and spinal cord, die if NGF is absent, or if anti-NGF antibodies are present.
Passage Summary
Paragraph One: Introduce the chemical NGF, its function, and its Nobel Prize winning discoverer.
Paragraph Two: Provide specific background on the hypotheses and research that lead to the discovery of
NGF.
Paragraph Three: Provide further information about subsequent research which shed light on sources of
NGF within an organism.