ScienceWeek

SCIENCE-WEEK

A Weekly Email Digest of the News of Science

A journal devoted to the improvement of communication
between the scientific disciplines, and between scientists,
science educators, and science policy makers.

April 23, 1999 -- Vol. 3 Number 17

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I have never met a bored biologist... Biologists suffer
from paranoia, frustrated ambition, angst about their
sex lives, lack of hard cash, and all the usual frets
that beset mankind. But they are not bored.
-- Martin Wells

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Chaos Theory
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Biotechnology
Human Evolution
Neurobiology
Evolutionary Biology

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nearly 200 titles; the Quantum Theory list nearly 100 titles).
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1999 are listed. Each title is directly linked to more
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Contents of This Issue:

1. Graduate Student Stress: A Proposal in the Wake of a Tragedy
2. On the Astronomer Gerard Kuiper
3. On the Pythagoras-Planck Program and Modern Physics
4. Neuron Pathfinding and Growth-Cone Calcium Ion Transients
5. Hunting Behavior of a Marine Mammal Beneath Antarctic Fast Ice
6. Effect of Race and Sex of Patients on Treatment for Chest Pain

-- In Focus: On the Impact of Quantum Theory

-----------------------------------------------------------

1. GRADUATE STUDENT STRESS: A PROPOSAL IN THE WAKE OF A TRAGEDY
In August of 1998, a 5th year graduate student in the Department
of Chemistry at Harvard University (US) wrote a note castigating
the department for the power professors have over the lives of
graduate students and then committed suicide by ingesting
cyanide. The student, Jason Altom, was the 3rd Harvard graduate
student to commit suicide since 1997, and the event prompted much
discussion, many recriminations, and the formation of committees
at Harvard and at other universities, in both chemistry
departments and other departments. Altom was working on the
synthesis of a complex molecule under the supervision of organic
chemist Elias J. Corey, winner of the 1990 Nobel Prize in
Chemistry. In his suicide note, Altom elaborated on the pressures
affecting graduate students: the pressure to succeed and the
pressure of an intense relationship with a single supervisor. In
an editorial in October 1998, the journal _Nature_ wrote of this
case: "Such situations raise a key issue that lies behind a broad
swathe of current concerns, from scientific misconduct to the
plight of contract research staff: is a culture of achievement,
fanned by an increasingly competitive job market and tight
competition for research grants, now in danger of driving out the
culture of mutual support from which both science and its
protagonists have gained so much in the past?"
... ... Now Carl Djerassi (Stanford University, US), an eminent
chemist, considers the Altom suicide case and proposes a solution
to the problems that apparently played a role in the tragedy.
Djerassi makes the following points: 1) Although in his suicide
note Altom suggested a 3-member faculty oversight committee would
"provide protection for graduate students from abusive research
advisors", Djerassi questions the efficacy of such a committee by
pointing out that the faculty members of such a committee would
generally be unwilling to confront a colleague with a complaint,
and any junior faculty member on such a committee might seriously
damage his or her career by confronting a senior renowned
colleague with a complaint. 2) Djerassi suggests that an
alternative solution concerning complaints about "abusive
research advisors" (Altom's terms) and other ill-defined
behaviors is to have the complaints handled anonymously outside
the "intensely collegial and competitive department setting." The
procedure would be similar to that now in place in many US
universities for evaluation of faculty by undergraduates, often
with written assessment and numerical ratings of various
qualities, the data gathered by a central university office.
Djerassi suggests annual evaluations by graduate students and
postdoctoral fellows "of the many components of an appropriate
mentor-disciple relationship". 3) Djerassi concludes: "The social
structure of the professor-graduate student relationship in the
sciences is distinct. Although an undergraduate mentoring fiasco
rarely causes permanent damage -- mainly because other mentors
are readily available -- the same can hardly be said of graduate
school, where the effects of this one-on-one mentor-disciple
relationship may last a lifetime. Must people die before research
universities will place serious emphasis on monitoring,
evaluating and, crucially, on mentoring the mentors in their
graduate school science faculties?"
-----------
Carl Djerassi: Who will mentor the mentors?
(Nature 28 Jan 99 397:291)
QY: Carl Djerassi [djerassi@stanford.edu]
-------------------
Summary by SCIENCE-WEEK [http://scienceweek.com] 23Apr99


2. ON THE ASTRONOMER GERARD KUIPER
In the 20th century, in the US and in many other places, the
scientific vocation is often a combat arena of egos, fashions,
funding, and public relations. Frequently, as one might expect,
it is only after the dust in the arena has settled that the real
lasting contribution of an individual scientist becomes clear.
Such is the case of Gerard Peter Kuiper (1905-1973), a
Netherlands-born American astronomer, now recognized as the
father of modern planetary astronomy, and a scientist whose
dossier of significant discoveries will keep him in the forefront
of any future accounts of the history of science in this century.
... ... S. Alan Stern (Southwest Research Institute, US) presents
a biographical review of the life and scientific achievements of
Gerard Kuiper, the author making the following points: 1)
Kuiper's interest in the nature and origin of the Solar System
was already formulated while he was an undergraduate. He was
trained at the University of Leiden (NL), as an undergraduate and
as a graduate student, by a physics and astronomy faculty that
included *Willem de Sitter, *Ejnar Hertzsprung, and *Paul
Ehrenfest. Kuiper's doctoral thesis, mentored by Hertzsprung and
the astronomer *Jan Oort, focused on the statistics of *binary
stars. When he completed his doctorate in 1933, Kuiper
immediately moved to the US as a postdoctoral research fellow at
the Lick Observatory in California. There Kuiper continued his
study of binary stars, providing evidence that 50 percent of the
nearest stars belong to binary systems. 2) During the first part
of his career, Kuiper made a seminal study of the relationship
between mass and luminosity for *Main Sequence stars, and his
investigation of this relation remained a standard in the field
for 50 years. 3) In the 1940s, Kuiper began his major work on the
Solar System, producing the following results: a) He surveyed the
asteroid belt and families of asteroids. b) He discovered the
atmosphere of Venus consists mostly of carbon dioxide. c) He
discovered the atmosphere of Mars consists mostly of carbon
dioxide. d) He deduced the maria on the Moon contain basalts. e)
He discovered the rings of Saturn are made of water ice. f) He
discovered the atmosphere of the Saturn moon Titan. g) He
discovered Miranda, the 5th moon of Uranus. g) He discovered
Nereid, the 2nd moon of Neptune. h) He suggested the existence of
what is now called the "*Kuiper Belt". 4) Following his death,
Kuiper's scientific colleagues named prominent craters on the
moon, Mars, and Mercury for him -- an honor no other human being
has earned. 5) The author concludes: "Yet perhaps the best
commemoration of his life is the simple statement that Gerard
Kuiper, more than anyone else, was responsible for restoring
Solar System astronomy to prominence in an era dominated by
stellar and galactic research."
----------
S. Alan Stern: Forging a new Solar System.
(Astronomy March 1999)
QY: S. Alan Stern, Southwest Research Group, Boulder CO, US
-----------
Text Notes:
... ... *Willem de Sitter: (1872-1934) Influential in bringing
the general theory of relativity to the attention of English-
speaking astronomers. His major work was in theoretical
cosmology.
... ... *Ejnar Hertzsprung: (1873-1967) Introduced the concept of
the absolute magnitude (brightness) of a star, and described the
relationship between the absolute magnitude and the temperature
of a star. The results were formulated in what came to be known
as the *Hertzsprung-Russell diagram.
... ... *Hertzsprung-Russell diagram: The Hertzsprung-Russell
diagram is a plot of stellar absolute magnitude against spectral
type, and is one of the most useful diagrammatic aids in
astrophysics.
... ... *Paul Ehrenfest: (1880-1933) Theoretical physicist, one
of the first to take Planck's quantum theory seriously. Assumed
the chair of theoretical physics at the University of Leiden in
1912.
... ... *Jan Hendrik Oort: (1900-1992) In 1927, Oort calculated
the mass and size of our Galaxy and the distance of the Sun from
its center from the observed movements of stars around the
galactic center. In 1950, Oort proposed that comets exist in a
vast swarm, now called the Oort cloud, at the edge of the Solar
System.
... ... *binary stars: Binary stars are a pair of stars revolving
around a common center of mass under the influence of their
mutual gravitational attraction, and apparently the majority of
stars in the universe are binaries and not singlets. In some
cases the binary system is resolvable into two components, and in
other cases the presence of a second star is inferred by
perturbations in the motion or emitted radiation of the first
star. If the binaries are close enough, they may share stellar
material, and this results in a particular kind of stellar
evolution.
... ... *Main Sequence stars: The Main Sequence is a region on
the Hertzsprung-Russell diagram where most stars, including our
own Sun, are situated. The course of a star's evolution can be
traced as a particular path in the H-R diagram, with the paths of
various types of stars showing significant differences.
... ... *Kuiper Belt: In 1951, Kuiper postulated the existence of
a belt of objects beyond the orbit of Pluto. Both the existence
and nature of the objects were matters of speculation for
decades, and finally in 1992 Jewitt and Luu identified the first
Kuiper object. The current estimate is that as many as 10^(8)
objects larger than 10 kilometers in diameter may exist in what
is called the "Kuiper belt", a disc that hugs the plane of the
planetary system and lies between 35 and 1000 *AU from the Sun.
Observations to date  have yielded some 55 trans-Neptune bodies
with radii on the order of 100 km or larger, and Pluto is
considered by some astronomers to be a member of this population.
... ... *AU: Astronomical Units. 1 AU is effectively the
mean distance between the Earth and the Sun.
-------------------
Summary & Notes by SCIENCE-WEEK [http://scienceweek.com] 23Apr99
-------------------
Related Background:
NEPTUNE'S ECCENTRICITY AND THE NATURE OF THE KUIPER BELT
In 1951 the astronomer Gerard P. Kuiper (1905-1973) postulated
the existence of a belt of objects beyond the orbit of Pluto.
Both the existence and nature of the objects were matters of
speculation for decades, and finally in 1992 Jewitt and Luu
identified the first Kuiper object. The current estimate is that
as many as 10^(8) objects larger than 10 kilometers in diameter
may exist in what is called the "Kuiper belt", a disc that hugs
the plane of the planetary system and lies between 35 and 1000
*AU from the Sun. Observations to date have yielded some 55
trans-Neptune bodies with radii on the order of 100 km or larger,
and Pluto is considered by some astronomers to be a member of
this population. ... ... Now Ward and Hahn (2 installations, US)
present calculations that indicate that the small *orbital
eccentricity of Neptune may be a direct consequence of *resonant
wave interaction between Neptune and the Kuiper belt. The Kuiper
belt is subject to resonant perturbations from Neptune, so that
the transport of angular momentum density waves can result in
orbital evolution of Neptune as well as changes in the structure
of the Kuiper belt. The calculations indicate Neptune's
eccentricity could damp to its current value over the age of the
solar system if the Kuiper belt contains slightly more than an
Earth mass of material out to about 75 AU.
QY: William R. Ward, Southwest Research Institute, 1050 Walnut
Street, Suite 429, Boulder, CO 80302 US.
(Science 26 Jun 98 280:2104) (Science-Week 24 Jul 98)
-------------------
Related Background:
... ... *AU: Astronomical Unit. 1 AU = the mean distance from the
Sun to the Earth = approximately 93 million miles, and exactly
149,597,870 kilometers.
... ... *orbital eccentricity: This is a measure of the extent to
which an elliptical orbit departs from circularity. For a
circular orbit, eccentricity = 0. Neptune's eccentricity is quite
low (0.009) compared with the other planets in the solar system
(Earth's eccentricity = 0.017), although the eccentricities of
the planets do vary over long time-frames.
... ... *resonant wave interaction: In general, resonance is a
marked increase in the oscillation amplitude of a system when the
system is subjected to an oscillating force whose frequency is
the same or close to the natural frequency of the system as
determined by the system parameters. The waves mentioned in this
report are waves excited at resonance sites, locations where a
forcing frequency matches some natural frequency of the Kuiper
belt.
... ... In August 1989, the Voyager 2 spacecraft passed only 4400
kilometers above the cloud tops of Neptune and revealed the first
details of the planet, its rings, and its satellites. Neptune has
an apparent rocky core, an inner mantle of liquid water, methane,
and ammonia, and an outer shell of hydrogen and helium. The
intense atmospheric activity on Neptune is apparently driven by
heat flow from the interior, but the cloud top temperature is
-216 degrees centigrade. The diameter of the planet is
approximately 4 times the diameter of Earth, and its average
distance from the sun is approximately 30 AU.
-------------------
Related Background:
EVIDENCE FOR KUIPER BELT ORIGIN OF PLUTO AND TRITON
... ... Robert H. Brown and his associates (University of
Arizona, NASA Ames Research Center, California Institute of
Technology) have succeeded in obtaining spectroscopic
information from Kuiper Object 1993SC, which is apparently 300
kilometers in diameter. Using the spectra to determine the
surface composition of the object, and comparing the data to
that already obtained from Pluto and Neptune's moon Triton, the
result is consistent with the idea that Pluto, Triton, and the
Kuiper Belt objects may have a common solar system history, with
Pluto and Triton being the largest members of the population of
bodies that made up the early Kuiper belt.
(Science 9 May 97) (Science-Week 15 May 97)


3. ON THE PYTHAGORAS-PLANCK PROGRAM AND MODERN PHYSICS
In modern physics, "strong interactions" are interactions between
elementary particles involving the strong interaction force, a
short range force approximately 100 times greater than the
electromagnetic force between charged particles. The strong force
is important only for particles separated by a distance of less
than approximately 10^(-15) meters, and is the force that holds
protons and neutrons together in atomic nuclei. Quantum field
theory is the mathematical fusion of quantum mechanics with
special relativity theory, and there are essentially 2 branches:
quantum electrodynamics (applicable to charged particles involved
in electromagnetic interactions) and *quantum chromodynamics
(applicable to nuclear particles involved in strong force
interactions). One of the major efforts of modern physics is the
construction of a unifying theoretical framework that can account
for all phenomena with a set of consistent principles and their
quantitative formulations, and one version of this effort
involves "a vision of a world derived from pure logic and
mathematics", a vision with an emphasis on the significance of
universal dimensionless constants. Because of its emphasis on
number, this vision has been called "Pythagorean".
... ... Frank Wilczek (Institute for Advanced Study Princeton,
US) presents a general "progress report" of current work in this
field, the author making the following points: 1) Quantum
mechanics provides a unique *ground-state configuration for each
atom and molecule, making it possible to understand why atoms and
molecules exhibit well-defined, universal chemistry. 2) At a yet
deeper level, quantum field theory, which is the logical
extension of quantum mechanics to include special relativity,
explains why the elementary constituents -- electrons and nuclei
-- exist in myriads of identical copies, each being an excitation
of a single universal field. 3) The objective of the modern
Pythagoras-Planck program is to formulate a theoretical framework
in which G (the gravitational constant), c (the velocity of light
constant), and h (the Planck constant) are all profoundly
incorporated, and to calculate within that framework all the
constants of nature, expressed in Planck units, as pure
dimensionless numbers. John Wheeler has termed this program
"getting its from bits". 4) Wilczek suggests that quantum
chromodynamics, the modern theory of the strong interaction,
which binds atomic nuclei together, has advanced the "its from
bits" program in 3 ways: a) Quantum chromodynamics accounts, in
principle, for the masses of nuclei. b) Quantum chromodynamics
brings to the fore a profound property of quantum field theories
-- the relativity of charge: because of the quantum properties of
the vacuum, the charge one measures is not an absolute concept
but depends on how it is measured. c) The relativity of charge,
which plays such a central role in quantum chromodynamics,
applies as well to the other interactions of the *Standard Model
of modern physics, and this brings up the possibility that all
the couplings (forces of interaction) might have a common value
when measured at exceedingly small distance scales. 5) Wilczek
concludes by suggesting that although all of the recent
developments justify optimism, "it remains conceivable that the
'its from bits' program will hit a wall... Attempts to calculate
the electron mass from first principles might be as futile as
attempts to calculate the shape of the Solar System, or the
anatomy of frogs. Still, we must try."
-----------
Editor's note: We use the term "filtering" to describe
explicating science by passing through to the reader only some of
the details and concepts and not all the details and concepts.
The summary above involves what may be called "second-order
filtering": Wilczek is filtering theoretical physics in a general
review, and ScienceWeek is filtering Wilczek. Caveat emptor.
-----------
Editor's note: In addition to the background material, see
several related SW Focus Reports available at URL
[http://scienceweek.com/swfr.htm].
Also, see the SW extensive list of new books on quantum theory at
URL [http://scienceweek.com/bklist1.htm] (Nearly 100 new and soon
to be published titles).
-----------
Frank Wilczek: Getting its from bits.
(Nature 28 Jan 99 397:303)
QY: Frank Wilczek [wilczek@sns.ias.edu]
-----------
Text Notes:
... ... *quantum chromodynamics: See below for some explications
concerning quantum chromodynamics. The "chromo-" in
chromodynamics derives from the use of designated "color"
attributes of quarks, fundamental entities involved in strong
force interactions.
... ... *ground-state: In this context, the ground state is the
state of lowest energy of a physical system.
... ... *Standard Model: In particle physics, the Standard Model
is a theoretical framework whose basic idea is that all the
visible matter in the universe can be described in terms of the
elementary particles leptons and quarks and the forces acting
between them. Leptons are a class of point-like fundamental
particles showing no internal structure and no involvement with
the strong forces. A quark is a hypothetical fundamental
particle, having charges whose magnitudes are one-third or
two-thirds of the electron charge, and from which the elementary
particles may in theory be constructed. 
-------------------
Summary & Notes by SCIENCE-WEEK [http://scienceweek.com] 23Apr99
-------------------
Related Background:
PARTICLE PHYSICS: ON GLUONS AND GLUEBALLS
The physics of elementary particles is in the midst of an era of
conceptual complexity that some people find unsettling and other
people find invigorating. A quark is a hypothetical fundamental
particle, having charges whose magnitudes are one-third or
two-thirds of the electron charge, and from which the elementary
particles that have an apparent internal structure may in theory
be constructed. Quarks are believed to be held together through
the exchange of gluons, massless particles that carry the *strong
force. At the present time, 18 different quarks with various
properties are thought to exist, with a corresponding number of
*antiquarks. Gluons have a "sticking" property -- they can
agglomerate -- and agglomerations of gluons alone are called
"glueballs". ... ... F.E. Close and P.R. Page review current
ideas concerning gluons and glueballs, and the authors make the
following points: 1) Along with fractional electric charge,
quarks also have "flavor" in 6 varieties (up, down, charm,
strange, top, and bottom), and "color" (red, yellow, or blue).
[*Note #1] 2) Quarks may also attach to antiquarks, particles
that have opposite charge, and an antiquark comes in anticolors
(antired, antiyellow, antiblue). An anticolor is mathematically
denoted by negative color, and a color and its anticolor attract.
3) The theory of electromagnetism describes the attraction
between opposite electric charges. In the 1940s, physicists
merged electromagnetism with relativity and quantum theory,
creating quantum electrodynamics (QED). This theory -- the most
successful theory known to physics -- holds that the
electromagnetic force is transmitted by massless objects called
photons. These quanta of light banish the classical idea of
action at a distance. It can be said that photons bounce between
an electron and an antiparticle (the positron) in such a manner
as to draw the two together. 4) The equivalent theory of color
charges, which communicate via the *strong force, is called
quantum chromodynamics (QCD). Gluons, the massless quanta of the
strong force, transmit the color interactions. 5) Gluons are
fundamentally different from photons. Photons do not have charge,
so one photon cannot push or pull on another photon. Gluons,
however, are themselves colored. A red quark, for example, can
turn into a blue quark by radiating a red/antiblue gluon.
Basically, a gluon can attract another gluon. Another difference
between photons and gluons is that while photons uniformly
surround electrons, forming a shell with spherical symmetry whose
density falls off with distance, gluons are not uniformly
distributed and instead clump together into a tube linking a
quark and an antiquark. The color originating in the quark can be
thought to "flow" through the tube to the antiquark, where it
becomes absorbed. 6) In 1972 H. Fritzch and M. Gell-Mann
predicted that two or more gluons can combine into a strongly
bound, neutral-colored particle of pure "glue". This hypothetical
object is called a "glueball". A glueball is thought to have a
radius of 0.5 x 10^(-15) meters (less than that of a proton), and
exist for less time than light takes to cross a hydrogen atom. 7)
The authors state that although the idea of glueballs was
elegant, quantum chromodynamics is a "rather messy theory", since
the peculiar "sticky" character of the strong force makes it
impossible to perform exact calculations. Almost everything known
about color and glue comes not from direct calculation but from
massive computer simulations known as "lattice QCD". 8) Finally,
the authors discuss various current and planned future attempts
to detect the existence of glueballs, and they conclude: "One of
these experiments will, we fondly hope, upturn unambiguous
evidence of unadulterated glue."
----------
F.E. Close and P.R. Gage (2 installations, UK US)
Glueballs.
(Scientific American November 1998)
QY: Frank E. Close, University of Oxford, UK.
-----------
Text Notes:
... ... *strong force: The fundamental forces comprise the
gravitational force, the electromagnetic force, the nuclear
strong force, and the nuclear weak force.
... ... *antiquarks: The antimatter quark entity. In general,
antiparticles are homologs of elementary particles but with
opposite charge. The positron, for example, is the antimatter
particle homologous to the electron. Matter composed entirely of
antiparticles is called antimatter.
... ... *Note #1: In this context, flavors and colors are labels
for specific sets of properties associated with specific types of
quarks. Some people call these labels "whimsical", but perhaps
there is some sense to the whimsy, since it emphasizes that at
the present time we are apparently unable to describe the
properties and behaviors of the fundamental particles with
classical language (i.e., with the language of old models).
-------------------
Summary & Notes by SCIENCE-WEEK  6Nov98
-------------------
Related Background:
EVIDENCE FOR A QUARK-GLUON PLASMA
... According to current theory, quarks and gluons cannot exist
in isolation. But theory also predicts that at temperatures
10^(12) degrees Kelvin or greater (such as existed during the
first 0.01 second of the history of the universe) a drastic
change in the structure of nuclear matter occurs, and only
descriptions in terms of quarks and gluons apply. A plasma is a
gas consisting entirely of equal numbers of positive and negative
charges. ... ... F. Wilczek (Institute for Advanced Study
Princeton, US), in a short review of recent experiments that for
the first time apparently produced a quark-gluon plasma, "an
extraordinary new state of matter", suggests that an important
question is whether, as a function of temperature, the transition
from ordinary matter to a quark-gluon plasma is continuous or
discontinuous. A discontinuous transition could imply explosive
instabilities, which in turn may have been important in the
evolution of the early universe.
QY: Frank Wilczek 
(Nature 22 Jan 98) (Science-Week 23 Jan 98)
-------------------
Related Background:
FIRST EVIDENCE OF AN EXOTIC MESON
In particle physics, the term "meson" has had an interesting
history. Between 1939 and 1947, it was used to refer to what are
now called "muons". In 1947, the definition changed, and meson
now refers to an unstable, strongly interacting sub-nuclear
particle that consists of a quark bound to an anti-quark. There
is more than one type of meson, but they all consist of quarks
and anti-quarks bound together by "gluons". In the 1970s,
theorists predicted the existence of "exotic" mesons whose gluon
linkages between quarks and anti-quarks had the mathematical
properties of vibrating strings. But no one had or has yet
provided evidence of exotic mesons. ... ... Now Suh-Urk Chung et
al (Brookhaven National Laboratory, Upton NY US) have apparently
finally identified such a particle in collisions of fast-moving
mesons called "pions" with protons in a liquid hydrogen target.
They have determined the exotic meson's mass to be approximately
1.4 Gev (billion-electron-volts), and another laboratory, using a
completely different experimental method, has evidently independ-
ently confirmed an exotic meson with the same mass of 1.4 Gev.
But whatever excitement there is about finally identifying the
exotic meson, it is apparently combined with puzzlement, because
the revealed mass is less than what had been predicted. Revisions
of theory may be in order, since in the arena of particle
physics, revisions are the usual consequence of puzzlement.
QY: S-H. Chung, Brookhaven National Lab. (516) 344-8000.
(Phys. Rev. Lett. 1 September) (Science-Week 12 Sep 97)


4. NEURON PATHFINDING AND GROWTH-CONE CALCIUM ION TRANSIENTS
After neurons have differentiated and migrated to their intended
specific destinations, they extend *axons that select connection
targets from an enormous number of possibilities, and eventually
these axons form *synapses with appropriate cells in the target
region. These events depend on a complex of cellular and
molecular signals that guide axons and facilitate correct
connections. The signals involve *cell adhesion molecules that
regulate the interactions between axons and the surfaces upon
which they grow, diffusible molecules that attract growing axons,
and a family of molecules called "*neurotrophins" that promotes
and maintains stable synapses between axons and their targets.
The circuitry of the developing nervous system is thus gradually
constructed by means of such intricate interactions. The local
dynamics of growing axons are now known to involve the properties
of the "growth cone", a specialized structure at the tip of the
extending axon. Growth cones are highly motile structures that
explore the extracellular environment and respond to local cues
by changing the speed or direction of growth. Experiments
indicate that in vitro the intracellular calcium ion
concentration of growth cones is correlated with their motility,
but the links between environmental cues and axon growth in vivo
are unknown. ... ... T.M. Gomez and N.C. Spitzer (University of
California San Diego, US) now report a study of the development
of axonal projections of various types of nerve cells in the
spinal cord of the embryo of the toad (Xenopus). The authors
report that axon growth cones generate transient elevations of
intracellular calcium ion concentration as they migrate within
the embryonic spinal cord, and that the rate of axon outgrowth is
inversely proportional to the frequency of transients.
Suppression of calcium ion transients by photorelease of a
calcium ion chelator accelerates axon extension, whereas
mimicking transients with photorelease of calcium ion slows
otherwise rapid axonal growth. The authors report that the
frequency of calcium ion transients is cell-type specific and
depends on the position of growth cones along their pathway. The
authors further report that growth-cone stalling and axon
retraction, which are two important aspects of pathfinding, are
associated with high frequencies of calcium ion transients. The
authors suggest their results indicate that environmentally
regulated growth-cone calcium transients control axon growth in
the developing spinal cord.
-----------
Editor's note: In addition to the background material below, see
the Neurobiology New Book List at URL:
http://scienceweek.com/bklist8.htm
A number of related SW Focus Reports can be found at URL:
http://scienceweek.com/swfr.htm
-----------
T.M. Gomez and N.C. Spitzer: In vivo regulation of axon extension
and pathfinding by growth-cone calcium transients.
(Nature 28 Jan 99 397:350)
QY: Timothy M. Gomez [tgomez@biomail.ucsd.edu]
-----------
Text Notes:
... ... *axons: In those animals that have nervous systems, one
task of embryological development is to ensure the proper
functional connections between nerve cells and other nerve cells,
and between nerve cells and muscle cells. The innervation must be
exact, in the sense that the growing nerve cell extension (the
axon), which will ultimately serve to propagate information, must
reach a specific and often distant target. In humans, for
example, there are nerve cells whose growing axons reach specific
targets as much as a meter distant from the cell body.
... ... *synapses: The junction between the terminal of a
neuron's axon and another neuron is called a "synapse". When
studying the synapse, the first neuron is called the
"presynaptic" neuron, and the second neuron is called the
"postsynaptic" neuron.
... ... *cell adhesion molecules: In general, cell adhesion is
simply the ability of cells to remain in association with each
other.
... ... *neurotrophins: In general, neurons in the central
nervous system apparently depend for their survival on a number
of secreted substances called neurotrophins (neurotrophic
factors). These substances are polypeptides of 200 to 300 amino
acids, and at least 4 different neurotrophins have been
identified.
-------------------
Summary & Notes by SCIENCE-WEEK [http://scienceweek.com] 23Apr99
-------------------
Related Background:
ACTIVITY-DEPENDENT CORTICAL TARGET SELECTION BY GROWING AXONS
Many of the connections between nerve cells (the "wiring" of the
nervous system) are programmed in mammals during development.
This is particularly true of the pathway connections of the
sensory systems and the basic motor output systems. During the
wiring of the connections between the *thalamus and *cortex in
mammals, there is an intermediate step in which thalamic axons
grow and interact with a special population of neurons (so-called
subplate neurons) before they contact their ultimate target
neurons within the cerebral cortex (cortical plate). Such
connections in the developing nervous system are thought to be
formed initially by a process not dependent on activity, the axon
pathfinding process and target selection only afterward refined
by neural activity. ... ... Now Catalano and Shatz (University of
California Berkeley, US) report that blockade of *sodium action
potentials by *intracranial infusion of *tetrodotoxin in cats
during the early period when axons from the *lateral geniculate
nucleus were in the process of selecting visual cortex as their
target altered the pattern and precision of this thalamo-cortical
projection. The majority of these neurons, rather than projecting
to visual cortex, elaborated a significant projection within the
subplate of cortical areas normally bypassed. Those axons that
did project to their correct target were *topographically
disorganized. The authors suggest that neural activity is thus
required for initial targeting decisions made by thalamic axons
as they cross the subplate, and that whatever the mechanisms, the
formation of connections between thalamus and *neocortex in
mammals be a special exception to the general rule that target
selection by developing axons is independent of neural activity.
QY: Carla J. Shatz 
(Science 24 Jul 98) (Science-Week 14 Aug 98)
-------------------
Related Background:
... ... *thalamus: The thalamus is a deep brain structure that
consists of groups of nerve cells that project to various other
regions of the brain. In general, these groups of nerve cells are
specific relay stations for sensory information (e.g., visual,
auditory, pain, temperature, etc.)
... ... *cortex: The term "cortex" is often used as the short
form for "cerebral cortex", but there are other anatomical
structures also called "cortex", so the meaning is context-
dependent.
... ... *sodium action potentials: In vertebrates, most action
potentials are "sodium action potentials", due to a transient
increase in sodium ion permeability that is propagated down the
axon to the axon terminal(s).
... ... *intracranial infusion: In general, the introduction of
any solution into the brain within the skull.
... ... *tetrodotoxin: A neurotoxin that specifically blocks the
change in sodium ion permeability necessary for the production of
an action potential. Tetrodotoxin acts on sodium ion channels in
the axon membrane.
... ... *lateral geniculate nucleus: A thalamic cell group that
acts as a relay station in the visual pathway from the retina to
the primary visual area of the cerebral cortex.
... ... *topographically disorganized: Ordinarily, the
topographical organization of visual (photon) input to the retina
is for the most part projected isomorphically to the primary
visual area of the brain for analysis. Any topographical
disorganization of information in the pathway or at its terminus
(a disruption of the "mapping") can thus have devastating effects
on the ability of the system to analyze visual inputs.
... ... *neocortex: The most recently evolved part of the
cerebral cortex.


5. HUNTING BEHAVIOR OF A MARINE MAMMAL BENEATH ANTARCTIC FAST ICE
The process by which mammalian predators search for, locate,
stalk, and subdue their prey has been the subject of considerable
research concerning terrestrial species, but less is known about
the foraging behavior of marine mammals, primarily because they
are difficult to observe underwater. Direct observation of marine
animal behavior with scuba, fixed-location cameras, remotely
operated vehicles, and manned submersibles is limited in depth or
duration, and often these technologies provide only fleeting
glimpses of highly mobile species. Animal-borne time-depth
recorders and acoustic tracking provide information on diving
performance but do not allow direct observation of animals at
depth. As a result our knowledge of the underwater behavior of
marine mammals, especially deep-diving species, is based
primarily on indirect information. ... ... R.W. Davis et al (8
authors at 4 installations, US) now report the development of an
animal-borne video system and data recorder that enabled the
observation of *Weddell seals (Leptonychotes weddellii) foraging
at depth beneath the *Antarctic fast ice and the computation of
their 3-dimensional dive paths. The authors report that Weddell
seals stalk *large Antarctic cod and the smaller sub-ice fish
Pagothenia borchgrevinki, often with the under-ice surface for
backlighting, which implies that vision is important for hunting.
The seals approached within centimeters of cod without startling
the fish. Seals flushed P. borchgrevinki by blowing air into sub-
ice crevices or pursued them into the *platelet ice. The authors
suggest these observations highlight the broad range of insights
that are possible with simultaneous recordings of video, audio,
3-dimensional dive paths, and locomotor effort of an animal.
-----------
R.W. Davis et al: Hunting behavior of a marine mammal beneath the
Antarctic fast ice.
(Science 12 Feb 99 283:993)
QY: R.W. Davis [davisr@tamug.tamu.edu]
-----------
Text Notes:
... ... *Weddell seals: These are large marine predators (450 to
500 kilograms) that are highly adapted for hunting in *fast ice
and *pack ice habitats. To forage beneath the extensive unbroken
fast ice, these seals must locate, pursue, and capture prey in 3
spatial dimensions under low-light conditions and while holding
their breath. Foraging apparently occurs in daily bouts
consisting of up to 40 consecutive dives to depths of 100 to 350
meters and less than 25 minutes in duration. Weddell seals are
named after James Weddell (1787-1834), a British sea captain who
sailed and charted Antarctic waters while hunting seals in the
post-Napoleonic period after 1815. The Weddell Sea is named after
him.
... ... *Antarctic fast ice: Fast ice is sea ice that is frozen
onto a shoreline and is therefore stationary.
... ... *pack ice: Any mass of floating pieces of ice 3 meters or
less in diameter, the pieces driven together to form a solid
layer.
... ... *large Antarctic cod: The large cod in this report grow
to 1.65 meters in length and weigh up to 77 kilograms.
... ... *platelet ice: In this context, a layer of floating sea
ice composed of ice-crystal platelets that serve as seeds for
further thickening of the ice cover. Platelet ice is generally
soft, composed of large loosely packed ice crystals, and its
depth can be more than 1 meter.
-------------------
Summary & Notes by SCIENCE-WEEK [http://scienceweek.com] 23Apr99


6. EFFECT OF RACE AND SEX OF PATIENTS ON TREATMENT FOR CHEST PAIN
Epidemiological studies have identified differences according to
race and sex in the US in the treatment of patients with
cardiovascular disease. Some studies have found that blacks and
women are less likely than whites and men, respectively, to
undergo *cardiac catheterization or coronary artery bypass graft
surgery when they are admitted to the hospital for treatment of
chest pain or *myocardial infarction. In contrast, other studies
were unable to confirm that invasive procedures are underused in
women. One question that has not been addressed directly by
previous studies is the extent to which attitudes of physicians
(in addition to any possible social and economic factors) are
responsible for the differences in treatment recommendations with
respect to race and sex. ... ... K.A. Schulman et al (12 authors
at 4 installations, US) now report the results of a study to
assess, in a controlled experiment, treatment recommendations by
physicians for patients presenting with various types of chest
pain. The authors report they developed a computerized survey
instrument, with actors portraying patients with particular
characteristics in scripted interviews about their symptoms. A
total of 720 physicians at 2 national meetings of organizations
of primary care physicians participated in the survey. Each
physician viewed a recorded interview and was given other data
about a hypothetical patient, and the physician then made
recommendations about the care of that patient. The authors
report that women and blacks were less likely to be referred for
cardiac catheterization than men and whites (*odds ratio = 0.6),
respectively, and that analysis of the race-sex interactions
indicated that black women were significantly less likely to be
referred for catheterization than white men (odds ratio = 0.4).
The authors suggest their finding indicate that the race and sex
of patients independently influence recommendations by physicians
for the management of chest pain, and that decision-making by
physicians may be an important factor in explaining differences
in the US in the treatment of cardiovascular disease with respect
to race and sex.
-----------
K.A. Schulman et al: The effect of race and sex on physicians'
recommendations for cardiac catheterization.
(New England J. Med. 25 Feb 99 340:619)
QY: Kevin A. Schulman, Georgetown University 202-687-3600.
-----------
Text Notes:
... ... *cardiac catheterization: (intracardiac catheterization)
This involves the passage of a catheter (a small-diameter tubular
instrument) into the heart through a vein or artery, to withdraw
samples of blood, measure pressures within the chambers of the
heart or the larger vessels of the heart, or to inject contrast
media for visualization techniques. The cardiac catheterization
technique is used primarily in the diagnosis and evaluation of
congenital, rheumatic, and coronary artery lesions, and to
evaluate various dynamic aspects of cardiac function.
... ... *myocardial infarction: (myocardial infarct) In general,
an "infarct" is an area of necrosis caused by a sudden
insufficiency of blood supply, and a "myocardial infarction"
(cardiac infarction) is such damage of an area of heart muscle,
usually as a result of occlusion of a coronary artery.
... ... *odds ratio: In this context, the ratio of the
probability of an event in one group to the probability of the
event in another group.
-------------------
Summary & Notes by SCIENCE-WEEK [http://scienceweek.com] 23Apr99


=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
 
IN FOCUS: ON THE IMPACT OF QUANTUM THEORY
"By the late 1920s, the interpretation of the new quantum theory
was intact. A generation of young physicists grew up with it, but
they were less interested in the problems of interpretation than
in applications. The new theory emphasized, as never before, the
paramount role of mathematics in theoretical physics. Individuals
with great technical power in abstract mathematics, and the
ability to apply it to physical problems, came to the fore. The
new quantum theory became the most powerful mathematical tool for
the explication of natural phenomena that ever fell into human
hands, an incomparable achievement in the history of science. The
theory released the intellectual energy of thousands of young
scientists in the industrial nations of the world. No single set
of ideas has ever had a greater impact on technology, and its
practical implications will continue to shape the social and
political destiny of our civilization. We have made contact with
new components of the cosmic code -- the immutable laws of the
Universe -- which are now programming our development. Practical
devices, such as the transistor, the microchip, lasers, and
cryogenic technology, have given rise to entire industries at the
vanguard of technical civilization. When the history of this
century is written, we shall see that political events -- in
spite of their immense cost in human lives and money -- will not
be the most influential events. Instead the main event will be
the first human contact with the invisible quantum world and the
subsequent biological and computer revolutions."

-- Heinz R. Pagels: _The Cosmic Code_
   (Simon & Schuster, New York 1982)

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