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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.
June 30, 2000 -- Vol. 4 Number 26
-----------------------------------------------
Our biology has made us into creatures who are
constantly recreating our psychic and material
environments, and whose individual lives are the
outcomes of an extraordinary multiplicity of
intersecting causal pathways. Thus, it is
our biology that makes us free.
-- Richard Lewontin
-----------------------------------------------
Contents of this Issue:
1. Science Policy:
A Call for More Opposition to Creationist Activism
--------------------------------------------------
The battle of creationist dogma vs. science is one that
apparently will be with us for some time, and there is a growing
consensus that the science community must accept the
confrontation and resist, with as much vigor as possible, the
corruption of the teaching of science.
(Includes related background material.)
2. Astrophysics:
Detection of Dark Matter by Weak Gravitational Lensing
------------------------------------------------------
Results of the first direct probe of the aggregate mass
distribution in the Universe at late times on the scale of
several billion light years are inconsistent with the standard
"cold-dark-matter" model. (Includes related background material.)
3. Astronomy:
On Small Bodies of the Solar System
-----------------------------------
Recent evidence is blurring the conceptual boundary between
asteroids and comets, the two major groups of small Solar System
bodies. (Includes related background material.)
4. Neurobiology:
On Absinthe and Neurotransmitter Receptors
------------------------------------------
The most important neuro-active ingredient in absinthe is the
terpenoid alpha-thujone, and it now appears the effect of this
terpenoid involves chloride ion channels in the central nervous
system.
5. Neurobiology:
London Taxi Drivers: Navigation and Brain Structural Changes
-----------------------------------------
A new study provides evidence of regionally specific structural
differences between the hippocampi of licensed London taxi
drivers compared with those of control subjects.
(Includes related background material.)
6. Medical Biology:
Transforming Growth Factor-Beta in Human Disease
------------------------------------------------
The polypeptides known as "transforming growth factors" are of
great important in various disease processes, and the study of
these cytokines in intensive.
7. In Focus: On Perseverance in Research
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
1. SCIENCE POLICY:
A CALL FOR MORE OPPOSITION TO CREATIONIST ACTIVISM
No matter how firm its evidentiary basis, any scientific
conclusion that contradicts strong popular notions may face an
intense public campaign aimed at discrediting that conclusion.
Such was the case with the scientific conclusion that the Earth
is an oblate sphere and not as flat as a pancake, that the Sun
and not the Earth is the focal point of planetary orbits, and
that mental illness is not the result of possession by the Devil.
And such is also the case with the scientific conclusion
concerning the evolutionary origins of life, and in particular,
the evolutionary origins of the human species. Fortunately,
evidence is usually ultimately victorious in the arena of ideas,
but the battle can last for some time and it may also damage the
social fabric.
Recent years have seen an intensification of the battle of
evolution vs. creationism, the latter an idea of divine origins,
the intensification in part due to a resurgence of politicized
fundamentalist religious views in the US. Of particular concern
to many scientists are the current campaigns by various
creationist groups to corrupt the teaching of evolutionary
biology by politically mandated associated teaching of anti-
evolutionism, or to do away with the teaching of evolutionary
biology altogether. Central to all of this is the fact that, in
the US, public education from kindergarten through high school is
controlled by local school boards that are often more interested
in perpetuating dogma than in educating children in a spirit of
enlightenment. This battle of creationist dogma vs. science is
one that apparently will be with us for some time, and there is a
growing consensus that the science community must accept the
confrontation and resist the corruption of the teaching of
science with as much vigor as possible.
... ... Eugenie C. Scott (National Center for Science Education,
US), who is a physical anthropologist, presents an essay on the
current evolution vs. creationism controversy in the US, the
author making the following points:
1) The US stands out among developed countries in its low
acceptance of one of the major organizing principles of science
-- evolution. The author suggests this reflects the unique
settlement and religious history of the US, in which frontier
communities set up their own school systems largely independent
of state and federal influence, much less control.
2) The author suggests that US religious history reflects an
equally decentralized "frontier" orientation. The US was
initially settled by religious dissidents, who formed
congregations, rather than hierarchical religious systems, in
which decisions largely were made locally. The US also has been
the nursery for a wide variety of spontaneously generated
independent sects, often inspired by charismatic leaders: Seventh
Day Adventists, the Church of Latter Day Saints, Jehovah's
Witnesses, Christian Science, and extinct sects such as Shakers
and Millerites -- all founded reflecting a decentralized
nonhierarchical religious past. But perhaps the most important
reason modern anti-evolutionism developed in the US rather than
in, for example, Europe, was the founding in 1910 to 1915 of
Fundamentalism, a Protestant view that stresses the inerrancy of
the Bible. Fundamentalism was not successfully exported to Europe
or Great Britain, but it formed the basis in the US for the anti-
evolutionism of the 1920s Scopes trial era, as well as for the
anti-evolutionism of the present day.
3) Although the US Supreme Court has ruled that teaching
creationism and creation "science" are unconstitutional,
creationists are using various methods to sidestep this obstacle:
... ... a) Various teachers give equal time to creationism and
evolution, even though their school districts do not (and cannot)
require them to do so.
... ... b) At school assemblies, in the name of "fairness", a
creationist is invited to tell students that the scientifically
well-accepted idea that living things shared common ancestry is a
"theory in crisis" with many "serious flaws", and also that the
world is only 10,000 years old. Given the requirement of the US
Constitution that schools be religiously neutral, such assemblies
provide an unconstitutional forum for a speaker who openly
proselytizes students to reject evolution in favor of a literal
Biblical interpretation of history.
... ... c) Certain school districts are considering leaving out
the teaching of evolution altogether, or limiting or separating
out evolution as somehow different from other scientific fields.
... ... d) Disclaimers that teachers must read to students or
paste into textbooks are becoming more popular. Typically, such
disclaimers declare that evolution is "only a theory" (in other
words, a guess, hunch, or half-baked idea) and therefore by
implication nothing that students should take seriously.
Oklahoma and Alabama textbooks contain a disclaimer which states
that evolution is a theory, not fact, because "no one was present
when life first appeared on Earth." No other subject in the
science curriculum is so disclaimed.
... ... e) Since the US Supreme Court struck down laws requiring
equal time for creation and evolution, the neocreationist
approach is to balance evolution with "evidence against
evolution", but such evidence is revealed as simply a euphemism
for creation science. Currently, a law is in progress in the
Arizona state legislature that would require that "evidence
against evolution" be taught along with evolution. Similar
legislation is in progress in certain other states.
4) The author concludes: "If scientists do not oppose anti-
evolutionism, it will reach more people with the mistaken idea
that evolution is scientifically weak, and further, that
scientists are clinging to it only because of previous commitment
to atheism -- and perhaps a selfish desire to keep the grant
money flowing. The subsequent further reduction of scientific
literacy (to say nothing of a decline of confidence in the
scientific community) is not something we should passively let
happen."
-----------
Eugenie C. Scott: Not (just) in Kansas anymore.
(Science 5 May 00 288:813)
QY: Eugenie C. Scott [scott@natcenscied.org]
-------------------
Summary by SCIENCE-WEEK http://scienceweek.com 30Jun00
For more information: http://scienceweek.com/swfr.htm
-------------------
Related Background:
SCIENCE AND SOCIETY: A CALL FOR ACTIVISM AGAINST CREATIONISM
One result of the decision last summer by education authorities
in Kansas (US) to reduce the teaching of Earth science and
evolution in Kansas public schools may be to galvanize the US
scientific community to activism against creationism. Certainly,
as evidenced by letters and editorials in the scientific media
during the past months, this issue has provoked responses among
scientists ranging from concern to outrage. Now, at a recent
meeting (December 1999), the American Geophysical Union (AGU) has
denounced the teaching of creationism and called for scientists
to become politically involved in promoting the teaching of
evolution. The AGU council states as follows: "The American
Geophysical Union affirms the central importance of scientific
theories of Earth history and organic evolution in science
education... Creationism is not science and does not have a
legitimate place in any science curriculum." In an unsigned
editorial commenting on the AGU statement, the journal _Nature_
states that the resurgence of creationism and the exploitation of
creationism by politicians "pose challenges to scientists that
cannot be ignored. More resolute activism is required if a decent
scientific education is not to be denied to some young
Americans." The editorial points out that most scientists tend to
avoid public confrontation. "But the key to the battle for the
teaching of good science in the presence of fundamentalism is to
be more resolute in informing the public of the important role of
science and actively oppose the use of distorted perceptions of
science as a political vehicle... Scientists need to reach out,
to become involved in local school-board issues and to seek
election to ensure appropriate scientific curricula." In
conclusion, the editorial states: "It will take coordination,
coherence and some powerful advocacy drawn from the ranks of many
independently minded scientists to carry the day."
-----------
Nature: Scientists rally to defend schools against creationists.
(Nature 23/30 Dec 99 402:847)
-----------
Nature: Combating the exploiters of creationism.
(Nature 23/30 Dec 99 402:843)
QY: feedback@nature.com
-------------------
Summary by SCIENCE-WEEK http://scienceweek.com 14Jan00
For more information: http://scienceweek.com/swfr.htm
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
2. ASTROPHYSICS:
DETECTION OF DARK MATTER BY WEAK GRAVITATIONAL LENSING
In general, in this context, the term "dark matter" refers
to material whose presence can be inferred from its effects on
the motions of stars and galaxies, but which cannot be seen
directly because it emits little or no radiation. It is believed
that at least 90 percent of the mass in the Universe exists as
some form or dark matter. In current cosmology, "hot dark matter"
is defined as particles that were still moving at nearly the
speed of light at about a year after the Big Bang -- the origin
of the Universe. "Cold dark matter" is defined as particles that
were moving sluggishly at that time.
What is known as the "cosmic microwave background radiation"
was discovered accidentally in 1964, when A.A. Penzius and
R. Wilson, measuring noise that might interfere with satellite
communications, noted a mysterious signal that was soon
interpreted to be the microwave background radiation originating
in the Big Bang. In 1978, Penzius and Wilson received the Nobel
Prize in Physics for this discovery. The cosmic microwave
background is black-body radiation (the emission radiation of a
perfect absorber of radiation) at a present temperature of 2.73
degrees Kelvin, and has an almost equal intensity in all
directions in space. The deviations from isotropic intensity,
however, are of extreme importance in theoretical cosmology.
The term "gravitational lensing" refers to the bending of
light and other radiation by a massive gravitational entity such
as a star, a black hole, a galaxy, or a cluster of galaxies. The
effect is predicted by Einstein's theory of relativity and was
first detected during a total solar eclipse by Eddington in 1919.
The effect produces various distortions of objects, including
shape distortion, luminosity distortion, double images, etc.,
depending on the size and character of the lens and nature of the
object.
Central to considerations of the structure of the Universe
are the distinctions between the geometries of a "flat"
(uncurved; infinite in both extent and lifetime), "closed"
(spherical; finite in both extent and lifetime), and "open"
(*hyperbolic; infinite and expanding forever) Universe. An
important quantity is the Omega parameter, defined as the ratio
of the density of matter (or energy) in the Universe to the
theoretical density required for flatness. An Omega with a value
of greater than 1 implies a closed Universe; a value less than 1
implies an open Universe; a value equal to 1 implies a flat
Universe. The problem for the past 60 years has thus been to
obtain an estimate of the mass density of the Universe from
observations. The current standard conception is that the
geometry of the Universe is flat. Recently, however, new data
have apparently indicated that the entire scheme upon which
models of the structure of the Universe are based may need
serious revision, and such revision may in turn force revision of
certain areas of fundamental physics.
What is called the "cosmological constant" refers to a
mathematical term introduced by Einstein into the equations of
general relativity, the purpose to obtain a solution of the
equations corresponding to a "static Universe" (i.e., flat
Universe). The term describes a pressure (if positive) or a
tension (if negative) which can cause the Universe to expand or
contract even in the absence of any matter ("vacuum energy").
When the expansion of the Universe was discovered, Einstein
apparently began to regard the introduction of this term as a
mistake, and he described the cosmological constant as the
"greatest mistake of my life". But the term has reappeared as the
proposed source of apparent accelerated cosmic expansion.
... ... D.M. Wittman et al (5 authors at 3 installations, US)
present a report on gravitational lensing distortions of distant
galaxies, and the implications for considerations of cosmic dark
matter at large scales. The authors make the following points:
1) The large-scale distribution of dark matter depends on
both the nature of the dark matter and the global cosmological
parameters that describe the Universe, and information on the
large-scale distribution of dark matter is thus one of the
primary goals of modern observational astronomy. To date, most of
what we know about the large-scale structure of the Universe
derives from the observed anisotropies in the cosmic microwave
background radiation, and from the distribution of galaxies. The
cosmic microwave background radiation provides the earliest
sample of mass fluctuations in the early Universe. Various
cosmological models predict different scenarios in the growth of
mass structures over cosmic time, so comparison of the mass
distribution derived from the cosmic microwave background
radiation with the mass distribution seen at later times is a
powerful test of cosmological models. The large-scale mass
distribution at later times has traditionally been characterized
through the large-scale distribution of galaxies on the
assumption that light traces mass, but the presence of
substantial dark mass confounds the analysis.
2) The distribution of cosmic dark mass can be investigated
via its gravitational effects on the appearance of background
galaxies. Any foreground mass bends light rays from a distant
source, moving the apparent position of the source to a new
position on the sky and stretching its image tangentially by an
amount proportional to the foreground mass. This weak lensing
effect has already been used to study the mass distribution
within clusters of galaxies, where the large mass associated with
the clusters makes the gravitationally induced ellipticity of the
background galaxies easily detectable. In principle, weak lensing
can also provide information about large-scale structure through
the cumulative effect of many intervening "overdensities".
3) A deep image of a patch of sky looks out through the
three-dimensional arrangement of galaxies seen in projection: any
two galaxies are not likely to be physical neighbors, and in the
absence of lensing, their projected shapes or ellipticities are
statistically uncorrelated. However, in the presence of
foreground mass overdensities (i.e., those occurring between
distant galaxies and the observer), the light rays from galaxies
narrowly separated on the sky travel similar paths past
intervening mass concentrations and thus undergo similar image
distortions. The resulting correlation of distant galaxy
ellipticities is highest at small angular separation and drops
for widely separated galaxies whose light bundles travel through
completely different structures. Different cosmological models
predict different behavior for correlations of galaxy
ellipticities versus angular separation on the sky.
4) The authors report they have imaged large areas of sky in
several directions using a mosaic of *CCD devices on a large
telescope (the 4-meter Blanco telescope at the Cerro Tololo
Inter-American Observatory, CL), the study covering hundreds of
thousands of galaxies, and the analysis selecting 145,000 of the
most reliable distant galaxy measurements. The authors report the
detection of angular distortion ("cosmic shear") of up to half a
degree along 3 separate lines of sight. The authors suggest their
analysis indicates that dark matter is distributed in a manner
consistent with either an open Universe, or a flat Universe
dominated by a cosmological constant, and that their results are
inconsistent with the standard "cold-dark-matter" model. The
authors state that their study is, "to our knowledge, the first
direct probe of the aggregate mass distribution in the Universe
at late times on the scale of several billion light years."
-----------
D.M. Wittman: Detection of weak gravitational lensing distortions
of distant galaxies by cosmic dark matter at large scales.
(Nature 11 May 00 405:143)
QY: David M. Wittman [wittman@physics.bell-labs.com]
-----------
Text Notes:
... ... *hyperbolic: This is a negative curvature, like the
surface of a saddle, and it is sometimes called a "saddle"
Universe. In such a geometry, the sum of the angles of a triangle
is less than 180 degrees. In a spherical (closed) geometry, the
sum of angles is more than 180 degrees; in a flat geometry, the
sum of angles is exactly 180 degrees.
... ... *CCD devices: (charge-coupled devices) A charge-coupled
device is a semiconductor device in which charge stored in a
surface layer can be moved about the surface by applied fields or
impacting radiation, and such devices are now in common use as
electromagnetic radiation sensors.
-------------------
Summary & Notes by SCIENCE-WEEK http://scienceweek.com 30Jun00
For more information: http://scienceweek.com/swfr.htm
-------------------
Related Background:
COSMOLOGY: OPEN, CLOSED, OR FLAT UNIVERSE?
Marc Kamionkowski (Columbia University, US) reviews current
research in cosmology, making the following points: 1)
Determination of the geometry of the universe has been a central
goal of cosmology ever since Hubble discovered its expansion 75
years ago. 2) The central question is whether the universe is a
multi- dimensional equivalent of a 2-dimensional surface
("flat"), a sphere ("closed"), or a saddle ("open"). The
geometry, in the context of current theory and observations,
determines whether the universe will expand forever or eventually
collapse. 3) Until now, most astronomers have pursued the
geometry by attempting to measure the mass density of the
universe. According to general relativity, if the density is
equal to, larger than, or smaller than a critical density fixed
by the expansion rate, then the universe is flat, open, or
closed, respectively. 4) Another possibility is to look directly
at the predicted observational effects of a curved (open or
closed) universe versus a flat universe, and in particular at the
angular power spectrum of the cosmic microwave background. The
authors suggest that in the near future a new generation of
experiments will provide substantial advances in these
observations, enabling more definitive statements about the
geometry of the universe, and that these results will in turn
provide clues to the new particle physics required to understand
the inflation phase following the Big Bang origin of the
universe.
QY: Marc Kamionkowski (kamion@phys.columbia.edu)
(Science 29 May 98 280:1397) (Science-Week 19 Jun 98)
-------------------
Related Background:
ON THE NATURE OF DARK MATTER
Joel R. Primack (University of California Santa Cruz, US)
presents a commentary on a paper by E. Gawiser and J. Silk
(University of California Berkeley, US) ((Science 29 May 98
280:1405), Primack making the following points: 1) One of the
fundamental issues facing cosmologists concerns the evidence that
observable matter in the universe makes up only a fraction of
what is needed to explain the properties of the universe. A large
portion of matter in the universe must therefore be unobserved,
or "dark matter". 2) Neutrinos are the standard example of hot
dark matter, although other more exotic possibilities have been
discussed. 3) Gawiser and Silk (ref. cited above) conclude that
of all the currently popular cosmological models, the only one
whose predictions agree with the data on the cosmic microwave
background anisotropies and the large-scale distribution of
galaxies is the cold + hot dark matter model, with 70% of the
matter cold dark, 20% hot dark, and 10% ordinary matter
(baryonic). 3) There are 3 species of neutrinos, and there are
mounting astrophysical and laboratory data suggesting that
neutrinos oscillate from one species to another, which can only
happen if they have nonzero mass. As dark-matter candidates,
neutrinos are entities with masses that may be 10^(-5) of the
mass of the electron, but with an expected density more than 8
orders of magnitude greater than the density of electrons and
protons in the universe. Neutrinos, therefore, can provide a
substantial fraction of dark matter. 4) The authors suggest that
the success of the cold plus hot dark matter model in fitting the
cosmic microwave background and galaxy distribution data
indicates that this type of model should be investigated in more
detail.
-----------
QY: Joel R. Primack (joel@physics.ucsc.edu)
(Science 29 May 98 280:1398) (Science-Week 19 Jun 98)
-----------
For more information: http://scienceweek.com/swfr.htm
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
3. ASTRONOMY:
ON SMALL BODIES OF THE SOLAR SYSTEM
Other than the moons of the various planets, the chief small
bodies of the solar system are comets and asteroids.
In general, a comet is a kilometer-size chunk of ice and
associated dust and debris. The *Oort cloud is an apparent
spherical shell of comets 10,000 to 100,000 *astronomical units
(AU) from the Sun and the proposed source of comets that orbit
the Sun. The cloud is at the extreme edge of the Sun's influence,
halfway to the nearest star, and it is believed that when the
cloud is perturbed by passing stars, comets may be sent into a
solar orbit. The size and structure of the Oort cloud have been
deduced from statistical studies of the orbits of comets; there
is no direct evidence for the cloud's existence. Approximately
900 comets are known.
Asteroids (also called "minor planets") are small rocky
objects, most of which orbit the Sun in a belt between the orbits
of Mars and Jupiter. A few asteroids follow orbits that bring
them into the inner Solar System, and several asteroids
occasionally pass within a few tens of millions of miles of
Earth. Some asteroids are located in the orbit of Jupiter, and
some asteroids have been detected as far away as the orbit of
Saturn. There are approximately 7200 known asteroids, and a
million asteroids are believed resident in the Solar System. The
consensus view is that asteroids are composed of material that
failed to build a planet at a distance of 2.8 astronomical units
from the Sun, perhaps due to the influence of massive Jupiter
just outside the asteroid belt. Until recently, the shapes and
surface features of asteroids were a matter of conjecture; during
the past decade, however, significant direct observations of
asteroids have been relayed back to Earth from spacecraft.
Classical astronomers have categorized comets and asteroids
as distinctly different entities with different histories and
compositions, but recent evidence is blurring the conceptual
boundary between these two groups of small Solar System bodies,
and there are several newly discovered objects that are
considered to be both comets and asteroids on the basis of their
characteristics.
... ... Don Yeomans (California Institute of Technology, US)
presents a review of recent research on comets and asteroids, the
author making the following points:
1) Recent observations have revealed comets in asteroid-like
orbits and asteroids in comet-like orbits. Both comets and
asteroids can evolve from the Oort cloud into highly inclined,
even *retrograde, orbits about the Sun, so orbital behavior is no
better than physical behavior for distinguishing comets from
asteroids. The author suggests that attempts to categorize comets
and asteroids as distinctly separate entities have failed, and
that astronomers should now consider these objects as members of
highly diverse family: the small bodies of the Solar System.
2) If all comets were solid dirty balls of water ice, then
their bulk densities would be approximately 1 gram per cubic
centimeter. But some comets have apparent low-density structures
that are made from several bits held together by little more than
their own self-gravity. This conclusion arose after some comets
were observed to break up as a result of tidal forces from either
the Sun or Jupiter, and more than two dozen other comets have
split apart for no obvious reason at all. In addition, comets
that have apparently transformed from active to quiescent objects
suggest that some cometary bodies do become defunct and join the
ranks of the asteroids. Low-density extinct comets can probably
explain a significant fraction of the near-Earth asteroid
population, "so we cannot assume that all objects that threaten
Earth will have the same composition or structure."
3) Asteroids have been classified according to the light
reflected from their surfaces -- their optical spectra. Although
no two spectra are exactly alike, most asteroids fall into one of
two groups, the C-type (carbonaceous) and S-type (silicaceous).
C-type asteroids have low reflectance (albedo) and may contain
mixtures of hydrated silicates, carbon, and organic compounds. S-
type asteroids have higher albedos and can contain pyroxene
(silicates containing magnesium, iron, and calcium), olivine
(magnesium and iron silicates), and nickel-iron metal. The C-type
asteroids are most common in the outer part of the main asteroid
belt, and the S-type asteroids are mostly found in the inner
asteroid belt.
4) Meteorites are asteroid collision fragments that have
fallen to Earth, and as such are thought to hold clues regarding
the early history of asteroids. Because most asteroid fragments
are rocky, they can survive the passage through the atmosphere of
the Earth. In contrast, debris from comet streams nearly always
burns up in the atmosphere, sometimes producing spectacular
meteor showers in the sky, but leaving little evidence on the
surface of the Earth. The most common meteorite is the ordinary
chondrite, which is composed mostly of rocky silicates, and so
has not experienced the chemical differentiation associated with
melting. Such chondrites are thought to be some of the most
primitive rocks in the Solar System, although their parent
asteroid type is not clear. On 22 March 1998, and ordinary
chondrite was observed to fall to Earth by 7 boys in Monahans,
Texas (US), and within 48 hours the meteorite was under
examination at the Johnson Space Center in Houston, Texas.
Laboratory analysis of the Monahans meteorite detected salt
crystals embedded with water in the form of brine, and the salt
crystals were dated to the very beginning of the Solar System,
approximately 4.6 billion years ago. This suggests the presence
of liquid water on the parent asteroid of this meteorite, and
unless this water derived from a collision with a salt-bearing
icy comet, the parent asteroid itself must have had flowing water
within its interior structure. Far from being the dry rocky
bodies they were once believed to be, it would seem that some
asteroids, along with comets, might be significant sources of
water.
-----------
Don Yeomans: Small bodies of the Solar System.
(Nature 20 Apr 00 404:829)
QY: Don Yeomans, California Institute of Technology 818-395-6811.
-----------
Text Notes:
... ... *Oort cloud: The cloud is named after Jan Hendrik Oort
(1900-1992). Oort first proposed the existence of the cloud in
1950. In 1927, Oort calculated the mass and size of the Galaxy,
and the distance of the Sun from its center, from the observed
movements of the stars around the center.
... ... *astronomical units (AU): 1 AU = the mean distance from
the Sun to the Earth = approximately 93 million miles, and
exactly 149,597,870 kilometers.
... ... *retrograde: Opposite direction as planets. Prograde =
same direction as planets.
-------------------
Summary & Notes by SCIENCE-WEEK http://scienceweek.com 30Jun00
For more information: http://scienceweek.com/swfr.htm
-------------------
Related Background:
FIRST DISCOVERY OF AN ASTEROID WATER INCLUSION
The term "meteor" refers to a piece of solid matter from
space that penetrates the Earth's atmosphere at a hypersonic
speed of typically 10 to 20 kilometers per second, with
atmospheric friction causing it to become incandescent. Outside
the Earth's atmosphere, it is known as a "meteoroid"; any part
that survives passage through the atmosphere and reaches the
surface of the Earth is called a "meteorite". Most meteorites are
thought to originate in the asteroid belt between the orbits of
Mars and Jupiter, although tracking of entry paths indicates that
before colliding with Earth meteorites have highly elliptical
counterclockwise orbits about the Sun (in the same sense as the
planets).
Meteorites are often named after the place on Earth where
they are found, and they divided roughly into 3 main classes
according to their composition. "Iron meteorites" consist of an
alloy of iron and nickel; "stony meteorites" consist of silicate
minerals; and "iron-stony meteorites" are a mixture of the two
previous types. The stony meteorites are further divided into
"chondrites" and "achondrites". Chondrites contain small
spherules of high-temperature silicates ("chondrules") and
constitute more than 85 percent of recovered meteorites. The
achondrites range in composition from rocks made up essentially
of single minerals (e.g., olivine) to rocks resembling *basaltic
lava. Each category is further subdivided on the basis of
chemical composition. "Carbonaceous chondrites" have little or no
metal but abundant carbon, and display evidence of chemical
alteration by water; they have the highest proportion of volatile
elements and are the most oxidized. "Ordinary chondrites" (the
most common type) are intermediate in volatile element abundance
and oxidation state.
All main types of meteorite have been dated isotopically,
with most studies involving the dominant chondrite fraction.
There are no obvious age differences between the meteorites of
the various groups, and chondrites, achondrites, and iron
meteorites consistently yield ages of approximately 4.45 to 4.50
billion years, which places the origin of these objects in the
era of the formation of the Solar System.
Over the past three decades, researchers have become
increasingly aware of the fundamental importance of water and
aqueous alteration on primitive Solar System bodies. Some
carbonaceous and ordinary chondrites, long proposed as primordial
material relatively unchanged since formation, have apparently
been altered by interactions with liquid water within the first
10 million years after formation of their parent asteroids. But
the location and timing of the aqueous alteration, or the nature
of the aqueous fluid itself, are not known. Researchers have
attempted to model this aqueous process through analysis of
hydrated minerals present in the meteorites, and through computer
simulations of the alteration process, but a major obstacle to
the understanding of aqueous alteration of meteorites has been
the absence of actual samples of aqueous fluids in meteorites.
... ... M.E. Zolensky et al (7 authors at 3 installations, US)
now report the discovery and characterization of aqueous fluid
inclusions in an ordinary chondrite, the Monahans (1998) object.
The Monohans (1998) meteorite fell on 22 March 1998 in Monahans,
Texas (US). The fall was witnessed by 7 boys, and the first of
two stones was recovered immediately and carried to the Johnson
Space Center, where it was broken open in a filtered-air, clean-
room facility less than 48 hours after the fall. The authors
suggest this effectively eliminated the opportunity for aqueous
or other contamination. The authors report the presence within
the Monahans (1998) meteorite of crystals of halite (NaCl) and
sylvite (KCl) containing aqueous fluid inclusions. The fluids are
dominantly sodium chloride-potassium chloride brines, but they
also contain divalent cations such as iron, magnesium, or
calcium. The authors suggest two possible origins for the brines
are a) indigenous fluids flowing within the asteroid, and b)
exogenous fluids delivered into the asteroid surface from a salt-
containing object such as a comet. The authors further suggest
that "in either case, the inclusions provide ground truth
concerning the nature of water in the early Solar System."
-----------
M.E. Zolensky et al: Asteroidal water within fluid inclusion-
bearing halite in an H5 chondrite, Monahans (1998).
(Science 27 Aug 99 285:1377)
QY: Michael E. Zolensky, NASA Johnson Space Center, Houston, TX
77058 US.
-----------
Text Notes:
... ... *basaltic lava: Basalt is a dark gray to black igneous
rock of volcanic origin that cools rapidly. "Igneous rocks" are
rocks that have congealed from a molten mass.
-------------------
Summary & Notes by SCIENCE-WEEK http://scienceweek.com 1Oct99
For more information: http://scienceweek.com/swfr.htm
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4. NEUROBIOLOGY:
ON ABSINTHE AND NEUROTRANSMITTER RECEPTORS
To a considerable degree, the practice of serious art
(painting, literature, etc.) requires originalities of
perception, and at the level of neurobiology what this usually
means is that the nervous system must be induced to respond in
new ways to old inputs. The key word here is "induced": how does
one induce the new responses of the nervous system that are
required for serious art? Some artists are apparently naturally
endowed with the ability to induce such responses almost at will;
other artists place themselves in ambient conditions that provoke
new responses of the nervous system; still other artists seek the
assistance of one or more of a wide variety of drugs that affect
the nervous system in degrees ranging from mild effects to
profound changes in personality, with toxicities ranging from
mild to lethal.
At the end of the 19th century, and during the first decade
of the 20th century, an era during which a generation of artists
in Europe produced an enormous output of significant original new
art, the notorious alcoholic drink called "absinthe" was a staple
in artistic circles, imbibed by artists and would-be artists and
the followers of artists almost as a ritual, until finally in
1910 to 1915 it was recognized that absinthe was a neurological
poison, and the drink was banned in most countries in Europe, and
also banned in the US.
But the legend of absinthe remains. In 1906, Paris had
33,330 bars, many of which were "absinthe houses", compared with
17,000 bakers baking bread for the Parisian public. The major
supplier of absinthe was the Swiss factory Pernod, established in
1787. Among the famous artists and writers who made heavy use of
absinthe was De Musset, Baudelaire, Verlaine, Zola, Oscar Wilde,
Gaugin, Toulouse-Lautrec, Van Gogh, and Picasso. The famous 1876
painting by Degas, "The Absinthe Drinkers" (or simply,
"Absinthe"), shows a man and a woman in a bistro, both persons in
an apparent stupor, glasses of the milky liquid (absinthe) on the
table in front of them. (During its bistro preparation as a
"liqueur", cold water was added to the ethyl alcohol solvent,
which caused the precipitation of alcohol-soluble herbal
ingredients in the drink, and thus the milky color.) Although it
had become the national drink of France by the end of the 19th
century, absinthe had a reputation for inducing "insane and
criminal acts" as well as convulsions and other effects of
toxicity. Oscar Wilde said of absinthe: "After the first glass,
you see things as you wish they were. After the second, you see
them as they are not. Finally, you see things as they really are,
which is the most horrible thing in the world."
The most important neuro-active ingredient in absinthe is
not the ethyl alcohol (which is also highly neuro-active), but
the terpenoid alpha-thujone, which is derived from oil of
wormwood, and it now appears the effect of this terpenoid
involves chloride ion channels in the central nervous system.
In neurobiology, ion channels are protein channels
in cell membranes that allow ions to pass from extracellular
solution to intracellular solution and vice versa. Most ion
channels are selective, allowing only certain ions to pass, and
an individual cell has ion channels with various ion
selectivities. From an electrical standpoint, each ion channel is
effectively a specific parallel conductance pathway through the
cell membrane, and the dynamic electrical behavior of nerve cells
is essentially directly determined by the opening and closing of
its ion channels.
Neurotransmitters are chemical substances released at the
terminals of nerve axons in response to the propagation of an
impulse to the end of that axon. The neurotransmitter substance
diffuses into the synapse, the junction between the presynaptic
nerve ending and the postsynaptic neuron, and at the membrane of
the postsynaptic neuron the transmitter substance interacts with
a receptor. Depending on the type of receptor, the result may be
an excitatory or an inhibitory effect on the postsynaptic nerve
cell.
GABA is the neurotransmitter substance gamma-aminobutyric
acid. The term "GABA receptor" refers to any of several membrane
proteins that bind GABA and mediate its effects as an inhibitory
neurotransmitter. GABA(subA) receptors (GABA-gated ion channels;
GABA type A receptors) are a type of GABA receptor that function
as chloride ion channels, which when opened produce an inhibitory
effect on postsynaptic nerve cell membranes.
... ... K.M. Hold et al (5 authors at 2 installations, US) report
a study of alpha-thujone neurotoxicity, the authors presenting
evidence that alpha-thujone in absinthe and certain herbal
medicines is a rapidly-acting and readily detoxified modulator of
the gamma-aminobutyric acid-gated chloride ion channel.
... ... Commenting in the same journal on this work, Richard W.
Olsen (University of California Los Angeles, US) points out that
the report of Hold et al convincingly demonstrates, by 4 lines of
evidence, that thujone acts as a GABA-type A receptor antagonist:
1) The symptoms of poisoning by alpha-thujone and protection
against these symptoms by *benzodiazepines and *barbiturates
resemble those of other GABA blockers such as *picrotoxin.
2) A strain of insects (fruit fly Drosophila) resistant to
picrotoxin and GABA-blocking insecticides such as dieldrin is
also resistant to thujone.
3) Thujone competitively inhibits the binding of the
radioactive convulsant [(sup3)H]ethynylbicycloorthobenzoate to
the known picrotoxin/convulsant site linked to GABA-type A
receptors in mammalian brain membranes.
4) In electrophysiological experiments, thujone reversibly
blocks GABA-type A receptor chloride ion currents in mammalian
neurons.
None of these actions are caused by the ethanol in the
absinthe drink.
-----------
K.M. Hold et al: Alpha-thujone (the active component of
absinthe): Gamma-aminobutyric acid type A receptor modulation and
metabolic detoxification.
(Proc. Natl. Acad. Sci. US 11 Apr 00 97:3826)
QY: John E. Casida [ectl@nature.berkeley.edu]
-----------
Richard W. Olsen: Absinthe and gamma-aminobutyric acid receptors.
(Proc. Natl. Acad. Sci. US 25 Apr 00 97:4417)
QY: Richard W. Olsen [rolsen@mednet.ucla.edu]
-----------
Text Notes:
... ... *benzodiazepines: A group of drugs with sedative, muscle-
relaxant, and anticonvulsive action. They are widely used in
psychiatry.
... ... *barbiturates: A class of sedative hypnotic drugs widely
used in medical practice.
... ... *picrotoxin: A stimulant that blocks the inhibitory
actions of gamma-aminobutyric acid by acting on a receptor linked
to the GABA site.
-------------------
Summary & Notes by SCIENCE-WEEK http://scienceweek.com 30Jun00
For more information: http://scienceweek.com/swfr.htm
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5. NEUROBIOLOGY:
LONDON TAXI DRIVERS: NAVIGATION AND BRAIN STRUCTURAL CHANGES
The term "plasticity" in the context of brain research
refers in general to the ability of the brain to alter its
connections or dynamics as a result of experience or changes in
conditions. So, for example, the ability of certain parts of the
brain, particularly the cerebral cortex, to assume new functions
following destruction by disease or trauma of other parts is an
example of brain plasticity. The various parts of the brain do
not show the same degree of plasticity, and in general the degree
of plasticity of any part may change with the life history of the
individual. The brains of infants and young children, for
example, are extremely plastic.
The hippocampus (plural: hippocampi) is a region of the
cerebral cortex in the medial part of the temporal lobe. In
humans, among other functions, the hippocampus is apparently
involved in short-term memory, and analysis of the neurological
correlates of learning behavior in animals indicates that the
hippocampus is also involved in memory in other species.
In this context, magnetic resonance imaging (MRI) is
essentially a technique for examining the morphology of living
brain tissue, the technique involving computerized analysis of
data. In general, MRI involves magnetic coils producing a static
magnetic field parallel to the long axis of the patient or
subject, combined with inner concentric magnetic coils producing
a static magnetic field perpendicular to the long axis. A
radio-frequency coil specifically designed for the head perturbs
the static fields to generate a magnetic resonance image. The
interaction physics in this technique is that between the
magnetic fields and atomic nuclei in brain tissue. "Sliced" views
can be obtained from any angle, and the resolution is quite high
and on the order of millimeters for magnetic field strengths of
1.5 tesla.
... ... E.A. Maguire et al (7 authors at University College
London, UK) present a study involving structural magnetic
resonance imaging of the brains of humans with extensive
navigation experience, licensed London taxi drivers, the results
analyzed and compared with those from control subjects who did
not drive taxis. The authors make the following points:
1) The authors point out that one important role of the
hippocampus is apparently to facilitate spatial memory as it
involves navigation. Increased volume of the hippocampus relative
to brain and body size has been reported in small mammals and
birds that engage in behaviors, such as food storing, that
require spatial memory. In some species, the volume of the
hippocampus is enlarged specifically during seasons when demand
for spatial ability is greatest. In the healthy human, structural
brain differences between distinct groups of subjects (e.g.,
males and females, or musicians and non-musicians) have been
documented, but from existing studies it is impossible to
determine whether the apparent differences in brain anatomy are
predetermined or whether the brain is susceptible to plastic
changes in response to environmental stimulation.
2) The authors point out that taxi drivers in the city of
London must undergo extensive training, the drivers learning how
to navigate between thousands of places in the city. This
training is colloquially known as "being on The Knowledge" and
takes on average approximately 2 years to acquire. To be licensed
to operate a taxi, it is necessary to pass a very stringent set
of police examinations. London taxi drivers are therefore ideally
suited for the study of the neurological correlates of spatial
navigation.
3) The experimental subjects in the study were right-handed
male licensed London taxi drivers (n = 16); mean age 44 years;
age range 32 to 62 years. All subjects had been licensed London
taxi drivers for more than 1.5 years (mean time as taxi driver
14.3 years; range 1.5 to 42 years). The average time spent
training to be a taxi driver before fully passing the licensing
tests was 2 years (range 10 months to 3.5 years). The comparison
control group consisted of 50 healthy right-handed males who did
not drive taxis.
4) The authors report their results provide evidence of
regionally specific structural differences between the hippocampi
of licensed London taxi drivers compared with those of control
subjects. Taxi drivers had a significantly greater volume in the
posterior hippocampus, whereas control subjects showed a greater
volume in the anterior hippocampus. Local hippocampal volumes
correlated with the amount of time spent as a taxi driver
(positively in the posterior and negatively in the anterior
hippocampus). Total hippocampal volumes did not differ
significantly between the two groups. No differences were
observed elsewhere in the brain. The authors suggest the
converging results from two independent MRI image analysis
techniques (voxel-based morphometry and pixel counting) indicate
that the professional dependence on navigational skills in
licensed London taxi drivers is associated with a relative
redistribution of gray matter in the hippocampus.
5) The authors suggest their finding that the posterior
hippocampus increases in volume when there is occupational
dependence on spatial navigation is evidence for functional
differentiation within the hippocampus. In humans, as in other
animals, the posterior hippocampus is apparently involved when
previously learned spatial information is used, whereas the
anterior hippocampal region may be more involved (in combination
with the posterior hippocampus) during the encoding of new
environmental layouts.
6) The authors suggest their results indicate that the
"mental map" of the city of London in the subject taxi-drivers is
stored in the posterior hippocampus and is accommodated by an
increase in tissue volume. The authors suggest these results
challenge the traditional view that the hippocampus has a
transient role in memory, at least in relation to spatial
navigation and the posterior hippocampus.
7) The authors point out their findings from two independent
measurement techniques are consistent with previous human
clinical and functional neuroimaging reports of bilateral
hippocampal involvement in successful navigation.
8) The authors suggest that although the hippocampus does
not support navigation in isolation from other brain regions, it
is apparently crucial to the storage and use of mental maps of
environments. Prolonged accumulation of non-navigational
information may also produce similar hippocampal changes.
However, the authors suggest their present findings, correlated
as they are with results of clinical and functional neuroimaging
studies, suggest that space and the posterior human hippocampus
are intimately linked (right hippocampus greater than left
hippocampus).
9) The authors conclude: "Given the macroscopic level of our
analysis, the data do not speak directly to the microscopic
mechanisms, such as [proliferation of new nerve cells
(neurogenesis)], that might underlie the structural changes we
report herein. The differential changes in posterior and anterior
hippocampus may represent two different processes. The most
parsimonious explanation, however, is that our findings reflect
an overall internal reorganization of hippocampal circuitry in
response to a need to store an increasingly detailed spatial
representation, where changes in one hippocampal region are very
likely to affect others. On a broader level, the demonstration
that normal activities can induce changes in the relative volume
of gray matter in the brain has obvious implications for
rehabilitation of those who have suffered brain injury or
disease. It remains to be seen whether similar environment-
related plasticity is possible in other regions of the human
brain outside the hippocampus."
-----------
E.A. Maguire et al: Navigation-related structural change in the
hippocampi of taxi drivers.
(Proc. Natl. Acad. Sci. US 11 Apr 00 97:4398)
-------------------
Summary by SCIENCE-WEEK http://scienceweek.com 30Jun00
For more information: http://scienceweek.com/swfr.htm
-------------------
Related Background:
ON NEW NERVE CELLS IN THE ADULT HUMAN BRAIN
During most of this century, one of the dogmas in neurobiology
was that in the adult human brain new connections between neurons
may arise, but never new neurons. The dogma, in other words, was
that in the adult human brain new nerve cells are not produced,
and the neurons present at birth are the neurons present in the
adult, albeit a maximum number of nerve cells at birth, since a)
the number of neurons in the healthy adult human brain apparently
decreases with age beginning at about age 35; and b) various
neurodegenerative diseases can markedly reduce the population of
neurons in either specific regions of the brain or globally
nearly everywhere in the brain. In recent years, this dogma, the
idea that new nerve cells are not produced in the adult human
brain, has effectively crumbled for at least one specific and
important brain locus called the "hippocampus"...
... ... G. Kempermann and F.H. Gage (2 installations, DE US)
present a review of past and current research in adult
neurogenesis in humans, the authors making the following points:
1) In 1965, Altman and Das reported neurogenesis in the
hippocampus of rats, in a subregion of the hippocampus called the
"dentate gyrus". But this data was not viewed as evidence of
significant neurogenesis in adult mammals, primarily because the
methods available then could not accurately estimate the number
of new neurons nor demonstrate definitively that the new cells
were indeed nerve cells. In addition, the concept of *stem cells
in the brain had not yet been introduced, and the belief was that
for new neurons to appear, the only source would be replication
(i.e., mitosis) of adult neurons. There was also no evidence that
neurogenesis occurred in non-human primates, and so the relevance
of the rat data for the human brain seemed remote.
2) In the mid 1980s, Nottebohm discovered that neurogenesis
occurred in adult canaries in brain centers responsible for song
learning, and that the process accelerated during the seasons in
which the adult birds acquired their songs. Nottebohm and his co-
workers then demonstrated that neurogenesis also occurred in the
hippocampus of adult chickadees, particularly during seasons when
the birds had to keep track of dispersed food storage sites.
3) In 1997, Gould and McEwan reported that some neurogenesis
occurs in the hippocampus of the primate-like tree shrew, and in
1998, these authors found the same phenomenon in marmoset
monkeys, which are classified as actual primates.
4) Because of research difficulties, demonstration of
neurogenesis in the adult human brain had to await special
techniques. In 1998, Peter S. Eriksson reported the use of
bromodeoxyruridine as a marker for neurogenesis and the first
evidence for neurogenesis in the hippocampus of adult humans. The
use of this marker depended on its already established use as a
tumor marker in cancer patients. Bromodeoxyuridine is a marker
that becomes integrated only into the DNA of cells preparing to
divide, and the marker was in use with terminally ill patients
with cancer of the tongue or larynx. Eriksson obtained consent
from a number of patients to investigate their brains after
death, and when 5 patients died, all 5 brains displayed new
neurons in the dentate gyrus subregion of the hippocampus. At the
same time as this study was reported, other research groups
reported nerve cell production in the hippocampus of adult rhesus
monkeys, which are primates closer to humans than marmoset
monkeys.
5) In their review, the authors refer to their own work,
noting that beginning in 1997, they have demonstrated that adult
mice given enriched living conditions generate substantial
increases in dentate gyrus hippocampal neurons over that found in
genetically identical control animals.
6) The authors suggest that studies of neurogenesis in the
adult human brain, while difficult, may lead to better treatments
for a variety of neurological diseases. The authors conclude:
"The expected benefits of unlocking the brain's regenerative
potential justify all the effort that will be required."
-----------
G. Kempermann and F.H. Gage: New nerve cells in the adult brain.
(Scientific American May 1999)
QY: Gerd Kempermann, University of Regensburg, DE.
-----------
Text Notes:
... ... *medial part of the temporal lobe: The temporal lobes are
roughly the lower sides of the brain, above the ears and behind
the temporal bones of the skull, but when the human brain is
viewed from the side, as it usually is in common gross
depictions, the large and functionally important ventral and
infolded parts of the temporal lobes are not visible. In general,
the larger anatomical regions of the human brain are best
visualized as highly corrugated lobular structures extensively
folded and densely packed to fit inside the volume-limiting
protective skull. Isolated verbal descriptions of the
architecture are of limited use: anatomical graphics are the best
sources for visualization of gross brain structures.
... ... *stem cells: In general, the term "stem" cells
refers to undifferentiated cells that upon differentiation can
give rise to various specialized cell lines such as blood cells,
skin cells, nerve cells, etc. Adult bone marrow, for example,
contains stem cells that are the precursors of the various
specialized types of blood cells.
-------------------
Summary & Notes by SCIENCE-WEEK [http://scienceweek.com] 18Jun99
For more information: http://scienceweek.com/swfr.htm
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6. MEDICAL BIOLOGY:
TRANSFORMING GROWTH FACTOR-BETA IN HUMAN DISEASE
In biology, the term "mitogen" refers to any substance,
produced by cells or applied to cells, that stimulates cell
division.
A "cytokine" is any substance released by cells that acts on
other cells and promotes cell growth and cell division. As a
promoter of cell growth and division, a cytokine acts as a
messenger to cells, and the transmission of the message requires
a binding of the cytokine molecule to a cytokine-specific
receptor on the cell surface.
In general, in this context, a "growth factor" is any
specific substance that must be present in a culture medium for
multiplication of the cultured cells to occur. Certain growth
factors have been identified as cytokine proteins (peptide
hormones) that stimulate the growth and division of target cells
by binding to cell membrane receptors. "Transforming growth
factors" are cytokine growth factors that produce in target cells
some of the growth characteristics of cancer cells. Two distinct
types of transforming growth factor are denoted as TGF-alpha and
TGF-beta, the former a small polypeptide and the latter a large
protein consisting of 2 polypeptide subunits.
The term "extracellular matrix", in this context, refers to
the complex network of macromolecules lying between cells where
the cells form tissues.
Research has revealed that transforming growth factors are
of great important in various disease processes, and the study of
these cytokines in intensive.
... ... G.C. Blobe et al (3 authors at 3 installations, US)
present a review of the role of transforming growth factor-beta
in human disease, the authors making the following points:
1) In human tissues, normal *homeostasis requires
intricately balanced interactions between cells and the network
of secreted proteins known as the "extracellular matrix". These
cooperative interactions involve numerous cytokines acting
through specific cell-surface receptors. When the balance between
the cells and the extracellular matrix is perturbed, disease can
result, and this is clearly evident in the interactions mediated
by the cytokine known as transforming growth factor-beta (TGF-
beta).
2) TGF-beta is a member of a family of dimeric polypeptide
growth factors that includes *bone morphogenic proteins and
*activins. All of these growth factors share a cluster of
evolutionary conserved cysteine residues that form a common
cysteine knot structure held together by intramolecular disulfide
bonds. Virtually every cell in the body, including *epithelial,
*endothelial, *hematopoietic, neuronal, and connective tissue
cells, produces TGF-beta and has receptors for it. TGF-beta
regulates the proliferation and differentiation of cells,
embryonic development, wound healing, and *angiogenesis. The
essential role of the TGF-beta signaling pathway in these
processes has been demonstrated by targeted deletion of the genes
encoding members of this pathway in mice.
3) Increases or decreases in the production of TGF-beta have
been linked to numerous disease states, including
*atherosclerosis and *fibrotic diseases of the kidney, liver, and
lung. Mutations in the genes for TGF-beta, its receptors, or
intracellular signaling molecules associated with TGF-beta are
also important in the pathogenesis of disease, particularly
cancer and *hereditary hemorrhagic telangiectasia.
-----------
G.C. Blobe et al: Role of transforming growth factor-beta in
human disease.
(New England J. Med. 4 May 00)
QY: Harvey F. Lodish [lodish@wi.mit.edu]
-----------
Text Notes:
... ... *homeostasis: The term "homeostasis" refers to a
physiological equilibrium necessary in general for the viability
of an organism, and in particular for the operation of many
cellular functions. Homeostatic mechanisms in biological systems
usually involve an element of negative feedback signaling. In
vertebrates, for example, when blood temperature is too high,
temperature receptors provoke a sequence of events involving many
pathways that ultimately results in a lowering of body
temperature. Similar homeostatic mechanisms operate at cellular
levels.
... ... *bone morphogenic proteins: Any of several enzymes (zinc
metallo-endopeptidases) involved in the induction of bone and
cartilage formation
... ... *activins: The term "activin" refers to a gonadal
glycoprotein and placental hormone that reaches maximum levels in
maternal serum during labor.
... ... *endothelial: Endothelial cells are flat cells forming a
layer lining blood vessels, lymphatic vessels, the heart, etc.)
... ... *hematopoietic: (hemopoietic) The term "hematopoiesis"
refers to the formation and development of the various types of
blood cells, and "hematopoietic cells" are the precursor cells of
these various types.
... ... *angiogenesis: The origin and development of blood
vessels. Angiogenesis is an important consideration in the growth
of cancerous tumors, since the tumor provokes directed
angiogenesis into itself with the end result that the tumor is
supplied with oxygen and nutrients. Without angiogenesis, tumors
can attain only a small size before becoming self-inhibiting.
... ... *atherosclerosis: "Arteriosclerosis" is a generic term
for several diseases in which the arterial wall becomes thickened
and loses elasticity, and "atherosclerosis" is a form of
arteriosclerosis characterized by patchy thickening (atheroma) in
the subintimal layer (i.e., immediately below the innermost layer
[intima]) of medium and large arteries, the thickening capable of
reducing or obstructing blood flow.
... ... *fibrotic diseases: In general, the term "fibrosis"
refers to the formation of connective tissue (fibrous tissue) in
tissue repair (e.g., scar tissue) or as a reactive process, as
opposed to the formation of fibrous tissue as a normal
constituent of an organ or tissue (e.g., in development).
... ... *hereditary hemorrhagic telangiectasia: In general,
telangiectasia is a dilation of existing small blood vessels, and
hereditary hemorrhagic telangiectasia is a disease characterized
by multiple small telangiectases and dilated small capillary
veins (venules) that develop slowly on the skin and mucous
membranes of various tissues. The disease is apparently caused by
mutation in a single gene.
-------------------
Summary & Notes by SCIENCE-WEEK http://scienceweek.com 30Jun00
For more information: http://scienceweek.com/swfr.htm
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7. IN FOCUS: ON PERSEVERANCE IN RESEARCH
"The School of Physics could give us no suitable premises, but
for lack of anything better, the Director permitted us to use an
abandoned shed which had been in service as a dissecting room of
the School of Medicine... Yet it was in this miserable old shed
that we passed the best and happiest years of our life, devoting
our entire days to our work. Often I had to prepare our lunch in
the shed, so as not to interrupt some particularly important
operation. Sometimes I had to spend a whole day mixing a boiling
mass with a heavy iron rod nearly as large as myself. I would be
broken with fatigue at the day's end. Other days, on the
contrary, the work would be a most minute and delicate fractional
crystallization, in the effort to concentrate the radium... Thus
the months passed, and our efforts hardly interrupted by short
vacations, brought forth more and more complete evidence. Our
faith grew ever stronger, and our work being more and more known,
we found means to get new quantities of raw material and to carry
on some of our crude processes in a factory, allowing me to give
more time to the delicate finishing treatment. At this stage I
devoted myself especially to the purification of the radium, my
husband being absorbed by the study of the physical properties of
the rays emitted by the new substances. It was only after
treating one ton of pitchblende residues that I could get
definite results. Indeed we know today that even in the best
minerals there are not more than a few decigrams of radium in a
ton of raw material. At last the time came when the isolated
substances showed all the characters of a pure chemical body.
This body, the radium, gives a characteristic spectrum, and I was
able to determine for it an atomic weight much higher than that
of the barium. This was achieved in 1902. I then possessed one
decigram of very pure radium chloride. It had taken me almost
four years to produce the kind of evidence which chemical science
demands, that radium is truly a new element. One year would
probably have been enough for the same purpose, if reasonable
means had been at my disposal."
-----------
Marie Curie: _Pierre Curie_ (1927)
(trans. Charlotte and Vernon Kellogg)
-----------
[Editor's note: Marie Curie (1867-1934) and her husband Pierre
Curie (1859-1906) shared the Nobel Prize for Physics in 1903.
Marie Curie also won the Nobel Prize for Chemistry in 1911. Three
years after receiving the Nobel Prize, Pierre Curie died at the
age of 47 in a traffic accident, run over by a horse-drawn
vehicle. During her work in the shed, Marie Curie also had to
care for her 5-year-old daughter Irene, later known as Irene
Joliot-Curie. Irene and her husband Frederic Joliot shared the
Nobel Prize in Chemistry in 1935. Marie Curie died at the age of
67 of a leukemia apparently caused by her exposure to high-energy
radiation (her notebooks are apparently still too contaminated to
handle). She died one year before her daughter was awarded the
Nobel Prize. Despite their poverty, and the chance for obvious
riches, the Curies refused to patent their radium isolation
process. Concerning the patenting of the process, Marie Curie
stated: "It would be impossible, it would be against the
scientific spirit... Physicists should always publish their
researches completely. If our discovery has a commercial future,
that is a circumstance from which we should not profit. If radium
is to be used in the treatment of disease, it is impossible for
us to take advantage of that."]
-------------------
SCIENCE-WEEK http://scienceweek.com 30Jun00
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