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.

December 4, 1998 -- Vol. 2 Number 49

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All these fifty years of conscious brooding have
brought me no nearer to the answer to the question,
What are light quanta? Nowadays every Tom, Dick,
and Harry thinks he knows it, but he is mistaken.
-- Albert Einstein (1879-1955)

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Contents of This Issue:

1. An Assault on High-Priced Journals
2. On Climate Forcings in the Industrial Era
3. On Field Theory in Physics
4. Evolution: Renewed Interest in the Lancelet (Amphioxus)
5. On Leptin and the Regulation of Mammalian Body Weight
6. Mice Without Myoglobin
7. Migraine: Hyperexcitability of Occipital Cortex

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1. AN ASSAULT ON HIGH-PRICED JOURNALS
The revolt of libraries against high prices for commercial
scientific journals has increased in intensity as the UK Royal
Society of Chemistry has announced plans to publish a low-cost
journal (*PhysChemComm*) that will directly compete with a more
expensive commercial publication (*Chemical Physics Letters*).
Also, Michael Rosenzweig, a prominent ecologist, and his 34-
member editorial board, have abandoned the commercial journal
*Evolutionary Ecology* to start a new journal (*Evolutionary
Ecology Research*). Librarians have complained that an increasing
share of their budgets are used for widely-cited "must-have"
scientific and technical journals published by a few dominant
commercial publishers (e.g., Reed Elsevier and Wolters Kluwer),
and that each journal typically has less than 500 subscribers and
can cost up to US$15,000 annually. Concerning the planned new
journals, here are the journals and their prices, and the prices
of their competitors:
 -- *Evolutionary Ecology Research* (Evolutionary Ecology Ltd.)
at a planned annual subscription price of US$305 to compete with
*Evolutionary Ecology* (Kluwer), annual subscription US$777.
 -- *Organic Letters* (American Chemical Society) at a planned
annual subscription price of US$2300 to compete with *Tetrahedron
Letters* (Elsevier), annual subscription US$8602.
 -- *PhysChemComm* (UK Royal Society of Chemistry) at a planned
annual subscription price of US$353 to compete with *Chemical
Physics Letters* (Elsevier), annual subscription US$8368.
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Summary by SCIENCE-WEEK http://scienceweek.com 4Dec98

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Related Background:

ON FREE INTERNET ACCESS TO TRADITIONAL JOURNALS
Thomas J. Walker (University of Florida, US) presents an analysis
of current problems involving the production costs and
subscription prices of scientific journals, the author making the
following points: 1) On the Web, publishers are now beginning to
charge for access to journal articles online through
subscriptions, site licenses, and "pay-per-view" plans. These
toll-gate approaches are an extension of the current economic
structure of scientific publishing and are being developed
largely by the organizations that benefit most from that economic
structure. On the other hand, many of those who do the research
and write the articles do not share these economic interests, nor
do many of the scientific societies to which they belong. 2) Some
scientific societies currently finance publishing through per-
page charges that are paid by authors or their grants or
institutions. Such charges now help hold down subscription
prices, and in the future similar charges might finance free
access. 3) The 1970s witnessed the beginning of extraordinary
increases in the real prices of science journals. Whereas the
costs of scholarly publishing in general closely followed the
Consumer Price Index, the average prices of science and technical
journals markedly diverged upward, so that by 1996 the relative
increase in the prices of scientific journals was an order of
magnitude greater than the relative increase in the prices of
scientific books. 4) In the past decade, research libraries have
spent more than twice what they spent in 1986 to purchase 7
percent fewer titles. Every year libraries must cancel journal
subscriptions in order to continue to receive other journals that
are increasingly costly. And publishers often raise subscription
prices as their subscriber base shrinks, creating a feedback loop
that worsens the situation. 5) Unfortunately, rather than ending
the journals crisis for libraries, the beginning of Web access to
traditional journals may have intensified it. Publishers now
offer licenses to electronic versions as add-ons to regular
subscriptions, in most cases with a substantial increase in
subscription price. 6) The author suggests that the economics of
electronic publication are so favorable that scientific societies
should be able to finance free access to all their articles from
page charges to authors who want their articles immediately
posted, and that the Florida Entomological Society is now doing
just that. 7) The author further suggests that if scientific
societies acknowledge that their mission is to serve members,
they should realize that restricting access to refereed research
results, when free access has finally become affordable, is
counter to that mission. The author concludes: "Free access to
traditional journals is affordable and achievable... Taking
action now can secure an information highway where toll gates do
not limit access to the literature of science."
QY: Thomas J. Walker 
(American Scientist Sep/Oct 1998) (Science-Week 11 Sep 98)


2. ON CLIMATE FORCINGS IN THE INDUSTRIAL ERA
A "climate forcing" is an imposed perturbation of the Earth's
energy balance with space, for example, a change of the solar
radiation incident on the planet, or a change of carbon dioxide
in the Earth's atmosphere. The unit of measure of climate forcing
is Watts per square meter. Thus, the forcing due to the increase
of atmospheric carbon dioxide since pre-Industrial times is
approximately 1.5 Watts per square meter. Climate change is
combination of deterministic response to forcings and *chaotic
fluctuations -- the chaos a consequence of the nonlinear
equations governing the dynamics of the system. Quantitative
knowledge of all significant climate forcings is needed to
establish the contribution of deterministic factors in observed
climate change and to predict future climate. J.E. Hansen et al,
in a review of current considerations concerning climate forcings
in the Industrial era, make the following points: 1) The forcings
that drive long-term climate change are not known with an
accuracy sufficient to define future climate change. 2)
Anthropogenic greenhouse gases, which are well-measured, cause a
strong positive (warming) force. But other, poorly measured,
anthropogenic forcings, especially changes of atmospheric
aerosols, clouds, and land-use patterns, cause a negative forcing
that tends to offset greenhouse warming. 3) One consequence of
this partial balance is that the natural forcing due to solar
irradiance changes may play a larger role in long-term climate
change than inferred from comparison with greenhouse gases alone.
Current trends in greenhouse gas climate forcings are smaller
than in popular "business as usual" or 1 percent per year carbon
dioxide growth scenarios. The authors suggest that a summary
implication of their considerations is a paradigm change for
long-term climate projections: uncertainties in climate forcings
have supplanted global climate sensitivity as the predominant
issue. The authors further suggest that climate forcing scenarios
are essential for climate predictions, but if only one forcing
scenario is used in climate simulations, as has been a recent
tendency, the scenario itself is likely to be taken as a
prediction, as well as the calculated climate change. The authors
recommend that the use of multiple scenarios will aid objective
analysis of climate change as it unfolds in coming years.
-----------
J.E. Hansen et al (6 authors at National Aeronautics and Space
Administration, US)
Climate forcings in the Industrial era.
(Proc. Natl. Acad. Sci. US 27 Oct 98 95:12753)
QY: James E. Hansen 
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Text Notes:
... ... *chaotic fluctuations: The term "chaotic", in this
context, is specific. In the study of physical systems, the
term "chaotic behavior" has a specific meaning: the behavior of a
system is said to be "chaotic" if its final state is so sensitive
to the system's precise initial conditions that the behavior of
the system is in effect unpredictable and cannot be distinguished
from a random process, even though the behavior of the system is
strictly determinate in a mathematical sense. In other words, a
deterministic system characterized by extremely sensitive
instabilities, despite the system being determinate, can exhibit
behavior that is unpredictable, and the system is then called
"chaotic". During the past several decades, the analysis of such
chaotic systems has intrigued both physicists and mathematicians.
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Summary & Notes by SCIENCE-WEEK http://scienceweek.com 4Dec98

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Related Background:

A SCIENTIFIC BASIS FOR CLIMATE FORECASTING
At the beginning of the 20th century it was believed that it
should be possible to predict weather by solving the mathematical
equations that describe the physical laws that govern the motion
of air. It took several decades to develop an appropriate set of
equations and numerical and computational techniques to solve
these equations, and by 1960, routine weather predictions using
global observations, complex mathematical equations, and fast
computers seemed immediately at hand. The promise, however, was
short lived, because in the early 1960s it was discovered that
the mathematical equations for weather forecasting represent a
forced *dissipative nonlinear dynamic system that exhibits
*chaotic behavior, which means that even an infinitesimally small
uncertainty in the initial conditions will grow exponentially to
make the forecast useless after a finite amount of time.
... ... J. Shukla now presents a study involving analyses of
weather observations coupled with model simulations. The author
reports that although the Earth's atmosphere is generally
considered to be an example of a chaotic system that is
sensitively dependent on initial conditions, certain regions of
the atmosphere are an exception, with wind patterns and rainfall
in certain regions of the tropics so strongly determined by the
temperature of the underlying sea surface that they do not show
sensitive dependence on the initial conditions of the atmosphere.
The author suggests it should therefore be possible to predict
the large-scale tropical circulation and rainfall for as long as
the ocean temperature can be predicted, and that if changes in
tropical Pacific sea-surface temperature are quite large, even
the extratropical circulation over some regions, especially over
the Pacific-North American sector, is predictable. In particular,
the author suggests that for all future major *El Nino events, it
should be possible to predict large-scale changes in the winter
season mean circulation over North America several months in
advance, provided we can predict tropical sea surface
temperatures.
-----------
J. Shukla (George Mason University, US)
Predictability in the midst of chaos: A scientific basis for
climate forecasting.
(Science 23 Oct 98 282:728)
QY: J. Shukla, George Mason University 703-993-2400
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Text Notes:
... ... *dissipative: In general, a dissipative system
is a system that loses energy by conversion of energy into heat.
... ... *El Nino: El Nino is an aperiodic intermittent (2 to 10
years) flow of unusually warm surface water along the western
coast of South America, the flow capable of causing abnormally
high rainfall in usually dry areas and severe local ecosystem
dislocations -- what is termed an El Nino "event". El Ninos are
regional phenomena, but they have global consequences. The name
"El Nino" ("The Child") arose because the phenomenon usually
occurs around Christmas. In 1986, M.A. Cane and S.A. Zebiak
proposed a model for making forecasts of El Nino several seasons
ahead by applying Newton's equations of motion and the laws of
thermodynamics to the dynamics of the ocean and atmosphere of the
tropical Pacific.
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Summary & Notes by SCIENCE-WEEK http://scienceweek.com 20Nov98


3. ON FIELD THEORY IN PHYSICS
In physics, a field is an entity that acts as intermediary in
interactions between particles, and which is distributed over
part or all of space, and whose properties are functions of space
coordinates, and except for static fields, also functions of
time. There is also a quantum-mechanical analog of this entity,
in which the function of space and time is replaced by an
operator at each point in space-time. ... ... Roman Jackiw
reviews present theoretical work in the theory of elementary
particles and forces, and the author makes the following points:
1) Present-day theory for fundamental processes (i.e.,
descriptions of elementary particles and forces) is phenomenally
successful. Experimental data confirms theoretical prediction,
and where accurate calculation and experiments are attainable,
agreement is achieved to 6 or 7 figures. Two examples: a) The
helium atom ground state energy (*Rydbergs) is experimentally
measured as -5.8071394 and theoretically calculated as
-5.8071380. b) The muon magnetic dipole moment is experimentally
measured as 2.00233184600 and theoretically calculated as
2.00233183478. 2) The theoretical structure within which this
success has been achieved is *local field theory, which offers a
wide variety of applications, and which provides a model for
fundamental physical reality as described by our theories of
*strong, electroweak, and gravitational processes. No other
framework exists in which one can calculate so many phenomena
with such ease and accuracy. 3) But is spite of these successes,
today there is little confidence that field theory will advance
our understanding of nature at its fundamental workings beyond
what has already been achieved. Although in principle all
observed phenomena can be explained by present-day field theory,
these accounts are still imperfect, requiring ad hoc inputs.
Moreover, because of conceptual and technical obstacles,
classical gravity theory has not been integrated into the
*quantum field description of nongravitational forces:
*quantizing the *metric tensor of Einstein's theory produces a
quantum field theory beset by infinities that apparently cannot
be controlled. 4) These shortcomings are actually symptoms of a
deeper lack of understanding concerning *symmetry and symmetry
breaking... Physicists are happy in the belief that Nature in its
fundamental workings is essentially simple, but observed physical
phenomena rarely exhibit overwhelming regularity. Therefore, at
the very same time that we construct a physical theory with
intrinsic symmetry, we must find a way to break the symmetry in
physical consequences of the model. 5) These problems have
produced a theoretical impasse for over two decades, and in the
absence of new experiments to channel theoretical speculation,
some physicists have concluded that it will not be possible to
make progress on these questions within field theory, and they
have turned to a new structure, "*string theory". In field
theory, the quantized excitations are point particles with point
interactions, and this gives rise to the infinities. In string
theory, the excitations are extended objects -- strings -- with
nonlocal interactions; there are no infinities in string theory,
and that enormous defect of field theory is absent. 6) Yet in
spite of its positive features, until now string theory has
provided a framework rather than a definite structure, and a
precise derivation of the *Standard Model has yet to be given.
The author concludes: "On previous occasions when it appeared
that quantum field theory was incapable of advancing our
understanding of fundamental physics, new ideas and new
approaches to the subject dispelled the pessimism. Today we do
not know whether the impasse within field theory is due to a
failure of imagination or whether indeed we have to present
fundamental physical laws in a new framework, thereby replacing
the field theoretic one, which has served us well for over 100
years."
-----------
Roman Jackiw (Massachusetts Institute of Technology, US)
Field theory: Why have some physicists abandoned it?
(Proc. Natl. Acad. Sci. US 27 Oct 98 95:12776)
QY: Roman Jackiw, Mass. Inst. of Technology 617-253-1000.
-----------

Text Notes:
... ... *Rydbergs: A unit of energy used in atomic physics,
value = 13.605698 electronvolts.
... ... *local field theory: In this context, "locality" is the
condition that two events at spatially separated locations are
entirely independent of each other, provided that the time
interval between the events is less than that required for a
light signal to travel from one location to the other. For
example, the quantum mechanical wave function is a "local" field.
... ... *strong, electroweak, and gravitational processes: The
fundamental forces comprise the gravitational force, the
electromagnetic force, the nuclear strong force, and the nuclear
weak force. The "electroweak" interactions are a unification of
the electromagnetic and nuclear weak interactions, and are
described by the Weinberg-Salam theory (sometimes called "quantum
flavordynamics"; also called the Glashow-Weinberg-Salam theory).
... ... *quantum field description: In general, a quantum field
theory is a quantum mechanical theory applied to systems having
an infinite number of *degrees of freedom.
... ... *degrees of freedom: In general, the number of
independent parameters required to specify the configuration of a
system.
... ... *quantizing: In experimental physics, a quantized
variable is a variable taking only discrete multiple values of a
quantum mechanical constant. In theoretical physics, "quantizing"
means the consistent application of certain rules that lead from
classical to quantum mechanics. In general, "quantization" is a
transition from a classical theory or a classical quantity to a
quantum theory or the corresponding quantity in quantum
mechanics.
... ... *metric tensor: The mathematical statement (involving a
set of quantities) that describes the deviation of the Pythagoras
theorem in a curved space.
... ... *symmetry and symmetry breaking: If a theory or process
does not change when certain operations are performed on it, the
theory or process is said to possess a symmetry with respect to
those operations. For example, a circle remains unchanged under
rotation or reflection, and a circle therefore has rotational and
reflection symmetry. The term "symmetry breaking" refers to the
deviation from exact symmetry exhibited by many physical systems,
and in general, symmetry breaking encompasses both "explicit"
symmetry breaking and "spontaneous" symmetry breaking. Explicit
symmetry breaking is a phenomenon in which a system is not quite,
but almost, the same for two configurations related by exact
symmetry. Spontaneous symmetry breaking refers to a situation in
which the solution of a set of physical equations fails to
exhibit a symmetry possessed by the equations themselves.
... ... *string theory: In particle physics, string theory is a
theory of elementary particles based on the idea that the
fundamental entities are not point-like particles but finite
lines (strings), or closed loops formed by strings, the strings
one-dimensional curves with zero thickness and lengths (or loop
diameters) of the order of the Planck length of 10^(-35) meters. 
... ... *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 4Dec98

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Related Background:

THEORETICAL PHYSICS: ON STRING THEORY
... ... B.R. Greene et al present a short review of recent
developments in string theory and make the following points: 1)
Particle physics has spent much of this century grappling with
one basic question in various forms: What are the fundamental
*degrees of freedom needed to describe nature, and what are the
laws that govern their dynamics. 2) The current "Standard Model"
of particle physics -- which is nearly 25 years old and which has
much experimental evidence in its favor -- involves 6 *quarks, 6
*leptons, 4 *forces, and the as yet unobserved *Higgs boson. But
this model contains internal indications that it too may be just
another step along the path of uncovering the truly fundamental
degrees of freedom. The Standard Model is valid to distances as
small as 10^(-16) cm, and there is some evidence that the next
level of structure will be detected only at a distance scale of
the order of 10^(-32) cm, which is far beyond our abilities to
measure in the laboratory. 3) A related important issue concerns
the unification of general relativity and quantum mechanics. A
serious problem arises when general relativity is extrapolated to
small distance scales of the order of 10^(-32) cm where quantum
effects must be taken into account: the relevant theoretical
equations produce uncontrollable divergences, and the history of
particle physics suggests this is an indication of a new physics
occurring at these distance scales. 4) String theory offers hope
of addressing both of these issues. There is only one known way
to cure the divergence problem in the quantum-mechanical
expansion of general relativity, and that is to model the
particles in the theory not as points but as one-dimensional
loops of "string". Every consistent such string model necessarily
contains a special kind of particle -- the "*graviton" --  whose
long-distance interactions are described by general relativity.
So in a sense, string theory predicts gravity. 5) An exciting new
frontier was opened during the past few years with the discovery
of "string duality", which predicts equivalences among various
different physical systems. This discovery has its roots in the
properties of "supersymmetry", a novel type of symmetry that all
consistent string theories possess. Briefly, supersymmetry
relates properties of two basic types of particles -- bosons and
*fermions --  which cannot be related by ordinary symmetry. There
is a current belief that supersymmetry will play a role in the
structure of particle physics beyond the Standard Model. One of
the important achievements of string duality has been the
determination of the behavior of the 5 consistent string theories
when interactions become strong. All the consistent string
theories are apparently related to each other, and to an
elaboration known as "membrane theory" (M-theory). String duality
has produced hope that there may be only one possible string-
theoretic model of the universe, and that it may be possible to
eventually predict such features as particle masses and
interaction strengths directly from such a theory. The authors
conclude: "Development has been rapid on many fronts since string
duality was introduced. We may be seeing glimpses of the
underlying principle manifested in these new results. The
challenging task that lies ahead is to discover that principle
and thereby find what may well be the truly fundamental degrees
of freedom in our universe."
-----------
B.R. Greene et al (3 authors at 3 installations, US)
String theory.
(Proc. Natl. Acad. Sci. US 15 Sep 98 95:11039)
QY: David R. Morrison 
-----------

Text Notes:
... ... *degrees of freedom: See previous report.
... ... *quarks: See previous report.
... ... *leptons: A class of elementary particles. Although they
are affected by electromagnetic and gravitational forces, apart
from that they are involved only with weak interactions, acted
upon by weak forces but not by strong forces, as opposed to
quarks, which are acted upon by strong forces but not by weak
forces. One further difference between leptons and quarks is that
leptons can be isolated as single particles, whereas quarks
apparently cannot. The leptons include the electron, the muon,
the tau, and their associated neutrinos. The mass of the tau is
approximately 3484 times the mass of the electron; the mass of
the muon is intermediate.
... ... *forces: See previous report (fundamental forces).
... ... *Higgs boson: Higgs fields (named after Peter W. Higgs,
University of Edinburgh, UK) constitute a set of fundamental
theoretical fields that induce spontaneous symmetry breaking. In 
general, spontaneous symmetry breaking occurs in systems whose
underlying symmetry state is unstable. A Higgs particle is
associated with a Higgs field in the same way that a photon is
associated with the electromagnetic field. Higgs bosons are
massive mesons whose existence is predicted by certain theories.
Mesons are apparently composed of quark and anti-quark pairs;
they are produced by various high-energy interactions and decay
into stable particles.
... ... *graviton: Several quantum field theories consistent with
both quantum mechanics and special relativity postulate that the
gravitational force between two quantum domain particles is
generated by the exchange of an intermediate particle called a
graviton.
... ... *fermions: Fermions (electrons, protons, neutrons) are
particles that obey the Pauli exclusion principle: i.e., no two
fermions of the same kind can occupy the same quantum state.
-------------------
Summary & Notes by SCIENCE-WEEK http://scienceweek.com 16Oct98

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

Related Background:

ON RECENT DEVELOPMENTS IN SUPERSTRING THEORY
Bose-Einstein statistics is the statistical mechanics of a system
of indistinguishable particles for which there is no restriction
on the number of particles that may simultaneously exist in the
same quantum energy state. Bosons are particles that obey Bose-
Einstein statistics, and they include photons, pi mesons, all
nuclei having an even number of particles, and all particles with
integer spin. Fermions (electrons, protons, neutrons) are
particles that obey the Pauli exclusion principle: i.e., no two
fermions of the same kind can occupy the same quantum state.
In particle physics, string theory is a theory of elementary
particles based on the idea that the fundamental entities are not
point-like particles but finite lines (strings), or closed loops
formed by strings, the strings one-dimensional curves with zero
thickness and lengths (or loop diameters) of the order of the
Planck length of 10^(-35) meters. The fundamental forces comprise
the gravitational force, the electromagnetic force, the nuclear
strong force, and the nuclear weak force, and the "grand unified
theories" are theories that aim to provide a mathematical frame-
work in which the electromagnetic forces, strong forces, and weak
forces emerge as parts of a single unified force, with the three
forces related by symmetry. Supersymmetry is an aspect of an
extension of the grand unified theories, an attempt to unify all
the four fundamental forces, i.e., linking gravitation to the
electromagnetic force, the strong force, and the weak force
through a supersymmetry scheme, and superstrings are strings in
this scheme that obey supersymmetry. ... ... John H. Schwarz
(California Institute of Technology, US) presents a brief
overview of some of the advances in understanding super-
string theory that have been achieved in the last few years.
String theories that have a symmetry relating bosons and
fermions, called "supersymmetry", are called "superstring"
theories. Major advances in understanding of the physical world
have been achieved during the past century by focusing on
apparent contradictions between well-established theoretical
structures. In each case the reconciliation required a better
theory, often involving radical new concepts and striking exper-
imental predictions. Four major advances of this type were the
discoveries of special relativity, quantum mechanics, general
relativity, and quantum field theory. This was quite an achieve-
ment for one century, but there is one fundamental contradiction
that still needs to be resolved, namely the clash between general
relativity and quantum field theory. Many theoretical physicists
are convinced that superstring theory will provide the answer.
QY: John H. Schwarz, Calif. Inst. of Technology 818-395-6811.
(Proc. Natl. Acad. Sci. US 17 Mar 98)
(Science-Week 10 Apr 98)

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

Related Background:

ON THE EVOLUTION OF STRING THEORY TO MEMBRANE THEORY
... Membrane theory (M-theory) is a recent extension of string
theory in which the fundamental physical entities are considered
as surfaces in a many-dimensional space (membranes) rather than
as lines or loop elements (open or closed strings). Given all of
the above, some caution is necessary: the translation of a highly
abstract mathematical model of physical reality into non-mathem-
atical language is often an exercise of limited usefulness, and
in this case in particular, we are presenting only the ghost of
the theoretical scheme. String theory was originally invented in
the 1960s as a theory of the strong force, became overshadowed by
the strong force theory of gluons and quarks, then had a revival
in the 1980s -- but with the history more dependent on new work
than on fashion. ... ... M. Duff (Texas A & M Univ., US), who is
active in string theory and membrane theory, in a review of
various aspects of the history and essentials of string theory
and membrane theory, suggests that future historians may judge
the 20th century as "a time when theorists were like children
playing on the seashore, diverting themselves with the smoother
pebbles or prettier shells of superstrings, while the great ocean
of M-theory lay undiscovered before them."
QY: Michael J. Duff, Texas A & M Univ. 409-847-9451.
(Scientific American February 1998)
(Science-Week 23 Jan 98)


4. EVOLUTION: RENEWED INTEREST IN THE LANCELET (AMPHIOXUS)
One of the important questions in evolutionary biology concerns
the details of the path of evolution of the vertebrates from the
invertebrates. The vertebrates constitute a subphylum of the
chordates, which are animals that possess a "notochord" as
embryos and/or as adults. The notochord is a stiff rod of
cartilage supporting the nerve cord and present only in the
embryos of vertebrates. During the 19th century, the biologist
*Ernst Haeckel promoted a now defunct theory of "recapitulation",
sloganized as "*ontogeny repeats *phylogeny", the essence of the
theory proposing that embryonic stages represent past stages in
the evolution of the organism. This theory had a powerful impact
on late 19th century research in embryology, and thus the
presence of a notochord in particular lower forms was taken as
suggestive of the role of these particular forms in the evolution
of vertebrates. Of all such lower forms, perhaps none received
such popular attention as the lancelet (also called amphioxus), a
1 to 2 inch long invertebrate fishlike marine animal, which as an
adult possesses a semi-rigid notochord running from one end to
the other. Apparently the interest of evolutionary biologists in
the lancelet has in recent years revived. ... ... M.D. Stokes and
N.D. Holland present an extensive review of the biology of the
lancelet and of its history as a research object, and the authors
make the following points: 1) Around the beginning of the 20th
century, the rate of publication of research papers in lancelet
biology declined sharply and did not pick up again until
approximately 1960, when advances in electron microscopy
stimulated a new surge of interest. A second surge of interest,
which is still in full swing, was triggered approximately 10
years ago when lancelets began to be studied by the methods of
molecular biology, with the techniques of comparative molecular
genetics now being used to address classical questions concerning
the evolutionary origin of the vertebrates. 2) Molecular
biological studies have now shown that the lancelet is the
closest living invertebrate relative of the vertebrates. A
phylogenetic tree based on the DNA sequence of the large
*ribosomal subunits in various animal subphyla supports the view
that the *cephalochordates (of which the lancelet is a member)
are the sister group of the vertebrates. 3) Other clues to early
vertebrate evolution have been provided by studies of
developmental genes, which are remarkable conserved throughout
the animal kingdom, and which are clustered on a single
chromosome in the lancelet and on 4 separate chromosomes in
vertebrates. The current consensus is that modern lancelets and
vertebrates apparently had a cephalochordate-like ancestor in
common. The authors conclude: "Molecular biology has now shown
that Haeckel was correct in placing a lancelet-like creature at
the base of the vertebrates... Thus lancelets seem to have come
full circle in the history of biology. After years of neglect,
they have now regained the prominence that they enjoyed in the
last decades of the 19th century when they were the centerpiece
of Haeckel's recapitulation theory."
-----------
M.D. Stokes and N.D. Holland (2 installations, US)
The lancelet.
(American Scientist Nov/Dec 1998 86:552)
QY: M. Dale Stokes, Univ. of Calif. San Diego 619-534-2230.
-----------

Text Notes:
... ... *Ernst Haeckel (1834-1919): Haeckel was apparently the
first German biologist to promote Darwinism and evolution, and he
was one of the centers of the intense and often vituperative 19th
century controversy between science and religion. Haeckel was
also apparently the first to use the term "ecology" to refer to
the study of living organisms in relation to one another and to
the inanimate environment. A major difficulty with Haeckel's
recapitulation theory is that it produces too many apparent
errors when used to delineate evolutionary connections.
... ... *ontogeny: The development of an individual from zygote
to maturity. The term "zygote" refers to the cell formed by the
union of male and female gametes (sperm and egg cells).
... ... *phylogeny: The evolutionary history of a species or
group of species in terms of their derivation and relationships.
A "phylogenetic tree" is a schematic diagram that represents that
evolution.
... ... *ribosomal subunits: A ribosome (not to be confused with
riboZYME) is a small particle, a complex of various ribonucleic
acid component subunits and proteins that functions as the site
of protein synthesis in cells.
... ... *cephalochordates: (Acrania) A subphylum of marine
chordates characterized by the presence of a notochord, dorsal
nerve cord, and gill slits in both embryo and adult. They lack a
brain and vertebral column.
-------------------
Summary & Notes by SCIENCE-WEEK http://scienceweek.com 4Dec98


5. ON LEPTIN AND THE REGULATION OF MAMMALIAN BODY WEIGHT
The assimilation, storage, and use of energy from nutrients
constitute a *homeostatic system essential for life. In
vertebrates, the ability to store sufficient quantities of
energy-dense triglycerides in *adipose tissue allows survival
during periods of food deprivation. However, the presence of
excess adipose tissue can be evolutionary maladaptive, and a
complex physiological system has evolved to regulate fuel stores
and energy balance at an optimum level. Leptin is a hormone
secreted by adipose tissue, and this hormone and its receptor are
apparently integral components of the fuel-energy regulatory
system. Leptin also apparently signals nutritional status to
several other physiological systems and modulates their function.
... ... J.M. Friedman and J.L. Halaas review the role of leptin
in the control of body weight and its relevance to the
pathogenesis of obesity, and the authors make the following
points: 1) The belief that obesity is largely the result of a
lack of willpower, though widely held, is unsatisfactory. Studies
of twins, analyses of *familial aggregation, adoption studies,
and animal models of obesity all indicate that obesity is the
result of both genetic and environmental factors. Moreover,
weight is stable in lean and obese individuals even though much
of the population actively practices weight control. Dieting is
not usually successful in long-term maintenance of reduced body
weight, and most reduced obese individuals eventually regain the
lost weight. 2) *Recessive mutations in the mouse obese and
diabetes genes result in obesity and diabetes in a syndrome
resembling pathological human obesity... The *cloning and
characterization of the obese gene has indicated that it
encodes a hormone, leptin (from the Greek leptos = thin), that is
expressed in adipose tissue and, at lower levels, in *gastric
epithelium and *placenta. 3) Early data indicated that leptin
might be an *afferent signal in a negative-feedback loop
regulating the size of adipose tissue mass... The *plasma levels
of leptin are highly correlated with adipose tissue mass and fall
in both humans and mice after weight loss. Levels of leptin are
increased in obese humans and in several genetic and
environmentally induced forms of rodent obesity. 4) The role of
leptin in the pathogenesis of obesity can be inferred by
measurement of plasma leptin. An increase in plasma leptin
suggests that obesity is the result of resistance to leptin
(e.g., a dysfunction that reduces the effectiveness of leptin as
a signal messenger). A low or normal plasma concentration of
leptin in the context of obesity suggests decreased production of
leptin. This interpretation is similar to that used in studies of
*insulin and the pathogenesis of *type I and type II diabetes. 5)
The possible therapeutic benefits of leptin treatment in humans
is now being studied in clinical trials, and early data indicate
that 4 weeks of daily leptin injections are safe and cause small
but significant weight loss in lean and obese subjects compared
with placebo effects. A subset of 8 obese subjects treated for a
total of 6 months lost an average of 7.1 kilograms compared with
1.7 kilograms in a group receiving placebo. Some of the obese
subjects lost substantial amounts of weight but others did not...
This limited study indicates that leptin might be an effective
therapy for some obese subjects, although more patients need to
be investigated. The authors conclude: "Whether leptin finds its
way into general usage as an anti-obesity drug, the use of modern
methods to identify and target the components of the leptin
signalling pathway will form the basis for new pharmacological
approaches to the treatment of obesity and other nutritional
disorders. Further studies of leptin are also likely to reveal
additional links between nutritional state and animal physiology.
-----------
J.M. Friedman and J.L. Halaas (2 installations, US)
Leptin and the regulation of body weight in mammals.
(Nature 22 Oct 98 395:763)
QY: Jeffrey M. Friedman 
-----------

Text Notes:
... ... *homeostatic system: 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 temper-
ature. Similar homeostatic mechanisms operate at cellular levels.
... ... *adipose tissue: Connective tissue consisting chiefly of
fat cells, which are cells distended with one or more fat
globules, the cytoplasm usually compressed into a thin envelope.
Fat cells are also called "adipocytes".
... ... *familial aggregation: This refers to the occurrence of a
trait in more members of a family than can be readily accounted
for by chance -- i.e., presumptive but not cogent evidence of the
operation of genetic factors.
... ... *Recessive mutations: A variant of a particular gene that
fails to be expressed except when occurring in both alleles of
the gene.
... ... *cloning: In general, the term "cloning" has two
meanings. 1) With reference to cells, cloning is any process by
which a line of identical cells is produced from one or a few
originating cells. 2) With reference to DNA, cloning is any
process by which a gene or fragment of DNA is spliced into a
*vector so that the DNA can be amplified many times by
transferring the recombinant (i.e., foreign) DNA molecule into a
host organism (usually a bacterium or yeast) that can be grown in
large quantities.
... ... *vector: In this context, a vector is any DNA that can
propagate itself rapidly in a host cell and maintain this
capability after insertion of foreign DNA into the vector. For
example, one can introduce a human DNA fragment (e.g., a gene)
into the DNA of a virus, have this virus infect its usual host
cells (e.g., bacteria or animal cells), and if the virus is
rapidly replicating, the fragment of human DNA will also be
rapidly replicated. The procedure, in other words, uses viral DNA
as a means (a vector) to introduce the foreign DNA (here a human
DNA fragment incorporated into the viral DNA) into a host cell to
use the host cell-virus system as a chemical factory to produce
relatively large quantities of the foreign DNA fragment.
... ... *gastric epithelium: In animals, epithelial cells
(epithelium) compose the cell layers that form the interface
between a tissue and the external environment, for example, the
cells of the skin, the lining of the intestinal tract, and the
lung airway passages. "Gastric epithelium" is epithelium of the
gastrointestinal tract.
... ... *placenta: In general, the organ of metabolic interchange
between the fetus and the mother.
... ... *afferent signal: In general, an "afferent" signal in
physiology is a signal *to* a control center, and an "efferent"
signal in physiology is a signal *from* a control center.
... ... *plasma levels: In general, the noncellular portion of
circulating blood.
... ... *insulin: A polypeptide hormone that promotes uptake by
body cells of free glucose and/or amino acids, depending on
target cell type.
... ... *type I and type II diabetes: (type I and type II
diabetes mellitus) Diabetes is a metabolic disease in which
carbohydrate utilization is reduced and that of lipid and protein
enhanced. The disease is caused by an absolute or relative
deficiency of insulin. There are many forms of diabetes, with
primary (essential) diabetes comprising two types: type I
diabetes is insulin-dependent, requiring chronic insulin
treatment, and usually occurring before age 30; type II diabetes
is non-insulin-dependent, usually occurs after age 30, and is the
diabetes type commonly associated with obesity. In the US there
are 14 million known cases of diabetes, and approximately 90
percent of these are type II.
-------------------
Summary & Notes by SCIENCE-WEEK http://scienceweek.com 4Dec98

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

Related Background:

BIOLOGICAL ACTION OF LEPTIN AS AN ANGIOGENIC FACTOR
Angiogenesis is the generation of new blood vessels, a controlled
sequence of cell differentiation and tissue formation programmed
by the genome. It is of obvious importance during embryological
development, since new tissues need a blood supply in order to
continue macroscopic growth, and the angiogenesis process is also
of great importance during tissue trauma repair. Like new
embryological tissue, a neoplasm (a tumor) also needs a blood
supply, and one of the characteristics of tumor growth is the
provocation of angiogenesis by the cancer cells so that the mass
of such cells becomes supplied with adequate vascularization. It
is known, for example, that tumors will not grow beyond a few
millimeters in diameter in the absence of a newly forming blood
supply. Cancer cells apparently provoke angiogenesis by secreting
growth factor substances, and if this is prevented, tumor growth
will be severely limited. Leptin is a recently discovered
circulating hormone secreted by *adipocytes (fat cells). The
hormone influences body weight *homeostasis through effects on
food intake and energy expenditure. It also modulates other
physiological actions, including lipid metabolism,
*hematopoiesis, *pancreatic beta-cell function, ovarian function,
and *thermogenesis. Despite this multiplicity of effects in
tissues outside the nervous system, the leptin receptor is
expressed predominantly in the *hypothalamus. One apparent
variant of the leptin receptor is a trans-membrane protein (OB-
Rb) expressed at high levels in discrete hypothalamic regions,
and evidence indicates this leptin receptor has a *cytoplasmic
domain that transduces the *leptin signal via the *Jak-STAT
pathway. The current consensus is that adipose tissue mass is
regulated by a hormone (possibly leptin) produced by adipocytes
and released into the bloodstream. This implies a plastic
microvascular bed that can provide an adequate blood supply for
new adipose tissue and be capable of undergoing adaptive changes
required by physiological or pathological fluctuations in
adiposity. ... ... M.R. Sierra-Honigmann et al now report that
the leptin receptor OB-Rb is expressed in human blood vessels and
in primary cultures of human *endothelial cells, and that in
vitro and in vivo assays reveal that leptin has angiogenic
activity. The authors suggest their observations indicate that
the vascular endothelium is a target for leptin, that leptin-
induced angiogenesis may facilitate increased energy expenditure,
and that leptin, acting as a functional link between adipocytes
and the vasculature, might also play an important extra-
hypothalamic and localized role in the modulation of adipose
tissue mass.
-----------
M.R. Sierra-Honigmann et al (11 authors at 3 installations, US):
Biological action of leptin as an angiogenic factor.
(Science 11 Sep 98 281:1683)
QY: M. R. Sierra-Honigmann 
-----------

Text Notes:
... ... *adipocytes: These are fat cells in connective tissue,
each cell containing one or more fat globules that compress the
cytoplasm of the cell into a thin envelope. The fat globules are
essentially energy storage bins.
... ... *homeostasis: See notes for previous report.
... ... *hematopoiesis: (hemopoiesis, hematogenesis) Refers to
the formation and development of the various types of blood
cells. 
... ... *pancreatic beta-cell: These are the pancreatic cells
that secrete the hormone insulin.
... ... *thermogenesis: In this context, the physiological
process of heat production in the body.
... ... *hypothalamus: A deep brain structure with various
clusters of nerve cells controlling several important homeostatic
functions such as temperature regulation and food intake, and in
addition the sex drive, aggressive emotions, psychosomatic
effects, etc. The hypothalamus essentially integrates the
activity of the autonomic nervous system, and it acts as an
intermediary between the endocrine (hormone) system and the
nervous system, with various hypothalamic neuron types secreting
hormones themselves. In general, the term "hormones" refers to
chemical messengers which are distributed systemically via the
bloodstream.
... ... *cytoplasmic domain: A "trans-membrane" protein receptor
essentially has 3 domains: extracellular, membrane, and
cytoplasmic (intracellular). In other words, the protein extends
completely through the plasma membrane, protruding from the outer
surface and inner surface of the membrane. The outer protrusion
apparently acts as a receptor for an extracellular ligand (e.g.,
a hormone), the binding of ligand and receptor providing a
"signal" that causes some alteration in the other end of the
protein, the protrusion of the protein into the cytoplasm. This
alteration in turn provokes a cascade of intracellular chemical
interactions that result in a signal transmitted to one or more
intracellular genetic or physiological control centers. 
... ... *leptin signal: Refers to the "signal" (ultimate effect
on some intracellular control mechanism) produced by the binding
of leptin as a ligand to its membrane receptor.
... ... *Jak-STAT pathway: The term "STATs" refers to signal
transducers and activators of transcription, and together with
enzymes known as Janus kinases they mediate the signaling
mechanism known as the JAK-STAT pathway, which is known to
provoke the transcription of certain regulated genes.
("Transcription" is the process by which genetic information in
DNA is converted into RNA.)
... ... *endothelial cells: Flat cells forming a layer lining
blood vessels, lymphatic vessels, the heart, etc.
-------------------
Summary & Notes by SCIENCE-WEEK http://scienceweek.com 9Oct98

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

Related Background:

FIRST IDENTIFICATION OF MOUSE OBESITY GENE IN HUMANS
In 1994 an obesity gene and its protein product (leptin), were
discovered in obese mice. It has been determined that a defect in
the gene causes a severe reduction in the output of functional
leptin by fat cells (adipocytes). Leptin apparently acts as a
messenger to the hypothalamus in the brain, the absence of the
protein causing excessive eating behavior without satiation. Now
a similar gene has been discovered in humans, this gene also
responsible for the production of leptin by human adipocytes.
Carl T. Montague et al (15 authors at various installations, UK)
studied a homozygous genetic defect in two children suffering
from extreme obesity, and have isolated and characterized the
gene, and related it to the previously identified mouse gene
known as ob/ob. As in mice, the result of a defect in the gene is
an order of magnitude reduction in the circulating blood
concentration of the protein leptin. The results do not mean that
all instances of obesity in humans are produced by defects in
this gene, but certainly a new area of research into the
molecular genetics of human obesity has now been defined. In
addition, the authors offer the hope that recombinant human
leptin may be found to correct leptin deficiency in clinical
cases. (Nature 26 Jun 97) (Science-Week 3 Jul 97)

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

Related Background:

CONCERN OVER WORLD INCREASE IN OBESITY PREVALENCE
Obesity, which is defined as the excessive accumulation of body
fat, has apparently become a problem of international concern.
The World Health Organization and the International Obesity Task
Force have declared "an obesity epidemic on a global scale." The
index used to assess obesity is the so-called Body-Mass Index,
defined as the ratio of weight in kilograms to height in meters
squared: W/M^(2). Clinical obesity is defined as a Body-Mass
Index greater than 30. At the present time, 22.5 percent of the
US population is considered to be clinically obese, compared to
only 14.5 percent in 1980. The increase is apparently seen in all
demographic groups, including children. Comparable increases have
been noted in the United Kingdom, Brazil, Canada, and Australia.
Although experts evidently agree the worldwide increase has been
substantial during the past 15 years, the cause remains a puzzle.
QY: Gary Taubes (science_editors@aaas.org)
(Science 29 May 98 280:1367) (Science-Week 10 Jul 98)

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

Related Background:

OBESITY AND MORTALITY: SPINNING SCIENCE NEWS
Stevens et al (6 authors at 4 installations, US), in a study of
the mortality of 62,116 men and 262,019 women during a 12 year
period (1960-1972), report that excess body weight increases the
risk of death from any cause and from cardiovascular disease in
adults between 30 and 74 years of age, and that the relative risk
associated with greater body weight is higher among younger
subjects. The above words are essentially the exact conclusions
chosen to be published by the authors. Nevertheless, two variants
of contrary journalistic "spin" have appeared, an interesting
illustration of how public health news is formulated. In the
first variant, in an editorial in the same journal in which the
Stevens et al report appeared, two journal editors emphasize that
the mortality increase with body-mass is modest and age-
dependent, and they urge an end to people "suffering immeasurable
torment in fruitless weight-loss schemes and scams." In the
second variant, published by the New York Times and echoed by
many newspapers across the US, news items took note of the
journal editorial and went a step further in headlines suggesting
excess weight has now been shown to be harmless. The spin-logic
in the case of both the journal editors and the news media is
apparently that since the effect is small, the public can well
disregard it. The researchers and authors of the article,
however, apparently believe otherwise, and the last sentence of
their article is unequivocal: "In healthy white adults below the
age of 75 who have never smoked cigarettes, our results are
consistent with the healthy weight ranges proposed in the 1995
Dietary Guidelines for Americans." QY: June Stevens, Univ. of
North Carolina, Dept. of Epidemiology 919-966-7458
(New England J. Med. 1 Jan 98) (Science-Week 9 Jan 98)


6. MICE WITHOUT MYOGLOBIN
Heme is an iron-containing porphyrin associated with several
physiologically important pigments and proteins. Organisms as
diverse as *annelid worms, molluscs, flowering plants, and
*protochordates express cytoplasmic hemoproteins (tissue
hemoglobins) that reversibly bind oxygen, presumably to
facilitate oxygen transfer to sites of use. In vertebrates, only
cardiac muscle cells and certain *mitochondria-rich skeletal
muscle fibers express the hemoprotein myoglobin, a monomeric
protein distantly related to the oxygen-binding hemoglobin of
blood cells. Myoglobin concentrations in skeletal muscles are
increased in mammals adapted for deep-sea diving or life at high
altitude, or in response to sustained muscle contractions. In
general, myoglobin readily binds oxygen but gives up its oxygen
only during periods of intense mitochondrial activity (i.e.,
intense muscle activity). Muscle fibers involved in sustained
intensive activity (e.g., the flight muscles of insects, cardiac
muscle, certain skeletal muscles) usually contain high
concentrations of mitochondria (as much as 50 percent of total
cell volume) and also high concentrations of myoglobin that give
these muscle a red color ("red muscle"). ... ... D.J. Garry et al
now report that mice without myoglobin, the mice produced by
*gene-knockout genetic engineering, are fertile and exhibit
normal exercise capacity and a normal *ventilatory response to
low oxygen levels (hypoxia). Heart and soleus muscles from these
animals are depigmented, but function normally in standard assays
of muscle performance. The authors suggest these data indicate
that myoglobin is not required to meet the metabolic needs of
pregnancy or exercise in a terrestrial mammal, which raises new
questions about oxygen transport and metabolic regulation in
working muscles.
-----------
D.J. Garry et al (8 authors at 2 installations, US)
Mice without myoglobin.
(Nature 29 Oct 98 395:905)
QY: R. Sanders Williams 
-----------

Text Notes:
... ... *annelid worms: A phylum of segmented worms with a true
body cavity, and with well-developed circulatory and nervous
systems.
... ... *protochordates: In general, the chordates possess a
notochord, a flexible rod (present only in vertebrate embryos)
that supports the nerve cord. Protochordates are an invertebrate
chordate subphylum.
... ... *mitochondria: Mitochondria are double-membrane enclosed
organelles of cells that are involved with several important
biochemical pathways, including electron transport and oxidative
metabolism. Various types of eukaryotic cells may contain from a
few to several thousand mitochondria in each cell type. The
mitochondria are relatively large cylindrical structures up to 10
microns long and up to 2 microns in diameter, and they are
believed to have originated as organisms that became symbiotic
with eukaryotic cells (i.e., cells containing membrane-bound
organelles such as a nucleus). In biology, "symbiosis" is an
intimate and protracted association of individuals of different
species.
... ... *gene-knockout genetic engineering: One approach widely-
used to test the importance of a particular protein is the
genetic manipulation of animals such as mice or fruit flies to
produce a "knockout" of a selected protein. By a technique known
as "homologous recombination", it is possible to replace the
normal gene for a selected mouse protein by a nonfunctional
mutant gene. Such mutant animals can then be bred to produce
strains of mice that lack the functional protein.
... ... *ventilatory response: In the context of this report, the
"ventilatory response" is measured as the increase in
respiration
rate as a function of reduced oxygen in the ambient air supplied
to the animal.
-------------------
Summary & Notes by SCIENCE-WEEK http://scienceweek.com 4Dec98


7. MIGRAINE: HYPEREXCITABILITY OF OCCIPITAL CORTEX
Migraine is a *paroxysmal disorder characterized by recurrent
attacks of headache, with or without associated visual and
gastrointestinal disturbances. The cause is unknown, but there is
evidence that suggests a genetically transmitted functional
disturbance of intra- and extra-cranial circulation. Regional
alterations in cerebral blood flow due to intracranial arterial
*vasodilation are known to accompany the migraine attack and
possibly to cause it. The mechanism is believed to involve
*episodic reduction in *systemic serotonin concentrations, which
in turn lead to the observed *vasomotor changes. ... ... S.K.
Aurora et al now report a study to test the hypothesis that the
hyperexcitability of *occipital cortex neurons may predispose
migraine subjects to develop *spreading depression, which many
researchers believe is the basis of migraine with *visual aura.
The authors evaluated the differences in the threshold of
occipital cortex excitation between migraine-with-aura patients
and normal controls using transcranial magnetic stimulation. The
procedure involved the application of a circular coil 9.5 cm in
diameter to the occipital scalp, followed by a stimulus-response
sequence designed to determine the threshold for *phosphene
production. The authors report that with 11 migraine-with-aura
patients and 11 control subjects, all threshold levels for
migraine-with-aura patients were lower than the lowest threshold
for control subjects, and that the migraine-with-aura patient
with the lowest threshold had an aura after stimulation. The
authors conclude that the threshold of excitability of occipital
cortex is lower in migraine-with-aura patients compared with
control subjects, and they suggest their results provide a direct
neurophysiological correlate for clinical observations that have
indicated hyperexcitability of the occipital cortex in migraine
patients.
-----------
S. K. Aurora et al (Henry Ford Health Sciences Cntr. Detroit, US)
Transcranial magnetic stimulation confirms hyperexcitability of
occipital cortex in migraine.
(Neurology 1998 50:1111)
QY: Sheena K. Aurora, Henry Ford Health Sciences Center,
Department of Neurology, 2799 W. Grand Blvd, K-11, Detroit, MI
48202 US.
-----------

Text Notes:
... ... *paroxysmal: In this context, a paroxysm is the sudden
onset of a symptom.
... ... *vasodilation: Widening of the lumen of blood vessels.
... ... *episodic reduction: In this context, a reduction
occurring during a specific time-frame, as opposed to a
continuous reduction. 
... ... *systemic serotonin concentrations: (5-hydroxytryptamine,
5-HT) Synthesized from tryptophan. Acts as both a *peripheral
*neurotransmitter in the gut and a central neurotransmitter in
the brain. Serotonin is apparently involved in nearly everything
occurring in the brain, including psychological states such as
anxiety and depression, and dysfunctions producing migraine and
epilepsy. In this context, the term "systemic" means system-wide,
as opposed to local concentrations.
... ... *peripheral: In this context, the term "peripheral"
refers to the peripheral nervous system, as opposed to the
central nervous system. In general, the "central" nervous system
comprises the brain and spinal cord, and all other parts of the
nervous system comprise the "peripheral" nervous system.
... ... *neurotransmitter: 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.
... ... *vasomotor changes: Changes that involve dilation or
constriction of blood vessels. Dilation or constriction of blood
vessels is physiologically produced by muscles in the walls of
blood vessels, and these muscles are under neural and hormonal
control.
... ... *occipital cortex: This is the area of brain cortex
directly under the occipital bone of the skull (i.e., the back of
the head), and this area of brain cortex is known to be
associated with vision.
... ... *spreading depression: In this context, the term
"depression" refers to reduced activity at neuron synapses, and
the term has nothing to do with psychological depression. The
"spreading" in this context is a spreading throughout an area of
cerebral cortex. Synaptic depression is believed to be associated
with neurotransmitter depletion, but the causes of such depletion
are variable, ranging from metabolic dysfunction to hyperactivity
of presynaptic terminals.
... ... *visual aura: In this context, an aura is a subjective
symptom occurring at the onset of a migraine headache.
... ... *phosphene: A phosphene is a sensation of light produced
by mechanical or electrical stimulation of the peripheral or
central optic pathway of the nervous system.
-------------------
Summary & Notes by SCIENCE-WEEK http://scienceweek.com 4Dec98