aspect of the new report is that cells well on
the path to becoming rods—rather than
stem cells with more developmental
options—appear to be the most promising
transplant candidates.
The maturity of the successfully transplanted mouse cells corresponds to that of
human retinal cells late in the first trimester of pregnancy, Swaroop says.
Says MacLaren, “At the moment, we simply don’t have a source of the immature
photoreceptor cells.”
However, scientists might someday convert stem cells from either adults or
embryos into cells that would succeed as
transplants. Last year, Reh and his team
reported coaxing embryonic stem cells to
resemble immature rod cells.
Using those ripened stem cells, the team
is now attempting to replicate MacLaren’s
results. The experiments could lead to trials that use embryonic stem cells in people
with progressive blindness. —B. HARDER
Hot, Hot, Hot
Peppers and spiders reach
same pain receptor
The burn of hot peppers and the searing
pain of a spider bite may have a common
cause. New research suggests that molecules
in hot peppers and in a certain spider’s venom
target the same receptor on nerve cells.
Several years ago, scientists identified a
channel on neurons that’s opened by capsaicin, the molecule responsible for peppers’ burn. Follow-up research showed that
this channel is a member of a family of cell-surface receptors that sense both chemicals
and temperature. When these channels are
activated, ions flood into nerve cells and
cause them to fire.
Although scientists have already studied
components of spider venom that cause
shock, paralysis, and death, little is known
about the molecules that cause the pain.
David Julius of the University of California, San Francisco and his colleagues wondered whether pain-inducing venom ingredients might activate the dual-purpose
cell-surface channels.
The team purchased venoms collected
from a variety of spider, scorpion, and snail
species known to deliver painful bites. The
researchers diluted the venoms and added
them to dishes containing human-kidney
cells that had been genetically altered to
carry various types of channels.
JAXA
Only the venom of one West Indian tarantula species, Psalmopoeus cambridgei, sent
a flood of ions into cells that sported the
same receptor that’s sent by capsaicin. When
the scientists broke down that venom, they
identified three component molecules
responsible for the rush of ions.
To confirm that these molecules opened
the capsaicin-responsive channel, the
researchers added each compound separately to dishes containing nerve cells from
normal mice or from mice engineered to be
missing just that channel. The team found
that ions entered only the cells from normal
mice. Furthermore, only animals with the
capsaicin-responsive channel appeared to
feel pain in response to any of the molecules.
The team reports its results in the Nov. 9
Nature.
Julius notes that because triggering the
receptor produces such strong pain sensations, it’s not surprising that organisms as
distantly related as pepper plants and tarantulas use the same defensive mechanism.
“Different organisms have figured out
how to tap this site as a way of telling predators, ‘ You won’t be comfortable if you mess
with me,’” he says.
Michael Caterina, who studies this family of dual-purpose cell-surface channels at
Johns Hopkins University School of Medicine in Baltimore, notes that spider venom
could eventually become a powerful tool
for researchers to use in investigating channels active in several types of chronic pain.
“Anything that helps us understand how
these channels are activated will facilitate
[development of] drugs that block these
channels,” he says. —C. BROWNLEE
Birds Beware
Several veterinary drugs
may kill scavengers
Scavenging birds worldwide could be at
risk of accidental poisoning from carcasses
of livestock that farmers had dosed with
certain anti-inflammatory drugs, according to a survey of veterinarian records.
The work grows out of discoveries in the
New eye on the sun
The recently launched Hinode spacecraft made this X-ray portrait of several-mil-lion-degree gas in the sun’s outer atmosphere on Oct. 28. The test image reveals
that features known as X-ray bright points (two examples are in box) are simple
magnetic loops entraining hot gas. Astronomers will monitor the bright points to
find out why the sun’s atmosphere, or corona, is so much hotter than its interior.
In addition to an X-ray telescope, Hinode carries a visible-light telescope to study
the sun’s surface and a magnetograph to monitor magnetic fields associated with
sunspots. The craft also has an extreme-ultraviolet imaging spectrometer to track
hot gas in the corona (SN: 8/19/06, p. 120). After further testing, Hinode, which
means sunrise in Japanese, will begin its 3-year mission in December. —R. CO WEN
