View
214
Download
0
Category
Preview:
Citation preview
8/8/2019 HIV Attacks Gut First
http://slidepdf.com/reader/full/hiv-attacks-gut-first 1/1
30ASTRONOMY—Sightings of
shifting sand dunes,rolling boulders, and adwindling polar ice capin the past year demon-strate that the RedPlanet is a far more dy-namic world than sci-entists suspected.
NASA’s orbiting MarsGlobal Surveyor revealedfresh gullies as long asthree football fields on adune west ofthe HellasBasin. The same slopewas smooth and un-blemished in 2002. Sci-entists suspect thatcarbon dioxide trappedbeneath the surface dur-
ing winter vaporizedwhen temperatures rose,releasing gas and causingsand to pour down thedune’s face. The probealso photographeddozens ofboulders thathad tumbled down a five-mile-wide crater, goug-
ing shallow troughs not
seen a year before.Possi-ble causes include windand seismic activity, al-though Mars’s atmos-phere is justone-hundredth as denseas Earth’s,and researchershave not yet found reli-able evidence of Marsquakes.Meanwhile,carbon dioxide depositsat the south pole havedwindled for three con-secutive summers, sug-gesting long-term climatechange is under way.
None of these sight-ings would be possible if not for the extraordinary
durabi li ty of M arsGlobal Surveyor, whichhas been orbiting theplanet since 1997.Mean-while,the Opportunity and Spirit rovers,whichlanded in January 2004,have kept rolling longpast their predicted shelf
life of90 days.In Sep-
tember Spirit completeda 14-month climb upHusband Hill in Gusev Crater and sent back apanorama of weatheredrocks containing detailsof past Mars environ-ments. “Everyone isamazed at the longevity,excited about the results,and perhaps a littletired,” says MichaelMeyer, chiefscientist of NASA’s Mars Explo-ration Program.
Next up:the Mars Re-connaissance Orbiter,launched last August 12,enters Mars orbit in
March. Its radar sounderwill seek buried water,while its camera willmap features as small asa coffee table,aiding thesearch for potential habi-tats of past or presentlife.“Stay tuned,” saysMeyer. — Jack Kelley
Mars Looks Lively
46
MC K
Y
2D I S COV E R J A NUA RY 2006
PSYCHOLOGY—Patientswho have suffered strokeor head injuries oftenlose the ability to makegood decisions.For in-stance, they will make re-peated bets on aparticular outcome,evenwhen the odds of win-ning are obviously very low.In July Michael Sad-doris,a psychology grad-uate student at JohnsHopkins University,helped pinpoint why.
Previous studies sug-gested that the abnor-
malities occurred in abrain area known as theorbital frontal cortex.
To test how this partof the brain functionsduring decisionmaking,Saddoris and his collab-orators presented a taskto a group of normal rats
and a group with dam-age in this region:Bothgroups had to figure outwhich oftwo differentodors led to a sugary treat and which to a bit-ter one.“It’s like if yousaw a soda machine withforeign writing on it,”Saddoris explains.“Youmight push one buttonand get something really odd,so you wouldn’t try that again.But if youcame back the next day and got something youreally liked,you’d push
that button again andagain.”In the same way,the animals had to learnto use the smell cue topredict a particular out-come.
The next step was toreverse the cues for thesweet and salty sub-
stances,then see howlong it took for the ratsto catch on.Those withdefective brain circuitry had much more diffi-culty figuring it out.Datafrom electrodes im-planted into their brainsoffered a clue: Neuronsin the impaired rats firedless in the presence of odors.They weren’t ableto monitor the new cir-cumstances and formnew associations.
Understanding howthe orbital frontal cor-
tex influences judgmentmay lead to therapies.“We’re not at the level of using neuroprostheticsor implants to affect de-cision making yet,but itmight be possible to getthere,”Sadd oris says.
—Elizabeth Svoboda
M
C KY
1 D I S COV E R J A NUA RY 2005
driving simulator to mea-sure reaction times,psy-chologist David Strayerfound teenagers have thegreatest trouble combin-ing driving and talking,but the problem affects
all generations.“We seethat accident rates, if you’re using a cell phone,are about four timesgreater than if you’re notusing a cell phone,” hesays.“Cell phones seemto be a distraction acrossthe age range.”
—Kurt Repanshek
TECHNOLOGY—High-techgadgets make it possiblefor people to travelthrough time .. .well,sortof.To leap forward 40 to50 years,merely talk ona cell phone while cruis-
ing down the road.Re-search at the University of Utah shows that whendrivers between 18 and25 chat on a cell phone,their reactions to a brak-ing car resemble those of a 65- to 74-year-old mo-torist with no such dis-tractions.Employing a
86Cell Phones Simulate Premature Aging
Why StrokeVictims Can’t Make
Good Decisions54
MEDICINE—For more than a
decade,scienti sts have tracked
the insidious progression of HIV
by measuring the amount of virus
in a patient’s blood.Over a pe-riod of years,the replication of
the virus gradually and steadily
destroys the immune system’s
defenses—or so it was thought.
In April two studies of simian im-
munodeficiency virus, a kin of
HIV that infects monkeys, re-
ported that the virus swiftly in-
fects and decimates key immune
cells in the gut within days,not
years,of infection.“This basically
changes our whole view of the
pathogenesis of HIV infection,”
says Daniel Douek,chief of the
Human Immunology Section at
the National Institutes of Health’s
Vaccine Research Center.
Virologists have long known
that HIV infects and kills CD4+T cells,which mediate the body’s
immune response to viruses.
What has emerged over the past
few years is that the virus thrives
not only in the blood and the
lymph system but also in mu-
cosal tissues, which are rich in
immune cells.The mucosae line
parts of the body,such as themouth,nose, and rectum,that
are exposed to the environment.
The gut,the largest of the mu-
cosal tissues,harbors most of
the body’s CD4+ T cells.
“What we now know is that
within the first few weeks of in-
fection,probably two to three
weeks,the majority of those cells
are depleted by HIV infection,”
says Douek.About half the T cells
were wiped out over just four
days within the first two weeks
of infection..
The findings have profound
implications for the control of HIV
infection.These results under-
score the importance of starting
antiretroviral therapy very earlyin the infection. And they high-
light the importance of a vac-
cine that can protect mucosal
surfaces.— Apoorva Mandavilli
HIV AttacksGut First
HIV-positive gut (top) lacks immune cells seen in HIV-free gut.
Tests on simulators show that the likelihood of accidents increases if a driver is multitasking.Fresh gullies have appeared in dunes inside this Martian crater within the past three years.
PLEASE FILLOUT CAPTION.
Which tie will it be today? Ask your orbital frontal cortex.
PAGE PROOF Date ________
AS____ SR____ CSP____ Copy____ JT_ ___ DG____ SLP____
REVERSE
AS____
SR____ AB____
JT _____ Copy____
MF_____AUCX
JK_____
AM_____
ES_____
KR_____
Recommended