Sled Dog Science

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					NEWS SCAN

tional genetic or environmental factors.         that includes variants as short as 500 base     small CNVs and more common CNVs as-
   As researchers hunt for more links be-        pairs. The analysis suggests that about         sociated with disease — 2009 is going to be
tween known CNVs and disease, Scherer            1,000 copy number variations exist in           a watershed year.”
and Hurles are scouting out new variants         each person, spanning at least 1 percent of
to add to the mix. Their 2006 map identi-        the genome. “We’ve come really far and          Melinda Wenner is based in
fied CNVs only down to 20,000 base               really fast,” Scherer says. But “over the       New York City.
pairs; now they are finishing a revised map      next year, we’re going to be finding more


PHYSIOLOGY

Sled Dog Science
Cracking the metabolic secrets of distance-racing canines BY K R I STA W EST


W        ith tongue and tail wagging wild-
         ly, Larry the lead dog crossed the
finish line in March in sunny Nome, Alas-
                                                 from glycogen stored inside muscle cells.
                                                 But instead of depleting glycogen stores
                                                 and tiring the muscles, the animals sud-
                                                                                                 40 percent carbohydrates and proteins).
                                                                                                    According to Raymond Geor, an exer-
                                                                                                 cise physiologist at Michigan State Uni-
ka— after running 1,131 miles to win the         denly switch to a glycogen-sparing metab-       versity, sled dog muscle cells are well
Iditarod Trail Sled Dog Race for the third       olism. They start drawing energy from           equipped to use this fat because they have
year in a row. To most mortals, Larry            sources outside of the muscles.                 a higher mitochondrial density— more cel-
looks like a happy but nondescript, scraw-          Davis suggests that the muscle cells start   lular power plants — than other animals.
ny mutt. To sled dog mushers, he is a mini       extracting fat directly from the blood and      The mystery is how the blood-borne fat
legend that simply needs no introduction.        somehow transport this fat across the cell      gets into cells in the first place. Increasing
To scientists, Larry may hold the key to a       membrane and into the cell, where it can be     evidence suggests that fat is transported
physiological mystery.                           burned as fuel. During race times, fat builds   into the cells along similar pathways as
   Specifically, sled dogs seem to flip an in-   up in a sled dog’s blood, most likely be-       glucose, Davis says, with the hormone in-
ternal switch that acutely changes how they      cause of the high-fat racing diet. Each         sulin playing an important role. Research-
burn fat calories, allowing them to keep go-     50-pound canine consumes about 12,000           ers are currently exploring the sled dog’s
ing and going and going with no obvious          calories daily (typically 60 percent fat and    sensitivity to insulin to better understand
pain. Figuring out how that mechanism                                                            this pathway.
works may have implications for human                                                               Breeding probably had much to do
diabetics and those battling obesity.                                                            with the development of the metabolic
   Researchers first discovered the meta-                                                        switch. Larry is descended from a long
bolic switch in 2005, when a team headed                                                         line of racing dogs. “The bloodlines of my
by Oklahoma State University’s Michael                                                           dogs date back 100 years,” says Lance
Davis — who has been investigating the                                                           Mackey, Larry’s owner and legendary
metabolism, gastrointestinal, respiratory                                                        racing musher, the only person to win the
and blood systems of sled dogs for 10                                                            long-distance Iditarod and the Yukon
years — did a controlled study at a profes-                                                      Quest in the same year with the same dog
sional racing kennel in Alaska. Mushers                                                          team. “They are mixed breeds — mutts —
ran the dogs in mock, 100-mile races for                                                         but they’ve been bred to run.”
four to five days in a row. Every 100 miles,                                                        Selective breeding, though, may not be
the researchers took matchstick-size sam-                                                        the whole story. The dogs may have learned
ples of leg muscle (about 60 milligrams                                                          to switch metabolic strategies on demand
apiece) from the dogs to test for protein                                                        through intense training. If so, then re-
levels, enzyme activity and glycogen, a                                                          searchers might have an easier time apply-
starchlike compound that stores energy                                                           ing what they learn about the canines to
for quick release.                                                                               humans training for an endurance event or
   Glycogen turns out to be a crucial piece      RE eraestrud magnis nonsed euguer iriurem       those seeking treatment for diabetes or
of the metabolic switch. During the first        zzriurem vel ea feum iriuscil ulluptatum nos    obesity by, for instance, pinpointing the
few days of racing, sled dogs draw energy        doluptat prat aut lum dolor adit dignit aute    mechanisms that boost the body’s sensitiv-


26    Scientific AmericAn                                                                                                          June 2009
                           NEWS SCAN

                           ity to insulin or that better utilize fat that    participating for eight of his nine living
                           builds up in muscle tissue.                       years. He will officially retire from rac-
                               This year Mackey won the Iditarod by          ing at the end of this year for a well-de-
                           one of the widest margins ever, finishing         served, if unneeded, rest.
                           a comfortable eight hours ahead of his
                           closest competitor. That Iditarod, how-           Krista West lives in Fairbanks, Alaska,
                           ever, will be the last one for Larry, after       with a dog-chasing cat.


                             A Challenge to Health
                             The rigors of the Iditarod sled dog race, in which a musher and a team of 16 dogs cover
                             some 1,100 miles in 16 days, takes its toll on the health of its athletes. On average, three
                             dogs die every year in the race; 2009 saw double that number. Some animal-rights
                             groups have criticized the event as cruel. And in this age of juiced jocks, some observers
                             also wonder if steroids are involved.
                                 To monitor the dogs’ health and watch for performance-enhancing drugs, volunteer
                             veterinarians keep watch during runs. At the Iditarod, for example, a dedicated plane
                             follows the canines and samples urine of dog teams for drugs without warning. Mushers
                             must carry sick or injured dogs to the next checkpoint for treatment and continue the
                             race without that canine.




                           PERCEPTION

                           A Real Stretch
                           Pulling your mouth around affects which words you hear BY ERIC A WESTLY


                           N     euroscience textbooks typically
                                 portray the five senses as separate
                           entities, but in the real world the senses
                                                                             heard words differently when their
                                                                             mouths were stretched into different po-
                                                                             sitions. The results have implications for
                           frequently interact, as anyone who has            neuroscientists studying speech and
                           tried to enjoy dinner with a stuffy nose          hearing as well as for therapists looking
                           can attest. Hearing and vision seem sim-          for new ways to treat speech disorders.
                           ilarly connected, the most famous exam-               In the study, a specially designed ro-
                           ple being the “McGurk effect,” where vi-
                           sual cues, such as moving lips, affect how
                           people hear speech. And now new re-
                           search shows that touch can influence
                           speech perception, too.
                              David Ostry, a neuroscientist with co-
                           appointments at McGill University and
                           the New Haven, Conn.–based speech
                           center Haskins Laboratories, has been
                           studying for years the relation between
                           speech and the somatosensory system,
                           the network of receptors in skin and mus-
                           cle that report information on tactile
                           stimuli. In his most recent study, pub-           RE eraestrud magnis nonsed euguer iri-
                           lished in the Proceedings of the National         urem zzriurem vel ea feum iriuscil ulluptat-
                           Academy of Sciences USA, he and two               um nos doluptat prat aut lum dolor adit
                           Haskins colleagues found that subjects            dignit aute dunt ut lore veleniam zzrilit


28   Scientific AmericAn                                                                                        June 2009

				
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