Contact: Tina Hilding, 509-335-5095, thilding@wsu.edu
Sleep and run--How do they do that?
Dr. Lynne Nelson with a 17-month-old grizzly raised in captivity. Nelson works with David Lin, who studies muscle atrophy in bears.
When it comes to human muscles, the adage "use it or lose it''
universally applies. Whether they belong to a senior citizen who
breaks a bone or an astronaut in space, human muscles atrophy, or
weaken, due to lack of use. A couple weeks of bed rest makes it
difficult for humans to walk, so rehabilitation from injury or
surgery, especially for older people, tends to be a long and
expensive process.
But oh, to be a grizzly bear! Waking from a four- to six-month
hibernation marked by virtually no activity, grizzlies are not only
able to start foraging immediately, they're also ready to run.
David Lin, assistant professor in Bioengineering and Neuroscience
at Washington State University, would like to know what mechanisms
prevent muscle atrophy in bears, in hopes that some day the
research may help humans. In particular, he is interested in muscle
plasticity, or the way that muscles change their properties to meet
demands. When human muscles atrophy, not only do they lose
strength, they also convert muscle fibers from slow-twitch to
fast-twitch. Slow-twitch muscles are the postural muscles that
allow us to hold ourselves upright when we stand, whereas
fast-twitch are those that enable us to move rapidly. By the end of
hibernation, grizzly bears experience just a 20-percent loss in
muscle strength and minimal conversion of slow to fast muscles.
Among the factors that determine muscle plasticity are neural
input, hormonal levels, and how much the muscle is worked. In order
to better understand what sorts of neural inputs are sent to the
muscles of grizzly bears, Lin implanted tiny transmitters into the
leg muscle of a bear during hibernation. The transmitters relayed
the electrical activity of the muscle, a measurement of neural
input, to a computer in another room. In addition, neuroscience
graduate student Jack Hershey will be looking at the microstructure
of muscle biopsies from summer-active and hibernating bears.
Lin has been working with Charles Robbins, professor, Zoology and
Natural Resource Sciences, and director of the Bear Research,
Education, and Conservation Program, and Lynne Nelson, assistant
professor, Veterinary Clinical Science, who is studying the heart
muscle function of bears. Working with the Bear Research Center,
the only facility in the world to house adult grizzlies for
research, enables the researchers to have access to the bears
throughout the year, including winter hibernation.