Both humans and mice are particularly vulnerable to noise- and drug-induced hearing loss at young ages.
Sound levels measured by Clark and Weathers showed that premature infants being airlifted tested were exposed to almost 100 decibels for a period of 12 minutes before takeoff, similar to a lawn mower or chain saw. These levels could be especially damaging to premature babies.
"The laboratory mouse is a well-established model for human hearing," says coauthor Kevin K. Ohlemiller, Ph.D., research associate professor of otolaryngology. "They possess similar inner ear anatomy and physiology and similar patterns of age-related, noise-induced and drug-related hearing loss."
Ohlemiller worked with Elizabeth A. Fernandez, then a doctoral student in the Program in Audiology and Communication Sciences, to see if loud noise and a low dose of kanamycin would exacerbate each other's effects. Because the first month of life is when mice are most vulnerable to noise and drugs that damage hearing, 20- to 30-day old mice were injected with either kanamycin or saline solution twice a day for 11 days. They were then exposed to 110 decibels of noise for 30 seconds.
Two surprising
findings arose.
First, this particular strain of mice was very
sensitive to noise-induced hearing loss. Significant loss of some
sensory cells in the ear resulted in permanent hearing damage, even
over the short time span.
Second, a regular, low dose of kanamycin completely protected the mice against this sensory cell damage and hearing loss. The protective effect of repeated doses persists for at least two days after the last injection, the scientists noted.
Researchers
plan to use these hearing research findings in a number of ways.
They can map
the genes in this strain of mice to determine what makes them so
noise-sensitive and possibly figure out how kanamycin protects sensory
cells in the ear.
In addition, the findings open up new possibilities
for clinical research.
Learning how kanamycin protects the ear's sensory cells could help scientists develop drugs with similar effects. Medications that protect the ears from damaging noise levels could benefit a wide range of groups, from soldiers to airline workers to premature babies.
Basic Science Research PLUS Clinical Problem & Practice
"This very dramatically points out the benefits
of having basic scientists who can take a clinical problem and find a
result opposite of what we expected," Clark says. "These results not
only energize laboratory scientists and begin new lines of research,
but they also have implications for clinical practice. This has been an
amazing sequence of events, to start a project in a helicopter and end
up under a microscope."
Fernandez EA, Ohlemiller KK, Gagnon PM, Clark WW. Protection against noise-induced hearing loss in young CBA/J mice by low-dose kanamycin. Journal of the Association for Research in Otolaryngology. Jan. 22, 2010 (advance online publication).
Funding from National Institutes of Health and the Washington University School of Medicine in St. Louis Department of Otolaryngology supported this research.