According to researchers at the University of Iowa, the common fruit fly Drosophila melanogaster is an ideal model for studying noise-induced hearing loss in humans, due to the similar molecular underpinnings of both species’ hearing.
Scientists will likely use the fruit fly to quicken the pace of research into the cause behind noise-induced hearing loss and potential treatments, according to a paper published this week in the online edition of the journal Proceedings of the National Academy of Sciences.
“As far as we know, this is the first time anyone has used an insect system as a model for NHL (noise-induced hearing loss),” Daniel Eberl, a University of Iowa biology professor and the study’s corresponding author, told Science Daily.
Noise-induced Hearing Loss
Noise-induced hearing loss is an expensive and growing trend, as more children and teenagers use headphones to listen to loud music and more aging Baby Boomers enter retirement. However, the condition is still somewhat mysterious at the molecular and physiological level.
“The molecular and physiological models involved in the problem or the recovery are not fully understood,” Eberl told Science Daily.
Eberl and Kevin Christie, the paper’s lead author and a post-doctoral biology researcher, claim they were motivated to find a model to study how loud noises can damage the human ear in order to alleviate the problem. The fruit fly study arose from a pilot project conducted in Eberl’s lab by University of Iowa undergraduate student Wes Smith.
“The fruit fly is superior to other models in genetic flexibility, cost and ease of testing,” Christie told Science Daily.
How Does a Fruit Fly Hear?
In order to hear, the fruit fly uses its antenna, which resonates in response to courtship songs generated by wing vibration. The study’s researchers exposed the test group of fruit flies to a loud, 120 decibel tone that lies in the center of the fruit fly’s range of audible sounds. This tone over-stimulated the fruit flies’ auditory systems, much like noise exposure at a rock concert or to a jack hammer would over-stimulate a human’s auditory system.
The researchers later tested the fruit flies’ hearing by playing a series of song pulses at a lower, more natural volume, then measuring the physiological response by inserting tiny electrodes into the flies’ antennae. The fruit flies that had received the loud tone had more impaired hearing than the control group.
When the researchers tested the flies again a week later, the flies exposed to loud noise had recovered normal hearing levels. However, when the structure of the fruit flies’ ears were examined in further detail, researchers discovered the noise-rattled flies’ nerve cells displayed a signs of exposure to stress, including altered shapes of the mitochondria, responsible for generating a cell’s energy supply.
Fruit flies with a mutation that made them more susceptible to stress displayed more severe reductions in hearing ability and prominent changes in mitochondria shape. They also still experienced hearing deficits a week later, while the normal flies with no mutation had recovered. This effect on the fruit fly’s molecular underpinnings are similar to that experienced by humans, making such tests applicable to people, according to the researchers.
“We found that fruit flies exhibit acoustic trauma effects resembling those found in vertebrates, including inducing metabolic stress in sensory cells,” Eberl told Science Daily. “Our report is the first to report noise trauma in Drosophila and is a foundation for studying molecular and genetic conditions resulting from NHL.”
“We hope eventually to use the system to look at how genetic pathways change in response to NHL,” Christie told Science Daily. “Also, we would like to learn how the modification of genetic pathways might reduce the effects of noise trauma.”
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