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Hearing loss partially reversed in noise-damaged ears of mice

January 10, 2013|By Rosie Mestel
  • Drug treatment caused regeneration of sound-sensing cells in the inner ears of noise-exposed mice. On the left, damaged cells not treated with the drug. On the right, cells that were treated. Hair cells are shown in green.
Drug treatment caused regeneration of sound-sensing cells in the inner… (Kunio Mizutari et al. / Neuron )

Anyone who’s gone to too many rock concerts or worked with loud machinery for too long  (or listened to too many kazillion-decibel advertisements at a movie theater) may eventually pay the price: hearing loss caused by damage to tiny, sound-transmitting cells in the inner ear.

Researchers now report they can regenerate some of these crucial  “hair cells” in the inner ears of mice and restore noise-induced damage to some extent. It’s something that hearing scientists have been hoping for ages (though we will avoid using the term “holy grail”). The experiments, by Albert Edge of Harvard Medical School and his colleagues, were published in the Jan. 10 issue of the journal Neuron.

Our ability to hear goes this way: Sound waves enter the gristly outer ear, travel down the ear canal and then buffet up against the eardrum, causing the drum to vibrate and jostle three bones in the so-called middle ear: the hammer, anvil and stirrup. The stirrup, in turn, presses against a membrane that divides the middle ear from the fluid-filled inner ear.

The fluid in the inner ear then moves, causing arrays of tiny sensory cells called hair cells to wave about and send signals to the sound-processing parts of the brain. Based on the frequency of a given sound, hair cells at different points along the inner ear will activate. Our brains interpret the signals from those different points in the inner ear as different frequencies of sound.

Loud noises, among other noxious assaults, can damage the fragile hair cells. That’s why habitual exposure to loud noise or one-off insults such as close-range gunshots or explosions can damage our hearing.

The cells, once damaged, don’t regenerate -- not in mammals, anyway. (They do in fish and birds.) But Edge’s team showed they could coax some hair cells to do so in adult mice if they were treated with a certain drug.

The drug, which goes by the natty name of LY41175, allows other cells in the inner ear to change into hair cells. Normally, these cells are inhibited from making the switch. LY41175 releases that inhibition by interfering with the activity of a protein called Notch.

In mice with noise damage, scientists found putting the drug into the middle ear and allowing it to diffuse into the inner ear increased numbers of hair cells in parts of the inner ear and, in step with that, increased the rodents' ability to detect sounds that matched up to those parts of the inner ear. The effects lasted for at least three months, the longest period of time that the scientists tested.

Want to know more?

From L.A.’s own House Research Institute, a primer on how hearing works,  how to protect your ears from noise damage and types of hearing loss

Lots of information about hearing and hearing loss at the website of the American Speech-Language-Hearing Assn.

Finally, here’s a link to the Rock and Roll Hard of Hearing Hall of Fame. Among the honorees: Pete Townshend, Eric Clapton and Bono.

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