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By tweaking(1) a system in the ear that limits how much sound is heard, a global team of researchers(2) has discovered one alteration(3) that shows that the ability of the ear to turn(4) itself down contributes to(5) protecting against permanent hearing loss(6). The report appears this week in PLoS Biology(7).

“There’s some uncertainty(8) in the field about what this sound-limiting system is used for,” says Paul Fuchs, Ph.D. (9), an author on the paper and professor of otolaryngology(10)-head and neck surgery(11) and co-director(12) of the Center for Sensory(13) Biology at the Institute for Basic Biomedical Sciences(14) at Johns Hopkins. “Now we’ve definitively(15) shown that this system functions in part(16) to prevent acoustic trauma(17).”

To get a better handle on(18) this sound-limiting system in the ear, the research team built on previous findings in the field and focused their efforts on the nAChR(19) protein(20) found on so-called(21) sensory hair cells(22) in the ear. Nerve cells(23) from the brain(24) release signals that are picked up(25) by nAChR and turn down these sensory hair cells.

The team genetically(26) altered a single building block(27) in the nAChR protein and tested mice(28) for their ability to hear. “This point mutation(29) was designed to produce a so-called gain of function(30) in which the inhibitory(31) effect of ACh should be greater than normal,” says Fuchs.

The altered mice were less able to hear soft sounds than normal mice, showing that the genetic alteration made in the nAChR protein did indeed further “turn down” the ear. The team then asked if the alteration in nAChR, and therefore the improved sound-blocking ability of these altered mice, also could protect from sound damage.