Improved Hearing? The Answer May Be In Your Aquarium

Who knew fish had ears?

Well, theyre not exactly ears in the way we usually think of them a couple of projections sticking out of the head of a human or other higher life forms. (Look at ears on an elephant. Those are some BIG ears!)



Aquarium fish provides insight into hearing loss

So, any way, back to the fish. Researchers at the University of Washington recently published the results of a study conducted on zebra fish those freshwater staples of any home aquarium. These black-and-white striped critters (thats why theyre called zebra fish, btw) have something called a lateral line running down each side of the fish. You can barely see it but, in zebra fish, these lateral lines act much like the human hearing mechanism.

The study may lead researchers to a solution to hearing loss caused by some medications, a fairly common cause of hearing loss.

Heres How You Hear

You step outside and hear the birds chirping in the distant branches. With each chirp, a bird causes a disturbance in the air a disturbance that travels in waves. Sound waves.

Your outer ear, the ear lobe which is called the pinna, captures these airborne sound waves, directing them down the ear canal. At the end of the ear canal is the ear drum or tympanic membrane. (Stay with me.) The ear drum vibrates in time with the sound waves. In turn, these vibrations are picked up by three little bones.

The hearing sequence continues. The three tiny bones carry the vibrations to a small, fluid-filled organ called the cochlea a snail shaped organ thats lined with millions of tiny hair-like cells. Its here that sound waves created by the chirping birds are converted to electrical impulses that are sent to the brain for processing.

Once in the brain, these electrical signals are identified, processed and you remark, Hey, the birds are out. And all of this activity takes place in a split second from birds beak to recognition that the birds are out. And, our hearing mechanism is so sensitive, we can not only tell what kind of bird made the sound, we can also localize the sound and get a birds-eye view of where that little sparrow is resting even at a hundred yards away!

Think about all of those steps air disturbance, vibrations, bones and membranes theres a lot of stuff going on just listening to the birds. So, what does all of this have to do with zebra fish?

Screening Tools to Protect Against Hearing Loss

Heres the thing.

In humans, once hearing loss occurs its unlikely that youll ever hear at the levels you did previously. Why? Remember those millions of hair-like protrusions waving in cochlear fluid? Well, when those hair-like nerve endings are damaged they dont grow back. Same if someone loses an appendage. A new arm doesnt grow back. Neither do the nerve cells in the human cochlea.

However, and heres where those zebra fish come in, these fish do reproduce hearing follicles along their lateral lines the fishs hearing mechanism. That means if a zebra fish is injured, it has the remarkable ability to regenerate the hair-like nerves that run along the lateral line, enabling the fish to pick-up vibrations in the water. (So stop tapping on the aquarium glass. Its annoying.)

The Potential for Humans

The study partially funded by the National Institute on Deafness and Other Communication Disorders (NIDCD) offers a degree of hope for those who have experienced hearing loss due to the use of certain ototoxic medications.

The fishs lateral line contains sensory cells that are functionally similar to those found in the inner ear, except these are on the surface of the fishs body, making them more easily accessible, said James F. Battey, Jr., M.D., Ph.D., director of the NIDCD. This means that scientists can very efficiently analyze the sensory structures under different conditions to find out what is likely to cause damage to these structures and, conversely, what can protect them from damage.

In other words, researchers, using genetic techniques, have examined zebra fish DNA searching for clues as to what gives this little aquarium dweller the ability to regenerate nerves. The research team also examined certain medications known to be ototoxic poisonous to those cochlear hair cells, screening more than 10,000 compounds. After all of this testing, the results showed that two, similar chemicals are able to provide protection of cochlear hair cells from damage caused by neomycin, a common class of medicines.

According to a media release from the NIDCD, the authors [of the study] suggest that their research technique, which combines chemical screening with traditional genetic approaches, offers a fast and efficient way to identify potential drugs and drug targets that may one day provide therapies for people with hearing loss and balance disorders.

Further, tests may be developed to determine the susceptibility of an individual to the damaging effects of certain medications so alternative therapies can be employed by medical professionals.

Bottom line? Researchers under laboratory conditions have isolated compounds that protect against hearing loss side effects of medications by examining the genetics of the zebra fish. By discovering how this little creature is able to regenerate nerves along its lateral lines, scientists offer hope that someday, regeneration of these cochlear hair cells will be possible in humans.

And in the meantime, tests will be developed to identify those humans most susceptible to hearing loss due to the use of certain medicines.

Science marches on. Ooops, time to feed the fish.