Impaired hearing affects over 1.2 billion people worldwide. But crocodiles, who live almost as long as humans and can surpass 70 years of age, have good hearing throughout their lives. One reason is that crocodiles can create new hair cells, and a research group from Uppsala University is now on the path to finding out why. Hopefully, knowledge from the world of crocodiles will be able to help people with impaired hearing.
The most common cause of hearing impairment is receptors in the ears that have stopped working, and these receptors cannot be regenerated in humans. But they can in animals that are not mammals, such as crocodiles.
“We can see that new hair cells seem to be formed from the activation of so-called support cells, which is connected to crocodiles having certain cell structures that humans appear to lack. Our hypothesis is that nerves that carry impulses from the brain, so-called efferent nerves, trigger that regrowth,” says Helge Rask-Andersen, professor of experimental otology at Uppsala University.
Why do humans lose their hearing?
Hundreds of millions of people experience impaired hearing – and as a result, come across significant problems. Their quality of life decreases as well.
The most common cause of hearing impairment is receptors in the ears cease working. These delicate receptors do not regenerate in humans.
What do we know about hair regeneration?
Animals can quickly regenerate the hair cells in their ears if they were to get damaged, but scientists to this day are not sure how they do it.
Crocodiles, with their precise hearing abilities on land and underwater, are highly attuned to different pitches. Their receptors’ sensitivity to different pitches is affected by external temperature – allowing them to encounter different kinds of dangers in different environments during evolution.
One interesting discovery was that small cell particles are secreted in the crocodile’s ear. The particles resemble exosomes and can secrete enzymes that break down or form the membrane against which the cilia in the ear rub as sound comes in. The exosomes form small alveoli, cavities, that make it easier for the cilia to bend when sound vibrations reach the ear.
Also observed was a “remarkable” renewal of the cochlea’s acellular tectorial membrane, whose exact function in auditory health is still not fully understood.
The researchers hope to learn how crocodiles regenerate their hair cells and eventually be able to use that on people.