A New Crocodile Hypothesis Could Help People With Hearing Loss

Hearing loss can reduce your opportunities, cause social withdrawal, and result in emotional problems. 

A new hypothesis about crocodile ears.

Over 1.2 billion individuals worldwide have hearing loss. Crocodiles, on the other hand, have excellent hearing for their whole lives and can live up to 70 years. One reason is that crocodiles can create new hair cells, and an Uppsala University research team is currently investigating why. Hopefully, understanding crocodile biology can benefit those who have hearing loss.

Light microscopic image showing the auditory organ in the crocodile. The wedge-like structure contains thousands of sensory cells with hair-like processes projecting into a porous membrane to which they are rubbed against. (Note that its shape is similar to a crocodile head.) Credit: Uppsala University

“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 and one of the researchers behind the study, which was recently published in the journal Frontiers in Cell and Developmental Biology.

More than a billion people worldwide have hearing loss, which causes significant difficulties for individuals and often lowers the perceived quality of life. The most common cause of hearing loss is the failure of receptors in the ears, and these receptors cannot be regenerated in humans. They may, however, be in non-mammal creatures such as crocodiles, which maintain strong hearing throughout their lives despite living up to 70 years.

This image shows the hair cell of a crocodile magnified around 5000 times. Many hairs (or cilia) project against the porous membrane. Credit: Uppsala University

It is known that animals can quickly regenerate the hair cells in their ears if they are damaged. But it is not really known how. Crocodiles have excellent hearing that is adapted for being on land and underwater. One distinctive characteristic is that the receptors’ sensitivity to different pitches is affected by external temperature, making it perfect for different kinds of dangers in different environments during evolution.

The crocodile ear has been examined in a new study by ear researchers at Uppsala University Hospital together with researchers at Uppsala University. Few research groups in the world have studied the inner ear of the crocodile, and the researchers in this study have used electron microscopy and molecular technologies.

The image shows regenerating hair cells (green) moving from the lower supporting cells up to the sensory surface. The sensory cells are of two types. Credit: Uppsala University

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.

“One hypothesis is that this increases sensitivity to sound and hearing improves. Our hope is to learn how crocodiles regenerate their hair cells and to eventually be able to use that on people in the future,” says Helge Rask-Andersen.

Reference: “Regeneration in the Auditory Organ in Cuban and African Dwarf Crocodiles (Crocodylus rhombifer and Osteolaemus tetraspis) Can We Learn From the Crocodile How to Restore Our Hearing?” by Hao Li, Karin Staxäng, Monika Hodik, Karl-Gunnar Melkersson, Mathias Rask-Andersen and Helge Rask-Andersen, 4 July 2022, Frontiers in Cell and Developmental Biology.
DOI: 10.3389/fcell.2022.934571

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