Approximately 1.5 billion individuals have hearing loss, which can cause them serious issues and frequently lower their overall quality of life. Damage to the non-regenerative receptors known as hair cells is the most frequent cause of these deficits. Many new technologies, such as speech diagnosis tests or regenerative stem cell therapy, are being developed to combat hearing loss.
Auditory receptors in a number of non-mammalian species go through cell renewal after injury including crocodiles. As a result, there is now more hope for innovative treatments for human sensorineural deafness. The trigger mechanisms and hair cells renew even under typical circumstances in animals, which is still unknown. Researchers looked at the crocodile’s auditory organ to confirm any potential ongoing spontaneous hair cell renewal.
It is now understood that numerous non-mammalian animals’ auditory receptors can experience cell renewal and regeneration. Trauma, like noise and aminoglycoside injection, can cause post-embryonic production of hair cells (HCs), triggering cell growth and the formation of new HCs.
By stimulating regeneration, which is still largely assumed to be nonexistent, has increased optimism for new treatments for sensorineural deafness in humans.
Why crocodiles?
Crocodiles are being studied by researchers from Uppsala University in Sweden as a possible solution to this conundrum. Crocodiles can live as long as 70 years, just about as long as humans, even though they continue to hear well into old age. Crocodiles, unlike humans, can quickly replace damaged hair cells, however it is unclear exactly how they achieve this.
We can observe that the stimulation of the support cells appears to result in the formation of new hair cells, which is related to the fact that crocodiles have particular cell configurations that humans don’t seem to have. Helge Rask-Andersen, the study’s principal author, states that “our belief is that neurons that convey signals from the brain known as efferent nerves, activate that regrowth.
What approach was taken for this research?
Transmission electron microscopy and confocal microscopy were used to examine two male Cuban crocodiles and an adult male African dwarf crocodile . The crocodile ears went under micro-computed tomography (micro-CT) and 3D reconstruction after being preserved in formaldehyde and glutaraldehyde the temporal bones were drilled-out and decalcified
Two male Cuban crocodiles specimens, each weighing around 250 g, were put to sleep with 5 mg of ketamine and 0.05 mg of medetomidine before being put down with a 0.4 ml intracardial injection of T-61. An oscillating saw was used to separate the skull and remove the temporal bones. After removing the eardrum and columella, the ears were submerged in 2.5% glutaraldehyde and 1% paraformaldehyde in 2.5% phosphate buffer.
The ears were then placed in 1% osmium tetroxide after more bone around them was removed. The samples were embedded in Epon after being dehydrated in graded ethanol.
What were the results of the research?
A mosaic of closely knit supporting cells joined by gap junctions encircled inner and outer hair cells in the crocodile papilla basilaris. Both types of hair cells were innervated by afferent neurons, both of which had ribbon synapses. Occasionally, supporting cells displayed evidence of trans-differentiation into hair cells. They expressed the transcription factors SOX2 and MAFA. Organelles found in supporting cells, such as the efferent nerve fibers during the regeneration process, may be used to transport genetic information across cells. There were indications of tectorial membrane replenishment.
The crew investigated many inner crocodile ears in an effort to learn more about their method of perpetual hearing. They discovered that the crocodile’s ear secretes tiny particles, which is thought to be an important element of the process. “One theory is that this improves hearing and increases sensitivity to sound. The study’s lead author, Helge Rask-Andersen, adds that the team’s ultimate goal is to understand how crocodiles replenish their hair cells so that they can one day apply that knowledge to humans.
Research on this theory is still in its early stages, but if everything goes right, it may inspire a whole future of hearing restoration.
Information source: www.frontiersin.org
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