Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Critical hearing gene helps send auditory messages to brain

23.10.2006
By studying a gene earlier linked to deafness in humans, researchers now have new insight into the molecular process by which components of the inner ear send messages to the brain. The team reports its findings in the October 20, 2006, issue of the journal Cell, published by Cell Press.

The researchers found that mice lacking the gene otoferlin are profoundly deaf. The animals' deafness results from an inability to translate sound stimulation into the release of a chemical nerve messenger, or neurotransmitter, that would usually pass that information to auditory nerves and on to the brain, they reported. The sensory structures within the mutant animals' ears otherwise appeared to develop normally.

"Study of the genes responsible for deafness can bring new insight into the molecular basis of how hearing works," said Christine Petit of the Institut Pasteur in Paris, France.

The sensory machinery within the inner ear is particularly intriguing, she added, "in the sense that it operates with extreme temporal precision."

In mammals, the hearing organ, or cochlea, is a snail-shaped structure of the inner ear that is filled with a watery fluid. When that liquid moves in response to sound vibrations, thousands of sensory "hair" cells are set into motion.

Those sensory receptors come in two types: inner and outer hair cells. Outer hair cells amplify sound within the cochlea, allowing for hearing sensitivity. In contrast, inner hair cells are "the genuine sensory cells transmitting information on the temporal structure and intensity of sound to the central nervous system," Petit said.

While outer hair cell defects can lead to considerable hearing loss, she added, a loss of inner hair cell function results in total deafness as messages cannot get through.

Inner hair cells operate in a manner comparable to neurons, she said. When an inner hair cell is stimulated, channels open up allowing calcium to flow in. In turn, that influx of calcium leads small "sacs" full of neurotransmitter to fuse with the cell membrane, releasing their contents into the space, or synapse, between the sensory cells and auditory nerve endings.

That chemical release allows nerve messages to be passed from one neuron to another. In inner hair cells, those neurotransmitter-filled vesicles are held in place at the cell membrane by tethers known as "ribbons."

The current study follows up a report by Petit's team several years ago that people with a recessive form of deafness harbor two abnormal copies of the otoferlin gene. They also had some evidence hinting that the gene might act as a calcium sensor with an important role in neurotransmitter release by the inner hair cells. For example, otoferlin resembles a calcium-sensing protein involved in release of chemicals by sensory neurons elsewhere in the body. Their current study provides additional evidence to confirm that notion.

They now report that otoferlin activity in the cochlea occurs only in the inner hair cells, where it concentrates in the ribbon-associated synaptic vesicles. They also found that the otoferlin protein binds calcium and interacts with other proteins known to play a role in neurotransmitter release.

To further examine the gene's role in a living animal, the researchers studied "knockout" mice completely lacking a functional otoferlin gene. When exposed to sounds of various frequencies, the mice showed no detectable activity in parts of the brain that normally process sound.

They further found that the profoundly deaf mice suffered a complete loss of neurotransmitter release from their inner hair cells, despite having an apparently normal "ribbon synapse" and calcium flow.

The findings led the researchers to conclude that "otoferlin is essential for a late step of [neurotransmitter release] and may act as the major [calcium] sensor triggering membrane fusion at the inner hair cell ribbon synapse."

The findings also have therapeutic implications, as they suggest that people who are deaf as a result of defects in otoferlin "will benefit from cochlear implants," the researchers said. Cochlear implants analyze sound messages and convert them into electrical signals, bypassing the cochlea to directly stimulate the auditory nerves.

"That's good news," Petit said, since otoferlin-linked deafness is an auditory neuropathy, a class of hearing impairment for which the best course of treatment had remained uncertain.

Heidi Hardman | EurekAlert!
Further information:
http://www.cell.com

Further reports about: Calcium Cochlea Neurotransmitter Sensor auditory deafness hair hair cells otoferlin sensory

More articles from Life Sciences:

nachricht Are there sustainable solutions in dealing with dwindling phosphorus resources?
16.10.2017 | Leibniz-Institut für Nutzierbiologie (FBN)

nachricht Strange undertakings: ant queens bury dead to prevent disease
13.10.2017 | Institute of Science and Technology Austria

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Smart sensors for efficient processes

Material defects in end products can quickly result in failures in many areas of industry, and have a massive impact on the safe use of their products. This is why, in the field of quality assurance, intelligent, nondestructive sensor systems play a key role. They allow testing components and parts in a rapid and cost-efficient manner without destroying the actual product or changing its surface. Experts from the Fraunhofer IZFP in Saarbrücken will be presenting two exhibits at the Blechexpo in Stuttgart from 7–10 November 2017 that allow fast, reliable, and automated characterization of materials and detection of defects (Hall 5, Booth 5306).

When quality testing uses time-consuming destructive test methods, it can result in enormous costs due to damaging or destroying the products. And given that...

Im Focus: Cold molecules on collision course

Using a new cooling technique MPQ scientists succeed at observing collisions in a dense beam of cold and slow dipolar molecules.

How do chemical reactions proceed at extremely low temperatures? The answer requires the investigation of molecular samples that are cold, dense, and slow at...

Im Focus: Shrinking the proton again!

Scientists from the Max Planck Institute of Quantum Optics, using high precision laser spectroscopy of atomic hydrogen, confirm the surprisingly small value of the proton radius determined from muonic hydrogen.

It was one of the breakthroughs of the year 2010: Laser spectroscopy of muonic hydrogen resulted in a value for the proton charge radius that was significantly...

Im Focus: New nanomaterial can extract hydrogen fuel from seawater

Hybrid material converts more sunlight and can weather seawater's harsh conditions

It's possible to produce hydrogen to power fuel cells by extracting the gas from seawater, but the electricity required to do it makes the process costly. UCF...

Im Focus: Small collisions make big impact on Mercury's thin atmosphere

Mercury, our smallest planetary neighbor, has very little to call an atmosphere, but it does have a strange weather pattern: morning micro-meteor showers.

Recent modeling along with previously published results from NASA's MESSENGER spacecraft -- short for Mercury Surface, Space Environment, Geochemistry and...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

World Health Summit 2017: International experts set the course for the future of Global Health

10.10.2017 | Event News

Climate Engineering Conference 2017 Opens in Berlin

10.10.2017 | Event News

Conference Week RRR2017 on Renewable Resources from Wet and Rewetted Peatlands

28.09.2017 | Event News

 
Latest News

A single photon reveals quantum entanglement of 16 million atoms

16.10.2017 | Physics and Astronomy

The melting ice makes the sea around Greenland less saline

16.10.2017 | Earth Sciences

On the generation of solar spicules and Alfvenic waves

16.10.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>