Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

How Cells in the Developing Ear ‘Practice’ Hearing

30.11.2015

Before the fluid of the middle ear drains and sound waves penetrate for the first time, the inner ear cells of newborn rodents practice for their big debut. Researchers at Johns Hopkins report they have figured out the molecular chain of events that enables the cells to make “sounds” on their own, essentially “practicing” their ability to process sounds in the world around them.

The researchers, who describe their experiments in the Dec. 3 edition of the journal Cell, show how hair cells in the inner ear can be activated in the absence of sound. “The multistep process we uncovered reminds me of a Rube Goldberg invention,” says Dwight Bergles, Ph.D., professor of neuroscience at the Johns Hopkins University School of Medicine, a reference to Goldberg’s construction of complicated gadgets to perform seemingly simple tasks.


Han Chin Wang and Dwight E. Bergles

Cross section of the sensory epithelium of the developing inner ear in a mouse showing the calcium activated chloride channel TMEM16A (green) in the membranes of supporting cells that surround inner hair cells (red).


Han Chin Wang and Dwight E. Bergles

A 3D image showing the relationship between TMEM16A-positive supporting cells (green) and hair cells (red) in a mouse inner ear.

“Cells in the inner ear exploit a system used for fluid secretion in other organs to simulate the effect of sound before hearing begins, preparing them for the real deal.”

Normal hearing in most mammals, Bergles says, is a multistep process that begins with sound waves hitting the ear drum, which transfers energy to the air-filled middle ear and its three tiny bones. Then the fluid in the inner ear vibrates at a corresponding electrical frequency, which bends the “antennas” of just the right “hair cells,” causing them to release chemical messengers that tell nearby nerves to fire. That signal then travels to the brain, where it is interpreted as a particular sound.

Scientists, Bergles says, already knew that hair cells and nearby “supporting” cells in the developing inner ear show synchronous bursts of activity that are triggered by release of the “energy” chemical ATP, which is also used as a potent communication signal. This activity is then conveyed to the brain in the same way that sound-evoked information is, leading to burst firing of neurons in different auditory centers of the brain. What was unknown was how ATP activates hair cells.

To find out, Bergles and his team homed in on biochemical elements of the system and found that chloride ion channels in the supporting cells seemed crucial. They knew that ATP triggers a rise in calcium levels inside supporting cells, so they guessed that the calcium was the cue for a calcium-activated chloride channel to open.

An analysis of gene activity in the supporting cells pointed to involvement of the TMEM16A chloride channel, and they found high levels of this channel within supporting cells that surround inner hair cells. Experiments in mice revealed that when this channel was removed from supporting cells or blocked with drugs, the spontaneous excitation of the hair cells decreased.

Further biochemical tests, combined with electrical recordings and imaging of calcium changes in the inner ears of mice, allowed the team to piece together a full chain of events. First, supporting cells release ATP, leading to self-stimulation of their own ATP receptors, triggering an increase in calcium levels inside the cells.

This rise in calcium opens the TMEM16A channels to let chloride out, which also drags potassium ions and water out. The potassium that is released during these events activates the hair cells, stimulating the nerve cells with which they have formed weak connections.

It’s this pairing, says Bergles, that is thought to stabilize connections that help the brain make sense of sounds. “This step happens during the first two weeks after birth in mice and rats, when the middle ear is still filled with fluid and outside sounds can’t reach the inner ear.”

He adds: “The hair cells are arranged in a line and respond to different frequencies based on their location, like keys on a piano. Their connection with nearby nerve cells is strengthened every time a hair cell is activated and causes its partner nerve cell to fire.” When the brain receives a signal from hair cells near the entrance of the inner ear, he says, it “hears” a high-pitched sound; when the signal comes from farther in, it “hears” a deeper sound.

“There’s a beauty to this seemingly overly complex process,” Bergles says. “It uses the capabilities of the cells in a novel way to trigger nerve cell activity. We think this helps establish and refine the connections between ear and brain so that the animals can properly hear sounds as soon as they are exposed to them.”

Because mice can’t tell researchers if they are hearing anything, researchers can only surmise that they do based on activity they record in the auditory centers of the brain. Bergles says their research suggests that these “sounds” might be perceived as single tones played in succession, something like tests of an emergency response system. He says that the self-made sounds are for the ear what a batting machine is for a baseball player. “The machines don’t have all the richness and unpredictability of a pitcher throwing a ball, but they nevertheless help players prepare for the big event.”

Although this self-stimulation process disappears after hearing begins, Bergles says that if this pathway were reactivated following injury, it could lead to tinnitus, or “ringing” in the ear. Further understanding of this early signaling, he says, may lead to new strategies for improving the integration and performance of cochlear implants and speeding recovery from sound-induced trauma.

Other authors of the report include Han Chin Wang, Chun-Chieh Lin, Rocky Cheung, YingXin Zhang-Hooks and Amit Agarwal of the Johns Hopkins University School of Medicine; Graham Ellis-Davies of the Icahn School of Medicine at Mount Sinai; and Jason Rock of the University of California, San Francisco.

This work was supported by grants from the National Institute of Neurological Disorders and Stroke (NS050274, NS06972), the National Institute of Mental Health (MH084020), the National Institute on Deafness and other Communication Disorders (DC008860), and the National Institute of General Medical Sciences (GM053395).

Contact Information
Shawna Williams
Communications Manager
shawna@jhmi.edu
410-955-8236

www.jhmi.edu

Shawna Williams | newswise

More articles from Life Sciences:

nachricht A Map of the Cell’s Power Station
18.08.2017 | Albert-Ludwigs-Universität Freiburg im Breisgau

nachricht On the way to developing a new active ingredient against chronic infections
21.08.2017 | Deutsches Zentrum für Infektionsforschung

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: Fizzy soda water could be key to clean manufacture of flat wonder material: Graphene

Whether you call it effervescent, fizzy, or sparkling, carbonated water is making a comeback as a beverage. Aside from quenching thirst, researchers at the University of Illinois at Urbana-Champaign have discovered a new use for these "bubbly" concoctions that will have major impact on the manufacturer of the world's thinnest, flattest, and one most useful materials -- graphene.

As graphene's popularity grows as an advanced "wonder" material, the speed and quality at which it can be manufactured will be paramount. With that in mind,...

Im Focus: Exotic quantum states made from light: Physicists create optical “wells” for a super-photon

Physicists at the University of Bonn have managed to create optical hollows and more complex patterns into which the light of a Bose-Einstein condensate flows. The creation of such highly low-loss structures for light is a prerequisite for complex light circuits, such as for quantum information processing for a new generation of computers. The researchers are now presenting their results in the journal Nature Photonics.

Light particles (photons) occur as tiny, indivisible portions. Many thousands of these light portions can be merged to form a single super-photon if they are...

Im Focus: Circular RNA linked to brain function

For the first time, scientists have shown that circular RNA is linked to brain function. When a RNA molecule called Cdr1as was deleted from the genome of mice, the animals had problems filtering out unnecessary information – like patients suffering from neuropsychiatric disorders.

While hundreds of circular RNAs (circRNAs) are abundant in mammalian brains, one big question has remained unanswered: What are they actually good for? In the...

Im Focus: RAVAN CubeSat measures Earth's outgoing energy

An experimental small satellite has successfully collected and delivered data on a key measurement for predicting changes in Earth's climate.

The Radiometer Assessment using Vertically Aligned Nanotubes (RAVAN) CubeSat was launched into low-Earth orbit on Nov. 11, 2016, in order to test new...

Im Focus: Scientists shine new light on the “other high temperature superconductor”

A study led by scientists of the Max Planck Institute for the Structure and Dynamics of Matter (MPSD) at the Center for Free-Electron Laser Science in Hamburg presents evidence of the coexistence of superconductivity and “charge-density-waves” in compounds of the poorly-studied family of bismuthates. This observation opens up new perspectives for a deeper understanding of the phenomenon of high-temperature superconductivity, a topic which is at the core of condensed matter research since more than 30 years. The paper by Nicoletti et al has been published in the PNAS.

Since the beginning of the 20th century, superconductivity had been observed in some metals at temperatures only a few degrees above the absolute zero (minus...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Call for Papers – ICNFT 2018, 5th International Conference on New Forming Technology

16.08.2017 | Event News

Sustainability is the business model of tomorrow

04.08.2017 | Event News

Clash of Realities 2017: Registration now open. International Conference at TH Köln

26.07.2017 | Event News

 
Latest News

Nagoya physicists resolve long-standing mystery of structure-less transition

21.08.2017 | Materials Sciences

Chronic stress induces fatal organ dysfunctions via a new neural circuit

21.08.2017 | Health and Medicine

Scientists from the MSU studied new liquid-crystalline photochrom

21.08.2017 | Materials Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>