New nerve cell connections on sensory cells in mice could be at fault
Conventional wisdom has long blamed age-related hearing loss almost entirely on the death of sensory hair cells in the inner ear, but research from neuroscientists at Johns Hopkins has provided new information about the workings of nerve cells that suggests otherwise.
In a paper published July 1 in The Journal of Neuroscience, the Johns Hopkins team says its studies in mice have verified an increased number of connections between certain sensory cells and nerve cells in the inner ear of aging mice. Because these connections normally tamp down hearing when an animal is exposed to loud sound, the scientists think these new connections could also be contributing to age-related hearing loss in the mice, and possibly in humans.
“The nerve cells that connect to the sensory cells of the inner ear are known to inhibit hearing, and although it’s not yet clear whether that’s their function in older mice, it’s quite likely,” says Paul Fuchs, Ph.D., the John E. Bordley Professor of Otolaryngology–Head and Neck Surgery at the Johns Hopkins University School of Medicine. “If confirmed, our findings give us new ideas for how physicians may someday treat or prevent age-related hearing loss.”
Fuchs says the new research builds on the knowledge that inside the ear lies a coiled row of sensory cells responsible for converting sound waves into electrical signals sent through nerve cells to the brain, which processes and tells animals what they “hear.” Two sets of these so-called hair cells — named for the filaments that act like antennae picking up sound waves — exist, an inner tier closest to the brain and an outer tier. The outer ones have a secondary function: to amplify the sound waves within the inner ear. Not surprisingly, Fuchs notes, a loss of outer hair cells closely correlates with a loss of hearing.
But studies over the last decade have suggested that changes over time also occur in the connections between hair cells and the nerve cells to which they are attached.
Each of those nerve cells is like a one-way street, Fuchs says, taking signals either from the ear to the brain or vice versa. The nerve cells that take signals to the ear are known to turn down the amplification provided by outer hair cells when an animal is, for example, exposed to a noisy environment for an extended period of time.
Previous research has suggested that with age, inner hair cells in mice and humans experience a decrease in outgoing nerve cell connections, while incoming nerve cell connections increase.
To find out if the new connections worked — or worked normally — Stephen Zachary, a graduate student in Fuchs’ laboratory, painstakingly recorded electrical signals from within the inner hair cells of young and old mice.
He found that the incoming nerve cells were indeed active and that their activity levels correlated with the animals’ hearing abilities: The harder of hearing an animal was, the higher the activity of its incoming nerve cells.
“These nerve cell connections seem to be reverting back to the way they worked during early development before the animals’ sense of hearing was operating,” says Fuchs. “We don’t know why the new connections form, but it might be as simple as a lack of competition for space once the outgoing nerve cells have retracted.”
If the same phenomenon is occurring in human ears, Fuchs and his team say there may be ways of preventing the incoming nerve cells from forming new connections with inner hair cells, a technique that could help maintain normal hearing through old age.
This work was supported by grants from the National Institute on Deafness and Other Communication Disorders (R01 DC001508, T32 DC000023, P30 DC005211, F31 DC014184).
Senior Communications Specialist
Catherine Kolf | newswise
Antimicrobial substances identified in Komodo dragon blood
23.02.2017 | American Chemical Society
New Mechanisms of Gene Inactivation may prevent Aging and Cancer
23.02.2017 | Leibniz-Institut für Alternsforschung - Fritz-Lipmann-Institut e.V. (FLI)
In the field of nanoscience, an international team of physicists with participants from Konstanz has achieved a breakthrough in understanding heat transport
Cells need to repair damaged DNA in our genes to prevent the development of cancer and other diseases. Our cells therefore activate and send “repair-proteins”...
The Fraunhofer IWS Dresden and Technische Universität Dresden inaugurated their jointly operated Center for Additive Manufacturing Dresden (AMCD) with a festive ceremony on February 7, 2017. Scientists from various disciplines perform research on materials, additive manufacturing processes and innovative technologies, which build up components in a layer by layer process. This technology opens up new horizons for component design and combinations of functions. For example during fabrication, electrical conductors and sensors are already able to be additively manufactured into components. They provide information about stress conditions of a product during operation.
The 3D-printing technology, or additive manufacturing as it is often called, has long made the step out of scientific research laboratories into industrial...
Nature does amazing things with limited design materials. Grass, for example, can support its own weight, resist strong wind loads, and recover after being...
Nanometer-scale magnetic perforated grids could create new possibilities for computing. Together with international colleagues, scientists from the Helmholtz Zentrum Dresden-Rossendorf (HZDR) have shown how a cobalt grid can be reliably programmed at room temperature. In addition they discovered that for every hole ("antidot") three magnetic states can be configured. The results have been published in the journal "Scientific Reports".
Physicist Dr. Rantej Bali from the HZDR, together with scientists from Singapore and Australia, designed a special grid structure in a thin layer of cobalt in...
13.02.2017 | Event News
10.02.2017 | Event News
09.02.2017 | Event News
23.02.2017 | Physics and Astronomy
23.02.2017 | Earth Sciences
23.02.2017 | Life Sciences