Osmotic Stabilization Prevents Cochlear Synaptopathy After Blast Trauma

Very interesting paper out of John Oghalai's lab along with Brian Applegate. It may provide some insight into how synapses are damaged and a way to fix it. Please note, this is basic science research in mice so there is no trial scheduled, no drug, no timeline, just perhaps some insight into how the damage occurs.

Significance
Trauma due to roadside bombs is an unfortunate consequence of modern warfare and terrorist attacks. Hearing loss often occurs because the cochlea is the body’s most sensitive pressure transducer. Here, we used in vivo imaging of the mouse cochlea using optical coherence tomography to show that increased endolymph volume correlates with damage to the auditory synapse. Reducing endolymph volume by increasing perilymph tonicity treated the synaptic loss. Therefore, this study identifies a treatment for noise-induced hearing loss. Furthermore, it suggests that this treatment may help patients with Meniere’s disease, a disabling syndrome of vertigo and hearing loss due to increased endolymph volume.


Abstract
Traumatic noise causes hearing loss by damaging sensory hair cells and their auditory synapses. There are no treatments. Here, we investigated mice exposed to a blast wave approximating a roadside bomb. In vivo cochlear imaging revealed an increase in the volume of endolymph, the fluid within scala media, termed endolymphatic hydrops. Endolymphatic hydrops, hair cell loss, and cochlear synaptopathy were initiated by trauma to the mechanosensitive hair cell stereocilia and were K+-dependent. Increasing the osmolality of the adjacent perilymph treated endolymphatic hydrops and prevented synaptopathy, but did not prevent hair cell loss. Conversely, inducing endolymphatic hydrops in control mice by lowering perilymph osmolality caused cochlear synaptopathy that was glutamate-dependent, but did not cause hair cell loss. Thus, endolymphatic hydrops is a surrogate marker for synaptic bouton swelling after hair cells release excitotoxic levels of glutamate. Because osmotic stabilization prevents neural damage, it is a potential treatment to reduce hearing loss after noise exposure.

Link to paper: http://www.pnas.org/content/early/2018/05/01/1720121115

Other articles/press releases about this: https://cen.acs.org/biological-chemistry/Osmosis-prevent-noise-induced-hearing/96/web/2018/05 and https://news.usc.edu/142599/simple-treatment-may-minimize-hearing-loss-caused-by-loud-noises/

 

It is great that it is also linked with endolymphatic hydrops and Meniere's... a set of conditions who could also use some help.

 

I was exactly the same and always heard like Charlie Brown for awhile when people talked

 

Not really prevent T - my T started the minute I left the shooting range and hasn't stopped since. It's due to the destruction of those hair cells which isn't fixed by the salt/sugar injection.

About a week later I experienced hearing loss, distortion and H and yes those is due to nerve damage which could be prevented by those injections , but 3 years later the H and sound issue has greatly improved because neurons in nerve cells can regenerate to an extent but not hair cells

 

Interesting comments. Thank you! But one thing, they have not totally ruled out nerve damage from tinnitus. As far as I know, they are just not quite sure what causes tinnitus. And maybe the nerve damage prevents the healing process. So it could or could not be related all to each other, that is the problem with these things. In any case, more good news about possible progress in the hearing field. I feel like we are making great strides at the moment.

 

I'm not convinced to be honest

Depending on the type and intensity of noise, it can cause synaptopathy where the connections at synaptic level between the base of the hair cell and dendrites are lost (e.g. broken/snapped).

I really don't see how an injection of salt into the eardrum (which is nowhere near the basal ganglia) could reverse this but I'm open to be corrected