Synaptopathy in the noise-exposed and aging cochlea: primary neural degeneration in acquired sensorineural hearing loss
By Sharon G. Kujawa, M. Liberman. Hearing Research, 2015
681 citations recorded by the source corpus.
The classic view of sensorineural hearing loss (SNHL) is that the “primary” targets are hair cells, and that cochlear-nerve loss is “secondary” to hair cell degeneration. Our recent work in mouse and guinea pig has challenged that view. In noise-induced hearing loss, exposures causing only reversible threshold shifts (and no hair cell loss) nevertheless cause permanent loss of >50% of cochlear-nerve / hair-cell synapses. Similarly, in age-related hearing loss, degeneration of cochlear synapses precedes both hair cell loss and threshold elevation. This primary neural degeneration has remained hidden for three reasons: 1) the spiral ganglion cells, the cochlear neural elements commonly assessed in studies of SNHL, survive for years despite loss of synaptic connection with hair cells, 2) the synaptic terminals of cochlear nerve fibers are unmyelinated and difficult to see in the light microscope, and 3) the degeneration is selective for cochlear-nerve fibers with high thresholds. Although not required for threshold detection in quiet (e.g. threshold audiometry or auditory brainstem response threshold), these high-threshold fibers are critical for hearing in noisy environments. Our research suggests that 1) primary neural degeneration is an important contributor to the perceptual handicap in SNHL, and 2) in cases where the hair cells survive, neurotrophin therapies can elicit neurite outgrowth from spiral ganglion neurons and re-establishment of their peripheral synapses.
Subfields: Cognitive Neuroscience, Neurology, Sensory Systems
View Paper: https://www.semanticscholar.org/paper/952cad2f24cd422ca5cc90147e60d6dff787ea4d
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Citations in the corpus
- Toward a Differential Diagnosis of Hidden Hearing Loss in Humans (2016, background): “However, recent animal work has led to the novel idea that significant de-afferentation of surviving IHCs may be the rule rather than the exception in acquired sensorineural hearing loss and that significant hair cell de-afferentation occurs well before elevation of audiometric thresholds in the noi”