Spiral ganglion neuron survival and function in the deafened cochlea following chronic neurotrophic treatment
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Date
2011-12
Journal Title
Journal ISSN
Volume Title
Publisher
Elsevier
Abstract
Cochlear implants electrically stimulate residual spiral ganglion neurons (SGNs) to provide auditory cues
for the severe-profoundly deaf. However, SGNs gradually degenerate following cochlear hair cell loss,
leaving fewer neurons available for stimulation. Providing an exogenous supply of neurotrophins (NTs)
has been shown to prevent SGN degeneration, and when combined with chronic intracochlear electrical
stimulation (ES) following a short period of deafness (5 days), may also promote the formation of new
neurons. The present study assessed the histopathological response of guinea pig cochleae treated with
NTs (brain-derived neurotrophic factor and neurotrophin-3) with and without ES over a four week
period, initiated two weeks after deafening. Results were compared to both NT alone and artificial
perilymph (AP) treated animals. AP/ES treated animals exhibited no evidence of SGN rescue compared
with untreated deafened controls. In contrast, NT administration showed a significant SGN rescue effect
in the lower and middle cochlear turns (two-way ANOVA, p < 0.05) compared with AP-treated control
animals. ES in combination with NT did not enhance SGN survival compared with NT alone. SGN function
was assessed by measuring electrically-evoked auditory brainstem response (EABR) thresholds. EABR
thresholds following NT treatment were significantly lower than animals treated with AP (two-way
ANOVA, p ¼ 0.033). Finally, the potential for induced neurogenesis following the combined treatment
was investigated using a marker of DNA synthesis. However, no evidence of neurogenesis was observed
in the SGN population. The results indicate that chronic NT delivery to the cochlea may be beneficial to
cochlear implant patients by increasing the number of viable SGNs and decreasing activation thresholds
compared to chronic ES alone.
Description
Keywords
SGN, Neurotrophin, Neural Survival, Deafness, Auditory System
Citation
Landry, T. G., Wise, A. K., Fallon, J. B., & Shepherd, R. K. (2011). Spiral ganglion neuron survival and function in the deafened cochlea following chronic neurotrophic treatment. Hearing Research, 282(1-2), 303-313. doi: 10.1016/j.heares.2011.06.007