Research On The Mechanism Of Spiral Ganglion Neuron Damage Induced By Salicylate In The Guinea Pig Cochlea

Objective: In the present study, in vivo experiments are conducted to test efficacy of caspase-3 inhibitor zDEVD-FMK for protecting spiral ganglion neuron (SGN) from salicylate-induced apoptosis in the guinea pig cochlea.Methods: Forty adult guinea pigs were divided randomly into four experimental groups, each for ten, they were: Group A, served as blank control without any disposal; Group B, APL only, The animals were disposed with APL through RWN by the means of cochlear micro-injection, the left ear was implemented with an operation; Group C, APL plus salicylate. The animals were treated with APL through RWN before drug injection, with a does of 400 mg·kg^-1·d^-1 i.p., for ten consecutive days; Group D, zDEVD-FMK plus sodium salicylate. The animals were treated with caspase-3 inhibitor zDEVD-FMK through RWN before drug exposure in the same way described in the Group C. All animals received ABR thresholds measurement before drug administration and after last injection; they were then sacrificed for cochleae followed by staining. Programmed cell death (PCD) executioner was evaluated with immunohistochemistry detection of activated caspase-3. Apoptosis was examined with a terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end-labeling (TUNEL) method. Transmission electron microscopy (TEM) was also used to evaluate morphological change in the auditory neuron.Results: Animals disposed with salicylate appeared a high elevation in response of ABR thresholds testing (p<0.01 vs. Group A and B). By contrast, for those received zDEVD-FMK in advance, their hearing improved (p<0.05 vs. Group C). Salicylate strengthened immune reaction in the fields of SGNs, which was in accordance with apoptotic auditory effectors emergence (p<0.01 vs. Group A and B). On the contrary, topical inhibitor delivery alleviated pigmentation of nuclei (p<0.01 vs. Group C), keeping pace with antigen expression decrease, but a few immunostaining could be still detected (p<0.01 vs. Group C). With TEM to SGNs, no ultrastructural change occurred in the Group A and B, while neurons obtained from Group C demonstrated obvious apoptotic changes, characterized with chromatin condensation and nucleus margination. Treatment with zDEVD-FMK prevented the salicylate-damaged SGNs by apoptosis in a highly significant manner.Conclusion: These findings suggest that long-term administration of high-dose salicylate can activate caspase-3 pathway to induce SGN apoptosis.