Long‑term treatment with salicylate enables NMDA receptors and impairs AMPA receptors in C57BL/6J mice inner hair cell ribbon synapse

Abstract

Salicylate is widely used to produce animal models of tinnitus in mice and/or rats. The side effects on auditory function, including hearing loss and tinnitus, are considered the results of the auditory nerve dysfunction. A recent study indicated that chronic treatment with salicylate for several weeks reduces compressed action potential amplitude, which is contradictory to the studies reporting excessive activation of N-methyl-D-aspartate receptors (NMDAR) in tinnitus-induced animals. The specific aims of the experiment were to detect the effect of salicylate on the inner hair cells (IHCs), ribbon synapse, as well as the association between the hearing threshold and the number of mismatched ribbon synapses. In the present study, mice were injected intraperitoneally with a low dose of salicylate (200 mg/kg) for 14 days. The auditory brainstem response and otoacoustic emission were measured to assess auditory function of the mice. The postsynaptic regions of IHC were identified with two types of immunostaining targets: Postsynaptic density protein 95 and Glu2/3. The number of spheres was counted and the synapses were reconstructed in 3-dimensional images. Increases in distortion product otoacoustic emissions amplitudes of the salicylate group were detected, however, an elevation in the hearing threshold was also observed. A mismatch between pre-and post-ribbon synapses was observed. In addition, the cochlear components, including the numbers of outer hair cells and IHCs, were unlikely to be affected by salicylate. IHC ribbon synapses were more susceptible to salicylate stimuli. Furthermore, mismatch of pre- and post-ribbon synapses may indicate a competitive inhibition between NMDAR and α-amino-3-hydroxy-5-methyl-4-isoxa-zole-propionate receptors and dysfunction of ribbon synapses.

Cellular Differences in the Cochlea of CBA and B6 Mice May Underlie Their Difference in Susceptibility to Hearing Loss

“…We used two primary antibodies directed against Ribeye, a major structural component of synaptic ribbons (Schmitz et al, 2000), and post-synaptic AMPA receptor subunit 2 (GluR2). We defined each punctum of double staining as a ribbon synapse and we found no significant difference in the number of ribbon synapses per IHC between the two mouse strains (14.5 ± 1.79 vs. 14.9 ± 2.01, for CBA and B6 mice, respectively, n = 22 and 28; unpaired Student's t -test, p > 0.05; Figure 6), consistent with previous studies (Wang and Ren, 2012; Ohlemiller et al, 2016; Hickox et al, 2017; Cui et al, 2018). This result suggests the smaller ABR Wave I amplitude in B6 mice is not due to a smaller number of SGNs contacting each IHC.…”

Photobiomodulation therapy in improvement of harmful neural plasticity in sodium salicylate-induced tinnitus

“…Another finding of ABR testing was the increase of the mean values of BTT and threshold in the tinnitus group and more importantly, the return of both parameters to the normal level in the PBMT group ( Fig 5 ). An increase in ABR threshold with a tinnitus-inducing dose of SS has also been reported in other animal studies [ 71 , 72 ]. A possible explanation for the increased threshold could be the mild mechanical disturbance caused by the SS injection in the cochlear outer hair cells.…”

Protective Effect of Resveratrol in an Experimental Model of Salicylate-Induced Tinnitus

“…Sci. 2022, 23, x FOR PEER REVIEW 2 of 13 aspartate (NMDA) receptor subunit 2B (NR2B) [7][8][9][10]. Several studies have suggested that an increase in the expression of NMDA receptors causes ototoxicity in the cochlea [11,12].…”

“…A consequential nerve malfunction is the result of abnormal excitability at the brainstem and cerebral cortex [6], which is induced by the overactivity of the N-methyl-Daspartate (NMDA) receptor subunit 2B (NR2B) [7][8][9][10]. Several studies have suggested that an increase in the expression of NMDA receptors causes ototoxicity in the cochlea [11,12].…”