Studying Of Salicylate Sodium-induced Tinnitus By Bilateral Auditory Nerves Section

Tinnitus is a subjective auditory perception that cannot be attributed to anexternal sound. It has been reported that tinnitus is experienced by a significantproportion of the general population. The living standard of tinnitus patient isseverely affected. Although much progress has been made in understanding thepathophysiological changes associated with salicylate sodium (SS)-inducedtinnitus, but the mechanisms by which SS-induced tinnitus may be generated areincompletely understood. The SS dose in SS-induced tinnitus is so high that aseries of side effects was induced. As a result, the present tinnitus model couldnot mimic human tinnitus well. There were many reports that suggested thateither peripheral auditory system (PAS) or central auditory system (CAS) mayplay an important role in SS-induced tinnitus. In the present study, rats wereconditioned to distinguish sound from silence in an approach to associate soundwith licking water and silence with stopping licking. Then they were underbilateral auditory nerves section (BANS) which indicated that PAS and CASwere separated in order to fully investigate these roles in SS-induced tinnitus.Objective1) To establish SS-induced tinnitus model by using low dose of SS.2) To investigate the mechanisms of SS-induced tinnitus, that is, the role ofPAS and CAS in SS-induced tinnitus. Methods1) In experiment1, after ten rats were conditioned to distinguish sound fromsilence in an approach to associate sound with licking water and silencewith stopping licking, they were divided into treatment and control groupsrandomly. Rats in SS and saline groups were injected respectively with120mg/kg SS (i.p.) and an equivalent volume of saline for2consecutive days,and were tested2h after injection in the behavioral test period. Make surethat SS-induced tinnitus was responsible for the high lick suppression ratio(R) in treatment group by investigating R and water consumption andauditory brainstem response (ABR).2) In experiment2, three rats were used to investigate the effect of BANSitself on rats’ behavior in order to exclude the interference that BANS itselfmay induce tinnitus.3) In experiment3, after seven rats and ten rats used in experiment1(with aninterval of at least one week) were conditioned, they were given BANSoperation. Rats in treatment group were given SS to investigate its effect.Results1) In experiment1, R in SS group was significantly higher than that in salinegroup on the first3days of the test period. Water consumption betweensaline and SS groups in the test period had no statistically significantdifference on the first3test days. ABR thresholds to click and tone burst inSS group were not changed before and after SS application.2) In experiment2, ABR thresholds to click and tone burst in bilateral ears ofall animals after BANS were more than90dB SPL and68dB SPL,respectively. Licks count and water consumption and R of the sessions andthe first trials on4consecutive days after BANS were not found to besignificant comparing to that before BANS; lick latency was not found to besignificant comparing to that before BANS on2consecutive days afterBANS. 3) In experiment3, water consumption of baseline and control and treatmentgroups was significantly lower than that before BANS; licks count andwater consumption and R of the sessions in saline group were not found tobe significant comparing to those in baseline group on4consecutive daysafter BANS and were not found to be significant comparing to those in SSgroup either; R of the first trials in saline group were not found to besignificant comparing to that in baseline group on2consecutive days afterBANS, but was found to be significantly lower than that in SS group; licklatency in saline group was not found to be significant comparing to that inbaseline group on2consecutive days after BANS, but was found to besignificantly longer than that in SS group; R of the first trials in saline groupin experiment3was not found to be significant comparing to that in salinegroup in experiment1on the first2test days, but R of the first trials in SSgroup in experiment3was significantly lower than that in SS group inexperiment1on the first test day; lick latency in saline group in experiment3was not found to be significant comparing to that in saline group inexperiment1on the first2test days, but lick latency of the first trials in SSgroup in experiment3was significantly longer than that in SS group inexperiment1on the first test day.Conclusion1) In experiment1, the R values of rats injected with120mg/kg SS2h beforetest period were significantly higher than those of the saline group on3consecutive days in the test period. Only SS-induced tinnitus could beresponsible for the effect because no changes in ABR thresholds before andafter SS application as well as in water consumption between saline and SSgroups were observed.2) In experiment2, the findings indicated that BANS had no significant effecton rats’ behavior and that no tinnitus performance was observed on at leasttwo days after the operation. 3) In experiment3, the findings suggested that after SS application on BANSrats, the effects of SS, if any, may not be indicated by licks count and waterconsumption and R of the sessions. The fact that the significant lower of theR of the first trials in control group than that in treatment group and thesignificant longer of lick latency in control group than that in treatmentgroup indicated that CAS was involved in SS-induced tinnitus; the fact thatR of the first trials in treatment group in experiment1was significantlyhigher than that in treatment group in experiment3and lick latency intreatment group in experiment1was significantly shorter than that intreatment group in experiment3indicated that PAS was also implicated inSS-induced tinnitus and played a more important role than CAS inSS-induced tinnitus.