An Investigation Of Salicylate-Motor Prestin Of Outer Hair Cell On Acoustic Injury To Cochlea Of Mice

Purpose: to study the characteristics of distortion product otoacoustic emissions on mice.Methods: using male C57BL/6 mice(P18d-P30d). DPOAEs were measured at 5kHz. 6kHz 7kHz å’Œ 8kHz. Data were recorded from input/output curve, including 1) the intensity of L₁ when the intensity of DPOAE is 0dB SPL, 2) the amplitude of DPOAEs when L₁/L₂=55/45dB, 65/55dB 75/65dB, and 3) the slope of I/O curve.Results: when L₁/L₂=75/65dB, the amplitude of DPOAE is 0.00±5dB at 5kHz, 5.35±5dB at 6kHz, 6.34±5dB at 7kHz and 6.12±4dB at 8kHz. When L₁/L₂=65/55dB, the amplitude of DPOAE is -7.35±4dB at 5kHz, 2.80±4dB at 6kHz, 3.06±3dBat 7kHz and 7.17±4dB at 8kHz. When L₁/L₂=55/45dB, the amplitude of DPOAE is -10.39±2dB at 5kHz, -0.66±4dB at 6kHz, -1.88±4dB7kHz and -1.99±5dB at 8kHz. When the amplitude of DPOAE is 0dB SPL, the in tensity of L₁ are 3.54±5dB, 57.31±8dB, 58.89±7dB and 57.04±4dB at 5kHz, 6kHz. 7kHz and 8kHz, respectively. The slope is 0.88±0.3, 0.36±0.2, 0.50±0.2 and 0.93±0.2 at the same four frequency.Conclusion: when the intensity of L₁ and L₂ are fixed, the amplituds of 2f₁-f₂ DPOAEs are increased while the frequencies are increased. When the f₁ and f₂ are fixed, the amplituds of 2f₁-f₂ DPOAEs are increased while the intensity of L₁ and L₂ are increased. The I/O curves are various, and the slope can not reflect the function of cochlea correctly.Purpose: to study the effects of sodium salicylate, injected intraperitoneally at dosage of 400mg/kg, on distortion product otoacoustic emission (DPOAE) in mice.Methods: DPOAEs were measured as baseline before administration. Then DPOAEs were measured again after 3 hours and 3 days of drug administration.Results: after 3 hours of drug administration, the thresholds and magnitudes of DPOAE at the 2f₁- f₂ frequency increased 12-15dB SPL and decreased 3-9 dB SPL, respectively. After 3 days of drug administration, the thresholds and magnitudes returned to the baseline level. On the contrary, the latencies of DPOAE were not affected by sodium salicylate statistically. After 3 hours of drug administration, the incidence rates of DPOAE induced by the primaries at 60dB SPL over 5 6 7 å’Œ 8k Hz frequencies were much lower than the incidence rates induced by the primaries at 70dB SPL. And the incidence rates of the lower frequencies lower than the higher frequencies.Conclusion: sodium salicylate can increase the thresholds and reduce magnitude of DPOAE in mice reversibly and the change were significant induced by lower-level primaries. Sodium salicylate had no effects on the latencies of DPOAE in mice.Part III: the effect of sodium salicylate on acoustic injury toC57BL/6 micePurpose: to study the effect of sodium salicylate on acoustic injury to prestin normal expression cochlea of mice.Methods: using male C57BL/6 mice(P18d-P30d). The animals were allocated into three groups (salicylate + noise, saline + noise, and salicylate only) and were exposed to a 8 kHz 1/3 octave band noise at 110 dB SPL for 4 hours consecutively.Dynamic changes of ABR and DPOAE thresholds were monitored. After physiological examination, the cochleae were processed for the morphological examination by scan and transmission electronic microscopy. The prestin mRNA were evaluated by real-time quantitative PCR.Results: Mean threshold shifts of ABRs evoked by clicks in the sodium salicylate group obtained on 1th day of the noise exposure was positively 27dB SPL lower than the saline groups, and 17dB SPL lower obtained on 10th day of the noise exposure. The exaction rates of 0dB SPL DPOAEs in the sodium salicylate group obtained on 1th and 10th day of the noise exposure are higher than saline group at 5kHz, 6kHz and 7kHz. The stereocilia displacement, confusion and rupture of outer hair cell in sodium salicylate group is more gentle than saline group by scan electronic microscopy; and ultrostructrue changes of outer hair cells and supporting cells are also more alliveated than saline group by transmission electronic microscopy. The total prestin mRNA obtained on 1the day of noise exposure are same between saline and salicylate group. But the prestin mRNA of salicylate group obtained on the 10th day after noise exposure is higher than saline group and baseline.Conclusion: sodium salicylate injected before noise exposure can alliveate significantly the injury to prestin normal expressed cochlea of mouse. Sodium salicylate can elevate prestin mRNA in outer hair cells.Part IV: the effect of sodium salicylate on acoustic injury to prestinknock-out micePurpose: to study the effect of sodium salicylate on acoustic injury to prestin knock-out mice.Methods: using prestin knock-out mice(P20d-P28d). The animals were allocated into three groups (salicylate + noise, saline + noise, and control) and were exposed to a 8 kHz 1/3 octave band noise at 110 dB SPL for 4 hours consecutively. Dynamicchanges of ABR thresholds were monitored. After physiological examination, the cochleae were processed for the morphological examination by scan and transmission electronic microscopy.Results: Mean threshold shifts of ABRs evoked by clicks and 8kHz in the saline group obtained on 1^th day after noise exposure were elevated to 27dB and 34dB, and 29dB and 35dB on 8^th day. Mean threshold shifts of ABRs are no difference between salicylate and saline group. There is no difference between the two group by scan and transmission electronic microscopy obtained on 1^th day. But on 8^th day, the contents loss of outer hair cells are more significant in saline group in salicylate group by transmission electronic microscopy, while manifestations of scan electronic microscopy are still same between the two groups.Conclusion: sodium salicylate injected before noise exposure can alliveate mildly the acoustic injury to prestin knock-out cochlea of mice, which can be reflected by morphological examination by transmission electronic microscopy. And it is more obvious as time goes on after noise exposure.