一氧化氮在豚鼠耳蜗作用的实验研究

为探讨ＮＯ在内耳的作用，采用外淋巴给药途径，观察一氧化氮气体（ＮＯ）、Ｌ－精氨酸、硝普钠及一氧化氮合酶（ＮＯＳ）拮抗剂Ｎ－甲基－Ｌ－精氨酸对耳蜗蜗内电位（ＥＰ）、复合动作电位（ＣＡＰ）及耳蜗微音器电位（ＣＭ）的影响。结果表明，Ｎ－甲基－Ｌ－精氨酸可以使ＥＰ减小５０％，ＣＡＰ振幅降低３３％及ＣＭ振幅略有降低，在此基础上，用Ｌ－精氨酸外淋巴灌流可以逆转Ｎ－甲基－Ｌ－精氨酸所致的改变。ＮＯ持续外淋巴缓释能使Ｎ－甲基－Ｌ－精氨酸导致的ＥＰ、ＣＡＰ及ＣＭ的改变恢复，并超过正常，随之出现快速下降。外淋巴灌流硝普钠后，ＥＰ、ＣＡＰ及ＣＭ短暂升高后逐渐下降，并维持在较低水平。ＣＡＰＮ１波及ＣＭ潜伏期的变化规律与其振幅的变化规律基本一致。结果提示，ＮＯ在生理条件下维持内耳功能，可能参与耳蜗毛细胞微机械特性及敏感性的调节，过量表达可以产生耳蜗毒性     

缺氧豚鼠耳蜗功能瑟结构的改变

观察豚鼠缺氧和窒息致死蜗内电位（ＥＰ）、微音电位（ＣＭ）和总和电位（ＳＰ）的变化，耳蜗的亚微结构改变和听毛细胞存活时间，发现在窒息和死亡过程中；①血管纹对缺氧比毛细胞更敏感；②８５％的ＣＭ对缺氧敏感，并依赖于耳蜗正常代谢，窒息致后仍有１５％ＣＭ残留，其消失的时间外毛细胞的存活时间有关；③－ＳＰ出现极性倒转现象；④－ＥＰ的消失与外毛细胞死亡和ＣＭ消失有关。     

顺铂中毒后豚鼠耳蜗电位变化的特征及形态学实验观察

目的 观察顺铂对耳蜗微音电位（ＣＭ）、总和电位（ＳＰ）及复合动作电位（ＣＡＰ）的影响及毛细胞形态学改变。方法 用人工外淋巴液和顺铂灌流豚鼠耳蜗，分别记录耳蜗第三回中阶的ＣＭ、－ＳＰ及ＣＡＰ，琥珀酸脱氢酶染色观察毛细胞的数量变化，透射电镜观察外毛细胞结构。结果 顺铂灌流１ｈ：≤６０ｄＢ ＳＰＬ声强级刺激时ＣＭ、－ＳＰ和ＣＡＰ幅度均较灌流顺铂前略下降，≥７０ｄＢ ＳＰＬ声强级刺激时幅度比灌流顺铂前明显     

5%CO2混合氧增强豚鼠耳蜗毛细胞抗缺氧能力的实验观察

本研究用急性缺氧动物模型，在耳蜗中阶记录蜗内电位（ＥＰ）、微音电位（ＣＭ）和复合动作电位（ＣＡＰ），分别观察直接缺氧、缺氧前先吸１０ｍｉｎ５％ＣＯ２混合氧及缺氧５ｍｉｎ后再给氧或５％ＣＯ２混合氧时三项指标的变化。结果提示：缺氧前先给１０ｍｉｎ的５％ＣＯ２混合氧，ＥＰ、ＣＭ和ＣＡＰ开始下降的时间比直接缺氧延缓３倍，而缺氧５ｍｉｎ后再给氧或５％ＣＯ２混合氧则无变化。表明缺氧前先给５％ＣＯ２混合氧可增强     

低供氧对清醒豚鼠耳蜗功能的影响

通过圆窗电极保持豚鼠在清醒状态下面罩供应５％氧及９５％氮混合气体３０分钟，记录耳蜗神经动作电位（ＡＰ）、总和电位（ＳＰ）以及微音器电位（ＣＭ）的改变，以提供低氧状态下清醒豚鼠的全耳蜗电生理反应的模型。实验发现：供５％氧后，１６ｋＨｚ声刺激下，ＡＰ振幅急剧下降；８及２ｋＨｚ声刺激下ＳＰ振幅明显增大；ＣＭ有所下降，但程度较轻；并可导致０．２５～３２ｋＨｚ全频程的１５～３０ｄＢ的ＡＰ暂时性阈移；正常供氧后，以上改变逐渐复原。１０只实验豚鼠对５％氧的耳蜗电位反应形式基本一致，但程度有不同。实验发现，低供氧所致ＡＰ变化，在高强度声刺激和阈值强度声刺激时的结果有分离现象，认为上述耳蜗电生理变化是由于低供氧导致了耳蜗能量（ＡＴＰ）减少，蜗内电位降低，并引起了神经传输（传入、传出或交感神经）功能的紊乱。     

卡因酸耳蜗毒性的电生理学研究

目的：观察谷氨酸类受体激动剂卡因酸（ＫＡ）对豚鼠耳蜗的毒性作用。方法：健康杂色豚鼠８只，每只动物经圆膜给予６０ｍＭ ＫＡ１μｌ，于用药前及用药后１２ｈ分别检测听神经复合动作电位（ＣＡＰ），耳蜗微音电位（ＣＭ）和畸变产物耳声发射（ＤＰＯＡＥ）之２ｆ２－ｆ２。结果：用药后ＣＡＰ明显下降或消失（Ｐ〈０．００１），而ＣＭ和ＤＰＯＡＥ无明显变化。结论：ＫＡ对初级听觉传入神经末梢具有选择性毒性作用。     

内皮舒张因子对耳蜗微循环作用的实验研究

为探讨内皮依赖性舒张因子（ＥＤＲＦ）对耳蜗微循环的调节作用，本实验应用活体显微镜结合电视摄象的图像分析技术及血管纹螺旋韧带铺片技术，观察了不同剂量ＥＤＲＦ合成前体Ｌ－精氨酸（Ｌ－Ａｒｇ）及ＥＤＲＦ的合成制抑制Ｌ－硝基－精氨酸（Ｌ－ＮＮＡ）对耳蜗血清（ｃｏｃｈｌｅａｒｂｌｏｏｄｆｒｏｗ，ＣｏＢＦ）的作用，结果显示：Ｌ－Ａｒｇ１００ｍｇ／ｋｇ组药物在给药５分钟后蜗血管流速开始加快，２０分钟时平均增加达     

NOS抑制剂对面神经损伤后运动神经元胞体凋亡的观察

目的：应用一氧化氮合酶（ＮＯＳ）竞争性抑制剂Ｌ－Ｎ＾ω－硝基精氨酸甲酯（Ｌ－ＮＡＭＥ）减少面神经损伤后一氧化氮（ＮＯ）的产生量,以探讨一氧化氮合酶抑制剂在面神经损伤后对面神经运动神经元的作用。方法：选用豚鼠４０只,手术方法制作面了断的豚鼠模型,随机分为两组,在再生内分别施加Ｌ－ＮＡＭＥ和生理盐水（ＳＡＬ）,运用光镜和透射电镜对面神经运动神经元（ＦＭＮｓ）形态学的变化进行定性,定量观察。结果：抑制剂     

化学修饰电极对雏鸡耳蜗神经元一氧化氮的定性检测

目的比较雏鸡和哺乳动物耳蜗生理功能的异同。过去已有哺乳动物耳蜗及前庭神经元中一氧化氮合酶（ＮＯＳ）活动证据的报道，其所释放的一氧化氮（ＮＯ）在听觉和平衡活动中可能发挥重要作用。方法用经化学修饰的碳纤维微电极，定性检测雏鸡离体耳蜗神经元在不同激动剂的诱发下所释放的ＮＯ。根据电极所检测的电流变化的幅度和持续时间判断ＮＯ的释放。结果由激动剂乙酰胆碱和Ｌ精氨酸所诱发的ＮＯ释放反应幅度相似，但乙酰胆碱的高电流持续时间较短，而ＡＴＰ所致者幅度大，持续时间长。预加ＮＧ硝基Ｌ精氨酸，再加上述激动剂，电流无变化。结论雏鸡耳蜗神经元细胞中存在ＮＯＳ。     

低供氧对清醒豚鼠耳蜗功能的影响

通过圆窗电极保持豚鼠在清醒状态下面罩供应５％氧及９５％氮混合气体３０例钟，记录耳蜗神经动作电位，总和电位以及微音器电位的改变，以提供低氧状态下清醒豚鼠的全耳蜗电生理反应的模型。实验发现：供５％氧后，１６ｋＨｚ声刺激下，ＡＰ振幅急剧下降；８及２ｋＨｚ声刺激下ＳＰ振幅明显增大；ＣＭ有所下降；但程度较轻；并可导致０．２５－３２ｋＨｚ全频程的１５－３０ｄＢ的ＡＰ暂时性阈移；正常供氧后，以上改变逐渐复原。１     

Effects of perilymphatic perfusion with cisplatin on the cochlear potential in guinea pigs

The effects of three concentrations of cisplatin, administered by acute perilymphatic perfusion on the endocochlear potential (EP) and the cochlear microphonic potential (CM) of the guinea pig cochleae, at 1 kHz are reported. No change in EP magnitude was discovered and a concentration-dependent reduction in CM amplitude occurred during 60 minutes' perfusion period. The results suggest that cisplatin-induced hearing loss is not necessarily progressive degradation of EP.     

Nitrosoglutathione suppresses cochlear potentials and DPOAEs but not outer hair cell currents or voltage-dependent capacitance

Biochemical and pharmacological evidence support a role for nitric oxide (NO) and glutathione (GSH) in the cochlea. GSH combines with NO in tissue to form nitrosoglutathione (GSNO) that can act as a storage form for GSH and NO. Therefore, we tested GSNO on sound-evoked responses of the cochlea (cochlear microphonic, CM; summating potential, SP; compound action potential, CAP; cubic distortion product otoacoustic emission, DPOAE), on the endocochlear potential (EP), on isolated outer hair cell (OHC) currents and voltage-dependent capacitance, and on Deiters' cell currents. In vivo application of GSNO in increasing concentrations reversibly reduced low-intensity sound-evoked CAP, SP and DPOAEs starting at about 1 mM (CAP) and 3.3 mM (SP, DPOAE). However, even at 10 mM, GSNO had little effect on the EP. In vitro, salicylate (10 mM) but not GSNO (3 and 10 mM) suppressed the early capacitative transients of OHCs. GSNO (3 and 10 mM) had no effect on the whole cell currents of OHCs or Deiters' cells. Results show that GSNO suppresses cochlear function. This suppression may be due to an effect of GSNO on the cochlear amplifier. The actions of GSNO were different from those of other NO donors; therefore, the effects of GSNO may not be mediated by NO. The mechanisms underlying GSNO effects seem to be different from those of salicylate.     

Effects of heavy metal ions in endocochlear DC potential and cochlear microphonics in the guinea pig--the influence of calcium on the cochlea]

Endocochlear DC potential (EP) and cochlear microphonics (CM) in the guinea pig under the influence of the divalent heavy metal cations of manganese, nickel, cobalt and cadmium, and the trivalent cation of lanthanum were investigated. The area from the scala tympani to the scala vestibuli was perfused with control and test solutions. CM decreased gradually to 50-80%, but EP showed no change after perfusion with a solution containing 1 mM of metal ions. At a concentration of 10 mM, EP decreased from 80 mV to 10-20 mV and CM decreased to 15-55%. At 100 mM, EP increased by about 10 mV at the beginning of perfusion, remained steady for 1 min, and then rapidly decreased to 0-10 mV. Meanwhile, CM continued to decrease, finally sustaining a 10-56% reduction. The decrease in EP and CM were irreversible, and perfusion of the area with the standard solution for 20 min had no effect. The osmolarity of the artificial perilymph containing 100 mM of metal ions was twice as high as that of the normal physiological solution. The effects of osmolarity, however, were excluded because perfusion with an artificial perilymphatic solution made hypertonic by either NaCl or sucrose changed neither EP nor CM. The application of 100 mM of metal ions topically to the round window membrane caused no change in EP. The alkali metal ions are known to inhibit inward Ca2+ current. Therefore, the present results suggest that Ca2+ ions play a role in maintaining EP generation in the stria vascularis and CM generation in the organ of Corti.     

An energy-dependent step in aminoglycoside ototoxicity: prevention of gentamicin ototoxicity during reduced endolymphatic potential

Guinea pigs received a bolus of gentamicin (10 mM for 5 min) by perilymphatic perfusion which normally led to an irreversible loss of the cochlear microphonic potential (CM). Various experimental conditions that reduced the endolymphatic potential (EP) were then superimposed on the gentamicin application. Reversible reductions in EP (and, concomitantly, in CM) were induced by asphyxia (3 min), intravenous furosemide (50 mg/kg), and perilymphatic perfusion of aminooxyacetic acid (10 mM). When the administration of gentamicin was initiated at the time of maximal EP reduction the usual irreversible gentamicin-induced decline of CM was prevented. The results indicate that a metabolic process is essential in the expression of gentamicin toxicity. The data are consistent with the inhibition of an energy-dependent transport of the aminoglycoside. Alternatively, the data are also compatible with the hypothesis that entry of gentamicin into hair cells is prevented by a reduction in their transmembrane electrical potential.     

Ototoxic effect of potassium canrenoate on the guinea pig cochlea

Potassium canrenoate (PC) is a diuretic with antialdosterone action, reducing the reabsorption of sodium in the efferent renal tubules. This drug has been reported to damage only the marginal cells of the stria vascularis in the cochlea. The perilymphatic space of the guinea pig cochlea was perfused with an artificial perilymph containing 5 x 10(-3) M potassium canrenoate. Following the onset of perfusion, the endocochlear dc potential (EP) gradually declined to around 10 mV but did not become negative even when the perfusion was continued. A similar decrease in EP was observed in kanamycin-deafened guinea pigs. When the respirator was turned off and perfusion discontinued, a large negative EP appeared during 5 min of anoxia in normal guinea pigs but not in the kanamycin-deafened guinea pigs. The decreased EP recovered to preanoxic level after resumption of ventilation. The cochlear microphonics (CM) also gradually declined in parallel with the EP. The summating potential (SP) showed only a minor change. The potassium ion activity in the endolymph decreased slightly but the sodium ion activity remained unchanged during perfusion. These findings suggest that the main target of the PC is the cells of the stria vascularis.     

甲状腺素对豚鼠耳蜗毛细胞的保护作用

应用耳蜗外淋巴灌流技术、微电极技术及扫描、透射电镜技术，观察先服甲状腺素（10mg)三次后行外淋巴灌流卡那霉素（10^-3g/ml)1小时的豚鼠实验组（T／K）蜗内电位（EP），耳蜗微音电位（CM）和毛细胞的亚微结构变化，并与单纯灌流卡那霉素（10^-3g/ml)的豚鼠对照组（KM）进行比较，发现3组动物EP无明显差异；实验组（T／K）的CM下降较对照组（KM）少，两者有显著差异；实验组动物外毛细胞损伤较对照组动物轻，提示甲状腺素可能直接作用于听毛细胞，减轻卡那霉素对内耳的毒副作用。     

The effect of vasopressin upon the cochlear potentials in the guinea pig

The change in the EP, CM, SP and AP during perilymphatic perfusion of vasopressin (antidiuretic hormone) was examined in the guinea pig. The EP was recorded with a microelectrode through the spiral ligament of the second turn. The CM, SP and AP were measured with the differential electrodes in the basal turn. The perfusion of vasopressin at concentration of more than 10(-5)M produced a reversible decrease in the EP. The extent of the EP decline was dependent upon the concentration of vasopressin. Abolition of the effect of vasopressin upon the EP by the resumption of respiration after transient asphyxia was observed. During the perfusion of vasopressin, the CM and AP decreased, while the negative component of the SP increased. The mechanism causing the effect of vasopressin upon the cochlear potentials is discussed.     

Effects of forskolin and 1,9-dideoxy-forskolin on cochlear potentials.

Endocochlear potential (EP) and cochlear microphonics (CM) were recorded during the perilymphatic perfusion with forskolin known as an adenylate cyclase stimulant. Forskolin produced a reversible EP elevation in a dose-dependent manner. Perfusion with 1,9-dideoxy-forskolin, an analogue of forskolin that does not stimulate adenylate cyclase, had no effect on EP, whereas perfusions with other agents that raise the cAMP-level (IBMX, a phosphodiesterase inhibitor, and dbcAMP) duplicated the effect of forskolin. The vigorous CM during the EP elevation and the large negative EP induced by anoxia superimposed on the elevated EP indicate that the K+ diffusion potential through the hair cell membrane cannot be altered by forskolin. The results suggest that the adenylate cyclase system in the stria vascularis and/or Reissner's membrane may modulate the generation of EP.     

Effect of perilymphatic air perfusion on cochlear potentials

Perilymphatic fistula is now widely recognized to cause acute profound hearing loss. It is still controversial, however, which mechanism it is that causes the reversible hearing loss. Recently, it has been suggested by two groups of researchers that the intrusion of air bubbles into the perilymphatic space (a condition called pneumolabyrinth or aerolabyrinth) through the ruptured labyrinthine window(s) may be one of the causes. In order to examine the mechanism underlying the hearing loss associated with pneumolabyrinth, the perilymphatic space of the guinea pig cochlea was perfused with air and cochlear potentials were recorded. Although perfusion of the scala tympani with air at a rate as high as 200 microliter/min caused an immediate and drastic decrease of the cochlear microphonics (CM) and the compound action potential (AP), it had little effect on the endocochlear dc potential (EP) during perfusion for 20 min. A decline in EP was seen in half the ears, but only when the duration of perfusion exceeded 30 min. These results show that the EP has an amazing resistance to air trapped in the scala tympani of the cochlea and that the initial decrease of hearing acuity after the elimination of perilymph from the scala tympani (or introduction of air into the scala tympani) is probably due to interference in CM and AP generation mechanisms rather than to strial dysfunction.