Nitric oxide synthase inhibitor reduces noise-induced cochlear damage in guinea pigs

CONCLUSION: The results obtained in this study indicate that NG-nitro-L-arginine methyl ester (L-NAME) protects cochlear damage from acoustic trauma through reducing the production of nitric oxide (NO). OBJECTIVES: This study aimed to explore whether NO synthase inhibitor L-NAME could reduce cochlear damage in acoustic trauma. MATERIALS AND METHODS: Seventy guinea pigs (300-350g) were divided randomly into four groups (n=20 in groups I, III, and IV; n=10 in group II). Two days consecutively and 30min before noise exposure (4kHz octave band, 115dB SPL 5h), subjects received an injection of 5ml saline/kg (groups I and III) or 10mg/kg L-NAME (groups II and IV). Sham-exposed guinea pigs were listed as groups I and II. Protection was assessed physiologically by the change in auditory brainstem response (ABR) threshold and histologically by survival of outer hair cells (OHCs). NO level of cochlear tissue was assayed 3days after noise exposure. RESULTS: Group III showed significantly greater OHC loss, threshold shifts and NO level compared with group I and group IV. Compared with group III, noise-induced elevation in NO level in the cochlea was significantly attenuated by L-NAME (p<0.001).     

一氧化氮合酶抑制剂和神经营养因子3对噪声暴露下豚鼠耳蜗的保护作用

目的观察一氧化氮合酶抑制剂——N-硝基左旋精氨酸甲酯（N^G-nitro-L-arginine methyl ester，L-NAME）和神经营养因子3（neurotrophin 3，NT3）对噪声性听力损失的保护作用。方法80只雄性杂色豚鼠按区组随机分为非噪声组（n=20）和噪声暴露组（n=60），噪声暴露组又分为生理盐水组（n=20）、L-NAME组（n=20）、L-NAME＋NT3组（n=20）。L-NAME组和L-NAME＋NT3组动物在噪声暴露（4kHz倍频程、声压级115dB，5h）之前2d和噪声暴露前30min给予L-NAME 10mg／kg（腹腔注射），生理盐水组动物给予等体积的生理盐水。NT3（10μg／ml）在噪声暴露前4d经微量渗透泵（200μl，0．5μl／h）输入到L-NAME＋NT3组动物的右侧耳蜗鼓阶，持续到噪声暴露后10d。噪声暴露前和暴露后10d测试听性脑干反应（auditory brainstem response，ABR），暴露后3d测试耳蜗组织一氧化氮（nitric oxide，NO）水平，最后一次ABR测试后计数耳蜗毛细胞的存活率。结果无噪声暴露组动物无明显的听力改变和毛细胞缺失；生理盐水组动物的ABR阈移、毛细胞缺失率及耳蜗组织NO水平均高于L-NAME组和L-NAME＋NT3组，差异有统计学意义（P值均〈0．01）；与L-NAME组相比，L-NAME＋NT3组豚鼠的ABR阈移减小，差异有统计学意义（P〈0．01），而耳蜗组织NO水平和毛细胞缺失率差异则没有统计学意义（P=0．197及P=0．095）。结论与单独给予L-NAME相比，联合使用NT3可以更大程度减轻噪声对豚鼠耳蜗的损伤。     

Ascorbic acid reduces noise-induced nitric oxide production in the guinea pig ear

OBJECTIVES: Noise-induced hearing loss can be caused, among other causes, by increased nitric oxide (NO) production in the inner ear leading to nitroactive stress and cell destruction. Some studies in the literature suggest that the degree of hearing loss (HL) could be reduced in an animal model through ascorbic acid supplementation. To identify the effect of ascorbic acid on tissue-dependent NO content in the inner ear of the guinea pig, we determined the local NO production in the organ of Corti and the lateral wall separately 6 hours after noise exposure. STUDY DESIGN: Prospective animal study in guinea pigs. METHODS: Over a period of 7 days, male guinea pigs were supplied with minimum (25 mg/kg body weight/day) and maximum (525 mg/kg body weight/day) ascorbic acid doses, and afterwards exposed to noise (90 dB sound pressure level for 1 hour). The acoustic-evoked potentials were recorded before and after noise exposure. The organ of Corti and the lateral wall were incubated differently for 6 hours in culture medium, and the degree of NO production was determined by chemiluminescence. RESULTS: Ascorbic acid treatment reduced the hearing threshold shift after noise exposure depending on concentration. When the maximum ascorbic acid dose was substituted, NO production was significantly reduced in the lateral wall after noise exposure and slightly reduced in the organ of Corti. CONCLUSIONS: Oral supplementation of the natural radical scavenger ascorbic acid reduces the NO-production rate in the inner ear in noisy conditions. This finding supports the concept of inner ear protection by ascorbic acid supplementation.     

白噪声对豚鼠耳蜗核一氧化氮合酶活性的影响

采用硫辛酰胺脱氢酶组织化学方法及图象分析技术，研究白噪声暴露后豚鼠耳蜗核一氧化氮合酶（ＮＯＳ）神经元及ＮＯＳ活性的变化与听阈的关系，探讨豚鼠耳蜗核ＮＯＳ神经元在白噪声损伤过程中可能的作用。结果表明，白噪声暴露后耳蜗核ＮＯＳ阳性神经元的数量及染色强度明显增加，２周达到高峰，３￣４周持续高表达，至５周有所恢复，仍高于正常水平。白噪声暴露后７ｄ以内，耳蜗核ＮＯＳ活性与ＡＢＲ阈值有分离现象，７ｄ后，ＮＯＳ     

Gentamicin increases nitric oxide production and induces hearing loss in guinea pigs

Objectives/Hypothesis: Gentamicin application is an important therapeutic option for Ménière's disease. However, even if given at intervals, a destruction of the cochlea was often observed in various animal models together with an increased content of nitric oxide (NO) and reactive oxygen species. The present study was undertaken to identify the correlation between hearing threshold alteration and the NO production in the lateral wall and organ of Corti of the guinea pig in response to gentamicin application. Study Design: Prospective animal study in guinea pigs. Methods: A single dose of gentamicin (10 mg/kg body weight) was injected intratympanally into male guinea pigs and the auditory brainstem responses were recorded before treatment and 1, 2, and 7 days after application. The organ of Corti and the lateral wall were removed from the bulla, incubated separately for 6 hours in cell culture medium and the amount of NO production was determined by chemiluminescence. Results: Gentamicin application resulted in a hearing threshold shift beginning on the second day after gentamicin application. This hearing impairment correlates simultaneously with an increased NO₂^? content—the stable oxidation product of NO—in the lateral wall. In the organ of Corti, a slight increase in NO₂^? production was seen as early as on day 1 after gentamicin injection. Conclusions: The correlation between hearing threshold shift and NO production in the cochlea leads to the assumption that increased NO contributes to gentamicin‐induced hearing impairment.     

噪声对豚鼠耳蜗核一氧化氮合酶阳性神经元及其基因表达的影响

为探讨豚鼠耳蜗核一氧化氮合酶（ｎｉｔｒｉｃｏｘｉｄｅｓｙｎｔｈａｓｅ，ＮＯＳ）神经元在白噪声损伤过程中可能的作用，采用硫辛酰胺脱氢酶（ＮＡＤＰＨ－ｄ）组织化学方法及半定量多聚酶链反应（ＰＣＲ）技术，研究白噪声暴露后豚鼠耳蜗核ＮＯＳ神经元及ＮＯＳｍＲＮＡ含量的变化以及与听阈的关系。结果表明，噪声暴露后耳蜗核ＮＯＳ阳性神经元的数量及染色强度明显增加，２周达高峰，３～４周持续高表达，５周有所恢复，但仍高于正常水平。耳蜗核ＮＯＳｍＲＮＡ含量的变化规律与形态学观察结果一致，２周组ＮＯＳｍＲＮＡ含量最高，是正常的５．０２倍。噪声暴露后ＡＢＲ阈移与耳蜗核ＮＯＳｍＲＮＡ含量呈正相关（ｒ＝０．９６５５，Ｐ＜０．０１）。提示耳蜗核ＮＯＳ阳性神经元可能参与了耳蜗神经损伤修复的调节，ＮＯＳ基因的高表达是噪声性聋发病机制中不可忽视的重要因素之一。     

Extended use of systemic steroid is beneficial in preserving hearing in guinea pigs after cochlear implant

Conclusion: Seven-day administration of systemic steroids was more effective in preserving hearing for 12 weeks after cochlear implantation (CI) than a 3-day delivery.

Objectives: To determine the effectiveness of extended delivery of systemic steroids to preserve hearing in guinea pigs after CI.

Methods: Dexamethasone (4?mg/ml) was delivered parenterally via a mini-osmotic pump for either 3 or 7 days. A dummy CI electrode was inserted via cochleostomy approach in 8-week-old guinea pigs. Auditory thresholds were assessed from tone burst auditory brainstem responses (2, 8, 16, 24, and 32?kHz) at 1?day prior to CI, and 1, 4, and 12 weeks after implantation. Histologic evaluation of the cochleae was carried out.

Results: No differences were observed in hearing thresholds among groups before CI. Significant hearing preservation was achieved at 8, 16, 24, and 32?kHz only in the 7-day infusion group compared with the control group at 1 week after CI. The same trend was maintained at 4 weeks (16, 24?kHz) and 12 weeks (16, 24, and 32?kHz). Histologic review of the 7-day infusion group revealed less fibrosis and ossification in the scala tympani and the preservation of more spiral ganglion cells, compared with the control group.     

西地那非对豚鼠噪声性听觉损伤阈移的影响

目的 探讨西地那非(sildenafil)对豚鼠噪声性听觉损伤阈移的影响.方法 将豚鼠按随机数字表法分为对照组、噪声暴露组和西地那非给药组,每组10只.西地那非组及噪声组豚鼠在白噪声(A计权声压级110 dB)暴露1周后分别腹腔注射西地那非10 mg/(kg·d)及生理盐水4mL/(kg·d),连续给药4周.分别测试噪声暴露前1日、噪声暴露后1、2及4周听性脑干反应(ABR)阈值,并通过扫描电镜观察噪声暴露后4周豚鼠耳蜗毛细胞的形态变化.结果 噪声暴露1后,噪声暴露组豚鼠ABR阈值(声压级)平均提高19.1 dB,随着时间推移,阈移逐渐加大,暴露后4周,阈值平均提高22.0 dB;西地那非组噪声暴露后ABR阈值提高19.8 dB,给药后阈移逐渐减小,给药后4周,阈值仅平均提高4.8 dB.西地那非组与噪声暴露组相比,除噪声暴露结束后这一时间点以外,其余给药后各时间点ABR阈值差异均具有统计学意义(P值均＜0.05).扫描电镜显示,噪声组豚鼠耳蜗内、外毛细胞均出现听毛紊乱、融合及缺失;而西地那非组耳蜗病变较轻,听毛仅有轻微倒伏、融合现象.结论 西地那非能够减轻噪声对豚鼠耳蜗毛细胞的损害,降低噪声性听觉损伤引起的ABR阈值升高.     

Improvement in inner ear blood flow by nitric oxide following experimentally induced cochlear thrombosis in anesthetized guinea pigs

The nitric oxide (NO) donor sodium nitroprusside (SNP) applied to the round window membrane has recently been found to increase cochlear blood flow (CoBF) in normal guinea pigs and in normal and presbyacusic mice. This study examined the effect of topical applications of SNP on experimentally impaired CoBF in anesthetized guinea pigs. Small (3 μl) portions of 3% SNP were applied to the round window niche of both normal and thrombosed cochleas. Local vascular impairment was produced by ferromagnetic thrombosis of cochlear blood vessels and the microcirculation measured using laser Doppler flowmetry. Ferromagnetic thrombosis resulted in a mean decrease of CoBF to 52% of baseline. There was a clear improvement in mean CoBF to 84% of baseline by the topical application of SNP that depended on the degree of ischemic damage produced. Under neuroleptanalgesia and ketamine-xylazine anesthesia, significant increases in CoBF were measured in normal ears as well as in the thrombosed ones. However, several SNP applications were needed to improve the impaired CoBF, while a single portion was sufficient in the normal cochlea to cause a drastic increase in mean CoBF to 234% of baseline. In urethane-anesthetized animals, no flow increase was found despite repeated drug administration. Careful evaluation of the laser Doppler signals was necessary to accurately determine the concentrations of the moving blood cells and their mean velocities. Received: 8 August 1997 / Accepted: 11 February 1998     

Increased prevalence of early cochlear damage in young patients with type 1 diabetes detected by distortion product otoacoustic emissions

Abstract

Objective: To evaluate the hearing of adolescents with diabetes mellitus type 1(DM1) by otoacoustic emissions (OAEs), and by comparing different tests with pure-tone audiometry to identify potential early cochlear impairments. Design: Pure-tone audiometry, transient evoked otoacoustic emissions (TEOAEs), and distortion product otoacoustic emissions (DPOAEs) were performed in a group of adolescents with and without DM1. Clinical characteristics, disease duration, and glycated haemoglobin levels were studied. Study sample: Participants were 40 adolescents with DM1 and 40 healthy subjects. Results: Sensorineural hearing loss, affecting frequencies of 6000 and 8000 Hz, was found only in DM1 subjects when compared to the controls (7.7% vs. 0%, p < 0.05). A higher prevalence of cochlear damage was detected by DPOAE responses, 32% belonging from the diabetic group, vs. 3.7% in the control group. Absent TEOAE responses were observed in only three individuals, all from the diabetic group (5.1% of the tests performed in the diabetic group). Additionally, hearing thresholds were better in diabetic subjects with good control when compared to ones with regular or poor control (p = 0.00). Hearing thresholds were higher in poorly controlled diabetics when compared to subjects with good (p = 0.000) or regular control (p = 0.006). Conclusion: Early evidence of cochlear damage was detected in adolescents with DM1 leading to hearing loss at high frequencies. Abnormal DPOAEs responses were found more frequently than the alterations in TEOAEs and pure-tone audiometry, suggesting that DPOAEs evaluation is the most sensitive and it could be used for monitoring the progression of cochlear damage during the early stages of hearing impairment.     

Nitric oxide mediates capsaicin-induced increase in cochlear blood flow

Capsaicin has been previously shown to increase cochlear blood flow (CBF) in a dose-dependent manner. The aim of this study was to define the role of nitric oxide (NO) in capsaicin-induced changes in CBF. This was investigated in the anesthetized guinea pig, utilizing laser Doppler flowmetry. Application of capsaicin (64.8 and 6.48 nmol in 2 μl of saline) to the round window membrane (RWM) caused increases in CBF (34 ± 2.8% of baseline (BL) and 28 ± 2.3% BL, respectively (P < 0.001)). Application of the NO synthase inhibitor, N^G-nitro-l-arginine methyl ester (l-NAME) (10 mg/kg intravenously or topically to the RWM) reduced blood flow in the cochlea, as previously reported. After pretreatment with i.v. l-NAME, the effect of capsaicin on CBF was significantly decreased. With the dose of capsaicin at 64.8 nmol, the increase in CBF fell from 34 ± 2.8% BL to 6.9 ± 1.5% BL (P < 0.001), and at 6.48 nmol it fell from 28 ± 2.3% BL to 4.8 ± 1.6% BL (P < 0.001). RWM l-NAME application also decreased the capsaicin vasodilatation effect. A capsaicin dose of 64.8 nmol resulted in only a 10 ± 2.5% BL increase in CBF, and with 6.48 nmol capsaicin the increase was 7.8 ± 2.2% of BL (P < 0.001). Capsaicin-sensitive sensory neurons in other systems are generally known to release substance P (SP), which in turn elicits release of endothelium derived relaxing factor (NO). The results of this study indicate that NO is a mediator of capsaicin-sensitive sensory neuronal function in CBF regulation.     

内源性一氧化碳对变应性鼻炎豚鼠诱导型一氧化氮合酶表达的影响

目的 制备豚鼠变应性鼻炎(allergic rhinitis,AR)动物模型,研究在AR豚鼠模型中内源性一氧化碳(carbon monoxide,CO)对诱导型一氧化氮合酶(inducible nitric oxide synthase,iNOS)表达的影响.方法 24只豚鼠以随机数字表法分为4组,每组6只.第1组以生理盐水处理作为正常对照组,第2(AR组)、3、4组以卵清蛋白(ovalbumin,OVA)致敏,制成AR动物模型,第3、4组再分别以血红素氧合酶1(hemeoxygenase 1,HO-1)诱导剂氯化血红素和抑制剂锌原卟啉干预处理,分别作为HO诱导组和HO抑制组,分别测定各组豚鼠血浆中碳氧血红蛋白(carboxyhemoglobin,COHb)的百分含量(用来代表血浆中CO含量),并采用实时荧光定量反转录聚合酶链反应(RT-PCR)法测定鼻黏膜中HO-1和iNOS的相对表达量.结果 第2、3、4组豚鼠AR造模成功.血浆COHb含量(x-±s,以下同)第2组(2.27%±1.13%)高于第1组(1.08%±0.24%),差异有统计学意义(q=4.10,P＜0.01);第3组(3.17%±0.68%)高于第2组,差异有统计学意义(q=3.12,P＜0.05).鼻黏膜中HO-1、iNOS的相对表达量(x-±s,以下同)第2组[分别为(7.80±1.60)×10~(-3)和(5.81±0.05)×10~(-3)]高于第1组[分别为(1.96±0.71)×10~(-3)和(0.97±0.05)×10~(-3)],差异有统计学意义(q值分别为5.52、7.21,P值均＜0.01),第3组[分别为(11.89±4.78)×10~(-3)和(7.42±0.70)×10~(-3)]高于第2组,差异有统计学意义(q值分别为3.86、2.22,P值均＜0.05),第4组[分别为(3.82±0.98)×10~(-3)和(2.34±0.04)×10~(-3)]低于第2组,差异有统计学意义(q值分别为3.76、5.18,P值均＜0.05).结论 内源性CO在AR中影响iNOS的表达.     

In vitro expression of inducible nitric oxide synthase in the nasal mucosa of guinea pigs after incubation with lipopolysaccharides or cytokines

In order to demonstrate the involvement of nitric oxide synthases (NOS) – in particular the inducible isoform (iNOS) – in inflammatory processes within the nasal airways, we used organ-bath incubation to study isolated inferior turbinates and mucosa of the maxillary sinus of guinea pigs. The pattern of the expression in various substructures of the nasal mucosa was of special interest. Mucosa was incubated for 6 h with lipopolysaccharides (LPS) produced by E. coli, interleukin II (IL-2) or tumor necrosis factor-alpha (TNF-α). Saline was used as the control solution. Following incubation the specimens were fixed in buffered 4% formaldehyde solution over a period of 4 h. Tissues were next exposed to nicotinamide adenine dinucleotide phosphate (NADPH)-diaphorase-reaction and immunostained with specific antibodies to iNOS. Results then showed a clearly increased or initiated expression of iNOS in epithelium, glands, leucocytes and blood vessels of treated tissues in comparison to the control specimens. The inflammatory mediator LPS and the cytokines Il-2 or TNF-α alone were found to be capable of increasing the expression of iNOS, although the effects of LPS clearly exceeded those of the cytokines. This finding implicates iNOS-generated nitric oxide as a key factor for causing nasal swelling, secretion and obstruction during nasal infections and allergic episodes. Received: 18 November 1997 / Accepted: 22 April 1998     

微量元素硒对噪声性聋防护作用的实验研究

目的探讨微量元素硒（Se）对豚鼠噪声性听力损伤的保护作用。方法雄性杂色豚鼠40只,体重250～350g,随机分为正常对照组、Se组、Nacl＋噪声组和Se＋噪声组,每组10只。正常对照组不作任何处理,Se组仅连续5d腹腔注射亚硒酸钠（Na2SeO30.7mg/kg,1次/d）,Nacl＋噪声组在噪声暴露前连续5d腹腔注射等量生理盐水（0.9%Nacl）,Se＋噪声组在噪声暴露前连续5d腹腔注射Na2SeO3,均为每日1次。采用窄带噪声,中心频率4kHz,强度为120dBSPL,持续4h。所有动物均于噪声暴露前行脑干诱发电位检测（ABR）;噪声暴露后每组各取5只立即断头处死,取出双侧耳蜗测谷胱甘肽过氧化物酶（GSH-Px）活性,各组剩余的5只于1、10d后测ABR,最后一次测完ABR后处死,取基底膜铺片染色。结果 Nacl＋噪声组和Se＋噪声组于1、10d后的ABR阈值较噪声暴露前有明显提高,差异有统计学意义;Nacl＋噪声组在噪声暴露前后的阈移较Se＋噪声组高,差异有统计学意义。Se组的GSH-Px活性比正常对照组及Se＋噪声组比Nacl＋噪声组高,差异有统计学意义。耳蜗基底膜铺片可见Nacl＋噪声组和Se＋噪声组中的凋亡、坏死和缺失的细胞,Nacl＋噪声组的受损率高于Se＋噪声组,具有统计学差异。结论硒能增加耳蜗组织中GSH-Px的活性,而GSH-Px作为一种抗氧化酶可能中和一部分因噪声刺激而产生的氧自由基/活性氧,对噪声性耳蜗损伤具有一定的防护作用。     

Lipopolysaccharide-induced expression of inducible nitric oxide synthase in the guinea pig organ of Corti

The purpose of the investigation was to ascertain whether inoculation of bacterial lipopolysaccharide (LPS) into the cochlea of the guinea pig could elicit formation of inducible nitric oxide synthase (iNOS). Immunohistochemical study revealed that immunoreactivity to iNOS was seen below outer hair cells representing nerve fibers and synaptic nerve endings. iNOS-staining could also be observed in phalangeal dendrites of Deiter’s cells pointing to the cuticular membrane, Hensen’s cells and on stria vascularis 48 h after inoculation with LPS. Immunohistochemical investigation with a specific anti-nitrotyrosine antibody also revealed intense immunoreactivity identical to that of iNOS, suggesting formation of peroxynitrite in the organ of Corti by the reaction of NO with O₂⁻. On the basis of these findings, it can be concluded that NO together with O₂⁻, which form the more reactive peroxynitrite, are the most important pathogenic agents in LPS-induced damage of cochlea in the guinea pig.     

The effect of noise-induced sloping high-frequency hearing loss on the gap-response in the inferior colliculus and auditory cortex of guinea pigs

Gap detection has been used as an evaluation tool for temporal processing in subjects with sensorineural hearing loss (SNHL). However, the results from other reports are varied making it difficult to clearly define the impact of SNHL on the temporal processing ability of the auditory system. Specifically, we do not know if and how a high-frequency hearing loss impacts, presumably through off-channel interaction, the temporal processing in low-frequency channels where hearing sensitivity is virtually normal. In this experiment, gap-evoked responses in a low-frequency band (0.5–8 kHz) were recorded in the inferior colliculus (IC) and auditory cortex (AC) of guinea pigs through implanted electrodes, before and after a slopping high-frequency hearing loss, which was induced by over-stimulation using a 12-kHz-tone. The results showed that the gap thresholds in the low-frequency region increased gradually and became significantly higher 8 weeks after the induced high-frequency hearing loss. In addition, the response latency was slightly increased in the IC but this was not true for the AC. These results strongly indicate that a high-frequency hearing loss exerted an off-channel impact on temporal processing in the low-frequency region of the auditory system.     

Lipopolysaccharide-induced expression of nitric oxide synthase II in the guinea pig vestibular end organ

The purpose of the investigation was to ascertain whether inoculation of bacterial lipopolysaccharide (LPS) into the vestibular organ of the guinea pig might induce formation of nitric oxide synthase (NOS) II. Forty-eight hours after the animals were injected with 1 mg transtympanic LPS, varying degrees of impaired caloric responses were observed with similar degeneration of vestibular hair cells. These effects could be blocked with N-nitro-l-arginine methylester, a competitive inhibitor of NOS. Findings suggested that NOS II, which was not normally detectable in the guinea pig vestibular organ but was present following inoculation of LPS, produced the nitric oxide as the toxic factor causing cell damage. If true, LPS may represent a reproducible method for studying the vestibular pathogenesis of inner ear disease. Received: 22 July 1997 / Accepted: 18 September 1997     

一氧化氮合酶和心钠素在豚鼠耳蜗的分布

目的 观察豚鼠耳蜗局部心钠素（atral natruretc peptde，ANP）和一氧化氮合酶（nitric oxide synthase，NOS）免疫组化反应产物的分布，为研究ANP和NOS在豚鼠耳蜗局部血流、淋巴以及神经调节中的相互作用提供形态学依据。方法 采用免疫组织化学双标法检测ANP和NOS在正常豚鼠耳蜗的分布特征。结果 在耳蜗各转螺旋动脉和血管纹．螺旋缘、螺旋韧带和Corti器显示双阳性染色，螺旋神经节细胞及囊斑神经上皮细胞膜及轴突NOS阳性染色，胞质ANP阳性染色；盖膜、前庭膜阴性染色。结论 ANP和NOS在内耳血 流调节，内、外淋巴平衡调节以及神经信号传递等方面可能具有重要作用，二者之间可能存在密切的相互作用机制，其分布特点与功能密切相关。     

Immunoelectron microscopic localization of nitric oxide synthase III in the guinea pig organ of Corti

Nitric oxide synthase III (NOS III) was identified in the guinea pig cochlea on an ultrastructural level using a post-embedding immunolabeling procedure. Ultrathin sections of London Resin (LR) White-embedded specimens were incubated with various concentrations of a commercially available antibody to NOS III and the immunoreactivity visualized by a gold-labeled secondary antibody. Analysis of ultrathin sections of the organ of Corti in the second turn of the cochlea showed that NOS III could be localized in the endothelial cells of the blood vessels under the basilar membrane, which was comparable to its location in similar cells types in various biological systems. Besides this, NOS III was also found in the cytoplasm and in the nuclei of inner and outer hair cells. Immunoreactivity was not distributed homogeneously within receptor cells. Numerous gold particles could be identified at the border of the cuticular plates, in the middle parts of the stereocilia and in the cytoplasm. Gold-labeled anti-NOS III antibodies in these sites were seen mostly on the cytoplasmic side of the submembranous cisterns in the vicinity of mitochondria and in the central parts of the hair cells, whereas the cisterns were nearly free from any immunoreactivity. NOS III was also detected in the efferent and afferent nerve endings that were located at the basal and basolateral side of the outer hair cells. Some immunoreactivity was visible in different nerve fibers of the inner and outer spiral tunnels. Besides this, gold-labeled antibodies were also present in the cuticular plate of inner and outer pillar cells, in the cytoskeletal elements located in the apical parts of Deiters cells, forming the lamina reticularis, and in the cytoskeletal-containing region of the cytoplasm of those Deiters cells located at the basal side of the outer hair cells. The role of the NOS III immunoreactivity identified in the organ of Corti was consistent with respect to hair cell and tissue modulation. Received: 24 September 1997 / Accepted: 26 June 1998