P物质抗体对豚鼠耳蜗核下丘核团内听觉诱发电位调谐曲线的影响

目的探索Ｐ物质在听觉脑干中枢中对声信号的频率分析作用。方法采用短音（ｔｏｎｅｐｉｐ）刺激、短纯音前掩蔽法和豚鼠耳蜗核（ｃｏｃｈｌｅａｒｎｕｃｌｅｕｓ,ＣＮ）、下丘（ｉｎｆｅｒｉｏｒｃｏｌｉｃｕｌｕｓ,ＩＣ）核团内电极,记录ＣＮ及ＩＣ核团内听觉诱发电位。观察核团内注射微量Ｐ物质抗体或对照注射等量兔血清后ＣＮ和ＩＣ核团内听觉诱发电位调谐曲线的变化。结果注入Ｐ物质抗体后,当探测音为１ｋＨｚ和２ｋＨｚ时,ＩＣ核团和ＣＮ核团内诱发电位调谐曲线的Ｑ１０ｄＢ值基本不变;当探测音为４ｋＨｚ和６ｋＨｚ时ＣＮ核团和ＩＣ核团内诱发电位调谐曲线的Ｑ１０ｄＢ值明显减小,与注入对照兔血清者相比差异非常显著（Ｐ＜０．０１）。高频侧斜率与低频侧斜率亦有相应改变。结论Ｐ物质可能作为听觉传入系统的神经递质或参与听觉脑干中枢的高频信号分析。     

SP抗体对豚鼠耳蜗核、下丘核团内听觉诱发电位调谐曲线的影响

为探索P物质（SP）在听觉脑干中枢中对声信号的频率分析作用，采用短音刺激、短纯音前掩蔽法和豚鼠耳蜗核（Cochlea nucleus,CN)、下丘（Inferior coliculus,IC)核团内电极，记录耳侵略者 内的听觉诱发电位（CN－AEP）及下丘核团内听觉诱发电位（IC－AEP）。采用核团内注射微量抗SP抗体和等量兔血清作为对照观察CN－AEP调谐曲线（IC－AEP－TC）、IC－AEP调谐曲线（CN-AEP－TC）的变化。结果表明：注入抗SP抗体后，当探测音为1kHz和2kHz时，IC－AEP－TC与CN－AEP－TC的Q10 dB值基本不变，当探测音为4kHz和6kHz时CN－AEP－TC的Q10 dB值明显减小，与注入兔血清对照组相比有显著性差异（P＜0.05)，且IC－AEP－TC的Q10dB值减小更显著，高频端斜率（HFS）与低频端斜率（LFS）亦有相应改变。结果提示：SP抗体可能作为听觉传入系统的神经递质，且主要与听觉脑干中枢的高频信号分析有关。     

豚鼠下丘核团内听觉诱发电位时域及频域分析

用计算机叠加平均技术和脑干神经核团立体定位技术，记录10只豚鼠下丘核团内听觉诱发电位（IC－AEP）。对其时域中主波的潜伏期，振幅进行分析，并与豚鼠脑干听觉诱发电位（BAEP）时域比较，认为IC－AEP是BAEP之V波的主要成份。对侧耳给声刺激时，诱发的IC－AEP的振幅较高，提示在耳蜗核上行纤维中，大部分在到达下丘之前已交叉至对侧。用自回归模型谱估计（AR谱估计）及数字滤波技术对IC－AEP进行频域分析，发现豚鼠IC－AEP的频谱成份主要是在1000Hz以下，在AR变图上有3个峰：F0，F1和F2，谱峰分别位于160Hz，465Hz，745Hz左右，略低于豚鼠BAEP的相应谱峰频率，这可能由于BAEP的F1，F2是由多个神经元核团的不同谐振频率所合成，这一推测有待于其它神经核团进一步研究证实。     

皮层听觉诱发电位在人工耳蜗植入中的应用

皮层听觉诱发电位（cortical auditory evoked potential, CAEP）是一种非侵入性脑电测量方式,能够通过波形的阈值、潜伏期与振幅评估听觉皮层的功能。近年来,CAEP的测试方式逐渐成熟,应用更加广泛。在人工耳蜗植入患者中,CAEP能够用于术前、术后听觉及言语能力、双耳听觉、音乐感知以及听觉可塑性的评估。相比较听性脑干反应（auditory brainstem response, ABR）、中潜伏期反应（middle latency response,MLR）等其它听觉诱发电位而言,CAEP潜伏期最长,能够反映完整听觉通路的情况、评价听觉皮层等高级中枢的功能及成熟度,具有独特优势。本文就CAEP在人工耳蜗患者中的研究进展进行综述。     

听觉中潜伏期诱发电位与人工耳蜗植入

人工耳蜗植入后听力及言语能力恢复与中枢听皮质功能密切相关,听觉中潜伏期诱发电位可反映中枢初级听觉皮层的功能状态。本文综述了听觉中潜伏期诱发电位的起源,声刺激和电刺激,测试方法,影响因素以及临床意义,并讨论其与人工耳蜗植入的相关关系。     

等调制深度时间调制转换曲线评估豚鼠下丘和听皮层的时间分辨率

目的探讨以听觉系统对调幅信号响应幅值随调制频率的改变计算等调制深度时间调制转换函数（temporal modulation transfer function，TMTF）来客观评估听觉系统时间分辨率的可行性。方法豚鼠下丘和听皮层分别埋植慢性电极，记录正弦调幅纯音（载频为8kHz，调制深度固定为100％）诱发电位，反应幅值经快速傅立叶变换（fast Fourier transform，F丌）得出相对反应幅值，并以相对反应幅值和调制频率绘制出等调制深度TMTF。记录正弦调幅纯音每个调制频率的调制深度从100％至10％的诱发电位，得出与传统的调制深度阈值TMTF方法相当的等幅值TMTF，与等调制深度TMTF相比较，判断等调制深度TMTF方法的有效性。结果豚鼠下丘和听皮层的等调制深度TMTF与等幅值TMTF都分别表现为带通和低通特性；等调制深度TMTF的截止频率与等幅值TMTF的截止频率差异无统计学意义（P值均〉0．05）。豚鼠听皮层等调制深度TMTF的截止频率与传统的行为学结果基本一致。结论以100％调制深度的正弦调幅纯音诱发反应幅值与调制频率绘制等调制深度TMTF是一种有效的客观评估听觉系统时间分辨率的方法，其中豚鼠听皮层的等调制深度TMTF可用于行为学预测。     

电刺激耳蜗记录下丘的空间调谐曲线

目的探索耳蜗电刺激的听觉中枢电活动机理，为多道人工耳蜗电刺激的部位代码提供生理依据。方法利用记录单单位和多单位电位反应的方法，分别描记１７只猫听觉下丘核团对耳蜗内单极电刺激，耳蜗内双极电刺激和纯音刺激反应的空间调谐曲线。结果耳蜗内双极电刺激能兴奋下丘中的特定区域，类似于对纯音刺激的反应；而耳蜗内单极电刺激使下丘细胞广泛地被兴奋，不能提供部位代码。结论使用双极电极时，刺激电流的局限范围是提高部位代码的关键；耳蜗内单极电刺激部位代码的电生理结果与心理物理学的结论以及人工耳蜗植入患者的临床效果相矛盾，对此的解释有待进一步研究。     

豚鼠下丘神经元声音时程调谐特性及γ氨基丁酸能抑制的作用

目的观察豚鼠下丘神经元的时程调谐特性并探讨γ氨基丁酸（gamma—aminobutyricacid，GABA）能抑制对时程调谐的作用。方法23只健康豚鼠，雌雄不拘。在麻醉状态下采用复合式多管微电极记录下丘中央核神经元响应：通过对等强度不同频率短纯音的响应确定神经元的最佳反应频率；通过对等强度不同时程信号的响应确定神经元的时程调谐特性。经微电泳仪将GABA—A受体阻断剂（荷包牡丹碱）注射到所记录的神经元周围，通过比较注射前后神经元响应模式的变化确定GABA能抑制对神经元时程调谐的作用或影响。结果豚鼠下丘神经元，特别是持续响应神经元的时程调谐特性往往表现在对声信号的瞬态给声响应（给声反应）中。在记录到的207个神经元中，共有93个神经元细胞表现出明显的时程选择特性。在其中67个神经元成功观察了注射荷包牡丹碱后的响应变化，发现44个细胞时程选择特性消失或者是转变为时程调谐弱的模式。结论与以往在蝙蝠的报道不同，豚鼠下丘神经元的时程调谐特性往往表现在其瞬时给声响应之中。GABA能抑制是时程选择性形成的重要因素之一。     

人工耳蜗植入术中电刺激中潜伏期听觉诱发电位的检测

目的 建立人工耳蜗植入术中电刺激中潜伏期听觉诱发电位(electrical evoked middle latency response,EMLR)的检测方法,为进一步评估植入者听觉传导通路及高位听觉反应的特点奠定基础.方法 20例人工耳蜗植入者,其中语前聋14例,语后聋6例,全部使用Cochlear公司Nucleus CI24R (CA)人工耳蜗.术中将言语处理器与计算机接口及听觉诱发电位仪触发端口连接,电极植入后,选取第3号电极,先常规进行电刺激听神经复合动作电位(electrically evoked auditory nerve compound active potentials,ECAP)测试初步了解听神经功能状态,然后进行EMLR检测.选择电刺激听性脑干反应(electrical auditory brainstem response,EABR)模式,采用单极刺激,双相交替脉冲电流方波,脉宽50 ～ 100μs,强度(电流级,current leve1,CL)由ECAP阈值上20 CL起,以5 CL为步长递减或递增,听觉诱发电位仪记录EMLR波形.对ECAP阈值与EMLR阈值进行相关性分析.另外选择6名听力正常健康受试者,行声刺激中潜伏期听觉诱发电位(auditory middle latency response,AMLR)测试,作为EMLR波形和潜伏期的声刺激对照.结果 6例听力正常受试者均可记录到AMLR波形,平均反应阈为(12.5±8.6)dBnHL,接近纯音测听阈值(10.8 ±7.3)dBHL.20例人工耳蜗植入者均可记录到EMLR波形,与AMLR波形相似,但各波潜伏期和波间期缩短,波幅变化不大;语前聋较语后聋总体上波幅小,潜伏期长.EMLR平均阈值为(140.55 ±9.92)CL,低于ECAP的平均阈值 ( 160.75±13.34) CL,差异具有统计学意义(t=10.467,P＜0.01);二者阈值之间呈正相关(r=0.763,P＜0.01).结论 人工耳蜗植入术中可成功记录到EMLR波形,其阈值较ECAP低,可以作为判断植入者中枢高位听觉传导功能的客观检查.     

豚鼠下丘P物质免疫反应显微及亚微结构特点

采用免疫组化ABC－GDN技术结合免疫电镜，研究正常豚鼠下丘（IC）P物质免疫反应（SP－IR）阳性产物的分布及超微定位。结果表明：下丘中央核团SP－IR阳性神经元数量较多，大部分呈多极或星状，根据细胞大小可分为两型，即Ⅰ型－神经元胞体呈圆形或椭圆形，直径约120－150μm；Ⅱ型－神经元胞体呈圆形或不规则形，直径60－70μm。中央核团内SP－IR阳性纤维及终末数量亦较少。下丘中央旁核SP－IR阳性细胞数量较少，但可见分布较密集的SP－IR阳性纤维及终末。免疫透射电镜发现：在下丘含有较多的SP－IR阳性的轴突终末与阴性的树突形成的轴－树突触结构，突触后膜明显增厚，后膜下可见明显的突触小体，属Ⅰ型兴奋性突触。阳性的轴突末梢内有70nm左右的圆形清亮囊泡。研究结果表明：P物质（SP）可能是下丘听觉传入神经递质或调质。     

Separate projections from the inferior colliculus to the cochlear nucleus and thalamus in guinea pigs

We used multiple-labeling techniques with retrograde fluorescent tracers to determine whether individual cells in the inferior colliculus project to the medial geniculate body (MG) and the cochlear nucleus (CN) in guinea pigs. Four possible projection patterns were examined: (1) to ipsilateral MG and ipsilateral CN; (2) to ipsilateral MG and contralateral CN; (3) to contralateral MG and ipsilateral CN; and, (4) to contralateral MG and contralateral CN. Following injections of different tracers into two or more sites, no inferior collicular cells were double-labeled from the two contralateral targets and only a few cells were double-labeled from each of the other pairs of targets. The double-labeled cells always totaled < 1% of the single-labeled populations. We conclude that collateral projections from the inferior colliculus to the MG and CN are virtually non-existent. Therefore, the ascending and descending projections to these targets arise from different cells. These cells could potentially receive different inputs and send different information to higher or lower centers of the auditory pathway.     

Local inhibition shapes duration tuning in the inferior colliculus of guinea pigs

Neural tuning to sound durations is a useful filter for the identification of a variety of sounds. Previous studies have shown that the interaction between excitatory and inhibitory inputs plays a role in duration selectivity in echolocating bats. However, this has not been investigated in non-echolocating mammals. In the inferior colliculus (IC) of these mammals, it is recognized that the excitatory responses to sounds are mediated through AMPA and NMDA receptors while the inhibitory input is mediated through gamma-aminobutyric acid (GABA) and glycine receptors. The present study explores the potential interplay between inhibitory and excitatory inputs and its role in the duration selectivity of IC neurons in guinea pigs. It was found that the application of bicuculline (BIC, a GABA A blocker) and/or strychnine (STRY, a glycine blocker) eliminated or reduced duration tuning in most units that were duration tuned (32 out of 39 for BIC, 50 out of 64 for STRY, respectively). The inhibitory input (either by GABA or by glycine) appeared to have a stronger regulating effect on the early excitation mediated by AMPA than on later excitation by NMDA. This is more distinguishable in neurons that show duration selectivity. In conclusion, the inhibitory effect on the early responses appears to be the main contributor for the duration selectivity of the IC in guinea pigs; potential mechanisms for this duration selectivity are also discussed.     

The effect of gap-marker spectrum on gap-evoked auditory response from the inferior colliculus and auditory cortex of guinea pigs

The objective of this study is to verify the effects of gap marker spectrum on gap-evoked auditory responses. The gap-evoked potentials were recorded using electrodes implanted in the inferior colliculus (IC) and auditory cortex (AC) of guinea pigs. The gap markers were noise bursts in four frequency bands (500-8,000 Hz, 500-16,000 Hz, 500-32,000 Hz, and 16,000-32,000 Hz), and were tested at three sound levels. The onset response to the post-gap marker was measured to obtain the gap response threshold, and to establish input-output functions for latency and amplitude. Similar to previous behavioural studies, it was found that the gap-response threshold decreased with increasing marker bandwidth. This change was more significant at the cortical level in which the averaged gap-threshold decreased by approximately 2 ms with the bandwidth change. However, the gap threshold in the high frequency region (16,000-32,000 Hz) was comparable to that of the low frequency region (500-16,000 Hz). These results suggest that the total bandwidth of all auditory channels that are recruited determine the temporal resolution measured in gap-evoked potentials.     

The effect of gap-marker spectrum on gap-evoked auditory response from the inferior colliculus and auditory cortex of guinea pigs

The objective of this study is to verify the effects of gap marker spectrum on gap-evoked auditory responses. The gap-evoked potentials were recorded using electrodes implanted in the inferior colliculus (IC) and auditory cortex (AC) of guinea pigs. The gap markers were noise bursts in four frequency bands (500–8?000?Hz, 500–16?000?Hz, 500–32?000?Hz, and 16?000–32?000?Hz), and were tested at three sound levels. The onset response to the post-gap marker was measured to obtain the gap response threshold, and to establish input-output functions for latency and amplitude. Similar to previous behavioural studies, it was found that the gap-response threshold decreased with increasing marker bandwidth. This change was more significant at the cortical level in which the averaged gap-threshold decreased by approximately 2?ms with the bandwidth change. However, the gap threshold in the high frequency region (16?000–32?000?Hz) was comparable to that of the low frequency region (500–16?000?Hz). These results suggest that the total bandwidth of all auditory channels that are recruited determine the temporal resolution measured in gap-evoked potentials.

Sumario

El objetivo de este estudio es verificar los efectos del espectro de marcadores de brecha sobre las respuestas auditivas evocadas por una brecha. Se registraron los potenciales evocados por brecha utilizando electrodos implantados en el colículo inferior (IC) y la corteza auditiva (AC) de cobayos. Los marcadores de brecha fueron bursts de ruido en cuatro bandas de frecuencia (500–8000?Hz, 500–16?000?Hz, 500–32?000?Hz and 16?000–32?000?Hz), y se evaluaron a tres niveles sonoros. Se midió la respuesta de inicio del marcador post-brecha para obtener el umbral de respuesta de brecha, y establecer las funciones de ingreso-salida para latencia y amplitud. Al igual que en estudios conductuales previos, se encontró que el umbral de respuesta de brecha disminuyó con el incremento de los anchos de banda del marcador. Este cambio fue más significativo a nivel cortical en donde el umbral promediado de brecha disminuyó en aproximadamente 2 mseg con el cambio de ancho de banda. Sin embargo, el umbral de brecha en la región de alta frecuencia (16?000–32?000?Hz) fue comparable al umbral de la región de baja frecuencia (500–16?000?Hz). Estos resultados sugieren que el ancho de banda total de todos los canales auditivos reclutados determina la resolución temporal medida en los potenciales evocados por brecha.     

Amino acid uptake and release in the guinea pig cochlear nucleus after inferior colliculus ablation

This study attempts to determine if the neurons in the guinea pig inferior colliculus that project to the cochlear nucleus could use certain amino acid transmitters. The left inferior colliculus was ablated surgically to destroy projections descending to the cochlear nuclei. Nissl and silver stained sections of the brain stem indicated that this procedure destroyed most of the left inferior colliculus, but spared a small amount of collicular tissue ventrally and rostrally. Six to seven days after the ablation, degenerated fibers were present in the right inferior colliculus, in the left lateral lemniscus, and in the cochlear nucleus, bilaterally. Three to five days after the ablation, the uptake and electrically-evoked release of exogenous, radiolabeled D-aspartate, gamma-aminobutyrate, and glycine were measured in the three major subdivisions of the cochlear nucleus, the anteroventral, posteroventral, and dorsal divisions. These activities were compared to those in unlesioned controls. The ablation did not alter the uptake and release of the amino acids in the dorsal and posteroventral divisions of the cochlear nucleus. However, it lowered slightly (by 10-18%) the uptake and release of gamma-aminobutyrate and glycine in the anteroventral division, although the difference from the control group was not statistically significant. These findings suggest that most of the neurons in the inferior colliculus that project to the cochlear nucleus probably do not use glutamate, aspartate, gamma-aminobutyrate, or glycine as a transmitter. However, the possibility remains that a small proportion of the collicular projections to the anteroventral cochlear nucleus might use gamma-aminobutyrate or glycine as a transmitter.     

电刺激耳蜗记录下丘的空间调谐曲线

探索耳蜗电刺激的听觉中枢电活动机理，为多道人工耳蜗电刺激的部位代码提供依据。方法 利用记录单单位和多单位电位反应的方法，分别描记１７只猫听觉下丘核团对耳蜗内单极电刺激，耳蜗内双极电刺激和纯音刺激反应的空间调谐曲线。结果 耳蜗内双极电刺激能兴奋下丘中的特定区域，类似于纯音刺激的反应；而耳蜗内单极电刺激使下丘细胞广泛地被兴奋，不能提供部位代码。     

Localization of substance P in middle ear mucosa and peripheral auditory pathways in guinea pigs]

The distribution and intracellular localization of substance P (SP) in middle ear mucosa (MEM), cochlea and spiral ganglion (SG) were studied by immunohistochemical technique and immunoelectron microscopy. There was a widespread distribution of SP positive nerve fibers (NF) along the median and small vessels of MEM. SP-immunoreactivity (SP-IR) positive cells could be seen in the MEM near the promontorium tympani. In the Corti's organ, SP-IR positive products were located at the base of inner hair cells. The majority of positive NF emerged like strings of beads and were radially distributed from osseous spiral laminal to the Corti's organ. About 50% of the SG cells were SP-IR positive. Two types of SP-IR positive NF were found in the VIII cranial nerve by light microscopy. Small clear vesicles with a diameter of 50-70nm were localized in the cytoplasm of the type-I SG cells by immunoelectron microscopy. In the outer membrane and inside the mitochondria, SP-IR positive substances could be distinguished as an electron dense matter. The possibility of SP as an afferent neurotransmitter or modulator in cochlea and the significance of its presence in the MEM were discussed.     

local inhibition mediated byγ -aminobutyric acid-a receptor and duration tuning in inferior colliculus in guinea pigs

Duration is a salient feature of acoustic signals including speech. Duration tuning was first reported in frogs and later in echolocating bats. More recently, duration tuning has been reported in non-echolocating mammals and appears to be a fundamental encoding mechanism throughout the animal kingdom. However, the duration tuning reported in these non-echolocating mammals appears to be much weaker than that in the previous studies on bats. In contrast to this finding, our recent study reported that duration tuning in the IC in guinea pigs appeared to be strong when it was measured using an appropriate temporal window. With such a temporal window, duration tuning was found to be compatible with that of echo-locating bats. In the present report, we further demonstrate that duration tuning in the IC of this species is established by interaction between excitation and GABAergic inhibition. In addition to overall increase in responsiveness, application of bicuculline(BIC), a GABA-A receptor antagonist, was found to significantly reduce or eliminate duration selectivity in 44 out of the 67 neurons that showed clear duration tuning from a sample of 340 neurons.     

Projections from auditory cortex contact cells in the cochlear nucleus that project to the inferior colliculus

Anterograde and retrograde tracing techniques were combined to determine whether auditory cortical axons contact cells in the cochlear nucleus that project to the inferior colliculus. FluoroRuby or fluorescein dextran was injected into auditory cortex to label cortical axons by anterograde transport. Different fluorescent tracers (Fast Blue, FluoroGold, FluoroRuby or fluorescein dextran) were injected into one or both inferior colliculi to label cells in the cochlear nucleus. After 12-15 days, the brain was processed for fluorescence microscopy and the cochlear nuclei were examined for apparent contacts between cortical axons and retrogradely labeled cochlear nucleus cells. The results suggest that axons from the ipsilateral or contralateral cortex contact fusiform and giant cells in the dorsal cochlear nucleus and multipolar cells in the ventral cochlear nucleus that project directly to the inferior colliculus. The contacts occur on cell bodies and dendrites. The target cells in the cochlear nucleus include cells that project ipsilaterally, contralaterally or bilaterally to the inferior colliculus. The results suggest that auditory cortex is in a position to exert direct effects on the monaural pathways that ascend from the cochlear nucleus.