小鼠下丘听神经元的反应潜伏期对特征频率的表达

频率是声音的基本参数之一. 听觉神经元对声音频率的反应可以表现为放电率和反应潜伏期的变化. 大部分神经元放电率随频率的改变呈多种变化, 而神经元对声音反应的放电潜伏期往往比较稳定, 提示潜伏期能有效地表达频率信息. 本文研究了BALB/C小鼠下丘听神经元对纯音频率反应的放电率及潜伏期特性, 实验结果表明: 神经元对特征频率的反应潜伏期通常最短, 随声强的变化改变不大; 而神经元对纯音频率反应的放电率随频率改变呈多种变化, 尤其当声强增强时. 实验结果提示小鼠下丘神经元的反应潜伏期具有较放电率更准确表征特征频率的特性.     

γ-氨基丁酸能抑制可锐化大棕蝠听皮层神经元频率调谐

本实验使用了 9只成年健康的大棕蝠 (Eptesicusfuscus)。采用双声刺激和多管电极电泳导入荷包牡丹碱 (bicuculline,Bic)的方法 ,研究了γ 氨基丁酸 (γ aminobutyricacid ,GABA)能抑制在锐化听皮层 (primaryauditorycortex ,AC ,即初级听皮层 )神经元频率调谐中的作用。结果发现 :正常AC神经元的频率调谐曲线表现出单峰开放式、多峰开放式和单峰封闭式 3种类型 ;用双声刺激方法研究证实 ,至AC神经元的抑制性输入能被抑制性声刺激所激活 ,且这种神经抑制有自身的最佳频率 ,根据其对兴奋反应的影响程度和系统地改变抑制性声刺激的强度 ,可在兴奋性频率调谐曲线或兴奋区的高频边或 /和低频边测出抑制性频率调谐曲线或抑制区 ;当这种抑制性输入被抑制性声刺激激活后 ,能降低阈上 10dB声强引起的兴奋反应的发放率 ,抑制效率随抑制声刺激强度的增强而加强 ;电泳GABAa受体拮抗剂荷包牡丹碱Bic后 ,可不同程度地去GABA能抑制 ,扩宽频率调谐曲线 ,使多峰调谐曲线变成单峰 ,封闭型变成开放型。表明GABA能抑制参与构成至AC神经元的抑制性输入 ,在正常情况下这种抑制有助于提高中枢听神经元的信号 /噪声比和频率分析能力 ,并锐化频率调谐。因此本结果提示 ,声音的各参量中所包含的信息从外周传入中枢后 ,随着中枢的升     

外侧丘系腹核在声信号加工和听觉上行传导中的作用

外侧丘系腹核(ventral nucleus of the lateral lemniscus,VNLL)是中枢听觉通路中连接耳蜗核等低位脑干和中脑下丘(inferior colliculus,IC)的重要核团,其神经元能够对声信号的不同参数进行检测与加工,进而形成多样的声反应特性。VNLL神经元对频率反应的调谐曲线有多种类型,但其锐化程度一般较低,对频率的分析亦不够精确;有关强度调谐的放电率函数分为两种类型:单调型与非单调型,它们对强度的加工和编码往往受到发放模式的影响;不同发放模式的VNLL神经元对时程的编码能力不同,其中起始型具有精确的时间特性,适合编码声刺激的起始时间信息,对蝙蝠的回声定位非常重要。VNLL接受来自低位核团的输入,并发出上行的抑制性投射至IC,在IC神经元的声信息检测过程中发挥重要作用。近来研究认为VNLL快速的抑制性投射延迟IC神经元的首次发放潜伏期,VNLL延迟的抑制性投射介导IC神经元的发放模式,但VNLL抑制性输入如何在IC进行整合,并增强IC神经元检测声信号能力的机制并不清楚,且缺乏VNLL对IC进行实时调控作用的直接证据。这些问题的研究有助于进一步认识上行输入在声信号加工过程中的作用,同时也是本实验室今后的研究重点。本文结合本实验室相关研究,围绕VNLL对听觉信号的加工和上行传导进行综述。     

听神经元的频率调谐

频率作为声音的一个重要参数,在听敏感神经元对声音进行分析和编码过程中扮演重要角色。一般用频率调谐曲线来表示听敏感神经元的频率调谐特性,并用Qn(10,30,50)值表达频率调谐曲线的尖锐程度,Qn值越大,频率调谐曲线也越尖锐,神经元的频率调谐能力越好,对频率的分辨能力越高。从听觉外周到中枢,听敏感神经元的频率调谐逐级锐化,而这种锐化主要是由听中枢的多种抑制性神经递质的作用而产生的,其中起主要作用的是GABA能和甘氨酸能神经递质。此外,离皮层调控,双侧下丘间的联合投射以及弱噪声前掩蔽等因素也会影响听敏感神经元的频率调谐特性。     

硕螽(Deracantha onos)听觉中间神经元的声反应特征

本文报道了硕螽听通路单个听觉中间神经元的声反应特征。依据动作电位发放模式的不同,听觉中间神经元可分为两类,即紧张型与相位型。紧张型听觉中间神经元属于窄凋谐带神经元,敏感的频率范围8—18千赫,反应最佳频率在12千赫附近,与同种雄硕螽叫声的主能峰相匹配。相位型听觉中间神经元属于宽调谐带神经元,有二个敏感频率范围,分别为5—8千赫和12—18千赫。它们对声强度的编码方式也不一样:分别以动作电位的数目与反应潜伏期对声强编码。本文还讨论了不同类型听觉中间神经元的功能意义。     

γ-氨基丁酸能抑制对大棕蝠听皮层神经元声反应特性的影响

为了探讨γ－氨基丁酸（γ-aminobutyric acid,GABA)能抑制对大棕蝠(Eptesicus fuscus)听皮层(auditory cortex,AC)神经元声反应特性的影响,采用多管微电极电泳方法,观察了8只大棕蝠AC神经元去ABA能抑制前后声刺激诱发的反应。结果显示,微电泳GABAa受体拮抗剂荷包牡丹碱(bicuculline,Bic)去ABA能抑制可改变声刺激诱发的反应模式;极大地增加神经元冲动发放率,缩短反应的潜伏期和降低反应的最小阈值;不同程度地改变强度－发放率和强度－潜伏期函数。结果提示：1、GABA能抑制对AC神经元声信号处理起重要作用;2、GABA能抑制可改变AC神经元兴奋性支配或输入的效应,并因此定型AC神经元的声反应性质,即发放模式、阈值、强度－发放率和强度－潜伏期函数;3、GABA能抑制为AC神经元的声诱发活动提供一种调制性抑制。     

听觉电生理实时分析系统及其在大鼠下丘信息编码研究中的应用

基于TDT神经电生理软硬件平台和Matlab软件环境,开发了专用于听觉电生理研究的实时分析软件。通过对神经元胞外记录信号的在线处理和分析,可以在实验过程中得到刺激后放电活动时间直方图、平均发放率、首次发放潜伏期等定量分析结果,以及刺激参数变化时神经元发放率的变化曲线,如发放率-刺激强度曲线等。此分析软件被用于大鼠下丘神经元听觉信息编码的研究中,观察到下丘神经元对于纯音和噪声刺激不同的时间响应模式,以及神经元发放率和首次发放潜伏期对声音刺激强度的编码。     

弱背景噪声对大鼠听皮层神经元频率调谐的影响

在自然环境中,人和动物常在一定的背景噪声下感知信号声刺激,然而,关于低强度的弱背景噪声如何影响听皮层神经元对声刺激频率的编码尚不清楚.本研究以大鼠听皮层神经元的频率反应域为研究对象,测定了阈下背景噪声对79个神经元频率反应域的影响.结果表明,弱背景噪声对大鼠初级听皮层神经元的听反应既有抑制性影响、又有易化性影响.一般来说,抑制性影响使神经元的频率调谐范围和最佳频率反应域缩小,易化性影响使神经元的频率调谐范围和最佳频率反应域增大.对于少数神经元,弱背景噪声并未显著改变其频率调谐范围,但却改变了其最佳频率反应域范围.弱背景噪声对63.64%神经元的特征频率和55.84%神经元的最低阈值无显著影响.神经元频率调谐曲线的尖部比中部更容易受到弱背景噪声的影响.该研究结果有助于我们进一步理解复杂声环境下大脑听皮层对听觉信息的编码机制.     

γ—氨基丁酸能抑制可镜化大棕蝠听皮层神经元频率调谐

本实验使用了9只成年健康的大棕蝠（Eptesicus fuscus）。采用双声刺激和多管电极电泳导入荷包牡丹碱（bicuculline,Bic）的方法,研究了γ－氨基丁酸（γ－aminobutyric,GABA）能抑制在锐化听皮层（primary auditory cortex,AC,即初级听皮层）神经元频率调谐中的作用。结果发现：正常AC神经元的频率调谐曲线表现出单峰开放式、多峰开放式和单峰封闭式2种类型;用双声刺激方法研究证实,至AC神经元的抑制性输入能被抑制性声刺激所激活,且这种神经抑制有自身的最佳频率,根据其对兴奋反应的影响程度和系统地改变抑制性声刺激的强度,可在兴奋性频率调谐曲线或兴奋区的高频边或／和低频边测出抑制性频率调谐曲线或抑制区;当这种抑制性输入被抑制性声刺激激活后,能降低阈上10fB声强引起的兴奋反应的发放率,抑制效率随抑制声刺激强度的增强而加强;电泳GABAa受体拮抗剂荷包牡丹碱Bic后,可不同程度地去GABA能抑制参与构成至AC神经元的抑制性输入,在正常情况下这种抑制有助于提高中枢听神经元的信号／噪声比和频率分析能力,并锐化频率调谐,因此本结果在正常情况下这种抑制有助于提高中枢听神经元的信号／噪声比和频率分析能力,并锐化频率调谐,因此本结果提示,声音的各参量中所包含的信息从外周传入中枢后,随着中枢的升级,逐级抽提整合成若干特征,直至在AC形成某种“声像（sound image)”,对大多数AC神经元而言,GABA能抑制在该过程中起关键作用。     

大鼠初级听皮层神经元对声音空间信息的编码

尽管大脑听皮层神经元对声音空间信息的编码已有不少的研究报道,但其编码机制并不十分清楚,相关研究在大鼠的初级听皮层也未见详细的研究报道．用神经电生理学方法在大鼠初级听皮层考察了151个听神经元的听空间反应域,分析了神经元对来自不同空间方位声刺激反应的放电数和平均首次发放潜伏期的关系．结果表明,多数(52.32%)神经元对来自对侧听空间的声刺激反应较强,表现为对侧偏好型特征,其他神经元分别归类为同侧偏好型(18.54%)、中间偏好型(18.54%)、全向型(3.31%)和复杂型(7.28%)．多数神经元偏好的听空间区域的几何中心位于记录部位对侧听空间的中部和上部．绝大多数初级听皮层神经元对来自偏好听空间的声刺激反应的放电数较多、反应潜伏期较短,对来自非偏好听空间的声刺激反应的放电数较少、反应潜伏期较长,放电数与平均首次发放潜伏期呈显著负相关．在对声音空间信息的编码中,大脑初级听皮层可能综合放电数和潜伏期的信息以实现对声源方位的编码．     

Corticofugal regulation of auditory sensitivity in the bat inferior colliculus

Under free-field stimulation conditions, corticofugal regulation of auditory sensitivity of neurons in the central nucleus of the inferior colliculus of the big brown bat, Eptesicus fuscus, was studied by blocking activities of auditory cortical neurons with Lidocaine or by electrical stimulation in auditory cortical neuron recording sites. The corticocollicular pathway regulated the number of impulses, the auditory spatial response areas and the frequency-tuning curves of inferior colliculus neurons through facilitation or inhibition. Corticofugal regulation was most effective at low sound intensity and was dependent upon the time interval between acoustic and electrical stimuli. At optimal interstimulus intervals, inferior colliculus neurons had the smallest number of impulses and the longest response latency during corticofugal inhibition. The opposite effects were observed during corticofugal facilitation. Corticofugal inhibitory latency was longer than corticofugal facilitatory latency. Iontophoretic application of γ-aminobutyric acid and bicuculline to inferior colliculus recording sites produced effects similar to what were observed during corticofugal inhibition and facilitation. We suggest that corticofugal regulation of central auditory sensitivity can provide an animal with a mechanism to regulate acoustic signal processing in the ascending auditory pathway. Accepted: 15 July 1998     

Bicuculline对小鼠中脑下丘听神经元

采用微电泳技术考察了GABAA受体拮抗剂荷包牡丹碱（bicuculline）,对小鼠中脑下丘听神经元强度-放电率曲线、频率调谐曲线和听空间反应域的影响。结果表明,微电泳bicuculline使听神经元的放电率显著提高,多数神经元的强度-放电率曲线变为单调型;听神经元频率调谐曲线加宽,并且对曲线上部的作用更加明显;听神经元的听空间反应域增大,方向敏感性降低。实验结果提示了GABA能抑制在下丘听信息处理中的重要作用。     

The inferior colliculus of the mustached bat has the frequency-vs-latency coordinates

In the mustached bat, the central auditory system contains FM–FM (delay-tuned) neurons which are specialized for processing target-distance information carried by echo delays. Mechanisms for creating the FM–FM neurons involve delay lines, coincidence detection and amplification. A neural basis for delay lines can be a map representing response latencies. The aim of the present study is to explore whether the central nucleus of the inferior colliculus has a latency axis incorporated into iso-best frequency slabs. Responses of single or multiple neurons were recorded from the inferior colliculus of unanesthetized mustached bats with tungsten-wire electrodes, and their response latencies were measured with tone bursts at their best frequencies and best amplitudes or 65 dB SPL. In the dorsoventral electrode penetrations across the inferior colliculus, response latency systematically shortens from ˜12 to ˜4␣ms. Tonotopic representation in the inferior colliculus is somewhat complex. Iso-best frequency slabs are tilted and/or curved, but they orient more or less ventrodorsally. Nevertheless, the latency axis is evident in each iso-best frequency slab, regardless of best frequency. The inferior colliculus has the frequency-vs-latency coordinates. Accepted: 2 October 1996     

The functional role of GABA and glycine in monaural and binaural processing in the inferior colliculus of horseshoe bats

Summary The functional role of GABA and glycine in monaural and binaural signal analysis was studied in single unit recordings from the central nucleus of the inferior colliculus (IC) of horseshoe bats (Rhinolophus rouxi) employing microiontophoresis of the putative neurotransmitters and their antagonists bicuculline and strychnine.Most neurons were inhibited by GABA (98%; N=107) and glycine (92%; N=118). Both neurotransmitters appear involved in several functional contexts, but to different degrees.Bicuculline-induced increases of discharge activity (99% of cells; N=191) were accompanied by changes of temporal response patterns in 35% of neurons distributed throughout the IC. Strychnine enhanced activity in only 53% of neurons (N=147); cells exhibiting response pattern changes were rare (9%) and confined to greater recording depths. In individual cells, the effects of both antagonists could markedly differ, suggesting a differential supply by GABAergic and glycinergic networks.Bicuculline changed the shape of the excitatory tuning curve by antagonizing lateral inhibition at neighboring frequencies and/or inhibition at high stimulation levels. Such effects were rarely observed with strychnine.Binaural response properties of single units were influenced either by antagonization of inhibition mediated by ipsilateral stimulation (bicuculline) or by changing the strength of the main excitatory input (bicuculline and strychnine).Abbreviations BF best frequency - Bic bicuculline - C control - CF constant frequency - CN cochlear nucleus - DNLL dorsal nucleus of the lateral lemniscus - FM frequency modulation - GABA gamma amino butyric acid - IC inferior colliculus - LSO lateral superior olive - Str strychnine     

N-甲基-D-天冬氨酸(NMDA)及荷包牡丹碱对不同年龄蝙蝠下丘神经元听反应的影响

分别对出生后第２周和第４周的中华鼠耳蝠（Ｍｙｏｔｉｓｃｈｉｎｅｎｓｉｓ）中脑下丘中央核１２１个听神经元进行了考察,同时与成年动物进行比较。结果表明,微电泳ＮＭＤＡ对下丘中央核绝大部分听神经元（２周龄、４周龄和成年动物分别为９６％、９５％和９６％）具有易化性影响,表现为听反应脉冲发放率增加、反应阈值下降、频率调谐曲线增宽。ＮＭＤＡ的易化性效应部分地与动物的周龄相关,表现为对听反应阈值和听反应脉冲发放率的易化效应在出生后２－４周逐渐增强,但４周以后的易化效应趋缓;微电泳ＧＡＢＡＡ受体的特异性拮抗剂Ｂｉｃｕｃｕｌｉｎｅ,对神经元的听反应也呈现易化性影响,表现为听反应脉冲发放率增加,反应阈值降低和频率调谐曲线增宽等。实验结果还提示,ｂｉｃｕｃｕｌｉｎｅ对下丘神经元听反应的易化作用,在出生后早期呈持续增强趋势。ＮＭＤＡ和ｂｉｃｕｃｕｌｉｎｅ的效应与动物周龄之间的关系略有差异,是否提示着下丘中央核ＮＭＤＡ受体和ＧＡＢＡＡ受体在出生后的发育进程有所差别,尚待进一步探讨。     

N-甲基-D-天冬氨酸(NMDA)及荷包牡丹碱对不同年龄蝙蝠下丘神经元听反应的影响

分别对出生后第２周和第４周的中华鼠隔蝠中脑下丘中央核１２１个听神经元进行了考察,同时与成年动物进行比较。结果表明,微电泳ＮＭＤＡ对下丘中央核绝大部分听神经元具有易化性影响,表现为听反应脉冲发放率增加,反应阈值下降,频率谐曲线增宽。     

Comparison of binaural release from forward masking in animals and humans. Electrophysiologic study

The EPs of the inferior colliculus and auditory cortex in anaesthetized guinea pigs and the long latency auditory EPs in alert humans were studied. The stimuli consisted of binaurally presented pairs of clicks used as a masker, and the probe, with a variable time delay between them. The greatest relative differences between out-of-phase and in-phase probe responses were observed at the beginning of the recovery course. They averaged as 1.6, 1.5 and 1.4 for the responses of the inferior colliculus, auditory cortex and long latency potentials, resp., at the stimuli intensities of 50-65 dB SPL, and then decreased to zero during the time course of the probe response recovery. Correlation of this parameter with the stimulus intensity was positive.     

Latency represents sound frequency in mouse IC

Frequency is one of the fundamental parameters of sound. The frequency of an acoustic stimulus can be represented by a neural response such as spike rate, and/or first spike latency (FSL) of a given neuron. The spike rates/frequency function of most neurons changes with different acoustic amplitudes, whereas FSL/frequency function is highly stable. This implies that FSL might represent the frequency of a sound stimulus more efficiently than spike rate. This study involved representations of acoustic frequency by spike rate and FSL of central inferior colliculus (IC) neurons responding to free-field pure-tone stimuli. We found that the FSLs of neurons responding to characteristic frequency (CF) of sound stimulus were usually the shortest, regardless of sound intensity, and that spike rates of most neurons showed a variety of function according to sound frequency, especially at high intensities.These results strongly suggest that FSL of auditory IC neurons can represent sound frequency more precisely than spike rate.     

Response characteristics of neurons in the medial geniculate body of the little brown bat to simple and temporally-patterned sounds

We examined the auditory response properties of neurons in the medial geniculate body of unanesthetized little brown bats (Myotis lucifugus). The units' selectivities to stimulus frequency, amplitude and duration were not significantly different from those of neurons in the inferior colliculus (Condon et al. 1994), which provides the primary excitatory input to the medial geniculate body, or in the auditory cortex (Condon et al. 1997) which receives primary input from the medial geniculate body. However, in response to trains of unmodulated tone pulses, the upper cutoff frequency for time-locked discharges (64 ± 46.9 pulses per second or pps) and the mean number of spikes per pulse (19.2 ± 12.2 pps), were intermediate to those for the inferior colliculus and auditory cortex. Further, in response to amplitude-modulated pulse trains, medial geniculate body units displayed a degree of response facilitation that was intermediate to that of the inferior colliculus and auditory cortex inferior colliculus: 1.32 ± 0.33; medial geniculate body: 1.75 ± 0.26; auditory cortex: 2.52 ± 0.96, P < 0.01). These data suggest that the representation of isolated tone pulses is not significantly altered along the colliculo-thalamo-cortical axis, but that the fidelity of representation of temporally patterned signals progressively degrades along this axis. The degradation in response fidelity allows the system to better extract the salient feature in complex amplitude-modulated signals. Accepted: 9 January 1999