幼小蝙蝠下丘神经元的听反应特性

实验在出生6—8天的8只幼龄鲁氏菊头蝠(Rhinolophus rouxi)上进行。使用玻璃微电极记录中脑下丘听神经元对超声信号的反应。共观察了162个听单位,它们对超声反应的最佳频率分布范围为25.8—60.9千赫,多数集中在43.0—47.0千赫。反应的潜伏期在6.0—38.0毫秒,平均为15.4±5.2毫秒。反应的最低阈值在25—84dB,平均为69.8±10.3dB.这些神经元对超声刺激的调谐曲线都较宽阔,故Q10-dB值都较小。当微电极由下丘表面垂直下插时,所记录到的神经元的最佳频率与记录深度之间不存在相关关系,即没有音调筑构现象。听神经元的这些特性与同种成年动物构成显著差异。     

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.     

荷包牡丹碱和马钱子碱对小鼠皮层及下丘听神经元声反应潜伏期的影响

频率和强度是声音的两个重要参数,通常以听觉神经元动作电位发放频次编码这两个参数 . 研究表明,声反应潜伏期也可编码声音频率和强度,但尚不清楚潜伏期编码这两个参数究竟发生于哪一级听觉核团 . 如果声音参数由同级中枢编码,则这样的编码方式可能发生改变 . 反之,如果编码方式未发生变化,则意味着声音信息是由低位神经元编码的 . GABA 和甘氨酸 (Gly) 是听中枢普遍分布的抑制性递质 . 通过施加它们的拮抗剂荷包牡丹碱和马钱子碱,观测小鼠皮层和下丘听觉神经元声反应潜伏期的变化 . 结果表明,由反应潜伏期表征声音频率和强度的关系不因 GABA 和 Gly 作用的改变而发生变化,提示频率和强度与反应潜伏期之间的编码关系可能是由低位听神经元编码并向上传递的,而不是在同级中枢 ( 皮层或下丘 ) 完成的 .     

皮层神经元动作电位不应期和阈电位与神经元动作电位编码的关系

目的：测量和比较感觉运动皮层Ⅱ/Ⅲ层锥体神经元和中间神经元的内在特性并研究其与动作电位编码频率和精确性的关系。方法：采用全细胞电流钳记录模式,获得的数据输入pClamp和Origin进行处理分析。结果：与锥体神经元相比,中间神经元群集动作电位具有较低的阈电位水平和较短的不应期,从而中间神经元具有较高的动作电位编码频率和精确性。结论：皮层神经元动作电位的阈电位水平和不应期调控动作电位的编码频率和精确性。     

螽斯听觉中间神经元TN2的声反应特征以及GABA对其影响

采用单细胞电生理记录技术,对螽斯Ｇａｍｐｏｃｌｅｉｓ ｇｒａｔｉｏｓａ听觉双轴突中间神经元ＴＮ２的声反应放电活动的基本特征进行了观测,发现ＴＮ２的放电模式为“ｐｈａｓｉｃ”型,最敏感频率为１３ｋＨｚ,反应阈值为３１ｄＢ ＳＰＬ,是一个高灵敏、宽带通的神经元。还研究了抑制性神经递质ＧＡＢＡ及其拮抗剂苦毒素对ＴＮ２声反应的影响,发现ＧＡＢＡ能抑制ＴＮ２的放电活动,而苦毒素则将其放电模式改变为“ｔｏｎｉ     

蟾蜍延脑听中枢的单位电反应的一些观察

我们利用电生理学的方法测定了蟾蜍延脑听反应的区域,并研究了延脑听神经元对短声及纯音的反应特性。结果表明:1.从内耳来的传入冲动主要是向同侧的延脑听区传递的。2.蟾蜍听觉系统感受的频率范围在4,000周/秒以下,对于500—600周/秒以及1,000—1,200周/秒的频率最为敏感。多数听神经元的反应阈值在人听阈上25—35分贝左右。少数在人听阈上5—10分贝或45—55分贝。3.根据短声及特征频率的纯音所引起的反应,可将延脑听神经元的反应分为长潜伏期(平均约12毫秒)及短潜伏期(平均约3毫秒)两种形式。反应潜伏期的长短,可能是由不同类型的神经元的特性所决定的,但在同一神经元,在改变声音刺激的频率或强度时,反应的潜伏期也有变化。4.延脑听神经元对纯音刺激的反应有连续发放的、给声的、给-撤声的以及撤声的几种形式。其中以连续发放的反应形式最为常见。5.有时,纯音引起的连续发放是迭加在振幅达十几毫伏的正相慢波之上的,发放的波形为正单相锋形电位,它的上升相较陡,下降相缓慢。短声也可以引起这样的锋形电位,它们可能是细胞内记录到的反应。     

小鼠下丘神经元声反应的性别差异

采用自由声场的纯音短声刺激研究昆明小鼠下丘神经元听反应特征的性别差异。结果表明,①下丘神经元放电形式雌性以相位型为主,雄性以持续紧张型为主,且持续紧张型出现率存在明显的性差(P<005);②最佳频率分布雌雄都主要集中在10～20kHz,而潜伏期分布雌性较雄性集中;③最小阈值分布雌性主要集中于40～63dBSPL,而雄性无明显的集中区;④神经元最大发放雌性明显高于雄性(P<001);⑤脉冲发放函数和潜伏期函数的类型雌雄相同,但非单调型潜伏期函数出现率雄性明显高于雌性(P<001);⑥小鼠下丘神经元频率调谐曲线被分成五类,各类出现率在雌雄间无明显差异,但宽阔型频率调谐曲线百分率雌性明显高于雄性(P<005),且雌性频率调谐曲线高频边反转斜率明显高于雄性(P<005)。因此提示,雌雄小鼠下丘神经元声反应特征存在一定的差异。     

褐菖鲉的听觉阈值研究

利用听觉诱发电位记录技术研究了褐菖鲉(Sebasticus marmoratus)的听觉阈值。通过采用听觉生理系统记录和分析了8尾褐菖鲉对频率范围在100—1000 Hz的7种不同频率的声音刺激的诱发电位反应。结果表明, 褐菖鲉的听觉阈值在整体上随着频率增加而增加, 对100—300 Hz的低频声音信号敏感, 最敏感频率为150 Hz, 对应的听觉阈值为70 dB re 1 μPa。褐菖鲉的听觉敏感区间与其发声频率具有较高的匹配性, 表明其声讯交流的重要性。同时, 人为低频噪声可能对其声讯交流造成影响。     

昆明小鼠下丘神经元对调频声的反应

尽管昆明小鼠下丘神经元对纯音的反应已有深入研究,但其对调频声的反应情况却未见报道。本研究在自由声场条件下,采用单单位细胞外记录方法,观察了昆明小鼠下丘神经元对调频声刺激的反应情况。根据神经元对调频声及纯音反应的阈值差异,所记录的99个下丘神经元可分为三种类型:对调频声刺激反应的阈值低于纯音的为Ⅰ型(57/99,57.6%),二者阈值相当的为Ⅱ型(12/99,12.1%),而纯音阈值低于调频声的为Ⅲ型(30/99,30.3%)。与Ⅲ型神经元相比,Ⅰ型神经元具有较低的CF和Q20dB(P<0.05和P<0.001)和较高的RB20dB(P<0.05)。通过分析下丘神经元对上、下扫时发放数的差异,发现有36个(36/99,36.4%)神经元表现出方向选择性,其中22个(22/99,22.2%)为上扫敏感,其余14个(14/99,14.2%)为下扫敏感,且上扫敏感性神经元比下扫敏感性神经元在Ⅰ、Ⅱ和Ⅲ型神经元中有更广的分布范围。通过比较发现,Ⅰ型神经元和方向选择性神经元的特征频率都非常集中地分布在10kHz-20kHz范围内(77.2%和83.3%)。此外,对其中24个神经元采取了不同调制速度的调频声刺激,大多数(15/24,62.5%)神经元对快调频声反应最为敏感,并且随着调制速度的升高,方向选择性神经元的比例有下降趋势(45.8%vs41.7%vs33.3%)。上述结果提示,昆明小鼠下丘神经元能有效处理调频声刺激,且具有方向选择性的调频声在昆明小鼠的声通讯中占有重要地位。     

家鸽Herbst小体对振动的反应特征

鸟类的Herbst小体是一种形态特殊的感觉性神经末梢器官.本文利用电生理学方法,研究了家鸽腿部胫骨-腓骨之间的Herbst小体对振动刺激的反应特征.这种小体对振动刺激非常敏感,当振动频率在600—800赫时,它们有反应的最低阈值约为0.3微米.不同的Herbst小体的反应阈值与频率的关系曲线表明:这种小体具有明显的带通滤波的特征,对振动反应的最佳频率范围为400—1000赫.在适宜频率、超阈值强度的振动刺激下,Herbst小体能以1:1的方式作出反应,即相对于每次正弦波振动刺激都有一个锁相的神经脉冲产生.在背根脊神经节内的细胞外记录表明:对振动敏感的神经节细胞具有和Herbst小体完全相似的反应特征.     

Physiology and tonotopic organization of auditory receptors in the cricketGryllus bimaculatus DeGeer

Summary Physiological recordings were obtained from identified receptors in the tympanal organ ofGryllus bimaculatus. By immersing the prothoracic leg in Ringer solution and removing the anterior tympanic membrane the auditory receptors were exposed without significantly altering the frequency response of the auditory organ (Fig. 1). Each receptor was tuned to a specific sound frequency. For sound frequencies below this characteristic frequency the roll-off in sensitivity decreased from 20–30 dB/octave to 10–15 dB/octave as the characteristic frequency of receptors increased from 3–11 kHz (Fig. 4A). For each individual receptor the slope, dynamic range and maximum spike response were similar for different sound frequencies (Fig. 9A). The receptors were tonotopically organized with the characteristic frequency of the receptors increasing from the proximal to the distal end of the array (Figs. 5, 6). Several receptors had characteristic frequencies of 5 kHz. These receptors were divided into two groups on the basis of their maximum spike response produced in response to pure tones of increasing intensity (Fig. 7). Independent of the tuning of the receptor no two-tone inhibition was observed in the periphery, thus confirming that such interactions are a property of central integration.     

Hearing and frequency dependence of auditory interneurons in the parasitoid fly <Emphasis Type="Italic">Homotrixa alleni</Emphasis> (Tachinidae: Ormiini)

The parasitoid tachinid fly Homotrixa alleni detects its hosts by their acoustic signals. The tympanal organ of the fly is located at the prothorax and contains scolopidial sensory units of different size and orientation. The tympanal membrane vibrates in the frequency range of approximately 4–35 kHz, which is also reflected in the hearing threshold measured at the neck connective. The auditory organ is not tuned to the peak frequency (5 kHz) of the main host, the bush cricket Sciarasaga quadrata. Auditory afferents project in the three thoracic neuromeres. Most of the ascending interneurons branch in all thoracic neuromeres and terminate in the deutocerebrum of the brain. The interneurons do not differ considerably in frequency tuning, but in their sensitivity with lowest thresholds around 30 dB SPL. Suprathreshold responses of most neurons depend on frequency and intensity, indicating inhibitory influence at higher intensities. Some neurons respond particularly well at low frequency sounds (around 5 kHz) and high intensities (80–90 dB SPL), and thus may be involved in detection of the primary host, S. quadrata. The auditory system of H. alleni contains auditory interneurons reacting in a wide range of temporal patterns from strictly phasic to tonic and with clear differences in frequency responses.     

Modulation of auditory responsiveness in the locust

The auditory responsiveness of a number of neurones in the meso- and metathoracic ganglia of the locust, Locusta migratoria, was found to change systematically during concomitant wind stimulation. Changes in responsiveness were of three kinds: a suppression of the response to low frequency sound (5 kHz), but an unchanged or increased response to high frequency (12 kHz) sound; an increased response to all sound; a decrease in the excitatory, and an increase in the inhibitory, components of a response to sound. Suppression of the response to low frequency sound was mediated by wind, rather than by the flight motor. Wind stimulation caused an increase in membrane conductance and concomitant depolarization in recorded neurones. Wind stimulation potentiated the spike response to a given depolarizing current, and the spike response to a high frequency sound, by about the same amount. The strongest wind-related input to interneuron 714 was via the metathoracic N6, which carries the axons of auditory receptors from the ear. The EPSP evoked in central neurones by electrical stimulation of metathoracic N6 was suppressed by wind stimulation, and by low frequency (5 kHz), but not high frequency (10 kHz), sound. This suppression disappeared when N6 was cut distally to the stimulating electrodes. Responses to low frequency (5 kHz), rather than high frequency (12 kHz), sounds could be suppressed by a second low frequency tone with an intensity above 50-55 dB SPL for a 5 kHz suppressing tone. Suppression of the electrically-evoked EPSP in neurone 714 was greatest at those sound frequencies represented maximally in the spectrum of the locust's wingbeat. It is concluded that the acoustic components of a wind stimulus are able to mediate both inhibition and excitation in the auditory pathway. By suppressing the responses to low frequency sounds, wind stimulation would effectively shift the frequency-response characteristics of central auditory neurones during flight.     

硕螽(Deracantha onos)听觉中间神经元的方向灵敏度

本文报道了利用神经生理学方法研究硕螽听觉中间神经元方向灵敏度的结果.     

Peripheral specialization for fine analysis of doppler-shifted echoes in the auditory system of the "CF-FM" bat Pteronotus parnellii.

Pteronotus parnellii uses the second harmonic (61-62 kHz) of the CF component in its orientation sounds for Doppler-shift compensation. The bat's inner ear is mechanically specialized for fine analysis of sounds at about 61-62 kHz. Because of this specialization, cochlear microphonics (CM) evoked by 61-62 kHz tone bursts exhibit prominent transients, slow increase and decrease in amplitude at the onset and cessation of these stimuli. CM-responses to 60-61 kHz tone bursts show a prominent input-output non-linearity and transients. Accordingly, a summated response of primary auditory neurones (N1) appears not only at the onset of the stimuli, but also at the cessation. N1-off is sharply tuned at 60-61 kHz, while N1-on is tuned at 63-64 kHz, which is 2 kHz higher than the best frequency of the auditory system because of the envelope-distortion originating from sharp mechanical tuning. Single peripheral neurones sensitive to 61-62 kHz sounds have an unusually sharp tuning curve and show phase-locked responses to beats of up to 3 kHz. Information about the frequencies of Doppler-shifted echoes is thus coded by a set of sharply tuned neurones and also discharges phase-locked to beats. Neurones with a best frequency between 55 and 64 kHz show not only tonic on-responses but also off-responses which are apparently related to the mechanical off-transient occuring in the inner ear and not to a rebound from neural inhibition.     

Noise filtering in the auditory system of Locusta migratoria L

Many acoustically communicating grasshoppers live in crowded populations where sound of many individuals may cause permanent noise. Tympanic receptors and first-order auditory interneurons of Locusta migratoria code such noise tonically, whereas many higher order interneurons react only weakly. In response to simultaneously presented sound they exhibit a better signal-to-noise ratio than their presynaptic elements. Two possible filter mechanisms are suggested for noise reduction in higher-order interneurons: (i) high-pass filtering of receptor spike frequencies and (ii) filtering due to synchronization of receptor spikes. Different receptor spike frequencies were elicited by series of short noise pulses with variable repetition rates. Receptor activities differing in their degree of synchronization were elicited by sound stimuli with variable rising times. In contrast to the first order interneurons some higher order interneurons responded best to receptor spike frequencies above 150–200 Hz, thus showing the postulated filtering. Only one higher order interneuron (AN4) distinguished between synchronous and asynchronous receptor activities. It is suggested that high-pass filtering of receptor spike frequencies is responsible for the noise filtering observed in these interneurons. The synchronization selectivity of AN4 is proposed to be responsible for temporal pattern detection of conspecific sounds.     

Ultrasound sensitive neurons in the cricket brain

1. The aim of this study was to identify neurons in the brain of the cricket, Teleogryllus oceanicus, that are tuned to high frequencies and to determine if these neurons are involved in the pathway controlling negative phonotaxis. In this paper we describe, both morphologically and physiologically, 20 neurons in the cricket brain which are preferentially tuned to high frequencies. 2. These neurons can be divided into two morphological classes: descending brain interneurons (DBINs) which have a posteriorly projecting axon in the circumesophageal connective and local brain neurons (LBNs) whose processes reside entirely within the brain. All the DBINs and LBNs have processes which project into one common area of the brain, the ventral brain region at the border of the protocerebrum and deutocerebrum. Some of the terminal arborizations of Int-1, an ascending ultrasound sensitive interneuron which initiates negative phonotaxis, also extend into this region. 3. Physiologically, ultrasonic sound pulses produce 3 types of responses in the DBINs and LBNs. (1) Seven DBINs and 6 LBNs are excited by ultrasound. (2) Ongoing activity in one DBIN and 5 LBNs is inhibited by ultrasound, and (3) one cell, (LBN-ei), is either excited or inhibited by ultrasound depending on the direction of the stimulus. 4. Many of the response properties of both the DBINs and LBNs to auditory stimuli are similar to those of Int-1. Specifically, the strength of the response, either excitation or inhibition, to 20 kHz sound pulses increases with increasing stimulus intensity, while the response latency generally decreases. Moreover, the thresholds to high frequencies are much lower than to low frequencies. These observations suggest that the DBINs and LBNs receive a majority of their auditory input from Int-1. However, the response latencies and directional sensitivity of only LBN-ei suggest that it is directly connected to Int-1. 5. The response of only one identified brain neuron, DBIN8, which is inhibited by 20 kHz sound pulses, is facilitated during flight compared to its response at rest. This suggests that suppression of activity in DBIN8 may be associated with ultrasound-induced negative phonotactic steering responses in flying crickets. The other DBINs and LBNs identified in this paper may also play a role in negative phonotaxis, and possibly in other cricket auditory behaviors influenced by ultrasonic frequencies.     

Dendritic properties of uropod motoneurons and premotor nonspiking interneurons in the crayfish Procambarus clarkii Girard

Dendritic properties of uropod motoneurons and premotor nonspiking interneurons of crayfish have been studied using intradendritic recording and current injection. The input resistance of phasic motoneurons (5.20 ± 0.5 M; mean ± standard error) measured by injecting constant hyperpolarizing current was significantly lower than that of tonic motoneurons (10.3 ± 2.6 M; 0.02 < P < 0.05). The membrane time constant of phasic motoneurons (7.3 ± 0.9 ms) was also significantly shorter than that of tonic motoneurons (24.3 ± 2.5 ms; P < 0.001). Both types of motoneurons behaved linearly during hyperpolarization and sub-threshold depolarization. Nonspiking interneurons showed outward rectification upon depolarization. During hyperpolarization, their membrane behaved linearly and showed significantly higher input resistance (19.5 ± 2.5 M) than phasic and tonic motoneurons (P < 0.001). Their membrane time constant (38.0 ± 5.7 ms) was significantly longer than that of phasic motoneurons (P < 0.001) but not than that of tonic motoneurons (P > 0.05). In response to intracellular injection of sinusoidally oscillating current, phasic motoneurons showed one or two spikes per depolarization period irrespective of oscillating frequency ranging from 1 to 16 Hz. Tonic motoneurons showed larger numbers of spikes per stimulus period at lower frequencies. Nonspiking interneurons also showed phase-locked effects on the motoneuron spike activity. The effective frequency range over which injected oscillating current could modulate motoneuron spike activity was similar for tonic motoneurons and nonspiking interneurons.     

Auditory interneurons in locusts produce directional head and abdomen movements

Locusts (Locusta migratoria) were stimulated with pulses of pure tones of frequencies between 5 kHz and 25 kHz. Interneurons responding to these stimuli (auditory interneurons) were recorded intracellularly and identified by dye injection. Their output functions were investigated by injection of depolarizing current during simultaneous registration of components of flight steering behavior of the animals, i.e. movements of the head and the abdomen and flight activity. Three different types of effects were found, corresponding to 3 functional classes of interneurons: