电刺激蝙蝠小脑对中脑上丘神经元听反应的影响

实验在２３只成年中华鼠耳蝠（Ｍｙｏｌｉｓｃｈｉｎｅｎｓｉｓ）上进行。使用常规电生理学方法,观察了电刺激小脑对上丘神经元听反应的影响。在所观察的１７１个上丘神经元中,有１１６个（占６７．８４％）神经元听反应受到影响,其中７２个（占４２．１１％）表现为抑制效应,４４个（占２５．７３％）为易化效应。刺激小脑对上丘神经听反应的影响是双侧的。抑制或易化程度与电刺激强度、声刺激强度以及声、电刺激间隔有关。结果提示,小脑可以对上丘神经元听反应进行调制,这种调制作用可能是小脑调控回声定位过程中听觉－运动的中枢机制之一。     

睡眠过程中内膝体神经元的听反应后抑制

内侧膝状体神经元接受来自离皮层系统的兴奋和抑制两种神经调节．听觉刺激诱发的内膝体神经元起始反应后会伴随着一段长时抑制．在可自由活动的大鼠上研究了内膝体神经元的听反应后抑制现象．利用植入电极阵列技术,记录了大鼠在睡眠过程中的脑电、肌电以及内膝体神经元胞外放电活动,发现在睡眠的快速眼动时期和非快速眼动时期内膝体神经元存在着听反应后抑制现象,并发现这种抑制更多地出现在非快速眼动睡眠期．在睡眠过程中,丘脑网状核听觉分区的失活会导致内膝体神经元的听反应后抑制消失或减弱．因此,我们推测丘脑网状核神经元参与了内膝体神经元在睡眠中的听反应后抑制,它在非快速眼动睡眠中对内膝体施加了更强的抑制作用．     

电刺激蝙蝠小脑对下丘神经元听反应的影响

实验在34只长翼蝠(Miniopterus schrebersi)上进行.使用玻璃微电极在中脑下丘中央核记录听神经元电反应.电刺激点分别位于小脑蚓部、半球和绒球小结叶共观察了515个对超声刺激产生反应的下丘听神经元.当电刺激小脑时,有171个(占33.2%)神经元听反应受到影响.其中126个(占24.5%)表现为抑制,45个(8.7%)表现为易化.抑制效应表现为神经元所反应放电频数降低和反应潜伏期延长.易化效应则相反.抑制与易化潜伏期一般都在6毫秒以上.抑制效应与电刺激强度、声刺激强度以及声刺激和电刺激的时间间隔有关.抑制和易化性影响都是双侧性的.     

小鼠听皮层对下丘神经元方位敏感性的调控

应用常规电生理学技术,研究小鼠听皮层对中脑下丘神经元方位敏感性的下行调制.实验记录了198个下丘神经元的听反应,这些神经元的最佳方位角大多数(84.8%)位于听空间对侧20°～50°范围内.根据神经元的方位敏感曲线特征,将这些神经元分为方位选择型,半场型、多峰型和全向型四种调谐模式.电刺激听皮层对绝大多数下丘神经元方位角的范围产生易化(42.0%)或抑制(45.0%)效应,并使59.3%的神经元的最佳方位角发生了转移.结果提示,小鼠下丘神经元具有明显的方位敏感性,听皮层对下丘神经元听觉方位信息处理具有下行调制作用.此研究结果为深入研究中枢听觉信息处理的离皮质调控机制提供了重要实验资料.     

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．     

Agrotis segetum雄蛾触角叶性信息素反应神经元对电刺激触角神经的反应

为探讨电刺激Agrotis segetum雄蛾触角神经是否可以作为MGC中神经元的识别手段,采用细胞内电生理记录方法,共记录34个对性信息素有反应的MGC神经元,并测试了其中12个神经元对性信息素刺激的反应,22个神经元对性信息素刺激和电刺激的反应。结果表明,MGC神经元对性信息素及电刺激的反应模式基本一致,为一种双相反应模式。两种刺激方式均能诱导出兴奋反应,电刺激得到的兴奋反应比由信息素刺激引起的要短;MGC神经元对两种刺激的超极化反应（抑制反应）幅度影响没有显著性差别,在电刺激实验的22个神经元上,超极化反应幅度和抑制时间都与神经元本身放电频率有一定的相关性。超极化反应是在LN参与下一定的神经回路对刺激所产生的反应而形成的。这提示两种刺激所作用的神经回路应是一致的,但从整个实验过程记录到的神经元情况来看,还须进一步结合形态学实验来验证电刺激触角神经作为MGC神经元的识别手段。     

电刺激大鼠内侧额叶前皮质对听皮层神经元频率感受野可塑性的调制

本文应用常规电生理学技术,研究电刺激大鼠内侧额叶前皮质（medial prefrontal cortex,mPFC）对初级听皮层神经元频率感受野（receptive field,RF）可塑性的调制。电刺激mPFC,137个听皮层神经元（72．8％）RF可塑性受到影响,其中抑制性调制71个神经元（37．7％）,易化性调制66个神经元（35．1％）,其余51个神经元（27．2％）不受影响。mPFC的抑制性调制效应表现为,RF的偏移时间延长,恢复时间缩短。相反,mPFC的易化性调制效应表现为,RF的偏移时间缩短,恢复时间延长。电刺激mPFC对RF可塑性的调制与声、电刺激之间的时间间隔有关,最佳时间间隔介于5-30ms之间。结果提示,大鼠mPFC可以调制听皮层神经元的功能活动,可能参与听觉学习记忆过程。     

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.     

大鼠皮层听-视多感觉神经元和听-视信息整合

应用常规电生理技术,研究SD大鼠皮层听-视多感觉神经元的分布和听-视信息整合.共记录到130个听-视双模态神经元,其中65个A-V型神经元,28个v-A型神经元和37个a-V型神经元.这些双模态神经元主要分布于听区的背侧,听皮层和视皮层的交界处,具有明显的区域性,呈条带状分布,v-A型神经元较多地位于近听皮层一侧,a-V型神经元则主要位于近视皮层一侧,A-V型神经元位于两者之间.在条带中,双模态神经元分布不均一,有片状分布趋势.双模态神经元的听-视信息整合效应分为增强型、抑制型和调制型.整合效应与声-光组合刺激的时间间隔有关,其中75%的神经元获得最大整合效应的时间间隔在30～50ms之间.研究结果提示,大鼠皮层存在听-视多感觉神经元分布区,这些神经元遵循存在于其他动物相关脑区多感觉信息整合规律,参与听-视感觉信息整合.     

幼年大鼠皮层听-视多感觉神经元和听-视信息整合

应用常规电生理学细胞外记录技术,研究了生后3周龄幼年大鼠皮层听-视双模态神经元及听-视信息整合特性,并与成年动物进行对照。在听皮层的背侧,听皮层和视皮层的交界处,即颞-顶-枕联合皮层区,共记录到了324个神经元,其中45个为听-视双模态神经元,占13.9%,远低于成年动物双模态神经元所占比例(42.8%)。这些双模态神经元可分为A-V型,v-A型和a-V型3种类型。根据它们对听-视信息的整合效应,可分为增强型、抑制型和调制型。整合效应与给予的声和光组合刺激的时间间隔有关,以获得整合效应的时间间隔范围为整合时间窗,幼年动物的平均整合时间窗为11.9 ms,远小于成年动物的整合时间窗(平均为23.2 ms)。结果提示,与单模态感觉神经元对模态特异性反应特性一样,皮层听-视双模态神经元生后有一个发育、成熟的过程。研究结果为深入研究中枢神经元多感觉整合机制提供了重要实验资料。     

Bilateral collicular interaction: modulation of auditory signal processing in amplitude domain

In the ascending auditory pathway, the inferior colliculus (IC) receives and integrates excitatory and inhibitory inputs from many lower auditory nuclei, intrinsic projections within the IC, contralateral IC through the commissure of the IC and from the auditory cortex. All these connections make the IC a major center for subcortical temporal and spectral integration of auditory information. In this study, we examine bilateral collicular interaction in modulating amplitude-domain signal processing using electrophysiological recording, acoustic and focal electrical stimulation. Focal electrical stimulation of one (ipsilateral) IC produces widespread inhibition (61.6%) and focused facilitation (9.1%) of responses of neurons in the other (contralateral) IC, while 29.3% of the neurons were not affected. Bilateral collicular interaction produces a decrease in the response magnitude and an increase in the response latency of inhibited IC neurons but produces opposite effects on the response of facilitated IC neurons. These two groups of neurons are not separately located and are tonotopically organized within the IC. The modulation effect is most effective at low sound level and is dependent upon the interval between the acoustic and electric stimuli. The focal electrical stimulation of the ipsilateral IC compresses or expands the rate-level functions of contralateral IC neurons. The focal electrical stimulation also produces a shift in the minimum threshold and dynamic range of contralateral IC neurons for as long as 150 minutes. The degree of bilateral collicular interaction is dependent upon the difference in the best frequency between the electrically stimulated IC neurons and modulated IC neurons. These data suggest that bilateral collicular interaction mainly changes the ratio between excitation and inhibition during signal processing so as to sharpen the amplitude sensitivity of IC neurons. Bilateral interaction may be also involved in acoustic-experience-dependent plasticity in the IC. Three possible neural pathways underlying the bilateral collicular interaction are discussed.     

电刺激蝙蝠中脑上丘对下丘听神经元电活动的影响

实验在24只鲁氏菊头蝠(Rhinolophus rouxi)上进行.使用玻璃微电极在中脑下丘中央核记录听神经元电反应.刺激点位于上丘核.共观察了294个对超声刺激产生反应的下丘听单位.当电刺激上丘时,有122个听单位的反应受到影响,占所观察总数的41.5%.其中96个单位表现为抑制性影响(占32.65%),26个单位表现为易代性效应(占8.84%).其余172个单位不受上丘刺激的影响(58.50%).实验中发现,上述抑制潜伏期一般在5毫秒以上,抑制时程较长.抑制程度与上丘刺激电流强度呈相关关系(r=0.99).实验中还发现,刺激上丘同样可抑制部分下丘神经元的自发放电活动,其抑制后效应相当长,有的可达120毫秒以上.     

幼年蝙蝠下丘神经元的听空间特性

实验分别在出生后４周龄的幼年和成年鲁氏菊头蝠（Ｒｈｉｎｏｌｏｐｈｕｓｒｏｕｘｉ）上进行。使用移动声刺激装置,高频喇叭可在动物头部前方水平方向１８０度、垂直方向６０度的范围内移动。玻璃微电极记录单个神经元的听反应。实验考察了幼年和成年动物下丘神经元的听空间特性,共观察了３０１个神经元,其中幼年动物１４８个,成年动物１５３个。结果表明,４周龄的幼年动物下丘听神经元已表现出方向敏感性,即每个听神经元均有一个特定的最佳反应中心和反应域。但神经元听反应中心在听空间的分布相当弥散,大多数位于对侧水平方向２０—８０度、垂直方向上下１５度范围内。而成年动物听神经元反应中心的分布则相当集中,局限地分布于对侧水平方向２８－５０度,垂直方向０—１０度范围内,两者构成明显差异。     

Changes in neuronal activity of the inferior colliculus in rat after temporal inactivation of the auditory cortex

The role of cortico-tectal pathways in auditory signal processing was studied in anesthetized rats by comparing the extracellular single unit activity in the inferior colliculus (IC) before and after functional ablation of the auditory cortex (AC) by tetrodotoxin (TTX). The responses of several IC neurons to sound stimuli were simultaneously recorded with a 16-channel electrode probe introduced into the IC. Click-evoked middle latency responses (MLR) recorded from the AC were suppressed for several hours after TTX injection. During AC inactivation the firing rate of IC neurons increased (40 % of neurons), decreased (44 %) or did not change (16 %) in comparison with control conditions. In several IC neurons, TTX injection resulted in alterations in the shape of the rate-level functions. Response thresholds, tuning properties and the type of discharge pattern of IC neurons were not altered during AC inactivation. However, in one-third of the neurons, the initial part of the response was less altered than the later, sustained part. In two-thirds of neuronal pairs, functional decortication resulted in a change in the cross-correlation coefficient. The results reveal the complex changes that appear in IC neuronal activity after functional ablation of the ipsilateral auditory cortex.     

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     

Real-time imaging of neural activity during binaural interaction in the guinea pig auditory cortex

Spatio-temporal patterns of binaural interaction in the guinea pig auditory cortex (AC) were observed using optical recording with a 12 × 12 photodiode array and a voltage-sensitive dye. The amplitudes of the sound-induced light signals from the cortex were transformed into sequential two-dimensional images every 0.58 ms. Binaural sound stimuli evoked an excitatory response followed by a strong inhibition, and contralateral stimuli evoked a strong excitatory response followed by a weak inhibition. Ipsilateral sound stimuli evoked a weak response. Binaural stimulation induced two types of ipsilateral inhibition: a fast binaural inhibition which was detected only after the contralateral and ipsilateral responses were subtracted from the binaural responses, and which appeared 12–25 ms after the onset of stimulation, and a slow binaural inhibitory effect which was clearly observed in the binaural responses themselves, appearing 70–95 ms after the onset of stimulation. The fast binaural inhibition was observed in the same area as the contralateral excitatory response. The inhibited area became stronger and more widespread with increasing intensity of ipsilateral stimulation. We did not observe the specialized organization of binaural neurons as electrophysiologically found in the cat AC, in which binaural neurons of the same binaural response type are clustered together and alternate with clusters of other response types. Accepted: 14 August 1997     

The influence of the auditory cortex on acoustically evoked cerebellar responses in the CF-FM bat,Rhinolophus pearsonic chinesis

1. Acoustically evoked responses of 284 neurons isolated from the cerebellar vermis, hemispheres and paraflocculus of Rhinolophus pearsonic chinesis were studied under free field acoustic stimulation conditions. 2. The BFs of these cerebellar auditory neurons ranged from 24 to 76 kHz but they mostly fall either between 48 and 64 kHz or between 65 and 76 kHz. However, the BF distribution varies among vermal, hemispheric and parafloccular neurons. 3. Threshold curves of cerebellar neurons are generally broad but those tuned to the frequency of the predominant CF component are extremely narrow. 4. Response latencies of cerebellar neurons ranged from 2 to 48 ms suggesting multiple auditory cerebellar pathways. The latency distribution also varies among vermal, hemispheric and parafloccular neurons. 5. Although both the vermis and hemispheres contain a disproportionate number of 65-74 kHz neurons, the response latencies of those neurons isolated from the vermis are scattered over a wide range of 2.2-28 ms while those neurons isolated from the hemispheres are generally stabilized between 5 and 12 ms. 6. Electrical stimulation of the auditory cortex evokes discharges from a recorded cerebellar auditory neuron. Cortical stimulation also facilitates the response of an acoustically evoked cerebellar neuron by increasing its number of impulses. The degree of facilitation is dependent upon the amplitude of the acoustic stimulus. 7. For a given electrical and acoustic stimulation condition, the facilitative latency and the degree of facilitation varied with the interstimulus interval. Among 23 neurons studied, most of them (19 neurons, 82.6%) had a maximal facilitative latency between 2 and 10 ms. 8. By examining the difference in the facilitative effect in each isolated cerebellar auditory neuron before and after a topical application of local anesthetic, procaine, onto the point of electrical stimulation in the auditory cortex, we found that the facilitative pathways to vermal and hemispheric neurons may be different from the pathway to parafloccular neurons. 9. Possible auditory pathways to different parts of the cerebellum are discussed in relation to the wide range of recorded response latencies. 10. The facilitative influence of the auditory cortex on the cerebellar auditory neurons is assumed to enhance the cerebellar role in acoustic motor orientation.