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。     

大鼠视皮层神经元电生理和形态学特性在发育中的变化

为研究大鼠不同发育阶段视皮层神经元电的生理学与形态学特性,实验观察了神经元电生理和形态学特性的变化与年龄的同步化程度,探讨视皮层视觉依赖性突触的形成和重新分布的细胞内机制。应用脑片膜片钳全细胞记录技术和细胞内生物家标记相结合的方法,记录4—28d SD大鼠视皮层神经元的突触后电流(postsynaptic currents,PSCs)。共记录156个大鼠视皮层神经元,睁眼前与睁眼后组中无反应型细胞数量,多突触反应型细胞数量、细胞的输入阻抗有显著性差异。成功标记23例神经元,不同年龄的神经元的形态学成熟度不同。低输入阻抗神经元在形态学上属成熟型,高输入阻抗神经元属幼稚型。该结果表明,大鼠在发育过程中,视皮层神经元功能的成熟表现为在形觉刺激以及局部神经元网络的整合作用下的视觉依赖性突触的形成和重新分布。在视觉发育可塑性关键期内,视皮层神经元形态和电生理特性的变化与年龄的同步化程度大于皮层下结构。     

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。     

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．     

金黄地鼠视皮层中乙酰胆碱(Ach)阳性神经元及纤维

本文通过色疫组织化学方法-PAP法,使用乙酰胆碱(Ach)抗体对金黄地鼠视皮层中的Ach进行定位Ach阳性神经元分布于视皮层的第Ⅱ—Ⅵ层,主要集中在Ⅱ、Ⅲ层.其细胞形态除大部分为非锥体神经元外,还发现有极少数锥体型神经元.这些神经元的数量和树突形态在视皮层17区和18区存在某些区域性差异.17区细胞比较密集,18区比较稀疏.17区第IA层细胞排列整齐,顶树突特别粗大,18区这种现象不太明显.皮层白质中也有少量的Ach阳性神经元.视皮层Ach阳性神经元的相对含量约为10%.视皮层中遍布外源性和内源性Ach阳性神经纤维,它们主要分布在第Ⅳ层.在视皮层微血管周围有大量Ach阳性神经元,说明对血管有舒张作用的Ach可能来源于血管内壁.     

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.     

初级视皮层神经元非经典感受野研究的新进展

感觉皮层神经元的非经典感受野(简称"外周")对经典感受野(简称"中心")的调节作用广泛存在于哺乳动物中,被认为是感觉皮层神经元的基本特性.以初级视皮层神经元为例,刺激其外周能有效地调节刺激其中心引起的反应,这种作用主要是抑制性的.理解初级视皮层神经元的外周对中心的调节机制能够深入揭示哺乳动物的感觉皮层神经元信息处理的基本原则.本文综述了引起初级视皮层神经元非经典感受野对经典感受野调节作用的神经环路机制和计算模型研究的进展.     

大鼠离体视皮层神经元短时程时间整合特性的研究

用双脉冲白质电刺激研究了８７个大鼠视皮层神经元的短时程时间整合特性。第一个脉冲所引起的细胞反应对第二个反应有影响的细胞占被记录细胞总数的５５．２％,其中表现为突触作用增强的占４１．７％,表现为突触作用压抑的占５８．３％。整合作用的强度决定于两个脉冲之间的时间间隔,作用形式主要表现为第二个刺激所引起的反应的幅度和时程的改变。电反应可以ＥＰＳＰ或ＩＰＳＰ为主,或由ＥＰＳＰ和ＩＰＳＰ混合组成。部分细胞的反应包含快慢两个成份,时间整合作用对不同反应成份的影响程度有明显的不同。在锥体神经元中,增强型和压抑型的比例大致相等,而非锥体神经元只显示压抑型作用。位于皮层深层的神经元有时间整合作用的比率（３７．５％）比位于浅层的神经元（６０．５％）要低得多。     

金黄地鼠视皮层17、18区乙酰胆碱阳性神经元

利用乙酰胆碱( acetylcholine,Ach)自身抗体对金黄地鼠视皮层17、18区乙酰胆碱阳性神经元及其分布进行免疫学显示并进行量化分析.实验发现,Ach阳性细胞大部分为非锥体神经元,也有少量锥体神经元.Ach阳性神经元在视皮层的Ⅱ～Ⅵ层,主要分布在Ⅱ～Ⅳ层.在不同层次中其阳性神经元类型存在某些差异,Ⅱ～Ⅳ中双极细胞居多,其他层次中多极细胞占优势.17区的这类神经元数量较多且集中成垂直于皮层表面的细胞带,18区的神经元数量相对较少且多呈分散状态.     

Asynchrony adaptation reveals neural population code for audio-visual timing

The relative timing of auditory and visual stimuli is a critical cue for determining whether sensory signals relate to a common source and for making inferences about causality. However, the way in which the brain represents temporal relationships remains poorly understood. Recent studies indicate that our perception of multisensory timing is flexible--adaptation to a regular inter-modal delay alters the point at which subsequent stimuli are judged to be simultaneous. Here, we measure the effect of audio-visual asynchrony adaptation on the perception of a wide range of sub-second temporal relationships. We find distinctive patterns of induced biases that are inconsistent with the previous explanations based on changes in perceptual latency. Instead, our results can be well accounted for by a neural population coding model in which: (i) relative audio-visual timing is represented by the distributed activity across a relatively small number of neurons tuned to different delays; (ii) the algorithm for reading out this population code is efficient, but subject to biases owing to under-sampling; and (iii) the effect of adaptation is to modify neuronal response gain. These results suggest that multisensory timing information is represented by a dedicated population code and that shifts in perceived simultaneity following asynchrony adaptation arise from analogous neural processes to well-known perceptual after-effects.     

Auditory-visual crossmodal integration in perception of face gender

Whereas extensive neuroscientific and behavioral evidence has confirmed a role of auditory-visual integration in representing space [1-6], little is known about the role of auditory-visual integration in object perception. Although recent neuroimaging results suggest integrated auditory-visual object representations [7-11], substantiating behavioral evidence has been lacking. We demonstrated auditory-visual integration in the perception of face gender by using pure tones that are processed in low-level auditory brain areas and that lack the spectral components that characterize human vocalization. When androgynous faces were presented together with pure tones in the male fundamental-speaking-frequency range, faces were more likely to be judged as male, whereas when faces were presented with pure tones in the female fundamental-speaking-frequency range, they were more likely to be judged as female. Importantly, when participants were explicitly asked to attribute gender to these pure tones, their judgments were primarily based on relative pitch and were uncorrelated with the male and female fundamental-speaking-frequency ranges. This perceptual dissociation of absolute-frequency-based crossmodal-integration effects from relative-pitch-based explicit perception of the tones provides evidence for a sensory integration of auditory and visual signals in representing human gender. This integration probably develops because of concurrent neural processing of visual and auditory features of gender.     

Integration of Visual Information in Auditory Cortex Promotes Auditory Scene Analysis through Multisensory Binding

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Recent advances in the study of Kaposi's sarcoma-associated herpesvirus replication and pathogenesis

It has now been over twenty years since a novel herpesviral genome was identified in Kaposi's sarcoma biopsies. Since then, the cumulative research effort by molecular biologists, virologists, clinicians, and epidemiologists alike has led to the extensive characterization of this tumor virus, Kaposi's sarcoma-associated herpesvirus(KSHV; also known as human herpesvirus 8(HHV-8)), and its associated diseases. Here we review the current knowledge of KSHV biology and pathogenesis, with a particular emphasis on new and exciting advances in the field of epigenetics. We also discuss the development and practicality of various cell culture and animal model systems to study KSHV replication and pathogenesis.     

The structure, reproduction and taxonomy of Vidalia and Osmundaria (Rhodophyta, Rhodomelaceae)

Comprises species occurring mostly in subtidal habitats in tropical, subtropical and warm-temperate areas of the world. An analysis of the type species, V. spiralis (Sonder) Lamouroux ex J. Agardh, a species from Australia, establishes basic characters for distinguishing species in the genus. These characters are (1) branching patterns of thalli, (2) flat blades that may be spiralled on their axis, (3) width of the blade, (4) primary or secondary derivation of sterile and fertile branchlets and (5) position of sterile and fertile branchlets on the thalli. Application of the latter two characters provides an important basic method for separation of species into three major groups. Osmundaria , a genus known only in southern Australia, was studied in relation to Vidalia , and its separation from the Vidalia assemblage is not accepted. Species of Vidalia therefore are transferred to the older genus name, Osmundaria. Two new species, Osmundaria papenfussii and Osmundaria oliveae are described from Natal. Confusion in the usage of the epithet, Vidalia fimbriala Brown ex Turner has been clarified, and Vidalia gregaria Falkenberg, described as an epiphyte on Osmundaria pro/ifera Lamouroux, is revealed to be young branches of the host, Osmundaria prolifera.