POSTSYNAPTIC TRANSDUCTION IN THE COCHLEAR NUCLEUS

这个项目研究了神经细胞的膜特性。 鸟类耳蜗核，即大细胞核(NM)。网管包含 与哺乳动物的丛生细胞同源的细胞 耳蜗前腹核。NM神经元投射到板层核 作为声音空间定位基础的神经元通过产生 动作电位响应于来自 同侧和对侧NM。为了实现准确的定位 声音，NM神经元必须传递关于听觉的精确计时信息 刺激。对听神经的刺激会导致快速的抽搐 NM神经元中的EPSP。由于NM神经元在反应中发出动作电位 对于交流输入而不是直流输入，EPSPS的时间总和将 不会在NM神经元产生动作电位的放电。我们已经证明了 在NM神经元上存在K+电流，这是导致大突触的原因 势能以最小的时间总和迅速衰减。 内侧核是紧张性组织的：后外侧内侧核中的神经元 接收由最低声音频率激活的听神经输入 而位于前内侧NM的那些人则接受由最高 声音频率。一个耐人寻味的问题是，是否存在差异 在允许前内侧NM神经元反应的膜特性中 对高频刺激和后外侧NM神经元的最佳反应 最好是低频率的刺激。我们有证据表明这种膜 属性确实有所不同，因为动作电位阈值 NM神经元核前区的去极化比 后脑区的神经元。 这项建议的目的是确定NM的转导特性 神经元沿着紧张轴变化。需要检验的假设是： I.假设：NM神经元含有几种不同类型的K+通道 而且它们的表达在音调轴上也不同。 2.假设：钠离子通道的密度和/或特性各不相同 沿着NM的音调轴线。 3.假设：NM神经元膜特性的强直性变化 导致沿音调轴不同的响应属性。 电性致密的NM神经元是理想的中枢神经元 电压钳研究。K+和Na+的电导将被隔离在 以及它们在突触后转导中的作用将被绘制出来 相对于单元格在调色轴上的位置。 这项研究将提供有关听觉系统如何 行得通。它还将为未来关于以下问题的调查提供基础 离子通道的表达是如何在空间中被调节的。

This project investigates the membrane properties of neurons from the avian cochlear nucleus, the nucleus magnocellularis (NM). The NM contains the cells which are homologous to the bushy cells of the mammalian anteroventral cochlear nucleus. NM neurons project to nucleus laminaris neurons which underlie the spatial localization of sound by generating action potentials in response to appropriately timed inputs from the ipsilateral and contralateral NM. In order for accurate localization of sound, NM neurons must relay precise timing information about the auditory stimulus. Stimulation of the auditory nerve results in rapid volleys of EPSPs in NM neurons. Since NM neurons fire action potentials in response to AC inputs but not to DC inputs, temporal summation of the EPSPs would not produce firing of action potentials in NM neurons. We have shown that there is a K+ current in NM neurons which causes the large synaptic potentials to decay rapidly with minimal temporal summation. The NM is tonotopically organized: neurons in the posterolateral NM receive auditory nerve inputs activated by the lowest sound frequencies while those in the anteromedial NM receive inputs activated by the highest sound frequencies. An intriguing question is whether there are differences in the membrane properties that permit anteromedial NM neurons to respond best to high frequency stimuli and posterolateral NM neurons to respond best to low frequency stimuli. We have evidence that the membrane properties do indeed vary because action potential threshold is more depolarized in NM neurons from the anterior region of the nucleus than neurons from the posterior region. The aim of this proposal is to determine how transduction properties of NM neurons vary along the tonotopic axis. The hypotheses to be tested are: I. Hypothesis: NM neurons contain several different types of K+ channels and their expression varies along the tonotopic axis. 2. Hypothesis: The density and/or characteristics of Na+ channels vary along the tonotopic axis of NM. 3. Hypothesis: The tonotopic variation of NM neuron membrane properties results in response properties that differ along the tonotopic axis. The electrotonically compact NM neurons are ideal central neurons for voltage-clamp studies. The K+ and Na+ conductances will be isolated in vitro and their contribution to post-synaptic transduction will be mapped with respect to the position of the cells on the tonotopic axis. This study will provide basic information about how the auditory system works. It will also provide a foundation for future investigations about how ion channel expression is regulated over space.