Effects of somatosensory and parallel stimulation on neurons in dorsal cochlear nucleus
Effects of somatosensory and parallel stimulation on neurons in dorsal cochlear nucleus
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DOI：
10.1152/jn.1996.76.5.3012
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发表时间：
1996-11-01
影响因子：
2.5
通讯作者：
Young, ED
中科院分区：
文献类型：
--
作者：
Davis, KA;Miller, RL;Young, ED
1.在麻痹的去大脑猫的耳蜗背核（DCN）中记录了对两个部位的电刺激的响应的单个单位和诱发电位：1）在躯体感觉背柱核（下面对于延髓体感核一起称为MSN），其激活苔藓纤维输入到浅表DCN中的颗粒细胞，和2）在DCN的游离表面上，其直接激活颗粒细胞轴突（平行纤维）。目的是评估关于浅表DCN小脑样回路中突触相互作用的假设。一个四脉冲促进范式（50毫秒脉冲间隔），这允许识别的三个组成部分的DCN主细胞（IV型单位）对这些刺激的反应。将反应成分的潜伏期与DCN中诱发电位的潜伏期进行比较，DCN中的诱发电位表示平行纤维齐射到达记录点。第一个组成部分是短潜伏期抑制反应;该组成部分仅在MSN刺激时可见，并且几乎仅在还显示第二个组成部分（瞬时兴奋性反应）的单位中可见。短潜伏期抑制成分先于诱发电位。目前还不能对短延迟分量给出令人满意的解释;它很可能反映了一种快速传导的抑制性输入，这种输入在缓慢传导的平行光纤之前到达IV型单元。第二个组成部分是一个短暂的兴奋性反应;该组件都看到MSN和平行纤维刺激;它是弱的，似乎很容易被掩盖的抑制性反应组件。兴奋性成分发生在相同的潜伏期作为诱发电位，可能反映直接兴奋的颗粒细胞轴突的主细胞。兴奋成分被认为是在约一半的IV型单位的两个刺激网站。在MSN刺激下，某些单位缺乏兴奋表明耳蜗颗粒细胞的异质性，有些携带体感信息，有些不携带这种信息;在平行纤维刺激下，兴奋可能需要刺激电极和记录电极排列在平行纤维的同一“梁”上。第三个组成部分是一个持久的抑制反应，观察到几乎所有的IV型单位与MSN和平行纤维刺激;其潜伏期长于诱发电位。有证据表明，这是由来自侧手翻细胞的抑制性输入提出的。这种抑制成分在几乎所有IV型单位中的出现可以通过侧手翻细胞轴突在垂直于平行纤维的方向上的相当大的扩散来解释。诱发电位和单位反应的所有三个分量在四个电刺激脉冲上在大小上系统地变化。这些结果可以用两种现象来解释：1）在所有细胞类型上的颗粒细胞突触的易化，其通过四个脉冲产生稳定增长的反应，类似于突触前易化，并且在MSN和平行纤维刺激中都可以看到;和2）仅对于MSN刺激，颗粒细胞反应在第一和第二脉冲之间强烈降低。这种减少可能发生在肾小球或颗粒细胞本身的突触前，可能反映了抑制性输入。在DCN的梭形细胞和深层中记录的IV型单位中可以看到上述反应成分;这表明锥体细胞和巨细胞的激活相似。最简单的解释是，这两种主要的细胞类型都被表层DCN中的小脑样回路激活。另外，由于巨细胞似乎与浅表DCN的颗粒细胞回路接触有限，这一发现可能表明在深层DCN中存在目前未描述的颗粒细胞回路，其功能与浅表DCN相似。
1. Single units and evoked potentials were recorded in the dorsal cochlear nucleus (DCN) of paralyzed decerebrate cats in response to electrical stimulation at two sites: 1) in the somatosensory dorsal column nuclei (together called MSN below for medullary somatosensory nuclei), which activates mossy-fiber inputs to granule cells in superficial DCN, and 2) on the free surface of the DCN, which activates granule cell axons (parallel fibers) directly. The goal was to evaluate hypotheses about synaptic interactions in the cerebellum-like circuitry of the superficial DCN. A four-pulse facilitation paradigm was used (50-ms interpulse interval); this allows identification of three components of the responses of DCN principal cells (type IV units) to these stimuli. The latencies of the response components were compared with the latency of the evoked potential in DCN, which signals the arrival of the parallel fiber volley at the recording site.2. The first component is a short-latency inhibitory response; this component is seen only with MSN stimulation and is seen almost exclusively in units also showing the second component, the transient excitatory response. The short-latency inhibitory component precedes the evoked potential. No satisfactory explanation for the short-latency component can be given at present; it most likely reflects a fast-conducting inhibitory input that arrives at the type IV unit before the slowly conducting parallel fibers.3. The second component is a transient excitatory response; this component is seen with both MSN and parallel fiber stimulation; it is weak and appears to be masked easily by the inhibitory response components. The excitatory component occurs at the same latency as the evoked potential and probably reflects direct excitation of principal cells by granule cell axons. The excitatory component is seen in about half the type IV units for both stimulating sites. With MSN stimulation, the lack of excitation in some units suggests a heterogeneity of cochlear granule cells, with some carrying somatosensory information and some not carrying this information; with parallel fiber stimulation, excitation probably requires the stimulating and recording electrodes to be lined up on the same ''beam'' of parallel fibers.4. The third component is a long-lasting inhibitory response that is observed in virtually all type IV units with both MSN and parallel-fiber stimulation; its latency is longer than the evoked potential. Evidence suggests that is proposed by inhibitory input from cartwheel cells. The appearance of this inhibitory component in almost all type IV units can be accounted for by the considerable spread of cartwheel-cell axons in the direction perpendicular to the parallel fibers.5. The evoked potential and all three components of the unit response vary systematically in size over the four pulses of the electrical stimulus These results can be accounted for by two phenomena; 1) a facilitation of the granule cell synapses on all cell types that produces a steadily growing response through the four pulses, resembles presynaptic facilitation, and is seen with both MSN and parallel-fiber stimulation; and 2) a strong reduction in the granule cell response between the first and second pulse for MSN stimulation only. This reduction probably occurs presynaptically in the glomerulus or in the granule cell itself and could reflect inhibitory inputs.6. The response components described above are seen in type IV units recorded in both the fusiform-cell and deep layers of the DCN; this suggests that both pyramidal and giant cells are activated similarly. The simplest interpretation is that both principal cell types are activated by the cerebellum-like circuitry in superficial DCN. Alternatively, because giant cells appear to make limited contact with granule-cell circuits of superficial DCN, this finding may suggest the existence of currently undescribed granule cell circuits in deep DCN that are similar in function to those in superficial DCN.