Shunting versus inactivation: Analysis of presynaptic inhibitory mechanisms in primary afferents of the crayfish
Shunting versus inactivation: Analysis of presynaptic inhibitory mechanisms in primary afferents of the crayfish
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DOI：
10.1523/jneurosci.19-14-06079.1999
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发表时间：
1999-07-15
影响因子：
5.3
通讯作者：
El Manira, A
中科院分区：
文献类型：
--
作者：
Cattaert, D;El Manira, A
初级传入去极化（pad）与脊椎动物和无脊椎动物的突触前抑制有关。在本研究中，我们使用解剖和电生理技术来分析分流机制与钠通道失活在介导动作电位振幅降低从而突触前抑制中的相对重要性。在小龙虾体外制备中，对拉伸受体的感觉传入进行了实验。结合GABA免疫组化的路西法黄细胞内标记显示GABA免疫反应（ir）纤维与感觉轴突密切相关。大多数接触点位于神经节入口处的主轴突上，靠近神经节内的第一个分支点。相比之下，目标神经元的感觉传入输出突触位于远端分支。通过对单个感觉轴突进行双胞内记录，电生理学上确定了介导自发性pad的突触输入的位置。产生pad的输入似乎发生在第一个轴突分支点周围，与解剖学数据一致。在这一区域，3-15 mV的小电流注入可显著降低动作电位振幅，而15 mV的电流注入对膜电位去极化没有影响。这些结果表明，单个pad的动作电位幅度的降低是由分流机制引起的，但似乎与钠通道的失活无关。我们的研究结果还表明，gaba能突触前抑制可能作为一种全局控制机制，通过某些反射通路阻断传递。
Primary afferent depolarizations (PADs) are associated with presynaptic inhibition in both vertebrates and invertebrates. In the present study, we have used both anatomical and electrophysiological techniques to analyze the relative importance of shunting mechanisms versus sodium channel inactivation in mediating the decrease of action potential amplitude, and thereby presynaptic inhibition. Experiments were performed in sensory afferents of a stretch receptor in an in vitro preparation of the crayfish. Lucifer yellow intracellular labeling of sensory axons combined with GABA immunohistochemistry revealed close appositions between GABA-immunoreactive (ir) fibers and sensory axons. Most contacts were located on the main axon at the entry rone of the ganglion, close to the first branching point within the ganglion. By comparison, the output synapses of sensory afferents to target neurons were located on distal branches. The location of synaptic inputs mediating spontaneous PADs was also determined electrophysiologically by making dual intracellular recordings from single sensory axons. Inputs generating PADs appear to occur around the first axonal branching point, in agreement with the anatomical data. In this region, small PADs (3-15 mV) produced a marked reduction of action potential amplitude, whereas depolarization of the membrane potential by current injection up to 15 mV had no effect. These results suggest that the decrease of the amplitude of action potentials by single PADs results from a shunting mechanism but does not seem to involve inactivation of sodium channels. Our results also suggest that GABAergic presynaptic inhibition may act as a global control mechanism to block transmission through certain reflex pathways.