SYNAPTIC PHYSIOLOGY OF SPINAL MOTONEURONS OF NORMAL AND SPASTIC MICE - AN INVITRO STUDY
SYNAPTIC PHYSIOLOGY OF SPINAL MOTONEURONS OF NORMAL AND SPASTIC MICE - AN INVITRO STUDY
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DOI：
10.1113/jphysiol.1986.sp016253
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发表时间：
1986-10-01
影响因子：
5.5
通讯作者：
DUCHEN, MR
中科院分区：
文献类型：
--
作者：
BISCOE, TJ;DUCHEN, MR
1. 在体外维持的小鼠脊髓标本中研究了脊髓反射。比较了正常小鼠和痉挛突变小鼠的运动神经元群体对节段性背根刺激的反应。在正常脊髓中，典型的是具有极少多突触兴奋的单突触反应，随后是一个去极化波，其上叠加有异步复合动作电位。在一些痉挛性脊髓中，观察到一个振荡的去极化波，持续长达500毫秒。正常小鼠和突变小鼠从阈值到最大反应的刺激范围相同。背根反射（d.r.r.）和背根电位（d.r.p）在正常小鼠和突变小鼠中都很显著，未发现一致的差异。
2. 使用填充有醋酸钾的电极从运动神经元进行细胞内记录。突变小鼠和正常小鼠的平均静息电位和输入电阻没有显著差异。在逆向动作电位之后看到的作为后去极化和后超极化的电压依赖性电导以及运动神经元对去极化电流注入的反应在两组中是相似的。
3. 在突变小鼠中，节段性背根刺激后运动神经元的突触反应明显异常。在正常小鼠中，在低刺激强度下看到单突触兴奋性突触后电位（e.p.s.p.），在较高刺激强度下接着是持续长达100毫秒的多突触活动，其很少达到动作电位发放的阈值。在突变小鼠中，单突触反应通常接着是去极化突触反应，这些反应常常在单突触反应达到阈值之前就诱发动作电位。在较高刺激强度下，单突触反应之后接着是在延长的去极化突触活动上产生的至少一个且常常是多个动作电位。
4. 当用填充有醋酸钾的电极穿刺细胞时，在正常小鼠和突变小鼠中都很少看到自发突触活动。当用氯化钾填充电极时，在正常运动神经元中自发去极化突触后电位（p.s.p.s）很显著，并且通过向细胞内离子电泳氯离子其幅度增加。在这些条件下，刺激腹根诱发一个去极化p.s.p.，并且伦肖抑制性突触后电位（i.p.s.p.）反转。自发p.s.p.s被离子电泳或浴槽应用甘氨酸拮抗剂士的宁所阻断。在突变运动神经元中，在细胞内离子电泳氯离子之后，既不能证明有自发的也不能证明有反复诱发的去极化p.s.p。
5. 在细胞内离子电泳氯离子之后，正常运动神经元对正向刺激的突触反应发生了深刻的改变。现在单突触反应之后接着是一个去极化波，该波诱发多个动作电位，随着刺激强度的增加而增加，持续长达1秒。在痉挛性脊髓中，用填充有氯化钾的电极进行的记录与用填充有醋酸钾的电极进行的记录无法区分。
6. 因此，痉挛突变小鼠的异常运动输出与显著降低的依赖氯离子、由甘氨酸介导的突触电导有关。这与该突变影响甘氨酸受体蛋白的表达、相关的氯离子通道或它们之间的相互作用这一假设是一致的。
1. Spinal cord reflexes have been examined in a preparation of the mouse spinal cord maintained in vitro. Responses of the motoneurone population of normal and spastic mutant mice to stimulation of a segmental dorsal root were compared. In the normal spinal cord, a monosynaptic response with very little polysynaptic excitation was typical followed by a depolarizing wave on which asynchronous compound action potentials were superimposed. In some spastic cords, an oscillating depolarizing wave was seen, lasting up to 500 ms. The stimulus range from threshold to maximal response was the same for the normal and mutant. The dorsal root reflex (d.r.r.) and dorsal root potential (d.r.p) were prominent in both normal and mutant, and no consistent difference could be identified. 2. Intracellular recordings were made from motoneurones using electrodes filled with potassium acetate. Mean resting potentials and input resistances were not significantly different in mutant and normal mice. The voltage-dependent conductances, seen as the after-depolarization and after-hyperpolarizations following antidromic action potentials and the responses of motoneurones to depolarizing current injection were similar in both populations. 3. The synaptic responses of motoneurones following stimulation of the segmental dorsal root were clearly abnormal in the mutant. In the normal mice, a monosynaptic excitatory post-synaptic potential (e.p.s.p.), seen at low stimulus intensities, was followed at higher stimulus intensities by polysynaptic activity lasting up to 100 ms, which rarely reached threshold for action potential discharge. In the mutant mice, the monosynaptic response was typically followed by depolarizing synaptic responses which often evoked action potentials before the monosynaptic response reached threshold. At higher stimulus intensities, the monosynaptic response was followed by at least one and often multiple action potentials generated on prolonged depolarizing synaptic activity. 4. When cells were impaled with potassium-acetate-filled electrodes, very little spontaneous synaptic activity was seen in either normal or mutant mice. Spontaneous depolarizing post-synaptic potentials (p.s.p.s) were prominent in normal motoneurones when potassium chloride was used to fill electrodes and were increased in amplitude by ionophoresis of chloride into the cells. Under these conditions stimulation of a ventral root evoked a depolarizing p.s.p. and the Renshaw i.p.s.p. reversed. The spontaneous p.s.p.s. were blocked by ionophoresis or bath application of the glycine antagonist strychnine. In mutant motoneurones neither spontaneous nor a recurrent evoked depolarizing p.s.p could be demonstrated following intracellular ionophoresis of chloride. 5. Synaptic responses of normal motoneurones to orthodromic stimulation were profoundly altered following intracellular ionophoresis of chloride. The monosynaptic response was now followed by a depolarizing wave which evoked multiple action potentials, increasing with increasing stimulus intensities to last up to 1 s. In spastic cords recordings made with electrodes filled with potassium chloride were indistinguishable from those made with electrodes filled with potassium acetate. 6. The abnormal motor output of the spastic mutant mouse is thus related to a dramatically reduced chloride-dependent, glycine-medicated synaptic conductance. This is consistent with the hypothesis that the mutation affects the expression of the glycine receptor protein, the associated chloride channel or the interaction between them.