Development of Inhibitory Pathways in the Rat Spinal Cord

利用分离脊髓制备胎鼠和新生大鼠，电生理学研究了腰椎抑制通路的发展。反射通路抑制的发展：不同年龄腰椎运动神经元的细胞内记录显示，刺激背根后的抑制性突触后电位（IPSPs）首次出现在胚胎日(E) 16.5，出生前5天。在这一阶段，单个运动神经元中IPSPs的出现频率低于兴奋性突触后电位（EPSPs）的出现频率，说明反射弧中抑制性通路的出现要晚于兴奋性通路。在E15.5时慢性横断下胸索不影响抑制通路的后期发展。节律产生器抑制作用的发展：n -甲基- d， l-天冬氨酸（NMA）可激活产生节律性运动活动的神经元回路。腰腹根的节律性活动在E15.5时首次出现，尽管在E17.5时该神经元回路中对松子碱敏感的抑制作用开始起作用。抑制作用改变了两侧腹侧根的活动模式，运动模式也由同步模式转变为交替模式。

Development of inhibitory pathways in the lumbar spinal cord was investigated electrophysiologically using an isolated spinal cord preparation in fetal and new-born rats.1. Development of inhibition in the reflex pathway : Intracellular recordings from lumbal motoneurones at different ages revealed that inhibitory postsynaptic potentials (IPSPs) following stimulation of the dorsal root first appeared at embryonic days (E) 16.5, 5 days before birth. The frequency of occurrence of IPSPs were less than that of excitatory postsynaptic potentials (EPSPs) in individual motoneurones at this stage, indicating that inhibitory pathways would develop later than excitatory ones in the reflex arc. Chronic transection of the lower thoracic cord at E15.5 could not affect the later development of the inhibitory pathways.2. Development of inhibition in the rhythm generator : A neuronal circuit generating rhythmic motor activity was activated by bath application of N-methyl-D, L-aspartate (NMA). Rhythmic activities in the lumbar ventral roots first appeared at E15.5, though srychnine-sensitive inhibitoty action began toqfunction at E17.5 in this neuronal ciruit. The inhibition changed the pattern of activities in the ventral root on two sides from synchronized to alternating, as is the pattern of locomotion.