PDF(Pubmed)
Abstract：
We are studying the mechanisms of H-reflex operant conditioning, a simple form of learning. Modelling studies in the literature and our previous data suggested that changes in the axon initial segment (AIS) might contribute. To explore this, we used blinded quantitative histological and immunohistochemical methods to study in adult rats the impact of H-reflex conditioning on the AIS of the spinal motoneuron that produces the reflex. Successful, but not unsuccessful, H-reflex up-conditioning was associated with greater AIS length and distance from soma; greater length correlated with greater H-reflex increase. Modelling studies in the literature suggest that these increases may increase motoneuron excitability, supporting the hypothesis that they may contribute to H-reflex increase. Up-conditioning did not affect AIS ankyrin G (AnkG) immunoreactivity (IR), p-p38 protein kinase IR, or GABAergic terminals. Successful, but not unsuccessful, H-reflex down-conditioning was associated with more GABAergic terminals on the AIS, weaker AnkG-IR, and stronger p-p38-IR. More GABAergic terminals and weaker AnkG-IR correlated with greater H-reflex decrease. These changes might potentially contribute to the positive shift in motoneuron firing threshold underlying H-reflex decrease; they are consistent with modelling suggesting that sodium channel change may be responsible. H-reflex down-conditioning did not affect AIS dimensions. This evidence that AIS plasticity is associated with and might contribute to H-reflex conditioning adds to evidence that motor learning involves both spinal and brain plasticity, and both neuronal and synaptic plasticity. AIS properties of spinal motoneurons are likely to reflect the combined influence of all the motor skills that share these motoneurons. KEY POINTS: Neuronal action potentials normally begin in the axon initial segment (AIS). AIS plasticity affects neuronal excitability in development and disease. Whether it does so in learning is unknown. Operant conditioning of a spinal reflex, a simple learning model, changes the rat spinal motoneuron AIS. Successful, but not unsuccessful, H-reflex up-conditioning is associated with greater AIS length and distance from soma. Successful, but not unsuccessful, down-conditioning is associated with more AIS GABAergic terminals, less ankyrin G, and more p-p38 protein kinase. The associations between AIS plasticity and successful H-reflex conditioning are consistent with those between AIS plasticity and functional changes in development and disease, and with those predicted by modelling studies in the literature. Motor learning changes neurons and synapses in spinal cord and brain. Because spinal motoneurons are the final common pathway for behaviour, their AIS properties probably reflect the combined impact of all the behaviours that use these motoneurons.
摘要：
我们正在研究H反射操作条件的机制，一种简单的学习形式。文献中的建模研究和我们以前的数据表明，轴突初始段（AIS）的变化可能有所贡献。为了探索这个，我们使用盲法定量组织学和免疫组织化学方法在成年大鼠中研究了H反射调节对产生反射的脊髓运动神经元AIS的影响.成功,但并非不成功，H反射上调与AIS长度和与体细胞的距离更大有关；长度越大，H反射增加越大。文献中的模型研究表明，这些增加可能会增加运动神经元的兴奋性，支持它们可能有助于H反射增加的假设。上调不影响AIS锚蛋白G(AnkG)免疫反应性(IR),p-p38蛋白激酶IR,或GABA能终端。成功,但并非不成功，H反射向下调节与AIS上更多的GABA能终末相关，较弱的AnkG-IR，和更强的p-p38-IR。更多的GABA能终末和较弱的AnkG-IR与更大的H反射降低相关。这些变化可能会导致H反射降低的基础运动神经元放电阈值的正变化；它们与建模一致，表明钠通道变化可能是原因。H反射向下调节不影响AIS尺寸。AIS可塑性与H反射调节相关并可能有助于H反射调节的证据增加了运动学习涉及脊髓和大脑可塑性的证据。以及神经元和突触可塑性。脊髓运动神经元的AIS特性可能反映了共享这些运动神经元的所有运动技能的综合影响。关键点：神经元动作电位通常在轴突起始段（AIS）开始。AIS可塑性影响发育和疾病中的神经元兴奋性。在学习中是否这样做是未知的。脊髓反射的有效调节，一个简单的学习模型，改变大鼠脊髓运动神经元AIS。成功,但并非不成功，H反射上调与AIS长度和与体细胞的距离更大有关。成功,但并非不成功，下调与更多的AISGABA能终端相关，少了一点ankyrinG,和更多的p-p38蛋白激酶。AIS可塑性与成功的H反射调节之间的关联与AIS可塑性与发育和疾病的功能变化之间的关联一致。以及文献中建模研究预测的结果。运动学习改变脊髓和大脑中的神经元和突触。因为脊髓运动神经元是行为的最终共同途径，它们的AIS特性可能反映了使用这些运动神经元的所有行为的综合影响。
