Gackière Florian, Vinay Laurent
Institut de Neurosciences de la Timone, UMR 7289, CNRS, Aix Marseille Université, 13385 Marseille cx 5, France.
Institut de Neurosciences de la Timone, UMR 7289, CNRS, Aix Marseille Université, 13385 Marseille cx 5, France
J Neurosci. 2015 Apr 1;35(13):5307-16. doi: 10.1523/JNEUROSCI.1674-14.2015.
In healthy mature motoneurons (MNs), KCC2 cotransporters maintain the intracellular chloride concentration at low levels, a prerequisite for postsynaptic inhibition mediated by GABA and glycine. KCC2 expression in lumbar MNs is reduced after spinal cord injury (SCI) resulting in a depolarizing shift of the chloride equilibrium potential. Despite modeling studies indicating that such a downregulation of KCC2 function would reduce the strength of postsynaptic inhibition, physiological evidence is still lacking. The present study aimed at investigating the functional impact of a modification of KCC2 function. We focused on a well characterized disynaptic inhibitory pathway responsible for reciprocal inhibition between antagonistic muscles. We performed in vitro extracellular recordings on spinal cords isolated from rodents at the end of the first postnatal week. Genetic reduction of KCC2 expression, pharmacological blockade of KCC2, as well as SCI-induced downregulation of KCC2 all resulted in a reduction of the strength of reciprocal inhibition. We then tried to restore endogenous inhibition after SCI by means of zinc ions that have been shown to boost KCC2 function in other models. Zinc chloride indeed hyperpolarized the chloride equilibrium potential in MNs and increased reciprocal inhibition after neonatal SCI. This study demonstrates that the level of KCC2 function sets the strength of postsynaptic inhibition and suggests that the downregulation of KCC2 after SCI likely contributes to the high occurrence of flexor-extensor cocontractions in SCI patients.
在健康成熟的运动神经元（MNs）中，KCC2共转运体将细胞内氯离子浓度维持在较低水平，这是γ-氨基丁酸（GABA）和甘氨酸介导的突触后抑制的前提条件。脊髓损伤（SCI）后，腰段运动神经元中KCC2的表达降低，导致氯离子平衡电位发生去极化偏移。尽管模型研究表明KCC2功能的这种下调会降低突触后抑制的强度，但仍缺乏生理学证据。本研究旨在调查KCC2功能改变的功能影响。我们聚焦于一条特征明确的双突触抑制通路，该通路负责拮抗肌之间的交互抑制。我们在出生后第一周结束时从啮齿动物分离的脊髓上进行了体外细胞外记录。KCC2表达的基因敲减、KCC2的药理学阻断以及SCI诱导的KCC2下调均导致交互抑制强度降低。然后，我们试图通过锌离子恢复SCI后的内源性抑制，锌离子在其他模型中已被证明可增强KCC2功能。氯化锌确实使运动神经元中的氯离子平衡电位超极化，并增加了新生大鼠SCI后的交互抑制。本研究表明，KCC2功能水平决定了突触后抑制的强度，并提示SCI后KCC2的下调可能是SCI患者屈肌-伸肌共同收缩高发的原因。
