Requirement of neuronal connexin36 in pathways mediating presynaptic inhibition of primary afferents in functionally mature mouse spinal cord
Requirement of neuronal connexin36 in pathways mediating presynaptic inhibition of primary afferents in functionally mature mouse spinal cord
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DOI：
10.1113/jphysiol.2011.225987
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发表时间：
2012-08-01
影响因子：
5.5
通讯作者：
McCrea, David A.
中科院分区：
文献类型：
--
作者：
Bautista, Wendy;Nagy, James I.;McCrea, David A.
含有连接蛋白36 （Cx36）的间隙连接形成的电突触促进了哺乳动物大脑许多区域间神经元的同步活动；然而，关于电突触在脊髓神经网络中的作用的信息有限。在这里，我们发现Cx36广泛分布于脊髓中，并参与控制初级传入终端的突触前抑制机制。对8 ~ 11日龄野生型和Cx36基因敲除小鼠的脊髓标本进行电生理记录。在Cx36基因敲除小鼠中，与低阈值后肢传入事件条件刺激引起的突触前抑制相关的几个特征基本受损。低强度感觉传入刺激引起的背根电位（DRPs）在Cx36敲除后振幅降低了79%，持续时间降低了67%。在野生型中，大量应用间隙结阻滞剂对DRPs也有类似的影响。与在成年猫中描述的Ia组肌纺锤体传入终端在运动神经元上的突触前抑制一致，对相邻背根的条件反射刺激在野生型小鼠中引起了对腹根单突触反射的长时间抑制，这种抑制被二胡兰拮抗。同样的条件刺激不能抑制Cx36基因敲除小鼠的单突触反射。Cx36的免疫荧光标记遍布幼鼠脊髓的背角和腹角，并在成熟动物中持续存在。在深背角层，参与突触前大直径肌肉传入抑制的中间神经元位于，细胞内注射神经生物素后，细胞广泛染料偶联。偶联细胞沿其突起显示cx36阳性点。我们的研究结果表明，脊髓中由Cx36形成的间隙连接是维持突触前抑制所必需的，包括调节来自肌纺锤体传入的传递。除了在幼年动物的突触前抑制中发挥作用外，Cx36在成年小鼠脊髓神经元群体中的持续表达表明，电突触对完全成熟脊髓整合过程的贡献可能与在中枢神经系统其他区域发现的一样多样化。
Electrical synapses formed by gap junctions containing connexin36 (Cx36) promote synchronous activity of interneurones in many regions of mammalian brain; however, there is limited information on the role of electrical synapses in spinal neuronal networks. Here we show that Cx36 is widely distributed in the spinal cord and is involved in mechanisms that govern presynaptic inhibition of primary afferent terminals. Electrophysiological recordings were made in spinal cord preparations from 8- to 11-day-old wild-type and Cx36 knockout mice. Several features associated with presynaptic inhibition evoked by conditioning stimulation of low threshold hindlimb afferents were substantially compromised in Cx36 knockout mice. Dorsal root potentials (DRPs) evoked by low intensity stimulation of sensory afferents were reduced in amplitude by 79% and in duration by 67% in Cx36 knockouts. DRPs were similarly affected in wild-types by bath application of gap junction blockers. Consistent with presynaptic inhibition of group Ia muscle spindle afferent terminals on motoneurones described in adult cats, conditioning stimulation of an adjacent dorsal root evoked a long duration inhibition of monosynaptic reflexes recorded from the ventral root in wild-type mice, and this inhibition was antagonized by bicuculline. The same conditioning stimulation failed to inhibit monosynaptic reflexes in Cx36 knockout mice. Immunofluorescence labelling for Cx36 was found throughout the dorsal and ventral horns of the spinal cord of juvenile mice and persisted in mature animals. In deep dorsal horn laminae, where interneurones involved in presynaptic inhibition of large diameter muscle afferents are located, cells were extensively dye-coupled following intracellular neurobiotin injection. Coupled cells displayed Cx36-positive puncta along their processes. Our results indicate that gap junctions formed by Cx36 in spinal cord are required for maintenance of presynaptic inhibition, including the regulation of transmission from Iamuscle spindle afferents. In addition to a role in presynaptic inhibition in juvenile animals, the persistence of Cx36 expression among spinal neuronal populations in the adult mouse suggests that the contribution of electrical synapses to integrative processes in fully mature spinal cord may be as diverse as that found in other areas of the CNS.