Cruikshank Scott J, Landisman Carole E, Mancilla Jaime G, Connors Barry W
Department of Neuroscience, Division of Biology & Medicine, Brown University, Providence, RI 02912, USA.
Prog Brain Res. 2005;149:41-57. doi: 10.1016/S0079-6123(05)49004-4.
Electrical synapses are composed of gap junction channels that interconnect neurons. They occur throughout the mammalian brain, although this has been appreciated only recently. Gap junction channels, which are made of proteins called connexins, allow ionic current and small organic molecules to pass directly between cells, usually with symmetrical ease. Here we review evidence that electrical synapses are a major feature of the inhibitory circuitry in the thalamocortical system. In the neocortex, pairs of neighboring inhibitory interneurons are often electrically coupled, and these electrical connections are remarkably specific. To date, there is evidence that five distinct subtypes of inhibitory interneurons in the cortex make electrical interconnections selectively with interneurons of the same subtype. Excitatory neurons (i.e., pyramidal and spiny stellate cells) of the mature cortex do not appear to make electrical synapses. Within the thalamus, electrical coupling is observed in the reticular nucleus, which is composed entirely of GABAergic neurons. Some pairs of inhibitory neurons in the cortex and reticular thalamus have mixed synaptic connections: chemical (GABAergic) inhibitory synapses operating in parallel with electrical synapses. Inhibitory neurons of the thalamus and cortex express the gap junction protein connexin 36 (C x 36), and knocking out its gene abolishes nearly all of their electrical synapses. The electrical synapses of the thalamocortical system are strong enough to mediate robust interactions between inhibitory neurons. When pairs or groups of electrically coupled cells are excited by synaptic input, receptor agonists, or injected current, they typically display strong synchrony of both subthreshold voltage fluctuations and spikes. For example, activating metabotropic glutamate receptors on coupled pairs of cortical interneurons or on thalamic reticular neurons can induce rhythmic action potentials that are synchronized with millisecond precision. Electrical synapses offer a uniquely fast, bidirectional mechanism for coordinating local neural activity. Their widespread distribution in the thalamocortical system suggests that they serve myriad functions. We are far from a complete understanding of those functions, but recent experiments suggest that electrical synapses help to coordinate the temporal and spatial features of various forms of neural activity.
电突触由连接神经元的缝隙连接通道组成。它们存在于整个哺乳动物大脑中，不过直到最近才被人们所认识。缝隙连接通道由一种叫做连接蛋白的蛋白质构成，它能使离子电流和小分子有机物质直接在细胞间通过，通常这种通过是对称且容易的。在此，我们综述相关证据，表明电突触是丘脑皮质系统抑制性回路的一个主要特征。在新皮层中，相邻的抑制性中间神经元对常常通过电耦合连接，而且这些电连接具有显著的特异性。迄今为止，有证据表明皮层中五种不同亚型的抑制性中间神经元选择性地与相同亚型的中间神经元形成电连接。成熟皮层中的兴奋性神经元（即锥体细胞和棘状星状细胞）似乎并不形成电突触。在丘脑内，网状核中观察到电耦合，该核完全由γ-氨基丁酸能神经元组成。皮层和丘脑网状核中的一些抑制性神经元对具有混合突触连接：化学性（γ-氨基丁酸能）抑制性突触与电突触并行运作。丘脑和皮层的抑制性神经元表达缝隙连接蛋白36（Cx36），敲除其基因几乎会消除它们所有的电突触。丘脑皮质系统的电突触强大到足以介导抑制性神经元之间的强劲相互作用。当电耦合的细胞对或细胞群受到突触输入、受体激动剂或注入电流的刺激时，它们通常在阈下电压波动和动作电位方面都表现出强烈的同步性。例如，激活耦合的皮层中间神经元对或丘脑网状神经元上的促代谢型谷氨酸受体，可诱导出具有毫秒级精度同步的节律性动作电位。电突触为协调局部神经活动提供了一种独特的快速双向机制。它们在丘脑皮质系统中的广泛分布表明它们具有多种功能。我们远未完全了解这些功能，但最近的实验表明，电突触有助于协调各种形式神经活动的时间和空间特征。
