Department of Neuroscience, Division of Biology and Medicine, Brown University, Providence, RI 02912, USA.
J Physiol. 2010 Jul 1;588(Pt 13):2403-15. doi: 10.1113/jphysiol.2010.187096. Epub 2010 May 10.
Gap junction-mediated electrical synapses interconnect diverse types of neurons in the mammalian brain, and they may play important roles in the synchronization and development of neural circuits. Thalamic relay neurons are the major source of input to neocortex. Electrical synapses have not been directly observed between relay neurons in either developing or adult animals. We tested for electrical synapses by recording from pairs of relay neurons in acute slices of developing ventrobasal nucleus (VBN) of the thalamus from rats and mice. Electrical synapses were common between VBN relay neurons during the first postnatal week, and then declined sharply during the second week. Electrical coupling was reduced among cells of connexin36 (Cx36) knockout mice; however, some neuron pairs remained coupled. This implies that electrical synapses between the majority of coupled VBN neurons require Cx36 but that other gap junction proteins also contribute. The anatomical distribution of a beta-galactosidase reporter indicated that Cx36 was expressed in some VBN neurons during the first postnatal week and sharply declined over the second week, consistent with our physiological results. VBN relay neurons also communicated via chemical synapses. Rare pairs of relay neurons excited one another monosynaptically. Much more commonly, spikes in one relay neuron evoked disynaptic inhibition (via the thalamic reticular nucleus) in the same or a neighbouring relay neuron. Disynaptic inhibition between VBN cells emerged as electrical coupling was decreasing, during the second postnatal week. Our results demonstrate that thalamic relay neurons communicate primarily via electrical synapses during early postnatal development, and then lose their electrical coupling as a chemical synapse-mediated inhibitory circuit matures.
缝隙连接介导的电突触将哺乳动物大脑中的不同类型的神经元相互连接，它们可能在神经回路的同步和发育中发挥重要作用。丘脑中继神经元是新皮质的主要输入源。在发育中的或成年动物的丘脑腹侧基底核（VBN）的急性切片中，尚未直接观察到中继神经元之间的电突触。我们通过记录来自大鼠和小鼠 VBN 中的中继神经元对来检测电突触。在出生后的第一周，VBN 中继神经元之间存在常见的电突触，然后在第二周急剧下降。在连接蛋白 36（Cx36）敲除小鼠中，电耦合减少；然而，一些神经元对仍然耦合。这意味着大多数耦合的 VBN 神经元之间的电突触需要 Cx36，但其他缝隙连接蛋白也有贡献。β-半乳糖苷酶报告基因的解剖分布表明，Cx36 在出生后的第一周在一些 VBN 神经元中表达，并在第二周急剧下降，与我们的生理结果一致。VBN 中继神经元也通过化学突触进行通讯。少数中继神经元对彼此单突触兴奋。更常见的是，一个中继神经元的尖峰在同一或相邻的中继神经元中诱发双突触抑制（通过丘脑网状核）。在第二周的出生后，随着电耦合的减少，VBN 细胞之间出现了双突触抑制。我们的结果表明，在出生后的早期发育过程中，丘脑中继神经元主要通过电突触进行通讯，然后随着化学突触介导的抑制回路的成熟，它们失去了电耦合。
