Pereda A, O'Brien J, Nagy J I, Bukauskas F, Davidson K G V, Kamasawa N, Yasumura T, Rash J E
Department of Neuroscience, Albert Einstein College of Medicine, Bronx, New York 10461, USA.
J Neurosci. 2003 Aug 20;23(20):7489-503. doi: 10.1523/JNEUROSCI.23-20-07489.2003.
Auditory afferents terminating as "large myelinated club endings" on goldfish Mauthner cells are identifiable "mixed" (electrical and chemical) synaptic terminals that offer the unique opportunity to correlate physiological properties with biochemical composition and specific ultrastructural features of individual synapses. By combining confocal microscopy and freeze-fracture replica immunogold labeling (FRIL), we demonstrate that gap junctions at these synapses contain connexin35 (Cx35). This connexin is the fish ortholog of the neuron-specific human and mouse connexin36 that is reported to be widely distributed in mammalian brain and to be responsible for electrical coupling between many types of neurons. Similarly, connexin35 was found at gap junctions between neurons in other brain regions, suggesting that connexin35-mediated electrical transmission is common in goldfish brain. Conductance of gap junction channels at large myelinated club endings is known to be dynamically modulated by the activity of their colocalized glutamatergic synapses. We show evidence by confocal microscopy for the presence of the NR1 subunit of the NMDA glutamate receptor subtype, proposed to be a key regulatory element, at these large endings. Furthermore, we also show evidence by FRIL double-immunogold labeling that the NR1 subunit of the NMDA glutamate receptor is present at postsynaptic densities closely associated with gap junction plaques containing Cx35 at mixed synapses across the goldfish hindbrain. Given the widespread distribution of electrical synapses and glutamate receptors, our results suggest that the plastic properties observed at these identifiable junctions may apply to other electrical synapses, including those in mammalian brain.
在金鱼Mauthner细胞上以“大的有髓鞘杵状终末”形式终末的听觉传入神经是可识别的“混合”（电突触和化学突触）突触终末，这提供了一个独特的机会，可将生理特性与单个突触的生化组成及特定超微结构特征联系起来。通过结合共聚焦显微镜和冷冻断裂复型免疫金标记（FRIL），我们证明这些突触处的缝隙连接含有连接蛋白35（Cx35）。这种连接蛋白是神经元特异性的人类和小鼠连接蛋白36在鱼类中的同源物，据报道后者广泛分布于哺乳动物大脑中，并负责多种类型神经元之间的电偶联。同样，在其他脑区的神经元之间的缝隙连接处也发现了连接蛋白35，这表明连接蛋白35介导的电传递在金鱼大脑中很常见。已知大的有髓鞘杵状终末处缝隙连接通道的电导会受到与其共定位的谷氨酸能突触活动的动态调节。我们通过共聚焦显微镜提供证据表明，在这些大终末处存在NMDA谷氨酸受体亚型的NR1亚基，该亚基被认为是一个关键调节元件。此外，我们还通过FRIL双免疫金标记提供证据表明，在金鱼后脑混合突触中，NMDA谷氨酸受体的NR1亚基存在于与含有Cx35的缝隙连接斑块紧密相关的突触后致密部。鉴于电突触和谷氨酸受体广泛分布，我们的结果表明，在这些可识别的连接处观察到的可塑性特性可能适用于其他电突触，包括哺乳动物大脑中的电突触。
