Molecular mechanisms of error siganl-induced synaptic plasticity related to bird song learning

1.鸣禽前脑前脑通路的输出信号(错误信号)对幼鸟的歌唱学习和成年歌唱的维持是必不可少的。在成年孟加拉雀类中，歌唱模式在震耳欲聋后发生显著变化，保持不稳定，然后稳定，与幼鸟的歌唱习得类似。作为突触可塑性的分子标记物的PKC的表达与SONG的改变平行，在RA中的表达在耳聋后一过性增加，然后逐渐降低。我们单方面使用了IMAN，它投射到RA。一周后，我们通过去除耳蜗来剥夺他们的听觉输入。耳聋后2周，正常大脑半球RA中PKC亚型PKCβ1的免疫反应增强。而在患侧RA中，PKC免疫反应弱于非患侧。也就是说，损毁IMAN可抑制耳聋诱导的PKC表达。这些结果表明，错误信号诱导了RA中PKC活性的增加，这与歌曲改变的可塑性有关。为了阐明错误信号诱导PKC激活的分子机制，我们进行了两个实验。首先，用荧光指示剂Fura-2-AM测定斑雀脑片制备过程中的钙离子浓度。谷氨酸可引起RA神经元细胞内钙离子浓度升高。这种增加被NMDA受体拮抗剂AP5抑制。其次，用β-1免疫组织化学方法检测谷氨酸刺激10min后大鼠RA切片中PKC的表达。因此，谷氨酸通过从胞浆转位到细胞膜来诱导PKC的激活。这些结果表明，在错误信号诱导类风湿关节炎可塑性的初始阶段，通过NMDA受体引起的细胞内钙升高导致的PKC的移位可能与类风湿关节炎的可塑性有关。

1. An output signal (error signal) from the anterior forebrain pathway in songbird is essential for juvenile song learning and adult song maintenance. In adult Bengalese finches, song patterns remarkably alter after deafening, remain unstable, then stabilize, similarly to the song acquisition in young. In parallel with the song alteration, expression of PKC, considered a molecular marker of synaptic plasticity, increased transiently after deafening, and then decreased gradually in the RA. We lesioned unilaterally the IMAN, which projects to the RA. Following a week, we then deprived them of auditory input by cochlear removal. The immunoreactivity of PKC β1, a subtype of PKC, increased in the RA of intact hemisphere at 2 weeks after deafening. However, in the RA of the lesioned side, PKC immunoreactivity was less intense than that of the non-lesioned side. Namely, the deafened-induced PKC expression was suppressed by the lesion of IMAN. These results suggest that the error signal induces the increase of PKC activity in the RA related to the plasticity of song alterations.2. In order to clarify the molecular mechanism of error signal-induced PKC activation, two experiments were carried out. First, Ca^<2+> concentration was measured in the brain slice preparation of zebra finch using the fluorescent Ca^<2+> indicator FURA-2-AM. Glutamate caused an increase of intracellular Ca^<2+> concentration in RA neurons. This increase was inhibited by the NMDA receptor antagonist, AP5. Second, we examined the PKC expression in the RA slice preparation after glutamate stimulation for 10 min using PKCβ1 immunohistochemistry. Consequently, glutamate induced the activation of PKC by the translocation from cytosol to membrane. These results indicate that the translocation of the PKC by intracellular Ca^<2+> elevation through NMDA receptor is concerned in the initial stage of error signal-induced-plasticity in RA.