The selective antagonist EPPTB reveals TAAR1-mediated regulatory mechanisms in dopaminergic neurons of the mesolimbic system
The selective antagonist EPPTB reveals TAAR1-mediated regulatory mechanisms in dopaminergic neurons of the mesolimbic system
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DOI：
10.1073/pnas.0906522106
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发表时间：
2009-11-24
影响因子：
11.1
通讯作者：
Bettler, Bernhard
中科院分区：
文献类型：
--
作者：
Bradaia, Amyaouch;Trube, Gerhard;Bettler, Bernhard
微量胺相关受体1 （TAAR1）是一种G蛋白偶联受体（GPCR），可被内源性氨基酸代谢物非选择性激活。TAAR1被认为是治疗精神和神经退行性疾病的一个有希望的药物靶点。然而，目前还没有选择性配体来识别taar1特异性的信号机制。在这里，我们报道了一种选择性TAAR1拮抗剂EPPTB，并表征了其对腹侧被盖区（VTA）多巴胺（DA）神经元的生理作用。我们发现EPPTB可以阻止非选择性TAAR1激动剂对酪胺（p-tyr）诱导的DA神经元放电频率的降低。当单独应用时，EPPTB增加了DA神经元的放电频率，这表明TAAR1要么表现出构成活性，要么被环境水平的内源性激动剂强直激活。我们进一步表明，EPPTB阻断了taar1介导的内向整流K+电流的激活。当单独应用时，EPPTB诱导一个明显的内向电流，表明闭合张力激活的K+通道。重要的是，这些EPPTB效应在Taar1敲除小鼠中不存在，从而排除了脱靶效应。我们还发现，急性应用EPPTB和TAAR1的构成性遗传缺乏都会增加DA神经元中D2受体的DA效力。综上所述，我们的数据支持TAAR1强直性激活向内整流的K+通道，从而降低VTA内DA神经元的基础放电频率。我们假设，epptb诱导D2受体DA效价的增加是一种稳态反馈机制的一部分，补偿了TAAR1抑制性张力的缺乏。
Trace amine-associated receptor 1 (TAAR1) is a G protein-coupled receptor (GPCR) that is nonselectively activated by endogenous metabolites of amino acids. TAAR1 is considered a promising drug target for the treatment of psychiatric and neurodegenerative disorders. However, no selective ligand to identify TAAR1-specific signaling mechanisms is available yet. Here we report a selective TAAR1 antagonist, EPPTB, and characterize its physiological effects at dopamine (DA) neurons of the ventral tegmental area (VTA). We show that EPPTB prevents the reduction of the firing frequency of DA neurons induced by p-tyramine (p-tyr), a nonselective TAAR1 agonist. When applied alone, EPPTB increases the firing frequency of DA neurons, suggesting that TAAR1 either exhibits constitutive activity or is tonically activated by ambient levels of endogenous agonist(s). We further show that EPPTB blocks the TAAR1-mediated activation of an inwardly rectifying K+ current. When applied alone, EPPTB induces an apparent inward current, suggesting the closure of tonically activated K+ channels. Importantly, these EPPTB effects were absent in Taar1 knockout mice, ruling out off-target effects. We additionally found that both the acute application of EPPTB and the constitutive genetic lack of TAAR1 increase the potency of DA at D2 receptors in DA neurons. In summary, our data support that TAAR1 tonically activates inwardly rectifying K+ channels, which reduces the basal firing frequency of DA neurons in the VTA. We hypothesize that the EPPTB-induced increase in the potency of DA at D2 receptors is part of a homeostatic feedback mechanism compensating for the lack of inhibitory TAAR1 tone.