Ancestry of basal ganglia circuits: New evidence in teleosts
Ancestry of basal ganglia circuits: New evidence in teleosts
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基底神经节回路的祖先：硬骨鱼的新证据
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发表时间：
2014
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通讯作者：
M. Wullimann
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作者：
M. Wullimann
Filippi、Mueller 和 Driever 在本期《比较神经学杂志》中提出了迟来的优雅分析，解决了与基底神经节电路的系统起源相关的问题，特别是斑马鱼 (Danio rerio) 大脑中的多巴胺能（和去甲肾上腺素能）神经元是否表达谷氨酸和 GABA 共释放的分子特征。这对于理解羊膜脊椎动物中基底神经节控制运动功能的直接和间接途径的进化起源非常重要。艰难的比较研究之路导致了目前对脊椎动物基底神经节进化的理解。在哺乳动物中，基底神经节电路的运动环路始于同皮质，并激活两个不同的纹状体抑制（GABA 能）神经元群，从而产生直接和间接通路（见图 1）。这两条通路形成穿过内部和外部苍白球、黑质网状部分（SNr）和丘脑背核回到前运动皮层的神经回路。这些中心中直接和间接途径的特定突触相互作用及其 GABA 能与谷氨酸能性质导致对异皮质的兴奋性（直接途径）和抑制性（间接途径）反馈。在行为相关的情况下，基底中脑的多巴胺能致密黑质群体（SNc）对于触发选定运动行为的执行具有关键作用，因为 SNc 向纹状体 GABA 能群体释放多巴胺。它们携带不同的多巴胺受体，即直接途径细胞 D1 受体、间接途径细胞 D2 受体。因此，纹状体直接通路细胞中 D1 介导的兴奋性细胞内信号支持直接通路到皮质的兴奋性反馈。相反，D2 介导的纹状体间接通路细胞的抑制信号改变神经元输出的信号，因此也导致兴奋性皮层反馈。通过这种方式，黑质多巴胺的释放导致哺乳动物通过基底神经节运动环路执行计划的运动行为（Mink，2008）。已经达成的共识是，在鸟类中（Reiner，2002；Reiner 等人，2004）也存在同源的基底神经节结构和回路，包括下行通路（朝向脑干）和折返通路（返回背侧大脑皮层或 Wulst）。尽管爬行动物（海龟、一些蜥蜴；Medina 和 Smeets，1991）的情况类似，但它们的运动环路有所不同，因为主要的爬行动物基底神经节输出通向前顶盖、中脑和脑干的运动中心（下降通路），而不通过丘脑返回背侧皮层（折返通路）。 Anamniote 四足动物（两栖动物）本质上表现出爬行动物的情况；它们缺乏重入通路，但显示了上述运动环路的其他元素，包括下降输出通路（Mar ın et al., 1998a,b；Wullimann，2011；见图 2）。因此，重入途径可能在鸟类和哺乳动物中趋同进化。 Sten Grillner 实验室的令人兴奋的报告（Stephenson-Jones 等人，2011 年；Ericsson 等人，2013 年）最近证明了七鳃鳗（无颌类分支的代表）的基底神经节回路、神经化学和神经生理学的核心要素（Braun，1996 年；图 2）。结合追踪和递质研究证明了纹状体 GABA 能神经元群在神经化学上不同，并表明存在汇聚成下降输出通路的直接和间接通路。然而，七鳃鳗缺乏重入途径（参见Wullimann，2011年的讨论；和图2），与基础四足动物的组织模式一致，即显着的下降输出和缺乏重入途径（Medina和Smeets，1991；Mar ın等人，1998a,b；Reiner，2002）。
The elegant and long overdue analysis presented by Filippi, Mueller, and Driever in this issue of Journal of Comparative Neurology addresses questions relating to phyletic origins of basal ganglia circuitry, specifically whether dopaminergic (and noradrenergic) neurons in the zebrafish (Danio rerio) brain express molecular features characteristic of corelease of glutamate and GABA. This is important for understanding the evolutionary origins of the direct and indirect pathways for basal ganglia control of motor function as known in amniote vertebrates. A hard road of comparative research led to the current evolutionary understanding of vertebrate basal ganglia. In mammals, the motor loop of basal ganglia circuitry starts in the isocortex and activates two different striatal inhibitory (GABAergic) neuronal populations, which give rise to a direct and an indirect pathway (see Fig. 1). These two pathways form neural circuits running through internal and external pallidum, reticular portion of the substantia nigra (SNr), and a dorsal thalamic nucleus back to premotor–motor cortex. The specific synaptic interactions of direct and indirect pathways in these centers and their GABAergic vs. glutamatergic nature leads to excitatory (direct pathway) and inhibitory (indirect pathway) feedback onto isocortex. In behaviorally relevant situations, the dopaminergic compact nigral population (SNc) of the basal midbrain has a pivotal role for triggering the execution of a selected motor behavior, because the SNc releases dopamine onto both striatal GABAergic populations. These carry different dopamine receptors, i.e., direct pathway cells D1 receptors, indirect pathway cells D2 receptors. As a consequence, the D1-mediated excitatory intracellular signal in the striatal, direct pathway cells supports the excitatory feedback of the direct pathway onto cortex. In contrast, the D2-mediated inhibitory signal to striatal indirect pathway cells changes the sign of the neuronal output and, thus, results also in excitatory cortical feedback. In this way, nigral dopamine release leads to execution of a planned motor behavior through the basal ganglia motor loop in mammals (Mink, 2008). Consensus has been reached that in birds (Reiner, 2002; Reiner et al., 2004) homologous basal ganglia structures and circuitry also occur, including both descending (towards brainstem) and re-entrant pathways (back to dorsal pallium or Wulst). Although the situation is similar in reptiles (turtles, some lizards; Medina and Smeets, 1991), their motor loop differs because the major reptilian basal ganglia output leads to motor centers of pretectum, midbrain, and brainstem (descending pathway) and does not lead through thalamus back to dorsal cortex (re-entrant pathway). Anamniote tetrapods (amphibians) show essentially the reptilian situation; they lack the re-entrant pathway but show the other elements of the motor loop described above, including the descending output pathway (Mar ın et al., 1998a,b; Wullimann, 2011; see Fig. 2). Thus, the re-entrant pathway probably evolved convergently in birds and mammals. Exciting reports from Sten Grillner’s laboratory (Stephenson-Jones et al., 2011; Ericsson et al., 2013) recently demonstrated core elements of basal ganglia circuitry, neurochemistry, and neurophysiology in the river lamprey, a representative of an agnathan clade (Braun, 1996; Fig. 2). Combined tracing and transmitter studies demonstrate neurochemically different striatal GABAergic neuron populations and indicate the presence of direct and indirect pathways converging into a descending output pathway. However, lampreys lack the re-entrant pathway (see discussion in Wullimann, 2011; and Fig. 2), consistent with the organizational pattern of basal tetrapods, i.e., a dominant descending output and absence of a re-entrant pathway (Medina and Smeets, 1991; Mar ın et al. 1998a,b; Reiner, 2002).
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