Santagata Scott
C. W. Post Campus of Long Island University, 720 Northern Boulevard, Brookville, New York, NY 11709, USA.
J Morphol. 2011 Oct;272(10):1153-69. doi: 10.1002/jmor.10975. Epub 2011 May 19.
Recent structural analyses of invertebrate nervous systems have supported hypotheses stating that specific developmental and cytological aspects of larval and adult brains are conserved among bilaterian animals. Opposing views argue that structural similarities in larval nervous systems may be the result of convergent evolution and that the developmental diversity of adult brains is more indicative of several independent origins. Here, I use various cytological probes, confocal microscopy, and reconstruction techniques to investigate the cellular diversity within the larval nervous systems of Glottidia pyramidata and Terebratalia transversa (Brachiopoda). Neuronal cell types are compared among the rhynchonelliform, linguliform, and craniiform brachiopods as well as the phoronids. Although the respective larval types of the previously mentioned systematic groups clearly diverge in the neuroarchitecture of their larval apical organs (and nervous systems in general), a ground plan is proposed based on shared, centrally-located, peptidergic neuronal cell types that can be compared with similar cell types in other lophotrochozoan phyla (bryozoans and spiralians). Assessing hierarchal levels of homology within and among the nervous systems of morphologically disparate phyla is challenging in that many phyla share early developmental signals that induce the specification of the neural ectoderm, clouding our ability to discern divergent larval and juvenile brain structure. Solving these problems will require a combined effort involving both traditional and more recent cytological techniques with a diversity of molecular probes that will better map the neuronal complexity of diverse invertebrate nervous systems.
近期对无脊椎动物神经系统的结构分析支持了一些假说，这些假说认为幼虫和成虫大脑的特定发育和细胞学特征在两侧对称动物中是保守的。相反的观点则认为，幼虫神经系统的结构相似性可能是趋同进化的结果，而成虫大脑的发育多样性更能表明其有多个独立起源。在这里，我使用各种细胞学探针、共聚焦显微镜和重建技术，来研究金字塔形舌形贝和横向穿孔贝（腕足动物门）幼虫神经系统内的细胞多样性。在长身贝类、舌形贝类和头形贝类腕足动物以及帚虫动物中比较神经元细胞类型。尽管上述分类群各自的幼虫类型在其幼虫顶端器官（以及一般的神经系统）的神经结构上明显不同，但基于共享的、位于中央的肽能神经元细胞类型提出了一个基础模式，这些细胞类型可与其他触手冠动物门（苔藓虫类和螺旋类）中的类似细胞类型进行比较。评估形态差异较大的门的神经系统内部和之间的同源性层次具有挑战性，因为许多门共享诱导神经外胚层特化的早期发育信号，这模糊了我们辨别不同幼虫和幼年大脑结构的能力。解决这些问题需要综合运用传统和最新的细胞学技术以及多种分子探针，以便更好地描绘不同无脊椎动物神经系统的神经元复杂性。
