Strausfeld N J, Li Y
Arizona Research Laboratories, Division of Neurobiology, The University of Arizona, Tucson 85721, USA.
J Comp Neurol. 1999 Jul 12;409(4):626-46. doi: 10.1002/(sici)1096-9861(19990712)409:4<626::aid-cne8>3.0.co;2-b.
Previous studies of honey bee and cockroach mushroom bodies have proposed that afferent terminals and intrinsic neurons (Kenyon cells) in the calyces are arranged according to polar coordinates. It has been suggested that there is a transformation by Kenyon cell axons of the polar arrangements of their dendrites in the calyces to laminar arrangements of their terminals in the lobes. Findings presented here show that cellular organization in the calyx of an evolutionarily basal neopteran, Periplaneta americana, is instead rectilinear, as it is in the lobes. It is shown that each calyx is divided into two halves (hemicalyces), each supplied by its own set of Kenyon cells. Each calyx is separately represented in the medial lobe where the dendritic trees of some efferent neurons receive inputs from one calyx only. Kenyon cell dendrites are arranged as narrow elongated fields, organized as rows in each hemicalyx. Dendritic fields arise from 14 to 16 sheets of Kenyon cell axons stacked on top of each other lining the inner surface of the calyx cup. A sheet consists of approximately 60 small bundles, each containing 5-15 axons that converge from the rim of the calyx to its neck. Each sheet contributes to a pair oflaminae, one dark one pale, called a doublet, that extends through the mushroom body. Dark laminae contain Kenyon cell axons packed with synaptic vesicles. Axons in pale laminae are sparsely equipped with vesicles. By analogy with photoreceptors, and with reference to field potential recordings, it is speculated that dark laminae are continuously active, being modulated by odor stimuli, whereas pale laminae are intermittently activated. Timm's silver staining and immunocytology reveal a second type of longitudinal division of the lobes. Five layers extend through the pedunculus and lobes, each composed of subsets of doublets. Four layers represent zones of afferent endings in the calyces. A fifth (the y layer) represents a specific type of Kenyon cell. It is concluded that the mushroom bodies comprise two independent modular systems, doublets and layers. Developmental studies show that new doublets are added at each instar to layers that are already present early in second instar nymphs. There are profound similarities between the mushroom bodies of Periplaneta, an evolutionarily basal taxon, and those of Drosophila melanogaster and the honey bee.
此前对蜜蜂和蟑螂蘑菇体的研究表明，花萼中的传入终末和内在神经元（肯扬细胞）是按照极坐标排列的。有人提出，肯扬细胞轴突会将其在花萼中树突的极坐标排列转化为其终末在叶中的层状排列。此处呈现的研究结果表明，一种进化上较为原始的新翅类昆虫——美洲大蠊花萼中的细胞组织却是直线排列的，就像在叶中一样。研究表明，每个花萼被分为两半（半花萼），每一半由其自己的一组肯扬细胞提供神经支配。每个花萼在中叶中分别有对应的代表区域，在该区域一些传出神经元的树突仅从一个花萼接收输入。肯扬细胞的树突排列成狭窄的细长区域，在每个半花萼中呈排状排列。树突区域由14到16层肯扬细胞轴突堆叠而成，这些轴突排列在花萼杯状结构的内表面。一层大约由60个小束组成，每个小束包含5 - 15条从花萼边缘汇聚到其颈部的轴突。每一层都形成一对薄片，一个深色一个浅色，称为双联体，贯穿蘑菇体。深色薄片包含充满突触小泡的肯扬细胞轴突。浅色薄片中的轴突突触小泡较少。通过与光感受器类比，并参考场电位记录推测，深色薄片持续活跃，受气味刺激调节，而浅色薄片则间歇性激活。蒂姆斯银染法和免疫细胞学法揭示了叶的第二种纵向划分。五层贯穿柄节和叶，每层由双联体的子集组成。四层代表花萼中传入终末的区域。第五层（y层）代表一种特定类型的肯扬细胞。得出的结论是，蘑菇体由两个独立的模块化系统组成，即双联体和层。发育研究表明，在每一龄若虫中都会向二龄若虫早期就已存在的层中添加新的双联体。在进化上较为原始的分类单元美洲大蠊的蘑菇体与黑腹果蝇和蜜蜂的蘑菇体之间存在深刻的相似性。
