A study on the metamorphosis of neural circuitry in the mushroom body calyx in Drosophila melanogaster

果蝇的蘑菇体在嗅觉学习和记忆中起着重要的作用。然而，到目前为止，MBS的突触回路还没有得到任何详细的研究。MBS的花冠是主要的输入区域，固有的Kenyon细胞从触角叶接收投射神经元(PN)携带的嗅觉信息。为了获得有关参与嗅觉信息处理的突触回路的基本信息，我们研究了果蝇MB的突触连接，特别是在变态过程中神经回路的重组。成体MB有花蕾，小球呈重复模式，每个小球由一个大的胆碱能Pn-bouton组成，其核心是对胆碱乙酰转移酶(Cha-T-ir)免疫反应，周围环绕着许多微小的Kenyon细胞树突以及GABA能外源神经元的终末。Chat-ir Boutons在众多的…上形成发散的突触更多围绕着凯尼恩细胞的树突。GABA能终末也向这些树突和Pn-Bouton贡献了发散的突触输入，提示GABA能成分可能在突触前和突触后抑制Kenyon细胞树突中起作用。幼虫的肾小球内也有小球的结构。在早期(化蛹后12小时)，花萼退化。PN小球变得内卷，结果小球消失。然而，有趣的是，少数Chat-ir三叉神经节仍然保持与树突纤维的突触联系。在蛹中期(48h)，PN终末再次膨胀，形成未成熟的微球，并被树突纤维疏松地包围。PN-Bouton在周围纤维上形成发散突触。这些观察表明，三叉神经节细胞和凯尼恩细胞之间的特定突触持续到蛹阶段，可能与变态过程中的记忆保持不太相关。

The mushroom bodies (MBs) of Drosophila play an important part in olfactory learning and memory. However, the synaptic circuitry of MBs has so far not been investigated in any detail. The calyces of MBs are the main input regions, where the intrinsic Kenyon cells receive olfactory information carried by the projection neurons (PNs) from the antennal lobes. To obtain fundamental information about the synaptic circuits involved in olfactory information processing we have studied the synaptic connections in the calyces of the Drosophila MB, with special reference to the reorganization of neural circuits during metamorphosis. The adult MB, with calyces contained a pattern of repeated microglomeruli, each of which comprised a large cholinergic PN-bouton immunoreactive to choline acetyltransferase (ChA T-ir), at its core, encircled by a number of tiny Kenyon cell dendrites as well as by the terminals of GABAergic extrinsic neuron. ChAT-ir boutons formed divergent synapses upon multitudinous … More surrounding Kenyon cell dendrites. GABAergic terminals also contributed divergent synaptic input to these dendrites as well as to PN-boutons, indicating that GABAergic elements may play a role in pre- and postsynaptic inhibition of Kenyon cell dendrites. The structure of microglomeruli was also found in larval calyces. In early pupae (12 hours after puparium formation; APF), the calyces showed a degenerated appearance. The PN-boutons became involuted and, as a result, the microglomeruli disappeared. Interestingly, however, a small number of ChAT-ir PNs still continued to maintain the synaptic connections with the dendritic fibers. In the middle stage of pupae (48hours APF), the PN-terminals swelled out again and formed immature microglomeruli loosely surrounded by the dendritic fibers. The PN-boutons formed divergent synapses on the surrouding fibers. These observations suggest that the specific synapses between the PNs and Kenyon cells, which persist through the pupal stage, might be responsible for memory retention during metamorphosis Less