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作用。然而，到目前为止，MBs的突触电路还没有得到详细的研究。胼胝体的萼部是主要的嗅觉输入区域，内源性Kenyon细胞在此接收来自触角叶的投射神经元（PNs）携带的嗅觉信息。为了获得参与嗅觉信息处理的突触回路的基本信息，我们研究了果蝇脑花萼中的突触连接，特别是在变态过程中神经回路的重组。具有萼的成体MB含有重复的微肾小球，每个微肾小球的核心由一个对胆碱乙酰转移酶（ChA T-ir）具有免疫反应的大胆碱能pn钮扣组成，被许多微小的凯尼恩细胞树突和gaba能外源性神经元的末端所包围。ChAT-ir钮扣在众多…更多周围的凯尼恩细胞树突上形成了不同的突触。GABAergic终端也为这些树突和pn键提供了不同的突触输入，这表明GABAergic元件可能在Kenyon细胞树突的突触前和突触后抑制中发挥作用。在幼虫萼中也发现了微肾小球的结构。在蛹期早期（蛹形成后12小时），花萼呈现退化的外观。pn钮扣开始缠结，导致微肾小球消失。然而，有趣的是，少量的ChAT-ir PNs仍然继续维持与树突纤维的突触连接。在蛹期中期（48h APF）， pn末端再次膨胀，形成未成熟的微肾小球，被树突纤维松散包裹。pn钮扣在周围的纤维上形成发散的突触。这些观察结果表明，在蛹期持续存在的PNs和Kenyon细胞之间的特定突触可能负责在蜕变过程中保持记忆

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