Department of Biology, University of Fribourg, 1700 Fribourg, Switzerland.
J Comp Neurol. 2011 Dec 1;519(17):3415-32. doi: 10.1002/cne.22713.
Whereas the "vertical" elements of the insect olfactory pathway, the olfactory receptor neurons and the projection neurons, have been studied in great detail, local interneurons providing "horizontal" connections in the antennal lobe were ignored for a long time. Recent studies in adult Drosophila demonstrate diverse roles for these neurons in the integration of odor information, consistent with the identification of a large variety of anatomical and neurochemical subtypes. Here we focus on the larval olfactory circuit of Drosophila, which is much reduced in terms of cell numbers. We show that the horizontal connectivity in the larval antennal lobe differs largely from its adult counterpart. Only one of the five anatomical types of neurons we describe is restricted to the antennal lobe and therefore fits the definition of a local interneuron. Interestingly, the four remaining subtypes innervate both the antennal lobe and the suboesophageal ganglion. In the latter, they may overlap with primary gustatory terminals and with arborizations of hugin cells, which are involved in feeding control. This circuitry suggests special links between smell and taste, which may reflect the chemosensory constraints of a crawling and burrowing lifestyle. We also demonstrate that many of the neurons we describe exhibit highly variable trajectories and arborizations, especially in the suboesophageal ganglion. Together with reports from adult Drosophila, these data suggest that wiring variability may be another principle of insect brain organization, in parallel with stereotypy.
虽然昆虫嗅觉途径的“垂直”元素，即嗅觉受体神经元和投射神经元，已经被详细研究，但在很长一段时间内，提供“水平”连接的触角叶内局部中间神经元都被忽视了。最近对成年果蝇的研究表明，这些神经元在气味信息整合中具有多种作用，与鉴定出的大量解剖学和神经化学亚型一致。在这里，我们专注于果蝇的幼虫嗅觉回路，其在细胞数量方面大大减少。我们表明，幼虫触角叶中的水平连接与成虫的对应物有很大的不同。我们描述的 5 种神经元类型中，只有一种局限于触角叶，因此符合局部中间神经元的定义。有趣的是，其余的 4 种亚型既支配触角叶也支配食管下神经节。在后一种情况下，它们可能与初级味觉末梢和参与摄食控制的 hugin 细胞的分支重叠。这种电路表明嗅觉和味觉之间存在特殊联系，这可能反映了爬行和挖掘生活方式的化学感觉限制。我们还证明，我们描述的许多神经元表现出高度可变的轨迹和分支，特别是在食管下神经节中。与成年果蝇的报告一起，这些数据表明，布线变异性可能是昆虫大脑组织的另一个原则，与刻板性平行。
