Milde J J, Strausfeld N J
Zoologisches Institut der Universität, Köln, Federal Republic of Germany.
J Comp Neurol. 1990 Apr 1;294(1):59-75. doi: 10.1002/cne.902940106.
Intersegmental descending neurons (DNs) link the insect brain to the thoracic ganglia. Iontophoresis of cobalt or fluorescent dyes reveals DNs as uniquely identifiable elements, the dendrites of which are situated within a characteristic region of the lateral deutocerebrum. Here we demonstrate that DNs occur as discrete groups of elements termed DN clusters (DNCs). A DNC is a characteristic combination of neurons that arises from a multiglomerular complex in which the main components of each glomerulus are a characteristic ensemble of sensory afferents. Other neurons involved in the complex are local interneurons, heterolateral interneurons that connect DNCs on both sides of the brain, and neurons originating in higher centers of the brain. We describe the structure, relationships, and projections of eight DNs that contribute to a descending neuron cluster located ventrally in the lateral deutocerebrum, an area interposed between the ventral antennal lobes and the laterally disposed optic lobes. We have named this cluster the GDNC because its most prominent member is the giant descending neuron (GDN), which plays a cardinal role in the midleg "jump" response and which is implicated in the initiation of flight. The GDN and its companion neurons receive primary mechanosensory afferents from the antennae, terminals of wide- and small-field retinotopic neurons originating in the lobula, and endings derived from sensory interneurons that originate in leg neuropil of the thoracic ganglia. We demonstrate that DNs of this cluster share morphological and functional properties. They have similar axon trajectories into the thoracic ganglia, where they invade functionally related neuropils. Neurons of the GDNC respond to identical stimulus paradigms and share similar electrophysiological characteristics. Neither the GDN nor other members of its cluster show spontaneous activity. These neurons are reluctant to respond to unimodal stimuli, but respond to specific combinations of visual and mechanosensory stimulation. These results suggest that in flies groups of morphologically similar DNs responding to context-specific environmental cues may cooperate in motor control.
节段间下行神经元（DNs）将昆虫大脑与胸神经节相连。钴或荧光染料的离子电渗法显示，DNs是独特可识别的元素，其树突位于侧中脑的一个特征区域内。在此，我们证明DNs以被称为DN簇（DNCs）的离散元素群形式存在。一个DNC是神经元的一种特征组合，它起源于一个多小球复合体，其中每个小球的主要成分是感觉传入神经的一个特征集合。参与该复合体的其他神经元包括局部中间神经元、连接大脑两侧DNCs的异侧中间神经元以及起源于大脑更高中心的神经元。我们描述了八个DNs的结构、关系和投射，它们构成了位于侧中脑腹侧的一个下行神经元簇，该区域介于腹侧触角叶和外侧视神经叶之间。我们将这个簇命名为GDNC，因为其最突出的成员是巨型下行神经元（GDN），它在中腿“跳跃”反应中起主要作用，并且与飞行启动有关。GDN及其伴随神经元接收来自触角的初级机械感觉传入神经、起源于小叶的广域和小视野视网膜拓扑神经元的终末，以及起源于胸神经节腿部神经纤维的感觉中间神经元的末梢。我们证明这个簇中的DNs具有共同的形态和功能特性。它们具有相似的轴突轨迹进入胸神经节，在那里它们侵入功能相关的神经纤维。GDNC的神经元对相同的刺激模式做出反应，并具有相似的电生理特征。GDN及其簇中的其他成员都不表现出自发活动。这些神经元对单峰刺激反应迟钝，但对视觉和机械感觉刺激的特定组合有反应。这些结果表明，在果蝇中，形态相似的DNs组对特定环境线索做出反应，可能在运动控制中协同作用。
