Sensory Neuron-Derived Eph Regulates Glomerular Arbors and Modulatory Function of a Central Serotonergic Neuron

Olfactory sensory neurons connect to the antennal lobe of the fly to create the primary units for processing odor cues, the glomeruli. Unique amongst antennal-lobe neurons is an identified wide-field serotonergic neuron, the contralaterally-projecting, serotonin-immunoreactive deutocerebral neuron (CSDn). The CSDn spreads its termini all over the contralateral antennal lobe, suggesting a diffuse neuromodulatory role. A closer examination, however, reveals a restricted pattern of the CSDn arborization in some glomeruli. We show that sensory neuron-derived Eph interacts with Ephrin in the CSDn, to regulate these arborizations. Behavioural analysis of animals with altered Eph-ephrin signaling and with consequent arborization defects suggests that neuromodulation requires local glomerular-specific patterning of the CSDn termini. Our results show the importance of developmental regulation of terminal arborization of even the diffuse modulatory neurons to allow them to route sensory-inputs according to the behavioural contexts.嗅觉感觉神经元（olfactory sensory neurons）与果蝇的触角叶（antennal lobe）相连，构成处理气味信号的基本单元——嗅觉肾小球（glomeruli）。在触角叶神经元中，存在一种已被鉴定的独特宽视野血清素能神经元（wide-field serotonergic neuron）：对侧投射型5-羟色胺免疫反应性中脑神经元（contralaterally-projecting, serotonin-immunoreactive deutocerebral neuron，简称CSDn）。CSDn的轴突末梢遍布对侧触角叶，提示其承担弥散性神经调控功能。但进一步的细致研究发现，CSDn的轴突分支（arborization）在部分肾小球中呈现受限的分布模式。本研究证实，感觉神经元来源的Eph受体（Eph）与CSDn表面的Ephrin配体（Ephrin）相互作用，以此调控此类轴突分支。对Eph-Ephrin信号通路异常且伴随轴突分支缺陷的动物开展行为学分析后发现，该神经调控过程依赖于CSDn末梢在肾小球局部的特异性分布模式。本研究结果表明，即便对于弥散性调控神经元，其末梢轴突分支的发育调控同样至关重要，这使得它们能够依据行为情境精准处理感觉输入信息。