Department of Biology, Animal Physiology, Philipps-Universität Marburg, Marburg, Germany.
Center for Mind, Brain and Behavior (CMBB), University of Marburg and Justus Liebig University Giessen, Marburg, Germany.
J Comp Neurol. 2023 Oct;531(14):1482-1508. doi: 10.1002/cne.25529. Epub 2023 Jul 21.
Serotonin (5-hydroxytryptamine) acts as a widespread neuromodulator in the nervous system of vertebrates and invertebrates. In insects, it promotes feeding, enhances olfactory sensitivity, modulates aggressive behavior, and, in the central complex of Drosophila, serves a role in sleep homeostasis. In addition to a role in sleep-wake regulation, the central complex has a prominent role in spatial orientation, goal-directed locomotion, and navigation vector memory. To further understand the role of serotonergic signaling in this brain area, we analyzed the distribution and identity of serotonin-immunoreactive neurons across a wide range of insect species. While one bilateral pair of tangential neurons innervating the central body was present in all species studied, a second type was labeled in all neopterans but not in dragonflies and firebrats. Both cell types show conserved major fiber trajectories but taxon-specific differences in dendritic targets outside the central body and axonal terminals in the central body, noduli, and lateral accessory lobes. In addition, numerous tangential neurons of the protocerebral bridge were labeled in all studied polyneopteran species except for Phasmatodea, but not in Holometabola. Lepidoptera and Diptera showed additional labeling of two bilateral pairs of neurons of a third type. The presence of serotonin in systems of columnar neurons apparently evolved independently in dragonflies and desert locusts. The data suggest distinct evolutionary changes in the composition of serotonin-immunolabeled neurons of the central complex and provides a promising basis for a phylogenetic study in a wider range of arthropod species.
血清素（5-羟色胺）在脊椎动物和无脊椎动物的神经系统中作为一种广泛的神经调质发挥作用。在昆虫中，它促进进食，增强嗅觉敏感性，调节攻击性行为，并且在果蝇的中枢复合体中，在睡眠稳态中起作用。除了在睡眠-觉醒调节中的作用外，中枢复合体在空间定向、目标导向运动和导航向量记忆方面也具有突出作用。为了进一步了解血清素信号在该脑区中的作用，我们分析了广泛的昆虫物种中血清素免疫反应神经元的分布和身份。虽然所有研究的物种中都存在一对双侧的切线神经元，它们支配中央体，但在所有新翅类动物中都标记了第二种类型，而在蜻蜓和火蝾螈中则没有。这两种细胞类型显示出保守的主要纤维轨迹，但在中央体以外的树突靶标和中央体、神经节、和外侧附属小叶中的轴突末端具有分类特异性差异。此外，除了 Phasmatodea 外，所有研究的多翅目昆虫物种的protocerebral 桥都标记了许多切线神经元，但在完全变态类中则没有。鳞翅目和双翅目显示出第三种类型的两个双侧神经元对的额外标记。柱状神经元系统中血清素的存在显然在蜻蜓和沙漠蝗中独立进化。这些数据表明中枢复合体中血清素免疫标记神经元的组成发生了明显的进化变化，为更广泛的节肢动物物种的系统发育研究提供了有希望的基础。
