Graduate School of Comprehensive Human Sciences, Kansei, Behavioral and Brain Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, 305-8577, Japan.
Department of Pharmaceutical Sciences, Southwest University, Chongqing, 400715, PR China.
Neuropharmacology. 2019 Nov 1;158:107712. doi: 10.1016/j.neuropharm.2019.107712. Epub 2019 Jul 17.
Serotonin (5-HT) homeostasis is critical for the brain development which influences neurogenesis, neuronal migration, and circuit formation. Distinctive distribution patterns of serotonin receptors (5-HTRs) in the brain govern various physiological activities. Amongst the 5-HTRs, serotonin 4 receptor (5-HT4R) is widely expressed in embryonic forebrain and affects neuronal development, synaptogenesis, and behavior, but its specific role in brain development is still not completely understood. Therefore, in the present study, we addressed the roles of 5-HT4R in the growth of hippocampal neurons during the development of mice brain. We cultured hippocampal neurons of the mouse at embryonic day 18 and then treatment of 5-HT4R agonist RS67333 was employed. We found RS67333 significantly increased the axonal length, diameter and branching along with total dendritic length, number of primary dendrites and their branching. In addition, these effects were neutralized by the concomitant treatment of 5-HT4R antagonist GR125487, which confirmed the specific role of the 5-HT4R in the growth of axon and dendrites. Further, the treatment of RS67333 upregulated the mRNA expression of collapsin response mediator protein-2 (CRMP2) and non-phosphorylated CRMP2 (npCRMP2) together with neurotrophic factors (BDNF, NT-3, NGF) and TRK-A. Additionally, the current research findings reveal that the knockdown of CRMP2 inhibited RS67333-induced growth of the axons and dendrites, which indicates that CRMP2 is required for the 5-HT4R-mediated growth of the axons and dendrites. Overall, the findings of the present in vitro study enrich the understanding and provide insight roles of 5-HT4R in embryonic brain development by promoting the growth of hippocampal neurons.
5-羟色胺（5-HT）的动态平衡对大脑发育至关重要，它影响神经发生、神经元迁移和回路形成。5-羟色胺受体（5-HTRs）在大脑中的独特分布模式控制着各种生理活动。在 5-HTRs 中，5-羟色胺 4 受体（5-HT4R）广泛表达于胚胎前脑中，影响神经元发育、突触形成和行为，但它在大脑发育中的具体作用仍不完全清楚。因此，在本研究中，我们研究了 5-HT4R 在小鼠大脑发育过程中海马神经元生长中的作用。我们在胚胎第 18 天培养了小鼠的海马神经元，然后用 5-HT4R 激动剂 RS67333 进行处理。结果发现，RS67333 显著增加了轴突长度、直径和分支，以及总树突长度、初级树突数量及其分支。此外，这些作用可被 5-HT4R 拮抗剂 GR125487 中和，证实了 5-HT4R 在轴突和树突生长中的特定作用。进一步研究发现，RS67333 处理可上调神经生长因子（BDNF、NT-3、NGF）和 TRKA 的 mRNA 表达以及 collapsin 反应介质蛋白 2（CRMP2）和非磷酸化 CRMP2（npCRMP2）。此外，本研究发现 CRMP2 的敲低抑制了 RS67333 诱导的轴突和树突生长，表明 CRMP2 是 5-HT4R 介导的轴突和树突生长所必需的。总之，本体外研究的结果丰富了我们对 5-HT4R 在胚胎大脑发育中作用的理解，并提供了新的见解，即 5-HT4R 通过促进海马神经元的生长来发挥作用。
