Kozono Naoki, Ohtani Akiko, Shiga Takashi
University of Tsukuba, Graduate School of Comprehensive Human Sciences, 1-1-1 Tennodai, Tsukuba 305-8577, Japan.
University of Tsukuba, Graduate School of Comprehensive Human Sciences, 1-1-1 Tennodai, Tsukuba 305-8577, Japan; Department of Neurobiology, Faculty of Medicine, University of Tsukuba, 1-1-1 Tennodai, Tsukuba 305-8577, Japan.
Brain Res. 2017 Jan 15;1655:114-121. doi: 10.1016/j.brainres.2016.11.021. Epub 2016 Nov 25.
Serotonin (5-HT) is involved in various aspects of hippocampal development, although the specific roles of 5-HT receptors are poorly understood. We investigated the roles of 5-HT receptors in the dendrite formation of hippocampal neurons. We focused on the 5-HT4 receptor, which is coupled with Gs protein, and compared the effects with those of the Gi-coupled 5-HT1A receptor. Neurons from rat hippocampi at embryonic day 18 were dissociated and treated for 4 days with the 5-HT4 receptor agonist BIMU8 or the 5-HT1A receptor agonist 8-OH DPAT. The formation of primary dendrites and dendrite branching were promoted by BIMU8, whereas the dendrite branching was inhibited by 8-OH DPAT. BIMU8-induced promotion of dendrite formation was neutralized by concomitant treatment with the 5-HT4 receptor antagonist, confirming the specific actions of the 5-HT4 receptor. We then examined the signaling mechanisms underlying the actions of the 5-HT4 receptor by using a protein kinase A (PKA) inhibitor. The BIMU8-induced promotion of dendrite formation was reversed partially by the PKA inhibitor, suggesting involvement of PKA signaling downstream of the 5-HT4 receptor. Finally, we examined the contribution of brain-derived neurotrophic factor (BDNF) to the promotion of dendrite formation by BIMU8. Quantitative RT-PCR analysis showed that BIMU8 increased the BDNF mRNA expression and that treatment of cultured neurons with the TrkB antagonist reversed the BIMU8-induced increase in dendrite formation. In summary, the present study suggests a novel role for the 5-HT4 receptor in facilitation of dendrite formation in which intracellular signaling of PKA and the BDNF-TrkB system may be involved.
血清素（5-羟色胺，5-HT）参与海马体发育的各个方面，尽管5-HT受体的具体作用尚不清楚。我们研究了5-HT受体在海马神经元树突形成中的作用。我们聚焦于与Gs蛋白偶联的5-HT4受体，并将其作用与Gi偶联的5-HT1A受体的作用进行比较。将胚胎第18天大鼠海马体中的神经元解离，并用5-HT4受体激动剂BIMU8或5-HT1A受体激动剂8-羟基二丙胺基四氢萘（8-OH DPAT）处理4天。BIMU8促进初级树突的形成和树突分支，而8-OH DPAT抑制树突分支。同时用5-HT4受体拮抗剂处理可中和BIMU8诱导的树突形成促进作用，证实了5-HT4受体的特异性作用。然后，我们使用蛋白激酶A（PKA）抑制剂研究了5-HT4受体作用的信号传导机制。PKA抑制剂部分逆转了BIMU8诱导的树突形成促进作用，提示PKA信号传导参与了5-HT4受体的下游作用。最后，我们研究了脑源性神经营养因子（BDNF）对BIMU8促进树突形成的作用。定量逆转录聚合酶链反应（RT-PCR）分析表明，BIMU8增加了BDNF mRNA表达，用酪氨酸激酶受体B（TrkB）拮抗剂处理培养的神经元可逆转BIMU8诱导的树突形成增加。总之，本研究提示5-HT4受体在促进树突形成中具有新作用，其中可能涉及PKA的细胞内信号传导和BDNF-TrkB系统。
