Serotonin receptor 4 in the hippocampus modulates mood and anxiety

Serotonin receptor 4 (5-HT4R) plays an important role in regulating mood, anxiety, and cognition, and drugs that activate this receptor have fast-acting antidepressant (AD)-like effects in preclinical models. However, 5-HT4R is widely expressed throughout the central nervous system (CNS) and periphery, making it difficult to pinpoint the cell types and circuits underlying its effects. Therefore, we generated a Cre-dependent 5-HT4R knockout mouse line to dissect the function of 5-HT4R in specific brain regions and cell types. We show that the loss of functional 5-HT4R specifically from excitatory neurons of hippocampus led to robust AD-like behavioral responses and an elevation in baseline anxiety. 5-HT4R was necessary to maintain the proper excitability of dentate gyrus (DG) granule cells and cell type specific molecular profiling revealed a dysregulation of genes necessary for normal neural function and plasticity in cells lacking 5-HT4R. These adaptations were accompanied by an increase in the number of immature neurons in ventral, but not dorsal, dentate gyrus, indicating a broad impact of 5-HT4R loss on the local cellular environment. This study is the first to use conditional genetic targeting to demonstrate a direct role for hippocampal 5-HT4R signaling in modulating mood and anxiety. Our findings also underscore the need for cell type-based approaches to elucidate the complex action of neuromodulatory systems on distinct neural circuits. Polysome-bound mRNAs from TRAP IPs were compared to whole tissue mRNAs (input) or TRAP IP mRNAs were compared between wildtype (WT) and conditional Htr4 knockouts (cKO). Data was collected from neurons in the ventral dentate gyrus using TRAP. We collected three replicates for WT IP and inputs, while cKO data was collected in duplicate.5-羟色胺受体4（Serotonin receptor 4，5-HT4R）在调控情绪、焦虑与认知过程中发挥关键作用，靶向激活该受体的药物可在临床前模型中呈现快速抗抑郁（antidepressant, AD）样效应。然而，5-HT4R在中枢神经系统（CNS）及外周组织中广泛表达，这使得精准定位其功能相关的细胞类型与神经环路极具挑战。因此，本研究构建了Cre依赖型5-HT4R基因敲除小鼠品系，以解析5-HT4R在特定脑区与细胞类型中的功能。 研究结果显示，仅在海马体兴奋性神经元中敲除功能性5-HT4R，即可引发显著的抗抑郁样行为反应，并升高基础焦虑水平。5-HT4R对于维持齿状回（DG）颗粒细胞的正常兴奋性不可或缺；细胞类型特异性分子谱分析表明，缺失5-HT4R的细胞中，维持正常神经功能与神经可塑性所需的基因出现表达失调。 这些适应性变化伴随腹侧而非背侧齿状回中未成熟神经元数量的增加，提示5-HT4R缺失对局部细胞微环境具有广泛影响。本研究首次利用条件性基因靶向技术，证实了海马体5-HT4R信号通路在调控情绪与焦虑中的直接作用。本研究结果也凸显了基于细胞类型的研究方法，对于阐明神经调节系统在不同神经环路中的复杂调控机制的必要性。 本研究通过翻译核糖体亲和纯化（translating ribosome affinity purification, TRAP）技术获取腹侧齿状回神经元样本，将TRAP免疫沉淀得到的多聚核糖体结合mRNA与全组织mRNA（输入对照样本）进行对比，同时比较野生型（WT）与条件性Htr4基因敲除（cKO）样本的免疫沉淀mRNA。其中野生型免疫沉淀与输入对照样本均设置3次生物学重复，条件性敲除样本设置2次生物学重复。