Gene expression underlying serotonin axon regrowth in the adult mammalian brain

项目摘要 人们普遍认为成年哺乳动物大脑中受损的轴突几乎没有再生的能力，因此 阻碍损伤后的功能恢复。5-羟色胺神经元似乎是一个明显的例外。我们有 制作了成年小鼠新皮质中5-羟色胺轴突的延时图像。5-羟色胺轴突经历 苯丙胺治疗后出现大规模退行性变，并显示出随后缓慢、远距离的 重生。刺伤横断新皮质内的5-羟色胺轴突，继之局部消退。 通过切断5-羟色胺轴突和从穿过刺裂隙区域的切断端重新生长。相反， 起源于腹侧被盖区(VTA)神经元的多巴胺纤维也是小直径的无髓 轴突，然而它们不会被苯丙胺处理破坏，它们在刺伤横断后不能再生。什么 5-羟色胺轴突再生，而大脑中其他受损轴突失效的分子特化 要这么做吗？为了解决这个问题，我们收集了中缝背侧的5-羟色胺神经元池。 为了使用全基因组RNA测序(RNA-Seq)来测量基因表达。这是 在安非他明或生理盐水治疗结束后1周完成。我们的初步数据揭示了一组 在安非他明诱导的轴突再生过程中，5-羟色胺神经元中显著上调的基因。 在这里，我们建议完成并扩展此屏幕，作为定义以下分子要求的第一步 5-羟色胺轴突再生。目的1.在5-羟色胺神经元中差异表达的基因有哪些 安非他命能在大脑皮层引起轴突再生吗？我们的初步数据显示~50 苯丙胺治疗结束后~1周检测到的上调和~60个下调的基因 与生理盐水对照组相比(使用p&lt；0.05的错误发现率)。为了完成这个数据集，我们将 使用安非他明和生理盐水处理的小鼠在t=1天的时间过程来扩展这些RNA-Seq测量， 1周和18周。每组将有8只动物(4只雄性，4只雌性)，我们将验证 对原位杂交和免疫组织化学感兴趣。我们还将比较基因的表达 5-羟色胺神经元对苯丙胺刺激反应的变化与多巴胺产生的变化 室旁核的神经元。目的2.在5-羟色胺神经元再生过程中，哪些基因有差异表达 新皮质刺伤后的5-羟色胺轴突？与苯丙胺损伤不同的是，刺伤 仅产生5-羟色胺和多巴胺轴突的局部轴突退化。刺伤会形成神经胶质疤痕。 中风和其他形式的急性脑损伤。我们将比较中缝背侧5-羟色胺神经元和VTA。 刺伤和苯丙胺损伤后相同部位的多巴胺神经元表达谱 时间点。再生和非再生神经元的这两种互补损伤的结果将 为以后的操纵性实验提供信息，以调节5-羟色胺轴突的再生，并最终赋予 在大脑中的非5-羟色胺能神经元上再生。

Project Summary It is widely believed that damaged axons in the adult mammalian brain have little capacity to regrow, thereby impeding functional recovery after injury. Serotonin neurons appear to be a notable exception. We have produced time-lapse images of serotonin axons in the neocortex of the adult mouse. Serotonin axons undergo massive retrograde degeneration following amphetamine treatment and show subsequent slow, long-distance regrowth. A stab injury that transects serotonin axons running in the neocortex is followed by local regression of cut serotonin axons and by regrowth from cut ends that projects across the stab rift zone. By contrast, dopamine fibers originating in neurons of the ventral tegmental area (VTA) are also small-diameter unmyelinated axons, yet they are not damaged by amphetamine treatment and they fail to regrow after stab transection. What are the molecular specializations that allow serotonin axons to regrow while other injured axons in the brain fail to do so? To begin to address this question we have harvested pools of serotonin neurons from the dorsal raphe of adult mice in order to measure gene expression using genome-wide RNA sequencing (RNA-Seq). This was done 1 week after the end of either amphetamine or saline treatment. Our preliminary data have revealed a set of genes that are significantly upregulated in serotonin neurons during amphetamine-evoked axon regrowth. Here, we propose to complete and extend this screen as a first step to define the molecular requirements for serotonin axon regrowth. Aim 1. What genes are differentially expressed in serotonin neurons during amphetamine-evoked regrowth of their axons in the neocortex? Our preliminary data reveal ~50 upregulated and ~60 downregulated genes measured ~1 week after the end of amphetamine treatment as compared with saline-treated-controls (using a false-discovery rate of p<.05). To complete this data set, we shall extend these RNA-Seq measurements using a time course of amphetamine and saline-treated mice at t= 1 day, 1 week and 18 weeks. There will be 8 animals per group (4 male, 4 female), and we shall validate genes of interest with in situ hybridization and immunohistochemistry. We shall also compare the gene expression changes in response to amphetamine challenge in serotonin neurons with those changes produced in dopamine neurons of the VTA. Aim 2. What genes are differentially expressed in serotonin neurons during regrowth of serotonin axons following a neocortical stab lesion? In contrast to amphetamine lesions, stab lesions produce only local axonal regression of serotonin and dopamine axons. Stab lesions form a glial scar, as occurs in stroke and other forms of acute brain injury. We shall compare dorsal raphe serotonin neuron and VTA dopamine neuron expression profiles in response to stab and amphetamine injury using the same post-injury time points. The results of these two complementary injuries in regenerating and non-regenerating neurons will inform later manipulative experiments to modulate serotonin axon regrowth and, ultimately, confer the capacity to regrow on non-serotonergic neurons in the brain.