Live imaging of brain circuitry in mouse models of PTSD

描述（由申请人提供）：PTSD小鼠模型脑回路的实时成像创伤后应激障碍（PTSD）发生在经历危及生命的事件后，预计会影响许多返回的退伍军人，但主要的未满足的医疗需求是可靠的预测、诊断和治疗方法。患有 PTSD 的人表现出大脑功能解剖学和大脑结构的改变，许多人经历了选择性血清素再摄取抑制剂的缓解，这将 PTSD 的解剖学变化与血清素能系统联系起来。遗传学研究表明，血清素转运蛋白（SERT、5-HTT）基因的多态性与包括创伤后应激障碍（PTSD）在内的情感障碍风险相关。血清素代谢是压力激活精神病理学基础的证据来自三方面的研究：1）啮齿动物模型，具有 SERT 基因改变或在捕食者气味的恐惧刺激后； 2）人类SERT、SLC6A4的基因剖析，以及等位基因与行为的关联； 3) 人类受试者和小鼠模型的功能和结构磁共振成像 (MRI)。我们的工作假设是，恐惧会引起神经活动，在某些个体中，这种活动在创伤事件解决后仍会持续很长时间，导致中脑边缘皮质回路的功能解剖结构发生变化。我们进一步假设，当 SERT 水平较低和/或在早年经历过创伤的成年人中，会出现持续活动。我们的具体目标是：（1） 绘制并测量野生型和 SERT 突变体对恐惧的神经反应的强度和持续时间； (2) 测量恐惧对功能回路的影响； (3) 量化早期生活创伤对成人神经活动和中皮质边缘回路的影响。我们将使用 11.7T 活体小鼠的延时、定量锰增强 MRI 测量恐惧前后的神经活动和回路变化，提供 90 µm3 体素分辨率，并使用 DTI 和组织学对解剖学的影响。转基因小鼠，包括经过验证的 PTSD 小鼠模型（SERT 敲除），以及新的转基因小鼠，其中 50kb 的小鼠 SERT 基因座已被人类 SERT 等位基因（长或短变体）取代，将对转基因小鼠进行成像并与野生型同窝小鼠进行比较。捕食者的气味将被用来引发恐惧反应。为了揭示 SERT 突变体是否影响共同的神经网络，将对行为表型与 SERT 突变体相似的胆囊收缩素敲除小鼠进行成像和并行分析。来自每个基因型群体的 3D 全脑 MR 图像数据集将使用定制设计的计算软件在体素基础上进行统计分析。这项研究首次在携带人类血清素转运蛋白等位基因的转基因小鼠模型中将遗传学、功能性和结构性 MRI 与恐惧反应联系起来。这项拟议的临床前研究的成功完成将为解决未满足的需求提供必要的信息，方法是确定： a) 用于预测风险的遗传易感性； b) 发展为 PTSD 期间大脑功能变化的顺序，用于设计阶段特定的诊断和治疗干预措施。

DESCRIPTION (provided by applicant): Live imaging of brain circuitry in mouse models of PTSD Post-traumatic stress disorder (PTSD) occurs after experiencing a life-threatening event and is predicted to affect many returning veterans, yet a major unmet medical need is for reliable methods of prediction, diagnosis and treatment. People with PTSD display alterations in brain functional anatomy and in brain structures, and many experience relief from selective serotonin reuptake inhibitors, linking anatomical changes in PTSD to the serotonergic system. Genetic studies show an association with polymorphisms in the serotonin transporter (SERT, 5-HTT) gene with risk of affective disorders including PTSD. Evidence that serotonin metabolism underlies stress-activated psychopathologies comes from three lines of research: 1) Rodent models, with genetic alterations of SERT or after fear provocation with predator odor; 2) Genetic dissection of human SERT, SLC6A4, and association of alleles with behavior; and 3) Magnetic resonance imaging (MRI), both functional and structural, of human subjects and mouse models. Our working hypothesis is that fear evokes neural activity that in some individuals continues long after the traumatic event resolves, leading to changes in functional anatomy of the mesolimbic cortical circuit. We further hypothesize that persistent activity occurs when SERT levels are low and/or in adults who experienced trauma early in life. Our specific aims are to: (1) Map and measure the intensity and duration of neural responses to fear in wild-type and SERT mutants; (2) Measure the impact of fear on functional circuitry; and (3) Quantify effects of early life trauma on neural activity and mesocortical limbic circuitry in the adult. We will measure the neural activity and circuitry changes before and after fear with time-lapse, quantitative manganese-enhanced MRI of living mice at 11.7T giving 90¿m3 voxel resolution, and the effects on anatomy with DTI and histology. Transgenic mice, including the validated mouse model of PTSD (SERT knock-out), and new transgenics in which 50kb of the mouse SERT locus has been replaced with human SERT alleles (long or short variants), will be imaged and compared with wild-type littermates. Predator odor will be used to provoke fear responses. To reveal whether SERT mutants affect a common neural network, cholecystokinin knock-out mice with a behavioral phenotype similar to SERT mutants will be imaged and analyzed in parallel. Datasets of 3D whole brain MR images from cohorts of each genotype will be analyzed statistically on a voxel-wise basis with custom-designed computational software. This study is the first to link genetics, functional and structural MRI with fear responses in this new transgenic mouse model carrying human gene alleles of the serotonin transporter. The successful completion of this proposed preclinical study will provide information necessary to address the unmet need by identifying: a) genetic susceptibilities for prediction of risk; and b) sequence of functional changes in the brain during progression to PTSD for design of stage-specific diagnoses and therapeutic interventions.