Modeling 5-HT-absorbing neurons in neuropathology of autism

描述(由申请人提供)：自闭症是一种出生后神经发育障碍，诊断基于沟通、社会互动和刻板印象行为模式的核心缺陷。尸检研究显示，前额叶皮质、杏仁核和海马区的解剖组织以及轴突和树突分支发生了变化，导致了自闭症是一种突触连接疾病的概念，关键神经元电路的中断突显了行为和认知缺陷。基于家族的关联研究表明，5-羟色胺再摄取转运体(SERT)基因SLC6A4的表达/功能降低与自闭症之间存在联系。与SERT功能降低扰乱自闭症背后的神经元电路的想法一致，SERT基因敲除小鼠表现出躯体感觉图缺陷，边缘下区域和杏仁核中锥体细胞树突形态的变化，以及焦虑特征的增强。然而，选择性5-羟色胺再摄取转运体抑制剂(SSRIs)被发现有助于改善自闭症患者的重复和强迫行为，这是一个悖论。克服这一悖论将有助于我们理解自闭症神经病理生理学的潜在机制，并设计合理的治疗方法。为了了解SERT缺陷在自闭症神经病理生理学中的作用，阐明原发脑损害发生在哪个发育阶段及其机制是至关重要的。这项建议的目标是通过利用我们独特的条件性SERT基因敲除小鼠，研究SERT在新生阶段特定神经元--5-羟色胺吸收神经元--中的瞬时表达如何调节特定大脑区域的神经元突触模式，以及消除这一SERT功能是否会导致自闭症中出现的行为缺陷。这一建议的灵感来自我们最近的发现，即5-羟色胺吸收神经元通过SERT吸收突触外的5-羟色胺，但不合成5-羟色胺，控制线虫的应激行为。我们证明了SERT在5-羟色胺吸收神经元中的转基因表达对于纠正SERT缺失蠕虫的夸大行为是必要的和充分的。值得注意的是，5-羟色胺吸收神经元在新生啮齿动物和人脑中是瞬时存在的。在小鼠中，5-羟色胺吸收神经元存在于初级感觉区域，包括躯体感觉、视觉和听觉皮质、海马体和前脑部位，包括边缘下部。拟议的实验将确定5-羟色胺吸收神经元特异性SERT失活对躯体感觉图模式、额叶皮质和杏仁核轴突和树突树枝形成的影响，以及应激和社会行为。我们将评估消融这种短暂的SERT功能是否会导致大脑解剖和行为的持久变化，以及这些影响是否存在性别偏见。这些结果将为5-羟色胺神经传递的基本机制提供新的见解，并阐明SERT如何在正确的时间作用于正确的细胞，以调节与自闭症有关的大脑解剖和行为回路。

DESCRIPTION (provided by applicant): Autism is a postnatal neurodevelopmental disorder diagnosed based on a core of deficits in communication, social interaction, and stereotypic patterns of behavior. Postmortem studies revealed alterations in anatomical organizations and axonal and dendritic arborization in the prefrontal cortex, amygdala and hippocampus, leading to the notion that autism is a disease of synaptic connectivity and that disruption of critical neuronal circuitry underscores the behavioral and cognitive deficits. Family based association studies indicated a link between reduced expression/function of serotonin reuptake transporter (SERT) gene SLC6A4 and autism. Consistent with the idea that reduced SERT function perturbs neuronal circuitry underlying autism, SERT knockout mice exhibit deficits in somatosensory maps, alterations in pyramidal cell dendritic morphology in the infralimbic area and amygdala and enhanced anxiety traits. However, Selective Serotonin Reuptake Transporter Inhibitors (SSRIs) are found to be useful for improving repetitive and compulsive behavior of autistic patients, posting a paradox. Overcoming this paradox will help our understanding the mechanisms underlying the neuropathophysiology of autism and designing rational treatments. To understand the role of SERT deficiency in neuropathophysiology of autism, it is critical to elucidate at which developmental stage do the primary brain lesions occur and what are the mechanisms. The goal of this proposal is to investigate how a transient expression of SERT in a particular set of neurons -- 5-HT-absorbing neurons, during the neonatal stage regulates neuronal synaptic patterning in particular brain regions and whether ablating this SERT function would lead to behavioral deficits seen in autism, by making use of our unique conditional SERT knockout mouse. This proposal is inspired by our recent discovery that 5-HT-absorbing neurons, which absorb extra-synaptic 5-HT via SERT but do not synthesize 5-HT, control stress behavior in C. elegans. We demonstrated that transgenic expression of SERT in the 5-HT-absorbing neurons is necessary and sufficient to correct exaggerated behavior of SERT-null worms. Remarkably, 5-HT-absorbing neurons are present transiently in the neonatal rodent and human brains. In mouse, 5-HT-absorbing neurons are present in primary sensory areas including somatosensory, visual and auditory cortices, the hippocampus, and forebrain sites including the infralimbic area. The proposed experiments will determine the effects of 5-HT-absorbing neuron- specific inactivation of SERT on somatosensory map patterning, axonal and dendritic arborization in the frontal cortex and amygdala, and stress and social behavior. We will assess whether ablating this transient SERT function would lead to lasting alterations in brain anatomy and behavior, and if those effects are sex biased. The results will provide new insights into fundamental mechanisms of 5-HT neurotransmission and illuminate how SERT acts in right cells at right time to regulate brain anatomy and behavioral circuits implicated in autism.