Background Of the many genetic mutations known to increase the risk of autism spectrum disorder, a large proportion cluster upon synaptic proteins. One such family of presynaptic proteins are the neurexins (NRXN), and recent genetic and mouse evidence has suggested a causative role for NRXN2 in generating altered social behaviours. Autism has been conceptualised as a disorder of atypical connectivity, yet how single-gene mutations affect such connectivity remains under-explored. To attempt to address this, we have developed a quantitative analysis of microstructure and structural connectivity leveraging diffusion tensor MRI (DTI) with high-resolution 3D imaging in optically cleared (CLARITY) brain tissue in the same mouse, applied here to the Nrxn2α knockout (KO) model. Methods Fixed brains of Nrxn2α KO mice underwent DTI using 9.4 T MRI, and diffusion properties of socially relevant brain regions were quantified. The same tissue was then subjected to CLARITY to immunolabel axons and cell bodies, which were also quantified. Results DTI revealed increases in fractional anisotropy in the amygdala (including the basolateral nuclei), the anterior cingulate cortex, the orbitofrontal cortex and the hippocampus. Axial diffusivity of the anterior cingulate cortex and orbitofrontal cortex was significantly increased in Nrxn2α KO mice, as were tracts between the amygdala and the orbitofrontal cortex. Using CLARITY, we find significantly altered axonal orientation in the amygdala, orbitofrontal cortex and the anterior cingulate cortex, which was unrelated to cell density. Conclusions Our findings demonstrate that deleting a single neurexin gene (Nrxn2α) induces atypical structural connectivity within socially relevant brain regions. More generally, our combined within-subject DTI and CLARITY approach presents a new, more sensitive method of revealing hitherto undetectable differences in the autistic brain.

中文翻译：

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扩散张量 MRI 和 CLARITY 的受试者内应用揭示了 Nrxn2 缺失小鼠的大脑结构变化。

背景 在已知会增加自闭症谱系障碍风险的许多基因突变中，很大一部分聚集在突触蛋白上。一个这样的突触前蛋白家族是 neurexins (NRXN)，最近的遗传和小鼠证据表明 NRXN2 在产生改变的社会行为中具有致病作用。自闭症已被概念化为一种非典型连通性障碍，但单基因突变如何影响这种连通性仍未得到充分探索。为了解决这个问题，我们利用扩散张量 MRI (DTI) 在同一只小鼠的光学透明 (CLARITY) 脑组织中进行了高分辨率 3D 成像，开发了微观结构和结构连接性的定量分析，在此应用于 Nrxn2α 敲除。 KO) 模型。方法 Nrxn2α KO 小鼠的固定大脑使用 9.4 T MRI 进行 DTI，与社会相关的大脑区域的扩散特性被量化。然后对相同的组织进行 CLARITY 免疫标记轴突和细胞体，它们也被量化。结果 DTI 显示杏仁核（包括基底外侧核）、前扣带皮层、眶额皮质和海马的分数各向异性增加。在 Nrxn2α KO 小鼠中，前扣带皮层和眶额皮质的轴向扩散率显着增加，杏仁核和眶额皮质之间的区域也是如此。使用 CLARITY，我们发现杏仁核、眶额皮质和前扣带皮层的轴突方向发生了显着改变，这与细胞密度无关。结论 我们的研究结果表明，删除单个神经突蛋白基因 (Nrxn2α) 会在与社会相关的大脑区域内诱导非典型的结构连接。更一般地说，我们结合的受试者内 DTI 和 CLARITY 方法提出了一种新的、更敏感的方法来揭示自闭症大脑中迄今为止无法检测到的差异。