Connecting the mechanobiology of tissue and cells in cerebral cortical folding

摘要 在受许多神经发育障碍影响的个体的大脑皮层中观察到的折叠模式 这些疾病不同于典型发育的“对照”个体中的疾病。人类的大脑皮层 从怀孕中期到出生后最初几个月的时期。尽管我们对 大脑在这段时间内是如何发育的，包括增殖活动，许多 细胞类型、突触连接的建立、皮质回路的发育、宏观生长，以及 虽然大脑中的系统级生理变化，但对这些变化如何关联的了解相对较少 到成熟时产生正常或不正常的折叠模式。在我们的理解中， 细胞水平发育事件与宏观行为（生长和 组织的生物力学性质）限制了我们解释特定折叠异常的能力， 神经发育来源，或在潜在的病因学因素方面的重要性，为特定的 神经发育障碍本申请提出了一系列的研究，以连接高精度的实验 测量大脑的生长和机械性能，并进行计算机模拟， 了解影响大脑皮质折叠的生物力学因素。这种结合实验 用理论方法分析雪貂大脑皮层的折叠。与人类大脑一样， 雪貂的大脑在成熟时具有脑回和脑沟，但与人类不同的是，这些褶皱在出生后出现， 雪貂具体重点将放在枕颞沟（OTS），在初级视觉皮层， 与其他沟相比，其折叠相对较晚，在P35处结束。最近，我们发现OTS 形成受到严重影响（或OTS根本不形成），在雪貂经历了双边 在P7时摘除眼球。因此，生长和机械性能将在视力控制（SC）中表征 并在P8至P38的6个时间点在P7（BEP7）雪貂上双侧去核。这些数据将 与大脑生长的多尺度理论和计算模型的发展相结合。在目标1中， 生长将通过体内MRI在宏观尺度上表征，并且通过测量如何在细胞水平上表征。 P7去核影响增殖动力学，并改变细胞体和神经元体积。 皮质折叠在目标2中，将在相同的年龄范围内量化组织的机械性能。剪切 皮质灰质和发育中的白色物质的模量将使用原子力显微镜测定。 通过观察切口后的组织变形来测量组织应力。较小的组织应力 空间尺度将从细胞核的形状和细胞核的取向分布中推断出来。 流程.在目标3中，将目标1和2的实验数据整合到组织生长模型中 模型的有效性将通过观察其概括能力来评估。 SC和BEP7雪貂之间折叠模式的差异。

ABSTRACT The folding patterns observed in the cerebral cortex of individuals affected by many neurodevelopmental disorders differ from those in typically-developing "control" individuals. The human cerebral cortex folds over the period from the middle of gestation through the first months of postnatal life. Although much is known about how the brain develops over this time period, including proliferative activity, morphological maturation of many cell types, establishment of synaptic connections, development of cortical circuitry, macroscopic growth, and system-level physiological changes in the brain, relatively little is understood about how these changes relate to the production of a normal, or abnormal, folding pattern at maturity. Shortcomings in our understanding of the relationship between cellular-level developmental events and macroscopic behavior (growth and biomechanical properties of tissue) limit our ability to explain a given folding abnormality in terms of its neurodevelopmental source, or in terms of potential etiological factors important for a specific neurodevelopmental disorder. This application proposes a series of studies to link high-precision experimental measures of brain growth and mechanical properties with computational simulations to advance our understanding of the biomechanical factors that influence cerebral cortical folding. This combined experimental and theoretical approach will be used to analyze folding of the ferret cerebral cortex. As with the human brain, the ferret brain possesses gyri and sulci at maturity, but in contrast to humans, these folds arise postnatally in ferrets. Specific focus will be placed on the occipital temporal sulcus (OTS), within the primary visual cortex, which folds relatively late compared to other sulci, concluding by P35. Recently, we have discovered that OTS formation is severely affected (or that the OTS does not form at all) in ferrets that have undergone bilateral enucleation at P7. Growth and mechanical properties will therefore be characterized in sighted control (SC) and bilaterally enucleated on P7 (BEP7) ferrets at 6 time points ranging from P8 through P38. This data will be integrated with the development of a multiscale theoretical and computational model of brain growth. In Aim 1, growth will be characterized on a macroscopic scale by in vivo MRI, and on a cellular level by measuring how P7 enucleation affects proliferation dynamics and changes cell body and neuropil volumes over the period of cortical folding. In Aim 2, mechanical properties of the tissue will be quantified over the same age range. Shear moduli of cortical gray matter and developing white matter will be determined using atomic force microscopy. Tissue stress will be measured by observing tissue deformations following incisions. Tissue stress on a smaller spatial scale will be inferred from the shapes of nuclei and from the orientation distributions of cellular processes. In Aim 3, the experimental data from Aims 1 and 2 will be integrated into a model of tissue growth and deformation, and the validity of the model will be evaluated by observing its ability to recapitulate differences in folding patterns between SC and BEP7 ferrets.