Postnatal Cajal-Retzius neurons as pacemakers of neocortical network activity

描述（由申请人提供）：精神分裂症、自闭症、双相情感障碍等神经精神疾病可能是由于发育过程中大脑皮层脑细胞之间连接的成熟变化引起的。在小鼠的新皮层中，我们和其他人已经证明，在出生后的第二周，树突棘变得稳定，突触密度急剧增加，自发活动突然变得不同步。这也是大多数Cajal-Retzius （CR）细胞经历细胞死亡的时期，尽管我们最近发现一小部分细胞存活到成年期。尽管CR细胞因其在皮层层压中的关键作用而闻名，但其作为神经元的功能却鲜为人知。事实上，考虑到CR神经元自发活动，同步放电，并与锥体神经元的顶端树突形成突触，我们设想它们可能起皮层网络活动起搏器的作用。具体地说，我们建议测试出生后的CR神经元可以触发新皮层的同步活动，并且那些存活到成年的神经元继续影响锥体神经元放电的假设。先前的脑切片研究无法证明CR神经元和锥体神经元在功能上是连接的，这可能是因为轴突和树突的完整性被破坏了。我们打算通过使用体内双光子Ca2+成像和电生理学来记录完整大脑中这些细胞类型来克服这一缺点。我们已经确定了CR神经元的特定启动子，这将使我们不仅能够在第1层特异性地可视化这些细胞，而且还可以使用病毒载体和Cre-Lox方法有条件地表达通道视紫红质。在第一个目标中，我们将检查出生后早期与成年期CR神经元的形态和电生理特性，以确定成熟动物中存活的CR神经元是否与那些在早期发育中注定死亡的CR神经元不同。在第二个目标中，我们打算用光遗传学来调节CR神经元群的放电，同时记录它们在更深皮层的突触伙伴。目的是测试CR神经元是否可以影响锥体神经元的放电，并有助于在发育中的新皮层中出现同步网络活动。这些实验将为进一步探索CR神经元功能障碍导致神经精神疾病的机制奠定基础。

DESCRIPTION (provided by applicant): Neuropsychiatric disorders like schizophrenia, autism and bipolar disorder may be caused by changes in the maturation of connections between brain cells of the cerebral cortex during development. In mouse neocortex, we and others have shown that the 2nd postnatal week is a time when dendritic spines become stabilized, the density of synapses increases dramatically, and spontaneous activity becomes abruptly desynchronized. This is also a period when most Cajal-Retzius (CR) cells undergo cell death, although we recently showed that a small subset survives into adulthood. Although CR cells are well-known for their critical role in cortical lamination much less is known about their function as neurons. Indeed, considering that CR neurons are spontaneously active, fire synchronously, and make synapses with apical dendrites of pyramidal neurons, we envision that they might function as pacemakers of cortical network activity. Specifically, we propose to test the hypothesis that postnatal CR neurons can trigger synchronous activity in neocortex and that those that survive into adulthood continue to influence pyramidal neuron firing. Previous work in brain slices has been unable to demonstrate that CR neurons and pyramidal neurons are functionally connected probably because the integrity of axons and dendrites was disrupted. We intend to overcome this shortcoming by using in vivo two-photon Ca2+ imaging and electrophysiology to record from these cell types in the intact brain. We have identified a specific promoter for CR neurons that will allow us not only to specifically visualize these cells in Layer 1 but also to conditionaly express channel-rhodopsin using viral vectors and a Cre-Lox approach. In the first aim, we will examine morphological and electrophysiological properties of CR neurons at early postnatal vs. adult stages to determine whether surviving CR neurons in mature animals are distinct from those that are destined to die during early development. In the second aim, we intend to modulate the firing of cohorts of CR neurons with optogenetics while recording from their synaptic partners in deeper cortical layers. The goal is to test whether CR neurons can influence the firing of pyramidal neurons and contribute to the emergence of synchronous network activity in the developing neocortex. These experiments will lay the foundation for future studies exploring the mechanisms by which dysfunction of CR neurons could cause neuropsychiatric diseases.