Postnatal Cajal-Retzius neurons as pacemakers of neocortical network activity

描述（由申请人提供）：神经精神障碍，如精神分裂症、自闭症和双相情感障碍，可能是由于发育期间大脑皮层脑细胞之间连接成熟的变化引起的。在小鼠新皮层中，我们和其他人已经证明，出生后第2周是树突棘变得稳定的时候，突触密度急剧增加，自发活动突然变得不稳定。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细胞在皮层分层中的关键作用是众所周知的，但对其作为神经元的功能知之甚少。事实上，考虑到CR神经元是自发活动的，同步发射，并与锥体神经元的顶端树突形成突触，我们设想它们可能作为皮层网络活动的起搏器。具体来说，我们建议测试的假设，出生后CR神经元可以触发同步活动在新皮层和那些生存到成年继续影响锥体神经元放电。以前在脑切片中的工作一直无法证明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。我们打算克服这一缺点，在体内使用双光子钙离子成像和电生理记录从这些细胞类型在完整的大脑。我们已经确定了CR神经元的特异性启动子，这将使我们不仅能够在第1层中特异性地可视化这些细胞，而且还能够使用病毒载体和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CR神经元在出生后早期与成人阶段的形态学和电生理特性，以确定在成熟动物中存活的CR神经元是否与那些注定在早期发育过程中死亡的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神经元的群体的放电，同时记录它们在更深的皮质层中的突触伙伴。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研究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.