Enabling precise cell-type-specific dissection of orientation and memory circuits in retrosplenial cortex

项目总结/摘要 在人类中，一个叫做压后皮质的大脑区域的损伤会导致明显的空间定向障碍 以及严重的逆行和顺行记忆缺陷类似的导航和记忆障碍也 在啮齿类动物中观察到，其压后皮质有损伤或化学发生失活。尽管它的批评 压后皮质的重要功能、细胞、电路和计算仍然没有得到充分的研究， 尤其是与海马体和内嗅皮层相比。 我们最近发现，一个小的，兴奋的，锥体神经元-只发现在层2/3（L2/3）的颗粒 压后皮质（RSG）-具有与其更标准（规则尖峰; RS）非常不同的特性 邻居，并且唯一适合于计算长持续时间内的类似罗盘的方向信息。我们有 将这种神经元命名为低基强度（LR）细胞。使用光遗传学离体电路映射，我们有 随后发现来自丘脑（方向信息来源）和背侧 下托（空间信息源）选择性地会聚到这些小LR细胞上，同时避免靠近 RS细胞。因此，LR神经元被理想地定位以支持RSG的空间定向计算。 在非快速眼动睡眠期间，海马波纹（已知对记忆巩固很重要）传播， 通过背侧下托到达RSG的L2/3。由于这些背侧下托输出选择性地募集LR， 邻近的RS细胞，LR神经元也理想地定位在巩固的核心作用， 从海马体转移到RSG尽管有这种强烈的理由来剖析行为的作用， LR细胞在体内，两个关键的障碍仍然能够在不久的将来提交TargetedBCP R 01。一是 从体内大量同时LR细胞进行电生理记录在技术上具有挑战性。 这是因为它们位于一个狭窄的~120 um的RSG带内，隐藏在中线附近， 通过血管阻止垂直进入。第二，LR神经元的转录组特征仍然存在， 未知的，阻止了选择性和选择性的转基因小鼠品系的合理选择或生产， 特异性标记LR神经元。为了克服这些障碍，在目标1中，我们将开发和测试定制设计的 探针优化记录大量的L2/3 RSG神经元。在目标2中，我们将利用艾伦大脑研究所 数据库，10 x Next-Gen测序和Patch-seq，以确定对应于 LR神经元的形态生理学类别。这些目标的完成将为随后的 有针对性的BCP R 01提交将利用大规模记录和因果光学/化学遗传学， 解读LR神经元在空间信息的表征和整合中的重要性。

PROJECT SUMMARY/ABSTRACT In humans, damage to a brain region called the retrosplenial cortex leads to pronounced spatial disorientation and severe retrograde and anterograde memory deficits. Similar navigational and memory impairments are also seen in rodents with either lesions or chemogenetic inactivation of the retrosplenial cortex. Despite its critically important functions, the cells, circuits, and computations of the retrosplenial cortex remain understudied, especially when compared to those of the hippocampus and entorhinal cortex. We have recently shown that a small, excitable, pyramidal neuron – only found in layers 2/3 (L2/3) of the granular retrosplenial cortex (RSG) – has properties that are very different from its more standard (regular-spiking; RS) neighbors and is uniquely suited to computing compass-like directional information over long durations. We have named this neuron the Low Rheobase (LR) cell. Using optogenetic ex vivo circuit mapping, we have subsequently found that inputs from the thalamus (source of directional information) and from the dorsal subiculum (source of spatial information) converge selectively onto these small LR cells, while avoiding nearby RS cells. Thus, LR neurons are ideally positioned to support the RSG’s spatial orientation computations. During non-REM sleep, hippocampal ripples (known to be important for memory consolidation) are propagated, via the dorsal subiculum, to L2/3 of the RSG. Since these dorsal subicular outputs selectively recruit LR but not neighboring RS cells, LR neurons are also ideally positioned to play a central role in the consolidation of memories from the hippocampus to the RSG. Despite this strong rationale to dissect the behavioral role of LR cells in vivo, two critical hurdles remain to enable a TargetedBCP R01 submission in the near future. First, it is technically challenging to electrophysiologically record from large numbers of simultaneous LR cells in vivo. This is because they are located within a narrow ~120 um band of RSG tucked away close to the midline, with vertical access prevented by blood vessels. Second, the transcriptomic signature of LR neurons remains unknown, preventing the rational selection or production of transgenic mouse lines that selectively and specifically label LR neurons. To overcome these hurdles, in Aim 1, we will develop and test custom-designed probes optimized to record large numbers of L2/3 RSG neurons. In Aim 2, we will utilize Allen Brain Institute databases, 10x Next-Gen sequencing, and Patch-seq to identify the transcriptomic class corresponding to the morphophysiological class of LR neurons. The completion of these Aims will set the stage for a subsequent TargetedBCP R01 submission that will utilize large-scale recordings and causal opto/chemogenetics to carefully decipher the importance of LR neurons in the representation and consolidation of spatial information.