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

项目摘要/摘要 在人类中，被称为脾后皮质的大脑区域的损伤会导致明显的空间定向障碍。 以及严重的逆行性和顺行性记忆缺陷。类似的导航和记忆障碍也是 见于脾后皮质受损或化学生成失活的啮齿动物。尽管它的批判性 脾后皮质的重要功能、细胞、回路和计算仍未得到研究， 尤其是与海马体和内嗅皮层相比。 我们最近发现了一个小的，可兴奋的锥体神经元--只在颗粒的2/3(L2/3)层中发现 脾后皮质(RSG)-具有与其更标准的(规则棘波；RS)非常不同的特性 它是唯一一种适用于长时间计算指南针方向信息的仪器。我们有 将该神经元命名为低Rheobase(LR)细胞。利用光遗传体外电路图，我们有 随后发现，来自丘脑(方向性信息的来源)和背侧的输入 下丘(空间信息源)选择性地汇聚到这些小的LR细胞上，同时避开附近 RS细胞。因此，LR神经元的位置非常适合支持RSG的空间方向计算。 在非快速眼动睡眠期间，海马波(已知对巩固记忆很重要)被传播， 通过背侧下丘脑束至RSG的L2/3。由于这些背侧亚束输出选择性地招募LR而不是 邻近的RS细胞，LR神经元也处于理想的位置，在巩固 从海马体到RSG的记忆。尽管有如此强大的理由来剖析 要在不久的将来实现TargetedBCP R01的提交，仍然存在两个关键障碍。首先，它 在体内从大量同时存在的LR细胞中进行电生理记录在技术上是具有挑战性的。 这是因为它们位于RSG的一个狭窄的~120微米范围内，隐藏在中线附近，具有 垂直通道被血管阻止。第二，保留了LR神经元的转录特征 未知，阻止合理选择或生产转基因小鼠品系 明确标记下丘脑神经元。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 用于记录大量L2/3 RSG神经元的探头。在目标2中，我们将利用艾伦大脑研究所 数据库、10倍下一代测序和Patch-seq以识别与 下丘脑神经元的形态生理学分类。这些目标的实现将为随后的 目标BCP R01提交，将利用大规模记录和因果光/化学遗传学仔细 解读LR神经元在空间信息表示和巩固中的重要性。

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.