Department of Psychological and Brain Sciences, Center for Cognitive Neuroscience, Dartmouth College, Hanover, New Hampshire 03755, USA.
Hippocampus. 2011 Oct;21(10):1062-73. doi: 10.1002/hipo.20820. Epub 2010 Jun 23.
The neural representation of directional heading is encoded by a population of cells located in a circuit that includes the postsubiculum (PoS), anterodorsal thalamus (ADN), and lateral mammillary nuclei (LMN). Throughout this circuit, many cells rely on both movement- and landmark-related information to discharge as a function of the animal's directional heading. The PoS projects to both the ADN and LMN, and these connections may convey critical spatial information about landmarks, because lesions of the PoS disrupt landmark control in head direction (HD) cells and hippocampal place cells [Goodridge and Taube (1997) J Neurosci 17:9315-9330; Calton et al. (2003) J Neurosci 23:9719-9731]. The PoS → ADN projection originates in the deep layers of PoS, but no studies have determined whether the PoS → LMN projection originates from the same cells that project to ADN. To address this issue, two distinct cholera toxin-subunit B (CTB) fluorophore conjugates (Alexa Fluor 488 and Alexa Fluor 594) were injected into the LMN and ADN of the same rats, and PoS sections were examined for cell bodies containing either or both CTB conjugates. Results indicated that the PoS → LMN projection originates exclusively from a thin layer of cells located superficial to the layer(s) of PoS → ADN projection cells, with no overlap. To verify the laminar distribution and morphological characteristics of PoS → LMN and PoS → ADN cells, biotinylated dextran amine was injected into LMN or ADN of different rats, and tissue sections were counterstained with thionin. Results indicated that the PoS → LMN projection arises from large pyramidal cells in layer IV, whereas the PoS → ADN projection arises from a heterogeneous cell population in layers V/VI. This study provides the first evidence that the PoS → ADN and PoS → LMN projections arise from distinct, nonoverlapping cell layers in PoS. Functionally, the PoS may provide landmark information to HD cells in LMN.
方向朝向的神经表示是由位于包括后下托（PoS）、前背侧丘脑（ADN）和外侧乳突核（LMN）在内的回路中的一群细胞编码的。在整个回路中，许多细胞都依赖于运动和地标相关信息来放电，作为动物方向朝向的函数。PoS 投射到 ADN 和 LMN，这些连接可能传递有关地标物的关键空间信息，因为 PoS 的损伤会破坏 HD 细胞和海马位置细胞中的地标物控制[Goodridge 和 Taube（1997）J Neurosci 17:9315-9330；Calton 等人（2003）J Neurosci 23:9719-9731]。PoS→ADN 投射起源于 PoS 的深层，但尚无研究确定 PoS→LMN 投射是否起源于投射到 ADN 的相同细胞。为了解决这个问题，将两种不同的霍乱毒素亚单位 B（CTB）荧光染料缀合物（Alexa Fluor 488 和 Alexa Fluor 594）注入同一大鼠的 LMN 和 ADN，并检查 PoS 切片中是否含有 CTB 缀合物。结果表明，PoS→LMN 投射仅起源于位于 PoS→ADN 投射细胞层上方的一层薄细胞，没有重叠。为了验证 PoS→LMN 和 PoS→ADN 细胞的层分布和形态特征，将生物素化葡聚糖胺注入不同大鼠的 LMN 或 ADN，并用硫堇对组织切片进行复染。结果表明，PoS→LMN 投射来自于第四层的大锥体细胞，而 PoS→ADN 投射则来自于 V/VI 层中的异质细胞群。这项研究首次提供了证据表明，PoS→ADN 和 PoS→LMN 投射来自于 PoS 中的不同、不重叠的细胞层。从功能上讲，PoS 可以向 LMN 中的 HD 细胞提供地标信息。
