Chawla M K, Guzowski J F, Ramirez-Amaya V, Lipa P, Hoffman K L, Marriott L K, Worley P F, McNaughton B L, Barnes C A
Arizona Research Laboratories Division of Neural Systems, Memory & Aging, University of Arizona, Tucson, Arizona, USA.
Hippocampus. 2005;15(5):579-86. doi: 10.1002/hipo.20091.
After a spatial behavioral experience, hippocampal CA1 pyramidal cells express the activity-regulated, immediate early gene Arc in an environment-specific manner, and in similar proportions ( 40%) to cells exhibiting electrophysiologically recorded place fields under similar conditions. Theoretical accounts of the function of the fascia dentata suggest that it plays a role in pattern separation during encoding. The hypothesis that the dentate gyrus (DG) uses a sparse, and thus more orthogonal, coding scheme has been supported by the observation that, while granule cells do exhibit place fields, most are silent in a given environment. To quantify the degree of sparsity of DG coding and its corresponding ability to generate distinct environmental representations, behaviorally induced Arc expression was assessed using in situ hybridization coupled with confocal microscopy. The proportion of Arc(+) cells in the "upper blade" of the fascia dentata (i.e., the portion that abuts CA1) increased in an environment-specific fashion, approximately 4-fold above cage-control activity, after behavioral exploration. Surprisingly, cells in the lower blade of the fascia dentata, which are capable of expressing Arc following electrical stimulation, exhibited virtually no behaviorally-induced Arc expression. This difference was confirmed using "line scan" analyses, which also revealed no patterns or gradients of activity along the upper blade of the DG. The expression of Arc in the upper blade was quantitatively similar after exploring familiar or novel environments. When animals explored two different environments, separated by 20 min, a new group of cells responded to the second environment, whereas two separated experiences in the same environment did not activate a new set of granular cells. Thus, granule cells generate distinct codes for different environments. These findings suggest differential contribution of upper and lower blade neurons to plastic networks and confirm the hypothesis that the DG uses sparse coding that may facilitate orthogonalization of information.
在经历空间行为后，海马CA1锥体细胞以环境特异性方式表达活动调节的即刻早期基因Arc，且表达比例（40%）与在相似条件下电生理记录到的具有位置野的细胞比例相似。关于齿状回功能的理论解释表明，它在编码过程中参与模式分离。齿状回（DG）使用稀疏且因此更正交的编码方案这一假设得到了以下观察结果的支持：虽然颗粒细胞确实表现出位置野，但在给定环境中大多数颗粒细胞是沉默的。为了量化DG编码的稀疏程度及其生成不同环境表征的相应能力，使用原位杂交结合共聚焦显微镜评估行为诱导的Arc表达。在行为探索后，齿状回“上叶片”（即邻接CA1的部分）中Arc(+)细胞的比例以环境特异性方式增加，比笼内对照活动高出约4倍。令人惊讶的是，齿状回下叶片中能够在电刺激后表达Arc的细胞几乎没有行为诱导的Arc表达。使用“线扫描”分析证实了这种差异，该分析还显示DG上叶片没有活动模式或梯度。在探索熟悉或新环境后，上叶片中Arc的表达在数量上相似。当动物探索两个间隔20分钟的不同环境时，一组新的细胞对第二个环境有反应，而在同一环境中的两次分开的经历并没有激活一组新的颗粒细胞。因此，颗粒细胞为不同环境生成不同的编码。这些发现表明上叶片和下叶片神经元对可塑性网络的贡献不同，并证实了DG使用可能促进信息正交化的稀疏编码这一假设。
