Medical Faculty, Department of Neurophysiology, Ruhr University Bochum, Universitätsstr. 150, MA 4/150, 44780, Bochum, Germany.
Brain Struct Funct. 2024 Apr;229(3):639-655. doi: 10.1007/s00429-023-02694-z. Epub 2023 Sep 10.
Hippocampal afferent inputs, terminating on proximal and distal subfields of the cornus ammonis (CA), enable the functional discrimination of 'what' (item identity) and 'where' (spatial location) elements of a spatial representation. This kind of information is supported by structures such as the retrosplenial cortex (RSC). Spatial content learning promotes the expression of hippocampal synaptic plasticity, particularly long-term depression (LTD). In the CA1 region, this is specifically facilitated by the learning of item-place features of a spatial environment. Gene-tagging, by means of time-locked fluorescence in situ hybridization (FISH) to detect nuclear expression of immediate early genes, can reveal neuronal populations that engage in experience-dependent information encoding. In the current study, using FISH, we examined if learning-facilitated LTD results in subfield-specific information encoding in the hippocampus and RSC. Rats engaged in novel exploration of small items during stimulation of Schaffer collateral-CA1 synapses. This resulted in LTD (> 24 h). FISH, to detect nuclear expression of Homer1a, revealed that the distal-CA1 and proximal-CA3 subcompartments were particularly activated by this event. By contrast, all elements of the proximodistal cornus ammonis-axis showed equal nuclear Homer1a expression following LTD induction solely by means of afferent stimulation. The RSC exhibited stronger nuclear Homer1a expression in response to learning-facilitated LTD, and to novel item-place experience, compared to LTD induced by sole afferent stimulation in CA1. These results show that both the cornus ammonis and RSC engage in differentiated information encoding of item-place learning that is salient enough, in its own right, to drive the expression of hippocampal LTD. These results also reveal a novel role of the RSC in item-place learning.
海马传入输入，终止于 Cornu ammonis（CA）的近端和远端亚区，使“什么”（项目身份）和“哪里”（空间位置）的空间表示的功能区分成为可能。这种信息由后穹窿皮质（RSC）等结构支持。空间内容学习促进海马突触可塑性的表达，特别是长时程抑郁（LTD）。在 CA1 区域，这特别通过空间环境的项目-位置特征的学习来促进。通过时间锁定荧光原位杂交（FISH）进行基因标记，以检测核内即时早期基因的表达，可以揭示参与经验依赖性信息编码的神经元群体。在当前研究中，我们使用 FISH 检查学习促进的 LTD 是否导致海马体和 RSC 中的亚区特异性信息编码。在刺激 Schaffer 侧支-CA1 突触时，大鼠参与小物品的新探索。这导致 LTD（>24 小时）。FISH 检测 Homer1a 的核表达，显示远端 CA1 和近端 CA3 亚区在这种情况下特别被激活。相比之下，仅通过传入刺激诱导 LTD 时，CA1 中的 cornus ammonis 轴的近端-远端所有元素均表现出相等的核 Homer1a 表达。与单独的传入刺激诱导的 LTD 相比，RSC 在学习促进的 LTD 以及新的项目-位置经验下显示出更强的核 Homer1a 表达。这些结果表明，cornu ammonis 和 RSC 都参与了项目-位置学习的差异化信息编码，这种编码本身就足以驱动海马体 LTD 的表达。这些结果还揭示了 RSC 在项目-位置学习中的新作用。
