Department of Neurosurgery, Osaka City University Graduate School of Medicine, Osaka 545-8585, Japan.
Department of Physiology, Osaka City University Graduate School of Medicine, Osaka 545-8585, Japan; PRESTO, Japan Science and Technology Agency (JST), Kawaguchi, Saitama 332-0012, Japan.
Neurosci Res. 2021 Oct;171:1-8. doi: 10.1016/j.neures.2021.01.006. Epub 2021 Jan 18.
As a major hippocampal output structure, the subiculum projects to diverse cortical and subcortical areas, and its projection to the medial mammillary nucleus (MM) has been implicated in memory. Major efferent targets of the MM are the anteroventral and anteromedial thalamic nuclei and Gudden's ventral tegmental nucleus. These projections may play a key role in distributing subicular information. However, it remains unknown whether neurons in the MM that receive monosynaptic input from the subiculum project to these target regions. We addressed this issue with anterograde transsynaptic tracing mediated using adeno-associated virus serotype 1 (AAV1). Injection of AAV1-Cre and a Cre-dependent AAV encoding enhanced yellow fluorescent protein (EYFP) into the rat dorsal subiculum and MM, respectively, labeled the soma of the MM and axons in the anteroventral / anteromedial thalamic nuclei and Gudden's ventral tegmental nucleus with EYFP. The EYFP-positive neurons in the MM were immunoreactive for glutamate and leu-enkephalin and received perisomatic GABAergic inputs. These results revealed monosynaptic projections from the subiculum to MM neurons projecting to the anteroventral / anteromedial thalamic nuclei and Gudden's ventral tegmental nucleus. This monosynaptic connection may support a fast and robust signal flow through the hippocampal-mammillothalamic and hippocampal-mammillotegmental pathways.
作为海马体的主要输出结构之一，下托投射到广泛的皮质和皮质下区域，其对内侧乳头体（MM）的投射与记忆有关。MM 的主要传出靶区是前腹侧和前内侧丘脑核以及 Gudden 的腹侧被盖核。这些投射可能在分布下托信息方面发挥关键作用。然而，目前尚不清楚从下托接受单突触输入的 MM 神经元是否投射到这些靶区。我们使用腺相关病毒血清型 1（AAV1）介导的顺行转导示踪技术解决了这个问题。将 AAV1-Cre 和依赖 Cre 的 AAV 编码增强型黄色荧光蛋白（EYFP）分别注入大鼠背侧下托和 MM，标记了 MM 的体和前腹侧/前内侧丘脑核和 Gudden 的腹侧被盖核中的 EYFP 轴突。MM 中的 EYFP 阳性神经元对谷氨酸和亮啡肽呈免疫反应性，并接受胞体 GABA 能输入。这些结果揭示了从下托到投射到前腹侧/前内侧丘脑核和 Gudden 的腹侧被盖核的 MM 神经元的单突触投射。这种单突触连接可能支持通过海马体-乳头体丘脑和海马体-乳头体被盖体途径的快速和强大的信号流。
