下丘脑乳头体上核输入到成年新生齿状回神经元的若干特性
Select properties of supramammillary input to adult-born dentate gyrus neurons
下丘脑乳头体上核（SUM）投射至海马齿状回（DG），该脑区对学习、记忆和成年神经发生至关重要。SUM输入如何调控成年新生DG（abDG）神经元以支持记忆加工仍不清楚。本研究利用成年小鼠的单突触示踪技术，鉴定出一个以胞体大、放电频率低为特征的、特异性靶向abDG的SUM神经元亚群。电生理记录显示，这些SUM神经元向abDG共释放谷氨酸和GABA，且自主跑轮运动选择性地增强GABA能传递。化学遗传学沉默SUM-DG GABA能投射损害了模式分离（即在相似刺激之间做出精细区分的能力），但不影响恐惧条件化和空间导航记忆。总之，我们的发现揭示了一个特定的SUM亚群对abDG神经元提供抑制性调控，为模式分离过程中的稀疏编码建立了一种新的环路机制。
用单突触示踪、电生理和化学遗传学把下丘脑 SUM 到成年新生齿状回细胞的通路拆开，区分出谷氨酸与 GABA 共释放中 GABA 成分对模式分离的作用。
The hypothalamic supramammillary nucleus (SUM) projects to the hippocampal dentate gyrus (DG), a brain area crucial for learning, memory, and adult neurogenesis. How SUM inputs regulate adult-born DG (abDG) neurons to support memory processing remains unclear. Here, using monosynaptic tracing in adult mice, we identified a distinct subpopulation of abDG-targeting SUM neurons defined by large somata and low firing rate. Electrophysiological recordings revealed that these SUM neurons co-release glutamate and GABA onto abDGs, and that voluntary running selectively enhances GABAergic transmission. Chemogenetic silencing of SUM-DG GABAergic projections impaired pattern separation, the ability to make fine distinctions between similar stimuli, but not fear conditioning and spatial navigation memory. Altogether, our findings reveal that a distinct SUM subpopulation provides inhibitory modulation to abDG neurons, establishing a novel circuit mechanism for sparse encoding during pattern separation.
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来源：bioRxiv · Neuroscience · biorxiv.org