The cerebellar involvement in cognitive functions such as attention, language, working memory, emotion, goal-directed behavior and spatial navigation is constantly growing. However, an exact connectivity map between the hippocampus and cerebellum in mice is still unknown. Here, we conducted a tracing study to identify the sequence of transsynaptic, cerebellar-hippocampal connections in the mouse brain using combinations of Recombinant adeno-associated virus (rAAV) and pseudotyped deletion-mutant rabies (RABV) viruses. Stereotaxic injection of a primarily anterograde rAAV-WGA (wheat germ agglutinin)-Cre tracer virus in the deep cerebellar nuclei (DCN) of a Cre-dependent tdTomato reporter mouse resulted in strong tdTomato labeling in hippocampal CA1 neurons, retrosplenial cortex (RSC), rhinal cortex (RC) as well as thalamic and cerebellar areas. Whereas hippocampal injections with the retrograde tracer virus rAAV-TTC (tetanus toxin C fragment)-eGFP, displayed eGFP positive cells in the rhinal cortex and subiculum. To determine the sequence of mono-transsynaptic connections between the cerebellum and hippocampus, we used the retrograde tracer RABVΔG-eGFP(EnvA). The tracing revealed a direct connection from the dentate gyrus (DG) in the hippocampus to the RSC, RC and subiculum (S), which are monosynaptically connected to thalamic laterodorsal and ventrolateral areas. These thalamic nuclei are directly connected to cerebellar fastigial (FN), interposed (IntP) and lateral (Lat) nuclei, discovering a new projection route from the fastigial to the laterodorsal thalamic nucleus in the mouse brain. Collectively, our findings suggest a new cerebellar-hippocampal connection via the laterodorsal and ventrolateral thalamus to RSC, RC and S. These results strengthen the notion of the cerebellum's involvement in cognitive functions such as spatial navigation via a polysynaptic circuitry.

中文翻译：

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从小鼠小脑深核到腹侧和外侧后丘脑到海马体的新投影。

小脑对诸如注意力，语言，工作记忆，情绪，目标行为和空间导航等认知功能的参与不断增长。但是，小鼠中海马和小脑之间的确切连接图仍然未知。在这里，我们进行了追踪研究，以使用重组腺相关病毒（rAAV）和假型缺失突变狂犬病（RABV）病毒的组合来鉴定小鼠脑中突触，小脑-海马连接的序列。在Cre依赖型tdTomato报告基因小鼠的小脑深核（DCN）中立体定向注射主要为顺行性的rAAV-WGA（小麦胚芽凝集素）-Cre示踪病毒，在海马CA1神经元，后脊髓皮层（RSC）中强烈标记了tdTomato，鼻皮质（RC）以及丘脑和小脑区域。海马注射逆行示踪病毒rAAV-TTC（破伤风毒素C片段）-eGFP，在鼻皮质和下丘脑显示eGFP阳性细胞。为了确定小脑和海马之间的单突触连接的序列，我们使用了逆行示踪剂RABVΔG-eGFP（EnvA）。追踪显示海马齿状回（DG）与RSC，RC和下丘脑（S）直接连接，后者与丘脑后外侧和腹侧区域单突触连接。这些丘脑核直接连接到小脑小脑顶（FN），插入的（IntP）和外侧（拉特）核，在小鼠脑中发现了从小脑皮到丘脑后外侧丘脑核的新投射途径。总的来说，