INSERM UMR1266, Institute of Psychiatry and Neuroscience of Paris, Team Synaptic Plasticity and Neural Networks, Université de Paris, Paris, France.
GHU Paris Psychiatrie and Neurosciences, Paris, France.
Elife. 2021 May 18;10:e63352. doi: 10.7554/eLife.63352.
The hippocampus is critical for memory formation. The hypothalamic supramammillary nucleus (SuM) sends long-range projections to hippocampal area CA2. While the SuM-CA2 connection is critical for social memory, how this input acts on the local circuit is unknown. Using transgenic mice, we found that SuM axon stimulation elicited mixed excitatory and inhibitory responses in area CA2 pyramidal neurons (PNs). Parvalbumin-expressing basket cells were largely responsible for the feedforward inhibitory drive of SuM over area CA2. Inhibition recruited by the SuM input onto CA2 PNs increased the precision of action potential firing both in conditions of low and high cholinergic tone. Furthermore, SuM stimulation in area CA2 modulated CA1 activity, indicating that synchronized CA2 output drives a pulsed inhibition in area CA1. Hence, the network revealed here lays basis for understanding how SuM activity directly acts on the local hippocampal circuit to allow social memory encoding.
海马体对于记忆的形成至关重要。下丘脑的穹隆上核（SuM）向海马体 CA2 区发出长程投射。虽然 SuM-CA2 连接对于社会记忆至关重要，但这种输入如何作用于局部回路尚不清楚。利用转基因小鼠，我们发现 SuM 轴突刺激在 CA2 锥体神经元（PNs）中引起混合的兴奋性和抑制性反应。表达 Parvalbumin 的篮状细胞主要负责 SuM 对 CA2 区的前馈抑制驱动。由 SuM 输入招募的抑制作用，在低和高胆碱能张力条件下均增加了动作电位发射的精确性。此外，在 CA2 区刺激 SuM 调节 CA1 活动，表明同步的 CA2 输出在 CA1 区驱动脉冲抑制。因此，这里揭示的网络为理解 SuM 活动如何直接作用于局部海马回路以允许社会记忆编码奠定了基础。
