Elfn1 regulates target-specific release probability at CA1-interneuron synapses.

Although synaptic transmission may be unidirectional, the establishment of synaptic connections with specific properties can involve bidirectional signaling. Pyramidal neurons in the hippocampus form functionally distinct synapses onto two types of interneurons. Excitatory synapses onto oriens-lacunosum moleculare (O-LM) interneurons are facilitating and have a low release probability, whereas synapses onto parvalbumin interneurons are depressing and have a high release probability. Here, we show that the extracellular leucine-rich repeat fibronectin containing 1 (Elfn1) protein is selectively expressed by O-LM interneurons and regulates presynaptic release probability to direct the formation of highly facilitating pyramidal-O-LM synapses. Thus, postsynaptic expression of Elfn1 in O-LM interneurons regulates presynaptic release probability, which confers target-specific synaptic properties to pyramidal cell axons.

虽然突触传递可能是单向的，但具有特定特性的突触连接的建立可能涉及双向信号传导。海马中的锥体神经元在两种中间神经元上形成功能不同的突触。在海马齿状回分子层（O - LM）中间神经元上的兴奋性突触是易化的，且释放概率低，而在小白蛋白中间神经元上的突触是抑制性的，且释放概率高。在此，我们表明富含亮氨酸重复序列的细胞外纤连蛋白1（Elfn1）由O - LM中间神经元选择性表达，并调节突触前释放概率以指导高度易化的锥体 - O - LM突触的形成。因此，O - LM中间神经元中Elfn1的突触后表达调节突触前释放概率，这赋予锥体细胞轴突以靶点特异性的突触特性。