Synapses are a key component of neural circuits, facilitating rapid and specific signalling between neurons. Synaptic engineering — the synthetic insertion of new synaptic connections into in vivo neural circuits — is an emerging approach for neural circuit interrogation. This approach is especially powerful for establishing causality in neural circuit structure–function relationships, for emulating synaptic plasticity and for exploring novel patterns of circuit connectivity. Contrary to other approaches for neural circuit manipulation, synaptic engineering targets specific connections between neurons and functions autonomously with no user-controlled external activation. Synaptic engineering has been successfully implemented in several systems and in different forms, including electrical synapses constructed from ectopically expressed connexin gap junction proteins, synthetic optical synapses composed of presynaptic photon-emitting luciferase coupled with postsynaptic light-gated channels, and artificial neuropeptide signalling pathways. This Perspective describes these different methods and how they have been applied, and examines how the field may advance.

突触是神经回路的关键组成部分，促进神经元之间快速且特定的信号传导。突触工程——将新的突触连接合成插入体内神经回路——是一种新兴的神经回路询问方法。这种方法对于建立神经回路结构-功能关系中的因果关系、模拟突触可塑性和探索回路连接的新模式特别有用。与其他神经回路操纵方法相反，突触工程针对神经元之间的特定连接并自主发挥作用，无需用户控制的外部激活。突触工程已在多个系统中以不同的形式成功实施，包括由异位表达的连接蛋白间隙连接蛋白构建的电突触、由突触前光子发射荧光素酶与突触后光门控通道耦合组成的合成光学突触，以及人工神经肽信号通路。本视角描述了这些不同的方法以及它们的应用方式，并探讨了该领域的发展前景。