Animal behavior is encoded in neuronal circuits in the brain. To elucidate the function of these circuits, it is necessary to identify, record from and manipulate networks of connected neurons. Here we present BAcTrace (Botulinum-Activated Tracer), a genetically encoded, retrograde, transsynaptic labeling system. BAcTrace is based on Clostridium botulinum neurotoxin A, Botox, which we engineered to travel retrogradely between neurons to activate an otherwise silent transcription factor. We validated BAcTrace at three neuronal connections in the Drosophila olfactory system. We show that BAcTrace-mediated labeling allows electrophysiological recording of connected neurons. Finally, in a challenging circuit with highly divergent connections, BAcTrace correctly identified 12 of 16 connections that were previously observed by electron microscopy.

动物的行为编码在大脑的神经元回路中。为了阐明这些电路的功能，有必要识别，记录并操纵所连接神经元的网络。在这里，我们介绍BAcTrace（肉毒杆菌激活示踪剂），一种遗传编码的，逆行的，经突触的标记系统。BAcTrace基于肉毒梭菌神经毒素A，肉毒杆菌毒素，我们将其设计为在神经元之间逆行，以激活原本沉默的转录因子。我们在果蝇的三个神经元连接处验证了BAcTrace嗅觉系统。我们表明，BAcTrace介导的标记允许连接的神经元的电生理记录。最终，在具有高度发散的连接的具有挑战性的电路中，BAcTrace正确地识别了先前通过电子显微镜观察到的16个连接中的12个。