Spatiotemporally precise optogenetic activation of sensory neurons in freely walking Drosophila

Previous work has characterized how walking Drosophila coordinate the movements of individual limbs (DeAngelis, Zavatone-Veth, and Clark, 2019). To understand the circuit basis of this coordination, one must characterize how sensory feedback from each limb affects walking behavior. However, it has remained difficult to manipulate neural activity in individual limbs of freely moving animals. Here, we demonstrate a simple method for optogenetic stimulation with body side-, body segment-, and limb-specificity that does not require real-time tracking. Instead, we activate at random, precise locations in time and space and use post hoc analysis to determine behavioral responses to specific activations. Using this method, we have characterized limb coordination and walking behavior in response to transient activation of mechanosensitive bristle neurons and sweet-sensing chemoreceptor neurons. Our findings reveal that activating these neurons has opposite effects on turning, and that activations in different limbs and body regions produce distinct behaviors.

既往研究已阐明行走果蝇（Drosophila）的单肢运动协调机制（DeAngelis、Zavatone-Veth与Clark，2019）。为解析该协调机制的环路基础，需明确每一侧肢体的感觉反馈如何影响行走行为。然而，在自由移动的动物个体中，精准操控单肢的神经活动仍颇具挑战。本研究中，我们提出了一种无需实时追踪、可实现身体侧别、体节及肢体特异性光遗传刺激（optogenetic stimulation）的简易方法。我们通过在时空维度上随机选取精准位点进行激活，并借助事后分析（post hoc analysis）来确定特定激活对应的行为响应。利用该方法，我们针对机械敏感鬃毛神经元（mechanosensitive bristle neurons）与甜味感受化学感受器神经元（sweet-sensing chemoreceptor neurons）的瞬时激活，表征了肢体协调模式与行走行为的变化。本研究结果显示，激活这两类神经元对昆虫转向行为具有相反的调控效应，且不同肢体与躯体区域的激活可引发差异化的行为表现。