Force-Controlled Mechanical Stimulation and Single-Neuron Fluorescence Imaging of <i>Drosophila</i> Larvae

Abstract

Studying the neural response of a Drosophila larva to touch stimulation could decipher neural basis of the creature's danger-escaping behaviors. This letter reports force-controlled robotic mechanical stimulation and single-neuron fluorescence imaging of Drosophila larvae. A force control architecture based on a model compensation-prediction scheme and a switched fuzzy-PID controller was used for regulating the touch force applied to a larva at the micronewton level. The developed force control system demonstrates a settling time of 0.15 s, zero overshoot and a resolution of <; 50 μN. Established based on a high-resolution inverted fluorescence microscope, our robotic system is capable of simultaneously applying a controlled touch force to a larva and quantifying the fluorescence signal transmission inside a single neuron responsive to body touch stimulation. Using this system, we examined, for the first time, the quantitative relationship between the applied force level (range: 0.25-2 mN) and the change in transmission signal of the class III ddaA neuron. The touch force threshold at which the neuron starts to get activated was determined to be in the range of 0.25-0.5 mN. This work may contribute to new studies on sensory mechanotransduction in Drosophila larvae.