Monitoring neuronal responses to defined sensory stimuli is a powerful and widely used approach for understanding sensory coding in the nervous system. However, providing precise, stereotypic and reproducible cues while concomitantly recording neuronal activity remains technically challenging. Here we describe the fabrication and use of a microfluidics system that allows precise temporally restricted stimulation of Drosophila chemosensory neurons with an array of different chemical cues. The system can easily be combined with genetically encoded calcium sensors, and it can measure neuronal activity at single-cell resolution in larval sense organs and in the proboscis or leg of the adult fly. We describe the design of the master mold, the production of the microfluidic chip and live imaging using the calcium sensor GCaMP, expressed in distinct types of Drosophila chemosensory neurons. Fabrication of the master mold and microfluidic chips requires basic skills in photolithography and takes ∼2 weeks; the same devices can be used repeatedly over several months. Flies can be prepared for measurements in minutes and imaged for up to 1 h.
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We thank the Bloomington Drosophila Stock Center for reagents. We thank R. Benton, P. Renaud, L. Pethö, K. Suter and J. Dorsaz for help with the experiments, and T. Graham and B. Egger for helpful discussion of the manuscript. This work was supported by grants from the Swiss National Science Foundation (CRSII3_136307 and 31003A_149499) and the European Research Council (ERC-2012-StG 309832-PhotoNaviNet) to S.G.S. We further thank our colleagues in the Sprecher laboratory for fruitful discussions of the manuscript.
The authors declare no competing financial interests.
Integrated supplementary information
(a) Representative fluorescent trace before and after movement artifact correction. The fluorescence intensity value before the moving frame was duplicated to mask the artifact. (b) In case of excessive movement the same procedure cannot be applied, and it is recommended to discard the recording.
Supplementary Figure 1 Correction of artifacts in the graph. (a,b) Representative fluorescence trace before and after movement artifact correction. (a) The fluorescence intensity value before the moving frame was duplicated to mask the artifact. (b) In case of excessive movement, the same procedure cannot be applied, and it is recommended that the recording be discarded. (PDF 290 kb)
Design of the photomask used for the microfluidic chip fabrication (.cif file). (ZIP 1032 kb)
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van Giesen, L., Neagu-Maier, G., Kwon, J. et al. A microfluidics-based method for measuring neuronal activity in Drosophila chemosensory neurons. Nat Protoc 11, 2389–2400 (2016). https://doi.org/10.1038/nprot.2016.144
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