Pan-neuronal screening in Caenorhabditis elegans reveals asymmetric dynamics of AWC neurons is critical for thermal avoidance behavior

Understanding neural functions inevitably involves arguments traversing multiple levels of hierarchy in biological systems. However, finding new components or mechanisms of such systems is extremely time-consuming due to the low efficiency of currently available functional screening techniques. To overcome such obstacles, we utilize pan-neuronal calcium imaging to broadly screen the activity of the C. elegans nervous system in response to thermal stimuli. A single pass of the screening procedure can identify much of the previously reported thermosensory circuitry as well as identify several unreported thermosensory neurons. Among the newly discovered neural functions, we investigated in detail the role of the AWC(OFF) neuron in thermal nociception. Combining functional calcium imaging and behavioral assays, we show that AWC(OFF) is essential for avoidance behavior following noxious heat stimulation by modifying the forward-to-reversal behavioral transition rate. We also show that the AWC(OFF) signals adapt to repeated noxious thermal stimuli and quantify the corresponding behavioral adaptation. DOI: http://dx.doi.org/10.7554/eLife.19021.001