Neuronal Processing of Noxious Thermal Stimuli Mediated

23 24 Adequate responses to noxious stimuli causing tissue damages are essential for 25 organismal survival. Class IV neurons in Drosophila larvae are polymodal 26 nociceptors responsible for thermal, mechanical, and light sensation. Importantly, 27 activation of Class IV provoked distinct avoidance behaviors, depending on the 28 inputs. We found that noxious thermal stimuli, but not blue light stimulation, 29 caused a unique pattern of Class IV, which were composed of pauses after high 30 frequency spike trains and a large Ca 2+ rise in the dendrite (the Ca 2+ transient). 31 Both of these responses depended on two TRPA channels and the L-type 32 voltage-gated calcium channel (L-VGCC), showing that the thermosensation 33 provokes Ca 2+ influx. The precipitous fluctuation of firing rate in Class IV neurons 34 enhanced the robust heat avoidance. We hypothesize that the Ca 2+ influx can be 35 a key signal encoding a specific modality. 36 37 Terada et al.