Alteration in dynamics of mdIV neuron activation in response to noxious heat. (AB) Larval noxious heat-induced rolling response. (A) mdIV neuron-specific expression of tetanus toxin (TNT-G) to block synaptic transmission strongly suppresses larval heat-induced behavioral response to noxious heat. (n = 7, 6, 16 and 10 respectively) ***p < 0.0001, one-way ANOVA with Tukey’s post comparison test vs ppk1GAL4/+ (B) ppk1 null mutant larvae (DfA/DfB) respond to noxious heat stimulus at levels comparable to wild-type (n = 16, 10 and 10, respectively). (C) Representative recordings of wild-type and ppk1 null v’ada mdIV neurons at indicated bath temperatures. Noxious heat (45°C) activated both wild-type and ppk1 null neurons with a spike frequency comparable to that in uninduced wild-type neurons (spontaneous activity) but with altered spike activation dynamics reflected as a broadened spike duration. (D) Comparable wild-type and ppk1 null spike frequency at 45-46°C consistent with previous work demonstrating that PPK1 is not required for the mdIV neuronal response to noxious heat (n = 15 and 7, respectively). Not statistically significant by student’s t-test. (E) Comparison of wild-type and ppk1 null mutant v’ada mdIV neuronal spike width at half maximum amplitude when recorded at 25°C vs 45°C. Wild-type and ppk1 null neurons display comparable spike frequency and broadened spike duration when exposed to noxious heat. (n = 7, 6 and 7 respectively), ***p < 0.0001, one-way ANOVA with Tukey’s post comparison test vs w1118 (25°C). All data are presented as mean±SEM.