Fig. 9. Molt-related differences in the loading of FM1-43. (A) Endogenous activity (open bars) produces fewer FM1-43-labeled synaptic terminals on the foreguts of early-molt larvae compared with late-molt and intermolt larval stages. Equal densities of labeled synapses were found when high K⁺ saline (filled bars) was used to stimulate FM1-43 loading. The mean number of fluorescent puncta per 20 µm² area (± S.E.M.) is given. The asterisk represents significant difference from the high K⁺ saline-loaded level (P<0.05, N=6–15). (B) FM1-43 was loaded into synapses by endogenous frontal ganglion activity (open bars), by stimulation with high K⁺ saline (grey bars) and unloaded with stimulation with high K⁺ saline (black bars). For each treatment, there were no significant differences between any of the larval stages in the luminosity of the FM1-43 labeled puncta (P>0.05). For all groups, high K⁺ saline resulted in a significant increase in mean fluorescent luminosity (± S.E.M.) compared with endogenous-load conditions. All of the terminals unloaded FM1-43 when incubated in high K⁺ saline. *Significant change from endogenous levels (P<0.05); **significant change from high K⁺ saline-load levels (P<0.05). N=7–20.