Fig. 8. Molt-related changes in FM1-43 loading of nerve terminals located on foregut esophageal dilator muscles of 4th instar intermolt (A,B), early-molt (C,D) and late-molt (E,F) stage larvae. (A) Endogenous activity was sufficient to load FM1-43 into the foregut synaptic terminals of the 4th instar intermolt larvae. (B) The FM1-43 unloaded when the labeled foreguts were incubated in a high K⁺ solution. (C) Endogenous activity failed to load the terminals of the early-molt stage larvae. (D) Exposing early-molt larvae to high K⁺ with FM1-43 resulted in the loading of FM1-43 into the synaptic terminals on the foregut. (E) Endogenous frontal ganglion (FG) activity was sufficient to cause FM1-43 dye labeling of neuronal terminals of late-molt larvae (>21 h after head capsule slippage) that had begun to swallow MF. (F) The terminals of the late-molt stage larvae unload the dye when the tissue is incubated in high K⁺ saline. (G,H) Two examples of synaptotagmin immunoreactivity, a marker of neuronal presynaptic terminals, present on the esophageal dilator muscles. Arrows indicate equivalent positions. Scale bar, 50 µm.