The DA neurotrophic signal is released from DA neurons. Knockdown of neuronal DTH synthesis in 5-HT neurons (DTRHGal4) and DA neurons (DTHGal4) was compared with pan-neuronal (elavC155) expression. A. Feeding. ***p < 0.001, one-way ANOVA followed by Tukey's multiple comparisons post-test. n = 40 animals for each genotype from 4-6 independent experiments. B - D. 5-HT gut fiber architecture. B. Branching. C. Number of large varicosities per 0.1 mm neurite length. D. Number of varicosities > 5 μm2. *p < 0.05, **p < 0.01, ***p < 0.001, one-way ANOVA followed by Tukey's multiple comparisons post-test. w1118/THA;THK, n = 66 fibers from 48 guts from 8 independent experiments; elav/THA;THK, n = 35 fibers from 18 guts from 3 independent experiments; DTRHGal4/THA;THK, n = 38 fibers from 24 guts from 10 independent experiments; DTHGal4/THA;THK, n = 31 fibers from 23 guts from 7 independent experiments. Lines above the graph depict standard error of the mean. E - H. Visual depiction of 5-HT axonal fibers from w1118/THA;THK (E), elavC155/THA;THK (F), DTRHGal4/THA;THK (G) and DTHGal4/THA;THK (H) guts. Scale bar = 30 μm.