Constitutive induction in neuronal DTH or increased systemic DA during late embryogenesis results in aberrant larval gut fiber architecture. elavC155/UAS27.6, its parental control, elavC155/w1118, and 16 hr old control (w1118;THA;THK) embryos were dechorionated, devitillenized, and exposed to serum-free media with or without 10-6M DA for 6 hours until hatching. A. Branching. B. Varicosity number. C. Large varicosities. D. Varicosities > 5 μm2 in diameter. elav/w1118, 28 fibers from 22 guts from 4 independent experiments; elavC155/27.6, 40 fibers from 32 guts from 7 independent experiments; w1118/THA;THK -DA, 45 fibers from 26 guts from 9 independent experiments; w1118/THA;THK + DA, 44 fibers from 34 guts from 13 independent experiments. *p < 0.05, **p < 0.01, ***p < 0.001, Student's unpaired t-test, comparing elav/w1118 with elavC155/UAS27.6 and w1118/THA;THK -DA with w1118/THA;THK + DA. Lines above the graph depict standard error of the mean. E - H. Visual depiction of 5-HT axonal fibers from elav/w1118 (E), elav/UAS27.6 (F), w1118/THA;THK -DA (G) and w1118/THA;THK + DA (H) guts. Scale bar = 30 μm.