a, ESI+ ion chromatograms for melatonin synthetic standard and WT C. elegans endo-metabolome extracts. Melatonin was only detected in WT treated with an unphysiologically high concentration (5 mM) of serotonin but was not detected in untreated WT animals. b, Relative abundances of known serotonin metabolites in exo- and endo-metabolome samples of WT treated with 5 mM serotonin. c, Abundances of N-acyl-glycoglycerophosphoethanolamines (GLEAs) in endo-metabolomes of WT treated with 5 mM serotonin. 15 ≤ m ≤ 19, 26 ≤ n ≤ 30, x = 0 or 1. d, Structures of indole-derived MOGLs whose abundances were decreased in WT treated with 5 mM serotonin. Data in b and c represent 3 biologically independent experiments and bars indicate mean ± s.d., p-values calculated via unpaired, two-tailed t-test with Welch correction.