D. melanogaster produces various neurotransmitters: (i) monoamines, including dopamine, tyramine, and octopamine (derived from L-tyrosine) and serotonin and melatonin (derived from L-tryptophan); (ii) amino acids, including L-glutamate, glycine, GABA, and D-serine; (iii) gasotransmitters, including nitric oxide (derived from L-arginine) and hydrogen sulfide (produced via the transsulfuration pathway); (iv) histamine (derived from L-histidine); and (v) acetylcholine.