Figure 5.

Summary of the effects of wake- (yellow) and sleep- (blue) promoting neurotransmitters across diverse animals that include mice, zebrafish, fruit flies, flatworms, and Hydra. Colored circles indicate behavioral responses; gray circles denote the absence of a behavioral response; and the absence of a circle itself means that compound has yet to be tested for that taxon and/or that the receptor has not been identified. The blue-within-yellow circle for dopamine-exposed zebrafish reflects the added complexity that receptor type matters for the behavioral output. Along the top of the panel is a phylogenetic tree showing evolutionary relatedness among the five species. Simple (Hydra) and secondarily simplified (flatworms) animals have fewer active neurotransmitters than more complex animals (mice, zebrafish, fruit flies). Only GABA maintains a somnogenic effect across all taxa studied. Created with BioRender.com. For Color, please refer the online images.