A novel small molecule, AS1, reverses the negative hedonic valence of noxious stimuli

AS1 is a small molecule that reverses the negative hedonic value of noxious stimuli in larval zebrafish, making painful heat attractive rather than aversive. Using thermal place preference and aversion assays, the researchers show AS1-induced attraction generalizes across other painful (chemical) and aversive (including dark) stimuli, and depends on stimulus intensity while not being inherently rewarding. Mechanistically, dopaminergic signaling is required: neuronal imaging links AS1 effects to upregulation in dopaminergic neurons and teleost basal-ganglia-like forebrain regions, and pharmacological manipulation indicates D1 dopamine receptor pathways. The findings suggest AS1 relieves a context-dependent “brake” on dopamine release, pointing to valence-targeting analgesic drug strategies with potential relevance to anxiety and PTSD-related valence dysfunction.