High-resolution tracking of unconfined zebrafish behavior reveals stimulatory and anxiolytic effects of psilocybin

Psilocybin, a psychedelic serotonin receptor agonist, has two behavioral effects in larval zebrafish: it stimulates spontaneous exploration and prevents irregular swim patterns that normally follow stress exposure, indicating an anxiolytic effect. These effects resemble those of ketamine, not SSRIs. Neural imaging suggests psilocybin inhibits serotonergic neurons in the dorsal raphe nucleus by activating local GABAergic neurons, a mechanism consistent with findings in mammals.

Study at a glance

Abstract

Abstract Serotonergic psychedelics are emerging therapeutics for psychiatric disorders, yet their underlying mechanisms of action in the brain remain largely elusive. Here, we developed a wide-field behavioral tracking system for larval zebrafish and investigated the effects of psilocybin, a psychedelic serotonin receptor agonist. Machine learning analyses of precise body kinematics identified latent behavioral states reflecting spontaneous exploration, visually-driven rapid swimming, and irregular swim patterns following stress exposure. Using this method, we found that acute psilocybin treatment has two behavioral effects: [i] facilitation of spontaneous exploration (“stimulatory”) and [ii] prevention of irregular swim patterns following stress exposure (“anxiolytic”). These effects differed from the effect of acute SSRI treatment and were rather similar to the effect of ketamine treatment. Neural activity imaging in the dorsal raphe nucleus suggested that psilocybin inhibits serotonergic neurons by activating local GABAergic neurons, consistent with psychedelic-induced suppression of serotonergic neurons in mammals. These findings pave the way for using larval zebrafish to elucidate neural mechanisms underlying the behavioral effects of serotonergic psychedelics.