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

Psilocybin produces two distinct behavioral effects in larval zebrafish: it facilitates spontaneous exploration (stimulatory) and reduces irregular swim patterns after stress (anxiolytic). The study uses a wide-field, high-resolution behavioral tracking system in a large, unconfined arena (about 90 mm) combined with machine learning to classify latent behavioral states from body kinematics. This avoids confining-chamber stress that can confound earlier zebrafish behavioral studies. Compared with acute SSRI treatment, psilocybin shows different behavioral signatures, while sharing similarities with ketamine. Neural activity imaging in the dorsal raphe nucleus suggests a mechanism where psilocybin inhibits serotonergic neurons through activation of local GABAergic neurons, linking behavioral changes to circuit-level effects in an evolutionarily conserved system.