Psilocybin causes repetitive movements and lowers defensive behavior in planarians through serotonin pathways

Psilocybin at 0.01 nM increased defensive responding in planarians, a simple animal model.

• Psilocybin caused an increase in various stereotyped movements, including head bops and twists, at concentrations of 0.01, 0.1, 1, and 10 nM.
• Higher concentrations of psilocybin led to a reduction in overall motility.
• The selective 5-HT2AR antagonist volinanserin did not produce any stereotyped movements or affect motility on its own.
• Volinanserin reduced stereotyped movements induced by low-dose psilocybin, specifically twists and head bops.
• At concentrations below 0.01 nM, psilocybin decreased defensive responding, indicated by increased time spent in the light area of the Petri dish.
• The anxiolytic-like effect of psilocybin at 0.01 nM was blocked by volinanserin.

Simplified