Chronic psilocin microdosing produces limited behavioral effects and does not enhance neurogenesis in rats

Psilocin (4-hydroxy-N, N-dimethyltryptamine) is a substituted tryptamine alkaloid and a nonselective serotonergic agonist acting predominantly at 5-HT2A/C receptors, with substantial binding to 5-HT1A and 5-HT2B receptors. Microdosing is the practice of taking a very small, sub-perceptual dose, typically 5% to 10% of a full recreational dose, to improve mood, creativity, and focus without hallucinogenic effects. However, rigorous preclinical evidence for its behavioral and neurobiological effects remains limited. We therefore examined whether chronic psilocin microdosing alters behavior and dentate gyrus (DG) cell proliferation in adult male Wistar rats. Psilocin was administered subcutaneously at 0.05 or 0.075 mg/kg. Animals received six doses of psilocin or saline on alternate days over 18 days prior to the first behavioral assessment, and microdosing on alternate days continued between behavioral tasks for five weeks. To minimize acute drug effects, all behavioral assessments were performed 48 h after the preceding dose. Animals were tested sequentially in the Elevated Plus Maze, Hole-Board, Open Field, Social Interaction, and modified Forced Swim Test, with six-day intervals between tests. DG cell proliferation was quantified by BrdU and Ki-67 immunohistochemistry. Across this regimen, psilocin microdosing did not measurably affect locomotor activity, depressive-like behavior, sociability, or novelty seeking, and it did not increase DG proliferation by either marker. A small anxiogenic effect was detected in the Elevated Plus Maze. These data indicate that, under the present dosing schedule and endpoints, chronic psilocin microdosing produces limited behavioral effects and does not enhance hippocampal progenitor proliferation in rats.