Psilocybin increased the release of dopamine, noradrenaline, serotonin, and acetylcholine in the frontal cortex of rats, with the 0.3 mg/kg dose producing the weakest effect. Glutamate release rose only for the first two hours after injection then fell, while γ-aminobutyric acid release increased. Unlike the 5-HT2A receptor agonist 25I-NBOMe, psilocybin did not cause hallucinogenic wet dog shakes or disrupt sensorimotor gating. It showed an anxiolytic effect in the light dark box test one hour after administration, transiently raised serum corticosterone, altered hypothalamic neurotransmitter turnover, and did not produce oxidative DNA damage in the frontal cortex or hippocampus.
Two doses of psilocybin (0.6 mg/kg, given subcutaneously seven days apart) reversed anhedonia, produced antidepressant-like effects in the forced swim test, and reduced anxiety in the light/dark box, elevated plus maze, and open field tests in rats exposed to chronic unpredictable mild stress. Psilocybin also increased hippocampal neurogenesis, shown by higher numbers of BrdU-positive, DCX-positive, and Ki-67-positive cells in stressed animals. Stress-induced reductions in brain-derived neurotrophic factor (BDNF) expression appeared linked to normalization of hypothalamic-pituitary-adrenal (HPA) axis activity. The findings highlight psilocybin-induced neuroplasticity as a key mechanism for its antidepressant and anxiolytic effects.