Psilocybin is a neuromodulatory compound found in psychedelic mushroom genus Psilocybe. For the past decade, psilocybin, along with other psychedelic compounds such as lysergic acid diethylamide (LSD) and N,N-Dimethyltryptamine (DMT) were found to have therapeutic effects for neuropsychiatric diseases such as major depressive disorder, anxiety, and drug addiction. It is known that psilocybin binds to 5-HT2A receptor in cortical neurons and increases synaptic density and causes changes in default mode network (DMN). However, the mechanism of action of psilocybin in human neurons are incompletely understood.

In order to assess neuromodulatory effects of psilocybin in human neurons, we used human iPSC-derived cortical organoids. Cortical organoids include the key cellular subtypes of human cortex; excitatory and inhibitory neurons, neural stem cells, astroglia and oligodendrocyte precursor cells, which we have confirmed in 6-month-old organoids using single cell RNA sequencing. Additionally, we found HTR2A (5-HT2A gene) expression to be the highest in excitatory neurons among other neuronal subtypes. To assess neural activity changes with psilocybin, we employed high density multi electrode assay and exposed cortical organoids with 6 µM of psilocin (active compound in psilocybin). Our analysis indicated that psilocin increased the number of network bursts and network connectivity, however, decreased the overall burst rate, as well as peak-to-peak amplitude of spikes in cortical organoids.

Our results show that cortical brain organoids are a suitable in vitro human neuronal model to study the effects of psilocybin at molecular level. This in vitro model can be utilised for safety and neurotoxicity effects of psychedelic substances.