Studying the Effects of Psychedelics on Human Cortical Neurons
INSTITUTION: Allen Institute for Brain Science / Human Cell Types
PROJECT LEADERS: Christof Koch, PhD, Jonathan Ting, PhD, Meanhwan Kim, PhD, Lindsay Ng
PROJECT DURATION: 2021 - 2022
LAB WEBSITE: AllenInstitute.org
Psilocybin and other serotonergic hallucinogenic drugs can profoundly alter consciousness and have recently come to the forefront in brain research regarding therapeutic potential for treating a range of debilitating conditions including PTSD, anxiety, and depression. Although it is known that psilocybin and other serotonergic hallucinogens bind to and activate specific serotonin receptors, almost nothing is known about the direct cellular mechanism of action of these drugs on single neurons of the human brain. To explore the effect of these drugs on individual neurons, we utilize the patch-seq method in human neocortical brain slices (from neurosurgical resected tissue) and from mouse neocortex to record changes in intrinsic membrane properties in response to bath wash-in of psilocybin or psilocin. Additionally, we extract the nucleus of these cells to characterize their transcriptomic profile and determine potential cell-type specific drug effects.
We continue data collection and analysis of mouse and human neocortical Patch-seq experiments with bath application of psilocin and psilocybin. So far, we recorded 56 human neurons and 156 mouse neurons with a primary focus on application of psilocin, the main psychoactive metabolite of psilocybin. The 56 human cortical neurons are derived from ~20 neurosurgical samples from mainly middle temporal gyrus, with a few samples from parietal or frontal cortex. As reported previously for drug-induced neuronal responses, we observe about 10% of the recorded excitatory neurons respond to psilocin application with strong but transient membrane depolarization, consistent with putative signaling through 5-HT2A receptors, while ~20% of recorded excitatory neurons exhibit modest membrane hyperpolarization of 2-4 mV in response to psilocin, which may be consistent with a Gi/Go signaling pathway via 5-HT1A receptor activation (see the Figure below).
Recently, we have worked to pilot additional experimental avenues, specifically targeting putative L5 pyramidal neurons. We piloted using a pico-spritzer to puff 50uM psilocin directly onto the soma region of the patched cell, allowing us to measure the effect of the drug on electrophysiology with improved temporal-spatial precision as compared to bath application. These experiments have so far corroborated our findings from bath wash-ins.
Figure: Summary of human supragranular pyramidal neuron responses to 50 micromolar bath application of psilocin in Patch-seq recording experiments. Two distinctive response profiles are observed as highlighted by the cells boxed in red. One example shows a neuron with a strong depolarization of the resting membrane potential (RMP), whereas the other shows a neuron with a transient and modest hyperpolarization of RMP. The location of each neuron in terms of depth from pia in microns is recorded for future correlation analysis.
Broader Impact:
This project brings together pharmacology, neurophysiology, and single cell transcriptomics applied to a human neurosurgical (as well as mouse control) tissue brain slice platform to uncover new mechanistic insights on the action of psilocybin and related drugs on the human brain. Insights from this work may help clarify the specific cell type- or species-specific actions of psilocybin and inform novel approaches to therapy in the clinic.