Serotonergic Psychedelics Rapidly Modulate Evoked Glutamate Release in Cultured Cortical Neurons

Serotonergic psychedelics like psilocybin, LSD, and DMT rapidly alter how neurons communicate at synapses. Using live-cell imaging in rat cortical neurons, the drugs reduced the fraction of synaptic vesicles that fuse in response to electrical stimulation within minutes, an effect that faded within 24 hours. DMT only reduced the total recycling pool of vesicles, while LSD and psilocin also shrank the readily releasable pool. Psilocin and DMT increased evoked glutamate release, yet LSD and psilocin lowered presynaptic calcium levels. Psilocin further depressed responses to paired stimuli. These drug-specific modulations of glutamatergic transmission may help explain their distinct therapeutic properties.

Study at a glance

Abstract

ABSTRACT The serotonergic psychedelics psilocybin, LSD and DMT hold great promise for the development of new treatments for psychiatric conditions such as major depressive disorder, addiction and end‐of‐life anxiety. Previous studies in both animals and humans have confirmed the effects of these drugs on neuronal activity and plasticity. However, the understanding of the mechanisms of action of these substances is limited. Here we show rapid effects of psychedelics on presynaptic properties, using live cell imaging at the level of single synapses in primary rat cortical neurons. Using the genetically encoded reporter of synaptic vesicle fusion synaptopHluorin, we detected a reduced fraction of synaptic vesicles that fused in response to mild or strong electrical stimulation 3–30 min after application of serotonergic psychedelics. These effects were transient and no longer present 24 h after treatment. While DMT only reduced the total recycling pool, LSD and psilocin also reduced the size of the readily releasable vesicle pool. Imaging with the sensors for glutamate, iGluSnFR, and presynaptic calcium, synGCaMP6, showed that while psilocin and DMT increased evoked glutamate release, LSD and psilocin reduced evoked presynaptic calcium levels. Interestingly, psilocin also affected short‐term plasticity leading to a depression of responses to paired stimuli. The rapid and drug‐specific modulation of glutamatergic neurotransmission described in this study may contribute to distinct anxiolytic and antidepressant properties of serotonergic psychedelics. image