Classic psychedelic drugs, such as LSD and psilocybin, are thought to boost brain cell activity in the prefrontal cortex by activating serotonin 2A receptors. However, this research shows that these drugs actually suppress the intrinsic excitability of pyramidal neurons in a dose-dependent manner. The suppression is stronger when drugs are applied outside cells than inside, and it occurs through a previously unknown mechanism: enhancement of potassium M-current channels, independent of serotonin 2A receptor activation. Computer models reveal that M-current activation interacts with other mechanisms to reduce excitability and shorten working memory span. This suggests psychedelics may trigger widespread homeostatic adjustments that contribute to therapeutic benefits.
Classic psychedelics can strengthen connections in the retrosplenial cortex, a brain region important for memory and spatial orientation that is impaired in Alzheimer's disease, even though its neurons lack the serotonin 2A receptors thought necessary for such effects. Using a new genetic tool in mice, the research shows that this strengthening depends on presynaptic serotonin 2A receptors on incoming nerve fibers from the anterior thalamus, not on the postsynaptic receptors of the retrosplenial cortex itself. The finding suggests psychedelics may have broader therapeutic potential than currently recognized, possibly aiding conditions like Alzheimer's disease and post-traumatic stress disorder by boosting retrosplenial circuit function.