Decreased dendritic spine density in the cortex is a hallmark of several neuropsychiatric diseases, and the ability to promote cortical neuron growth has been hypothesized to underlie the rapid and sustained therapeutic effects of psychedelics. Activation of 5-HT2ARs is essential for psychedelic-induced cortical plasticity, but it is unclear why some 5-HT2AR agonists promote neuroplasticity while others do not. Using molecular and genetic tools, the authors demonstrate that intracellular 5-HT2ARs mediate the plasticity-promoting properties of psychedelics, explaining why serotonin does not engage similar plasticity mechanisms. This work emphasizes location bias in 5-HT2AR signaling, identifies intracellular 5-HT2ARs as a therapeutic target, and raises the possibility that serotonin might not be the endogenous ligand for intracellular 5-HT2ARs in the cortex.
Activation of serotonin 2A receptors (5-HT2ARs) is essential for tryptamine-based psychedelics to produce antidepressant-like effects in rodents. While hallucinogenic properties are generally attributed to 5-HT2AR activation, it was unclear whether these receptors also mediate antidepressant effects, especially because some nonhallucinogenic analogues show antidepressant-like properties. Using pharmacological and genetic tools, the authors demonstrate that 5-HT2AR activation is required for the antidepressant-like effects of tryptamine psychedelics, suggesting that hallucinogenic and therapeutic effects can arise through the same receptor.
Psychedelics show promise for treating depression, PTSD, and substance use disorder, potentially by reversing cortical atrophy through effects on neurotrophic factors, neuronal growth, and immune modulation. This review argues that similar approaches could benefit neurodegenerative disorders like Alzheimer's disease, where the primary psychedelic target, the 5-HT2A receptor, is dysregulated. Evidence also suggests psychedelics might help manage behavioral and psychological symptoms of dementia (BPSD). The authors call for more research in neurodegenerative models, emphasizing that the compounds' robust effects on neuroplasticity and inflammation warrant further investigation.
A new genetic mouse model lacking the enzyme indolethylamine N-methyltransferase (INMT) shows that INMT is not required for the production of endogenous psychedelics, suggesting alternative biosynthetic pathways exist in rodents. INMT knockout mice had no major abnormalities in reproduction or growth but did exhibit altered behaviors across several domains. The study also describes highly sensitive mass spectrometry methods for quantifying endogenous psychedelics in mice. These findings challenge the assumption that INMT is the primary enzyme for endogenous psychedelic production and open new questions about the role of these compounds in health and disease.