Serotonergic psychedelics, like ketamine, can robustly increase the growth of neurons and their connections (neuritogenesis and spinogenesis) in the prefrontal cortex, both in lab dishes and in living animals. These structural changes are accompanied by more synapses and enhanced function, as shown by microscopy and electrophysiology. The effects appear to arise from stimulation of TrkB, mTOR, and 5-HT2A signaling pathways, which may explain the clinical effectiveness of these compounds. The findings highlight the therapeutic potential of psychedelics and identify several chemical scaffolds for developing fast-acting, safe antidepressants that promote brain plasticity.
A genetically encoded fluorescent sensor called psychLight, based on the 5-HT2A receptor structure, detects behaviorally relevant serotonin release and correctly predicts whether structurally similar 5-HT2AR ligands will cause hallucinogenic behavioral effects. Using psychLight, a non-hallucinogenic psychedelic analog was identified that produced rapid-onset and long-lasting antidepressant-like effects after a single administration. The sensor enables in vivo detection of serotonin dynamics, early identification of designer drugs of abuse, and development of non-hallucinogenic therapeutics targeting the 5-HT2AR.
Cortical neuron atrophy, including neurite retraction and spine loss, is a hallmark of depression. Psychoplastogens are small molecules hypothesized to reverse these changes. Ketamine and LSD, from two structurally distinct chemical classes, promote sustained growth of cortical neurons after brief stimulation. This growth occurs in two phases: an initial stimulation phase requiring TrkB activation, followed by a growth period needing sustained mTOR and AMPA receptor activation. These temporal details suggest that rapidly excreted psychoplastogens could be effective neurotherapeutics with advantages over ketamine and LSD.
Nonhallucinogenic psychoplastogens like tabernanthalog (TBG) promote cortical neuroplasticity through the same biochemical pathway as classic psychedelics—involving 5-HT2A, TrkB, mTOR, and AMPA receptor activation—but without inducing an immediate glutamate burst or immediate early gene activation. TBG-induced cortical spinogenesis is required for its sustained antidepressant-like behavioral effect in rodents. These findings clarify how certain psychoplastogens can produce neuroplasticity without hallucinogenic effects, challenging assumptions that glutamate burst and IEG activation are necessary for psychedelic-induced neuroplasticity.