Summary:
Researchers at the University of California, Santa Cruz (UCSC) used high-resolution neuroimaging and genetic tools to map how psilocybin remodels cortical circuits in living brains. Published in Nature Neuroscience, the study shows that a single dose of psilocybin rapidly stimulates the growth and maturation of dendritic spines, reshaping synaptic connections in ways that depend on the brain’s prior state. Importantly, the team demonstrated a clear dissociation between the drug’s structural, potentially therapeutic effects and the receptor signaling that produces hallucinogenic behavior in rodents.
Key Facts:
- Rapid synaptic maturation: Two-photon imaging revealed a surge of new dendritic spines within 24 hours of psilocybin, with many newly formed spines maturing quickly into stable, receptor-rich “mushroom” spines that lasted for weeks.
- State-dependent remodeling: In healthy animals, psilocybin prompted balanced pruning and new spine formation; in chronically stressed animals, it produced a larger burst of new spines and prevented further synaptic loss.
- Plasticity separable from psychedelic behavior: Genetic manipulation of serotonin 2A (5-HT2A) receptors in Layer 5 pyramidal neurons established that structural neuroplasticity can occur independently of the rodent head-twitch response, a behavioral proxy for hallucination.
Source: University of California, Santa Cruz
Psilocybin, the psychoplastogen found in Psilocybe mushrooms, is recognized for rapidly inducing structural and functional plasticity after a single dose. It has received Breakthrough Therapy designation from the U.S. Food and Drug Administration for certain forms of treatment-resistant depression and major depressive disorder.
Despite promising clinical outcomes, the cellular mechanisms by which psilocybin repairs or reshapes circuits in living mammalian brains have remained unclear. Scientists have also questioned whether the acute perceptual effects of psychedelics are necessary for their lasting therapeutic benefits. The UCSC study provides high-resolution timing of synaptic changes and uses cell-type-specific genetics to separate structural repair from hallucinogenic signaling.
Tracking Dendritic Spines in the Living Brain
The team used in vivo two-photon microscopy to follow individual dendritic spines—the small protrusions where neurons form synapses—on cortical neurons in mice over several weeks. Within 24 hours of psilocybin treatment, there was a pronounced increase in newly formed spines. Crucially, a large fraction of these nascent spines matured rapidly from thin, unstable “stubby” forms into larger, stable “mushroom” spines. Mushroom spines are enriched in scaffolding proteins and AMPA receptors and are associated with durable synaptic strength and stable circuit changes.
“These new connections can integrate with existing networks and persist, leaving a lasting structural trace of psilocybin’s action on the cortex,” said Jacob Baker, lead author and doctoral researcher at UC Santa Cruz.
Circuit Healing Depends on Prior Stress
A core finding is that psilocybin’s remodeling is not uniform but depends on the brain’s baseline condition. In healthy control mice, the drug induced a transient rise in spine formation accompanied by pruning of some pre-existing connections, preserving overall circuit balance. In contrast, mice subjected to chronic unpredictable mild stress—a common preclinical model of depressive synaptic atrophy—showed a markedly larger generation of new spines, and psilocybin prevented the ongoing pathological loss of existing synapses. In stressed circuits, psilocybin both promoted new synapse formation and halted degenerative changes.
“These results suggest psilocybin’s effects are tuned to the brain’s microenvironment, restoring circuits disrupted by stress rather than indiscriminately increasing connectivity,” said Yi Zuo, senior author and professor of molecular, cell, and developmental biology at UC Santa Cruz.
Decoupling Rewiring From the Psychedelic State
To determine whether hallucinogenic signaling is required for structural plasticity, the investigators focused on 5-HT2A receptors in cortical Layer 5 pyramidal neurons, a crucial output cell type in the cortex. Using cell type–specific genetic manipulations, they established a double dissociation:
- Plasticity without hallucination: Restoring 5-HT2A receptors selectively in Layer 5 pyramidal neurons allowed psilocybin to drive synaptic growth and maturation while mice did not exhibit the head-twitch response.
- Hallucination without plasticity: Deleting 5-HT2A receptors specifically from Layer 5 pyramidal neurons abolished psilocybin-induced synaptic remodeling, yet the head-twitch behavior remained intact.
These results indicate that the circuits and signaling that mediate durable structural changes are anatomically and mechanistically distinct from those that produce the acute perceptual effects associated with psychedelics.
Blueprints for Next-Generation Neurotherapeutics
As regulatory frameworks and clinical protocols for psychedelic-assisted therapies develop, this cell-type-specific insight offers a practical roadmap for designing psychoplastogen compounds that promote rapid synaptic regeneration without producing dissociative or hallucinogenic effects. By pinpointing the precise cortical subpopulation responsible for structural repair, the findings support efforts to develop non-hallucinogenic analogs that could be deployed more broadly and more easily in outpatient settings to treat depression and related disorders.
Funding: The study was led by Yi Zuo with co-authors Jacob Baker, Emily Kogan, Shaorong Ma, and Ju Lu. It was supported by grants from the National Institute of Mental Health and the National Institute on Aging. Psilocybin for the research was supplied by the National Institute on Drug Abuse (NIDA) Drug Supply Program.
Editorial Notes:
- This article was edited by a Neuroscience News editor.
- The journal paper was reviewed in full.
- Additional context was provided by staff editors.
About this neurotech and schizophrenia Research:
- Media Contact: Mike Peña
- Source: University of California – Santa Cruz
- Image Credit: Image credited to Neuroscience News
- Original Research (Open Access): Nature Neuroscience (Oct 1, 2026). Title: “5-HT2A receptors in layer 5 pyramidal neurons mediate the neuroplastic but not the hallucinogenic effects of psilocybin.” Authors: Jacob J. Baker, Emily Kogan, Shaorong Ma, Ju Lu & Yi Zuo.
- DOI: 10.1038/s41593-026-02490-y
Abstract
5-HT2A receptors in layer 5 pyramidal neurons mediate the neuroplastic but not the hallucinogenic effects of psilocybin
It remains unclear how 5-HT2A receptor signaling in Layer 5 pyramidal neurons differentially contributes to psilocybin-induced hallucinations versus neuroplasticity. The study shows that psilocybin promotes formation and maturation of synapses while accelerating elimination of other pre-existing synapses. Cell type–specific manipulations demonstrate that 5-HT2A signaling in cortical Layer 5 pyramidal neurons is necessary and sufficient for psilocybin-induced synaptic remodeling but is not required for the head-twitch response, a rodent proxy for hallucination.