Effects of psilocybin on hippocampal neurogenesis and extinction of trace fear conditioning.
Level 5 - mechanism / opinion, no new human data
Animal model study (preclinical rodent research)
PubMed 23727882 · doi:10.1007/s00221-013-3579-0
What was done
Mice received acute intraperitoneal injections of psilocybin, the 5-HT2A agonist 25I-NBMeO, or the 5-HT2A/C antagonist ketanserin. Trace fear conditioning and subsequent extinction were assessed by measuring immobility across trials during an auditory conditioned stimulus, silent trace interval, and post-trace interval. Dentate gyrus neurogenesis was quantified via unbiased counts of BrdU-labeled cells co-expressing a neuronal marker.
What was found
No exact numerical values, specific doses, or statistical metrics are reported in the abstract. Mice across psilocybin doses acquired robust conditioned fear. Low-dose psilocybin significantly accelerated the extinction of cued fear conditioning relative to high-dose psilocybin or saline controls. Psilocybin, 25I-NBMeO, and ketanserin produced significant dose-dependent decreases in hippocampal newborn neurons, though the low psilocybin dose that enhanced extinction did not decrease neurogenesis and trended toward an increase.
Why it matters
This study provides preclinical mechanistic evidence that low doses of psilocybin can facilitate the extinction of learned fear responses, supporting exploration of serotonergic psychedelics for conditions such as post-traumatic stress disorder.
Limits
The abstract reports animal data with no human participants, and exact sample sizes, doses, and numerical effect sizes are omitted. The disconnect between neurogenesis changes and behavioral extinction suggests non-hippocampal sites like the amygdala mediate the effect, and psilocybin lacks pure selectivity for 5-HT2A receptors.
Cited by
- supports An animal study in mice showed that psilocybin administration increased neurogenesis in the dentate gyrus and facilitated fear extinction.