Mice given a cannabinoid agonist during adolescence showed lasting deficits in sensorimotor gating and fear conditioning in adulthood, along with reduced hippocampal mGluR5 and altered endocannabinoid metabolism.
Read this if you want to understand the brain mechanism linking adolescent cannabis use to psychosis risk.
Adolescent exposure caused lasting changes; adult exposure did not
What the researchers found
Mice received the CB1 agonist WIN55,212-2 during adolescence (postnatal days 30-35) or early adulthood (days 63-70) and were tested after postnatal day 120. Only adolescent exposure produced lasting behavioral changes.
Adolescent-treated mice showed deficits in prepulse inhibition (a measure of sensorimotor gating commonly disrupted in schizophrenia) and fear conditioning (hippocampal-dependent learning). The hippocampus of these mice showed significantly reduced mGluR5 (a receptor involved in fear conditioning and endocannabinoid signaling).
Endocannabinoid metabolism enzymes were also altered: increased MAGL and FAAH levels suggested faster endocannabinoid breakdown, meaning reduced endocannabinoid tone in the hippocampus. Adult-treated mice showed none of these lasting changes.
Why it matters
This study provided a causal mechanism linking adolescent cannabis exposure to schizophrenia-relevant brain changes. The selectivity for adolescent but not adult exposure supported the epidemiological finding that earlier cannabis use carries higher psychosis risk.
The numbers in context
Adolescent treatment: PND 30-35. Adult treatment: PND 63-70. Testing after PND 120. Adolescent treatment reduced mGluR5 and increased MGL and FAAH in hippocampus. Adult treatment produced no lasting changes.
How the study worked
Mice received WIN55,212-2 during adolescence (PND 30-35) or early adulthood (PND 63-70). Behavioral testing after PND 120 included prepulse inhibition and fear conditioning. Hippocampal molecular markers (mGluR5, DGL, MGL, FAAH) were quantified.
What this study cannot tell us
Mouse model using synthetic cannabinoid, not THC. Very brief exposure window (5 days). The schizophrenia-like phenotype was limited to two behavioral measures. Human adolescence is much longer and more complex than mouse adolescence.
How to read the evidence
Animal study with direct age-of-exposure comparison and molecular mechanism. Strong for causal inference within the mouse model but limited human translation.
When this study was published
Published in 2012. The mGluR5 connection to cannabis-psychosis vulnerability has been explored further in subsequent research.
The bigger picture
This study offered mGluR5 as a potential therapeutic target. If adolescent cannabinoid exposure reduces mGluR5 and this contributes to psychosis vulnerability, drugs targeting mGluR5 might help at-risk individuals.
Questions still open
- Would mGluR5 agonists reverse the deficits from adolescent cannabinoid exposure? Is there a critical window within adolescence when exposure is most harmful? Does CBD co-exposure prevent these lasting changes?
Common questions
Does this prove teen cannabis use causes schizophrenia?
Why does age of exposure matter?
Read the original research
Susceptibility of the adolescent brain to cannabinoids: long-term hippocampal effects and relevance to schizophrenia.
Translational psychiatry, 2(11), e199
Citation
Gleason, K A; Birnbaum, S G; Shukla, A; Ghose, S. (2012). Susceptibility of the adolescent brain to cannabinoids: long-term hippocampal effects and relevance to schizophrenia.. Translational psychiatry, 2(11), e199. https://doi.org/10.1038/tp.2012.122
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