Blocking or enhancing endocannabinoid signaling in different prefrontal cortex subregions had opposing effects on fear-conditioned pain suppression and freezing behavior in rats.
Pain researchers, neuroscientists, and anyone interested in how the brain's cannabinoid system processes fear and pain.
Same drug had opposite effects in infralimbic vs. prelimbic cortex
What the researchers found
The CB1 receptor antagonist AM251 attenuated fear-conditioned analgesia (FCA) when injected into the infralimbic or prelimbic cortex, but reduced freezing only in the infralimbic region. The FAAH inhibitor URB597 attenuated FCA and freezing in the infralimbic cortex but prolonged FCA in the prelimbic cortex. Neither drug had effects in the anterior cingulate cortex.
Why it matters
The endocannabinoid system is a drug target for both pain and anxiety. This study reveals that its role varies dramatically even within adjacent brain subregions, which has implications for precision medicine approaches.
The numbers in context
Three prefrontal subregions tested: infralimbic, prelimbic, anterior cingulate cortex. AM251 and URB597 had distinct, subregion-specific effects on pain suppression and fear.
How the study worked
Male rats received intra-prefrontal cortex microinjections of AM251 (CB1 antagonist), URB597 (FAAH inhibitor), or combination, then underwent formalin-evoked pain testing in a fear-conditioned arena previously paired with footshock.
What this study cannot tell us
Rat study using microinjections that do not replicate systemic cannabis use. Only male rats were tested. The pharmacological tools used (AM251, URB597) affect endocannabinoids broadly, not just anandamide.
How to read the evidence
Preliminary: animal study with microinjections into specific brain subregions.
When this study was published
Published in 2019.
The bigger picture
Cannabis affects pain and fear/anxiety, but not always in the same direction for everyone. This study shows part of the reason: even within the prefrontal cortex, the endocannabinoid system plays different and sometimes opposing roles depending on the exact location.
Questions still open
- Do these subregion-specific effects translate to humans? Could targeted brain stimulation combined with cannabinoids produce better pain or anxiety outcomes? Why does the anterior cingulate appear uninvolved?
Common questions
What is fear-conditioned analgesia?
Why does location within the prefrontal cortex matter?
Read the original research
The prefrontal cortical endocannabinoid system modulates fear-pain interactions in a subregion-specific manner.
British journal of pharmacology, 176(10), 1492-1505
Citation
Rea, Kieran; McGowan, Fiona; Corcoran, Louise; Roche, Michelle; Finn, David P. (2019). The prefrontal cortical endocannabinoid system modulates fear-pain interactions in a subregion-specific manner.. British journal of pharmacology, 176(10), 1492-1505. https://doi.org/10.1111/bph.14376
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