Spinal μ-opioid receptors quietly hold pain sensitization in check after an acute injury
- Mice lacking spinal μ-opioid receptors kept mechanical hypersensitivity for one to two weeks after a brief C-fiber stimulus, while wild-type mice recovered quickly.
- Inverse agonists (naloxone, naltrexone, CTOP) brought the hypersensitivity back; the neutral antagonist 6β-naltrexol did not, pointing to ligand-independent, constitutive receptor activity.
- Hypersensitivity could be reinstated hours after the mice looked fully recovered, and C-fiber input raised spinal MOR phosphorylation.
💡 Points Based on the abstract
The inverse-agonist versus neutral-antagonist contrast is the cleanest experiment here, and it has a practical edge: naltrexone-type drugs may unmask latent sensitization, not just block opioids. What's missing is evidence that the same constitutive tone exists in humans and fades in chronic pain. I'd run a neutral antagonist in a chronic-pain model before reading anything clinical into it.