C57 mice showed strong stress-induced pain relief while DBA mice did not — the difference traced to how their opioid receptors respond to stress rather than peptide levels.
Receptor sensitivity, not peptide levelsDetermined which mouse strain got pain relief from stress
What the researchers found
DBA mice had higher baseline pain thresholds than C57 mice. But C57 mice showed much greater stress-induced analgesia (pain relief from stress).
The opioid systems differed genetically: DBA mice had significantly more dynorphin in the hypothalamus and neurointermediate pituitary. C57 mice had lower KD values (better affinity) for spinal mu receptors but higher KD (lower affinity) for cerebral kappa receptors.
Under stress, the two strains activated different opioid systems. C57 mice: beta-endorphin decreased in hypothalamus and increased in neurointermediate pituitary lobe. DBA mice: dynorphin decreased in hypothalamus and beta-endorphin increased in the anterior pituitary.
Both strains showed spinal cord dynorphin decreases under stress.
Why it matters
This study demonstrated that genetic differences in the opioid system produce dramatically different pain and stress responses. It helps explain why people respond differently to pain and stress, and why opioid medications work better in some people than others.
How the study worked
C57BL/6 and DBA/2 mice compared for baseline pain thresholds, opioid peptide concentrations (beta-endorphin and dynorphin in brain and pituitary), opioid receptor binding (mu and kappa), and stress-induced changes. Two stress procedures tested.
What this study cannot tell us
Tested in two inbred mouse strains, which represent extreme genetic uniformity. Human opioid system variation is much more complex. Only two stress procedures tested. The causal relationship between opioid differences and behavioral differences was not established.
How to read the evidence
Preliminary animal study comparing two inbred strains — good genetic control but limited to two genotypes.
When this study was published
Published in 1988 — early pharmacogenomics of opioid pain response.
The bigger picture
Genetic differences in opioid receptor sensitivity may explain why some people respond well to stress and pain while others do not — with implications for personalized pain medicine.
Questions still open
- Do similar receptor variants exist in humans?
- Could receptor profiling predict pain treatment response?
Common questions
Why do some people handle pain better than others?
What is stress-induced analgesia?
Read the original research
The difference in stress-induced analgesia in C57BL/6 and DBA/2 mice: a search for biochemical correlates.
Polish journal of pharmacology and pharmacy, 40(5), 497-506
Citation
Przewłocka, B; Vetulani, J; Lasoń, W; Dziedzicka, M; Silberring, J; Castellano, C; Przewłocki, R. (1988). The difference in stress-induced analgesia in C57BL/6 and DBA/2 mice: a search for biochemical correlates.. Polish journal of pharmacology and pharmacy, 40(5), 497-506.