Kainic acid seizures depleted hippocampal dynorphin and enkephalin peptides while simultaneously increasing their mRNA — the brain releases its opioid stores during seizures and ramps up production to replenish.
Peptides down, mRNA upSeizures simultaneously depleted stored opioid peptides and increased their gene expression, both proportional to seizure severity
What the researchers found
Kainic acid seizures increased hippocampal prodynorphin and proenkephalin mRNA while decreasing dynorphin A and met-enkephalin peptide levels, both proportional to seizure severity.
Why it matters
This study shows the hippocampus has a dynamic opioid response to seizures. The brain releases stored opioid peptides (possibly to limit seizure damage) and then ramps up production. This could be part of a natural protective mechanism.
How the study worked
Rats received subcutaneous kainic acid. Seizure severity was scored. Hippocampal mRNA was measured by Northern blot; peptide levels were measured by immunoassay at multiple time points.
What this study cannot tell us
Animal study in rats using a chemical seizure model. The kainic acid model may not perfectly represent human epilepsy. Only the hippocampus was studied.
How to read the evidence
Preliminary animal study using a chemical seizure model. Demonstrates the dynamic response but does not prove the functional role of released opioids.
When this study was published
Published in 1991. The endogenous opioid system's role in seizure modulation continues to be studied.
The bigger picture
Opioid peptide release during seizures may be a natural anticonvulsant mechanism. Understanding this could lead to new epilepsy treatments that harness or enhance the brain's own seizure-suppressing opioid system.
Questions still open
- Do the released opioid peptides actually suppress seizure activity?
- Is the opioid response impaired in treatment-resistant epilepsy?
Common questions
Why does the brain release opioids during seizures?
Could this be used to treat epilepsy?
Read the original research
Systemic administration of kainic acid differentially regulates the levels of prodynorphin and proenkephalin mRNA and peptides in the rat hippocampus.
Brain research. Molecular brain research, 9(1-2), 79-86
Citation
Douglass, J; Grimes, L; Shook, J; Lee, P H; Hong, J S. (1991). Systemic administration of kainic acid differentially regulates the levels of prodynorphin and proenkephalin mRNA and peptides in the rat hippocampus.. Brain research. Molecular brain research, 9(1-2), 79-86.