Seizures Dramatically Reshape the Brain's Opioid Peptide Balance in the Hippocampus | Research

The takeaway

Seizures initially release both enkephalin and dynorphin, but long-term they increase enkephalin production while drastically reducing dynorphin — potentially altering future seizure susceptibility.

Opposite long-term changes
Seizures increased enkephalin but drastically decreased dynorphin biosynthesis — two opioids moving in opposite directions

What the researchers found

Both seizure types caused initial opioid release. Long-term: enkephalin biosynthesis increased, dynorphin biosynthesis drastically decreased. These peptides are in distinct hippocampal pathways.

Why it matters

The opposite long-term changes in enkephalin vs. dynorphin could affect whether the brain becomes more or less susceptible to future seizures. This has implications for epilepsy treatment.

How the study worked

Molecular biology approach measuring mRNA levels and peptide content for prodynorphin and proenkephalin in rat hippocampus after electroconvulsive shocks and amygdala kindling.

What this study cannot tell us

Animal study using experimental seizure models. The electroconvulsive and kindling models may not perfectly represent human epilepsy. Only hippocampus studied.

How to read the evidence

Preliminary — animal study using electroconvulsive and kindling seizure models. Molecular biology approach provides mechanistic detail but uses experimental, not natural, seizures.

When this study was published

Published in 1992 (34 years ago). The role of opioid peptides in epilepsy is now well-established, building on findings like these.

The bigger picture

Epilepsy often worsens over time — a process called kindling. The finding that seizures deplete dynorphin (which normally inhibits excitatory signaling) while boosting enkephalin could help explain why the brain becomes progressively more seizure-prone.

Questions still open

Could restoring dynorphin levels after seizures help prevent epilepsy progression?
Does the enkephalin increase serve a protective or harmful role in seizure susceptibility?

Common questions

Why do seizures change opioid peptide levels?

Seizures cause massive neural activity that depletes stored peptides. The brain then tries to replenish them, but enkephalin and dynorphin recover differently — enkephalin production ramps up while dynorphin production collapses.

Could this explain why epilepsy gets worse over time?

Possibly. Dynorphin normally acts as a brake on excitatory brain activity. If seizures deplete dynorphin long-term, the brain loses a key protective mechanism, potentially making future seizures more likely and severe.

Read the original research

Hippocampal opioid peptides and seizures.

Epilepsy research. Supplement, 7, 187-95

View on PubMed ↗

Citation

Hong, J S. (1992). Hippocampal opioid peptides and seizures.. Epilepsy research. Supplement, 7, 187-95.