Cerebrospinal fluid from rats that had seizures contained opioid-like substances that protected other rats from seizures — evidence for a natural anticonvulsant system.
Transferable seizure protectionPost-seizure CSF raised seizure thresholds in naive recipient rats
What the researchers found
CSF from rats that had just experienced an electroshock seizure significantly raised seizure thresholds in recipient rats when injected into their brain ventricles.
This anticonvulsant activity was blocked by high-dose naloxone and by the selective delta-opioid antagonist ICI 174,864. This identified delta-opioid receptors as the mediators.
The active substance was destroyed by heat (90°C) and by trypsin (a protein-digesting enzyme), confirming it is a peptide. It passed through 10,000 dalton membranes but not 5,000 dalton membranes, putting its size between 5,000-10,000 daltons.
Post-seizure CSF had increased beta-endorphin (31 amino acids, ~3,500 daltons) but not dynorphin A, leu-enkephalin, or met-enkephalin. However, hidden met-enkephalin sequences (released by trypsin digestion of larger peptides) were found.
The size (5,000-10,000 Da) and delta-receptor specificity do not match any known opioid peptide, suggesting an undiscovered anticonvulsant opioid peptide.
Why it matters
The brain makes a protective opioid substance after seizures that prevents further seizures. This endogenous anticonvulsant has not been identified. If found and synthesized, it could become a new type of anti-seizure drug working through delta-opioid receptors, which are not targeted by current epilepsy medications.
How the study worked
Donor rats received maximal electroshock seizure. CSF collected and injected into recipient rats' brain ventricles. Seizure threshold measured with flurothyl. Opioid antagonists tested mechanism. Heat, trypsin, peptidase inhibitors, and ultrafiltration characterized the active substance. Opioid peptide levels measured by immunoassay.
What this study cannot tell us
The active substance was not fully identified. CSF transfer experiments are artificial. The amount of protection was moderate. Only one seizure model was tested. The relationship between the beta-endorphin increase and the anticonvulsant activity was unclear.
How to read the evidence
Preliminary animal study with elegant transfer experiment but unidentified active substance.
When this study was published
Published in 1988 — key evidence for endogenous opioid-based anticonvulsant mechanisms.
The bigger picture
The brain has a built-in anticonvulsant system using opioid peptides released during seizures. Identifying and harnessing these natural molecules could lead to new epilepsy treatments.
Questions still open
- What specific opioid peptide is the anticonvulsant agent?
- Could synthetic versions prevent seizure recurrence?
Common questions
How does the brain protect itself from seizures?
Could this help epilepsy patients?
Read the original research
Characterization of opioid peptide-like anticonvulsant activity in rat cerebrospinal fluid.
Brain research, 456(1), 139-46
Citation
Tortella, F C; Long, J B. (1988). Characterization of opioid peptide-like anticonvulsant activity in rat cerebrospinal fluid.. Brain research, 456(1), 139-46.