Traumatic brain injury increased dynorphin in five brain regions while other opioid peptides were unchanged — suggesting dynorphin specifically mediates secondary brain damage.
Dynorphin up in 5 regionsWithin 2 hours of severe brain injury — other opioids unchanged
What the researchers found
Severe brain injury (3.0 to 4.0 atmospheres of pressure) caused dynorphin to increase significantly in five brain regions: striatum, frontal cortex, parietal cortex, pons, and medulla. These were the same regions with the worst tissue damage.
Beta-endorphin decreased in the hypothalamus after severe injury but increased in the anterior pituitary after both mild and severe trauma. Enkephalin levels did not change at any injury level.
The dynorphin increase in the medulla was significantly correlated with falling mean arterial blood pressure after severe injury. This suggests dynorphin release may contribute to the cardiovascular collapse that worsens outcomes after head trauma.
Why it matters
This study provided the first direct measurement of opioid peptide changes after traumatic brain injury. The correlation between dynorphin and tissue damage suggested that the body's own opioid peptides might worsen brain injury, which is the rationale for testing opioid-blocking drugs like naloxone after head trauma.
How the study worked
Cats received fluid-percussion brain injury at low (1.0 to 2.0 atm) or high (3.0 to 4.0 atm) levels. Brain regions were collected at 2 hours after injury. Dynorphin, leucine-enkephalin, and beta-endorphin were measured by immunoassay. Blood pressure was monitored throughout. Tested in cats, not people.
What this study cannot tell us
Tested in cats, not people. Only measured at one time point (2 hours). The correlation between dynorphin and damage does not prove dynorphin caused the damage. It could be a consequence rather than a cause. Small sample sizes typical of large animal studies.
How to read the evidence
Preliminary animal study with two severity levels but limited to a 2-hour time point.
When this study was published
Published in 1987 — pioneering work linking dynorphin to traumatic brain injury pathology.
The bigger picture
Secondary brain damage after trauma often causes more harm than the initial impact. Identifying dynorphin as a specific mediator opened doors for targeted treatments using opioid receptor blockers.
Questions still open
- Could dynorphin-blocking drugs reduce brain damage after head injuries?
- Is the dynorphin increase protective or harmful?
Common questions
What is secondary brain damage?
Why does dynorphin increase after injury?
Read the original research
Alterations in regional concentrations of endogenous opioids following traumatic brain injury in the cat.
Brain research, 425(2), 225-33
Citation
McIntosh, T K; Head, V A; Faden, A I. (1987). Alterations in regional concentrations of endogenous opioids following traumatic brain injury in the cat.. Brain research, 425(2), 225-33.