How the Brain Releases Its Natural Painkiller Met-Enkephalin From Nerve Terminals | Research

The takeaway

Met-enkephalin release from nerve terminals requires calcium but follows different kinetics than classical neurotransmitters, suggesting a distinct release mechanism.

Distinct kinetics
Met-enkephalin release correlated with calcium but followed a different pattern than classical neurotransmitter release

What the researchers found

Met-enkephalin release from synaptosomes was calcium-dependent with distinct kinetics. Release correlated with intraterminal free calcium but showed a different relationship than classical transmitters.

Why it matters

Understanding the precise mechanics of opioid peptide release could help develop drugs that enhance or reduce natural opioid release in the brain.

How the study worked

Rat forebrain synaptosomes were stimulated with KCl, veratridine, and 4-aminopyridine. Met-enkephalin was measured by a highly specific radioimmunoassay. Intraterminal calcium was monitored with fluorescent indicators.

What this study cannot tell us

In vitro study using isolated nerve terminals. Synaptosomes lack the cellular context of intact neurons. Rat brain preparations mix multiple brain regions.

How to read the evidence

Preliminary — in vitro study using isolated nerve terminals. Provides detailed mechanistic data but in an artificial system removed from intact neural circuits.

When this study was published

Published in 1992 (34 years ago). Peptide release mechanisms are now better understood, with this work contributing foundational knowledge.

The bigger picture

Understanding exactly how opioid peptides are released gives scientists targets for developing drugs that could enhance natural pain relief by increasing endogenous opioid release — a potentially safer alternative to administering opioid drugs.

Questions still open

Could drugs that enhance met-enkephalin release provide non-addictive pain relief?
Why do peptide neurotransmitters have different release kinetics than classical ones?

Common questions

How is met-enkephalin release different from other brain chemicals?

Classical neurotransmitters like glutamate are stored in small vesicles and released quickly. Met-enkephalin is stored in larger dense-core vesicles and has different release kinetics — it requires stronger or more sustained stimulation to release.

Why does this matter for pain treatment?

If we understand exactly how the brain releases its natural painkillers, we could develop drugs that enhance this process — boosting the body's own pain relief system rather than adding external opioids with their addiction risks.

Read the original research

Characterization of the release of Met-enkephalin from isolated nerve terminals: release kinetics and cation-dependence.

Brain research, 598(1-2), 294-301

View on PubMed ↗

Citation

Verhage, M; Ghijsen, W E; Wiegant, V M. (1992). Characterization of the release of Met-enkephalin from isolated nerve terminals: release kinetics and cation-dependence.. Brain research, 598(1-2), 294-301.