Beta-Endorphin Produces Spinal Pain Relief by Releasing Met-Enkephalin Locally | Research

The takeaway

Beta-endorphin injected into the brain produces spinal analgesia by selectively releasing met-enkephalin in the spinal cord — morphine uses a completely different mechanism.

Two-step pain relay
Brain beta-endorphin → spinal met-enkephalin release → pain relief

What the researchers found

Beta-endorphin produces spinal analgesia by selectively releasing met-enkephalin. Morphine does not use this mechanism. The effect is specific to the tail-flick (spinal) but not hot-plate (supraspinal) response.

Why it matters

This proved that the body's natural painkiller beta-endorphin and the drug morphine relieve pain through fundamentally different spinal cord mechanisms, even though both activate opioid receptors.

How the study worked

Mice received intrathecal injections of opioid peptide antibodies followed by intracerebroventricular beta-endorphin or morphine. Pain was assessed by tail-flick and hot-plate tests.

What this study cannot tell us

Animal study in mice using antibody injection, which is an indirect approach. The antibodies may not completely neutralize all released peptide. Only two pain tests were used.

How to read the evidence

Preliminary animal study with elegant antibody blocking methodology.

When this study was published

Published in 1989 — revealed the brain-to-spinal cord opioid relay for pain control.

The bigger picture

The brain and spinal cord use a relay system for pain control: brain beta-endorphin triggers spinal enkephalin release. This two-step mechanism is distinct from how opioid drugs work, which has implications for developing more natural pain treatments.

Questions still open

Could enhancing spinal enkephalin release replace opioid drugs?
Why does morphine bypass this natural relay mechanism?

Common questions

How does the brain control pain at the spinal cord?

Beta-endorphin released in the brain triggers a descending signal that causes spinal cord nerve terminals to release met-enkephalin locally. This two-step relay suppresses pain signals before they reach the brain.

Why does morphine work differently?

Morphine directly activates opioid receptors at both brain and spinal cord levels simultaneously, bypassing the natural relay system. This more direct action may contribute to its side effects and addictive potential.

Read the original research

Intrathecal [Met5]enkephalin antibody blocks analgesia induced by intracerebroventricular beta-endorphin but not morphine in mice.

European journal of pharmacology, 173(2-3), 171-6

View on PubMed ↗

Citation

Tseng, L L; Suh, H H. (1989). Intrathecal [Met5]enkephalin antibody blocks analgesia induced by intracerebroventricular beta-endorphin but not morphine in mice.. European journal of pharmacology, 173(2-3), 171-6.