Enkephalins Reduce Stress Behavior While Dynorphin Amplifies It — Opposing Opioid Systems | Research

The takeaway

Enkephalins and dynorphin have opposite effects on stress behavior: enkephalins reduce anxiety-like responses while dynorphin worsens them, with selective cross-talk between the two systems.

Opposing opioid systems
Enkephalins attenuated stress behaviors while dynorphin potentiated them, with selective met-enkephalin/dynorphin cross-talk

What the researchers found

Enkephalin and dynorphin systems have opposing effects on stress behavior. The dynorphin system selectively interacts with the met-enkephalin system but not the leu-enkephalin system.

Why it matters

This shows the opioid system has both stress-reducing and stress-amplifying arms. The balance between enkephalin and dynorphin signaling may determine how well an individual copes with stress.

How the study worked

Rats received intracerebroventricular opioid peptide injections. Two behavioral tests measured stress responses: conditioned suppression of motility and forced swim immobility.

What this study cannot tell us

Animal study using brain-injected synthetic analogs at pharmacological doses. Natural stress responses involve complex interactions beyond just two peptide systems.

How to read the evidence

Preliminary animal study using pharmacological brain injections. Demonstrates opposing effects clearly but at non-physiological doses.

When this study was published

Published in 1990. The opposing roles of enkephalin and dynorphin in stress and mood have been extensively validated and inform current research on kappa opioid antagonists for depression.

The bigger picture

The balance between enkephalin and dynorphin signaling may be a key determinant of stress resilience. People with stronger enkephalin systems may cope better with stress, while dominant dynorphin signaling could predispose to anxiety and depression. This framework has influenced modern research on stress-related mental health conditions.

Questions still open

Is an imbalance between enkephalin and dynorphin signaling involved in anxiety disorders?
Could enhancing enkephalin signaling or blocking dynorphin improve stress resilience?

Common questions

Why do two opioid peptides have opposite effects on stress?

Enkephalins activate delta and mu receptors, which promote feelings of well-being and resilience. Dynorphin activates kappa receptors, which are associated with dysphoria and stress amplification. The body uses both systems to calibrate stress responses.

Could this explain why some people handle stress better than others?

Possibly. Individual differences in the balance between enkephalin and dynorphin systems could influence stress resilience. People with naturally higher enkephalin activity may cope better, while those with dominant dynorphin signaling may be more vulnerable to anxiety and depression.

Read the original research

Behavioral changes induced by stressful situations: effects of enkephalins, dynorphin, and their interactions.

The Journal of pharmacology and experimental therapeutics, 253(2), 600-7

View on PubMed ↗

Citation

Katoh, A; Nabeshima, T; Kameyama, T. (1990). Behavioral changes induced by stressful situations: effects of enkephalins, dynorphin, and their interactions.. The Journal of pharmacology and experimental therapeutics, 253(2), 600-7.