Dynorphin Injected Into the Brain Triggers Rapid Eating in Pigs | Research

The takeaway

Full-length dynorphin injected into pig brains triggered feeding within 2-5 minutes and increased meal size, while naloxone (an opioid blocker) reduced food intake — confirming opioid peptides drive appetite.

Feeding within 2-5 minutes
Full-length dynorphin A(1-17) injected into the brain triggered rapid meal initiation in pigs

What the researchers found

Full-length dynorphin A (1-17 or 1-13), leumorphin, and alpha-neo-endorphin induced rapid feeding in pigs. Shorter fragments were ineffective. Naloxone blocked all feeding effects.

Why it matters

Pigs are closer to humans than rodents in body size and feeding behavior. Demonstrating opioid-driven feeding in pigs strengthens the case that opioid peptides regulate human appetite.

How the study worked

Pigs with lateral ventricle cannulas received 200 µg injections of various opioid peptides. Food intake was measured using operant feeding panels with ad lib food and water.

What this study cannot tell us

Brain injections of 200 µg are pharmacological, not physiological doses. The study used young pigs. Human feeding behavior involves many additional psychological and social factors.

How to read the evidence

Preliminary animal study using pharmacological (supra-physiological) brain injections. Pigs are a more translatable model than rodents but doses were far above natural levels.

When this study was published

Published in 1990. The opioid system's role in appetite has been extensively confirmed, leading to clinical applications like naltrexone-bupropion (Contrave) for weight management.

The bigger picture

This study used pigs — which are physiologically closer to humans than rodents — to demonstrate that opioid peptides regulate appetite. This connection between the opioid system and eating behavior helps explain why opioid medications affect appetite and why naltrexone (a clinical opioid blocker) is used in weight management medications.

Questions still open

Could kappa opioid receptor antagonists help reduce overeating in humans?
Why does the full-length dynorphin peptide work while shorter fragments do not?

Common questions

Why do opioid peptides make you hungry?

Opioid peptides like dynorphin activate reward circuits in the brain that make food more pleasurable and increase motivation to eat. This is why opioid medications can increase appetite and why naltrexone can help reduce overeating.

Why are pigs better than rats for studying eating behavior?

Pigs are omnivores with digestive systems and body sizes closer to humans. Their feeding patterns and metabolic responses are more similar to ours than those of small rodents, making findings more translatable.

Read the original research

Effects of intracerebroventricular injection of dynorphin, leumorphin and alpha neo-endorphin on operant feeding in pigs.

Physiology & behavior, 48(6), 821-4

View on PubMed ↗

Citation

Baldwin, B A; de la Riva, C; Ebenezer, I S. (1990). Effects of intracerebroventricular injection of dynorphin, leumorphin and alpha neo-endorphin on operant feeding in pigs.. Physiology & behavior, 48(6), 821-4.