Only mu-opioid activation in the amygdala increased food intake — delta and kappa agonists had no effect — showing appetite control is receptor-specific in this brain region.
Mu-specific feedingOnly mu-opioid activation in the amygdala increased food intake
What the researchers found
The mu-selective opioid agonist DAGO (Tyr-D-Ala-Gly-(Me)Phe-Gly-ol) increased food intake when injected into the central nucleus of the amygdala at doses of 1 and 3 nanomoles.
Neither DSLET (a delta-selective agonist) nor dynorphin A (a kappa-selective agonist) affected food intake at the same location, even at the highest dose of 3 nanomoles.
Dynorphin A did increase food intake when injected into the medial hypothalamus at 2 nanomoles. This shows that different brain regions use different opioid receptor types to control eating.
Bilateral injections of DAGO were no more effective than unilateral injections. Naloxone and the long-acting antagonist beta-chlornaltrexamine both blocked DAGO's feeding effect, confirming opioid receptor involvement.
Why it matters
The amygdala processes emotions and reward. Finding that mu-opioid receptors there control feeding connects the emotional/reward aspects of eating with the opioid system. This is relevant to understanding binge eating, emotional eating, and food addiction.
How the study worked
Rats received unilateral or bilateral microinjections of receptor-selective opioid agonists into the central nucleus of the amygdala or medial hypothalamus. Food intake was measured. Antagonists (naloxone, beta-chlornaltrexamine) tested specificity. All tested in rats, not people.
What this study cannot tell us
Tested in rats, not people. Direct brain injection is not clinically relevant. Only three receptor types tested. The relationship between opioid-driven feeding in rats and human eating behavior is uncertain. Did not test whether this pathway is involved in normal eating or only pharmacological overstimulation.
How to read the evidence
Preliminary animal study with clear receptor discrimination but limited to one behavioral measure.
When this study was published
Published in 1988 — contributed to understanding of opioid-driven feeding circuits.
The bigger picture
Understanding which opioid receptors in which brain regions control appetite could lead to targeted treatments for obesity and eating disorders without the side effects of broad opioid manipulation.
Questions still open
- Could selective mu-opioid blockers in the amygdala reduce overeating?
- How do emotional eating patterns relate to amygdala mu-opioid activity?
Common questions
Why does the amygdala affect eating?
Could this help treat obesity?
Read the original research
Involvement of mu opioid receptors in the amygdala in the control of feeding.
Neuropharmacology, 27(3), 319-26
Citation
Gosnell, B A. (1988). Involvement of mu opioid receptors in the amygdala in the control of feeding.. Neuropharmacology, 27(3), 319-26.