Mice lacking melanocortin-3 receptors show persistently reduced food anticipatory activity linked to lower AgRP/NPY neuropeptide expression, while mice lacking ghrelin receptors can eventually compensate.
Mc3rKO mice never compensatedUnlike ghrelin receptor-deficient mice that eventually adapted, melanocortin-3 receptor knockout mice permanently lost food anticipatory activity, revealing a non-redundant role
What the researchers found
In a restricted feeding protocol, all three mutant groups (GhsrKO, Mc3rKO, and double knockouts) initially showed reduced food anticipatory activity. However, GhsrKO mice eventually developed a robust compensatory response, while Mc3rKO and double knockout mice did not recover. The continued FAA deficit in Mc3rKO mice was associated with lower expression of the orexigenic neuropeptides AgRP and NPY in the hypothalamus before mealtimes. AgRP and NPY expression positively correlated with FAA levels, and only Mc3r loss (not Ghsr loss) suppressed these hunger-signaling peptides, pointing to melanocortin-3 receptors as critical regulators of anticipatory hunger responses.
Why it matters
Understanding how the brain anticipates and prepares for meals is fundamental to appetite regulation and metabolic health. This study disentangles the roles of two important peptide signaling systems — ghrelin and melanocortins — showing they have distinct and non-redundant roles. The finding that melanocortin-3 receptors are essential (not just contributory) for maintaining food anticipation has implications for understanding eating disorders, meal timing, and metabolic conditions where appetite regulation is disrupted.
How the study worked
Researchers used knockout mice lacking the ghrelin receptor (GhsrKO), melanocortin-3 receptor (Mc3rKO), or both (DKO), and compared them to wild-type controls. Mice underwent hypocaloric restricted feeding protocols in both constant darkness and standard light-dark cycles. Locomotor activity was measured to quantify food anticipatory activity. Hypothalamic AgRP and NPY mRNA expression was measured by quantitative methods 1 hour before scheduled food presentation.
What this study cannot tell us
This study used genetically engineered knockout mice, which lack these receptors from birth and may develop compensatory mechanisms not present in adult-onset receptor dysfunction. Only male mice were studied, limiting generalizability to females. The restricted feeding protocol is an artificial paradigm that may not fully represent natural eating behavior. Hypothalamic gene expression was measured at a single time point, which may miss dynamic changes in neuropeptide signaling.
How to read the evidence
This is a preclinical mechanistic study using multiple knockout mouse models with appropriate behavioral and molecular readouts. The use of single and double knockouts provides rigorous genetic evidence for pathway interactions, but findings are in mice only.
When this study was published
Published in 2014 in Endocrinology, this is an established study that has contributed to the foundational understanding of ghrelin-melanocortin interactions in appetite regulation.
The bigger picture
The gut-brain axis controlling appetite involves multiple peptide systems that interact in complex ways. Ghrelin signals from the stomach, while melanocortin circuits in the hypothalamus integrate hunger and satiety signals. This study reveals that these systems are not simply redundant — they play distinct roles in anticipatory feeding behavior. As the field develops drugs targeting these pathways (GLP-1 agonists, melanocortin receptor modulators), understanding how they interact is crucial for predicting therapeutic effects and side effects.
Questions still open
- Could melanocortin-3 receptor agonists restore normal appetite anticipation in patients with disrupted meal patterns or eating disorders?
- Does the ghrelin system's ability to compensate for its own receptor loss have implications for ghrelin-based drug tolerance?
- Are AgRP/NPY neurons the primary downstream mediators through which melanocortin-3 receptors maintain food anticipatory behavior?
Common questions
What is food anticipatory activity and why does it matter?
Why can ghrelin receptor-deficient mice compensate but melanocortin-3 receptor-deficient mice cannot?
Read the original research
Assessing interactions between Ghsr and Mc3r reveals a role for AgRP in the expression of food anticipatory activity in male mice.
Endocrinology, 155(12), 4843-55
Citation
Girardet, Clemence; Mavrikaki, Maria; Southern, Mark R; Smith, Roy G; Butler, Andrew A. (2014). Assessing interactions between Ghsr and Mc3r reveals a role for AgRP in the expression of food anticipatory activity in male mice.. Endocrinology, 155(12), 4843-55. https://doi.org/10.1210/en.2014-1497