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Updated: Aug 20, 2026
Foraging Path-length Protocol for Drosophila melanogaster Larvae
Published on: April 23, 2016
Meal patterns and foraging in melanocortin receptor knockout mice
C H Vaughan1, Marcus C Moore, C Haskell-Luevano
1Department of Psychology, University of Florida, Gainesville, Fl 32611-2250, USA.
Abstract:
We report the meal patterns of mice with the deletion of either the melanocortin type 3 or 4 receptors (MC3RKO or MC4RKO) compared with that of the wild type (WT) under conditions of varying foraging costs. Mice lived in two-lever operant chambers; the completion of a designated number of responses (termed procurement fixed ratio or PFR) on the "foraging" lever activated the other lever. On this second lever, the completion of a designated number of responses (termed consumatory fixed ratio or CFR) caused the delivery of a 20-mg food pellet. Animals could complete as many CFRs as they wished to constitute a meal, but whenever 10 min elapsed without pressing on this second lever, the meal was terminated and pressing on the "foraging" lever was again required to initiate a new meal. At lower PFRs, mice of all three genotypes took 5-7 well-defined meals per day of approximately 35 pellets/meal. At the highest PFR, mice of all three groups took about half this number of meals, with some increase in meal size, and total intake was slightly reduced. MC4RKO mice were obese compared with WT or MC3RKO but failed to eat more food in the operant chambers and, as a consequence, lost weight, regardless of PFR. Thus, changes in meal-taking strategies as a function of imposed foraging cost are not critically dependent on either MC3 or MC4 receptors, but these conditions did not allow us to study meal patterns in MC4RKO mice that are hyperphagic.
Insights
Meal patterns in mice lacking melanocortin receptors (MC3RKO or MC4RKO) were studied. Foraging costs did not significantly alter meal-taking strategies in these mice, though MC4RKO mice lost weight.
Area of Science:
- Neuroscience
- Behavioral Neuroscience
- Metabolic Regulation
Background:
- Melanocortin receptors play a crucial role in regulating energy homeostasis.
- Understanding the specific roles of melanocortin type 3 (MC3R) and type 4 (MC4R) receptors in feeding behavior is essential.
Purpose of the Study:
- To investigate the meal patterns of mice with MC3R or MC4R gene deletions (MC3RKO or MC4RKO) compared to wild-type (WT) mice.
- To examine how varying foraging costs influence meal-taking strategies in these genetically modified mice.
Main Methods:
- Mice were housed in operant chambers where lever presses (procurement fixed ratio - PFR) initiated access to food pellets (consumatory fixed ratio - CFR).
- Meal patterns, including meal frequency and size, were recorded under different PFR conditions.
- Body weight and food intake were monitored for all genotypes.
Main Results:
- At low foraging costs, all mouse genotypes exhibited similar meal patterns (5-7 meals/day, ~35 pellets/meal).
- Increased foraging costs led to fewer meals and slightly reduced total intake across all groups.
- Despite being obese, MC4RKO mice consumed less food in the operant chambers and lost weight, irrespective of foraging cost.
Conclusions:
- Meal-taking strategies in response to foraging costs are not critically dependent on MC3 or MC4 receptors.
- The experimental setup did not fully capture the hyperphagic potential of MC4RKO mice, as they lost weight under these conditions.
