Table 1.
Summary of studies regarding MC3R and MC4R on food reward and motivation.
| Species | Experiment | Result | Ref. |
|---|---|---|---|
| MC3R KO vs. WT mice |
Sucrose preference test | ↓ sucrose intake and preference in female MC3R KO mice | [74] |
| MC3Rtm1Butl (MC3RTB/TB) vs. WT mice | Food self-administration under fixed and progressive ratio protocols | ↓ self-administration of a food reward in MC3RTB/TB mice exposed to caloric restriction | [21] |
| Rats | Food self-administration under fixed and progressive ratio protocols | ↑ operant response, but not free access to sucrose after injection of the MC3R agonist γ-MSH | [22] |
| Rats | Consumption of a high-fat vs. low-fat diet | ↑ intake of a high-fat diet vs. a low-fat diet after i.c.v. injection of AgRP | [112] |
| MC4R +/+ vs. MC4R −/− mice | Consumption of a three-choice diet (fat, protein, carbohydrate) | ↓ fat intake in MC4R +/+, but not in MC4R −/− mice after injections of the MC3R/MC4R agonist MTII and the MC4R agonist (pentacyclo(D-K)-Asp-cis Apc-(D)Phe-Arg-Trp-Lys-NH2) | [114] |
| Rats | High-fat vs. low-fat diet paradigm | ↓ the high-fat diet intake after injection of MTII in the CeA; ↑ high-fat diet consumption after the injection MCRs antagonists SHU-9119 and AgRP |
[115] |
| Rats | Fat and sugar consumption under an operant conditioning paradigm | ↑ active response to earn a peanut oil emulsion (100% fat) reinforcer, but not a sucrose (100% carbohydrate) reinforcer after i.c.v. injection of AgRP | [113] |
| Rats | Conditioned place preference for high-fat diet and sucrose pellets | AgRP supports conditioned place preference for a high-fat diet, while blocks the acquisition of place preference for sucrose pellets | [111] |
| Rats | Consumption of standard chow | ↓ intake of standard chow after intra-VTA injection of MTII; ↑ 24-h food intake with SHU-9119 |
[122] |
| Rats | Two-bottle choice paradigm for a sucrose solution | ↓ consumption of a 1 and 2% sucrose solutions with intra-VTA injections of MTII; ↓ intake of the more appetizing 10% sucrose solution only at the highest dose of MTII |
[39] |
| Rats | Food self-administration under fixed and progressive ratio protocols | ↓ operant response with α-MSH and ↑ operant response with AgRP injected in the NAc shell; no influence on free consumption of sucrose pellets |
[23] |
| Rats | Food self-administration under fixed and progressive ratio protocols | ↓ sucrose self-administration on both fixed and progressive ratio schedules with intra-VTA injections of MTII; ↑ self-administration, only under fixed ratio protocols with SHU-9119 |
[124] |
↓: decrease; ↑: increase; AgRP: Agouti-related protein; α-MSH: α-melanocyte-stimulating hormone; γ-MSH: γ-melanocyte-stimulating hormone; CeA: Central Amygdala; i.c.v.: Intracerebroventricular; KO: Knock-out; MCRs: Melanocortin receptors; MC3R: Melanocortin-3 receptor; MC4R: Melanocortin-4 receptor; MTII: Melanotan II; NAc: Nucleus Accumbens; VTA: Ventral Tegmental Area; WT: Wild-Type.