TY - JOUR
T1 - Meal patterns and foraging in melanocortin receptor knockout mice
AU - Vaughan, C. H.
AU - Moore, Marcus C.
AU - Haskell-Luevano, C.
AU - Rowland, N. E.
N1 - Funding Information:
This work was supported, in part, by NIH DK57080 (CHL).
PY - 2005/1/31
Y1 - 2005/1/31
N2 - 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 ∼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.
AB - 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 ∼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.
KW - Body weight
KW - Food intake
KW - Meal size
KW - Melanocortin type 3 receptor
KW - Melanocortin type 4 receptor
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U2 - 10.1016/j.physbeh.2004.10.016
DO - 10.1016/j.physbeh.2004.10.016
M3 - Article
C2 - 15642615
AN - SCOPUS:11844277590
SN - 0031-9384
VL - 84
SP - 129
EP - 133
JO - Physiology and Behavior
JF - Physiology and Behavior
IS - 1
ER -