Comparison of lever press and nose poke operants for acquiring the demand function for food intake and meal patterns in mice

Abstract

Much research in the field and in laboratory studies has focused on behavioral economics of food intake in several species. Operants such as lever press, nose poke, or key peck have been used to generate demand functions that express the relationship between the cost of food and the amount of food consumed. There have been very few such studies of motivated food seeking and demand in mice, and none has examined systematically consummatory cost or meal patterns. Using albino (CD1) male mice, the present study compares food intake and meal patterns across a series of ratio consummatory schedules. A closed economy was used in which the rats were in the test chambers for 23 h/day and earned all of their food via the operant. Two operants, lever press and nosepoke, were compared in a between groups (N=8) design. When each pellet cost a fixed price (FR5, 10, 25 or 50), food intake decreased slightly at the highest FRs. Meal number, compared using two criteria of meal termination (15 and 30 min), was constant across this series. Mice in the nosepoke group consumed ∼10% more food in slightly fewer meals, so their mean meal size was slightly greater, compared with the lever press group. Mice were run for 4 days at each ratio; there were no systematic differences between the first and last day indicating that behavioral adjustments to schedule changes occurred very rapidly. Data from variable ratios (VR10,20) were comparable to those in the corresponding the FRs. Support: NIH DK064712.