McALEER, M. W.*; GIRARD, I.; RHODES, J. S.; GARLAND, JR., T.: Motivation of House Mice Artificially Selected for High Wheel Running

We have conducted an artificial selection experiment in which 4 replicate lines of house mice were bred for high wheel running and 4 non-selected lines were maintained as controls. At generation 24, mice from selected lines were running approximately 2.77-times as many revolutions per day as individuals from random-bred control lines. As compared with the randombred control lines, our selected lines of mice may run more on wheels because they have (1) higher motivation to run but similar physiological capacities for wheel running; (2) similar motivation but higher physiological capacities; (3) both higher motivation and higher physiological capacities. Research to date has detected some differences in morphological and physiological traits that may support wheel running, including reduced body mass, more symmetrical hindlimb lengths, and enhanced capacity for insulin-stimulated glucose uptake in hindlimb muscles. To measure motivation, we followed R. C. Bolles’ definition of motivation as a cognitive state for which multiple measures can be used to assess its level. The most appropriate measure may depend on the specific question, and it is likely that no single measure can adequately capture differences in motivation. Hence, we used several ways to increase the difficulty of wheel running, and analyzed the proportional reduction in wheel running. Treatments included greater rotational resistance, 1 or 2 hurdles placed in wheels, and insertion of a tube between wheel and home cage. During treatments with either 1 or 2 hurdles, the proportional decrease in total number of wheel revolutions, the number of intervals spent running, and the maximum number of revolutions during any 1-min interval were all significantly less for selected-line animals. NSF IBN-9728434 and NIH P30 HD03352.