Norman D. Henderson1, T. Tritto2, D. W. Fulker2, and J. C. DeFries2.
DeFries, Gervais, and Thomas, 1978, Behavior Genetics,8, 3-13, used two replicate sets of F3 mice derived from a BALB/cJ ´ C57BL/6J crossto select for High- or Low open-field (OF) activity. Following 30 generations of bi-directional selection, the resulting replicate lines were maintained by within-line random mating for generations 31-48 and then inbred by brother-sister mating. At the time of this study the lines were at generation 90. Using a newly developed infra-red detector motion detector, we continuouslymeasured gross locomotor activity in the home cages of mice from both sets of High- and Low-OF Activity lines and their F1 crosses. In one set of replicate lines, the High-OF mice showed significantly higher levels of motor activity in their home environment during the dark phase of the diurnal cycle than did the Low-OF line. The High and Low lines differed by only one phenotypic SD, however, which was about 1/7 the size of the OF activity difference observed at generation 30. This H-L home cage activity difference is well within the limits expected by genetic drift alone among inbred lines (Henderson, 1997, Behavior Genetics, 27, 145-154). In the second replicate, High- and Low-OF lines showed nearly identical levels of home cage activity, whereas their OF activity at generation 30 differed by over 8 phenotypic SDs. In both replications, the F1 hybrid cross was more active in home cages during the dark phase than either of their parent lines. No significant line differences in home cage activity were observed during light-phase. These results suggest that the level of locomotor activity exhibited in a brightly lit OF is largely genetically independent of activity levels in familiar home-cage environments.
Address: Department of Psychology, Oberlin College, Oberlin, OH 44074, Phone: (440) 775-7695, FAX: (440) 775-8356, e-mail: fhenders@oberlin.edu
1 Department of Psychology, Oberlin College, Oberlin, OH 44074, 2 Institute for Behavioral Genetics, University of Colorado, Boulder, CO 80309, 3 Supported by NIMH Grant MH-53480.