0001-8244/04/0500-0267/0 © 2004 Plenum Publishing Corporation 267 Behavior Genetics, Vol. 34, No. 3, May 2004 (© 2004) QTL Analysis of Multiple Behavioral Measures of Anxiety in Mice Norman D. Henderson, 1,4 Maria Grazia Turri, 2 John C. DeFries, 3 and Jonathan Flint 2 Received 2 Dec. 2002—Final 31 July 2003 In a test battery consisting of an open-field arena, a light-dark box, a mirror-chamber box, an elevated plus maze, and an elevated square maze, 1,671 mice were tested, generating over 100 putative measures of anxiety in rodents. Quantitative trait loci (QTL) analysis was carried out on all measures, plus composite measures and phenotypic factor scores. Significant LOD scores were found for QTL on 17 chromosomes, with large and consistent QTL behavioral effects on chromosomes 1, 4, 7, 8, 14, 15, l8, and X. QTL on chromosomes 4 and 8 largely influence locomotor activity in both home cages and novel environments, whereas QTL on chromosomes 1, 15, and 18 influence anxiety-related behaviors. Five genetically separable, cross-test dimen- sions of anxiety could be identified: (i) the suppression of locomotor activity in low to moder- ately anxiogenic regions of the tests; (ii) a shift toward proportionally less time and activity spent in high-anxiogenic test areas; (iii) the suppression of rearing behavior; (iv) increased latency to enter novel areas; (v) increased autonomic responses, as assessed by defecation and urination. Patterns of QTL influence on cross-test composite scores were distinctive. For example, the QTL on chromosome 1 strongly influenced safe-area locomotor activity (LOD = 35) and autonomic responses (LOD = 16), whereas the QTL on chromosome 15 influenced the propor- tion of activity in high-anxiogenic areas (LOD = 16), latency to enter novel areas (LOD = 36) and rearing behavior (LOD = 57). Phenotypic factor analysis identified factors heavily loaded on single tests, rather than cross-test factors. The use of factor analysis or within-test principal components for data reduction before genetic analysis was less satisfactory than using genetic dissection methods on the original measures and logically derived composites. KEY WORDS: Open-field; light-dark box; elevated plus maze; elevated square maze; mirror chamber; anxiety; activity; emotionality; autonomic responses; anxiogenic environments; rearing; risk taking; home cage; quantitative trait loci (QTL); genetic dissection; chromosome; LOD scores; F2 mice; factor analysis. INTRODUCTION During the past decade we have been using molecular mapping strategies to investigate the genetic architec- ture responsible for individual behavioral differences in the DeFries strains of mice (Flint et al., 1995; Turri et al., 2001a, b). The DeFries strains are derived from a cross of two inbred strains (BALB/cJ and C57/BL6) that were selected for differences in open-field activity, a test that is believed to model susceptibility to anxiety in rodents. Thirty generations of artificial selection in the open-field arena resulted in large activity differ- ences among the lines, which persisted after 18 gener- ations of random mating and 35+ generations of inbreeding, that produced the six DeFries strains: two high (H1 and H2), two low (L1 and L2), and two con- trol lines (C1 and C2), that were not subject to selec- tion (DeFries and Hegman, 1970; DeFries et al., 1978). We have previously reported genetic mapping experiments using F2 intercrosses between both the H1 and L1 strains and the H2 and L2 strains, using several phenotypes to determine whether a common set of genetic loci influence behavior in tests that are believed 1 Oberlin College, Oberlin, Ohio. 2 Wellcome Trust Centre for Human Genetics, Oxford, United Kingdom. 3 Institute for Behavioral Genetics, University of Colorado, Boulder, Colorado. 4 To whom correspondence should be addressed at Department of Psychology, Oberlin College, Oberlin, Ohio 44074. Tel: 440-775- 7695; Fax: 440-775-8356. e-mail: nhenders@oberlin.edu