Behavioral profiles of genetically selected aggressive and nonaggressive male wild house mice in two anxiety tests.

Artificially selected aggressive (SAL) and non-aggressive (LAL) male house mice were tested in a hexagonal tunnel maze and light-dark preference (LD) box to determine if the bidirectional selection for aggressive behavior leads to a coselection for different levels of trait anxiety. The tunnel maze consists of an open, brightly lit central arena surrounded by a complex system of interconnecting tunnels. As in the LD box, animals which spend less time and are less active in the brightly illuminated section of the maze are considered to have higher anxiety levels. In the tunnel maze, the LAL mice showed more exploration and spent more time in the central arena than the SAL animals, but only during the final 2 min of the 6-min test. This reduced preference for the central arena was not due to general inactivity or a failure of the SAL to find the central arena and indicates a higher level of state anxiety in the aggressive animals. In contrast, no "anxiety-like" differences were found in the LD box, either for the percentage of time spent in the light compartment or for the number of crossings. SAL males actually showed higher levels of moving and rearing, and lower levels of freezing, than did LAL males.