Separation of activation and pattern in grooming development of weaver mice

The effects of environmental conditions and age on grooming behavior were examined in weaver mutant mice and control littermates. Due to deficits in both the cerebellum and the dopaminergic system, weaver mice provide an opportunity to investigate how both of these systems are involved in grooming. Although homozygous weaver (wv/wv mice display deficiencies in grooming behavior, our results indicate that these effects are both context and age dependent. Overall wv/wv mice spent less time grooming than did controls. However, during the post-swim period wv/wv, after day 13, reached the grooming levels of pre-swim control mice. After day 15 wv/wv mice showed a higher number of post-swim grooming bouts relative to pre-swim, and in fact exceeded the number of bouts performed by controls in either pre- or post-swim conditions. Although controls displayed longer bouts than mutants overall, during the post-swim period wv/wv mice, after day 13, produced bouts as long as the control animals did pre-swim. This could in part reflect activation by previous swimming. Our data indicate these activational effects can be separated from balance or posture problems. From examination of the individual grooming stroke types used by the two groups, it is evident that the strokes used by mutant animals clustered around the early grooming sequence phase. In contrast, some of the later strokes were never used by the wv/wv mice during the entire developmental period studied. Our results emphasize the importance of using multiple measures of an action sequence and testing under different conditions.