Contrasting grooming phenotypes in three mouse strains markedly different in anxiety and activity (129S1, BALB/c and NMRI)

129S1/SvImJ (129S1), NMRI and BALB/c mice are widely used in behavioural research, demonstrating marked strain differences in their behavioural phenotypes. Grooming is a complex and essential ritual in the rodent behavioural repertoire with a general cephalocaudal progression (forepaws-nose-face-body- legs-tail and genitals). Various stressors as well as genetic manipulations have been reported to alter mouse grooming and its patterning, underlying the importance of analysis of grooming behaviours. Although strain differences between these mice have been assessed in many studies, no comparative analyses of their grooming have been performed. Here we show strain differences in spontaneous (novelty-induced) grooming between 129S1, NMRI and BALB/c mice. Overall, 129S1 mice demonstrated lower grooming activity and impaired microstructure (more interrupted bouts and incorrect transitions contrary to the cephalocaudal rule), accompanied by lower vertical exploration. In contrast, BALB/c and NMRI mice showed high vertical activity and unimpaired grooming microstructure, also exhibiting different grooming levels (BALB/c > NMRI). Our study suggests that contrasting grooming phenotypes in these mice may not be due to the strain differences in their sensory abilities, general activity levels, brain anatomy or aggressiveness, but rather reflect a complex interplay between anxiety, motor and displacement activity in these strains (hypoactive anxious phenotype in 129S1 mice, active anxious phenotype in BALB/c and non-anxious high displacement phenotype in NMRI mice). We suggest that ethological analysis of mouse grooming, such as that reported here, may be a useful tool in neurobehavioural research.