Open field grid and rearing activity in Mtm1 KO, Mtm1 p.R69C and wild-type animals. (A) Open field activity in 1-month-old KO, Mtm1 p.R69C and wild-type animals (n = 12 for each group). KO animals (168 ± 217) have significantly fewer line breaks in 10 min than Mtm1 p.R69C (977 ± 221) or wild-type animals (747 ± 213) (ANOVA P < 0.001; F = 22.77). Mtm1 p.R69C and wild-type animals show no significant difference in activity at 1 month. (B) Mtm1 p.R69C animals tend to show less activity than wild-type littermates when studied over a 12-month period, and although this difference is significant at 2 months (*P = 0.01), it did not remain so over the entire period. (C) Rearing activity at 1 month is significantly reduced in KO (3.3 ± 5.4) relative to Mtm1 p.R69C (68.7 ± 43.8) and wild-type (88.3 ± 34.5) (ANOVA P < 0.001; F = 21.22). The difference between Mtm1 p.R69C and wild-type was not significant. (D) Mtm1 p.R69C animals tend to show less rearing activity than wild-type littermates over a 12-month interval and although this difference is significant at 2 months (*P = 0.003), it did not remain so over the entire period. The P-values reported in (A) and (C) were obtained from post hoc testing. Abbreviations: KI, Mtm1 p.R69C; KO, Mtm1 knockout; NS, not significant; WT, wild-type.