Next, we sought to evaluate and compare the effect of each of these forms of tau on mouse behavior. As tau was highly expressed throughout the mouse cortex including the somatosensory and motor regions, we assessed exploratory locomotion and motor coordination, as such behavioral readouts are typically impaired in mouse models of tauopathies21–23. We first evaluated the exploratory behavior of the mice in the open field, at 3 and 7 months after vector injection (Fig. 2a). At three months, there was no significant difference between groups in the distance travelled by the mice. However, when the same test was performed with 7-months old mice, the group injected with the AAV-P301S vector showed a significant increase in travelled distance compared to both the control and AAV-WT groups (Fig. 2a). This effect may denote the progressive development of a hyperactive behavior in these mice, which is consistent with previous observations in mice injected with an AAV1 vector overexpressing the P301L tau mutant24,25.Figure 2AAV-tau injection induces behavioral deficits: the effects of the P301S and 2P modifications. (a) Open field test performed at 3 and 7 months after AAV-tau injection, compared to the control group injected with AAV-maxFP. Data represent the distance travelled by each mouse on average, for each experimental group. (b) Rotarod test performed at 1.5 and 7 months after AAV-tau injection, compared to the control group injected with AAV-maxFP. The graph shows the average time on the rotating rod for each experimental group. AAV-maxFP: n = 15 mice; AAV-WT: n = 12; AAV-P301S: n = 13. Statistical analysis: two-way ANOVA (time × group) with repeated measures, followed by Newman-Keuls post-hoc test. Open field: group effect F(2,37) = 4.29; Rotarod: group × time effect F(2,37) = 4.38, *p < 0.05; **p < 0.01; ***p < 0.001. (c) Rotarod test to compare AAV-maxFP, AAV-WT and AAV-2P at 1.5, 3 and 7 months after vector injection. The graph shows the average time on the rotating rod for each experimental group. AAV-maxFP: n = 4 mice; AAV-WT: n = 16; AAV-P301S: n = 13. Statistical analysis: two-way ANOVA (time × group) with repeated measures, followed by Fisher’s LSD post-hoc test. Group effect F(2, 30) = 4.18, *p < 0.05.