Prevention of l-DOPA-induced dyskinesias. At Day 16 of daily l-DOPA treatment, 80% of the animals in the Les-Sham and GCH1-only groups displayed severe dyskinesias. In the TH + GCH1 group, the dyskinesias remained lower than in the control group during the entire peak of the l-DOPA 20–120 min post-l-DOPA injection (A). The dyskinesias were significantly lower in magnitude in this group when assessed as integrated scores (the sum of the individual scores for each assessed time point multiplied by the assessment interval in minutes, i.e. 20 min) presented as either total abnormal involuntary movements (AIM; axial + limb + orolingual) (B), or as individual axial (C), limb (D) and orolingual (E) components. Statistics: (A) Friedman test (non-parametric repeated measure); time effect P < 0.001; group effect P < 0.001. (B–E) Kruskal–Wallis (non-parametric one-way analysis) P ≤ 0.001. Kolmogorov–Smirnov post hoc analysis applied in all panels corrected for multiple comparisons (n = 6) using false discovery rate (FDR) compensation. Error bars in A represent 50% confidence interval (CI); boxes in B–E represent 50% CI, and whiskers 95% CI. Asterisk indicates different from Les-Sham group [P < FDR(0.05)], and hash indicates different from GCH1-only group [P < FDR(0.05)].