Fig. 3: Grm4 deletion protects nigral neurons and motor function after striatal a-syn PFF injection.

a Diagram illustrating the experimental design for α-syn PFF injection into wt and Grm4−/− mice striatum. Created in BioRender. Chen, M. (2025) https://BioRender.com/9w6mss6. b Representative images showing TH and p-α-syn co-staining in the caudate-putamen of wt and Grm4−/− mice injected with α-syn PFF. Scale bar, 100 µm. c Graph shows mean ± SEM of TH levels in the striatum of wt and Grm4−/− mice injected with α-syn PFF. N = mouse number is shown above each bar. One-way ANOVA with Tukey’s post hoc test. d Graph shows mean ± SEM of p-α-syn levels in the striatum of wt and Grm4−/− mice injected with α-syn PFF. N = mouse number is shown above each bar. One-way ANOVA with Tukey’s post hoc test. **p = 0.0052 for WT-PBS vs WT-PFF; **p = 0.0098 for Grm4−/− +PBS vs Grm4−/− +PFF. e Representative images of TH staining in the ipsilateral side of the SNc of wt and Grm4−/− mice injected with α-syn PFF. Coronal section with dorsal up and midline to left. Scale bar, 500 µm. f Graph shows mean ± SEM of TH positive neurons in the ipsilateral side of the SNc of wt and Grm4−/− mice injected with α-syn PFF. N = mouse number is shown above each bar. One-way ANOVA with Tukey’s post hoc test. ***p < 0.0001 for WT-PBS vs WT+PFF and WT+PFF vs Grm4−/− +PFF, mean ± SEM. g Graph shows the percentage of wt and Grm4−/− mice injected with α-syn PFF remaining in the inverted grid in the wire screen test. N = mouse number is shown next to the group label. Gehan–Breslow–Wilcoxon test. p = 0.11 for Grm4−/− +PBS vs Grm4−/− +PFF; p = 0.0008 for WT-+PFF vs Grm4−/− +PFF.