*2.2. Repetitive mTBI Did Not Cause Neurodegeneration, Glial Activation, and Synaptic Reorganization in the Lateral Geniculate Nucleus and the Superior Colliculus in Wild-Type and TDP-43G348C Mice at 6 Months Following the Last Head Impact*

The presence of neurodegenerative changes in the LGN and the SC, the regions that receive direct innervation from the retinal ganglion cells via the OT, were analyzed using Fluoro-Jade C and cresyl-violet staining. From the representative microphotographs of Fluoro-Jade C-stained sections of the LGN, shown in Figure S2A (Supplementary Materials), it is evident that the staining used was not detected in any of the experimental animals, suggesting no neurodegeneration in this structure at 6 months after the last mTBI. Moreover, individual Fluoro-Jade C-positive staining was detectable in the superficial SC of the injured mice of both genotypes (Figure S2D, Supplementary Materials). Quantitative analysis demonstrated a slight increase in the Fluoro-Jade C intensity levels in the SC of the traumatized wild-type and TDP-43G348C animals compared with sham control animals. However, a statistically significant difference between the experimental groups was not revealed (*p* = 0.235) (Figure S2E, Supplementary Materials).

Additionally, cresyl-violet staining revealed approximately equal neuronal cell density in the LGN (Figure S2B, Supplementary Materials) and the SC (Figure S2F, Supplementary Materials) of all the experimental groups of mice, which was confirmed by subsequent quantitative analysis (*p* = 0.113, *p* = 0.617) (Figure S2C,G, Supplementary Materials).

Repetitive mTBI did not cause changes in the activity of the glial cells in the LGN and the SC of wild-type and TDP-43 transgenic mice in our experimental conditions (Figure S3, Supplementary Materials). Specifically, in the investigated nuclei of the traumatized and sham-treated mice of both genotypes, the "resting" but not activated microglia was detected (Figure S3A,D, Supplementary Materials). Furthermore, a statistically significant difference in the number of Iba1-positive cells between the groups was not revealed for the LGN (*p* = 0.200) or for the SC (*p* = 0.446). Moreover, the signs of astrocytosis in the examined nuclei were not detected in any of the experimental animals (Figure S3C,F, Supplementary Materials).

To detect if repetitive mTBI affects synaptic density in wild-type and TDP-43G348C animals, anti-synaptophysin (SYP) immunostaining was performed. Although it seemed to be more pronounced in the LGN of the sham and injured TDP-43G348C animals compared with wild-type mice (Figure S4A, Supplementary Materials), a significant difference between the experimental groups in the SYP staining intensities was not obtained (*p* = 0.069) (Figure S4B, Supplementary Materials). Moreover, significant differences in the SYP expression (Figure S4C, Supplementary Materials) and density intensities (Figure S4D, Supplementary Materials) between the groups were not observed in the SC (*p* = 0.100).
