*3.5. Astrocytes*

Astrocytes were scored on a four-point scale (Figure 3), and we observed no cases with score 4. The frequencies of astrocyte scores did not differ significantly between regions or clusters. The mean astrocyte score was the highest in the lumbosacral spinal cord (2.9%), decreased in the cervical spinal cord and medulla oblongata (2.5%), and was the lowest in the hippocampus (2%, Table 2).

#### *3.6. Lesion Count and Laterality*

Lesions were marginally more frequent on the right side of the CNS (62.3%) (Figure 4), the side of virus injection, than on the left side (37.7%, *p* = 0.0450), although the total mean lesion count did not significantly differ between the right and the left sides (11.9 vs. 6.79, *p* = 0.3242). Similarly, differences in lesion numbers between the right and the left sides were not significant in cluster A (1.3 vs. 0.0, *p* = 0.2886) or cluster B (4.6 vs. 2.0, *p* = 0.224).

**Figure 3.** Grading of reactive astrogliosis in cervical spinal cord (**<sup>a</sup>**–**<sup>c</sup>**) using antibodies against GFAP. (**a**) Representative micrograph showing grade 1 (low) reactive astrogliosis. (**b**) Representative micrograph showing grade 2 (mild to moderate) reactive astrogliosis. (**c**) Representative micrograph showing grade 3 (severe) reactive astrogliosis.

**Figure 4.** Complete cross-section of the medulla oblongata immunostained for microglia, showing numerous glial foci on the same side of the tissue (right side) as virus injection. Inset: detail of the affected parenchyma.
