Fig. 4

4-AP benefit requires continued treatment during the first week post-TBI to protect against multiple features of axon damage. Electron microscopy imaging of axon and myelin ultrastructural features (left) with classification of axon pathology at 3 days (middle) or 7 days (right) after TBI or sham procedure. Left panels: Examples of axon and myelin ultrastructural features. A Intact healthy myelinated axons (arrows). B Swollen mitochondrion (i.e., occupying over 50% of the axon cross section; arrow) in contrast to the typical mitochondrion in the adjacent axon. C Damaged myelinated axon (arrow) exhibiting condensed cytoplasm and vesicle/organelle accumulation. D Demyelinated axon (arrow) lacking a myelin sheath but structurally intact with diameter > 0.3 µm, which is typically myelinated. Middle Panels: At the 3-day time point, TBI significantly reduced the number of intact myelinated axons (A; only TBI main effect significant). TBI significantly increased myelinated axons with swollen mitochondria (B) or axon damage (C), and induced demyelination of additional axons (D) in both vehicle and 4-AP groups at 3 days. 4-AP treatment on days 1–3 did not have a significant benefit as compared to vehicle (B) or the number of damaged (C) and demyelinated (D) axons post-TBI. Right Panels: With 4-AP treatment extended to 7 days, the number of intact myelinated axons post-TBI was statistically similar to sham levels (A). More specifically, 4-AP treatment significantly reduced axons exhibiting mitochondrial swelling (B), axon damage (C), or TBI-induced demyelination (D). A–D Bars represent mean ± SEM with an individual data point shown for each mouse. Two-way ANOVA for main effects of injury or drug with Holm-Sidak’s multiple comparisons test of significance for post-hoc pair effects. See Fig. 1 for mouse sample numbers and Table 2 for statistical details