Figure 9.

Toluidine blue staining and transmission electron microscopy visualization of hippocampal protection by orally administered (−)-P7C3–S243 after blast injury. Daily oral administration of the highly active enantiomer (−)-P7C3–S243 for 14 days, starting 24 hr after injury, dose-dependently preserved CA1 morphology as well as myelin and mitochondrial structures in the hippocampus after blast injury. Two weeks after either sham or blast injury, animals were perfused and processed for ultrastructural pathology. Toluidine-blue-stained semithin sections (left panel) of sham-injured mice treated with vehicle or (−)-P7C3–S243 showed normal CA1 histology, with densely packed neurons in the stratum pyramidale (1) and profuse dendritic profiles in the stratus radiatum (2; black arrows). Blast-injured animals treated with vehicle showed accumulation of chromatolytic and pyknotic neurons (white arrow) throughout the stratum pyramidale as well as fewer dendrites in the stratum radiatum. There is no protection in CA1 morphology at the lowest concentration of blast-injured animals treated with 0.3 mg/kg/day of (−)-P7C3–S243. However, treatment with 3 mg/kg/day (−)-P7C3–S243 lowered the abundance of chromatolytic and pyknotic neurons and resulted in a more densely packed stratum pyramidale. At the highest concentration (30 mg/kg/day) of (−)-P7C3–S243, there was complete preservation of CA1 morphology after blast-mediated TBI. Transmission electron micrographs (TEM; right panel) of immediately adjacent ultrathin sections showed normal myelin and axonal mitochondrial structures in the stratum radiatum of sham-injury mice treated with vehicle or (−)-P7C3–S243. Blast-injured mice treated with vehicle or 0.3 mg/kg/day of (−)-P7C3–S243 showed degeneration of myelin sheath (red arrows), along with abnormal outer membrane and internal cristae structures within neuronal mitochondria (blue arrows). At 3 and 30 mg/kg/day doses, however, both myelin and neuronal mitochondria were preserved. Pictures shown are representative of four animals per condition. Scale bars, 50 μM in Toluidine blue; 500 nm in TEM. (Reprinted from Cell Reports, 8(6), Yin et al., P7C3 Neuroprotective Chemicals Block Axonal Degeneration and Preserve Function after Traumatic Brain Injury, 1731–1740, 2014, with permission from Elsevier).