Effects of sodium and chloride on neuronal survival after neurite transection

Diffuse traumatic axonal injury in the optic nerve does not elicit retinal ganglion cell loss

Much of the morbidity after traumatic brain injury (TBI) is associated with traumatic axonal injury (TAI). Although most TAI studies focus on corpus callosum white matter, the visual system has received increased interest. To assess visual system TAI, we developed a mouse model of optic nerve TAI. It is unknown, however, whether this TAI causes retinal ganglion cell (RGC) death. To address this issue, YFP (yellow fluorescent protein)-16 transgenic mice were subjected to mild TBI and followed from 2 to 28 days. Neither TUNEL (terminal deoxynucleotidyl transferase dUTP nick end labeling)-positive or cleaved caspase-3-immunoreactive RGCs were observed from 2 to 28 days after TBI. Quantification of immunoreactivity of Brn3a, an RGC marker, demonstrated no RGC loss; parallel electron microscopic analysis confirmed RGC viability. Persistent RGC survival was also consistent with the finding of reorganization in the proximal axonal segments after TAI, wherein microglia/macrophages remained inactive. In contrast, activated microglia/macrophages closely enveloped the distal disconnected, degenerating axonal segments at 7 to 28 days after injury, thereby confirming that this model consistently evoked TAI followed by disconnection. Collectively, these data provide novel insight into the evolving pathobiology associated with TAI that will form a foundation for future studies exploring TAI therapy and its downstream consequences.

In-vitro approaches for studying blast-induced traumatic brain injury

Traumatic brain injury caused by explosive or blast events is currently divided into four phases: primary, secondary, tertiary, and quaternary blast injury. These phases of blast-induced traumatic brain injury (bTBI) are biomechanically distinct, and can be modeled in both in-vivo and in-vitro systems. The purpose of this review is to consider the mechanical phases of bTBI, how these phases are reproduced with in-vitro models, and to review findings from these models to assess how each phase of bTBI can be examined in more detail. Highlighted are some important gaps in the literature that may be addressed in the future to better identify the exact contributing mechanisms for bTBI. These in-vitro models, viewed in combination with in-vivo models and clinical studies, can be used to assess both the mechanisms and possible treatments for this type of trauma.

Time course studies on the effectiveness of tetrodotoxin in reducing consequences of spinal cord contusion

Focal injection of the sodium channel blocker tetrodotoxin (TTX) into the injury site at either 5 or 15 min after a standardized thoracic contusion spinal cord injury (SCI) reduces white matter pathology and loss of axons in the first 24 hr after injury. Focal injection of TTX at 15 min after SCI also reduces chronic white matter loss and hindlimb functional deficits. We have now tested the hypothesis that the reduction in chronic deficits with TTX treatment is associated with long-term preservation of axons after SCI and compared both acute (24 hr) and chronic (6 weeks) effects of TTX administered at 15 min prior to and 5 min or 4 hr after SCI. Our results indicate a significant reduction of acute white matter pathology in rats treated with TTX at 15 min before and 5 min after injury but no effect when treatment was delayed until 4 hr after contusion. Compared with injury controls, groups treated with TTX at 5 min and 4 hr after injury did not show a significant deficit reduction, nor was there a significant sparing of white matter at 6 weeks compared with injury controls. In contrast, the group treated with TTX at 15 min before SCI demonstrated significantly reduced hindlimb functional deficits beginning at 1 week after injury and throughout the 6 weeks of the study. This was associated with a significantly higher axon density in the ventromedial white matter at 6 weeks. The results demonstrate that blockade of sodium channels preserves axons from loss after SCI and points to the importance of time of administration of such drugs for therapeutic effectiveness.