The Effect of the Sodium Channel Blocker QX-314 on Recovery after Acute Spinal Cord Injury

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Abstract
There is evidence that elevated intracellular sodium ([Na+]i) activity potentiates spinal cord injury (SCI) and the hypoxic/ischemic cell death. In this study, we examined the effect of QX-314, a potent Na+ channel blocker, on recovery after SCI in vivo. QX-314 (2.0 and 10 nmol) or vehicle was microinjected (2 μL) into the injury site 15 min after SCI. Injury was performed by compression of the spinal cord at C7-T1 for 1 min with a modified aneurysm clip exerting a closing force of 35 g. Neurological function was assessed 1 day after injury and weekly thereafter until 6 weeks by the inclined plane method and by the modified Tarlov technique. After 6 weeks of injury, the origin of descending axons at the injury site was determined by retrograde labeling with fluorogold (FG), and a computer-assisted morphometric assessment of the injury site was performed. There was a significant improvement in counts of retrogradely labeled neurons in the red nucleus and rostral ventrolateral medulla (RVLM) in rats treated with either 2 nM (1338 ± 366 and 28.8 ± 16) or 10 nM (1390 ± 511 and 46.3 ± 31) QX-314 as compared to vehicle (902 ± 403 and 13.8 ± 8). There was a trend to increased neuronal counts in the sensorimotor cortex (170.8 ± 226.8) and vestibular nuclei (1096.2 ± 970.2) with QX-314 (10 nM) as compared to the vehicle-treated group. There was no significant difference in the extent of neurological recovery between the control and treated groups. Our results suggest that the Na+ channel blocker QX-314 partially preserves the integrity of descending motor axons after SCI. However, in this study, the effects were insufficient to result in sustained improvements in behavioral neurological function. Key words: axons; fluorogold; QX-314; rat; red nucleus; rostral ventrolateral medulla; sodium channels