2,3-Dihydroxy-6-Nitro-7-Sulfamoyl-Benzo(f)Quinoxaline Reduces Glial Loss and Acute White Matter Pathology after Experimental Spinal Cord Contusion

Abstract

Focal microinjection of 2,3-dihyro-6-nitro-7-sulfamoylbenzo( f )quinoxaline (NBQX), an antagonist of the AMPA/kainate subclass of glutamate receptors, reduces neurological deficits and tissue loss after spinal cord injury. Dose-dependent sparing of white matter is seen at 1 month after injury that is correlated to the dose-related reduction in chronic functional deficits. To determine whether NBQX exerts an acute effect on white matter pathology, female, adult Spague Dawley rats were subjected to a standardized weight drop contusion at T-8 (10 gm ϫ 2.5 cm) and NBQX (15 nmol) or vehicle (VEH) solution focally injected into the injury site 15 min later. At 4 and 24 hr, tissue from the injury epicenter was processed for light and electron microscopy, and the histopathology of ventromedial white matter was compared. The axonal injury index, a quantitative representation of axoplasmic and myelinic pathologies, was significantly lower in the NBQX group at 4 hr (2.7 Ϯ 0.24, mean Ϯ SE) and 24 hr (1.4 Ϯ 0.19) than in VEH controls (3.8 Ϯ 0.33 and 2.1 Ϯ 0.20, respectively). Counts of glial cell nuclei indicated a loss of at least 60% at 4 and 24 hr after injury in the VEH group compared with uninjured controls. NBQX treatment reduced this glial loss by half. Immunohistochemistry revealed that the spared glia were primarily oligodendrocytes. Thus, the chronic effects of NBQX in reducing white matter loss after spinal cord injury appear to be attributable to the reduction of acute pathology and may be mediated through the protection of glia, particularly oligodendrocytes. Key words: spinal cord injury; NBQX; CC1; oligodendrocytes; astrocytes; microglia; white matterTraumatic injury to the spinal cord produces loss of gray matter and white matter (W M) that leads to permanent neurological deficits. Most injuries are the result of spinal cord contusion, i.e., a bruising caused by the impact of vertebral bone onto the dura after rapid flexion -extension of the spinal column. Approximately half are initially classified as "incomplete," in that some function can be detected below the injury site (Bracken et al., 1990). E xperimental models of such incomplete contusion spinal cord injury (SCI) have been developed to investigate the basic pathophysiological mechanisms involved and to test potential therapeutic approaches to mitigate the long-term neurological consequences. From studies of such models, it has become clear that the effects of the initial mechanical destruction of tissue are exacerbated by physiological and biochemical alterations that produce "secondary injury" (Young, 1993;Tator and Fehlings, 1991).One important component of secondary injury is the elevation of extracellular excitatory amino acids (Panter, et al., 1990;Liu et al., 1991) to levels known to be toxic to neurons (Choi et al., 1987;Choi and Rothman, 1990). Antagonists of both the NMDA and AMPA / kainate subclasses of glutamate receptors, administered after experimental SCI, have been shown to reduce chronic neurological impairment (Faden et al., 1988;Gom...

Defining recovery neurobiology of injured spinal cord by synthetic matrix-assisted hMSC implantation

“…3D, Right) of the spinal cord tissue sampled at 1-mm intervals rostral and/or caudal to the injury epicenter of the same set of spinal cords (27,28). Relative to the controls, treatment with scaffolded hMSCs significantly spared white matter in tissue adjacent to the epicenter and enhanced the morphologic integrity of myelin determined by the solvent blue stain (27) (Fig. 3C, Center and Right, respectively); # , control vs. IFN-γ; n = 5; one-way ANOVA with Tukey's post hoc test).…”

Effects of the Sodium Channel Blocker Tetrodotoxin on Acute White Matter Pathology After Experimental Contusive Spinal Cord Injury

“…Rats received a contusion SCI followed by focal injection of 0.15 nmol of TTX into the injury site. The effects of TTX treatment on acute WM pathology were examined at 4 and 24 hr after SCI using a protocol for evaluating the extent of WM pathology that was developed in our laboratory (Rosenberg and Wrathall, 1997;Rosenberg et al, 1999). The results indicate that acute axonal pathology is significantly reduced with TTX treatment, supporting the hypothesis that axonal Na ϩ channels contribute to secondary injury of WM after SCI.…”

“…Sections were viewed with a JEOL Jem 1200 EX (Tokyo, Japan) transmission electron microscope. Electron micrographs (2000ϫ) were made of four fields of ventromedial W M, as defined by the 200 mesh grids on which the tissue sections were viewed, as described previously (Rosenberg and Wrathall, 1997;Rosenberg et al, 1999).…”

Excitotoxic Mechanisms of Ischemic Injury in Myelinated White Matter

“…At the same time, the challenged elements are interactive during energy deprivation in complex ways that are not well understood. Axons can be injured directly by ionic mechanisms leading to toxic accumulation of intracellular Ca 2 + (Fern et al, 1995;Ouardouz et al, 2003;Stys et al, 1990;Underhill and Goldberg, 2006;Wolf et al, 2001), oligodendrocytes, and the myelin they manufacture, can be damaged by glutamate (Alberdi et al, 2002;Li et al, 1999;Matute et al, 1997;McDonald et al, 1998;Rosenberg et al, 1999;Sanchez-Gomez and Matute, 1999) and, undoubtedly, astrocytes and microglia will also be shown to be involved.…”