Effect of transection on the blood-spinal cord barrier of the rat after isolation from descending sources

Behavioral and physiological methods for early quantitative assessment of spinal cord injury and prognosis in rats

Methods for reliable evaluation of spinal cord (SC) injury in rats at short periods (2 and 24 h) after lesion were tested to characterize the mechanisms implicated in primary SC damage. We measured the physiological changes occurring after several procedures for producing SC injury, with particular emphasis on sensorimotor functions. Segmental and suprasegmental reflexes were tested in 39 male Wistar rats weighing 250-300 g divided into three control groups that were subjected to a) anesthesia, b) dissection of soft prevertebral tissue, and c) laminectomy of the vertebral segments between T10 and L1. In the lesion group the SC was completely transected, hemisected or subjected to vertebral compression. All animals were evaluated 2 and 24 h after the experimental procedure by the hind limb motility index, Bohlman motor score, open-field, hot-plate, tail flick, and paw compression tests. The locomotion scale proved to be less sensitive than the sensorimotor tests. A reduction in exploratory movements was detected in the animals 24 h after the procedures. The hot-plate was the most sensitive test for detecting sensorimotor deficiencies following light, moderate or severe SC injury. The most sensitive and simplest test of reflex function was the hot-plate. The hemisection model promoted reproducible moderate SC injury which allowed us to quantify the resulting behavior and analyze the evolution of the lesion and its consequences during the first 24 h after injury. We conclude that hemisection permitted the quantitation of behavioral responses for evaluation of the development of deficits after lesions. Hind limb evaluation scores and spontaneous exploration events provided a sensitive index of immediate injury effects after SC lesion at 2 and 24 h. Taken together, locomotion scales, open-field, and hot-plate tests represent reproducible, quantitatively sensitive methods for detecting functional deficiencies within short periods of time, indicating their potential for the study of cellular mechanisms of primary injury and repair after traumatic SC injury.

Post-trauma Lipitor treatment prevents endothelial dysfunction, facilitates neuroprotection, and promotes locomotor recovery following spinal cord injury

We have previously reported neuroprotection in spinal cord injury (SCI) by Lipitor [atorvastatin (AT)]-pre-treatment. Though informative, pre-treatment studies find only limited clinical application as trauma occurrence is unpredictable. Therefore, this study investigates the efficacy of AT treatment post-SCI. In a rat model of contusion-SCI resulting in complete hindlimb paralysis, AT treatment (5 mg/kg; gavage) was begun 2, 4, or 6 h post-SCI followed by a once daily dose thereafter for 6 weeks. While the placebo vehicle (VHC)-SCI rats showed substantial functional deficit, AT-SCI animals exhibited significant functional recovery. AT diminished injury-induced blood-spinal cord barrier (BSCB) dysfunction with significantly reduced infiltration and tumor necrosis factor-alpha/interleukin-1beta/inducible nitric oxide synthase expression at site of injury. BSCB protection in AT-SCI was attributable to attenuated matrix metalloproteinase-9 (MMP9) expression - a central player in BSCB disruption. Furthermore, endothelial MMP9 expression was found to be RhoA/ROCK pathway-mediated and regulated by AT through an isoprenoid-dependent mechanism. Attenuation of these early inflammatory events reduced secondary damage. Significant reduction in axonal degeneration, myelin degradation, gliosis, and neuronal apoptosis with resultant enhancement in tissue sparing was observed in AT-SCI compared with VHC-SCI. In summary, this novel report presenting the efficacy of post-injury AT treatment might be of critical therapeutic value as effective treatments are currently unavailable for SCI.

A narrow time-window for access to the brain by exogenous protein after immunological targeting of a blood-brain barrier antigen

The endothelial barrier antigen (EBA) is a membrane protein expressed by endothelial cells of the rat blood-brain barrier (BBB). A previous short-term non-recovery study demonstrated that immunological targeting of EBA by intravenous administration of a monoclonal antibody (anti-EBA) led to acute opening of the BBB to exogenous and endogenous tracers. The aims of the present study were to determine whether opening of the BBB was reversible and compatible with survival, and whether a "therapeutic window" existed. A single intravenous injection of one of three doses (high, medium and low) of anti-EBA was used. Animals were allowed to survive for periods ranging from 17 min to 4 days. The tracer horseradish peroxidase (HRP) was administered intravenously 10 min before perfusion fixation, and its distribution was assessed in Vibratome sections of the brain and spinal cord. Leakage of HRP into the central nervous system was dose- and time-dependent. The medium dose produced incipient HRP leakage at 17 min and widespread pronounced leakage at 30 min. Progressive reduction in HRP permeability occurred from 45 min to 2 h, with barrier restoration by 3 h. At all subsequent time intervals (6 h-4 days) the BBB remained impermeable to HRP. The low and high doses produced less and greater HRP leakage, respectively, but restoration of the barrier still occurred at 3 h. The high dose, however, produced a number of deaths. Animals treated with an isotype control antibody showed no HRP leakage at comparable time intervals. The results indicated that (1) this model was compatible with survival, (2) opening of the BBB was monophasic and transient, occurring during a narrow "time-window", and (3) the barrier, once reconstituted, maintained its integrity.

Attenuated induction of heme oxygenase after intrathecal exposure to lysed blood in mice overexpressing superoxide dismutase

Induction of heme oxygenase-1 (HO-1) in the spinal cord was studied in adult wildtype and transgenic mice overexpressing the antioxidant copper, zinc superoxide dismutase (CuZn SOD) 24 h after intrathecal infusion of heterologous lysed blood. Double immunolabeling techniques were used to determine the extent to which HO-1 was induced in astrocytes and microglia/macrophages. HO-1 was induced in both astrocytes and microglia/macrophages in the dorsal horns near the site of infusion of lysed blood in all mice. However, the number of HO-1 labeled cells was significantly less in the transgenic as compared to the wildtype animals. Together, these findings suggest that lysed blood preferentially induces HO-1 in glia and macrophages through the generation of oxidative stress.

Vascular Events After Spinal Cord Injury: Contribution to Secondary Pathogenesis

Traumatic spinal cord injury results in the disruption of neural and vascular structures (primary injury) and is characterized by an evolution of secondary pathogenic events that collectively define the extent of functional recovery. This article reviews the vascular responses to spinal cord injury, focusing on both early and delayed events, including intraparenchymal hemorrhage, inflammation, disruption of the blood-spinal cord barrier, and angiogenesis. These vascular-related events not only influence the evolution of secondary tissue damage but also define an environment that fosters neural plasticity in the chronically injured spinal cord.

Transcytosis of macromolecules through the blood-brain barrier: a cell biological perspective and critical appraisal

A critical appraisal is presented of nearly two decades of research publications and review articles advocating the bidirectional transcytosis of fluid-phase molecules, most notably native horseradish peroxidase (HRP), through the normal and experimentally modified blood-brain barrier (BBB). Extracellular routes circumventing the BBB in normal and pathological states and artifact introduced in histological preparation of CNS tissue exposed to blood-borne peroxidase are emphasized. The potential for transcytosis of macromolecules entering the nonfenestrated cerebral endothelium by the processes of non-specific fluid phase endocytosis (e.g., HRP), adsorptive endocytosis (e.g., lectins) and receptor-mediated endocytosis (e.g., ligands) is analyzed in the context of the cellular secretory process and the complimentary events of endocytosis and exocytosis at the luminal and abluminal plasma membranes. Available data suggest that the cerebral endothelium is polarized with regard to endocytosis and the internalization of cell surface membrane; hence, the transcytosis of specific macromolecules through the BBB may be vectorial. If these data are correct, the blood-brain barrier is not absolute, whereas its counterpart, the brain-blood barrier, may be.