Effects of methylprednisolone on lesioned and uninjured mammalian spinal neurons: viability, ultrastructure, and network electrophysiology

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.

Effect of glutathione augmentation on lipid peroxidation after spinal cord injury

Lipid peroxidation (LPO) is considered a major factor in damage spread after spinal cord injury (SCI). Therapies that limit LPO after SCI have demonstrated some utility in clinical trials, but more effective treatments are needed. In the present study the effects of augmenting SC levels of the endogenous antioxidant glutathione (GSH) on LPO after SCI were studied in a rat contusion injury model. A significant decrease in GSH occurred 1h after SCI which was paralleled by increases of 123% in malondialdehyde (MDA) and >500% in the 4-hydroxyalkenals (4-HA's), two LPO products. SC irrigation with gamma-glutamylcysteine (GC) preserved GSH and reduced 4-HA's below naive levels but had no effect on MDA. By 24 h after SCI, MDA returned to naive levels but 4-HA's were still elevated. Once again, GC treatment reduced 4-HA's. 4-HA's are much more reactive than MDA and are considered among the most toxic LPO products. These results suggest that (1) conditions after SCI may favor particular branches of the LPO pathway leading to differential LPO product levels, (2) MDA measurement is not by itself an adequate test for the presence or magnitude of LPO after SCI, (3) binding of GSH to 4-HA's may be an important mechanism by which the GSH system confers protection against LPO after SCI, and (4) SC GSH can be augmented after trauma by local irrigation with GC. These results also suggest that GSH augmentation may be an effective strategy for curtailment of LPO-mediated damage in acute phase SCI.

Prostaglandin release by spinal cord injury mediates production of hydroxyl radical, malondialdehyde and cell death: a site of the neuroprotective action of methylprednisolone

The present study explores in vivo whether and how prostaglandin F(2alpha) (PGF(2alpha)), a membrane phospholipid hydrolysis product, causes neuronal death. The concentration of PGF(2alpha) measured by microdialysis sampling increased threefold immediately following impact injury to the rat spinal cord. Administration of PGF(2alpha) into the cord through a dialysis fiber caused significant cell loss, increased extracellular levels of hydroxyl radicals and malondialdehyde - an end product of membrane lipid peroxidation - to 3.3 and 2.3 times basal levels, respectively. This suggests that PGF(2alpha)-induced cell death is partly due to hydroxyl radical-triggered peroxidation. Generating hydroxyl radical by administering Fenton's reagents into the cord through the fibers significantly increased malondialdehyde production - the first direct in vivo evidence that hydroxyl radical triggers membrane lipid peroxidation. Methylprednisolone significantly reduced the release of PGF(2alpha) upon spinal cord injury and blocked PGF(2alpha)-induced hydroxyl radical and malondialdehyde production, but did not significantly reduce Fenton's reagent-induced malondialdehyde production, despite the production of more malondialdehyde by PGF(2alpha). This suggests that methylprednisolone may not directly scavenge hydroxyl radical, and that its 'antioxidant' effect is a consequence of blocking the pathways for producing toxic PGF(2alpha) and for PGF(2alpha)-induced hydroxyl radical formation, thereby reducing membrane lipid peroxidation.

In vitro central nervous system models of mechanically induced trauma: a review

Injury is one of the leading causes of death among all people below the age of 45 years. In the United States, traumatic brain injury (TBI) and spinal cord injury (SCI) together are responsible for an estimated 90,000 disabled persons annually. To improve treatment of the patient and thereby decrease the associated mortality, morbidity, and cost, several in vivo models of central nervous system (CNS) injury have been developed and characterized over the past two decades. To complement the ability of these in vivo models to reproduce the sequelae of human CNS injury, in vitro models of neuronal injury have also been developed. Despite the inherent simplifications of these in vitro systems, many aspects of the posttraumatic sequelae are faithfully reproduced in cultured cells, including ultrastructural changes, ionic derangements, alterations in electrophysiology, and free radical generation. This review presents a number of these in vitro systems, detailing the mechanical stimuli, the types of tissue injured, and the in vivo injury conditions most closely reproduced by the models. The data generated with these systems is then compared and contrasted with data from in vivo models of CNS injury. We believe that in vitro models of mechanical injury will continue to be a valuable tool to study the cellular consequences and evaluate the potential therapeutic strategies for the treatment of traumatic injury of the CNS.

The effects of ciliary neurotrophic factor on murine spinal cord neurons subjected to dendrite transection injury

Ciliary neurotrophic factor (CNTF) has been found to increase neuronal survival during development and after axotomy. The present study tested the effects of CNTF on lesioned and uninjured mouse spinal cord (SC) neurons grown in tissue culture. An initial toxicity study found that a 24-72 h exposure of SC cultures to concentrations of CNTF above 1000 ng/ml caused stress and death of unlesioned neurons and glia. Pre-selected SC neurons were then subjected to transection of a primary dendrite 100 microns from the edge of the perikaryon (approximately 50% average survival at 24 h). Application of CNTF at concentrations ranging from 0.5 to 1000 ng/ml immediately after lesioning had no statistically significant effects on SC neuron survival 24 h after dendrotomy. Separation of control (no CNTF) and CNTF-treated cells into groups of putative alpha-motor (multipolar with somal diameters > or = 25 microns) and non-alpha-motor neurons (< 25 microns somal diameters) also failed to reveal any significant differences in survival. The lack of protection by CNTF of lesioned SC neurons in mature (21-28 DIV) cultures may reflect a loss of sensitivity to CNTF that occurs with development. Alternatively, protection by CNTF may require co-factors or factors that are released from target or other cells after injury but that are not present in SC cultures.

Quantitative analysis of acute axonal pathology in experimental spinal cord contusion

The major sensorimotor deficits that result from traumatic spinal cord injury (SCI) are due to loss of axons in ascending and descending pathways of the white matter (WM). Experimental treatments administered after a standardized SCI can reduce WM loss and long-term functional deficits. Thus, a significant proportion of WM loss occurs secondary to the mechanical injury and may be a target for therapeutic intervention. Presently, we know little of how and when secondary injury mechanisms operate in the WM after SCI. We therefore used a standardized rat model of clinically relevant contusion injury to examine axonal pathology over the first 24 h by light and electron microscopy. Based on qualitative evaluation of tissue at 15 min, 4 h, and 24 h after a "mild" SCI produced with a weight-drop device (10 g x 2.5 cm), we selected areas from the ventromedial WM at the lesion epicenter for quantitative analyses. We compared axon number and the proportion of axons with various axoplasmic and myelin abnormalities over time after SCI, as well as the effect of axon size on degree of pathology and loss. We found by 4 h postinjury (pi) axonal pathology was more severe than at 15 min and that a significant loss of large diameter axons had occurred; no significant additional loss of axons was seen by 24 h pi. When we compared axonal pathology after a more severe contusion (10 g x 17.5 cm), we found a greater loss of axons at 4 h. In addition, a higher proportion of the remaining axons demonstrated pathological alterations. We developed a semi-quantitative Axonal Injury Index (AII) as an overall measure of axonal pathology that was sensitive to the effects of injury severity at 4 h pi. The AII has greater statistical power than our individual measures of axonal pathology. Our results suggest that it may be possible to use the AII at 4 h pi to assess effects of potential therapeutic agents on acute axonal pathology after SCI.