Acute activation of mitogen-activated protein kinases following traumatic brain injury in the rat: implications for posttraumatic cell death.

The regional activation (via phosphorylation) of c-Jun N-terminal kinase (JNK) and extracellular signal-regulated kinase (ERK) signaling pathways was examined using immunoblotting and immunohistochemistry following experimental brain injury. Anesthetized rats were subjected to lateral fluid-percussion brain injury of moderate severity (2.4-2.6 atm) and euthanized at 2, 6, 24, and 72 h after injury; sham-injured animals were surgically prepared but were not injured. Immunohistochemical evidence of activation of JNK and ERK1/2 pathways was observed predominantly in regions that exhibit neural cell apoptosis and axonal damage following brain trauma. Activation of the ERK1/2 pathway was observed as early as 2 h and up to 72 h postinjury in nonneuronal cells in all layers of the cortex at the site of maximal injury, in the white matter below the site of maximal cortical damage and in the thalamus. In contrast, activation of JNK signaling was observed only at 24 and 72 h postinjury in a few neurons at the core of the cortical injury site. However, robust JNK activation was observed between 2 and 72 h postinjury in both axons and nonneuronal cells in the white matter below the site of maximal cortical damage and in the thalamus. Activation of ERK1/2, but not JNK, was observed in cells in the dentate hilus in the hippocampus in both hemispheres between 2 and 24 h postinjury. Immunoblotting analyses of extracts from various brain regions did not reveal significant alterations in intensities of either total or phosphorylated proteins underscoring the focal nature of the immunohistochemical observations. However, these results suggest that activation of MAP kinase signaling pathways may be associated with posttraumatic cell damage and are indicative of the heterogeneous nature of the mechanisms underlying regional cell death following TBI.

S100B protein is released by in vitro trauma and reduces delayed neuronal injury.

S100B protein in brain is produced primarily by astrocytes, has been used as a marker for brain injury and has also been shown to be neurotrophic and neuroprotective. Using a well characterized in vitro model of brain cell trauma, we examined the potential role of exogenous S100B in preventing delayed neuronal injury. Neuronal plus glial cultures were grown on a deformable Silastic membrane and then subjected to strain (stretch) injury produced by a 50 ms displacement of the membrane. We have previously shown that this injury causes an immediate, but transient, nuclear uptake of the fluorescent dye propidium iodide by astrocytes and a 24-48 h delayed uptake by neurons. Strain injury caused immediate release of S100-beta with further release by 24 and 48 h. Adding 10 or 100 nm S100B to injured cultures at 15 s, 6 h or 24 h after injury reduced delayed neuronal injury measured at 48 h. Exogenous S100B was present in the cultures through 48 h. These studies directly demonstrate the release and neuroprotective role of S100B after traumatic injury and that, unlike most receptor antagonists used for the treatment of trauma, S100B is neuroprotective when given at later, more therapeutically relevant time points.

Lubeluzole treatment does not attenuate neurobehavioral dysfunction or CA3 hippocampal neuronal loss following traumatic brain injury in rats.

PURPOSE: One of the downstream consequences of glutamate-induced NMDA (N-methyl-D-aspartate) receptor activation following trau-matic brain injury (TBI) is production of nitric oxide (NO). In this study, we evaluated the ability of lubeluzole, a novel neuroprotective com-pound which downregulates the glutamate-activated nitric oxide pathway and blocks sodium and voltage-sensitive calcium channels, to improve behavioral and histological outcome in rats following TBI. METHODS: Rats were anesthetized and subjected to moderate lateral fluid percussion brain injury (2.4-2.6 atm) or were surgically prepared but not injured (sham). Fifteen minutes after injury, animals received a bolus of either vehicle (n = 12 injured, n = 14 uninjured) or lubeluzole (0.31 mg/kg, n = 12 injured, n = 8 uninjured) through the jugular vein followed by a one hour infusion of vehicle or lubeluzole (0.31 mg/kg). Animals were tested at 48 hours post-injury for cognitive performance in the Morris water maze, neuromotor function, and limb placing func-tion, and then sacrificed. RESULTS: While brain injury resulted in significant cognitive and motor deficits, injured animals treated with lubeluzole did not differ in spa-tial memory performance, neuromotor score, or limb placing function from injured, vehicle-treated animals. Furthermore, there was no differ-ence in the mean number of ipsilateral hippocampal CA3 neurons between injured rats treated with vehicle and those treated with lubeluzole. CONCLUSIONS: This single-dose study failed to demonstrate a beneficial effect of lubeluzole on the acute behavioral or histological sequelae following TBI.