Alan I. Faden

Early neuronal expression of tumor necrosis factor-α after experimental brain injury contributes to neurological impairment

Tumor necrosis factor-alpha (TNF alpha) is a pleiotropic cytokine involved in inflammatory cascades associated with CNS injury. To examine the role of TNF alpha in the acute pathophysiology of traumatic brain injury (TBI), we studied its expression, localization and modulation in a clinically relevant rat model of non-penetrating head trauma. TNF alpha levels increased significantly in the injured cortex at 1 and 4, but not at 12, 24 or 72 h after severe lateral fluid-percussion trauma (2.6-2.7 atm). TNF alpha was not elevated after mild injury. At 1 and 4 h after severe TBI, marked increases of TNF alpha were localized immunocytochemically to neurons of the injured cerebral cortex. A small population of astrocytes, ventricular cells and microvessels, also showed positive TNF alpha staining, but this expression was not injury-dependent. Macrophages that were present in a hemorrhagic zone along the external capsule, corpus callosum and alveus hippocampus at 4 h after TBI did not express TNF alpha. Intracerebroventricular administration of a selective TNF alpha antagonist--soluble TNF alpha receptor fusion protein (sTNFR:Fc) (37.5 microg)--at 15 min before and 1 h after TBI, improved performance in a series of standardized motor tasks after injury. In contrast, intravenous administration of sTNFR:Fc (0.2, 1 or 5 mg/kg) at 15 min after trauma did not improve motor outcome. Collectively, this evidence suggests that enhanced early neuronal expression of TNF alpha after TBI contributes to subsequent neurological dysfunction.

Interleukin-10 Improves Outcome and Alters Proinflammatory Cytokine Expression after Experimental Traumatic Brain Injury

Traumatic injury to the central nervous system initiates inflammatory processes that are implicated in secondary tissue damage. These processes include the synthesis of proinflammatory cytokines, leukocyte extravasation, vasogenic edema, and blood-brain barrier breakdown. Interleukin-10 (IL-10), a cytokine with antiinflammatory properties, negatively modulates proinflammatory cascades at multiple levels. We examined the hypothesis that IL-10 treatment can improve outcome in a clinically relevant model of traumatic brain injury (TBI). IL-10 was administered via different routes and dosing schedules in a lateral fluid-percussion model of TBI in rats. Intravenous administration of IL-10 (100 micrograms) at 30 min before and 1 h after TBI improved neurological recovery and significantly reduced TNF expression in the traumatized cortex at 4 h after injury. Such treatment was associated with lower IL-1 expression in the injured hippocampus, and to a lesser extent, in the injured cortex. Subcutaneous IL-10 administration (100 micrograms) at 10 min, 1, 3, 6, 9, and 12 h after TBI also enhanced neurological recovery. In contrast, intracerebroventricular administration of IL-10 (1 or 6 micrograms) at 15 min, 2, 4, 6, and 8 h after TBI was not beneficial. These results indicate that IL-10 treatment improves outcome after TBI and suggest that this improvement may relate, in part, to reductions in proinflammatory cytokine synthesis.

Gene profiling in spinal cord injury shows role of cell cycle in neuronal death

Spinal cord injury causes secondary biochemical changes leading to neuronal cell death. To clarify the molecular basis of this delayed injury, we subjected rats to spinal cord injury and identified gene expression patterns by high‐density oligonucleotide arrays (8,800 genes studied) at 30 minutes, 4 hours, 24 hours, or 7 days after injury (total of 26 U34A profiles). Detailed analyses were limited to 4,300 genes consistently expressed above background. Temporal clustering showed rapid expression of immediate early genes (30 minutes), followed by genes associated with inflammation, oxidative stress, DNA damage, and cell cycle (4 and 24 hours). Functional clustering showed a novel pattern of cell cycle mRNAs at 4 and 24 hours after trauma. Quantitative reverse transcription polymerase chain reaction verified mRNA changes in this group, which included gadd45a, c‐myc, cyclin D1 and cdk4, pcna, cyclin G, Rb, and E2F5. Changes in their protein products were quantified by Western blot, and cell‐specific expression was determined by immunocytochemistry. Cell cycle proteins showed an increased expression 24 hours after injury and were, in part, colocalized in neurons showing morphological evidence of apoptosis. These findings suggest that cell cycle–related genes, induced after spinal cord injury, are involved in neuronal damage and subsequent cell death. Ann Neurol 2003

Magnesium protects against neurological deficit after brain injury

The biochemical factors that mediate secondary or delayed damage to the central nervous system (CNS) remain speculative. We have recently demonstrated that brain injury in rats causes a rapid decline in brain intracellular free magnesium (Mg2+) and total magnesium concentrations that is significantly correlated with the severity of injury. In order to further investigate the relationship between Mg2+ and brain injury, we examined the effect of Mg2+ treatment on posttraumatic neurological outcome following fluid-percussion brain injury (2.0 atm) in rats. Since administration of ATP-MgCl2 has been shown to be beneficial in a variety of models of organ ischemia, we also examined the efficacy of ATP-MgCl2 or ATP alone in the treatment of experimental brain injury. Animals treated with low (12.5 mumol) or high (125 mumol) dose MgCl2 at 30 min postinjury showed a significant dose-dependent improvement in neurological function when compared to saline-treated controls. Treatment with ATP-MgCl2 (12.5 mumol) or ATP alone (12.5 mumol) caused no significant improvement in chronic neurological outcome. MgCl2-treated animals showed no change in postinjury mean arterial blood pressure (MAP), whereas animals treated with either ATP-MgCl2 or ATP alone showed a transient but significant fall in MAP (P less than 0.01) during the drug-infusion period. Our results suggest that postinjury treatment with MgCl2 is effective in limiting the extent of neurological dysfunction following experimental traumatic brain injury in the rat.

Thyrotropin-Releasing Hormone Improves Neurologic Recovery after Spinal Trauma in Cats

Abstract Naloxone treatment improves neurologic outcome after experimentally induced spinal trauma, but this opiate-receptor antagonist may increase post-traumatic pain. In contrast, thyrotropin-releasing hormone appears to act in vivo as a partial physiologic opiate antagonist that spares analgesic systems; this activity prompted us to evaluate its effect in spinal injury. Cervical-spine trauma was produced in anesthetized cats by the Allen method. Six animals each received thyrotropin-releasing hormone, saline, or dexamethasone as an intravenous infusion over four hours, beginning one hour after injury. Neurologic recovery was significantly better after treatment with thyrotropin-releasing hormone than after saline or dexamethasone (P<0.01): at six weeks, the average animal given thyrotropin-releasing hormone was normal, whereas average control animals had marked spasticity. The beneficial effect of thyrotropin-releasing hormone in experimental spinal injury and its lack of effect on nociception indicat...

Amyloid precursor protein secretases as therapeutic targets for traumatic brain injury

Amyloid-β (Aβ) peptides, found in Alzheimers disease brain, accumulate rapidly after traumatic brain injury (TBI) in both humans and animals. Here we show that blocking either β- or γ-secretase, enzymes required for production of Aβ from amyloid precursor protein (APP), can ameliorate motor and cognitive deficits and reduce cell loss after experimental TBI in mice. Thus, APP secretases are promising targets for treatment of TBI.

Selective mGluR5 antagonists MPEP and SIB-1893 decrease NMDA or glutamate-mediated neuronal toxicity through actions that reflect NMDA receptor antagonism

The metabotropic glutamate receptors (mGluRs) are a family of G‐protein linked receptors that can be divided into three groups (group I, II and III). A number of studies have implicated group I mGluR activation in acute neuronal injury, but until recently it was not possible to pharmacologically differentiate the roles of the two individual subunits (mGluR1 and mGluR5) in this group. We investigated the role of mGluR5 in acute NMDA and glutamate mediated neurodegeneration in cultured rat cortical cells using the mGluR5 antagonists MPEP and SIB‐1893, and found that they provide significant protection at concentrations of 20 or 200 μM. These compounds act as effective mGluR5 antagonists in our cell culture system, as indicated by the ability of SIB‐1893 to prevent phosphoinositol hydrolysis induced by the specific mGluR5 agonist, (RS)‐2‐chloro‐5‐hydroxyphenylglycine (CHPG). However, they also significantly reduce NMDA evoked current recorded from whole cells voltage clamped at −60 mV, and significantly decrease the duration of opening of NMDA channels recorded in the outside out patch configuration. This suggests that although MPEP and SIB‐1893 are effective mGluR5 antagonists, they also act as noncompetitive NMDA receptor antagonists. Therefore, the neuroprotective effects of these compounds are most likely mediated through their NMDA receptor antagonist action, and caution should be exercised when drawing conclusions about the roles of mGluR5 based on their use.

The tumor suppressor protein p53 is required for neurite outgrowth and axon regeneration

Axon regeneration is substantially regulated by gene expression and cytoskeleton remodeling. Here we show that the tumor suppressor protein p53 is required for neurite outgrowth in cultured cells including primary neurons as well as for axonal regeneration in mice. These effects are mediated by two newly identified p53 transcriptional targets, the actin‐binding protein Coronin 1b and the GTPase Rab13, both of which associate with the cytoskeleton and regulate neurite outgrowth. We also demonstrate that acetylation of lysine 320 (K320) of p53 is specifically involved in the promotion of neurite outgrowth and in the regulation of the expression of Coronin 1b and Rab13. Thus, in addition to its recognized role in neuronal apoptosis, surprisingly, p53 is required for neurite outgrowth and axonal regeneration, likely through a different post‐translational pathway. These observations may suggest a novel therapeutic target for promoting regenerative responses following peripheral or central nervous system injuries.

Changes in extracellular amino acid neurotransmitters produced by focal cerebral ischemia

Excitatory amino acids (EAAs) have been implicated in the pathophysiology of cellular injury after brain ischemia. Changes in extracellular levels of amino acids in rat cerebral cortex after permanent proximal middle cerebral artery (MCA) occlusion were examined using microdialysis. Significant increases were found in dialysate concentrations of glutamate, aspartate and gamma-aminobutyric acid (GABA) from the ischemic cortex during the first 90 min after MCA occlusion compared to pre-ischemic concentrations and contralateral hemispheric controls. Total tissue levels of these amino acids in the infarcted hemisphere 90 min after onset of ischemia were not different from the contralateral hemisphere. These results are consistent with the hypothesis that the release of EAAs may contribute to tissue damage in focal cerebral ischemia.

Dynorphin-related peptides cause motor dysfunction in the rat through a non-opiate action

1 We compared effects on motor function of four peptides belonging to the dynorphin family ‐dynorphin‐(1–17) (DYN‐(1–17)), dynorphin‐(1–13) (DYN‐(1–13)), dynorphin‐(1–8) (DYN‐(1–8)) and α‐neo‐endorphin (αNE). 2 After intrathecal administration, each of these peptides produced dose‐related, flaccid, hindlimb paralysis, with the order of potency being DYN‐(1–17) > DYN‐(1–13) > αNE ≏DYN‐(1–8). 3 This motor dysfunction was not reversed or blocked by the opiate receptor antagonist naloxone and was not produced by a variety of other κ‐selective agonists. 4 However, paralysis was produced by des‐Tyr‐dynorphin (DYN‐(2–17)), which does not act at the opioid receptor. 5 Taken together, the present studies show that dynorphin‐related peptides, uniquely amongst opioids, produce motor dysfunction, an action which does not appear to be mediated by opioid receptors.