Tumor necrosis factor alpha (TNFα) and Fas receptor contribute to cell death and cognitive dysfunction after focal traumatic brain injury (TBI). We examined the role of TNFα/Fas in postinjury functional outcome independent of cell death in a novel closed head injury (CHI) model produced with weight drop and free rotational head movement in the anterior-posterior plane. The CHI produced no cerebral edema or blood-brain barrier damage at 24 to 48 hours, no detectable cell death, occasional axonal injury (24 hours), and no brain atrophy or hippocampal cell loss (day 60). Microglia and astrocytes were activated (48 to 72 hours). Tumor necrosis factor-α mRNA, Fas mRNA, and TNFα protein were increased in the brain at 3 to 6 hours after injury (P<0.001 versus sham injured). In wild-type (WT) mice, CHI produced hidden platform (P=0.009) and probe deficits (P=0.001) in the Morris water maze versus sham. Surprisingly, injured TNFα/Fas knockout (KO) mice performed worse in hidden platform trials (P=0.036) but better in probe trials than did WT mice (P=0.0001). Administration of recombinant TNFα to injured TNFα/Fas KO mice reduced probe trial performance to that of WT. Thus, TNFα/Fas influence cognitive deficits independent of cell death after CHI. Therapies targeting TNFα/Fas together may be inappropriate for patients with concussive TBI.

Low-level laser light therapy (LLLT) exerts beneficial effects on motor and histopathological outcomes after experimental traumatic brain injury (TBI), and coherent near-infrared light has been reported to improve cognitive function in patients with chronic TBI. However, the effects of LLLT on cognitive recovery in experimental TBI are unknown. We hypothesized that LLLT administered after controlled cortical impact (CCI) would improve post-injury Morris water maze (MWM) performance. Low-level laser light (800 nm) was applied directly to the contused parenchyma or transcranially in mice beginning 60-80 min after CCI. Injured mice treated with 60 J/cm 2 (500 mW/cm 2 · 2 min) either transcranially or via an open craniotomy had modestly improved latency to the hidden platform ( p < 0.05 for group), and probe trial performance ( p < 0.01) compared to non-treated controls. The beneficial effects of LLLT in open craniotomy mice were associated with reduced microgliosis at 48 h (21.8 -2.3 versus 39.2 -4.2 IbA-1 + cells/200 · field, p < 0.05). Little or no effect of LLLT on post-injury cognitive function was observed using the other doses, a 4-h administration time point and 7-day administration of 60 J/cm 2 . No effect of LLLT (60 J/cm 2 open craniotomy) was observed on post-injury motor function (days 1-7), brain edema (24 h), nitrosative stress (24 h), or lesion volume (14 days). Although further dose optimization and mechanism studies are needed, the data suggest that LLLT might be a therapeutic option to improve cognitive recovery and limit inflammation after TBI.

We previously reported that tumor necrosis factor-a (TNF-a) and Fas receptor induce acute cellular injury, tissue damage, and motor and cognitive deficits after controlled cortical impact (CCI) in mice (Bermpohl et al. 2007); however, the TNF receptors (TNFR) involved are unknown. Using a CCI model and novel mutant mice deficient in TNFR1=Fas, TNFR2=Fas, or TNFR1=TNFR2=Fas, we tested the hypothesis that the combination of TNFR2=Fas is protective, whereas TNFR1=Fas is detrimental after CCI. Uninjured knockout (KO) mice showed no differences in baseline physiological variables or motor or cognitive function. Following CCI, mice deficient in TNFR2=Fas had worse post-injury motor and Morris water maze (MWM) performance than wild-type (WT) mice ( p < 0.05 group effect for wire grip score and MWM performance by repeated measures ANOVA). No differences in motor or cognitive outcome were observed in TNFR1=Fas KO, or in TNFR2 or TNFR1 single KO mice, versus WT mice. Additionally, no differences in propidium iodide (PI)-positive cells (at 6 h) or lesion size (at 14 days) were observed between WT and TNFR1=Fas or TNFR2=Fas KO mice. Somewhat surprisingly, mice deficient in TNFR1=TNFR2=Fas also had PI-positive cells, lesion size, and motor and MWM deficits similar to those of WT mice. These data suggest a protective role for TNFR2=Fas in the pathogenesis of TBI. Further studies are needed to determine whether direct or indirect effects of TNFR1 deletion in TNFR2=Fas KO mice mediate improved functional outcome in TNFR1=TNFR2=Fas KO mice after CCI.

Akt (protein kinase B) and mammalian target of rapamycin (mTOR) have been implicated in the pathogenesis of cell death and cognitive outcome after cerebral contusion in mice; however, a role for Akt/mTOR in concussive brain injury has not been well characterized. In a mouse closed head injury (CHI) concussion traumatic brain injury (TBI) model, phosphorylation of Akt (p-Akt), mTOR (p-mTOR), and S6RP (p-S6RP) was increased by 24 hours in cortical and hippocampal brain homogenates (Po0.05 versus sham for each), and p-S6RP was robustly induced in IBA-1 þ microglia and glial fibrillary acidic protein-positive (GFAP þ ) astrocytes. Pretreatment with inhibitors of Akt or mTOR individually by the intracerebroventricular route reduced phosphorylation of their respective direct substrates FOXO1 (Po0.05) or S6RP (Po0.05) after CHI, confirming the activity of inhibitors. Rapamycin pretreatment significantly worsened hidden platform (Po0.01) and probe trial (Po0.05) performance in CHI mice. Intracerebroventricular administration of necrostatin-1 (Nec-1) before CHI increased hippocampal Akt and S6RP phosphorylation and improved place learning (probe trials, Po0.001 versus vehicle), whereas co-administration of rapamycin or Akt inhibitor with Nec-1 eliminated improved probe trial performance. These data suggest a beneficial role for Akt/mTOR signaling after concussion TBI independent of cell death that may contribute to improved outcome by Nec-1.

No abstract