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The biochemical cascades associated with cell death after traumatic brain injury (TBI) involve both pro-survival and pro-apoptotic proteins. We hypothesized that elevated cerebrospinal fluid (CSF) Bcl-2 and cytochrome C (CytoC) levels over time would reflect cellular injury response and predict long-term outcomes after TBI. Cerebrospinal fluid Bcl-2 and CytoC levels were measured for 6 days after injury for adults with severe TBI (N=76 subjects; N=277 samples). Group-based trajectory analysis was used to generate distinct temporal biomarker profiles that were compared with Glasgow Outcome Scale (GOS) and Disability Rating Scale (DRS) scores at 6 and 12 months after TBI. Subjects with persistently elevated temporal Bcl-2 and CytoC profiles compared with healthy controls had the worst outcomes at 6 and 12 months (P⩽0.027). Those with CytoC profiles near controls had better long-term outcomes, and those with declining CytoC levels over time had intermediate outcomes. Subjects with Bcl-2 profiles that remained near controls had better outcomes than those with consistently elevated Bcl-2 profiles. However, subjects with Bcl-2 values that started near controls and steadily rose over time had 100% good outcomes by 12 months after TBI. These results show the prognostic value of Bcl-2 and CytoC profiles and suggest a dynamic apoptotic and pro-survival response to TBI.

Background

Traumatic brain injury (TBI) initiates a neuroinflammatory cascade that contributes to neuronal damage and behavioral impairment. This study was undertaken to investigate the effects of wogonin, a flavonoid with potent anti-inflammatory properties, on functional and histological outcomes, brain edema, and toll-like receptor 4 (TLR4)- and nuclear factor kappa B (NF-κB)-related signaling pathways in mice following TBI.

Methodology/Principal Findings

Mice subjected to controlled cortical impact injury were injected with wogonin (20, 40, or 50 mg·kg−1) or vehicle 10 min after injury. Behavioral studies, histology analysis, and measurement of blood-brain barrier (BBB) permeability and brain water content were carried out to assess the effects of wogonin. Levels of TLR4/NF-κB-related inflammatory mediators were also examined. Treatment with 40 mg·kg−1 wogonin significantly improved functional recovery and reduced contusion volumes up to post-injury day 28. Wogonin also significantly reduced neuronal death, BBB permeability, and brain edema beginning at day 1. These changes were associated with a marked reduction in leukocyte infiltration, microglial activation, TLR4 expression, NF-κB translocation to nucleus and its DNA binding activity, matrix metalloproteinase-9 activity, and expression of inflammatory mediators, including interleukin-1β, interleukin-6, macrophage inflammatory protein-2, and cyclooxygenase-2.

Conclusions/Significance

Our results show that post-injury wogonin treatment improved long-term functional and histological outcomes, reduced brain edema, and attenuated the TLR4/NF-κB-mediated inflammatory response in mouse TBI. The neuroprotective effects of wogonin may be related to modulation of the TLR4/NF-κB signaling pathway.

Sex influences histological and behavioral outcomes following traumatic brain injury (TBI), but the underlying sex-dependent pathomechanisms regulating outcome measures remain poorly defined. Here, we investigated the TBI-induced regulation of the X-linked inhibitor of apoptosis protein (XIAP) that, in addition to suppressing cell death by inhibition of caspases, is involved in signaling cascades, including immune regulation and cell migration. Since estrogen has been shown to have anti-apoptotic properties, we specifically examined sex differences and the influence of estrogen on XIAP processing after TBI. Sprague-Dawley male (TBI-M), female (TBI-F), ovariectomized female (TBI-OVX) and ovariectomized females supplemented with estrogen (TBI-OVX+EST) were subjected to moderate (1.7–2.2 atm) fluid percussion (FP) injury. Animals were sacrificed 24 hrs after FP injury; cortical tissue (ipsilateral and contralateral) was dissected and analyzed for XIAP processing by immunoblot analysis (n=6–7/group) or confocal microscopy (n=2–3/group). Significant differences in XIAP cleavage products in the ipsilateral cortex were found between groups (p<0.03). Post-hoc analysis showed an increase in XIAP processing in both TBI-F and TBI-OVX+EST compared to TBI-M and TBI-OVX (p<0.05), indicating that more XIAP is cleaved following injury in intact females and TBI-OVX+EST than in TBI-M and TBI-OVX groups. Co-localization of XIAP within neurons also demonstrated sex-dependent changes. Based on these data, it appears that the processing of XIAP after injury is different between males and females and may be influenced by exogenous estrogen treatment.

Traumatic brain injury (TBI) increases cell death in the hippocampus and impairs hippocampus-dependent cognition. The hippocampus is also the site of ongoing neurogenesis throughout the lifespan. Progesterone treatment improves behavioral recovery and reduces inflammation, apoptosis, lesion volume, and edema, when given after TBI. The aim of the present study was to determine whether progesterone altered cell proliferation and short-term survival in the dentate gyrus after TBI. Male Sprague-Dawley rats with bilateral contusions of the frontal cortex or sham operations received progesterone or vehicle at 1 and 6 hours post-surgery and daily through post-surgery Day 7, and a single injection of bromodeoxyuridine (BrdU) 48 hours after injury. Brains were then processed for Ki67 (endogenous marker of cell proliferation), BrdU (short-term cell survival), doublecortin (endogenous marker of immature neurons), and Fluoro-Jade B (marker of degenerating neurons). TBI increased cell proliferation compared to shams and progesterone normalized cell proliferation in injured rats. Progesterone alone increased cell proliferation in intact rats. Interestingly, injury and/or progesterone treatment did not influence short-term cell survival of BrdU-ir cells. All treatments increased the percentage of BrdU-ir cells that were co-labeled with doublecortin (an immature neuronal marker in this case labelling new neurons that survived 5 days), indicating that cell fate is influenced independently by TBI and progesterone treatment. The number of immature neurons that survived 5 days was increased following TBI, but progesterone treatment reduced this effect. Furthermore, injury increased cell death and progesterone treatment reduced cell death to levels seen in intact rats. Together these findings suggest that progesterone treatment after TBI normalizes the levels of cell proliferation and cell death in the dentate gyrus of the hippocampus.

We found that recombinant human erythropoietin (rhEPO) reduced significantly the development of brain edema in a rat model of diffuse traumatic brain injury (TBI) (impact-acceleration model). In this study, we investigated the molecular and intracellular changes potentially involved in these immediate effects. Brain tissue nitric oxide (NO) synthesis, phosphorylation level of two protein kinases (extracellular-regulated kinase (ERK)-1/-2 and Akt), and brain water content were measured 1 (H1) and 2 h (H2) after insult. Posttraumatic administration of rhEPO (5,000 IU/kg body weight, intravenously, 30 mins after injury) reduced TBI-induced upregulation of ERK phosphorylation, although it increased Akt phosphorylation at H1. These early molecular changes were associated with a reduction in brain NO synthesis at H1 and with an attenuation of brain edema at H2. Intraventricular administration of the ERK-1/-2 inhibitor, U0126, or the Akt inhibitor, LY294002, before injury showed that ERK was required for brain edema formation, and that rhEPO-induced reduction of edema could involve the ERK pathway. These results were obtained in the absence of any evidence of blood–brain barrier damage on contrast-enhanced magnetic resonance images. The findings of our study indicate that the anti edematous effect of rhEPO could be mediated through an early inhibition of ERK phosphorylation after diffuse TBI.

Traumatic brain injury (TBI) results in both focal and diffuse brain pathologies that are exacerbated by the inflammatory response and progress from hours to days after the initial injury. Using a clinically relevant model of TBI, the parasagittal fluid-percussion brain injury (FPI) model, we found injury-induced impairments in the cyclic AMP (cAMP) signaling pathway. Levels of cAMP were depressed in the ipsilateral parietal cortex and hippocampus, as well as activation of its downstream target, protein kinase A, from 15 min to 48 hr after moderate FPI. To determine if preventing hydrolysis of cAMP by administration of a phosphodiesterase (PDE) IV inhibitor would improve outcome after TBI, we treated animals intraperitoneally with rolipram (0.3 or 3.0 mg/kg) 30 min prior to TBI, and then once per day for three days. Rolipram treatment restored cAMP to sham levels and significantly reduced cortical contusion volume and improved neuronal cell survival in the parietal cortex and CA3 region of the hippocampus. Traumatic axonal injury, characterized by β-amyloid precursor protein deposits in the external capsule, was also significantly reduced in rolipram-treated animals. Furthermore, levels of the pro-inflammatory cytokines, interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α), were significantly decreased with rolipram treatment. These results demonstrate that the cAMP-PKA signaling cascade is downregulated after TBI, and that treatment with a PDE IV inhibitor improves histopathological outcome and decreases inflammation after TBI.

Abstract

Cyclosporin A (CsA) has recently been proposed for use in the early phase after traumatic brain injury (TBI), for its ability to preserve mitochondrial integrity in experimental brain injury models, and thereby provide improved behavioral outcomes as well as significant histological protection. The aim of this prospective, randomized, double-blind, dual-center, placebo-controlled trial was to evaluate the safety, tolerability, and pharmacokinetics of a single intravenous infusion of CsA in patients with severe TBI. Fifty adult severe TBI patients were enrolled over a 22-month period. Within 12 h of the injury patients received 5 mg/kg of CsA infused over 24 h, or placebo. Blood urea nitrogen (BUN), creatinine, hemoglobin, platelets, white blood cell count (WBC), and a hepatic panel were monitored on admission, and at 12, 24, 36, and 48 h, and on days 4 and 7. Potential adverse events (AEs) were also recorded. Neurological outcome was recorded at 3 and 6 months after injury. This study revealed only transient differences in BUN levels at 24 and 48 h and for WBC counts at 24 h between the CsA and placebo patients. These modest differences were not clinically significant in that they did not negatively impact on patient course. Both BUN and creatinine values, markers of renal function, remained within their normal limits over the entire monitoring period. There were no significant differences in other mean laboratory values, or in the incidence of AEs at any other measured time point. Also, no significant difference was demonstrated for neurological outcome. Based on these results, we report a good safety profile of CsA infusion when given at the chosen dose of 5 mg/kg, infused over 24 h, during the early phase after severe head injury in humans, with the aim of neuroprotection.

Background

Traumatic brain injury (TBI) initiates a complex series of neurochemical and signaling changes that lead to pathological events including neuronal hyperactivity, excessive glutamate release, inflammation, increased blood-brain barrier (BBB) permeability and cerebral edema, altered gene expression, and neuronal dysfunction. It is believed that a drug combination, or a single drug acting on multiple targets, may be an effective strategy to treat TBI. Valproate, a widely used antiepileptic drug, has a number of targets including GABA transaminase, voltage-gated sodium channels, glycogen synthase kinase (GSK)-3, and histone deacetylases (HDACs), and therefore may attenuate a number of TBI-associated pathologies.

Methodology/Principal Findings

Using a rodent model of TBI, we tested if post-injury administration of valproate can decrease BBB permeability, reduce neural damage and improve cognitive outcome. Dose-response studies revealed that systemic administration of 400 mg/kg (i.p.), but not 15, 30, 60 or 100 mg/kg, increases histone H3 and H4 acetylation, and reduces GSK-3 activity, in the hippocampus. Thirty min post-injury administration of 400 mg/kg valproate improved BBB integrity as indicated by a reduction in Evans Blue dye extravasation. Consistent with its dose response to inhibit GSK-3 and HDACs, valproate at 400 mg/kg, but not 100 mg/kg, reduced TBI-associated hippocampal dendritic damage, lessened cortical contusion volume, and improved motor function and spatial memory. These behavioral improvements were not observed when SAHA (suberoylanilide hydroxamic acid), a selective HDAC inhibitor, was administered.

Conclusion/Significance

Our findings indicate that valproate given soon after TBI can be neuroprotective. As clinically proven interventions that can be used to minimize the damage following TBI are not currently available, the findings from this report support the further testing of valproate as an acute therapeutic strategy.

Adenosine is a ubiquitous signaling molecule, with widespread activity across all organ systems. There is evidence that adenosine regulation is a significant factor in traumatic brain injury (TBI) onset, recovery, and outcome, and a growing body of experimental work examining the therapeutic potential of adenosine neuromodulation in the treatment of TBI. In the central nervous system (CNS), adenosine (dys)regulation has been demonstrated following TBI, and correlated to several TBI pathologies, including impaired cerebral hemodynamics, anaerobic metabolism, and inflammation. In addition to acute pathologies, adenosine function has been implicated in TBI comorbidities, such as cognitive deficits, psychiatric function, and post-traumatic epilepsy. This review presents studies in TBI as well as adenosine-related mechanisms in co-morbidities of and unfavorable outcomes resulting from TBI. While the exact role of the adenosine system following TBI remains unclear, there is increasing evidence that a thorough understanding of adenosine signaling will be critical to the development of diagnostic and therapeutic tools for the treatment of TBI.

Abstract

When provided individually, both the serotonin (5-HT1A)-receptor agonist 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) and environmental enrichment (EE) enhance behavioral outcome and reduce histopathology after experimental traumatic brain injury (TBI). The aim of this study was to determine whether combining these therapies would yield greater benefit than either used alone. Anesthetized adult male rats received a cortical impact or sham injury and then were randomly assigned to enriched or standard (STD) housing, where either 8-OH-DPAT (0.1 mg/kg) or vehicle (1.0 mL/kg) was administered intraperitoneally once daily for 3 weeks. Motor and cognitive assessments were conducted on post-injury days 1–5 and 14–19, respectively. CA1/CA3 neurons and choline acetyltransferase-positive (ChAT+) medial septal cells were quantified at 3 weeks. 8-OH-DPAT and EE attenuated CA3 and ChAT+ cell loss. Both therapies also enhanced motor recovery, acquisition of spatial learning, and memory retention, as verified by reduced times to traverse the beam and to locate an escape platform in the water maze, and a greater percentage of time spent searching in the target quadrant during a probe trial in the TBI + STD + 8-OH-DPAT, TBI + EE + 8-OH-DPAT, and TBI + EE + vehicle groups versus the TBI + STD + vehicle group (p ≤ 0.0016). No statistical distinctions were revealed between the TBI + EE + 8-OH-DPAT and TBI + EE + vehicle groups in functional outcome or CA1/CA3 cell survival, but there were significantly more ChAT+ cells in the former (p = 0.003). These data suggest that a combined therapeutic regimen of 8-OH-DPAT and EE reduces TBI-induced ChAT+ cell loss, but does not enhance hippocampal cell survival or neurobehavioral performance beyond that of either treatment alone. The findings underscore the complexity of combinational therapies and of elucidating potential targets for TBI.

Background

Traumatic brain injury (TBI) evokes a systemic immune response including leukocyte migration into the brain and release of pro-inflammatory cytokines; however, the mechanisms underlying TBI pathogenesis and protection are poorly understood. Due to the high incidence of head trauma in the sports field, battlefield and automobile accidents identification of the molecular signals involved in TBI progression is critical for the development of novel therapeutics.

Methods

In this report, we used a rat lateral fluid percussion impact (LFPI) model of TBI to characterize neurodegeneration, apoptosis and alterations in pro-inflammatory mediators at two time points within the secondary injury phase. Brain histopathology was evaluated by fluoro-jade (FJ) staining and terminal deoxynucleotidyl transferase dUTP nick end labelling (TUNEL) assay, polymerase chain reaction (qRT PCR), enzyme linked immunosorbent assay (ELISA) and immunohistochemistry were employed to evaluate the CCL20 gene expression in different tissues.

Results

Histological analysis of neurodegeneration by FJ staining showed mild injury in the cerebral cortex, hippocampus and thalamus. TUNEL staining confirmed the presence of apoptotic cells and CD11b+ microglia indicated initiation of an inflammatory reaction leading to secondary damage in these areas. Analysis of spleen mRNA by PCR microarray of an inflammation panel led to the identification of CCL20 as an important pro-inflammatory signal upregulated 24 h after TBI. Although, CCL20 expression was observed in spleen and thymus after 24h of TBI, it was not expressed in degenerating cortex or hippocampal neurons until 48 h after insult. Splenectomy partially but significantly decreased the CCL20 expression in brain tissues.

Conclusion

These results demonstrate that the systemic inflammatory reaction to TBI starts earlier than the local brain response and suggest that spleen- and/ or thymus-derived CCL20 might play a role in promoting neuronal injury and central nervous system inflammation in response to mild TBI.

Mitochondrial catastrophe can be the cause or consequence of apoptosis and is associated with a number of pathophysiological conditions. The exact relationship between mitochondrial catastrophe and caspase activation is not completely understood. Here we addressed the underlying mechanism, explaining how activated caspase could feedback to attack mitochondria to amplify further cytochrome c (cyto.c) release. We discovered that cytochrome c1 (cyto.c1) in the bc1 complex of the mitochondrial respiration chain was a novel substrate of caspase 3 (casp.3). We found that cyto.c1 was cleaved at the site of D106, which is critical for binding with cyto.c, following apoptotic stresses or targeted expression of casp.3 into the mitochondrial intermembrane space. We demonstrated that this cleavage was closely linked with further cyto.c release and mitochondrial catastrophe. These mitochondrial events could be effectively blocked by expressing non-cleavable cyto.c1 (D106A) or by caspase inhibitor z-VAD-fmk. Our results demonstrate that the cleavage of cyto.c1 represents a critical step for the feedback amplification of cyto.c release by caspases and subsequent mitochondrial catastrophe.

Apoptosis contributes to delayed neuronal cell death in traumatic brain injury (TBI). To investigate if Bax plays a role in neuronal cell death and functional outcome after TBI, Bax gene disrupted (null) mice and wild type (WT) controls were subjected to the controlled cortical impact (CCI) model of TBI. Motor function in WT and Bax null mice was evaluated using the round beam balance and the wire grip test on days 0–5. Spatial memory was assessed using a Morris Water Maze adopted for mice on days 14–18 post injury. For histopathological analysis, animals were sacrificed 24 hrs and 21 days post injury. In all three behavioral tests, the sham and TBI-injured Bax null mice performed significantly worse than their WT sham and TBI-injured counterparts. However, Bax null mice exhibited a higher percentage of surviving neurons in the CA1 and CA3 regions of hippocampus measured at 21 days post injury. Twenty four hours after trauma, Bax null mice had fewer TUNEL positive cells in the CA1 and dentate regions of hippocampus as compared to WT mice suggesting that deletion of the Bax gene ameliorates hippocampal cell death after TBI. Sham-operated Bax null mice had significantly greater brain volume as compared to WT mice. Thus, it is possible that Bax deficiency in the transgenic mice produces developmental behavioral effects, perhaps due to Bax’s role in regulating cell death during development.

Abstract

Apoptosis contributes to delayed neuronal cell death in traumatic brain injury (TBI). To investigate if Bax plays a role in neuronal cell death and functional outcome after TBI, Bax gene disrupted (null) mice and wild-type (WT) controls were subjected to the controlled cortical impact (CCI) model of TBI. Motor function in WT and Bax null mice was evaluated using the round beam balance and the wire grip test on days 0–5. Spatial memory was assessed using a Morris Water Maze adopted for mice on days 14–18 post-injury. For histopathological analysis, animals were sacrificed 24 h and 21 days post-injury. In all three behavioral tests, the sham and TBI-injured Bax null mice performed significantly worse than their WT sham and TBI-injured counterparts. However, Bax null mice exhibited a higher percentage of surviving neurons in the CA1 and CA3 regions of hippocampus measured at 21 days post-injury. At 24 h after trauma, Bax null mice had fewer TUNEL positive cells in the CA1 and dentate regions of hippocampus as compared to WT mice, suggesting that deletion of the Bax gene ameliorates hippocampal cell death after TBI. Sham-operated Bax null mice had significantly greater brain volume as compared to WT mice. Thus, it is possible that Bax deficiency in the transgenic mice produces developmental behavioral effects, perhaps due to Bax's role in regulating cell death during development.

An early (i.e., 15 min) single systemic administration of the 5-HT1A receptor agonist 8-OH-DPAT enhances behavioral recovery after experimental traumatic brain injury (TBI). However, acute administration of pharmacotherapies after TBI may be clinically challenging and thus the present study sought to investigate the potential efficacy of a delayed and chronic 8-OH-DPAT treatment regimen. Forty-eight isoflurane-anesthetized adult male rats received either a controlled cortical impact or sham injury and beginning 24 hrs later were administered 8-OH-DPAT (0.1 or 0.5 mg/kg) or saline vehicle (1.0 mL/kg) intraperitoneally once daily until all behavioral assessments were completed. Neurobehavior was assessed by motor and cognitive tests on post-operative days 1–5 and 14–19, respectively. The lower dose of 8-OH-DPAT (0.1 mg/kg) enhanced motor performance, acquisition of spatial learning, and memory retention vs. both the higher dose (0.5 mg/kg) and vehicle treatment (p < 0.05). These data replicate previous findings from our laboratory showing that 8-OH-DPAT improves neurobehavior after TBI, and extend those results by demonstrating that the benefits can be achieved even when treatment is withheld for 24 hrs. A delayed and chronic treatment regimen may be more clinically feasible.

Abstract

Intestinal barrier breakdown following traumatic brain injury (TBI) is characterized by increased intestinal permeability, leading to bacterial translocation, and inflammation. The hormone ghrelin may prevent intestinal injury and have anti-inflammatory properties. We hypothesized that exogenous ghrelin prevents intestinal injury following TBI. A weight-drop model created severe TBI in three groups of anesthetized Balb/c mice. Group TBI: animals underwent TBI only; Group TBI/ghrelin: animals were given 10 μg of ghrelin intraperitoneally prior and 1 h following TBI; Group sham: no TBI or ghrelin injection. Intestinal permeability was measured 6 h following TBI by detecting serum levels of FITC-Dextran after injection into the intact ileum. The terminal ileum was harvested for histology, expression of the tight junction protein MLCK and inflammatory cytokine TNF-α. Permeability increased in the TBI group compared to the sham group (109.7 ± 21.8 μg/mL vs. 32.2 ± 10.1 μg/mL; p < 0.002). Ghrelin prevented TBI-induced permeability (28.3 ± 4.2 μg/mL vs. 109.7 ± 21.8 μg/mL; p < 0.001). The intestines of the TBI group showed blunting and necrosis of villi compared to the sham group, while ghrelin injection preserved intestinal architecture. Intestinal MLCK increased 73% compared to the sham group (p < 0.03). Ghrelin prevented TBI-induced MLCK expression to sham levels. Intestinal TNF-α increased following TBI compared to the sham group (46.2 ± 7.1 pg/mL vs. 24.4 ± 2.2 pg/mL p < 0.001). Ghrelin reduced TNF-α to sham levels (29.2 ± 5.0 pg/mL; p = NS). We therefore conclude that ghrelin prevents TBI-induced injury, as determined by intestinal permeability, histology, and intestinal levels of TNF-α. The mechanism for ghrelin mediating intestinal protection is likely multifactorial, and further studies are needed to delineate these possibilities.

The aim of this study was to investigate the role of gender in histological and functional outcome, angiogenesis, neurogenesis and therapeutic effects of recombinant human erythropoietin (rhEPO) in mice after traumatic brain injury (TBI). TBI caused both tissue loss in the cortex and cell loss in the dentate gyrus (DG) in the injured hemisphere at day 35 post TBI without a significant gender difference. After TBI, sensorimotor deficits were significantly larger in male mice compared to females, while similar spatial learning deficits were present in both genders. TBI alone significantly stimulated angiogenesis and neurogenesis in the cortex and in the DG of injured hemispheres in both genders. rhEPO at a dose of 5,000 Units/kg body weight administered intraperitoneally at 6 h, and 3 and 7 days after injury significantly reduced lesion volume and DG cell loss examined at day 35 after TBI as well as dramatically improved sensorimotor and spatial learning performance without an obvious gender proclivity. rhEPO significantly enhanced neurogenesis in the cortex and the DG of the ipsilateral hemisphere in male TBI mice. rhEPO did not affect angiogenesis in the ipsilateral cortex and DG in both genders after TBI. The present data demonstrate that posttraumatic administration of rhEPO improves histological and functional outcome in both genders, which may be mediated by reducing cortical tissue damage and DG cell loss in the ipsilateral hemisphere. In addition, the major gender propensity observed in the present study with mice after TBI without treatment is limited to sensorimotor deficits and cell proliferation.

Traumatic brain injury (TBI) represents a significant cause of death and disability in industrialized countries. Of particular importance to patients the chronic effect that TBI has on cognitive function. Therapeutic strategies have been difficult to evaluate because of the complexity of injuries and variety of patient presentations within a TBI population. However, pharmacotherapies targeting dopamine (DA) have consistently shown benefits in attention, behavioral outcome, executive function, and memory. Still it remains unclear what aspect of TBI pathology is targeted by DA therapies and what time-course of treatment is most beneficial for patient outcomes. Fortunately, ongoing research in animal models has begun to elucidate the pathophysiology of DA alterations after TBI. The purpose of this review is to discuss clinical and experimental research examining DAergic therapies after TBI, which will in turn elucidate the importance of DA for cognitive function/dysfunction after TBI as well as highlight the areas that require further study.

Severe traumatic brain injury (TBI) is associated with a high incidence of acute mortality followed by chronic alteration of homeostatic network activity that includes the emergence of posttraumatic seizures. We hypothesized that acute and chronic outcome after severe TBI critically depends on disrupted bioenergetic network homeostasis, which is governed by the availability of the brain’s endogenous neuroprotectant adenosine. We used a rat lateral fluid percussion injury (FPI) model of severe TBI with an acute mortality rate of 46.7%. A subset of rats was treated with 25 mg/kg caffeine intraperitoneally within 1 minute of the injury. We assessed neuromotor function at 24 hours and 4 weeks, and video-EEG activity and histology at 4 weeks following injury. We first demonstrate that acute mortality is related to prolonged apnea and that a single acute injection of the adenosine receptor antagonist caffeine can completely prevent TBI-induced mortality when given immediately following the TBI. Second, we demonstrate that neuromotor function is not affected by caffeine treatment at either 24 hours or 4 weeks following injury. Third, we demonstrate development of epileptiform EEG bursts as early as 4 weeks post-injury that are significantly reduced in duration in the rats that received caffeine. Our data demonstrate that acute treatment with caffeine can prevent lethal apnea following fluid percussion injury, with no negative influence on motor function or histological outcome. Further, we show epileptiform bursting is reduced after caffeine treatment, suggesting a potential role in the modulation of epilepsy development after severe injury.

Abstract

Functional recovery is markedly restricted following traumatic brain injury (TBI), partly due to myelin-associated inhibitors including Nogo-A, myelin-associated glycoprotein (MAG) and oligodendrocyte myelin glycoprotein (OMgp), that all bind to the Nogo-66 receptor-1 (NgR1). In previous studies, pharmacological neutralization of both Nogo-A and MAG improved outcome following TBI in the rat, and neutralization of NgR1 improved outcome following spinal cord injury and stroke in rodent models. However, the behavioral and histological effects of NgR1 inhibition have not previously been evaluated in TBI. We hypothesized that NgR1 negatively influences behavioral recovery following TBI, and evaluated NgR1−/− mice (NgR1−/− study) and, in a separate study, soluble NgR1 infused intracerebroventricularly immediately post-injury to neutralize NgR1 (sNgR1 study) following TBI in mice using a controlled cortical impact (CCI) injury model. In both studies, motor function, TBI-induced loss of tissue, and hippocampal β-amyloid immunohistochemistry were not altered up to 5 weeks post-injury. Surprisingly, cognitive function (as evaluated with the Morris water maze at 4 weeks post-injury) was significantly impaired both in NgR1−/− mice and in mice treated with soluble NgR1. In the sNgR1 study, we evaluated hippocampal mossy fiber sprouting using the Timm stain and found it to be increased at 5 weeks following TBI. Neutralization of NgR1 significantly increased mossy fiber sprouting in sham-injured animals, but not in brain-injured animals. Our data suggest a complex role for myelin-associated inhibitors in the behavioral recovery process following TBI, and urge caution when inhibiting NgR1 in the early post-injury period.

Traumatic brain injury (TBI) causes selective hippocampal cell death which is believed to be associated with the cognitive impairment observed in both clinical and experimental settings. The endogenous neurotrophin NT-4/5, a TrkB ligand, has been shown to be neuroprotective for vulnerable CA3 pyramidal neurons after experimental brain injury. In this study, infusion of recombinant NT-4/5 increased survival of CA2/3 pyramidal neurons to 71% after lateral fluid percussion injury in rats, compared to 55% in vehicle-treated controls. The functional outcome of this NT-4/5-mediated neuroprotection was examined using three hippocampal-dependent behavioral tests. Injury-induced impairment was evident in all three tests, but interestingly, there was no treatment-related improvement in any of these measures. Similarly, injury-induced decreased excitability in the Schaffer collaterals was not affected by NT-4/5 treatment. We propose that a deeper understanding of the factors that link neuronal survival to recovery of function will be important for future studies of potentially therapeutic agents.

Objectives

Antipsychotics are routinely administered to traumatic brain injured (TBI) patients even though the benefits vs. risks of this approach on behavioral recovery are unclear. To clarify the issue, the present study evaluated the effect of single and multiple administrations of haloperidol and risperidone on functional outcome after TBI.

Design

Prospective and randomized study in rodents.

Setting

Experimental research laboratory at the University of Pittsburgh.

Subjects

Sixty adult male Sprague-Dawley rats weighing 300–325 g.

Interventions

Anesthetized rats received either a cortical impact or sham injury and then were randomly assigned to five TBI groups (risperidone 0.045 mg/kg, 0.45 mg/kg, 4.5 mg/kg, haloperidol 0.5 mg/kg, or vehicle 1 mL/kg) or three sham groups (risperidone 4.5 mg/kg, haloperidol 0.5 mg/kg, or vehicle 1 mL/kg). The experiment consisted of three phases. In the first phase, a single treatment was provided (i.p.) 24 hr after surgery and motor and cognitive function was assessed on post-operative days 1–5 and 14–18, respectively. During the second phase, after completion of the initial behavioral tasks, the same rats were treated once daily for 5 days and behavior was reevaluated. During the third phase, treatments were discontinued and 3 days later the rats were assessed one final time.

Measurements and Main Results

Time (sec) to maintain beam balance, traverse an elevated beam, and to locate a submerged platform in a Morris water maze. Neither motor nor cognitive performance was affected after a single treatment, regardless of group assignment (p > 0.05). In contrast, both behavioral deficits reoccurred after daily treatments of risperidone (4.5 mg/kg) and haloperidol (p < 0.05). The cognitive deficits persisted even after a 3-day washout period during the third phase.

Conclusions

These data suggest that while single or multiple low doses of risperidone and haloperidol may be innocuous to subsequent recovery after TBI, chronic high-dose treatments are detrimental.

Antipsychotics are often administered to traumatic brain injured (TBI) patients as a means of controlling agitation, albeit the rehabilitative consequences of this intervention are not well known. Hence, the goal of this study was to evaluate the effects of risperidone (RISP) and haloperidol (HAL) on behavioral outcome after experimental TBI. Anesthetized rats received either a cortical impact or sham injury and then were randomly assigned to five TBI (RISP 0.045 mg/kg, RISP 0.45 mg/kg, RISP 4.5 mg/kg, HAL 0.5 mg/kg, VEHicle 1 mL/kg) and three Sham (RISP 4.5 mg/kg, HAL 0.5 mg/kg, VEH 1 mL/kg) groups. Treatments began 24 hrs after surgery and were provided once daily for 19 days. Behavior was assessed with established motor (beam-balance/walk) and cognitive (spatial learning/memory in a water maze) tasks on post-operative days 1–5 and 14–19, respectively. RISP and HAL delayed motor recovery, impaired the acquisition of spatial learning, and slowed swim speed relative to VEH in both TBI and sham groups. These data indicate that chronic administration of RISP and HAL impede behavioral recovery after TBI and impair performance in uninjured controls.

Erythropoietin (EPO) and its receptor (EPOR), essential for erythropoiesis, are expressed in the nervous system. Recombinant human EPO treatment promotes functional outcome after traumatic brain injury (TBI) and stroke, suggesting that the endogenous EPO/EPOR system plays an important role in neuroprotection and neurorestoration. This study was designed to investigate effects of the EPOR on histological and functional outcomes after TBI. Experimental TBI was induced in adult EPOR-null and wild-type mice by controlled cortical impact. Neurological function was assessed using the modified Morris Water Maze and footfault tests. Animals were sacrificed 35 days after injury and brain sections stained for immunohistochemistry. As compared to the wild-type injured mice, EPOR-null mice did not exhibit higher susceptibility to TBI as exemplified by tissue loss in the cortex, cell loss in the dentate gyrus, impaired spatial learning, angiogenesis and cell proliferation. We observed that less cortical neurogenesis occurred and that sensorimotor function (i.e., footfault) was more impaired in the EPOR-null mice after TBI. Co-accumulation of amyloid precursor protein (axonal injury marker) and calcium was observed in the ipsilateral thalamus in both EPOR-null and wild-type mice after TBI with more calcium deposits present in the wild-type mice. This study demonstrates for the first time that EPOR null in the nervous system aggravates sensorimotor deficits, impairs cortical neurogenesis and reduces thalamic calcium precipitation after TBI.

Biologic sex and sex steroids are important factors in clinical and experimental stroke and traumatic brain injury (TBI). Laboratory data strongly show that progesterone treatment after TBI reduces edema, improves outcomes and restores blood brain barrier function. Clinical studies to date agree with these data, and there are ongoing human trials for progesterone treatment after TBI. Estrogen has accumulated an impressive reputation as a neuroprotectant when evaluated at physiologically relevant doses in laboratory studies of stroke, but translation to patients remains to be shown. The role of androgens in male stroke or TBI is understudied and important to pursue given the epidemiology of stroke and trauma in men. To date, male sex steroids remain largely evaluated at the bench rather than the bedside. This review evaluates key evidence and highlights the importance of the platform on which brain injury occurs, i.e. genetic sex and hormonal modulators.