Role of endothelin-1 in age-dependent cerebrovascular hypotensive responses after brain injury

Inhaled Nitric Oxide Protects Cerebral Autoregulation and Reduces Hippocampal Necrosis After Traumatic Brain Injury Through Inhibition of ET-1, ERK MAPK and IL-6 Upregulation in Pigs

OBJECTIVE

Traumatic brain injury (TBI) is an important contributor to morbidity and mortality. Cerebral autoregulation is impaired after TBI, contributing to poor outcome. Extracellular signal-related kinase (ERK) mitogen activated protein kinase (MAPK) and ET-1 are upregulated and contribute to impairment of cerebral autoregulation and histopathology after porcine fluid percussion brain injury (FPI). Recent studies show that inhaled nitric oxide (iNO) prevents impairment of cerebral autoregulation and histopathology after FPI in pigs. Unrelated studies indicated an association between ERK and increased IL-6 after FPI. However, the role of IL-6 in central nervous system (CNS) pathology is not well understood. We investigated whether iNO protects autoregulation and limits histopathology after FPI in pigs due to modulation of brain injury associated upregulation of ET-1, ERK MAPK, and IL-6.

METHODS

Lateral FPI was produced in anesthetized pigs equipped with a closed cranial window and iNO administered at 30 min or 2 h post injury.

RESULTS

CSF ET-1, ERK MAPK, and IL-6 were increased by FPI, but release was blocked by iNO administered at 30 min or 2 h after TBI. The IL-6 antagonist LMT-28 prevented impairment of cerebral autoregulation and hippocampal CA1 and CA3 neuronal necrosis after FPI. Papaverine induced dilation was unchanged by FPI and LMT-28. Protection lasted for at least 2 h after iNO administration was stopped.

CONCLUSIONS

These data indicate that iNO protects cerebral autoregulation and reduces hippocampal necrosis after traumatic brain injury through inhibition of ET-1, ERK MAPK, and IL-6 upregulation in pigs.

The pig as a preclinical traumatic brain injury model: current models, functional outcome measures, and translational detection strategies

Traumatic brain injury (TBI) is a major contributor of long-term disability and a leading cause of death worldwide. A series of secondary injury cascades can contribute to cell death, tissue loss, and ultimately to the development of functional impairments. However, there are currently no effective therapeutic interventions that improve brain outcomes following TBI. As a result, a number of experimental TBI models have been developed to recapitulate TBI injury mechanisms and to test the efficacy of potential therapeutics. The pig model has recently come to the forefront as the pig brain is closer in size, structure, and composition to the human brain compared to traditional rodent models, making it an ideal large animal model to study TBI pathophysiology and functional outcomes. This review will focus on the shared characteristics between humans and pigs that make them ideal for modeling TBI and will review the three most common pig TBI models-the diffuse axonal injury, the controlled cortical impact, and the fluid percussion models. It will also review current advances in functional outcome assessment measures and other non-invasive, translational TBI detection and measurement tools like biomarker analysis and magnetic resonance imaging. The use of pigs as TBI models and the continued development and improvement of translational assessment modalities have made significant contributions to unraveling the complex cascade of TBI sequela and provide an important means to study potential clinically relevant therapeutic interventions.

Inhaled Nitric Oxide Protects Cerebral Autoregulation and Reduces Hippocampal Necrosis After Traumatic Brain Injury Through Inhibition of ET-1, ERK MAPK and IL-6 Upregulation in Pigs

OBJECTIVE

Traumatic brain injury (TBI) is an important contributor to morbidity and mortality. Cerebral autoregulation is impaired after TBI, contributing to poor outcome. Extracellular signal-related kinase (ERK) mitogen activated protein kinase (MAPK) and ET-1 are upregulated and contribute to impairment of cerebral autoregulation and histopathology after porcine fluid percussion brain injury (FPI). Recent studies show that inhaled nitric oxide (iNO) prevents impairment of cerebral autoregulation and histopathology after FPI in pigs. Unrelated studies indicated an association between ERK and increased IL-6 after FPI. However, the role of IL-6 in central nervous system (CNS) pathology is not well understood. We investigated whether iNO protects autoregulation and limits histopathology after FPI in pigs due to modulation of brain injury associated upregulation of ET-1, ERK MAPK, and IL-6.

METHODS

Lateral FPI was produced in anesthetized pigs equipped with a closed cranial window and iNO administered at 30 min or 2 h post injury.

RESULTS

CSF ET-1, ERK MAPK, and IL-6 were increased by FPI, but release was blocked by iNO administered at 30 min or 2 h after TBI. The IL-6 antagonist LMT-28 prevented impairment of cerebral autoregulation and hippocampal CA1 and CA3 neuronal necrosis after FPI. Papaverine induced dilation was unchanged by FPI and LMT-28. Protection lasted for at least 2 h after iNO administration was stopped.

CONCLUSIONS

These data indicate that iNO protects cerebral autoregulation and reduces hippocampal necrosis after traumatic brain injury through inhibition of ET-1, ERK MAPK, and IL-6 upregulation in pigs.

Immature endothelial cells initiate endothelin-mediated constriction of newborn arteries

KEY POINTS

Endothelial expression and the release of endothelin-1 (ET-1) in levels sufficient to initiate vasoconstriction is considered to be a hallmark feature of pathological endothelial dysfunction. During the immediate postnatal period, arterial endothelial cells undergo remarkable structural and functional changes as they transition to a mature protective cell layer, which includes a marked increase in NO dilator activity. The present study demonstrates that endothelial cells lining newborn central arteries express high levels of ET-1 peptides and, in response to endothelial stimulation, rapidly release ET-1 and initiate powerful ET-1-mediated constriction. This activity is lost as the endothelium matures in the postnatal period. Heightened activity of ET-1 in the neonatal endothelium might contribute to inappropriate responses of immature arteries to stress or injury. Indeed, the immature endothelium resembles dysfunctional endothelial cells, and retention or re-emergence of this phenotype may contribute to the development of vascular disease.

ABSTRACT

Endothelial cells lining fetal and newborn arteries have an unusual phenotype, including reduced NO activity, prominent actin stress fibres and poorly developed cellular junctions. Experiments were performed to determine whether the immature endothelium of newborn arteries also expresses and releases endothelin-1 (ET-1) and initiates endothelium-dependent constriction. Carotid arteries were isolated from newborn (postnatal day 1; P1), postnatal day 7 (P7) and postnatal day 21 (P21) mice and assessed in a pressure myograph system. Endothelial stimulation with A23187 or thrombin caused constriction in P1 arteries, no significant change in diameter of P7 arteries, and dilatation in P21 arteries. In P1 arteries, constriction to thrombin or A23187 was inhibited by endothelial-denudation, by ET-1 receptor antagonists (BQ123 plus BQ788) or by inhibition of endothelin-converting enzyme (phosphoramidon or SM19712). ET-1 receptor antagonism did not affect responses to thrombin or A23187 in more mature arteries. Exogenous ET-1 caused similar concentration-dependent constrictions of P1, P7 and P21 arteries. Endothelial stimulation with thrombin rapidly increased the endothelial release of ET-1 from P1 but not P21 aortas. Endothelial expression of ET-1 peptides, as assessed by immunofluorescence analysis, was increased in P1 compared to P21 arteries. Therefore, newborn endothelial cells express high levels of ET-1 peptides, rapidly release ET-1 in response to endothelial stimulation, and initiate ET-1-mediated endothelium-dependent constriction. This activity is diminished as the endothelium matures in the immediate postnatal period. Heightened activity of ET-1 in neonatal endothelium probably reflects an early developmental role of the peptide, although this might contribute to inappropriate responses of immature arteries to stress or injury.

Long-Term Effects of Enriched Environment on Neurofunctional Outcome and CNS Lesion Volume After Traumatic Brain Injury in Rats

To determine whether the exposure to long term enriched environment (EE) would result in a continuous improvement of neurological recovery and ameliorate the loss of brain tissue after traumatic brain injury (TBI) vs. standard housing (SH). Male Sprague-Dawley rats (300-350 g, n=28) underwent lateral fluid percussion brain injury or SHAM operation. One TBI group was held under complex EE for 90 days, the other under SH. Neuromotor and sensorimotor dysfunction and recovery were assessed after injury and at days 7, 15, and 90 via Composite Neuroscore (NS), RotaRod test, and Barnes Circular Maze (BCM). Cortical tissue loss was assessed using serial brain sections. After day 7 EE animals showed similar latencies and errors as SHAM in the BCM. SH animals performed notably worse with differences still significant on day 90 (p<0.001). RotaRod test and NS revealed superior results for EE animals after day 7. The mean cortical volume was significantly higher in EE vs. SH animals (p=0.003). In summary, EE animals after lateral fluid percussion (LFP) brain injury performed significantly better than SH animals after 90 days of recovery. The window of opportunity may be wide and also lends further credibility to the importance of long term interventions in patients suffering from TBI.

A neurovascular perspective for long-term changes after brain trauma

Traumatic brain injury (TBI) affects all age groups in a population and is an injury generating scientific interest not only as an acute event, but also as a complex brain disease with several underlying neurobehavioral and neuropathological characteristics. We review early and long-term alterations after juvenile and adult TBI with a focus on changes in the neurovascular unit (NVU), including neuronal interactions with glia and blood vessels at the blood-brain barrier (BBB). Post-traumatic changes in cerebral blood-flow, BBB structures and function, as well as mechanistic pathways associated with brain aging and neurodegeneration are presented from clinical and experimental reports. Based on the literature, increased attention on BBB changes should be integrated in studies characterizing TBI outcome and may provide a meaningful therapeutic target to resolve detrimental post-traumatic dysfunction.

Dopamine prevents impairment of autoregulation after traumatic brain injury in the newborn pig through inhibition of Up-regulation of endothelin-1 and extracellular signal-regulated kinase mitogen-activated protein kinase

OBJECTIVE

Traumatic brain injury contributes to morbidity in children and boys are disproportionately represented. Autoregulation is impaired more in male compared with female piglets after traumatic brain injury through sex-dependent up-regulation of the spasmogen endothelin-1 and extracellular signal-regulated kinase (ERK) mitogen-activated protein kinase (MAPK), a family of three kinases: ERK, p38, and JNK). Elevation of mean arterial pressure leading to increased cerebral perfusion pressure via phenylephrine improves impairment of autoregulation after traumatic brain injury in female but not male piglets through modulation of endothelin-1 and ERK MAPK up-regulation, blocked in females, but aggravated in males. We hypothesized that pressor choice to elevate cerebral perfusion pressure is important in improving cerebral hemodynamics after traumatic brain injury and that dopamine will prevent impairment of autoregulation in both male and female piglets through blockade of endothelin-1 and ERK MAPK.

DESIGN

Prospective, randomized animal study.

SETTING

University laboratory.

SUBJECTS

Newborn (1-5 days old) pigs.

INTERVENTIONS

Cerebral perfusion pressure and pial artery diameter were determined before and after lateral fluid percussion brain injury was produced in piglets equipped with a closed cranial window. Dopamine (15 µg/kg/min IV) was administered 30 mins post fluid percussion injury. Cerebrospinal fluid ERK MAPK was determined by enzyme-linked immunosorbent assay.

MEASUREMENTS AND MAIN RESULTS

Dopamine increased cerebral perfusion pressure equivalently in both sexes and prevented sex-dependent reductions in pial artery diameter after fluid percussion injury. Loss of pial artery dilation during hypotension was greater in male than in female piglets after fluid percussion injury, but dopamine prevented such impairment equivalently in both sexes post injury. endothelin-1 and ERK MAPK release was greater in male compared to female piglets after fluid percussion injury, but dopamine also blocked their up-regulation equivalently in male and female piglets after fluid percussion injury.

CONCLUSIONS

These data indicate that dopamine is protective of autoregulation after fluid percussion injury in both sexes. These observations advocate for the consideration of development of sex based therapies for treatment of hemodynamic sequalae of pediatric traumatic brain injury.

Endothelin and the neurovascular unit in pediatric traumatic brain injury

OBJECTIVE

This study characterized the association between endothelin-1, cerebral hemodynamics, and histopathology after fluid percussion brain injury in the newborn pig.

METHODS

Lateral fluid percussion injury was induced in newborn pigs equipped with a closed cranial window. Cerebral blood flow was determined with radiolabeled microspheres and cerebrospinal fluid endothelin-1 was measured by radioimmunoassay.

RESULTS

Cerebrospinal fluid endothelin-1 was increased from 26±4 to 296±37 pg/ml (∼10(-10) M) at 8 hours following fluid percussion injury. Post-injury treatment (30 minutes) with the endothelin-1 antagonist BQ-123 (1 mg/kg, intravenous) blocked pial artery vasoconstriction to topical endothelin-1 (∼10(-10) M) and blunted fluid percussion injury-induced reductions in cerebral blood flow at 8 hours post-insult (56±6 and 26±4 ml/minute versus 57±6 and 40± ml/minute; 100 g for cerebral blood flow before injury and 8 hours post-fluid percussion injury in vehicle and BQ-123 post-treated animals, respectively). Fluid percussion injury resulted in neuronal cell loss and decreased microtubule associated protein 2 immunoreactivity in the parietal cortex, which were blunted by BQ-123.

DISCUSSION

These data indicate that fluid percussion injury-induced changes in cerebral hemodynamics are associated with neuronal damage and that endothelin-1 contributes to fluid percussion injury-induced histopathologic changes.

TBI sex dependently upregulates ET-1 to impair autoregulation, which is aggravated by phenylephrine in males but is abrogated in females

Traumatic brain injury (TBI) contributes to morbidity in children, and boys are disproportionately represented. Endothelin-1 (ET-1) contributes to impaired autoregulation via oxygen (O₂⁻) after TBI in piglets, but its relative role in males compared with females has not been previously investigated. Increased cerebral perfusion pressure (CPP) via phenylephrine (Phe) sex dependently improves impairment of autoregulation after TBI through modulation of extracellular signal-related kinase (ERK) mitogen-activated protein kinase (MAPK) upregulation, aggravated in males, but blocked in females. Activation of adenosine-5'-triphosphate (ATP) and Ca sensitive K channels produce vasodilation, contributing to autoregulation. We hypothesized that ET-1 upregulation is greater in males after TBI and that disturbed autoregulation will be prevented by Phe in a sex-dependent manner through modulation of ET-1, O₂⁻, and ERK. Results show that ET-1 release was greater in males after fluid percussion injury (FPI), blunted by Phe in females, but aggravated in males. K channel vasodilation was impaired more in males than in females after TBI. Phe prevented reductions in K channel vasodilation in females, but further reduced dilation in males after TBI. Co-administration of BQ-123, U0126, or PEG-SOD (ET-1, ERK antagonist, and O₂⁻ scavenger) with Phe restored dilation to K agonists and hypotension in males after TBI. ERK upregulation was blocked by BQ-123 and PEG-SOD. These data indicate that TBI upregulates ET-1 more in males than in females. Elevation of CPP with Phe sex dependently prevents impairment of cerebral autoregulation after TBI through modulation of ET-1, O₂⁻, and ERK mediated impairment of K channel vasodilation. These observations advocate for the consideration of development of sex-based therapies for the treatment of hemodynamic sequelae of pediatric TBI.

Cerebrovascular connexin expression: effects of traumatic brain injury

Traumatic brain injury (TBI) results in dysfunction of the cerebrovasculature. Gap junctions coordinate vasomotor responses and evidence suggests that they are involved in cerebrovascular dysfunction after TBI. Gap junctions are comprised of connexin proteins (Cxs), of which Cx37, Cx40, Cx43, and Cx45 are expressed in vascular tissue. This study tests the hypothesis that TBI alters Cx mRNA and protein expression in cerebral vascular smooth muscle and endothelial cells. Anesthetized (1.5% isoflurane) male Sprague-Dawley rats received sham or fluid-percussion TBI. Two, 6, and 24 h after, cerebral arteries were harvested, fresh-frozen for RNA isolation, or homogenized for Western blot analysis. Cerebral vascular endothelial and smooth muscle cells were selected from frozen sections using laser capture microdissection. RNA was quantified by ribonuclease protection assay. The mRNA for all four Cx genes showed greater expression in the smooth muscle layer compared to the endothelial layer. Smooth muscle Cx43 mRNA expression was reduced 2  h and endothelial Cx45 mRNA expression was reduced 24  h after injury. Western blot analysis revealed that Cx40 protein expression increased, while Cx45 protein expression decreased 24  h after injury. These studies revealed significant changes in the mRNA and protein expression of specific vascular Cxs after TBI. This is the first demonstration of cell type-related differential expression of Cx mRNA in cerebral arteries, and is a first step in evaluating the effects of TBI on gap junction communication in the cerebrovasculature.

Impaired cerebral blood flow autoregulation during posttraumatic arterial hypotension after fluid percussion brain injury is prevented by phenylephrine in female but exacerbated in male piglets by extracellular signal-related kinase mitogen-activated protein kinase upregulation

OBJECTIVE

Traumatic brain injury contributes to morbidity and mortality in children and boys are disproportionately represented. Hypotension is common and worsens outcome after traumatic brain injury. Extracellular signal-related kinase mitogen-activated protein kinase is upregulated and reduces cerebral blood flow after fluid percussion brain injury in piglets. We hypothesized that increased cerebral perfusion pressure through phenylephrine sex dependently reduces impairment of cerebral autoregulation during hypotension after fluid percussion brain injury through modulation of extracellular signal-related kinase mitogen-activated protein kinase.

DESIGN

Prospective, randomized animal study.

SETTING

University laboratory.

SUBJECTS

Newborn (1- to 5-day-old) pigs.

INTERVENTIONS

Cerebral blood flow, pial artery diameter, intracranial pressure, and autoregulatory index were determined before and after fluid percussion brain injury in untreated, preinjury, and postinjury phenylephrine (1 microg/kg/min intravenously) treated male and female pigs during normotension and hemorrhagic hypotension. Cerebrospinal fluid extracellular signal-related kinase mitogen-activated protein kinase was determined by enzyme-linked immunosorbent assay.

MEASUREMENTS AND MAIN RESULTS

Reductions in pial artery diameter, cerebral blood flow, cerebral perfusion pressure, and elevated intracranial pressure after fluid percussion brain injury were greater in males, which were blunted by phenylephrine pre- or postfluid percussion brain injury. During hypotension and fluid percussion brain injury, pial artery dilation was impaired more in males. Phenylephrine decreased impairment of hypotensive pial artery dilation after fluid percussion brain injury in females, but paradoxically caused vasoconstriction after fluid percussion brain injury in males. Papaverine-induced pial artery vasodilation was unchanged by fluid percussion brain injury and phenylephrine. Cerebral blood flow, cerebral perfusion pressure, and autoregulatory index decreased markedly during hypotension and fluid percussion brain injury in males but less in females. Phenylephrine prevented reductions in cerebral blood flow, cerebral perfusion pressure, and autoregulatory index during hypotension in females but increased reductions in males. Cerebrospinal fluid extracellular signal-related kinase mitogen-activated protein kinase was increased more in males than females after fluid percussion brain injury. Phenylephrine blunted extracellular signal-related kinase mitogen-activated protein kinase upregulation in females but increased extracellular signal-related kinase mitogen-activated protein kinase upregulation in males after fluid percussion brain injury.

CONCLUSIONS

These data indicate that elevation of cerebral perfusion pressure with phenylephrine sex dependently prevents impairment of cerebral autoregulation during hypotension after fluid percussion brain injury through modulation of extracellular signal-related kinase mitogen-activated protein kinase. These data suggest the potential role for sex-dependent mechanisms in cerebral autoregulation after pediatric traumatic brain injury.

Adrenomedullin prevents sex-dependent impairment of autoregulation during hypotension after piglet brain injury through inhibition of ERK MAPK upregulation

Cerebrospinal fluid (CSF) adrenomedullin (ADM) levels are increased in female, but remain unchanged in male, piglets after fluid percussion injury (FPI) of the brain. Subthreshold vascular concentrations of ADM restore impaired hypotensive pial artery dilation after FPI more in males than females. Extracellular signal-related kinase (ERK) mitogen-activated protein kinase (MAPK) is upregulated and contributes to reductions in cerebral blood flow (CBF) after FPI. We hypothesized that ADM prevents sex-dependent impairment of autoregulation during hypotension after FPI through inhibition of ERK MAPK upregulation. FPI increased ERK MAPK more in males than in females. CBF was unchanged during hypotension in sham animals, was reduced more in males than in females after FPI during normotension, and was further reduced in males than in females during hypotension and after FPI. ADM and the ERK MAPK antagonist U 0126 prevented reductions in CBF during hypotension and FPI more in males than in females. Transcranial Doppler (TCD) blood flow velocity was unchanged during hypotension in sham animals, was decreased during hypotension and FPI in male but not in female pigs, and was ameliorated by ADM. Intracranial pressure (ICP) was increased after FPI more in male than in female animals. ADM blunted elevated ICP during FPI and hypotension in males, but not in females. ADM prevented reductions in cerebral perfusion pressure (CPP) during FPI and hypotension in males but not in females. The calculated autoregulatory index was unchanged during hypotension in sham animals, but was reduced more in males than females during hypotension and FPI. ADM prevented reductions in autoregulation during hypotension and FPI more in males than females. These data indicate that ADM prevented loss of cerebral autoregulation after FPI in a sex-dependent and ERK MAPK-dependent manner.

Signaling, delivery and age as emerging issues in the benefit/risk ratio outcome of tPA For treatment of CNS ischemic disorders

Stroke is a leading cause of morbidity and mortality. While tissue-type plasminogen activator (tPA) remains the only FDA-approved treatment for ischemic stroke, clinical use of tPA has been constrained to roughly 3% of eligible patients because of the danger of intracranial hemorrhage and a narrow 3 h time window for safe administration. Basic science studies indicate that tPA enhances excitotoxic neuronal cell death. In this review, the beneficial and deleterious effects of tPA in ischemic brain are discussed along with emphasis on development of new approaches toward treatment of patients with acute ischemic stroke. In particular, roles of tPA-induced signaling and a novel delivery system for tPA administration based on tPA coupling to carrier red blood cells will be considered as therapeutic modalities for increasing tPA benefit/risk ratio. The concept of the neurovascular unit will be discussed in the context of dynamic relationships between tPA-induced changes in cerebral hemodynamics and histopathologic outcome of CNS ischemia. Additionally, the role of age will be considered since thrombolytic therapy is being increasingly used in the pediatric population, but there are few basic science studies of CNS injury in pediatric animals.

New concepts in treatment of pediatric traumatic brain injury

Emerging evidence suggests unique age-dependent responses following pediatric traumatic brain injury. The anesthesiologist plays a pivotal role in the acute treatment of the head-injured pediatric patient. This review provides important updates on the pathophysiology, diagnosis, and age-appropriate acute management of infants and children with severe traumatic brain injury. Areas of important clinical and basic science investigations germane to the anesthesiologist, such as the role of anesthetics and apoptosis in the developing brain, are discussed.

Cerebral blood flow and autoregulation after pediatric traumatic brain injury

Traumatic brain injury is a global health concern and is the leading cause of traumatic morbidity and mortality in children. Despite a lower overall mortality than in adult traumatic brain injury, the cost to society from the sequelae of pediatric traumatic brain injury is very high. Predictors of poor outcome after traumatic brain injury include altered systemic and cerebral physiology, including altered cerebral hemodynamics. Cerebral autoregulation is often impaired after traumatic brain injury and may adversely impact the outcome. Although altered cerebrovascular hemodynamics early after traumatic brain injury may contribute to disability in children, there is little information regarding changes in cerebral blood flow and cerebral autoregulation after pediatric traumatic brain injury. This review addresses normal pediatric cerebral physiology and cerebrovascular pathophysiology after pediatric traumatic brain injury.

Lateral fluid percussion brain injury: a 15-year review and evaluation

This article comprehensively reviews the lateral fluid percussion (LFP) model of traumatic brain injury (TBI) in small animal species with particular emphasis on its validity, clinical relevance and reliability. The LFP model, initially described in 1989, has become the most extensively utilized animal model of TBI (to date, 232 PubMed citations), producing both focal and diffuse (mixed) brain injury. Despite subtle variations in injury parameters between laboratories, universal findings are evident across studies, including histological, physiological, metabolic, and behavioral changes that serve to increase the reliability of the model. Moreover, demonstrable histological damage and severity-dependent behavioral deficits, which partially recover over time, validate LFP as a clinically-relevant model of human TBI. The LFP model, also has been used extensively to evaluate potential therapeutic interventions, including resuscitation, pharmacologic therapies, transplantation, and other neuroprotective and neuroregenerative strategies. Although a number of positive studies have identified promising therapies for moderate TBI, the predictive validity of the model may be compromised when findings are translated to severely injured patients. Recently, the clinical relevance of LFP has been enhanced by combining the injury with secondary insults, as well as broadening studies to incorporate issues of gender and age to better approximate the range of human TBI within study design. We conclude that the LFP brain injury model is an appropriate tool to study the cellular and mechanistic aspects of human TBI that cannot be addressed in the clinical setting, as well as for the development and characterization of novel therapeutic interventions. Continued translation of pre-clinical findings to human TBI will enhance the predictive validity of the LFP model, and allow novel neuroprotective and neuroregenerative treatment strategies developed in the laboratory to reach the appropriate TBI patients.

Traumatic Cerebral Vascular Injury: The Effects of Concussive Brain Injury on the Cerebral Vasculature

In terms of human suffering, medical expenses, and lost productivity, head injury is one of the major health care problems in the United States, and inadequate cerebral blood flow is an important contributor to mortality and morbidity after traumatic brain injury. Despite the importance of cerebral vascular dysfunction in the pathophysiology of traumatic brain injury, the effects of trauma on the cerebral circulation have been less well studied than the effects of trauma on the brain. Recent research has led to a better understanding of the physiologic, cellular, and molecular components and causes of traumatic cerebral vascular injury. A more thorough understanding of the direct and indirect effects of trauma on the cerebral vasculature will lead to improvements in current treatments of brain trauma as well as to the development of novel and, hopefully, more effective therapeutic strategies.

Differential role of PTK and ERK MAPK in superoxide impairment of K(ATP) and K(Ca) channel cerebrovasodilation

Previously, superoxide (O2 -) has been observed to impair pial artery dilation (PAD) to activators of the ATP-sensitive (KATP) and calcium-sensitive (KCa) K+ channels. This study tested the hypothesis that activation of protein tyrosine kinase (PTK) and the ERK isoform of MAPK by O2 - contribute to impairment of KATP and KCa channel PAD. Exposure of the cerebral cortex to a xanthine oxidase O2 --generating system (OX) blunted PAD to cromakalim, a KATP agonist, but preadministration of genistein, a PTK antagonist, or U-0126, an ERK MAPK inhibitor, almost completely prevented such impairment (11 +/- 1 and 22 +/- 1 vs. 3 +/- 1 and 7 +/- 1 vs. 10 +/- 1 and 16 +/- 2% for cromakalim with 10-8 and 10-6 M PAD during control, OX, and OX + genistein conditions). In contrast, neither genistein nor U-0126 robustly protected PAD to NS-1619, a KCa agonist, after OX exposure (11 +/- 1 and 18 +/- 2 vs. 1 +/- 1 and 2 +/- 1 vs. 4 +/- 1 and 6 +/- 1% for 10-8 and 10-6 M NS-1619 during control, OX, and OX + genistein conditions). These data show that PTK and ERK MAPK activation contribute to O2 --induced KATP and KCa channel PAD impairment and suggest a differential greater role for PTK and ERK MAPK in KATP vs. KCa channel PAD impairment.

Developing experimental models to address traumatic brain injury in children

Traumatic brain injury (TBI) is the leading cause of injury-related death and disability among children under the age of 15 years in the United States. Epidemiological studies have revealed that even within the pediatric population there are differences in incidence, gender differences, causes, types of injuries sustained, and mortality within age subdivisions. This heterogeneity must be taken into account when developing appropriate models to address TBI in children. This review explores the current developmental TBI models, including fluid percussion, weight drop, and controlled cortical impact. It also addresses unique considerations to modeling pediatric brain injury that require special attention when modeling and designing studies: age appropriateness, injury severity, evaluation of recovery, plasticity, and anesthesia.