Adrenomedullin reduces gender-dependent loss of hypotensive cerebrovasodilation after newborn brain injury through activation of ATP-dependent K channels

Neuroprotection or Sex Bias: A Protective Response to Traumatic Brain Injury in the Females

Traumatic brain injury (TBI) is a major healthcare problem and a common cause of mortality and morbidity. Clinical and preclinical research suggests sex-related differences in short- and longterm outcomes following TBI; however, males have been the main focus of TBI research. Females show a protective response against TBI. Female animals in preclinical studies and women in clinical trials have shown comparatively better outcomes against mild, moderate, or severe TBI. This reflects a favorable protective nature of the females compared to the males, primarily attributed to various protective mechanisms that provide better prognosis and recovery in the females after TBI. Understanding the sex difference in the TBI pathophysiology and the underlying mechanisms remains an elusive goal. In this review, we provide insights into various mechanisms related to the anatomical, physiological, hormonal, enzymatic, inflammatory, oxidative, genetic, or mitochondrial basis that support the protective nature of females compared to males. Furthermore, we sought to outline the evidence of multiple biomarkers that are highly potential in the investigation of TBI's prognosis, pathophysiology, and treatment and which can serve as objective measures and novel targets for individualized therapeutic interventions in TBI treatment. Implementations from this review are important for the understanding of the effect of sex on TBI outcomes and possible mechanisms behind the favorable response in females. It also emphasizes the critical need to include females as a biological variable and in sufficient numbers in future TBI studies.

Mild Traumatic Brain Injury Induces Time- and Sex-Dependent Cerebrovascular Dysfunction and Stroke Vulnerability

Mild traumatic brain injury (mTBI) produces subtle cerebrovascular impairments that persist over time and promote increased ischemic stroke vulnerability. We recently established a role for vascular impairments in exacerbating stroke outcomes 1 week after TBI, but there is a lack of research regarding long-term impacts of mTBI-induced vascular dysfunction, as well as a significant need to understand how mTBI promotes stroke vulnerability in both males and females. Here, we present data using a mild closed head TBI model and an experimental stroke occurring either 7 or 28 days later in both male and female mice. We report that mTBI induces larger stroke volumes 7 days after injury, however, this increased vulnerability to stroke persists out to 28 days in female but not male mice. Importantly, mTBI-induced changes in blood-brain barrier permeability, intravascular coagulation, angiogenic factors, total vascular area, and glial expression were differentially altered across time and by sex. Taken together, these data suggest that mTBI can result in persistent cerebrovascular dysfunction and increased susceptibility to worsened ischemic outcomes, although these dysfunctions occur differently in male and female mice.

Determining Sex-Based Differences in Inflammatory Response in an Experimental Traumatic Brain Injury Model

Introduction

Traumatic brain injury is a leading cause of injury-related death and morbidity. Multiple clinical and pre-clinical studies have reported various results regarding sex-based differences in TBI. Our accepted rodent model of traumatic brain injury was used to identify sex-based differences in the pathological features of TBI.

Methods

Male and female Sprague-Dawley rats were subjected to either controlled-cortical impact (CCI) or sham injury; brain tissue was harvested at different time intervals depending on the specific study. Blood-brain barrier (BBB) analysis was performed using infrared imaging to measure fluorescence dye extravasation. Microglia and splenocytes were characterized with traditional flow cytometry; microglia markers such as CD45, P2Y12, CD32, and CD163 were analyzed with t-distributed stochastic neighbor embedding (t-SNE). Flow cytometry was used to study tissue cytokine levels, and supplemented with ELISAs of TNF-⍺, IL-17, and IL-1β of the ipsilateral hemisphere tissue.

Results

CCI groups of both sexes recorded a higher BBB permeability at 72 hours post-injury than their respective sham groups. There was significant difference in the integrated density value of BBB permeability between the male CCI group and the female CCI group (female CCI mean = 3.08 x 108 ± 2.83 x 107, male CCI mean = 2.20 x 108 ± 4.05 x 106, p = 0.0210), but otherwise no differences were observed. Traditional flow cytometry did not distinguish any sex-based difference in regards to splenocyte cell population after CCI. t-SNE did not reveal any significant difference between the male and female injury groups in the activation of microglia. Cytokine analysis after injury by flow cytometry and ELISA was limited in differences at the time point of 6 hours post-injury.

Conclusion

In our rodent model of traumatic brain injury, sex-based differences in pathology and neuroinflammation at specified time points are limited, and only noted in one specific analysis of BBB permeability.

Sex differences in traumatic brain injury: a multi-dimensional exploration in genes, hormones, cells, individuals, and society

Traumatic brain injury (TBI) is exceptionally prevalent in society and often imposes a massive burden on patients' families and poor prognosis. The evidence reviewed here suggests that gender can influence clinical outcomes of TBI in many aspects, ranges from patients' mortality and short-term outcome to their long-term outcome, as well as the incidence of cognitive impairment. We mainly focused on the causes and mechanisms underlying the differences between male and female after TBI, from both biological and sociological views. As it turns out that multiple factors contribute to the gender differences after TBI, not merely the perspective of gender and sex hormones. Centered on this, we discussed how female steroid hormones exert neuroprotective effects through the anti-inflammatory and antioxidant mechanism, along with the cognitive impairment and the social integration problems it caused. As to the treatment, both instant and long-term treatment of TBI requires adjustments according to gender. A further study with more focus on this topic is therefore suggested to provide better treatment options for these patients.

Translational approach towards determining the role of cerebral autoregulation in outcome after traumatic brain injury

Cerebral autoregulation is impaired after traumatic brain injury (TBI), contributing to poor outcome. In the context of the neurovascular unit, cerebral autoregulation contributes to neuronal cell integrity and clinically Glasgow Coma Scale is correlated to intactness of autoregulation after TBI. Cerebral Perfusion Pressure (CPP) is often normalized by use of vasoactive agents to increase mean arterial pressure (MAP) and thereby limit impairment of cerebral autoregulation and neurological deficits. However, current vasoactive agent choice used to elevate MAP to increase CPP after TBI is variable. Vasoactive agents, such as phenylephrine, dopamine, norepinephrine, and epinephrine, clinically have not sufficiently been compared regarding effect on CPP, autoregulation, and survival after TBI. The cerebral effects of these clinically commonly used vasoactive agents are incompletely understood. This review will describe translational studies using a more human like animal model (the pig) of TBI to identify better therapeutic strategies to improve outcome post injury. These studies also investigated the role of age and sex in outcome and mechanism(s) involved in improvement of outcome in the setting of TBI. Additionally, this review considers use of inhaled nitric oxide as a novel neuroprotective strategy in treatment of TBI.

Improving Understanding and Outcomes of Traumatic Brain Injury Using Bidirectional Translational Research

Recent clinical trials in traumatic brain injury (TBI) have failed to demonstrate therapeutic effects even when there appears to be good evidence for efficacy in one or more appropriate pre-clinical models. While existing animal models mimic the injury, difficulties in translating promising therapeutics are exacerbated by the lack of alignment of discrete measures of the underlying injury pathology between the animal models and human subjects. To address this mismatch, we have incorporated reverse translation of bedside experience to inform pre-clinical studies in a large animal (pig) model of TBI that mirror practical clinical assessments. Cerebral autoregulation is impaired after TBI, contributing to poor outcome. Cerebral perfusion pressure (CPP) is often normalized by use of vasoactive agents to increase mean arterial pressure (MAP) and thereby limit impairment of cerebral autoregulation and neurological deficits. Vasoactive agents clinically used to elevate MAP to increase CPP after TBI, such as phenylephrine (Phe), dopamine (DA), norepinephrine (NE), and epinephrine (EPI), however, have not been compared sufficiently regarding effect on CPP, autoregulation, and survival after TBI, and clinically, current vasoactive agent use is variable. The cerebral effects of these clinically commonly used vasoactive agents are not known. This review will emphasize pediatric work and will describe bidirectional translational studies using a more human-like animal model of TBI to identify better therapeutic strategies to improve outcome post-injury. These studies in addition investigated the mechanism(s) involved in improvement of outcome in the setting of TBI.

Sex Differences in Animal Models of Traumatic Brain Injury

Traumatic brain injury (TBI) is highly prevalent and there is currently no adequate treatment. Understanding the underlying mechanisms governing TBI and recovery remains an elusive goal. The heterogeneous nature of injury and individual's response to injury have made understanding risk and susceptibility to TBI of great importance. Epidemiologic studies have provided evidence of sex-dependent differences following TBI. However, preclinical models of injury have largely focused on adult male animals. Here, we review 50 studies that have investigated TBI in both sexes using animal models. Results from these studies are highly variable and model dependent, but largely show females to have a protective advantage in behavioral outcomes and pathology following TBI. Further research of both sexes using newer models that better recapitulate mild and repetitive TBI is needed to characterize the nature of sex-dependent injury and recovery, and ultimately identifies targets for enhanced recovery.

Dopamine protects cerebral autoregulation and prevents hippocampal necrosis after traumatic brain injury via block of ERK MAPK in juvenile pigs

Traumatic brain injury (TBI) contributes to morbidity in children, and more boys experience TBI. Cerebral autoregulation is impaired after TBI, contributing to poor outcome. Cerebral Perfusion Pressure (CPP) is often normalized by use of vasoactive agents to increase mean arterial pressure (MAP). In prior studies of newborn and juvenile pigs, vasoactive agent choice influenced outcome after TBI as a function of age and sex, with none protecting cerebral autoregulation in both ages and sexes. Dopamine (DA) prevents impairment of cerebral autoregulation in male and female newborn pigs via inhibition of upregulation of ERK mitogen activated protein kinase (MAPK) after fluid percussion injury (FPI). We investigated whether DA protects autoregulation and limits histopathology after FPI in juvenile pigs and the role of ERK in that outcome. Results show that DA protects autoregulation in both male and female juvenile pigs after FPI. Papaverine induced dilation was unchanged by FPI and DA. DA blunted ERK MAPK and prevented loss of neurons in CA1 and CA3 hippocampus of males and females after FPI. These data indicate that DA protects autoregulation and limits hippocampal neuronal cell necrosis via block of ERK after FPI in male and female juvenile pigs. Of the vasoactive agents prior investigated, including norepinephrine, epinephrine, and phenylephrine, DA is the only one demonstrated to improve outcome after TBI in both sexes and ages. These data suggest that DA should be considered as a first line treatment to protect cerebral autoregulation and promote cerebral outcomes in pediatric TBI irrespective of age and sex.

The Role of Neurogenic Inflammation in Blood-Brain Barrier Disruption and Development of Cerebral Oedema Following Acute Central Nervous System (CNS) Injury

Acute central nervous system (CNS) injury, encompassing traumatic brain injury (TBI) and stroke, accounts for a significant burden of morbidity and mortality worldwide, largely attributable to the development of cerebral oedema and elevated intracranial pressure (ICP). Despite this, clinical treatments are limited and new therapies are urgently required to improve patient outcomes and survival. Originally characterised in peripheral tissues, such as the skin and lungs as a neurally-elicited inflammatory process that contributes to increased microvascular permeability and tissue swelling, neurogenic inflammation has now been described in acute injury to the brain where it may play a key role in the secondary injury cascades that evolve following both TBI and stroke. In particular, release of the neuropeptides substance P (SP) and calcitonin gene-related peptide (CGRP) appear to be critically involved. In particular, increased SP expression is observed in perivascular tissue following acute CNS injury, with the magnitude of SP release being related to both the frequency and degree of the insult. SP release is associated with profound blood-brain barrier disruption and the subsequent development of vasogenic oedema, as well as neuronal injury and poor functional outcomes. Inhibition of SP through use of a neurokinin 1 (NK1) antagonist is highly beneficial following both TBI and ischaemic stroke in pre-clinical models. The role of CGRP is more unclear, especially with respect to TBI, with both elevations and reductions in CGRP levels reported following trauma. However, a beneficial role has been delineated in stroke, given its potent vasodilatory effects. Thus, modulating neuropeptides represents a novel therapeutic target in the treatment of cerebral oedema following acute CNS injury.

Sex and age differences in phenylephrine mechanisms and outcomes after piglet brain injury

BackgroundTraumatic brain injury (TBI) is the leading cause of injury-related death in children, with boys and children under 4 years of age having particularly poor outcomes. Cerebral autoregulation is often impaired after TBI, contributing to poor outcome. In prior studies on newborn pigs, phenylephrine (Phe) preferentially protected cerebral autoregulation in female but not in male subjects after TBI. We hypothesized that, in contrast to the newborn, Phe prevents impairment of autoregulation and tissue injury following TBI in both sexes of older pigs.MethodsCerebral autoregulation, cerebrospinal fluid (CSF) extracellular signal-related kinase (ERK) and endothelin, and histopathology were determined after moderate fluid percussion brain injury (FPI) in male and female juvenile pigs after Phe.ResultsAutoregulation was more impaired in male than in female subjects. Phe protects autoregulation in both sexes after FPI, blocks ERK and endothelin, and decreases the number of necrotic neurons in male and female subjects after FPI.ConclusionsThese data indicate that Phe protects autoregulation and limits neuronal necrosis via blockage of ERK and endothelin after FPI in male and female subjects. Together with prior observations in newborn pigs where Phe protected autoregulation in female but not in male subjects, these data suggest that use of Phe to improve outcomes after TBI is both sex- and age-dependent.

K channel impairment determines sex and age differences in epinephrine-mediated outcomes after brain injury

Traumatic brain injury (TBI) is the leading cause of injury-related death in children, with boys and children under 4 years having particularly poor outcomes. Activation of ATP- and calcium-sensitive (K_ATP and K_Ca ) channels produces cerebrovasodilation and contributes to autoregulation, both of which are impaired after TBI, contributing to poor outcomes. Upregulation of the c-Jun-terminal kinase (JNK) isoform of mitogen-activated protein kinase produces K channel function impairment after CNS injury. Vasoactive agents can be used to normalize cerebral perfusion pressure. Epinephrine (EPI) prevents impairment of cerebral autoregulation and hippocampal neuronal cell necrosis after TBI in female and male newborn and female juvenile but not male juvenile pigs via differential modulation of JNK. The present study used anesthetized pigs equipped with a closed cranial window to address the hypothesis that differential K channel impairment contributes to age and sex differences in EPI-mediated outcomes after brain injury. Results show that pial artery dilation in response to the K_ATP and K_Ca channel agonists cromakalim and NS 1619 was impaired after TBI and that such impairment was prevented by EPI in female and male newborn and female juvenile but not male juvenile pigs. Using vasodilation as an index of function, these data indicate that EPI protects cerebral autoregulation and limits histopathology after TBI through protection of K channel function via blockade of JNK in an age- and sex-dependent manner. © 2017 Wiley Periodicals, Inc.

Cerebral Blood Flow Autoregulation and Dysautoregulation

This article provides a review of cerebral autoregulation, particularly as it relates to the clinician scientist experienced in neuroscience in anesthesia and critical care. Topics covered are biological mechanisms; methods used for assessment of autoregulation; effects of anesthetics; role in control of cerebral hemodynamics in health and disease; and emerging areas, such as role of age and sex in contribution to dysautoregulation. Emphasis is placed on bidirectional translational research wherein the clinical informs the study design of basic science studies, which, in turn, informs the clinical to result in development of improved therapies for treatment of central nervous system conditions.

Sex and Age Differences in Epinephrine Mechanisms and Outcomes after Brain Injury

Traumatic brain injury (TBI) is the leading cause of injury-related death in children, with boys and children <4 years of age having particularly poor outcomes. Cerebral autoregulation is often impaired after TBI, contributing to poor outcome. Cerebral perfusion pressure can be normalized by use of vasoactive agents. The c-Jun-terminal kinase (JNK) isoform of mitogen activated protein kinase (MAPK) produces hemodynamic impairment after TBI, but less is known about its role in histopathology. We investigated whether epinephrine (EPI), age, and sex dependently protected cerebral autoregulation and limited histopathology after TBI, and sought to determine the role of JNK in that outcome. Lateral fluid percussion injury (FPI) was produced in anesthetized pigs. Pial artery reactivity was measured via a closed cranial window. Phosphorylated JNK MAPK was quantified by enzyme-linked immunosorbent assay (ELISA). Results show that EPI preserves autoregulation, prevents histopathology, and blocks phosphorylated JNK upregulation in newborn males and females and juvenile females but not juvenile males after TBI. These data indicate that EPI preserves cerebral autoregulation and limits histopathology after TBI through blockade of JNK in an age- and sex-dependent manner.

Historical Review of the Fluid-Percussion TBI Model

Traumatic brain injury (TBI) is a major health concern worldwide. Laboratory studies utilizing animal models of TBI are essential for addressing pathological mechanisms of brain injury and development of innovative treatments. Over the past 75 years, pioneering head injury researchers have devised and tested a number of fluid percussive methods to reproduce the concussive clinical syndrome in animals. The fluid-percussion brain injury technique has evolved from early investigations that applied a generalized loading of the brain to more recent computer-controlled systems. Of the many preclinical TBI models, the fluid-percussion technique is one of the most extensively characterized and widely used models. Some of the most important advances involved the development of the Stalhammer device to produce concussion in cats and the later characterization of this device for application in rodents. The goal of this historical review is to provide readers with an appreciation for the time and effort expended by the pioneering researchers who have led to today's state of the art fluid-percussion animal models of TBI.

Norepinephrine Protects Cerebral Autoregulation and Reduces Hippocampal Necrosis after Traumatic Brain Injury via Blockade of ERK MAPK and IL-6 in Juvenile Pigs

Traumatic brain injury (TBI) contributes to morbidity in children, and boys are disproportionately represented. Cerebral autoregulation is impaired after TBI, contributing to poor outcome. Cerebral perfusion pressure (CPP) is often normalized by use of vasoactive agents to increase mean arterial pressure (MAP). In prior studies of 1- to 5-day-old newborn piglets, we observed that norepinephrine (NE) preferentially protected cerebral autoregulation and prevented hippocampal necrosis in females but not males after fluid percussion injury (FPI). The ERK isoform of mitogen activated protein kinase (MAPK) produces hemodynamic impairment after FPI, but less is known about the role of the cytokine interleukin-6 (IL-6). We investigated whether NE protects autoregulation and limits histopathology after FPI in older juvenile (4-week-old) pigs and the role of ERK and IL-6 in that outcome by sex. Results show that NE significantly protects autoregulation and prevents reduction in cerebral blood flow (CBF) in both male and female juvenile pigs after FPI; co-administration of the ERK antagonist U 0126 with NE fully protects both indices of outcome. Papaverine induced dilation was unchanged by FPI and NE. NE blunted ERK MAPK and IL-6 upregulation in both males and females after FPI. NE attenuated loss of neurons in CA1 and CA3 hippocampus of males and females after FPI. These data indicate that NE protects autoregulation and limits hippocampal neuronal cell necrosis via blockade of ERK and IL-6 after FPI in both male and female juvenile pigs. These data suggest that use of NE to improve outcome after TBI is both sex and age dependent.

Preferential Protection of Cerebral Autoregulation and Reduction of Hippocampal Necrosis With Norepinephrine After Traumatic Brain Injury in Female Piglets

OBJECTIVES

Traumatic brain injury contributes to morbidity in children and boys is disproportionately represented. Cerebral autoregulation is impaired after traumatic brain injury, contributing to poor outcome. Cerebral perfusion pressure is often normalized by the use of vasopressors to increase mean arterial pressure. In prior studies, we observed that phenylephrine prevented impairment of autoregulation in female but exacerbated in male piglets after fluid percussion injury. In contrast, dopamine prevented impairment of autoregulation in both sexes after fluid percussion injury, suggesting that pressor choice impacts outcome. The extracellular signal-regulated kinase isoform of mitogen-activated protein kinase produces hemodynamic impairment after fluid percussion injury, but the role of the cytokine interleukin-6 is unknown. We investigated whether norepinephrine sex-dependently protects autoregulation and limits histopathology after fluid percussion injury and the role of extracellular signal-regulated kinase and interleukin-6 in that outcome.

DESIGN

Prospective, randomized animal study.

SETTING

University laboratory.

SUBJECTS

Newborn (1-5 d old) pigs.

INTERVENTIONS

Cerebral perfusion pressure, cerebral blood flow, and pial artery diameter were determined before and after fluid percussion injury in piglets equipped with a closed cranial window and post-treated with norepinephrine. Cerebrospinal fluid extracellular-signal-regulated kinase mitogen-activated protein kinase was determined by enzyme-linked immunosorbent assay.

MEASUREMENTS AND MAIN RESULTS

Norepinephrine does not protect autoregulation or prevent reduction in cerebral blood flow in male but fully protects autoregulation in female piglets after fluid percussion injury. Papaverine-induced dilation was unchanged by fluid percussion injury and norepinephrine. Norepinephrine increased extracellular signal-regulated kinase mitogen-activated protein kinase up-regulation in male but blocked such up-regulation in female piglets after fluid percussion injury. Norepinephrine aggravated interleukin-6 upregulation in males in an extracellular signal-regulated kinase mitogen-activated protein kinase-dependent mechanism but blocked interleukin-6 up-regulation in females after fluid percussion injury. Norepinephrine augments loss of neurons in CA1 and CA3 hippocampus of male piglets after fluid percussion injury in an extracellular signal-regulated kinase mitogen-activated protein kinase-dependent and interleukin-6-dependent manner but prevents loss of neurons in females after fluid percussion injury.

CONCLUSION

Norepinephrine protects autoregulation and limits hippocampal neuronal cell necrosis via modulation of extracellular signal-regulated kinase mitogen-activated protein kinase and interleukin-6 after fluid percussion injury in a sex-dependent manner.

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.

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.

Phenylephrine infusion prevents impairment of ATP- and calcium-sensitive potassium channel-mediated cerebrovasodilation after brain injury in female, but aggravates impairment in male, piglets through modulation of ERK MAPK upregulation

Traumatic brain injury (TBI) contributes to morbidity in children and boys, and hypotension worsens outcome. Extracellular signal-related kinase (ERK) mitogen-activated protein kinase (MAPK) is upregulated more in males and reduces cerebral blood flow (CBF) after fluid percussion injury (FPI). Increased cerebral perfusion pressure (CPP) via phenylephrine (Phe) sex-dependently improves impairment of the cerebral autoregulation seen after FPI through modulation of ERK MAPK upregulation, which is aggravated in males, but is blocked in females. Activation of ATP- and calcium-sensitive (Katp and Kca) channels produces cerebrovasodilation and contributes to autoregulation, both of which are impaired after FPI. Using piglets equipped with a closed cranial window, we hypothesized that potassium channel functional impairment after FPI is prevented by Phe in a sex-dependent manner through modulation of ERK MAPK upregulation. The Katp and Kca agonists cromakalim and NS 1619 produced vasodilation that was impaired after FPI more in males than in females. Phe prevented reductions in cerebrovasodilation after cromakalim and NS 1619 in females, but reduced dilation after these potassium channel agonists were given to males after FPI. Co-administration of U 0126, an ERK antagonist, and Phe fully restored dilation to cromakalim, calcitonin gene-related peptide (CGRP), and NS 1619, in males after FPI. These data indicate that Phe sex-dependently prevents impairment of Katp and Kca channel-mediated cerebrovasodilation after FPI in females, but aggravates impairment in males, through modulation of ERK MAPK upregulation. Since autoregulation of CBF is dependent on intact functioning of potassium channels, these data suggest a role for sex-dependent mechanisms in the treatment of cerebral autoregulation impairment after pediatric TBI.

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.

SNP improves cerebral hemodynamics during normotension but fails to prevent sex dependent impaired cerebral autoregulation during hypotension after brain injury

Traumatic brain injury (TBI) is a leading cause of morbidity in children and boys are disproportionately represented. Hypotension is common and worsens outcome after TBI. Previous studies show that adrenomedullin, a cerebrovasodilator, prevented sex dependent impairment of autoregulation during hypotension after piglet fluid percussion brain injury (FPI). We hypothesized that this concept was generalizable and that administration of another vasodilator, sodium nitroprusside (SNP), may equally improve CBF and cerebral autoregulation in a sex dependent manner after FPI. SNP produced equivalent percent cerebrovasodilation in male and female piglets. Reductions in pial artery diameter, cortical CBF, and cerebral perfusion pressure (CPP) concomitant with elevated intracranial pressure (ICP) after FPI were greater in male compared to female piglets during normotension which was blunted by SNP. During hypotension, pial artery dilation (PAD) was impaired more in the male than the female after FPI. However, SNP did not improve hypotensive PAD after FPI in females and paradoxically caused vasoconstriction in males. SNP did not prevent reductions in CBF, CPP or autoregulatory index during combined hypotension and FPI in either sex. SNP aggravated ERK MAPK upregulation after FPI. These data indicate that despite prevention of reductions in CBF after FPI, SNP does not prevent impairment of autoregulation during hypotension after FPI. These data suggest that therapies directed at a purely hemodynamic increase in CPP will fail to improve outcome during combined TBI and hypotension.

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.