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

Pupillary Light Response Deficits in 4-Week-Old Piglets and Adolescent Children after Low-Velocity Head Rotations and Sports-Related Concussions

Neurological disorders and traumatic brain injury (TBI) are among the leading causes of death and disability. The pupillary light reflex (PLR) is an emerging diagnostic tool for concussion in humans. We compared PLR obtained with a commercially available pupillometer in the 4 week old piglet model of the adolescent brain subject to rapid nonimpact head rotation (RNR), and in human adolescents with and without sports-related concussion (SRC). The 95% PLR reference ranges (RR, for maximum and minimum pupil diameter, latency, and average and peak constriction velocities) were established in healthy piglets (N = 13), and response reliability was validated in nine additional healthy piglets. PLR assessments were obtained in female piglets allocated to anesthetized sham (N = 10), single (sRNR, N = 13), and repeated (rRNR, N = 14) sagittal low-velocity RNR at pre-injury, as well as days 1, 4, and 7 post injury, and evaluated against RRs. In parallel, we established human PLR RRs in healthy adolescents (both sexes, N = 167) and compared healthy PLR to values obtained <28 days from a SRC (N = 177). In piglets, maximum and minimum diameter deficits were greater in rRNR than sRNR. Alterations peaked on day 1 post sRNR and rRNR, and remained altered at day 4 and 7. In SRC adolescents, the proportion of adolescents within the RR was significantly lower for maximum pupil diameter only (85.8%). We show that PLR deficits may persist in humans and piglets after low-velocity head rotations. Differences in timing of assessment after injury, developmental response to injury, and the number and magnitude of impacts may contribute to the differences observed between species. We conclude that PLR is a feasible, quantifiable involuntary physiological metric of neurological dysfunction in pigs, as well as humans. Healthy PLR porcine and human reference ranges established can be used for neurofunctional assessments after TBI or hypoxic exposures (e.g., stroke, apnea, or cardiac arrest).

An ECM-Mimicking, Injectable, Viscoelastic Hydrogel for Treatment of Brain Lesions

Brain lesions can arise from traumatic brain injury, infection, and craniotomy. Although injectable hydrogels show promise for promoting healing of lesions and health of surrounding tissue, enabling cellular ingrowth and restoring neural tissue continue to be challenging. It is hypothesized that these challenges arise in part from the mismatch of composition, stiffness, and viscoelasticity between the hydrogel and the brain parenchyma, and this hypothesis is tested by developing and evaluating a self-healing hydrogel that not only mimics the composition, but also the stiffness and viscoelasticity of native brain parenchyma. The hydrogel is crosslinked by dynamic boronate ester bonds between phenylboronic acid grafted hyaluronic acid (HA-PBA) and dopamine grafted gelatin (Gel-Dopa). This HA-PBA/Gel-Dopa hydrogel could be injected into a lesion cavity in a shear-thinning manner with rapid hemostasis, high tissue adhesion, and efficient self-healing. In an in vivo mouse model of brain lesions, the multi-functional injectable hydrogel is found to support neural cell infiltration, decrease astrogliosis and glial scars, and close the lesions. The results suggest a role for extracellular matrix-mimicking viscoelasticity in brain lesion healing, and motivate additional experimentation in larger animals as the technology progresses toward potential application in humans.

Pediatric Traumatic Brain Injury: An Update on Preclinical Models, Clinical Biomarkers, and the Implications of Cerebrovascular Dysfunction

Traumatic brain injury (TBI) is a leading cause of pediatric morbidity and mortality. Recent studies suggest that children and adolescents have worse post-TBI outcomes and take longer to recover than adults. However, the pathophysiology and progression of TBI in the pediatric population are studied to a far lesser extent compared to the adult population. Common causes of TBI in children are falls, sports/recreation-related injuries, non-accidental trauma, and motor vehicle-related injuries. A fundamental understanding of TBI pathophysiology is crucial in preventing long-term brain injury sequelae. Animal models of TBI have played an essential role in addressing the knowledge gaps relating to pTBI pathophysiology. Moreover, a better understanding of clinical biomarkers is crucial to diagnose pTBI and accurately predict long-term outcomes. This review examines the current preclinical models of pTBI, the implications of pTBI on the brain's vasculature, and clinical pTBI biomarkers. Finally, we conclude the review by speculating on the emerging role of the gut-brain axis in pTBI pathophysiology.

Cerebral blood flow self-regulation in depression

BACKGROUND

Depression is a common neuropsychiatric disease with a high prevalence rate. Sleep problems, memory decline, dizziness and headaches are the most common neurological symptoms in depressed patients. Abnormality of cerebral blood flow (CBF) has been observed in depressive patients, but those patients did not have intracranial structural damage. Both of those phenomena might be related to cerebral blood flow self-regulation (CBFSR: cerebral blood flow self-regulation). CBFSR can maintain CBF relatively stable in response to changes in neurological and metabolic factors. Therefore, this review aimed to discuss CBFSR in depression.

METHODS

We searched for keywords such as "depression", "cerebral blood flow", "cerebral autoregulation", "cerebrovascular reactivity" and the words related to depression. We analyzed whether there is a change in the CBFSR in depression, further explored whether there is a relationship between the pathogenesis of depression and the CBFSR, and discussed the possible mechanism of impaired CBFSR in patients with depression.

RESULTS

Discovered by the literature review, CBFSR is significantly impaired in depressed patients. The level of circulating markers of endothelial dysfunction, nitric oxide, inflammatory cytokines, glucocorticoid and monoamine neurotransmitters is mostly abnormal in depression, which affected the CBFSR to varying degrees.

LIMITATIONS

Limitations include the small number of direct studies about depression and CBFSR mechanisms.

CONCLUSION

CBFSR is impaired in depression. The underlying mechanisms include endothelial dysfunction, overactivation of microglia and changes of cytokines, hyperactivation of the HPA axis, increased oxidative stress, monoamine neurotransmitter disorders, etc. These deepened our understanding of the clinical symptoms of depressed patients.

Regulation of the Cerebral Circulation During Development

The cerebral microcirculation undergoes dynamic changes in parallel with the development of neurons, glia, and their energy metabolism throughout gestation and postnatally. Cerebral blood flow (CBF), oxygen consumption, and glucose consumption are as low as 20% of adult levels in humans born prematurely but eventually exceed adult levels at ages 3 to 11 years, which coincide with the period of continued brain growth, synapse formation, synapse pruning, and myelination. Neurovascular coupling to sensory activation is present but attenuated at birth. By 2 postnatal months, the increase in CBF often is disproportionately smaller than the increase in oxygen consumption, in contrast to the relative hyperemia seen in adults. Vascular smooth muscle myogenic tone increases in parallel with developmental increases in arterial pressure. CBF autoregulatory response to increased arterial pressure is intact at birth but has a more limited range with arterial hypotension. Hypoxia-induced vasodilation in preterm fetal sheep with low oxygen consumption does not sustain cerebral oxygen transport, but the response becomes better developed for sustaining oxygen transport by term. Nitric oxide tonically inhibits vasomotor tone, and glutamate receptor activation can evoke its release in lambs and piglets. In piglets, astrocyte-derived carbon monoxide plays a central role in vasodilation evoked by glutamate, ADP, and seizures, and prostanoids play a large role in endothelial-dependent and hypercapnic vasodilation. Overall, homeostatic mechanisms of CBF regulation in response to arterial pressure, neuronal activity, carbon dioxide, and oxygenation are present at birth but continue to develop postnatally as neurovascular signaling pathways are dynamically altered and integrated. © 2021 American Physiological Society. Compr Physiol 11:1-62, 2021.

Wavelet Autoregulation Monitoring Identifies Blood Pressures Associated With Brain Injury in Neonatal Hypoxic-Ischemic Encephalopathy

Dysfunctional cerebrovascular autoregulation may contribute to neurologic injury in neonatal hypoxic-ischemic encephalopathy (HIE). Identifying the optimal mean arterial blood pressure (MAPopt) that best supports autoregulation could help identify hemodynamic goals that support neurologic recovery. In neonates who received therapeutic hypothermia for HIE, we hypothesized that the wavelet hemoglobin volume index (wHVx) would identify MAPopt and that blood pressures closer to MAPopt would be associated with less brain injury on MRI. We also tested a correlation-derived hemoglobin volume index (HVx) and single- and multi-window data processing methodology. Autoregulation was monitored in consecutive 3-h periods using near infrared spectroscopy in an observational study. The neonates had a mean MAP of 54 mmHg (standard deviation: 9) during hypothermia. Greater blood pressure above the MAPopt from single-window wHVx was associated with less injury in the paracentral gyri (p = 0.044; n = 63), basal ganglia (p = 0.015), thalamus (p = 0.013), and brainstem (p = 0.041) after adjustments for sex, vasopressor use, seizures, arterial carbon dioxide level, and a perinatal insult score. Blood pressure exceeding MAPopt from the multi-window, correlation HVx was associated with less injury in the brainstem (p = 0.021) but not in other brain regions. We conclude that applying wavelet methodology to short autoregulation monitoring periods may improve the identification of MAPopt values that are associated with brain injury. Having blood pressure above MAPopt with an upper MAP of ~50–60 mmHg may reduce the risk of brain injury during therapeutic hypothermia. Though a cause-and-effect relationship cannot be inferred, the data support the need for randomized studies of autoregulation and brain injury in neonates with HIE.

Exploratory Assessment of the Relationship Between Hemoglobin Volume Phase Index, Magnetic Resonance Imaging, and Functional Outcome in Neonates with Hypoxic-Ischemic Encephalopathy

BACKGROUND/OBJECTIVE

Near-infrared spectroscopy (NIRS)-based measures of cerebral autoregulation (CAR) can potentially identify neonates with hypoxic-ischemic encephalopathy (HIE) who are at greatest risk of irreversible brain injury. However, modest predictive abilities have precluded previously described metrics from entering clinical care. We previously validated a novel autoregulation metric in a piglet model of induced hypotension called the hemoglobin volume phase index (HVP). The objective of this study was to evaluate the clinical ability of the HVP to predict adverse outcomes neonates with HIE.

METHODS

This is a prospective study of neonates with HIE who underwent therapeutic hypothermia (TH) at a level 4 neonatal intensive care unit (NICU). Continuous cerebral NIRS and mean arterial blood pressure (MAP) from indwelling arterial catheters were measured during TH and through rewarming. Multivariate autoregressive process was used to calculate the coherence between MAP and the sum total of the oxy- and deoxygenated Hb densities (HbT), a surrogate measure of cerebral blood volume (CBV). The HVP was calculated as the cosine-transformed phase shift at the frequency of maximal MAP-HbT coherence. Brain injury was assessed by neonatal magnetic resonance imaging (MRI), and developmental outcomes were assessed by the Bayley Scales of Infant Development (BSID-III) at 15-30 months. The ability of the HVP to predict (a) death or severe brain injury by MRI and (b) death or significant developmental delay was assessed using logistic regression analyses.

RESULTS

In total, 50 neonates with moderate or severe HIE were monitored. Median HVP was higher, representing more dysfunctional autoregulation, in infants who had adverse outcomes. After adjusting for sex and encephalopathy grade at presentation, HVP at 21-24 and 24-27 h of life predicted death or brain injury by MRI (21-24 h: OR 8.8, p = 0.037; 24-27 h: OR 31, p = 0.011) and death or developmental delay at 15-30 months (21-24 h: OR 11.8, p = 0.05; 24-27 h: OR 15, p = 0.035).

CONCLUSIONS

Based on this pilot study of neonates with HIE, HVP merits further study as an indicator of death or severe brain injury on neonatal MRI and neurodevelopmental delay in early childhood. Larger studies are warranted for further clinical validation of the HVP to evaluate cerebral autoregulation following HIE.

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.

Cerebral Perfusion Pressure Directed-Therapy Modulates Cardiac Dysfunction After Traumatic Brain Injury to Influence Cerebral Autoregulation in Pigs

BACKGROUND

Traumatic brain injury (TBI) is an important contributor to morbidity and mortality. Low cerebral perfusion pressure (CPP, mean arterial pressure [MAP] minus intracranial pressure) after TBI is associated with cerebral ischemia, impaired cerebral autoregulation, and poor outcomes. Normalization of CPP and limitation of cerebral autoregulation impairment is a key therapeutic goal. However, some vasoactive agents used to elevate MAP such as phenylephrine (Phe) improve outcome in females but not male piglets after TBI while dopamine (DA) does so in both sexes. Clinical evidence has implicated neurological injuries as a cause of cardiac dysfunction, and we recently described cardiac dysfunction after TBI. Cardiac dysfunction may, in turn, influence brain health. One mechanism of myocyte injury may involve catecholamine excess. We therefore tested the hypothesis that TBI caused cardiac dysfunction and catecholamine excess which may reciprocally be modulated by vasoactive agent choice to normalize CPP and prevent impairment of cerebral autoregulation after injury.

METHODS

TBI was produced in anesthetized pigs equipped with a closed cranial window, and Phe or DA administered to normalize CPP.

RESULTS

Plasma cardiac enzymes troponin and creatine kinase and catecholamines epinephrine and norepinephrine were elevated by TBI, such release potentiated by Phe in males but blocked in female piglets and blocked in both sexes after DA. Cerebral autoregulation was impaired after TBI, worsened by Phe in males but protected in females and males treated with DA. Papaverine-induced dilation was unchanged by fluid percussion brain injury, DA, and Phe.

CONCLUSIONS

These data indicate that pressor choice in elevation of CPP is important in limiting cardiac dysfunction and suggest that DA protects cerebral autoregulation in both sexes via reduction of cardiac biomarkers of injury and catecholamines released after TBI.

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.

The potential roles of dopamine in traumatic brain injury: a preclinical and clinical update

Traumatic brain injury (TBI) is one of the leading causes of death and disability, particularly among the young and the elderly. Several therapeutic options have been investigated, including drug interventions or combinational therapies. Although many drugs have shown promising results in the preclinical stage, all have failed in large clinical trials. Targeting the dopamine system is a novel TBI approach that provides benefits to functional outcomes. TBI could damage the dopaminergic system. Alterations in dopamine levels can impact cellular dysfunction and central nervous system (CNS) inflammation. Experimental evidence suggests that dopamine should be considered a first-line treatment to protect cerebral autoregulation and promote cerebral outcomes in TBI. Furthermore, investigation of dopamine-related genetic factors in relation to injury severity could also be of great significance for promoting TBI treatment. Importantly, various clinical lines of evidence have indicated that many dopamine agonists are beneficial when administered following injury in TBI patients. However, side effects of dopamine treatment prevent their use in TBI treatment, and there is a need for ongoing large, prospective, double-blind randomized controlled trials (RCTs) with these medications by the use of standardized criteria and outcomes to fully understand their effectiveness in this patient group. Here, we review the roles of dopamine in TBI and discuss the role that dopaminergic therapies have in neuroprotective strategies.

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.

Sex differences in pediatric traumatic brain injury

The response of the developing brain to traumatic injury is different from the response of the mature, adult brain. There are critical developmental trajectories in the young brain, whereby injury can lead to long term functional abnormalities. Emerging preclinical and clinical literature supports the presence of significant sex differences in both the response to and the recovery from pediatric traumatic brain injury (TBI). These sex differences are seen at all pediatric ages, including neonates/infants, pre-pubertal children, and adolescents. As importantly, the response to neuroprotective therapies or treatments can differ between male and females subjects. These sex differences can result from several biologic origins, and may manifest differently during the various phases of brain and body development. Recognizing and understanding these potential sex differences is crucial, and should be considered in both preclinical and clinical studies of pediatric TBI.

Inhaled nitric oxide protects cerebral autoregulation through prevention of impairment of ATP and calcium sensitive K channel mediated cerebrovasodilation after traumatic brain injury

Hypotension and low cerebral perfusion pressure are associated with low cerebral blood flow, cerebral ischemia, and poor outcomes after traumatic brain injury (TBI). Cerebral autoregulation is impaired after TBI, contributing to poor outcome. In prior studies, ERK mitogen activated protein kinase (MAPK) and ET-1 had been observed to be upregulated and contribute to impairment of cerebral autoregulation and histopathology after fluid percussion brain injury (FPI). Activation of ATP and Calcium sensitive (Katp and Kca) channels produce cerebrovasodilation and contribute to autoregulation, both impaired after TBI. Upregulation of ERK MAPK and endothelin-1 (ET-1) produces K channel function impairment after CNS injury. Inhaled nitric oxide (iNO) has recently been observed to prevent impairment of cerebral autoregulation and hippocampal CA1 and CA3 neuronal cell necrosis after FPI via block of upregulation of ERK MAPK and ET-1. We presently investigated whether iNO prevented impairment of Katp and Kca-mediated cerebrovasodilation after FPI in pigs equipped with a closed cranial window. Results show that pial artery dilation in response to the Katp agonist cromakalim, the Kca agonist NS1619, PGE2 and the NO releaser sodium nitroprusside (SNP) were blocked by FPI, but such impairment was prevented by iNO administered at 2 h post injury. Protection lasted for at least 1 h after iNO administration was stopped. Using vasodilaton as an index of function, these data indicate that iNO prevents impairment of cerebral autoregulation and limits histopathology after TBI through protection of K channel function via blockade of ERK MAPK and ET-1.

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.

Neonatal cerebrovascular autoregulation

Cerebrovascular pressure autoregulation is the physiologic mechanism that holds cerebral blood flow (CBF) relatively constant across changes in cerebral perfusion pressure (CPP). Cerebral vasoreactivity refers to the vasoconstriction and vasodilation that occur during fluctuations in arterial blood pressure (ABP) to maintain autoregulation. These are vital protective mechanisms of the brain. Impairments in pressure autoregulation increase the risk of brain injury and persistent neurologic disability. Autoregulation may be impaired during various neonatal disease states including prematurity, hypoxic-ischemic encephalopathy (HIE), intraventricular hemorrhage, congenital cardiac disease, and infants requiring extracorporeal membrane oxygenation (ECMO). Because infants are exquisitely sensitive to changes in cerebral blood flow (CBF), both hypoperfusion and hyperperfusion can cause significant neurologic injury. We will review neonatal pressure autoregulation and autoregulation monitoring techniques with a focus on brain protection. Current clinical therapies have failed to fully prevent permanent brain injuries in neonates. Adjuvant treatments that support and optimize autoregulation may improve neurologic outcomes.

Inhaled Nitric Oxide Protects Cerebral Autoregulation and Reduces Hippocampal Neuronal Cell Necrosis after Traumatic Brain Injury in Newborn and Juvenile Pigs

Traumatic brain injury (TBI) contributes to morbidity in children, and boys are disproportionately represented. Cerebral blood flow (CBF) is reduced and 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 male and female newborn and juvenile pigs, we observed that phenylephrine, norepinephrine, epinephrine, and dopamine demonstrated different sex- and age-dependent abilities to prevent impairment of cerebral autoregulation and limit histopathology after TBI, despite equivalent CPP values. This observation complicated treatment choice. Alternatively, administration of a cerebral vasodilator may improve cerebral hemodynamics after TBI by increasing CBF. In prior studies, intravenous sodium nitroprusside, a nitric oxide (NO) releaser, elevated CBF after TBI but failed to prevent impairment of cerebral autoregulation due to a confounding decrease in MAP, which lowered CPP. We presently test the hypothesis that inhaled NO (iNO) will protect cerebral autoregulation and prevent hippocampal histopathology after TBI. Results show that iNO administered at 30 min or 2 h after TBI protected cerebral autoregulation and prevented neuronal cell necrosis in CA1 and CA3 hippocampus equivalently in male and female newborn and juvenile pigs without change in MAP. Protection lasted for at least 2 h after iNO administration was stopped. Papaverine-induced dilation was unchanged by TBI and iNO. These data indicate that iNO offers the opportunity to have a single therapeutic that uniformly protects autoregulation and limits hippocampal neuronal cell necrosis across both ages and sexes.

Sex-related responses after traumatic brain injury: Considerations for preclinical modeling

Traumatic brain injury (TBI) has historically been viewed as a primarily male problem, since men are more likely to experience a TBI because of more frequent participation in activities that increase risk of head injuries. This male bias is also reflected in preclinical research where mostly male animals have been used in basic and translational science. However, with an aging population in which TBI incidence is increasingly sex-independent due to falls, and increasing female participation in high-risk activities, the attention to potential sex differences in TBI responses and outcomes will become more important. These considerations are especially relevant in designing preclinical animal models of TBI that are more predictive of human responses and outcomes. This review characterizes sex differences following TBI with a special emphasis on the contribution of the female sex hormones, progesterone and estrogen, to these differences. This information is potentially important in developing and customizing TBI treatments.

Do microglia play a role in sex differences in TBI?

Traumatic brain injury (TBI) is one of the leading causes of morbidity and mortality for both males and females and is, thus, a major focus of current study. Although the overall death rate of TBI for males is roughly three times higher than that for females, males have been disproportionately represented in clinical and preclinical studies. Gender differences are known to exist in many neurologic disorders, such as multiple sclerosis and stroke, and differences appear to exist in TBI. Furthermore, it is known that microglia have sexually dimorphic roles in CNS development and other neurologic conditions; however, most animal studies of microglia and TBI have focused on male subjects. Microglia are a current target of many preclinical and clinical therapeutic trials for TBI. Understanding the relationship among sex, sex hormones, and microglia is critical to truly understanding the pathophysiology of TBI. However, the evidence for sex differences in TBI centers mainly on sex hormones, and evidenced-based conclusions are often contradictory. In an attempt to review the current literature, it is apparent that sex differences likely exist, but the contradictory nature and magnitude of such differences in the existing literature does not allow definite conclusions to be drawn, except that more investigation of this issue is necessary. © 2016 Wiley Periodicals, Inc.

Large animal models of traumatic brain injury

Purpose/Aim: Animal models of traumatic brain injury (TBI) provide powerful tools to study TBI in a controlled, rigorous and cost-efficient manner. The mostly used animals in TBI studies so far are rodents. However, compared with rodents, large animals (e.g. swine, rabbit, sheep, ferret, etc.) show great advantages in modeling TBI due to the similarity of their brains to human brain. The aim of our review was to summarize the development and progress of common large animal TBI models in past 30 years.

MATERIALS AND METHODS

Mixed published articles and books associated with large animal models of TBI were researched and summarized.

RESULTS

We majorly sumed up current common large animal models of TBI, including discussion on the available research methodologies in previous studies, several potential therapies in large animal trials of TBI as well as advantages and disadvantages of these models.

CONCLUSIONS

Large animal models of TBI play crucial role in determining the underlying mechanisms and screening putative therapeutic targets of TBI.

Pre-clinical models in pediatric traumatic brain injury-challenges and lessons learned

PURPOSE

Despite the enormity of the problem and the lack of new therapies, research in the pre-clinical arena specifically using pediatric traumatic brain injury (TBI) models is limited. In this review, some of the key models addressing both the age spectrum of pediatric TBI and its unique injury mechanisms will be highlighted. Four topics will be addressed, namely, (1) unique facets of the developing brain important to TBI model development, (2) a description of some of the most commonly used pre-clinical models of severe pediatric TBI including work in both rodents and large animals, (3) a description of the pediatric models of mild TBI and repetitive mild TBI that are relatively new, and finally (4) a discussion of challenges, gaps, and potential future directions to further advance work in pediatric TBI models.

METHODS

This narrative review on the topic of pediatric TBI models was based on review of PUBMED/Medline along with a synthesis of information on key factors in pre-clinical and clinical developmental brain injury that influence TBI modeling.

RESULTS

In the contemporary literature, six types of models have been used in rats including weight drop, fluid percussion injury (FPI), impact acceleration, controlled cortical impact (CCI), mechanical shaking, and closed head modifications of CCI. In mice, studies are largely restricted to CCI. In large animals, FPI and rotational injury have been used in piglets and shake injury has also been used in lambs. Most of the studies have been in severe injury models, although more recently, studies have begun to explore mild and repetitive mild injuries to study concussion.

CONCLUSIONS

Given the emerging importance of TBI in infants and children, the morbidity and mortality that is produced, along with its purported link to the development of chronic neurodegenerative diseases, studies in these models merit greater systematic investigations along with consortium-type approaches and long-term follow-up to translate new therapies to the bedside.

Autoregulation in paediatric TBI-current evidence and implications for treatment

BACKGROUND

Children who survive acute traumatic brain injury are at risk of death from subsequent brain swelling and secondary injury. Strict physiologic management in the ICU after traumatic brain injury is believed to be key to survival, and cerebral perfusion pressure is a prominent aspect of post brain injury care. However, optimal cerebral perfusion pressure targets for children are not known. Autoregulation monitoring has been used to delineate individualized optimal perfusion pressures for patients with traumatic brain injury. The methods to do so are diverse, confusing, and not universally validated.

METHODS

In this manuscript, we discuss the history of autoregulation monitoring, outline and categorize the methods used to measure autoregulation, and review the available validation data for methods used to monitor autoregulation.

CONCLUSIONS

Impaired autoregulation after traumatic brain injury is associated with a poor prognosis. Observational data suggests that optimal neurologic outcome and survival are associated with optimal perfusion pressure defined by autoregulation monitoring. No randomized, controlled, interventional data is available to assess autoregulation monitoring after pediatric traumatic brain injury.

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 Anesthesiologist's Role in Treating Abusive Head Trauma

Abusive head trauma (AHT) is the most common cause of severe traumatic brain injury (TBI) in infants and the leading cause of child abuse-related deaths. For reasons that remain unclear, mortality rates after moderate AHT rival those of severe nonintentional TBI. The vulnerability of the developing brain to injury may be partially responsible for the poor outcomes observed after AHT. AHT is mechanistically more complex than nonintentional TBI. The acute-on-chronic nature of the trauma along with synergistic injury mechanisms that include rapid rotation of the brain, diffuse axonal injury, blunt force trauma, and hypoxia-ischemia make AHT challenging to treat. The anesthesiologist must understand the complex injury mechanisms inherent to AHT, as well as the pediatric TBI treatment guidelines, to decrease the risk of persistent neurologic disability and death. In this review, we discuss the epidemiology of AHT, differences between AHT and nonintentional TBI, the severe pediatric TBI treatment guidelines in the context of AHT, anesthetic considerations, and ethical and legal reporting requirements.

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.

Sex-specific associations between cerebrovascular blood pressure autoregulation and cardiopulmonary injury in neonatal encephalopathy and therapeutic hypothermia

BACKGROUND

Cardiopulmonary injury is common in neonatal encephalopathy, but the link with cerebrovascular dysfunction is unknown. We hypothesized that alterations of cerebral autoregulation are associated with cardiopulmonary injury in neonates treated with therapeutic hypothermia (TH) for neonatal encephalopathy.

METHODS

The cerebral hemoglobin volume index (HVx) from near-infrared spectroscopy was used to identify the mean arterial blood pressure (MAP) with optimal autoregulatory vasoreactivity (MAPOPT). We measured associations between MAP relative to MAPOPT and indicators of cardiopulmonary injury (duration of mechanical respiratory support and administration of inhaled nitric oxide (iNO), milrinone, or steroids).

RESULTS

We identified associations between cerebrovascular autoregulation and cardiopulmonary injury that were often sex-specific. Greater MAP deviation above MAPOPT was associated with shorter duration of intubation in boys but longer ventilatory support in girls. Greater MAP deviation below MAPOPT related to longer intensive care stay in boys. Milrinone was associated with greater MAP deviation below MAPOPT in girls.

CONCLUSION

MAP deviation from MAPOPT may relate to cardiopulmonary injury after neonatal encephalopathy, and sex may modulate this relationship. Whereas MAP above MAPOPT may protect the brain and lungs in boys, it may be related to cardiopulmonary injury in girls. Future studies are needed to characterize the role of sex in these associations.

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.

Dopamine therapy does not affect cerebral autoregulation during hypotension in newborn piglets

Background

Hypotensive neonates who have been treated with dopamine have poorer neurodevelopmental outcome than those who have not been treated with dopamine. We speculate that dopamine stimulates adrenoceptors on cerebral arteries causing cerebral vasoconstriction. This vasoconstriction might lead to a rightward shift of the cerebral autoregulatory curve; consequently, infants treated with dopamine would have a higher risk of low cerebral blood flow at a blood pressure that is otherwise considered “safe”.

Methods

In anaesthetized piglets, perfusion of the brain, monitored with laser-doppler flowmetry, and cerebral venous saturation was measured at different levels of hypotension. Each piglet was studied in two phases: a phase with stepwise decreases in MAP and a phase with stepwise increases in MAP. We randomized the order of the two phases, whether dopamine was given in the first or second phase, and the infusion rate of dopamine (10, 25, or 40 μg/kg/min). In/deflation of a balloon catheter, placed in vena cava, induced different levels of hypotension. At each level of hypotension, fluctuations in MAP were induced by in/deflations of a balloon catheter in descending aorta.

Results

During measurements, PaCO₂ and arterial saturation were stable. MAP levels ranged between 14 and 82 mmHg. Cerebral autoregulation (CA) capacity was calculated as the ratio between %-change in cerebrovascular resistance and %-change in MAP induced by the in/deflation of the arterial balloon. A breakpoint in CA capacity was identified at a MAP of 38±18 mmHg without dopamine and at 44±18, 31±14, and 24±14 mmHg with dopamine infusion rates of 10, 25, and 40 μg/kg/min (p = 0.057). Neither the index of steady-state cerebral perfusion nor cerebral venous saturation were affected by dopamine infusion.

Conclusion

Dopamine infusion tended to improve CA capacity at low blood pressures while an index of steady-state cerebral blood flow and cerebral venous saturation were unaffected by dopamine infusion. Thus, dopamine does not appear to impair CA in newborn piglets.

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.

Optimizing Cerebral Autoregulation May Decrease Neonatal Regional Hypoxic-Ischemic Brain Injury

BACKGROUND

Therapeutic hypothermia provides incomplete neuroprotection for neonatal hypoxic-ischemic encephalopathy (HIE). We examined whether hemodynamic goals that support autoregulation are associated with decreased brain injury and whether these relationships are affected by birth asphyxia or vary by anatomic region.

METHODS

Neonates cooled for HIE received near-infrared spectroscopy autoregulation monitoring to identify the mean arterial blood pressure with optimized autoregulatory function (MAPOPT). Blood pressure deviation from MAPOPT was correlated with brain injury on MRI after adjusting for the effects of arterial carbon dioxide, vasopressors, seizures, and birth asphyxia severity.

RESULTS

Blood pressure deviation from MAPOPT related to neurologic injury in several regions independent of birth asphyxia severity. Greater duration and deviation of blood pressure below MAPOPT were associated with greater injury in the paracentral gyri and white matter. Blood pressure within MAPOPT related to lesser injury in the white matter, putamen and globus pallidus, and brain stem. Finally, blood pressures that exceeded MAPOPT were associated with reduced injury in the paracentral gyri.

CONCLUSIONS

Blood pressure deviation from optimal autoregulatory vasoreactivity was associated with MRI markers of brain injury that, in many regions, were independent of the initial birth asphyxia. Targeting hemodynamic ranges to optimize autoregulation has potential as an adjunctive therapy to hypothermia for HIE.

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.

The differential effects of norepinephrine and dopamine on cerebrospinal fluid pressure and spinal cord perfusion pressure after acute human spinal cord injury

STUDY DESIGN

Prospective vasopressor cross-over interventional studyObjectives:To examine how two vasopressors used in acute traumatic spinal cord injury (SCI) affect intrathecal cerebrospinal fluid pressure and the corresponding spinal cord perfusion pressure (SCPP).

SETTING

Vancouver, British Columbia, Canada.

METHODS

Acute SCI patients over the age of 17 with cervical or thoracic ASIA Impairment Scale (AIS). A, B or C injuries were enrolled in this study. Two vasopressors, norepinephrine and dopamine, were evaluated in a 'crossover procedure' to directly compare their effect on the intrathecal pressure (ITP). The vasopressor cross-over procedures were performed in the intensive care unit where ITP, mean arterial pressure (MAP) and heart rate were being continuously measured. The SCPP was calculated as the difference between MAP and ITP.

RESULTS

A total of 11 patients were enrolled and included in our analysis. There were 6 patients with AIS A, 3 with AIS B and 2 with AIS C injuries at baseline. We performed 24 cross-over interventions in these 11 patients. There was no difference in MAP with the use of norepinephrine versus dopamine (84±1 mm Hg for both; P=0.33). Conversely, ITP was significantly lower with the use of norepinephrine than with dopamine (17±1 mm Hg vs 20±1 mm Hg, respectively, P<0.001). This decrease in ITP with norepinephrine resulted in an increased SCPP during the norepinephrine infusion when compared with dopamine (67±1 mm Hg vs 65±1 mm Hg respectively, P=0.0049).

CONCLUSION

Norepinephrine was able to maintain MAP with a lower ITP and a correspondingly higher SCPP as compared with dopamine in this study. These results suggest that norepinephrine may be preferable to dopamine if vasopressor support is required post SCI to maintain elevated MAPs in accordance with published guidelines.

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.

Secondary Increase of Lactate Levels in Asphyxiated Newborns during Hypothermia Treatment: Reflect of Suboptimal Hemodynamics (A Case Series and Review of the Literature)

Objective To evaluate whether a secondary increase of serum lactate levels in asphyxiated newborns during hypothermia treatment may reflect suboptimal dynamics. Methods-Retrospective case series and review of the literature. We present the clinical course of four asphyxiated newborns treated with hypothermia who presented with hypotension requiring inotropic support, and who displayed a secondary increase of serum lactate levels during hypothermia treatment. Serial serum lactate levels are correlated with blood pressure and inotropic support within the first 96 hours of life. Results Lactate levels initially decreased in the four patients. However, each of them started to present lower blood pressure, and lactate levels started to increase again. Inotropic support was started to raise blood pressure. The introduction of an epinephrine drip consistently worsened the increase of lactate levels in these newborns, whereas dopamine and dobutamine enabled the clearance of lactate in addition to raising the blood pressure. Rewarming was associated with hemodynamics perturbations (a decrease of blood pressure and/or an increase of lactate levels) in the three newborns who survived. Conclusions Lactate levels during the first 4 days of life should be followed as a potential marker for suboptimal hemodynamic status in term asphyxiated newborns treated with hypothermia, for whom the maintenance of homeostasis during hypothermia treatment is of utmost importance to alleviate brain injury.

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.

Catecholaminergic based therapies for functional recovery after TBI

Among the many pathophysiologic consequences of traumatic brain injury are changes in catecholamines, including dopamine, epinephrine, and norepinephrine. In the context of TBI, dopamine is the one most extensively studied, though some research exploring epinephrine and norepinephrine have also been published. The purpose of this review is to summarize the evidence surrounding use of drugs that target the catecholaminergic system on pathophysiological and functional outcomes of TBI using published evidence from pre-clinical and clinical brain injury studies. Evidence of the effects of specific drugs that target catecholamines as agonists or antagonists will be discussed. Taken together, available evidence suggests that therapies targeting the catecholaminergic system may attenuate functional deficits after TBI. Notably, it is fairly common for TBI patients to be treated with catecholamine agonists for either physiological symptoms of TBI (e.g. altered cerebral perfusion pressures) or a co-occuring condition (e.g. shock), or cognitive symptoms (e.g. attentional and arousal deficits). Previous clinical trials are limited by methodological limitations, failure to replicate findings, challenges translating therapies to clinical practice, the complexity or lack of specificity of catecholamine receptors, as well as potentially counfounding effects of personal and genetic factors. Overall, there is a need for additional research evidence, along with a need for systematic dissemination of important study details and results as outlined in the common data elements published by the National Institute of Neurological Diseases and Stroke. Ultimately, a better understanding of catecholamines in the context of TBI may lead to therapeutic advancements. This article is part of a Special Issue entitled SI:Brain injury and recovery.

Effect of persistent pulmonary hypertension on brain oxygenation in asphyxiated term newborns treated with hypothermia

OBJECTIVE

To better understand the impact of persistent pulmonary hypertension (PPHN) on brain oxygenation in term asphyxiated newborns treated with hypothermia.

METHODS

The regional cerebral oxygenation saturation (rSO2) measured by near-infrared spectroscopy was compared to pre/post-ductal oxygen saturation and mean arterial blood pressure in three term asphyxiated newborns with documented PPHN during their first 4 days of life while they were being treated with hypothermia.

RESULTS

The cerebral oxygen saturation remained relatively stable when oxygen saturation was more than 92% and when there was no difference between pre- and post-ductal oxygen saturations. Episodes of desaturations with a difference between pre- and post-ductal saturations, as well as episodes of hypotension, caused a significant decrease in rSO2 in these newborns.

CONCLUSION

This case series demonstrates that PPHN has a profound impact on brain oxygenation in term asphyxiated newborns treated with hypothermia during the first days of life after birth. PPHN may represent an additional risk factor for brain injury in these newborns during the first days of life.

Microparticles Impair Hypotensive Cerebrovasodilation and Cause Hippocampal Neuronal Cell Injury after Traumatic Brain Injury

Endothelin-1 (ET-1), tissue plasminogen activator (tPA), and extracellular signal-regulated kinases-mitogen activated protein kinase (ERK-MAPK) are mediators of impaired cerebral hemodynamics after fluid percussion brain injury (FPI) in piglets. Microparticles (MPs) are released into the circulation from a variety of cells during stress, are pro-thrombotic and pro-inflammatory, and may be lysed with polyethylene glycol telomere B (PEG-TB). We hypothesized that MPs released after traumatic brain injury impair hypotensive cerebrovasodilation and that PEG-TB protects the vascular response via MP lysis, and we investigated the relationship between MPs, tPA, ET-1, and ERK-MAPK in that process. FPI was induced in piglets equipped with a closed cranial window. Animals received PEG-TB or saline (vehicle) 30-minutes post-injury. Serum and cerebrospinal fluid (CSF) were sampled and pial arteries were measured pre- and post-injury. MPs were quantified by flow cytometry. CSF samples were analyzed with enzyme-linked immunosorbent assay. MP levels, vasodilatory responses, and CSF signaling assays were similar in all animals prior to injury and treatment. After injury, MP levels were elevated in the serum of vehicle but not in PEG-TB-treated animals. Pial artery dilation in response to hypotension was impaired after injury but protected in PEG-TB-treated animals. After injury, CSF levels of tPA, ET-1, and ERK-MAPK were all elevated, but not in PEG-TB-treated animals. PEG-TB-treated animals also showed reduction in neuronal injury in CA1 and CA3 hippocampus, compared with control animals. These results show that serum MP levels are elevated after FPI and lead to impaired hypotensive cerebrovasodilation via over-expression of tPA, ET-1, and ERK-MAPK. Treatment with PEG-TB after injury reduces MP levels and protects hypotensive cerebrovasodilation and limits hippocampal neuronal cell injury.

Carotid artery blood flow decreases after rapid head rotation in piglets

Modification of cerebral perfusion pressure and cerebral blood flow (CBF) are crucial components of the therapies designed to reduce secondary damage after traumatic brain injury (TBI). Previously we documented a robust decrease in CBF after rapid sagittal head rotation in our well-validated animal model of diffuse TBI. Mechanisms responsible for this immediate (<10 min) and sustained (∼24 h) reduction in CBF have not been explored. Because the carotid arteries are a major source of CBF, we hypothesized that blood flow through the carotid arteries (Q) and vessel diameter (D) would decrease after rapid nonimpact head rotation without cervical spine injury. Four-week-old (toddler) female piglets underwent rapid (<20 msec) sagittal head rotation without impact, previously shown to produce diffuse TBI with reductions in CBF. Ultrasonographic images of the bilateral carotid arteries were recorded at baseline (pre-injury), as well as immediately after head rotation and 15, 30, 45, and 60 min after injury. Diameter (D) and waveform velocity (V) were used to calculate blood flow (Q) through the carotid arteries using the equation Q=(0.25)πD(2)V. D, V, and Q were normalized to the pre-injury baseline values to obtain a relative change after injury in right and left carotid arteries. Three-way analysis of variance and post-hoc Tukey-Kramer analyses were used to assess statistical significance of injury, time, and side. The relative change in carotid artery diameter and flow was significantly decreased in injured animals in comparison with uninjured sham controls (p<0.0001 and p=0.0093, respectively) and did not vary with side (p>0.39). The average carotid blood velocity did not differ between sham and injured animals (p=0.91). These data suggest that a reduction in global CBF after rapid sagittal head rotation may be partially mediated by a reduction in carotid artery flow, via vasoconstriction.