Brain injury impairs ATP-sensitive K+ channel function in piglet cerebral arteries

Nervous System Response to Neurotrauma: A Narrative Review of Cerebrovascular and Cellular Changes After Neurotrauma

Neurotrauma is a significant cause of morbidity and mortality worldwide. For instance, traumatic brain injury (TBI) causes more than 30% of all injury-related deaths in the USA annually. The underlying cause and clinical sequela vary among cases. Patients are liable to both acute and chronic changes in the nervous system after such a type of injury. Cerebrovascular disruption has the most common and serious effect in such cases because cerebrovascular autoregulation, which is one of the main determinants of cerebral perfusion pressure, can be effaced in brain injuries even in the absence of evident vascular injury. Disruption of the blood-brain barrier regulatory function may also ensue whether due to direct injury to its structure or metabolic changes. Furthermore, the autonomic nervous system (ANS) can be affected leading to sympathetic hyperactivity in many patients. On a cellular scale, the neuroinflammatory cascade medicated by the glial cells gets triggered in response to TBI. Nevertheless, cellular and molecular reactions involved in cerebrovascular repair are not fully understood yet. Most studies were done on animals with many drawbacks in interpreting results. Therefore, future studies including human subjects are necessarily needed. This review will be of relevance to clinicians and researchers interested in understanding the underlying mechanisms in neurotrauma cases and the development of proper therapies as well as those with a general interest in the neurotrauma field.

Traumatic Brain Injury Impairs Systemic Vascular Function Through Disruption of Inward-Rectifier Potassium Channels

Trauma can lead to widespread vascular dysfunction, but the underlying mechanisms remain largely unknown. Inward-rectifier potassium channels (Kir2.1) play a critical role in the dynamic regulation of regional perfusion and blood flow. Kir2.1 channel activity requires phosphatidylinositol 4,5-bisphosphate (PIP₂), a membrane phospholipid that is degraded by phospholipase A₂ (PLA₂) in conditions of oxidative stress or inflammation. We hypothesized that PLA₂-induced depletion of PIP₂ after trauma impairs Kir2.1 channel function. A fluid percussion injury model of traumatic brain injury (TBI) in rats was used to study mesenteric resistance arteries 24 hours after injury. The functional responses of intact arteries were assessed using pressure myography. We analyzed circulating PLA₂, hydrogen peroxide (H₂O₂), and metabolites to identify alterations in signaling pathways associated with PIP₂ in TBI. Electrophysiology analysis of freshly-isolated endothelial and smooth muscle cells revealed a significant reduction of Ba²⁺-sensitive Kir2.1 currents after TBI. Additionally, dilations to elevated extracellular potassium and BaCl₂- or ML 133-induced constrictions in pressurized arteries were significantly decreased following TBI, consistent with an impairment of Kir2.1 channel function. The addition of a PIP₂ analog to the patch pipette successfully rescued endothelial Kir2.1 currents after TBI. Both H₂O₂ and PLA₂ activity were increased after injury. Metabolomics analysis demonstrated altered lipid metabolism signaling pathways, including increased arachidonic acid, and fatty acid mobilization after TBI. Our findings support a model in which increased H₂O₂-induced PLA₂ activity after trauma hydrolyzes endothelial PIP₂, resulting in impaired Kir2.1 channel function.

Hyaluronic Acid Improves Hydrogen Peroxide Modulatory Effects on Calcium Channel and Sodium-Potassium Pump in 4T1 Breast Cancer Cell Line

Maintaining homeostasis of ion concentrations is critical in cancer cells. Under hypoxia, the levels of channels and pumps in cancer cells are more active than normal cells suggesting ion channels as a suitable therapeutic target. One of the contemporary ways for cancer therapy is oxidative stress. However, the effective concentration of oxidative stress on tumor cells has been reported to be toxic for normal cells as well. In this study, we benefited from the modifying effects of hyaluronic acid (HA) on H2O2, as a free radical source, to make a gradual release of oxidative stress on cancer cells while preventing/decreasing damage to normal cells under normoxia and hypoxic conditions. To do so, we initially investigated the optimal concentration of HA antioxidant capacity by the DPPH test. In the next step, we found optimum H2O2 dose by treating the 4T1 breast cancer cell line with increasing concentrations (0, 10, 20, 50,100, 200, 500, and 1000 μM) of H2O2 alone or H2O2 + HA (83%) for 24 hrs. The calcium channel and the sodium-potassium pumps were then evaluated by measuring the levels of calcium, sodium, and potassium ions using an atomic absorption flame spectrophotometer. The results revealed that treatment with H2O2 or H2O2+ HA led to an intracellular increase of calcium, sodium, and potassium in the normoxic and hypoxic circumstances in a dose-dependent manner. It is noteworthy that H2O2 + HA treatment had more favorable and controllable effects compared with H2O2 alone. Moreover, HA optimizes the antitumor effect of oxidative stress exerted by H2O2 making H2O2 + HA suitable for clinical use in cancer treatment along with chemotherapy.

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 effect of tamoxifen on opening ATP-sensitive K+ channels enhances hydroxyl radical generation in rat striatum

The present study was examined the antioxidant effect of tamoxifen, a synthetic non-steroidal antiestrogen, on cromakalim or nicorandil (ATP-sensitive K⁺ (K_ATP) channels opener)-enhanced hydroxyl radical (OH) generation induced by 1-methyl-4-phenylpyridinium ion (MPP⁺) in extracellular fluid of rat striatum. Rats were anesthetized, and sodium salicylate in Ringer's solution (0.5 mM or 0.5 nmol/µl/min) was infused through a microdialysis probe to detect the generation of OH as reflected by the non-enzymatic formation of 2,3-dihydroxybenzoic acid (DHBA) in the striatum. Cromakalim (100 µM) or nicorandil (1 mM) enhanced the formation of OH trapped as DHBA induced by MPP⁺ (5 mM). Concomitantly, these drugs enhanced dopamine (DA) efflux induced by MPP⁺. Tamoxifen (30 µM) significantly decreased the level of DA enhanced by cromakalim or nicorandil. Tamoxifen suppressed DHBA formation induced by MPP⁺ and cromakalim or nicorandil. When iron(II) was administered to cromakalim treated animals, a marked elevation of DHBA was observed, compared with the tamoxifen-treated rats These results indicated that the effects of tamoxifen on opening of K_ATP channels enhances OH generation in the extracellular space of striatum during of DA release by MPP⁺. These results indicated that estrogen protects against neuronal degeneration by as an anti-oxidant.

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.

Hydrogen peroxide constricts rat arteries by activating Na+-permeable and Ca2+-permeable cation channels

Oxidative stress is associated with many cardiovascular diseases, such as hypertension and arteriosclerosis. Oxidative stress reportedly activates the L-type voltage-gated calcium channel (VDCC_L) and elevates [Ca²⁺]_i in many cells. However, how oxidative stress activates VDCC_L under clinical setting and the consequence for arteries are unclear. Here, we examined the hypothesis that hydrogen peroxide (H₂O₂) regulates membrane potential (Em) by altering Na⁺ influx through cation channels, which consequently activates VDCC_L to induce vasoconstriction in rat mesenteric arteries. To measure the tone of the endothelium-denuded arteries, a conventional isometric organ chamber was used. Membrane currents and Em were recorded by the patch-clamp technique. [Ca²⁺]_i and [Na⁺]_i were measured with microfluorometry using Fura2-AM and SBFI-AM, respectively. We found that H₂O₂ (10 and 100 µM) increased arterial contraction, and nifedipine blocked the effects of H₂O₂ on isometric contraction. H₂O₂ increased [Ca²⁺]_i as well as [Na⁺]_i, and depolarised Em. Gd³⁺ (1 µM) blocked all these H₂O₂-induced effects including Em depolarisation and increases in [Ca²⁺]_i and [Na⁺]_i. Although both nifedipine (30 nM) and low Na⁺ bath solution completely prevented the H₂O₂-induced increase in [Na⁺], they only partly inhibited the H₂O₂-induced effects on [Ca²⁺]_i and Em. Taken together, the results suggested that H₂O₂ constricts rat arteries by causing Em depolarisation and VDCC_L activation through activating Gd³⁺-and nifedipine-sensitive, Na⁺-permeable channels as well as Gd³⁺-sensitive Ca²⁺-permeable cation channels. We suggest that unidentified Na⁺-permeable cation channels as well as Ca²⁺-permeable cation channels may function as important mediators for oxidative stress-induced vascular dysfunction.

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.

Chronic cerebrovascular dysfunction after traumatic brain injury

Traumatic brain injuries (TBI) often involve vascular dysfunction that leads to long-term alterations in physiological and cognitive functions of the brain. Indeed, all the cells that form blood vessels and that are involved in maintaining their proper function can be altered by TBI. This Review focuses on the different types of cerebrovascular dysfunction that occur after TBI, including cerebral blood flow alterations, autoregulation impairments, subarachnoid hemorrhage, vasospasms, blood-brain barrier disruption, and edema formation. We also discuss the mechanisms that mediate these dysfunctions, focusing on the cellular components of cerebral blood vessels (endothelial cells, smooth muscle cells, astrocytes, pericytes, perivascular nerves) and their known and potential roles in the secondary injury cascade. © 2016 Wiley Periodicals, Inc.

ABCC9/SUR2 in the brain: Implications for hippocampal sclerosis of aging and a potential therapeutic target

The ABCC9 gene and its polypeptide product, SUR2, are increasingly implicated in human neurologic disease, including prevalent diseases of the aged brain. SUR2 proteins are a component of the ATP-sensitive potassium ("KATP") channel, a metabolic sensor for stress and/or hypoxia that has been shown to change in aging. The KATP channel also helps regulate the neurovascular unit. Most brain cell types express SUR2, including neurons, astrocytes, oligodendrocytes, microglia, vascular smooth muscle, pericytes, and endothelial cells. Thus it is not surprising that ABCC9 gene variants are associated with risk for human brain diseases. For example, Cantu syndrome is a result of ABCC9 mutations; we discuss neurologic manifestations of this genetic syndrome. More common brain disorders linked to ABCC9 gene variants include hippocampal sclerosis of aging (HS-Aging), sleep disorders, and depression. HS-Aging is a prevalent neurological disease with pathologic features of both neurodegenerative (aberrant TDP-43) and cerebrovascular (arteriolosclerosis) disease. As to potential therapeutic intervention, the human pharmacopeia features both SUR2 agonists and antagonists, so ABCC9/SUR2 may provide a "druggable target", relevant perhaps to both HS-Aging and Alzheimer's disease. We conclude that more work is required to better understand the roles of ABCC9/SUR2 in the human brain during health and disease conditions.

Cellular and molecular mechanisms of injury and spontaneous recovery

Until recently, most have assumed that traumatic brain injury (TBI) was singularly associated with the overt destruction of brain tissue resulting in subsequent morbidity or death. More recently, experimental and clinical studies have shown that the pathobiology of TBI is more complex, involving a host of cellular and subcellular changes that impact on neuronal function and viability while also affecting vascular reactivity and the activation of multiple biological response pathways. Here we review the brain's response to injury, examining both focal and diffuse changes and their implications for post-traumatic brain dysfunction and recovery. TBI-induced neuronal dysfunction and death as well as the diffuse involvement of multiple fiber projections are discussed together with considerations of how local axonal membrane changes or channelopathy translate into local ionic dysregulation and axonal disconnection. Concomitant changes in the cerebral microcirculation are also discussed and their relationship with the parallel changes in the brain's metabolism is considered. These cellular and subcellular events occurring within neurons and their blood supply are correlated with multiple biological response modifiers evoked by generalized post-traumatic inflammation and the parallel activation of oxidative stress processes. The chapter closes with considerations of recovery following focal or diffuse injury. Evidence for dynamic brain reorganization/repair is presented, with considerations of traumatically induced circuit disruption and their progression to either adaptive or in some cases, maladaptive reorganization.

RBC-coupled tPA Prevents Whereas tPA Aggravates JNK MAPK-Mediated Impairment of ATP- and Ca-Sensitive K Channel-Mediated Cerebrovasodilation After Cerebral Photothrombosis

The sole Food and Drug Administration-approved treatment for acute stroke is tissue-type plasminogen activator (tPA), but tPA aggravates impairment of cerebrovasodilation during hypotension in a newborn pig photothrombotic model of stroke. Coupling to carrier red blood cells (RBC) enhances thrombolytic effects of tPA, while reducing its side effects. ATP- and Ca-sensitive K channels (Katp and Kca) are important regulators of cerebrovascular tone and mediate cerebrovasodilation during hypotension. Mitogen-activated protein kinase, a family of at least three kinases, ERK, p38, and c-Jun-N-terminal kinase (JNK), is upregulated after photothrombosis. This study examined the effect of photothrombosis on Katp- and Kca-induced cerebrovasodilation and the roles of tPA and JNK during/after injury. Photothrombosis blunted vasodilation induced by the Katp agonists cromakalim, calcitonin gene-related peptide, and the Kca agonist NS 1619, which was aggravated by injection of tPA. In contrast, both pre- or post-injury thrombosis injection of RBC-tPA and JNK antagonist SP 600125 prevented impairment of Katp- and Kca-induced vasodilation. Therefore, JNK activation in thrombosis impairs K channel-mediated cerebrovasodilation. Standard thrombolytic therapy of central nervous system ischemic disorders using free tPA poses the danger of further dysregulation of cerebrohemodynamics by impairing cation-mediated control of cerebrovascular tone, whereas RBC-coupled tPA both restores reperfusion and normalizes cerebral hemodynamics.

Vascular neural network phenotypic transformation after traumatic injury: potential role in long-term sequelae

The classical neurovascular unit (NVU), composed primarily of endothelium, astrocytes, and neurons, could be expanded to include smooth muscle and perivascular nerves present in both the up- and downstream feeding blood vessels (arteries and veins). The extended NVU, which can be defined as the vascular neural network (VNN), may represent a new physiological unit to consider for therapeutic development in stroke, traumatic brain injury, and other brain disorders (Zhang et al., Nat Rev Neurol 8(12):711-716, 2012). This review is focused on traumatic brain injury and resultant post-traumatic changes in cerebral blood flow, smooth muscle cells, matrix, blood-brain barrier structures and function, and the association of these changes with cognitive outcomes as described in clinical and experimental reports. We suggest that studies characterizing TBI outcomes should increase their focus on changes to the VNN, as this may yield meaningful therapeutic targets to resolve posttraumatic dysfunction.

Influence of Sex and ERK MAPK on the Pressure Reactivity Index in Newborn Piglets After Fluid Percussion Injury

Greater impairment in autoregulation is seen in male versus female piglets following fluid percussion injury (FPI). This is partially mediated by a greater upregulation of extracellular signal-related kinase mitogen-activated protein kinase (ERK MAPK). We hypothesized that these trends would be reflected by the pressure reactivity index (PRx), a clinical measure of autoregulation. We further hypothesized that PRx values would correlate well with pial artery dilatory responses to hypotension. Male and female piglets were subjected to FPI and treated with a vehicle or ERK MAPK antagonist U 0126 (1 mg/kg IV) 30 min post-injury. FPI led to upregulation of CSF ERK MAPK in untreated piglets of both sexes, however significantly higher PRx values were seen in male versus female piglets. Following administration of U 0126, elevation of ERK MAPK levels was blocked in both sexes and PRx values were significantly improved in the male. A strong correlation was seen between the PRx and pial artery vasomotor activity. These data support previous observations that male piglets demonstrate reversible ERK MAPK-mediated impairment in autoregulation following FPI, which is reflected by the PRx. The strong correlation between the PRx and pial artery vasomotor activity supports the practice of continuously monitoring cerebrovascular autoregulation in patients using this index.

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.

Influence of Sex and ERK MAPK on the Pressure Reactivity Index in Newborn Piglets After Fluid Percussion Injury

Greater impairment in autoregulation is seen in male versus female piglets following fluid percussion injury (FPI). This is partially mediated by a greater upregulation of extracellular signal-related kinase mitogen-activated protein kinase (ERK MAPK). We hypothesized that these trends would be reflected by the pressure reactivity index (PRx), a clinical measure of autoregulation. We further hypothesized that PRx values would correlate well with pial artery dilatory responses to hypotension. Male and female piglets were subjected to FPI and treated with a vehicle or ERK MAPK antagonist U 0126 (1 mg/kg IV) 30 min post-injury. FPI led to upregulation of CSF ERK MAPK in untreated piglets of both sexes, however significantly higher PRx values were seen in male versus female piglets. Following administration of U 0126, elevation of ERK MAPK levels was blocked in both sexes and PRx values were significantly improved in the male. A strong correlation was seen between the PRx and pial artery vasomotor activity. These data support previous observations that male piglets demonstrate reversible ERK MAPK-mediated impairment in autoregulation following FPI, which is reflected by the PRx. The strong correlation between the PRx and pial artery vasomotor activity supports the practice of continuously monitoring cerebrovascular autoregulation in patients using this index.

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.

tPA contributes to impairment of ATP and Ca sensitive K channel mediated cerebrovasodilation after hypoxia/ischemia through upregulation of ERK MAPK

The sole FDA approved treatment for acute stroke is tissue type plasminogen activator (tPA). However, tPA potentiates impairment of pial artery dilation in response to hypotension after hypoxia/ischemia (H/I) in pigs. ATP and Ca sensitive K channels (Katp and Kca) are important regulators of cerebrovascular tone and mediate cerebrovasodilation in response to hypotension. Mitogen activated protein kinase (MAPK), a family of at least 3 kinases, ERK, p38 and JNK, is upregulated after H/I, with the ERK isoform contributing to vasodilator impairment. This study examined the effect of H/I on Katp and Kca induced pial artery dilation and the roles of tPA and ERK during/after injury in piglets equipped with a closed cranial window. H/I blunted vasodilation induced by the Katp agonists cromakalim, calcitonin gene related peptide (CGRP) and the Kca agonist NS 1619; the effect of each was exacerbated by tPA. Pre- or post-injury treatment with EEIIMD, a hexapeptide derived from plasminogen activator-1, and ERK antagonist U 0126 prevented Katp and Kca channel agonist induced vasodilator impairment while the inactive analogue EEIIMR had no effect. ERK was upregulated after H/I, which was potentiated by tPA. These data indicate that H/I impairs K channel mediated cerebrovasodilation. tPA augments loss of K channel function after injury by upregulating ERK. These data suggest that thrombolytic therapy for treatment of CNS ischemic disorders can dysregulate cerebrohemodynamics by impairing cation-mediated control of cerebrovascular tone.

Blast-induced brain injury and posttraumatic hypotension and hypoxemia

Explosive munitions account for more than 50% of all wounds sustained in military combat, and the proportion of civilian casualties due to explosives is increasing as well. But there has been only limited research on the pathophysiology of blast-induced brain injury, and the contributions of alterations in cerebral blood flow (CBF) or cerebral vascular reactivity to blast-induced brain injury have not been investigated. Although secondary hypotension and hypoxemia are associated with increased mortality and morbidity after closed head injury, the effects of secondary insults on outcome after blast injury are unknown. Hemorrhage accounted for approximately 50% of combat deaths, and the lungs are one of the primary organs damaged by blast overpressure. Thus, it is likely that blast-induced lung injury and/or hemorrhage leads to hypotensive and hypoxemic secondary injury in a significant number of combatants exposed to blast overpressure injury. Although the effects of blast injury on CBF and cerebral vascular reactivity are unknown, blast injury may be associated with impaired cerebral vascular function. Reactive oxygen species (ROS) such as the superoxide anion radical and other ROS, likely major contributors to traumatic cerebral vascular injury, are produced by traumatic brain injury (TBI). Superoxide radicals combine with nitric oxide (NO), another ROS produced by blast injury as well as other types of TBI, to form peroxynitrite, a powerful oxidant that impairs cerebral vascular responses to reduced intravascular pressure and other cerebral vascular responses. While current research suggests that blast injury impairs cerebral vascular compensatory responses, thereby leaving the brain vulnerable to secondary insults, the effects of blast injury on the cerebral vascular reactivity have not been investigated. It is clear that further research is necessary to address these critical concerns.

Oxidative stress and the muscle reflex in heart failure

Muscle contraction stimulates thin fibre muscle afferents and evokes a reflex increase in blood pressure. In heart failure (HF) this reflex is accentuated. Of note, superoxide and other reactive oxygen species are increased in HF. In this report, we tested the hypothesis that excess superoxide contributes to the exaggerated muscle reflex in HF. HF was induced in rats by coronary artery ligation. Electrically induced 30 s hindlimb muscle contraction in decerebrate rats with myocardial infarction (MI) (left ventricular fractional shortening (FS) = 24 +/- 1%; n = 15) evoked larger (P < 0.05) increases in mean arterial pressure (MAP) and renal sympathetic nerve activity (RSNA) as compared to control rats (FS = 47 +/- 1%; n = 14). In the MI rats, the pressor and RSNA responses to contraction were reduced by intra-arterial injection into the hindlimb circulation of tempol (10 mg), a superoxide dismutase mimetic (DeltaMAP: 22 +/- 2 vs. 11 +/- 1 mmHg; integral DeltaRSNA: 1032 +/- 204 vs. 431 +/- 73 arbitrary units (a.u.); before vs. after tempol; P < 0.05). Tempol also attenuated the RSNA response to 1 min intermittent (1-4 s stimulation to relaxation) bouts of static contraction in the MI rats (116 +/- 17 vs. 72 +/- 11 a.u.; P < 0.05; n = 16). In the control rats, tempol had no effect on these responses. These results suggest that excess superoxide in HF sensitizes mechanically sensitive muscle afferents engaged during contraction. We hypothesize that oxidative stress contributes to the exaggerated muscle reflex in HF.

Urokinase plasminogen activator impairs SNP and PGE2 cerebrovasodilation after brain injury through activation of LRP and ERK MAPK

Pial artery dilation in response to prostaglandin (PG)E(2) and the nitric oxide (NO) releaser sodium nitroprusside (SNP) are blunted after fluid percussion brain injury (FPI), whereas responses to papaverine are unchanged. Urokinase plasminogen activator (uPA) and ERK mitogen-activated protein kinase (MAPK) are upregulated and contribute to the impairment of cerebrohemodynamics seen after FPI. PA vascular activity is mediated through the low-density lipoprotein receptor (LRP). Therefore, we investigated the role of uPA, LRP, and ERK MAPK in the impaired cerebrovasodilation response to PGE(2) and SNP after FPI. Lateral FPI (2 atm) was induced in anesthetized piglets equipped with a closed cranial window. Cerebrospinal fluid (CSF) ERK MAPK was quantified by enzyme-linked immunosorbent assay (ELISA). Pretreatment with soluble uPA receptor (suPAR), which antagonizes the vascular action of uPA, blunted the impairment of SNP and PGE(2)-mediated dilation seen after FPI. Pretreatment with the LRP antagonist RAP, a monoclonal antibody against LRP (Mab ag LRP) and the ERK MAPK antagonist, U 0126, all provided similar protection, whereas control immunoglobulin G (IgG) had no effect. Responses to papaverine were unchanged after FPI. Upregulation of ERK MAPK phosphorylation in CSF after FPI was blunted in animals pretreated with suPAR, RAP, MAb ag LRP, or U 0126, whereas control IgG had no effect. These data indicate that uPA contributes to the impairment of SNP and PGE(2)-mediated cerebrovasodilation seen after brain injury through activation of LRP and ERK MAPK.

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

Cerebrovascular dysregulation during hypotension occurs after fluid percussion brain injury (FPI) in the newborn pig owing to impaired K channel function. This study was designed to (1) determine the role of gender and K channel activation in adrenomedullin (ADM) cerebrovasodilation, (2) characterize the role of gender in the loss of hypotensive cerebrovasodilation after FPI, and (3) determine the role of gender in the ability of exogenous ADM to modulate hypotensive dysregulation after FPI. Lateral FPI (2 atm) was induced in newborn male and female newborn pigs (1 to 5 days old) equipped with a closed cranial window, n=6 for each protocol. Adrenomedullin-induced pial artery dilation was significantly greater in female than male piglets and blocked by the K(ATP) channel antagonist glibenclamide, but not by the K(ca) channel antagonist iberiotoxin. Cerebrospinal fluid ADM was increased from 3.8+/-0.7 to 14.6+/-3.0 fmol/mL after FPI in female but was unchanged in male piglets. Hypotensive pial artery dilation was blunted to a significantly greater degree in male versus female piglets after FPI. Topical pretreatment with a subthreshold vascular concentration of ADM (10(-10) mol/L) before FPI reduced the loss of hypotensive pial artery dilation in both genders, but protection was significantly greater in male versus female piglets. These data show that hypotensive pial artery dilation is impaired after FPI in a gender-dependent manner. By unmasking a gender-dependent endogenous protectant, these data suggest novel gender-dependent approaches for clinical intervention in the treatment of perinatal traumatic brain injury.

Perivascular nerve damage in the cerebral circulation following traumatic brain injury

Traumatic brain injury (TBI) causes cerebral vascular dysfunction. Most have assumed that it was the result of endothelial and/or smooth muscle alteration. No consideration, however, has been given to the possibility that the forces of injury may also damage the perivascular nerve network, thereby contributing to the observed abnormalities. To test this premise, we subjected rats to impact acceleration. At 6 h, 24 h and 7 days post-TBI, cerebral basal arteries were removed and processed with antibody targeting protein gene product 9.5 (PGP-9.5), with parallel assessments of 5-hydroxytryptamine (5-HT) accumulation in the perivascular nerves. Additionally, Fluoro-Jade was also used as a marker of axonal degeneration. The perivascular nerve network revealed no abnormality in sham animals. However, by 6 h post injury, Fluoro-Jade reactivity appeared in the perivascular regions, with the number of fibers increasing with time. By 24 h post injury, a significant reduction in the perivascular 5-HT accumulation occurred, together with a reduction in PGP-9.5 fiber staining. At 7 days, a recovery of the PGP-9.5 immunoreactivity occurred, however, it did not reach a control-like distribution. These studies suggest that neurogenic damage occurs following TBI and may be a contributor to some of the associated vascular abnormalities.

NOC/oFQ activates ERK and JNK but not p38 MAPK to impair prostaglandin cerebrovasodilation after brain injury

Fluid percussion brain injury (FPI) elevates the CSF concentration of the opioid nociceptin/orphanin FQ (NOC/oFQ), which contributes to impairment of pial artery dilation to the prostaglandins (PG) PGE2 and PGI2. This study investigated the role of the ERK, p38, and JNK isoforms of mitogen-activated protein kinase (MAPK) in impaired PG cerebrovasodilation after FPI, and the relationship of brain injury induced release of NOC/oFQ to MAPK in such vascular impairment in newborn pigs equipped with a closed cranial window. FPI blunted PGE2 pial artery dilation, but U 0126 and SP 600125 (10(-6) M) (ERK and JNK MAPK inhibitors, respectively) partially prevented such impairment (7 +/- 1, 12 +/- 1, and 17 +/- 1 vs. 2 +/- 1, 3 +/- 1, and 5 +/- 1 vs. 4 +/- 1, 7 +/- 1, and 12 +/- 1% for 1, 10, and 100 ng/ml PGE2 in control, FPI, and FPI + U 0126 pretreated animals, respectively). In contrast, administration of SB 203580 (10(-5) M) (p38 MAPK inhibitor) did not prevent FPI impairment of PGE2 dilation. Co-administration of NOC/oFQ at the dose of 10(-10) M, the cerebrospinal fluid concentration observed after FPI, with PGE2 under non-brain injury conditions blunted PG dilation, but U 0126 or SP 600125 partially prevented such impairment (7 +/- 1, 11 +/- 1, and 16 +/- 2 vs. 0 +/- 1, 1 +/- 1, and 2 +/- 1, vs. 5 +/- 1, 9 +/- 1, and 13 +/- 2 for responses to PGE2 in control, NOC/oFQ, and NOC/oFQ + U 0126 treated animals, respectively). Administration of SB 203580 did not prevent impairment of PG pial artery dilation by NOC/oFQ. These data show that activation of ERK and JNK but not p38 MAPK contributes to impairment of PG cerebrovasodilation after FPI. These data suggest that NOC/oFQ induced ERK and JNK but not p38 MAPK activation contributes to impaired cerebrovasodilation to PG after FPI.

Altered NO function contributes to impairment of uPA and tPA cerebrovasodilation after brain injury

Urokinase (uPA) and tissue plasminogen activator (tPA) are serine proteases implicated in fibrinolysis, but their role in the regulation of the cerebrovascular response to brain trauma has not been investigated. This study was designed to (1) characterize the cerebrovascular activity of uPA and tPA, (2) investigate the role of nitric oxide (NO) in uPA and tPA vascular activity, and (3) characterize the effect of fluid percussion brain injury (FPI) on vascular responses to uPA and tPA. The closed cranial window technique in chloralose anesthetized newborn pigs was used to measure pial artery diameter and collect CSF for radioimmunoassay (RIA) of cGMP concentration. Topical uPA (10(-9), 10(-7) M) elicited pial artery dilation that was blunted by the NO synthase inhibitor, L-NNA (10(-6) M) (8 +/- 1% and 13 +/- 1 vs. 3 +/- 1% and 7 +/- 2%, respectively). Vasodilation in response to uPA was associated with an increase in CSF cGMP concentration (645 +/- 20, 865 +/- 39 and 1088 +/- 33 fmol/mL cGMP for control, uPA 10(-9), 10(-7) M, respectively). Similar data were obtained for tPA. Pial artery dilation to uPA was blunted following FPI (7 +/- 1% and 12 +/- 1% vs. 3 +/- 1% and 6 +/- 1%, respectively), while uPA-associated release of cGMP was blocked (677 +/- 45, 909 +/- 53, and 1110 +/- 55 vs. 283 +/- 10, 316 +/- 18, and 333 +/- 26 fmol/mL for control, uPA 10(-9), 10(-7) M before and after FPI, respectively). Similar data were obtained for tPA. These data show that uPA and tPA produce pial artery dilation in an NO-dependent manner. FPI blunted uPA and tPA induced pial artery dilation as well as the associated release of cGMP. These data suggest therefore that altered NO function contributes to the impairment of uPA and tPA cerebrovasodilation after brain injury.

Nociceptin/orphanin FQ alters prostaglandin cerebrovascular action following brain injury

Previous studies have observed that fluid percussion brain injury (FPI) elevated the CSF concentration of the opioid nociceptin/orphanin FQ (NOC/oFQ). In separate studies, FPI impaired pial artery dilation to the prostaglandins PGI2 and PGE2. This study was designed to investigate the following: (1) role of NOC/oFQ in impaired dilation to PGI2 and PGE2, (2) the effects of FPI on vasoconstriction to the TXA2 mimic U46619 and PGF2alpha, and (3) the role of NOC/oFQ in such FPI induced effects on U46619 and PGF(2alpha). Lateral FPI was induced in newborn pigs equipped with a closed cranial window. PGI2 (1, 10, 100 ng/ml) vasodilation was blunted by FPI and fully restored by the NOC/oFQ antagonist, [F/G] NOC/oFQ (1-13) NH2 (10(-6)M) (9 +/- 1, 13 +/- 1, and 19 +/- 1 vs. 2 +/- 1, 4 +/- 1, and 5 + 1 vs 7 +/- 1, 12 +/- 2, and 17 +/- 3% for control, FPI, and FPI + [F/G] NOC/oFQ (1-13) NH2, respectively). Similar effects were observed for PGE2. In contrast, U46619 (1, 10 ng/ml) induced vasoconstriction was potentiated by FPI but returned to the response observed prior to FPI by [F/G] NOC/oFQ (1-13) NH2 ( -8 +/- 1 and -14 +/- 1 vs. -15 +/- 1 and -25 +/- 1 vs. -7 +/- 1 and -12 +/- 2% for control, FPI, and FPI + [F/G] NOC/oFQ (1-13) NH2, respectively). Similar effects were observed for PGF(2alpha). Coadministration of NOC/oFQ (10(-10)M), the CSF concentration observed after FPI, with agonists under nonbrain injury conditions blunted PGI2 and PGE2 vasodilation, but potentiated U46619 and PGF2alpha vasoconstriction similarly to that observed after FPI. These data show that FPI blunted PGI2 and PGE2 vasodilation but potentiated U46619 and PGF2alpha vasoconstriction. Additionally, these data show that administration of a NOC/oFQ receptor antagonist prevented such FPI associated events. NOC/oFQ administrated in a concentration observed after FPI produced blunted dilator prostaglandin and potentiated vasoconstriction prostaglandin vascular responses under nonbrain injury conditions. Finally, these data suggest that NOC/oFQ alters prostaglandin cerebrovascular action following brain injury.

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

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

The effects of large-dose propofol on cerebrovascular pressure autoregulation in head-injured patients

In healthy individuals, cerebrovascular pressure autoregulation is preserved or even improved when propofol is infused. We examined the effect of an increase in propofol plasma concentration on pressure autoregulation in 10 head-injured patients. Using target-controlled infusions, the static rate of autoregulation was determined at a moderate (2.3 +/- 0.4 microg/mL) and a large (4.3 +/- 0.04 microg/mL) plasma target concentration of propofol. Using norepinephrine to control cerebral perfusion pressure, transcranial Doppler measurements from the middle cerebral artery were made at a cerebral perfusion pressure of 70 and 85 mm Hg at each propofol concentration. Middle cerebral artery flow velocities at the large propofol concentration were significantly lower than at the moderate concentration, without any concurrent increase in arterio-jugular difference in oxygen content, a finding compatible with maintained flow-metabolism coupling. Despite this, static rate of autoregulation decreased significantly from 54% +/- 36% to 28% +/- 35% (P = 0.029). Our data suggest that after head injury, the cerebrovascular effects of propofol are different from those observed in healthy individuals. We propose that large doses of propofol should be used cautiously in head-injured patients, because there is the potential to increase the injured brain's vulnerability to secondary insults.

IMPLICATIONS

Propofol is used for sedation and control of intracranial pressure in head-injured patients. In contrast to previous data from healthy individuals, we show a deterioration of cerebrovascular pressure autoregulation with fast propofol infusion rates after head injury. Large propofol doses may increase the injured brain's vulnerability to secondary insults.

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

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

Cerebrovascular pressure reactivity is related to global cerebral oxygen metabolism after head injury

BACKGROUND

After head injury, impaired cerebrovascular autoregulation has been associated with abnormally high or low cerebral blood flow. The physiological relevance of cerebral blood flow levels is difficult to assess in these patients, whose cerebral metabolic rate for oxygen (CMRO(2)) is known to be abnormal. Investigation of these relations requires quantitative measures of cerebral blood flow and CMRO(2), to allow assessment of oxygen supply and demand relations.

OBJECTIVES

To investigate the relation between dysautoregulation and global cerebral oxygen metabolism following head injury.

METHODS

Using positron emission tomography, global cerebral blood flow, CMRO(2), and oxygen extraction fraction were determined in 22 patients who were investigated in 26 examinations on days 1 to 11 (mean (SD), 3.5 (2.3)) after head injury. Cerebrovascular pressure reactivity was assessed using a pressure reactivity index, calculated as the moving linear correlation coefficient between mean arterial blood pressure and intracranial pressure. Outcome was assessed six months after injury using the Glasgow outcome scale.

RESULTS

Low CMRO(2) was associated with disturbed pressure reactivity (inverse function, R(2) = 0.21, p = 0.018) and there was a correlation between disturbed pressure reactivity and oxygen extraction fraction (quadratic function, R(2) = 0.55, p = 0.0001). There was no significant relation between pressure reactivity and cerebral blood flow. An unfavourable outcome was associated with disturbed pressure reactivity. There was no significant relation between outcome and CMRO(2) or oxygen extraction fraction.

CONCLUSIONS

There is a close relation between dysautoregulation and abnormal cerebral metabolism but not blood flow. Further studies are needed to determine whether metabolic dysfunction is a result of or a cause of disturbed pressure reactivity, and to establish if there is a relation between cerebral oxygen metabolism and outcome.

Protein kinase C activation generates superoxide and contributes to impairment of cerebrovasodilation induced by G protein activation after brain injury

Previous studies have observed that activation of protein kinase C (PKC) contributes to generation of superoxide anion (O(-)(2)) after fluid percussion brain injury (FPI). This study was designed to characterize the effects of FPI on the vascular activity of two activators of a pertussis toxin sensitive G protein, mastoparan and mastoparan-7, and the role of PKC dependent O(-)(2) generation in such effects in newborn pigs equipped with a closed cranial window. Mastoparan (10(-8), 10(-6) M) elicited pial artery dilation that was blunted by FPI and partially restored by the PKC inhibitor chelerythrine (10(-7) M) or the O(-)(2) free radical scavengers polyethylene glycol superoxide dismutase and catalase (SODCAT) (9+/-1 and 16+/-1, sham control; 3+/-1 and 5+/-1, FPI; and 7+/-1 and 11+/-1%, FPI SODCAT pretreated). Similar results were observed for mastoparan-7 but the inactive analogue mastoparan-17 had no effect on pial artery diameter. Exposure of the cerebral cortex to a xanthine oxidase O(-)(2) generating system blunted mastoparan induced pial artery dilation similar to FPI (10+/-1 and 17+/-1 vs. 2+/-1 and 3+/-1%). Pertussis toxin (1 microg/ml) exposure blocked mastoparan and mastoparan-7 vasodilation. These data show that pertussis toxin sensitive G protein activation elicits cerebrovasodilation that is blunted following FPI in a PKC dependent manner. These data also show that O(-)(2) generation similarly blunts G protein mediated cerebrovasodilation. These data suggest that PKC dependent O(-)(2) generation contributes to impaired G protein mediated cerebrovasodilation after FPI.

Effect of mild hypothermia on inodilator-induced vasodilation of pial arterioles in cats

BACKGROUND

Mild hypothermia has been proposed as a means of providing cerebral protection after traumatic brain injury. However, hypothermia has been shown to alter not only physiologic but also pharmacologic responses. The purpose of this study was to investigate whether mild hypothermia (3-4 degrees C temperature reduction) could alter cerebral vasodilation induced by inodilators, which are characterized by having an inotropic effect in addition to a vasodilatory effect. Isoproterenol (a beta-adrenergic receptor agonist), colforsin dapropate (an adenylate cyclase stimulant), and amrinone (a phosphodiesterase inhibitor) were chosen as inodilators.

METHODS

The cranial window technique, combined with microscopic video recording, was used. Forty-eight cats were randomly assigned to either a normothermic or a hypothermic group (33 degrees C). Isoproterenol, colforsin dapropate, or amrinone was topically applied in the cranial window and the diameter of pial arterioles was measured.

RESULTS

Topical administration of isoproterenol, colforsin dapropate, and amrinone produced a significant dilation in a dose-dependent manner during normothermia. The vasodilation induced by these inodilators was not affected by mild hypothermia.

CONCLUSION

The vasodilation induced by topical administration of isoproterenol, colforsin dapropate, and amrinone was not affected by mild hypothermia.

Protein tyrosine kinase and mitogen-activated protein kinase activation contribute to K(ATP) and K(ca) channel impairment after brain injury

Previous studies have observed that pial artery dilation to activators of the ATP sensitive K (K(ATP)) and calcium sensitive K (K(ca)) channel was blunted following fluid percussion brain injury (FPI) in the piglet. In recent studies in the rat, protein tyrosine kinase (PTK) activation was observed to contribute to K(ATP) channel impairment after FPI, but such a role in K(ca) channel impairment was unclear. This study investigated the role of PTK and mitogen activated protein kinase (MAPK) activation in blunted pial dilation to K(ATP) and K(ca) channel agonists following FPI in piglets equipped with a closed cranial window. Cromakalim and NS1619 (10(-8), 10(-6) M) induced pial artery dilation was blunted after FPI, but partially restored by the PTK inhibitors genistein (10(-6) M) and tyrphostin A23 (10(-5) M) (10+/-1 and 19+/-1%, sham control; 2+/-1 and 4+/-1%, FPI; and 7+/-1 and 11+/-1% FPI-genistein pretreated for NS1619 10(-8), 10(-6) M, respectively). Cromakalim- and NS1619-induced pial dilation was also partially restored after FPI by pretreatment with the MAPK inhibitors U0126 (10(-6) M) and PD98059 (10(-5) M) (12+/-1 and 21+/-1%, sham control; 2+/-1 and 4+/-1%, FPI; and 6+/-1 and 10+/-2%, FPI-U0126 pretreated for NS1619 10(-8), 10(-6) M, respectively). These data suggest that PTK and MAPK activation contribute to K(ATP) and K(ca) channel impairment following FPI.

Gene transfer of Cu/Zn SOD to cerebral vessels prevents FPI-induced CBF autoregulatory dysfunction

The goal of this study was to determine whether gene transfer of human copper-zinc (Cu/Zn) superoxide dismutase (SOD) has preventive effects on cerebral blood flow (CBF) autoregulatory dysfunction after fluid percussion injury (FPI). Rats subjected to FPI (2-2.5 atm) exhibited enhanced activity of reduced NADP (NADPH) oxidase in the cerebral vasculature. In line with these findings, the rats showed not only reduced vasodilation of the pial artery in response to calcitonin gene-related peptide and levcromakalim but also impaired autoregulatory vasodilation in response to acute hypotension. The FPI-induced hemodynamic alterations were significantly prevented by pretreatment with diphenyleneiodonium (10 micromol/l), an NAD(P)H oxidase inhibitor. Intracisternal application of recombinant adenovirus (100 microl of 1 x 10(10) pfu/ml)-encoding human Cu/Zn SOD 3 days before FPI prevented the impairment of vasodilation to hypotension and vasorelaxants, resulting in the restoration of CBF autoregulation. Our findings demonstrate that FPI-induced impairment of CBF autoregulation is closely related with NAD(P)H oxidase-derived superoxide anion, and these alterations can be prevented by the recombinant adenovirus-mediated transfer of human Cu/Zn SOD gene to the cerebral vasculature.

Oxidative stress and potassium channel function

1. Modulation of K+ channel activities by cellular oxidative stress has emerged as a significant determinant of vasomotor function in multiple disease states. 2. Evidence from in vitro and in vivo studies suggest that superoxide (O2-) and hydrogen peroxide (H2O2) enhance BKCa channel activity in rat and cat cerebral arterioles; however, activity is decreased by peroxynitrite (ONOO-) in rat cerebral arteries. The mechanisms of changes in BKCa channel properties are not fully understood and may involve oxidation of cysteine residues that are located in the cell membranes. 3. Studies further suggest that O2- increases KATP channel activity in guinea-pig cardiac myocytes, but decreases opening in cerebral vasculature. Both H2O2 and ONOO- enhance KATP channel activity in the myocardium and in coronary, renal, mesenteric and cerebral vascular beds. Alteration of KATP channels by free radicals may be due to oxidation of SH groups or changes in the cytosolic concentration of ATP. 4. It does appear that O2- produced by either reaction of xanthine and xanthine oxidase or elevated levels of glucose reduces Kv channel activity and the impairments can be partially restored by free radical scavengers, superoxide dismutase and catalase. 5. Thus, redox modulation of potassium channel activity is an important mechanism regulating cell vascular smooth muscle membrane potential.

Endothelin-Induced cyclooxygenase-dependent superoxide generation contributes to K+ channel functional impairment after brain injury

This study determined if endothelin (ET-1) generates superoxide anion (O2-) in a cyclooxygenase-dependent manner and if such production contributes to impairment of dilation to activators of ATP-sensitive K+ (KATP) and calcium-sensitive K+ (Kca) channels following fluid percussion brain injury (FPI) in newborn pigs equipped with closed cranial windows. Superoxide dismutase (SOD)-inhibitable nitroblue tetrazolium (NBT) reduction was determined as an index of O2- generation. Under non-brain injury conditions, topical ET-1 (10(-10) M, the concentration present in CSF following FPI) increased SOD-inhibitable NBT reduction from 1 +/- 1 to 17 +/- 3 pmol/mm2. Indomethacin, a cyclooxygenase inhibitor, blunted such NBT reduction (1 +/- 1 to 4 +/- 1 pmol/mm2), while the ET-1 antagonist BQ123 blocked NBT reduction. BQ123 and indomethacin also blunted the NBT reduction observed after FPI. Under non-brain injury conditions, ET-1 (10(-10) M) coadministered with the KATP and Kca channel agonists cromakalim and NS1619 (10-8, 10(-6) M) diminished dilation to these K+ channel agonists, while indomethacin partially prevented such impairment (13 +/- 1 and 23 +/- 1 vs. 2 +/- 1 and 6 +/- 1 vs. 6 +/- 1 and 14 +/- 2% for cromakalim in untreated, ET-1, and ET-1 plus indomethacin-treated piglets, respectively). Cromakalim- and NS1619-induced pial artery dilation was attenuated following FPI, while indomethacin or BQ123 preadministration partially prevented such impairment (13 +/- 1 and 23 +/- 1, sham control; 1 +/- 1 and 4 +/- 1, FPI; 8 +/- 1 and 16 +/- 3%, FPI and indomethacin-pretreated for responses to cromakalim 10(-8), 10-6 M, respectively). These data show that ET-1 increased O2- production in a cyclooxygenase-dependent manner and contributed to this production after FPI. These data also show that ET-1 blunted KATP and Kca channel-mediated cerebrovasodilation in a cyclooxygenase dependent manner. These data suggest that ET-1-induced cyclooxygenase-dependent O2- generation contributes to KATP and Kca channel function impairment after FPI.

Vasopressin induced cyclooxygenase dependent superoxide generation contributes to K(+) channel function impairment after brain injury

This study determined if vasopressin generates superoxide anion (O2(-)) in a cyclooxygenase dependent manner and if such production contributes to impairment of dilation to activators of ATP sensitive K(+) (K(ATP)) and calcium sensitive K(+) (K(ca)) channels following fluid percussion brain injury (FPI) in newborn pigs equipped with closed cranial windows. Superoxide dismutase (SOD) inhibitable nitroblue tetrazolium (NBT) reduction was determined as an index of O2(-) generation. Under non-brain injury conditions, topical vasopressin (40 pg/ml, the concentration present in CSF following FPI) increased SOD inhibitable NBT reduction from 1+/-1 to 25+/-4 pmol/mm(2). Indomethacin, a cyclooxygenase inhibitor, blunted such NBT reduction (1+/-1 to 5+/-1 pmol/mm(2)), while the vasopressin antagonist, l-(beta-mercapto-beta beta-cyclopentamethylene propionic acid) 2-(o-methyl)-Tyr-AVP (MEAVP) blocked NBT reduction. MEAVP and indomethacin also blunted the NBT reduction observed after FPI. Under non-brain injury conditions, vasopressin (40 pg/ml) coadministered with the K(ATP) and K(ca) channel agonists, cromakalim and NS1619 (10(-8), 10(-6) M) diminished dilation to these K(+) channel agonists while indomethacin partially prevented such impairment (13+/-1 and 23+/-1 vs. 4+/-1 and 10+/-2 vs. 8+/-1 and 19+/-1% for cromakalim in untreated, vasopressin, and vasopressin plus indomethacin treated piglets, respectively). Cromakalim and NS1619 induced pial artery dilation was attenuated following FPI, while indomethacin or MEAVP preadministration partially prevented such impairment (13+/-1 and 23+/-1, sham control; 1+/-1 and 4+/-1, FPI; 8+/-1 and 16+/-3%, FPI-indomethacin pretreated for responses to cromakalim 10(-8), 10(-6) M, respectively). These data show that vasopressin increased O2(-) production in a cyclooxygenase dependent manner and contributed to this production after FPI. These data also show that vasopressin blunted K(ATP) and K(ca) channel mediated cerebrovasodilation in a cyclooxygenase dependent manner. These data suggest that vasopressin induced cyclooxygenase dependent O2(-) generation contributes to K(ATP) and K(ca) channel function impairment after FPI.

Restoration of vasodilation and CBF autoregulation by genistein in rat pial artery after brain injury

This study determined whether, after fluid percussion injury (FPI), tyrosine kinase activation is coupled to inhibition of K(+) channels and alteration in cerebral blood flow (CBF) autoregulation in the rat pial artery. Injury of moderate severity (2--2.5 atm) was produced by FPI in anesthetized rats equipped with a closed cranial window. The suppressed vasodilation of the pial arterioles to calcitonin gene-related peptide (CGRP) and levcromakalim (LMK) and altered lower limit of CBF autoregulation after FPI were restored by genistein but not by daidzein, an inactive analog. Vasodilation to S-nitroso-N-acetyl penicillamine (0.1--10 micromol/l) was, however, little influenced after FPI. The restored vasodilation was decreased by sodium orthovanadate, suggesting the reciprocal action of tyrosine phosphorylation and dephosphorylation. After FPI, CGRP-induced vasodilation restored by genistein (10 micromol/l) was strongly antagonized by iberiotoxin but not by glibenclamide, whereas LMK-induced vasodilation was, in contrast, inhibited by glibenclamide but not by iberiotoxin. Taken together, we suggest that, after FPI, activation of tyrosine kinase links the inhibition of K(+) channels to impaired autoregulatory vasodilation in response to acute hypotension and alteration in CBF autoregulation in the rat pial artery.

Vasopressin impairs K(ATP) and K(ca) channel function after brain injury

This study was designed to characterize the role of vasopressin in impaired pial artery dilation to activators of the ATP sensitive K (K(ATP)) and calcium sensitive K (K(ca)) channel following fluid percussion brain injury (FPI) in newborn pigs equipped with a closed cranial window. Topical vasopressin was coadministered with the K(ATP) and K(ca) channel agonists cromakalim and NS1619 in a concentration approximating that observed in CSF following FPI. Vasopressin so administered attenuated pial artery dilation to these K(+) channel activators under conditions of equivalent baseline diameter during non injury conditions (13+/-1 and 23+/-1 vs. 4+/-1 and 10+/-2% for cromakalim 10(-8), 10(-6) M before and after vasopressin, respectively). Attenuated responses were fully restored when these agonists were coadministered with vasopressin and the vasopressin antagonist [l-(beta-mercapto-beta, beta-cyclopentamethylene propionic acid) 2-(o-methyl)-Tyr-AVP] (MEAVP). Cromakalim and NS1619 induced pial artery dilation was attenuated following FPI and MEAVP preadministration partially prevented such impairment (13+/-1 and 23+/-1, sham control; 2+/-1 and 5+/-1, FPI; and 9+/-1 and 15+/-2%, FPI-MEAVP pretreated for responses to cromakalim 10(-8), 10(-6) M, respectively). These data show that vasopressin blunts K(ATP) and K(ca) channel mediated cerebrovasodilation. These data suggest that vasopressin contributes to impaired K(ATP) and K(ca) channel function after brain injury.

NOC/oFQ contributes to age-dependent impairment of NMDA-induced cerebrovasodilation after brain injury

This study characterized the effects of fluid percussion brain injury (FPI) on N-methyl-D-aspartate (NMDA)-induced vasodilation and determined the role of nociceptin/orphanin FQ (NOC/oFQ) in such changes as a function of age and time postinsult. FPI elevated cerebrospinal fluid (CSF) NOC/oFQ from 70 +/- 3 to 444 +/- 56 pg/ml ( approximately 10(-10) M) within 1 h and to 1,931 +/- 112 pg/ml within 8 h, whereas values returned to control levels within 168 h in the newborn pig. In contrast, FPI elevated CSF NOC/oFQ from 77 +/- 4 to 202 +/- 16 pg/ml within 1 h and values returned to control levels within 8 h in the juvenile pig. Topical NOC/oFQ (10(-10) M) had no effect on pial artery diameter but attenuated NMDA (10(-8), 10(-6) M)-induced dilation (9 +/- 1 and 16 +/- 1 vs. 5 +/- 1 and 10 +/- 1%) in both age groups. In the newborn, NMDA-induced pial artery dilation was reversed to vasoconstriction within 1 h post-FPI and responses remained impaired for 72 h, but such vasoconstriction was attenuated by pretreatment with [F/G]NOC/oFQ(1-13)-NH(2) (10(-6) M, 1 mg/kg iv), an NOC/oFQ antagonist (9 +/- 1 and 16 +/- 1 vs. -7 +/- 1 and -12 +/- 1 vs -2 +/- 1 and -3 +/- 1% for control, FPI, and FPI pretreated with the NOC/oFQ antagonist). In contrast, in the juvenile, NMDA-induced vasodilation was only attenuated within 1 h post-FPI and returned to control within 8 h. Such dilation was also partially restored by the NOC/oFQ antagonist. These data indicate that NOC/oFQ contributes to impaired NMDA pial artery dilation after FPI. These data suggest that the greater NOC/oFQ release in the newborn versus the juvenile may contribute to age-related differences in FPI effects on excitatory amino acid-induced pial dilation.

Role of nociceptin/orphanin FQ in age-dependent cerebral hemodynamic effects of brain injury

This study was designed to compare the role of the newly described endogenous opioid nociceptin/orphanin FQ (NOC/oFQ) in the reductions of cerebral blood flow (CBF) and pial artery diameter observed following fluid percussion brain injury (FPI) in chloralose anesthetized newborn and juvenile pigs as a function of time postinsult. FPI elevated CSF NOC/oFQ concentration from 70 +/- 3 to 444 +/- 51 within 1 h and to 1,931 +/- 112 pg/mL (n = 7) within 8 h, whereas concentrations returned to control value within 168 h in the newborn. In contrast, FPI elevated CSF NOC/oFQ from 77 +/- 4 to 202 +/- 16 pg/mL (n = 7) within 1 h, while values returned to control value within 8 h in the juvenile. Topical NOC/oFQ (10(-8), 10(-6) M) induced vasodilation was reversed to vasoconstriction by FPI in the newborn while such responses were only attenuated in the juvenile at 1 h post insult (control, 9 +/- 1 and 16 +/- 1%; FPI newborn, -8 +/- 1 and -14 +/- 1%; FPI juvenile, 2 +/- 1 and 5 +/- 1%, n = 7). Such altered dilation returned to control value within 168 h in newborns and 8 h in juveniles. Blood flow in the cerebrum was reduced from 57 +/- 4 to 23 +/- 3 mL x min(-1) x 100 g(-1) (n = 7) within 1 h and returned to control value with 168 h post FPI in newborns. In animals pretreated with [F/G] NOC/oFQ (1-13) NH2 (1 mg/kg, i.v.), a NOC/oFQ antagonist, however, CBF only fell to 39 +/- 4 mL x min(-1) x 100 g(-1) (n = 7) at 1 h post insult in newborns. In contrast, CBF was only reduced from 57 +/- 6 to 32 +/- 2 in untreated and to 39 +/- 3 mL/min(-1) x 100 g(-1) (n = 7) in treated juveniles within 1 h post FPI. Similar observations for reductions in pial artery diameter were made in untreated and treated newborns and juveniles. These data suggest that an elevated CSF NOC/oFQ concentration and altered vascular responsiveness to this opioid contribute to reductions in CBF and pial artery diameter observed following FPI. Because such NOC/oFQ changes were greater in newborns versus juveniles, these data further suggest that NOC/oFQ contributes to age-related cerebral hemodynamic differences in the effects of FPI.

Potassium channels modulate cerebral autoregulation during acute hypertension

We tested the hypothesis that constriction of cerebral arterioles during acute increases in blood pressure is attenuated by activation of potassium (K(+)) channels. We tested the effects of inhibitors of calcium-dependent K(+) channels [iberiotoxin (50 nM) and tetraethylammonium (TEA, 1 mM)] on changes in arteriolar diameter during acute hypertension. Diameter of cerebral arterioles (baseline diameter = 46 +/- 2 microm, mean +/- SE) was measured using a cranial window in anesthetized rats. Arterial pressure was increased from a control value of 96 +/- 1 mmHg to 130, 150, 170, and 200 mmHg by intravenous infusion of phenylephrine. Increases in arterial pressure from baseline to 130 and 150 mmHg decreased the diameter of cerebral arterioles by 5-10%. Greater increases in arterial pressure produced large increases in arteriolar diameter (i.e., "breakthrough of autoregulation"). Iberiotoxin or TEA inhibited increases in arteriolar diameter when arterial pressure was increased to 170 and 200 mmHg. The change in arteriolar diameter at 200 mmHg was 20 +/- 3% and -1 +/- 4% in the absence and presence of iberiotoxin, respectively. These findings suggest that calcium-dependent K(+) channels attenuate cerebral microvascular constriction during acute increases in arterial pressure, and that increases in arteriolar diameter at high levels of arterial pressure are not simply a passive phenomenon.

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

This study was designed to compare the effect of fluid percussion brain injury (FPI) on the hypotensive cerebrovascular response in newborn and juvenile pigs as a function of time postinsult and to determine the role of endothelin-1 (ET-1) in any age-dependent differences in hypotensive cerebrovascular regulation after injury. Ten minutes of hypotension (10-15 ml blood/kg) decreased mean arterial blood pressure uniformly in both groups ( approximately 45%). In the newborn, hypotensive pial artery dilation (PAD) was blunted within 1 h, remained diminished for at least 72 h, but was resolved within 168 h postinjury (66 +/- 4, 69 +/- 4, 71 +/- 4, and 64 +/- 4% inhibition at 1, 4, 8, and 72 h post-FPI). During normotension, regional cerebral blood flow (rCBF) was decreased by FPI, and hypotension further reduced the already decremented rCBF for at least 72 h. Cerebrospinal fluid (CSF) ET-1 was increased from 26 +/- 4 to 206 +/- 25 pg/ml within 72 h post-FPI, whereas an ET-1 antagonist partially restored impaired hypotensive PAD and altered hypotensive rCBF. In contrast, hypotensive PAD and altered CBF were only inhibited for 4 h post-FPI in the juvenile (56 +/- 3 and 34 +/- 4% inhibition at 1 and 4 h post-FPI). CSF ET-1 was only increased from 27 +/- 4 to 67 +/- 9 pg/ml at 4 h, whereas the concentration returned to preinjury value by 8 h post-FPI. ET-1 antagonism similarly partially restored impaired hypotensive PAD and altered hypotensive rCBF. These data show that FPI disturbs cerebral autoregulation during hypotension both to a greater magnitude and for a longer duration in the newborn than in the juvenile. These data suggest that the greater FPI-induced ET-1 release in the newborn could contribute to age-dependent differences in impaired hypotensive cerebral autoregulation after FPI.

Age-dependent impairment of K(ATP) channel function following brain injury

Previous studies observed that endothelin-1 (ET-1) contributed to ATP-sensitive K+ (K(ATP)) channel impairment 1 h following fluid percussion brain injury (FPI) in the newborn pig. The present study was designed to determine the effect of FPI on K(ATP) channel activity as a function of time in newborn (1-5 days old) and juvenile (3-4 weeks old) pigs equipped with a closed cranial window. FPI of moderate severity (1.9-2.1 atm) was produced by using a pendulum to strike a piston on a saline-filled cylinder that was fluid coupled to the brain via a hollow screw inserted through the cranium. Cromakalim, a K(ATP) agonist, produced dilation that was blunted for at least 72 h post FPI, but dilator responsiveness was restored within 168 h post FPI in the newborn pig (15+/-1% and 27+/-2% vs. 5+/-1% and 11+/-1% vs. 13+/-1% and 26+/-2% for responses to 10(-8), 10(-6) M cromakalim before, and 72 and 168 h after FPI). Similar inhibited responses were observed for calcitonin gene-related peptide, 8-Bromo cGMP, and the nitric oxide (NO) releasers SNP and SNAP. In contrast, cromakalim-induced dilation was blunted for at least 4 h, but dilator responsiveness was restored within 8 h post FPI in the juvenile pig (15+/-1% and 27+/-1% vs. 9+/-1% and 15+/-2% vs. 18+/-1% and 28+/-1% for 10(-8), 10(-6) M cromakalim before, and 4 and 8 h post FPI). Similar inhibition of dilations of other agonists also occurred in the juvenile. CSF ET-1 increased to a greater level and remained elevated for a longer period of time in the newborn compared to the juvenile pig. BQ123, an ET-1 antagonist, pretreatment partially restored decremented agonist induced dilation following FPI in the newborn and juvenile pig (5+/-1% and 11+/-1% vs. 11+/-1% and 21+/-1% for responses to 10(-8), 10(-6) M cromakalim 72 h post FPI in the newborn in the absence and presence of BQ123). These data indicate that K(ATP) channel function is impaired to a greater extent and for a longer time period in the newborn versus the juvenile pig. These data also show that ET-1 contributes to such impaired vascular responsiveness to a greater extent in the newborn versus the juvenile pig. These data furthermore suggest that the newborn is more sensitive to traumatic vascular injury than the juvenile.

The consequences of traumatic brain injury on cerebral blood flow and autoregulation: a review

In this decade, the brain argueably stands as one of the most exciting and challenging organs to study. Exciting in as far as that it remains an area of research vastly unknown and challenging due to the very nature of its anatomical design: the skull provides a formidable barrier and direct observations of intraparenchymal function in vivo are impractical. Moreover, traumatic brain injury (TBI) brings with it added complexities and nuances. The development of irreversible damage following TBI involves a plethora of biochemical events, including impairment of the cerebral vasculature, which render the brain at risk to secondary insults such as ischemia and intracranial hypertension. The present review will focus on alterations in the cerebrovasculature following TBI, and more specifically on changes in cerebral blood flow (CBF), mediators of CBF including local chemical mediators such as K+, pH and adenosine, endothelial mediators such as nitric oxide and neurogenic mediators such as catecholamines, as well as pressure autoregulation. It is emphasized that further research into these mechanisms may help attenuate the prevalence of secondary insults and therefore improve outcome following TBI.

Cerebral hemodynamics after traumatic brain injury of immature brain

These studies were designed to characterize the cerebral hemodynamic effects of fluid percussion brain injury (FPI) in the newborn pig equipped with a closed cranial window. Reductions in cerebral blood flow, pial artery diameter, and cerebral oxygenation following FPI were greater in newborn (1-3 days old) vs. juvenile (3-4 weeks old) pigs, suggesting that newborns were exquisitely sensitive to brain injury. Additionally, in piglets, there was decremented dilation to nitric oxide, cGMP, and cAMP dependent stimuli following FPI. The membrane potential of vascular muscle is an important contributor to vascular tone and the activity of K+ channels is an important regulator of membrane potential. Recent studies indicate that altered dilator responsiveness and cerebral hemodynamic control following FPI results from impaired K+ ATP sensitive (KATP) and calcium sensitive (Kca+2) channel function. Impaired KATP channel function results, at least in part, from protein kinase C activation by the peptide endothelin-1. These observations indicate that the effects of brain injury on cerebral hemodynamics in the newborn are multifaceted and multifactorial.