Effect of graded hypoxia on brain cell membrane injury in newborn piglets

Lipid peroxidation increases membrane tension, Piezo1 gating, and cation permeability to execute ferroptosis

The ongoing metabolic and microbicidal pathways that support and protect cellular life generate potentially damaging reactive oxygen species (ROS). To counteract damage, cells express peroxidases, which are antioxidant enzymes that catalyze the reduction of oxidized biomolecules. Glutathione peroxidase 4 (GPX4) is the major hydroperoxidase specifically responsible for reducing lipid peroxides; this homeostatic mechanism is essential, and its inhibition causes a unique type of lytic cell death, ferroptosis. The mechanism(s) that lead to cell lysis in ferroptosis, however, are unclear. We report that the lipid peroxides formed during ferroptosis accumulate preferentially at the plasma membrane. Oxidation of surface membrane lipids increased tension on the plasma membrane and led to the activation of Piezo1 and TRP channels. Oxidized membranes thus became permeable to cations, ultimately leading to the gain of cellular Na⁺ and Ca²⁺ concomitant with loss of K⁺. These effects were reduced by deletion of Piezo1 and completely inhibited by blocking cation channel conductance with ruthenium red or 2-aminoethoxydiphenyl borate (2-APB). We also found that the oxidation of lipids depressed the activity of the Na⁺/K⁺-ATPase, exacerbating the dissipation of monovalent cation gradients. Preventing the changes in cation content attenuated ferroptosis. Altogether, our study establishes that increased membrane permeability to cations is a critical step in the execution of ferroptosis and identifies Piezo1, TRP channels, and the Na⁺/K⁺-ATPase as targets/effectors of this type of cell death.

Epidermal Growth Factor Receptor Inhibition Reverses Cellular and Transcriptomic Alterations Induced by Hypoxia in the Neonatal Piglet Brain

Acute hypoxia (HX) causes extensive cellular damage in the developing human cerebral cortex. We found increased expression of activated-EGFR in affected cortical areas of neonates with HX and investigated its functional role in the piglet, which displays a highly evolved, gyrencephalic brain, with a human-like maturation pattern. In the piglet, HX-induced activation of EGFR and Ca²⁺/calmodulin kinase IV (CaMKIV) caused cell death and pathological alterations in neurons and glia. EGFR blockade inhibited CaMKIV activation, attenuated neuronal loss, increased oligodendrocyte proliferation, and reversed HX-induced astrogliosis. We performed for the first time high-throughput transcriptomic analysis of the piglet cortex to define molecular responses to HX and to uncover genes specifically involved in EGFR signaling in piglet and human brain injury. Our results indicate that specific molecular responses modulated by EGFR may be targeted as a therapeutic strategy for HX injury in the neonatal brain.

Iron overload: Effects on cellular biochemistry

Iron is an essential element for human life. However, it is a pro-oxidant agent capable of reacting with hydrogen peroxide. An iron overload can cause cellular changes, such as damage to the plasma membrane leading to cell death. Effects of iron overload in cellular biochemical processes include modulating membrane enzymes, such as the Na, K-ATPase, impairing the ionic transport and inducing irreversible damage to cellular homeostasis. To avoid such damage, cells have an antioxidant system that acts in an integrated manner to prevent oxidative stress. In addition, the cells contain proteins responsible for iron transport and storage, preventing its reaction with other substances during absorption. Moreover, iron is associated with cellular events coordinated by iron-responsive proteins (IRPs) that regulate several cellular functions, including a process of cell death called ferroptosis. This review will address the biochemical aspects of iron overload at the cellular level and its effects on important cellular structures.

Noninvasive monitoring of brain edema after hypoxia in newborn piglets

BackgroundDevelopment of cerebral edema after brain injury carries a high risk for brain damage and death. The present study tests the ability of a noninvasive cerebral edema monitoring system that uses near-infrared spectroscopy (NIRS) with water as the chromophore of interest to detect brain edema following hypoxia.MethodsVentilated piglets were exposed to hypoxia for 1 h, and then returned to normal oxygen levels for 4 h. An NIRS sensor was placed on the animal's head at baseline, and changes in light attenuation were converted to changes in H₂O. Cerebral water content and aquaporin-4 protein (AQP4) expression were measured.ResultsThe system detected changes in NIRS-derived water signal as early as 2 h after hypoxia, and provided fivefold signal amplification, representing a 10% increase in brain water content and a sixfold increase in AQP4, 4 h after hypoxia. Changes in water signal correlated well with changes in cerebral water content (R=0.74) and AQP4 expression (R=0.97) in the piglet brain.ConclusionThe data show that NIRS can detect cerebral edema early in the injury process, thus providing an opportunity to initiate therapy at an earlier and more effective time-point after an insult than is available with current technology.

Iron overload impact on P-ATPases

Iron is a chemical element that is active in the fundamental physiological processes for human life, but its burden can be toxic to the body, mainly because of the stimulation of membrane lipid peroxidation. For this reason, the action of iron on many ATPases has been studied, especially on P-ATPases, such as the Na⁺,K⁺-ATPase and the Ca²⁺-ATPase. On the Fe²⁺-ATPase activity, the free iron acts as an activator, decreasing the intracellular Fe²⁺ and playing a protection role for the cell. On the Ca²⁺-ATPase activity, the iron overload decreases the enzyme activity, raising the cytoplasmic Ca²⁺ and decreasing the sarco/endoplasmic reticulum and the Golgi apparatus Ca²⁺ concentrations, which could promote an enzyme oxidation, nitration, and fragmentation. However, the iron overload effect on the Na⁺,K⁺-ATPase may change according to the tissue expressions. On the renal cells, as well as on the brain and the heart, iron promotes an enzyme inactivation, whereas its effect on the erythrocytes seems to be the opposite, directly stimulating the ATPase activity, or stimulating it by signaling pathways involving ROS and PKC. Modulations in the ATPase activity may impair the ionic transportation, which is essential for cell viability maintenance, inducing irreversible damage to the cell homeostasis. Here, we will discuss about the iron overload effect on the P-ATPases, such as the Na⁺,K⁺-ATPase, the Ca²⁺-ATPase, and the Fe²⁺-ATPase.

Effect of Intranasally Delivered rh-VEGF165 on Angiogenesis Following Cerebral Hypoxia-Ischemia in the Cerebral Cortex of Newborn Piglets

Background: Vascular endothelial growth factor (VEGF) stimulates vascular genesis and angiogenesis. Cerebral Hypoxia-Ischemia (HI) leads to the reduction of vasculature in the cerebral cortex of newborn piglets. Objective: The present study tests the hypothesis that post-hypoxia intranasal administration of recombinant human VEGF₁₆₅ (rh-VEGF165) for 3 days increases the vascular density in the cerebral cortex of newborn piglets without promoting neovascularization. Design/Methods: Ventilated newborn piglets were divided into three groups (n = 5/group): normoxic (Nx), hypoxic-ischemic (HI), and HI treated with intranasal rh-VEGF165rh-VEGF165 (HI-VEGF). HI piglets were exposed to HI (0.05 FiO2) for 30 min. Recombinant h-VEGF165 (100 ng/kg) was administered 15 min after HI and then once daily for 3 days. The animals were perfused transcardially and coronal brains sections were processed for Isolectin, Hoechst, and ki-67 cell proliferation marker staining. To assess the vascular density, 30–35 fields per animal section were manually counted using image J software. Results: The vascular density (vessels/mm²) was 42.0 ± 8.0 in the Nx group, 26.4 ± 4.8 (p < 0.05 vs. Nx) in the HI group, and 46.0 ± 11.9 (p < 0.05 vs. HI) in the HI-VEGF group. When stained for newly formed vessels, via Ki-67 staining, the vascular density was 5.4 ± 3.6 in the Nx group (p < 0.05 vs. HI), 10.2 ± 2.1 in the HI group, and 10.9 ± 2.9 in the HI-VEGF group (p = 0.72 vs. HI). HI resulted in a decrease in vascular density. Intranasal rh-VEGF165rh-VEGF165 resulted in the attenuation of the HI-induced decrease in vascular density. However, rh-VEGF165 did not result in the formation of new vascularity, as evident by ki-67 staining. Conclusions: Intranasal rh-VEGF165 may prevent the HI-induced decrease in the vascular density of the brain and could serve as a promising adjuvant therapy for hypoxic-ischemic encephalopathy (HIE).

Role of mitochondrial permeability transition in the immature brain following intrauterine ischemia

Recirculation following 30 minutes of intrauterine ischemia due to uterine artery occlusion has previously been found to be accompanied by delayed deterioration of the cellular bioenergetic state and of mitochondrial function in the fetal rat brain. The objective of this study was to assess whether the delayed deterioration is due to the activation of mitochondrial permeability transition (MPT), which is observed ultrastructurally as mitochondrial swelling. The respiratory activities and ultrastructure of isolated mitochondria and the cellular bioenergetic state in the fetal rat brain were examined at the end of 30 minutes of intrauterine ischemia and after 1, 2, 3 or 4 hours of recirculation. Cyclosporin A (CsA), a potent and specific MPT blocker, or vehicle was given 1 hour after recirculation. In the vehicle-treated animals, the transient ischemia was associated with a delayed deterioration of the cellular bioenergetic state and mitochondrial activities 4 hours of recirculation. The number of swollen mitochondria increased markedly after 4 hours of recirculation. Both the deterioration and swelling were prevented by CsA. The present study indicates that treatment with CsA improves recovery of energy metabolism and inhibits mitochondrial swelling following transient intrauterine ischemia in the fetal brain. The results suggest that mitochondria and MPT may be involved in the development of ischemic brain damage in the immature rat.

Effect of resuscitation with 21% oxygen and 100% oxygen on NMDA receptor binding characteristics following asphyxia in newborn piglets

The present study investigated the effect of reventilation with 21% and 100% oxygen following asphyxia in newborn piglets on NMDA receptor binding characteristics, Na(+), K(+)-ATPase activity, and lipid peroxidation. After achieving a heart rate less than 60 beats per minute, asphyxiated piglets were reventilated with 21% oxygen or 100% oxygen. (3)[H]MK-801 binding showed the Bmax in the 21% and 100% groups to be 1.53 +/- 0.43 and 1.42 +/- 0.35 pmol/mg protein (p = ns). Values for Kd were 4.56 +/- 1.29 and 4.17 +/- 1.05 nM (p = ns). Na(+), K(+)-ATPase activity in the 21% and 100% groups were 23.5 +/- 0.9 and 24.4 +/- 3.9 micromol Pi/mg protein/h (p = ns). Conjugated dienes (0.05 +/- 0.02 vs. 0.07 +/- 0.03 micromol/g brain) and fluorescent compounds (0.54 +/- 0.05 vs. 0.78 +/- 0.19 microg quinine sulfate/g brain), were similar in both groups (p = ns). Though lipid peroxidation products trended higher in the 100% group, these data show that NMDA receptor binding and Na(+), K(+)-ATPase activity were similar following reventilation with 21% or 100% oxygen after a single episode of mild asphyxia.

Large animal models of traumatic injury to the immature brain

Large animal models have been used much less frequently than rodent models to study traumatic brain injury. However, large animal models offer distinct advantages in replicating specific mechanisms, morphology and maturational stages relevant to age-dependent injury responses. This paper reviews how each of these features is relevant in matching a model to a particular scientific question and discusses various scaling strategies, advantages and disadvantages of large animal models for studying traumatic brain injury in infants and children. Progress to date and future directions are outlined.

Developing a long-term surviving piglet model of neonatal hypoxic-ischemic encephalopathy

OBJECTIVE

This study was designed to develop a piglet model of neonatal hypoxic-ischemic encephalopathy, which would allow for serial assessments of long-term neurodevelopmental impairment.

METHODS

In 12 newborn piglets, we produced hypoxia by 8% oxygen breathing for 5-91 minutes. We combined ischemia by reversible bilateral common carotid artery occlusion for varying times. Outcome measures were clinical neurological evaluation, magnetic resonance spectroscopy studies and brain histology.

RESULTS

Those animals which received intravenous sedation and no mechanical ventilation showed poor tolerance to hypoxia-ischemia and died early in the course of the experiments. The use of inhalation anesthesia during surgical procedures and mechanical ventilation during hypoxia-ischemia was associated with long-term survival. Seven of eight animals that survived > or = 48 hr showed clinical neurological abnormalities, that later resolved. Magnetic resonance spectroscopy measurements did not change significantly following hypoxia-ischemia. None of the animals had histopathological brain lesions.

CONCLUSION

When subjected to acute hypoxia-ischemia, piglets were likely to survive only if they were given such supportive measures as anesthesia and mechanical ventilation. Even with hypoxic-ischemic injury sufficient to produce acute signs of neurological dysfunctions, longterm, stable survival with no evident brain histopathological abnormalities was possible.

Cerebral oxidative stress and depression of energy metabolism correlate with severity of diffuse brain injury in rats

OBJECTIVE

The combined effect of traumatic brain injury (TBI) and secondary insult on biochemical changes of cerebral tissue is not well known. For this purpose, we studied the time-course changes of parameters reflecting ROS-mediated oxidative stress and modifications of cell energy metabolism determined in rats subjected to cerebral insult of increasing severity.

METHODS

Rats were divided into four groups: 1) sham-operated, 2) subjected to 10 minutes of hypoxia and hypotension (HH), 3) subjected to severe diffuse TBI, and 4) subjected to severe diffuse TBI + HH. Rats were killed at different times after injury, and analyses of malondialdehyde, ascorbate, high-energy phosphates, nicotinic coenzymes, oxypurines, nucleosides, and N-acetylaspartate (NAA) were made by high-performance liquid chromatography on whole-brain tissue extracts.

RESULTS

Data indicated a close relationship between degree of oxidative stress and severity of brain insult, as evidenced by the highest malondialdehyde values and lowest ascorbate levels in rats subjected to TBI + HH. Similarly, modifications of parameters related to cell energy metabolism were modulated by increasing severity of brain injury, as demonstrated by the lowest values of energy charge potential, nicotinic coenzymes, and NAA and the highest levels of oxypurines and nucleosides recorded in TBI + HH rats. Both the intensity of oxidative stress-mediated cerebral damage and perturbation of energy metabolism were minimally affected in rats subjected to HH only.

CONCLUSION

These results showed that the severity of brain insult can be graded by measuring biochemical modifications, specifically, reactive oxygen species-mediated damage, energy metabolism depression, and NAA, thereby validating the rodent model of closed-head diffuse TBI coupled with HH and proposing NAA as a marker with diagnostic relevance to monitor the metabolic state of postinjured brain.

Cyclooxygenase-mediated generation of free radicals during hypoxia in the cerebral cortex of newborn piglets

Previous studies have demonstrated that free radicals are formed under hypoxic conditions in newborn piglet brain. To test the hypothesis that the cyclooxygenase pathway serves as a source of free radical generation during hypoxia studies were performed on 24 piglets divided into four groups. Six saline (group 3) and six indomethacin treated (group 4) were exposed to hypoxia (FiO2 0.05-0.07) for 60 min. Cerebral hypoxia was documented biochemically by determination of ATP and phosphocreatine. Fluorescent compounds and conjugated dienes were determined as indices of lipid peroxidation. Free radical formation was determined by using n-tert butyl phenyl nitrone (PBN) as a spin trap agent and measuring spin adduct formation in duplicate using a Varian E-109 spectrometer. Groups 1 and 2 (normoxic) showed no spin adduct formation. Group 3 showed a significant increase in spin adduct formation compared to normoxia (372+/-125 vs. 63+/-15, P<0.001). Hypoxic animals pretreated with indomethacin had a spin adduct level of 197+/-132 and were similar to normoxic animals. ATP/PCr levels were the same in groups 3 and 4 denoting the same degree of cerebral hypoxia in all hypoxic animals. Conjugated dienes increased significantly during hypoxia as compared to normoxia (0.142+/-0.017 vs. 0.0+/-0.0) and were decreased insignificantly with indomethacin treatment. Fluorescent compounds were not significantly different among the four groups. Na+,K+-ATPase activity decreased during hypoxia but was not preserved in hypoxic animals pretreated with indomethacin. These data provide direct evidence of the presence of free radicals during hypoxia and the contribution of cyclooxygenase metabolism to their formation.

Effect of hypoxia on protein tyrosine kinase activity in cortical membranes of newborn piglets—the role of nitric oxide

Previous studies have shown that cerebral hypoxia results in increased tyrosine phosphorylation of cerebral cortical cell membrane proteins as well as nuclear membrane anti-apoptotic protein, Bcl-2. The present study tests the hypothesis that hypoxia results in increased protein tyrosine kinase activity in cortical cell membranes of newborn piglets and that the inhibition of neuronal NOS by administration of 7-nitroindazole sodium salt (7-NINA), a selective inhibitor of nitric oxide synthase (NOS), will prevent the hypoxia-induced increase in protein tyrosine kinase activity. To test this hypothesis, protein tyrosine kinase activity was determined in cerebral cortical membranes of 2- to 4-day-old newborn piglets divided into normoxic (n=6), hypoxic (n=5) and 7-NINA-treated hypoxic (n=5) (7-NINA, 1mg/kg, i.p., prior to hypoxia) groups. Tissue hypoxia was achieved by exposing the animals to an FiO(2) of 0.07 for 60 min and was documented biochemically by determining tissue ATP and phosphocreatine (PCr) levels. Cortical P(2) membranes were isolated and protein tyrosine kinase activity determined by (33)P incorporation into a specific peptide substrate for 15 min at 37 degrees C in a medium containing 100 mM HEPES, pH 7.0, 1mM EDTA, 125 mM MgCl(2), 25 mM MnCl(2), 2mM DTT, 0.2 mM sodium orthovanadate, 2mM EGTA, 150 microM tyrosine kinase peptide substrate [Lys 19] cdc2(6-20)-NH(2), (33)P-ATP, and 10 microg of membrane protein. Protein tyrosine kinase activity was determined by the difference between (33)P incorporation in the presence and absence of specific peptide substrate and expressed as pmol/mg protein/h. The ATP values in the normoxic, hypoxic and 7-NINA-treated hypoxic animals were ATP: 4.57+/-0.45 micromol/g, 1.29+/-0.23 micromol/g (p<0.05 versus normoxic) and 1.50+/-0.14 micromol/g brain (p<0.05 versus normoxic), respectively. The PCr values in the normoxic, hypoxic and 7-NINA-treated hypoxic animals were: 3.77+/-0.36 micromol/g, 0.77+/-0.13 micromol/g (p<0.05 versus normoxic) and 1.02+/-0.24 micromol/g brain (p<0.05 versus normoxic), respectively. Protein tyrosine kinase activity in the normoxic, hypoxic and the 7-NINA-treated groups was 378+/-77 pmol/mg protein/h, 854+/-169 pmol/mg protein/h (p<0.05 versus normoxic) and 464+/-129 pmol/mg protein/h (p<0.05 versus hypoxic), respectively. The data show that cerebral tissue hypoxia results in increased protein tyrosin kinase activity in cortical membranes of newborn piglets and pretreatment with 7-NINA prevents the hypoxia-induced increase in protein tyrosine kinase activity. We conclude that the hypoxia-induced increase in protein tyrosine kinase activity is NO-mediated. We propose that the hypoxia-induced increase in protein tyrosine kinase activity leading to increased phosphorylation of Bcl-2 is a critical link to hypoxic neuronal injury pathway.

Effect of neuronal nitric oxide synthase inhibition on CA2+/calmodulin kinase kinase and CA2+/calmodulin kinase IV activity during hypoxia in cortical nuclei of newborn piglets

The present study tests the hypothesis that cerebral tissue hypoxia results in increased Ca(2+)/calmodulin (CaM) kinase kinase activity and that the administration of nitric oxide synthase inhibitors (N-nitro-l-arginine [NNLA], or 7-nitroindazole sodium [7-NINA]) prior to the onset of hypoxia will prevent the hypoxia-induced increase in the enzyme activity. To test this hypothesis, CaM kinase kinase and CaM kinase IV activities were determined in normoxic, hypoxic, NNLA-treated hypoxic, and 7-NINA-treated hypoxic piglets. Hypoxia was induced (FiO(2)=0.05-0.08x1 h) and confirmed biochemically by tissue levels of ATP and phosphocreatine. CaM kinase kinase activity was determined in a medium containing protein kinase and phosphatase inhibitors, calmodulin, and a specifically designed CaM kinase kinase target peptide. CaM kinase IV activity was determined by (33)P-incorporation into syntide-2 in a buffer containing protein kinase and phosphatase inhibitors. Compared with normoxic animals, ATP and phosphocreatine levels were significantly lower in all hypoxic piglets whether or not pretreated with nitric oxide synthase inhibitors. There was a significant difference among CaM kinase kinase activity (pmol/mg protein/min) in normoxic (76.84+/-14.1), hypoxic (138.86+/-18.2, P<0.05 vs normoxia), NNLA-pretreated hypoxic (91.34+/-19.3; P=NS vs normoxia, P<0.05 vs hypoxia) and 7-NINA-pretreated hypoxic animals (100.12+/-23.3; P=NS vs normoxia, P<0.05 vs hypoxia). There was a significant difference among CaM kinase IV activity (pmol/mg protein/min) in normoxia (1270.80+/-126.1), hypoxia (2680.80+/-136.7; P<0.05 vs normoxia), NNLA-pretreated hypoxia (1666.00+/-154.8; P<0.05 vs normoxia, P<0.05 vs hypoxia), and 7-NINA-pretreated hypoxic (1712.9+/-231.5; P=NS vs normoxia, P<0.05 vs hypoxia). We conclude that the hypoxia-induced increase in CaM kinase kinase and CaM kinase IV activity is mediated by neuronal NOS-derived NO.

NMDA receptor and neonatal hypoxic brain injury

The NMDA-type glutamate receptor is a predominant mediator of excitotoxicity in the immature brain due to overexpression of the receptor in the developing brain. Within the development period however, the extent of NMDA receptor mediated processes including hypoxia-induced excitotoxicity may depend on the ontogeny of the NMDA receptor recognition and modulation sites, and subunits leading to altered function of the ion-channel comples. The function of the receptor may be modified by intracellular mechanisms such as phosphorylation/dephosphorylation, nitration, and generation of free radicals including nitric oxide. The susceptibility of the developing brain to hypoxia depends on several factors: the lipid composition of the brain cell membrane; the rate of membrane lipid peroxidation and the status of anti-oxidant defenses; the development and modulation of the NMDA receptor sites; the intracellular Ca(2+) influx mechanisms; expression of apoptotic and antiapoptotic genes such as Bax and Bcl-2; and the activation of initiator caspases and caspase-3, the "executioner" of cell death. The developmental status of these cellular mechanisms and their response to hypoxia determine the fate of the hypoxic cell in the developing brain in the fetus and the newborn.

Effect of hypothermia on bilirubin-induced alterations in brain cell membrane function and energy metabolism in newborn piglets

The aim of this study was to evaluate the effects of hypothermia on bilirubin-induced alterations in brain cell membrane function and energy metabolism in the developing brain. Thirty-seven newborn piglets were divided randomly into four groups: normothermic control (NC, n=9); hypothermic control (HC, n=7); normothermic bilirubin infusion (NB, n=11); and hypothermic bilirubin infusion (HB, n=10) groups. In bilirubin infusion groups (NB and HB), a loading dose of bilirubin (35 mg/kg) was given over 5 min, followed by a continuous infusion (25 mg/kg/h) for 4 h. The control groups (NC, HC) received a bilirubin-free buffer solution. Sulfadimethoxine was administered to animals in all experimental groups. Rectal temperature was maintained between 38.0 and 39.0 degrees C in normothermic groups, and between 34.0 and 35.0 degrees C in hypothermic groups for 4 h after the start of bilirubin infusion. The final blood and brain bilirubin concentrations in the bilirubin infusion groups (NB and HB) were not significantly different. Decreased cerebral cortical cell membrane Na(+),K(+)-ATPase activity and increased lipid peroxidation products observed in the NB group, indicative of bilirubin-induced brain damage, were significantly attenuated in the HB group. Hypothermia also significantly improved the bilirubin-induced reduction in brain ATP and phosphocreatine levels and increase in blood and brain lactate levels. In summary, hypothermia significantly attenuated the bilirubin-induced alterations in brain cell membrane function and energy metabolism in the newborn piglet. These findings suggest the possibility that hypothermia could be a good neuroprotective therapeutic modality in neonatal bilirubin encephalopathy.

3-Aminobenzamide, a poly (ADP-ribose) synthetase inhibitor, attenuates the acute inflammatory responses and brain injury in experimental Escherichia coli meningitis in the newborn piglet

The aim of the present study was to evaluate the anti-inflammatory and neuroprotective effects of a poly (ADP-ribose) synthetase inhibitor 3-aminobenzamide during the early phase of experimental bacterial meningitis in the newborn piglet. Meningitis was induced by intracisternal injection of 10(8) colony forming units of Escherichia coli in 100 microl of saline. 3-Aminobenzamide, given 30 mg kg(-1) as a bolus i.v. injection 30 min before induction of meningitis, significantly attenuated the meningitis-induced acute inflammatory responses such as increased cerebrospinal fluid (CSF) lactate concentration, CSF leukocytosis and increased CSF tumor necrosis factor-alpha level. However, meningitis-induced increase in intracranial pressure and decrease in CSF glucose level were not significantly improved. Increased cerebral cortical cell membrane lipid peroxidation products (conjugated dienes) and decreased brain ATP/phosphocreatine levels observed in the meningitis group were also significantly improved with 3-aminobenzamide treatment. However, the improvement of reduced Na+, K+-ATPase activity did not reach a statistical significance (p = 0.06). In summary, 3-aminobenzamide significantly attenuated the acute inflammatory responses and the ensuing brain injury during the early phase of neonatal bacterial meningitis. These findings suggest that poly (ADP-ribose) synthetase inhibitors such as 3-aminobenzamide might be a promising novel anti-inflammatory and neuroprotective adjuvant therapy in neonatal bacterial meningitis.

Developmental changes in tolerance to transient intrauterine ischemia in rat cerebral mitochondria

OBJECTIVE

Mitochondfial respiratory activities were measured in neonatal rat brain to compare the influence of transient intrauterine ischemia in the preterm fetus with that in the term fetus and to evaluate the effect of alpha-phenyl-N -tert-butyl-nitrone treatment.

STUDY DESIGN

Intrauterine ischemia was induced by a 30-minute occlusion of the right uterine artery. The control group consisted of term fetuses (20 days old) exposed to normoxia (n = 8) and ischemia (n = 8). For the investigation into maturity effect, preterm fetuses (14 days old) were exposed to normoxia (n = 8) or ischemia (n = 8), and for the alpha-phenyl-N -tert-butyl-nitrone treatment investigation, term fetuses were exposed to ischemia with alpha-phenyl-N -tert-butyl-nitrone (n = 8). All subjects underwent cesarean delivery at 21 days of gestation, and the mitochondrial respiration was measured polarographically 1 hour after delivery.

RESULTS

In the control group the neonatal cortical tissue exposed to ischemia showed a significant decrease in mitochondrial activities compared with those in normoxic control animals. In the preterm group the mitochondrial activities of ischemic fetuses were maintained close to normoxic levels. The neonatal mitochondrial deterioration caused by term ischemia was prevented by alpha-phenyl-N -tert-butyl-nitrone.

CONCLUSION

The results indicate that preterm fetuses are more capable than term fetuses of maintaining mitochondrial function under conditions of transient intrauterine ischemia and suggest that oxygen derived free radicals may play a crucial role in the development of neonatal neurologic deficit.

Effects of deferoxamine, a chelator of free iron, on NA(+), K(+)-ATPase activity of cortical brain cell membrane during early reperfusion after hypoxia-ischemia in newborn lambs

Free iron chelation after hypoxia-ischemia can reduce free radical-induced damage to brain cell membranes and preserve electrical brain activity. We investigated whether chelation of free iron with deferoxamine (DFO) preserved cortical cell membrane activity of Na(+),K(+)-ATPase and electrocortical brain activity (ECBA) of newborn lambs during early reperfusion after severe hypoxia-ischemia. Hypoxia was induced in 16 lambs by decreasing the fraction of inspired oxygen to 0.07 for 30 min, followed by a 5-min period of hypotension (mean arterial blood pressure <35 mm Hg). ECBA (in microvolts) was measured using a cerebral function monitor. Immediately after hypoxia and additional ischemia, eight lambs received DFO (2.5 mg/kg, i.v.), and seven lambs received a placebo (PLAC). Two lambs underwent sham operation. One hundred eighty minutes after completion of hypoxia and ischemia, the brains were obtained and frozen. Na(+),K(+)-ATPase activity was measured in the P(2) fraction of cortical tissue. Na(+),K(+)-ATPase activity was 35.1 +/- 7.4, 42.0 +/- 7.6, and 40.7 +/- 1.4 micromol inorganic phosphate/mg protein per hour in PLAC-treated, DFO-treated, and sham-operated lambs, respectively (p < 0.05: DFO versus PLAC). ECBA was 11.2 +/- 6.1, 14.8 +/- 4.8, and 17.5+/-.0.5 microV in PLAC-treated, DFO-treated, and sham-operated lambs, respectively (p = 0.06: DFO versus PLAC). Na(+),K(+)-ATPase activity correlated with ECBA at 180 min of reperfusion (r = 0.85, p < 0.001). We conclude that Na(+),K(+)-ATPase activity of cortical brain tissue was higher in DFO-treated lambs compared with PLAC-treated animals during the early reperfusion phase after severe hypoxia-ischemia, suggesting a reduction of free radical formation by DFO. Furthermore, a positive relationship was found between Na(+),K(+)-ATPase activity and ECBA.

Maturation-dependent response of the piglet brain to scaled cortical impact

OBJECT

The goal of this study was to investigate the relationship between maturational stage and the brain's response to mechanical trauma in a gyrencephalic model of focal brain injury. Age-dependent differences in injury response might explain certain unique clinical syndromes seen in infants and young children and would determine whether specific therapies might be particularly effective or even counterproductive at different ages.

METHODS

To deliver proportionally identical injury inputs to animals of different ages, the authors have developed a piglet model of focal contusion injury by using specific volumes of rapid cortical displacement that are precisely scaled to changes in size and dimensions of the growing brain. Using this model, the histological response to a scaled focal cortical impact was compared at 7 days after injury in piglets that were 5 days, 1 month, and 4 months of age at the time of trauma. Despite comparable injury inputs and stable physiological parameters, the percentage of hemisphere injured differed significantly among ages, with the youngest animals sustaining the smallest lesions (0.8%, 8.4%, and 21.5%, for 5-day-, 1-month-, and 4-month-old animals, respectively, p = 0.0018).

CONCLUSIONS

These results demonstrate that, for this particular focal injury type and severity, vulnerability to mechanical trauma increases progressively during maturation. Because of its developmental and morphological similarity to the human brain, the piglet brain provides distinct advantages in modeling age-specific responses to mechanical trauma. Differences in pathways leading to cell death or repair may be relevant to designing therapies appropriate for patients of different ages.

Mechanisms of perinatal cerebral injury in fetus and newborn

Cerebral hypoxia in the fetus and newborn results in neonatal morbidity and mortality as well as long-term sequelae such as mental retardation, seizure disorders, and cerebral palsy. In the developing brain, determinants of susceptibility to hypoxia should include the lipid composition of the brain cell membrane, the rate of lipid peroxidation, the presence of antioxidant defenses, and the development and modulation of excitatory amino acid neurotransmitter receptors such as the N-methyl-D-aspartate (NMDA) receptor, the intracellular Ca2+, and the intranuclear Ca(2+)-dependent mechanisms. In addition to the developmental status of these cellular components, the response of these potential mechanisms to hypoxia determines the fate of the hypoxic brain cell in the developing brain. Using electron spin resonance spectroscopy of alpha-phenyl-N-tert-butyl-nitrone spin adducts, studies from our laboratory demonstrated that tissue hypoxia results in increased free radical generation in the cortex of fetal guinea pigs and newborn piglets. Pretreatment with MgSO4 significantly decreased the hypoxia-induced increase in free radical generation in the term fetal brain. We also showed that brain tissue hypoxia modifies the NMDA receptor ion-channel recognition and modulatory sites. Furthermore, a higher increase in NMDA receptor agonist-dependent Ca2+ in synaptosomes was demonstrated. The increase in intracellular Ca2+ may activate several enzymatic pathways such as phospholipase A2 and metabolism of archidonic acid by cyclooxygenase and lipoxygenase, conversion of xanthine dehydrogenase to xanthine oxidase by proteases, and activation of nitric oxide synthase. Using inhibitors of each of these enzymes such as cyclooxygenase (indomethacin), lipoxygenase (nordihydroguaiaretic acid), xanthine oxidase (allopurinol), and nitric oxide synthase (N-nitro-L-arginine), studies have shown that these enzyme reactions result in oxygen free radical generation, membrane peroxidation, and cell membrane dysfunction in the hypoxic brain. Specifically, generation of nitric oxide free radicals during hypoxia may lead to nitration and nitrosylation of specific membrane proteins and receptors, resulting in dysfunction of receptors and enzymes. We conclude that hypoxia-induced modification of the NMDA receptor leading to increased intracellular Ca2+ results in free radical generation and cell injury. We suggest that during hypoxia the increased intracellular Ca2+ may lead to increased intranuclear Ca2+ concentration and alter nuclear events including transcription of specific apoptotic genes and activation of endonucleases, resulting in programmed cell death.

Effects of fasting and insulin-induced hypoglycemia on brain cell membrane function and energy metabolism during hypoxia-ischemia in newborn piglets

This study was done to determine the effects of 12 h fasting-induced mild hypoglycemia (blood glucose 60 mg/dl) and insulin-induced moderate hypoglycemia (blood glucose 35 mg/dl) on brain cell membrane function and energy metabolism during hypoxia-ischemia in newborn piglets. Sixty-three ventilated piglets were divided into six groups; normoglycemic control (NC, n=8), fasting-induced mildly hypoglycemic control (FC, n=10), insulin-induced moderately hypoglycemic control (IC, n=10), normoglycemic/hypoxic-ischemic (NH, n=11), fasting-induced mildly hypoglycemic/hypoxic-ischemic (FH, n=12) and insulin-induced moderately hypoglycemic/hypoxic-ischemic (IH, n=12) group. Cerebral hypoxia-ischemia was induced by occlusion of bilateral common carotid arteries and simultaneous breathing with 8% oxygen for 30 min. The brain lactate level was elevated in NH group and this change was attenuated in FH and IH groups. The extent of cerebral lactic acidosis during hypoxic-ischemic insult showed significant positive correlation with blood glucose level (r=0.55, p<0.001). Cerebral Na+, K+-ATPase activity and concentrations of high-energy phosphate compounds were reduced in NH group and these changes were not ameliorated in FH or IH group. Cortical levels of conjugated dienes, measured as an index of lipid peroxidation of brain cell membrane, were significantly elevated in NH, FH and IH groups compared with NC, FC and IC groups and these increases were more profound in FH and IH with respect to NH. Blood glucose concentration showed significant inverse correlation with levels of conjugated dienes (r=-0.35, p<0.05). These findings suggest that, unlike in adults, mild or moderate hypoglycemia, regardless of methods of induction such as fasting or insulin-induced, during cerebral hypoxia-ischemia is not beneficial and may even be harmful in neonates.

Effect of allopurinol on hypoxia-induced modification of the NMDA receptor in newborn piglets

The present study tests the hypothesis that pretreatment with allopurinol, a xanthine oxidase inhibitor, will prevent modification of the NMDA receptor during cerebral hypoxia in newborn piglets. Eighteen newborn piglets were studied. Six normoxic control animals were compared to six untreated hypoxic and six allopurinol (20 mg/kg i.v.) pretreated hypoxic piglets. Cerebral hypoxia was induced by lowering the FiO2 to 0.05-0.07 for 1 hour and tissue hypoxia was confirmed biochemically by the measurement of ATP and phosphocreatine. Brain cell membrane Na+,K+-ATPase activity was determined to assess membrane function. Na+,K+-ATPase activity was decreased from control in both the untreated and treated hypoxic animals (46.0+/-1.0 vs 37.9+/-2.5 and 37.3+/-1.4 micromol Pi/mg protein/hr, respectively, p < 0.05). [3H]MK-801 binding was determined as an index of NMDA receptor modification. The receptor density (Bmax) in the untreated hypoxic group was decreased compared to normoxic control (1.09+/-0.17 vs 0.68+/-0.22 pmol/mg protein, p < 0.01). The dissociation constant (Kd) was also decreased in the untreated group (10.0+/-2.0 vs 4.9+/-1.4 nM, p < 0.01), indicating an increase in receptor affinity. However, in the allopurinol treated hypoxic group, the Bmax (1.27+/-0.09 pmol/mg protein) was similar to normoxic control and the Kd (8.1+/-1.2 nM, p < 0.05) was significantly higher than in the untreated hypoxic group. The data show that the administration of allopurinol prior to hypoxia prevents hypoxia-induced modification of the NMDA receptor-ion channel binding characteristics, despite neuronal membrane dysfunction. By preventing NMDA receptor-ion channel modification, allopurinol may produce a neuromodulatory effect during hypoxia and attenuate NMDA receptor mediated excitotoxicity.

Mg2+-dependent modification of the N-methyl-D-aspartate receptor following graded hypoxia in the cerebral cortex of newborn piglets

The present study tests the hypothesis that Mg2+ modification of N-methyl-D-aspartate receptor ion channel opening is altered during hypoxia and correlates with the progressive decrease in cerebral energy metabolism induced by hypoxia. Studies were performed in five normoxic and nine hypoxic ventilated piglets. In the hypoxic group, varying degrees of cerebral energy metabolism were achieved by administration of different fractions of inspired oxygen (FiO2) (5-9%) for varying durations of time and were documented by cortical tissue phosphocreatine levels. [3H]Dizocilpine maleate binding was performed with increasing concentrations of MgSO4 from 0.01 to 15 mM in cortical P2 membrane fractions. Mg2+ percentage activation and Mg2+ 50% inhibitory concentrations (IC50) were determined. The mean +/- S.D. phosphocreatine value was 3.0 +/- 1.3 micromol/g brain in the normoxic group and 1.4 +/- 1.0 micromol/g brain in the hypoxic group (P < 0.01). Low concentrations of Mg2+ (0.01-1 mM) increased [3H]dizocilpine maleate binding in the normoxic group (to 137 +/- 26% of baseline), significantly greater than in the hypoxic group (109 +/- 13%, P < 0.05). Receptor activation correlated with brain tissue levels of phosphocreatine, with percentage maximal activation decreasing linearly as phosphocreatine levels decreased (r=0.7). Higher levels of Mg2+ (1.5-15 mM) caused inhibition of [3H]dizocilpine maleate binding, with IC50 levels significantly higher in the normoxic group (3.2 +/- 1.1 mM) than in the hypoxic group (1.9 +/- 0.4 mM). Mg2+ IC50 values decreased in a linear fashion as phosphocreatine values decreased (r=0.9). The data demonstrate that, as brain cell energy metabolism decreases during hypoxia, maximal receptor activation by low levels of Mg2+ decreases and receptor inhibition by high levels of Mg2+ increases in a linear fashion. We speculate that, during hypoxia, dephosphorylation of the ion channel of the N-methyl-D-aspartate receptor increases Mg2+ blockade of the receptor by increasing Mg2+ accessibility to its binding site and that receptor modification may be initiated by subtle decreases in cortical oxygenation in the newborn brain.

Effects of hypoxia-ischemia and inhibition of nitric oxide synthase on cerebral energy metabolism in newborn piglets

The present study was designed to examine the effects of inhibition of nitric oxide synthase on cerebral energy metabolism after hypoxia-ischemia in newborn piglets. Ten 1- to 3-d-old piglets received N(omega)-nitro-L-arginine (NNLA), an inhibitor of nitric oxide synthase (NNLA-hypoxia, n = 5), or normal saline (hypoxia, n = 5) 1 h before cerebral hypoxia-ischemia. After the infusion, hypoxia-ischemia was induced by bilateral occlusion of the carotid arteries and decreasing FiO2 to 0.07 and maintained for 60 min. Thereafter, animals were resuscitated and ventilated for another 3 h. Using 1H- and 31P-magnetic resonance spectroscopy, cerebral energy metabolism was measured in vivo at 15-min intervals throughout the experiment. Phosphocreatine to inorganic phosphate ratios decreased from 2.74 +/- 0.14 to 0.74 +/- 0.36 (hypoxia group) and 2.32 +/- 0.17 to 0.18 +/- 0.10 (NNLA-hypoxia group) during hypoxia-ischemia. Thereafter, phosphocreatine to inorganic phosphate ratios returned rapidly to baseline values in the hypoxia group, but remained below baseline values in the NNLA-hypoxia group. Intracellular pH decreased during hypoxia-ischemia and returned to baseline values on reperfusion in both groups. Intracellular pH values were lower in the NNLA-hypoxia group (p < 0.001, ANOVA). Lactate was not present during the baseline period. After hypoxia-ischemia, lactate to N-acetylaspartate ratios increased to 1.34 +/- 0.28 (hypoxia group) and 2.22 +/- 0.46 (NNLA-hypoxia group). Lactate had disappeared after 3 h of reperfusion in the hypoxia group, whereas lactate to N-acetylaspartate ratios were 1.37 +/- 1.37 in the NNLA-hypoxia group. ANOVA demonstrated a significant effect of NNLA on lactate to N-acetylaspartate ratios (p < 0.001). Inhibition of nitric oxide synthase by NNLA tended to compromise cerebral energy status during and after cerebral hypoxia-ischemia in newborn piglets.

NMDA receptor-mediated calcium influx in cerebral cortical synaptosomes of the hypoxic guinea pig fetus

Calcium influx via the NMDA receptor has been proposed as a mechanism of hypoxia-induced neuronal injury. The present study tests the hypothesis that the increase of [Ca2+]i observed under hypoxic conditions is the result of an NMDA-mediated Ca2+ influx. Changes of [Ca2+]i, measured fluorometrically with Fura-2, were followed after activation of the NMDA receptor with NMDA and glutamate, in the presence of glycine, in cortical synaptosomes prepared from six normoxic and six hypoxic guinea pig fetuses. [Ca2+]i was significantly higher in hypoxic vs normoxic synaptosomes, at baseline and in the presence of glycine as well as following activation of the NMDA receptor. Increase in [Ca2+]i was not observed in a Ca2+ free medium and was significantly decreased by MK-801 and thapsigargin. These results demonstrate that hypoxia-induced modifications of the NMDA receptor ion-channel results in increased [Ca2+]i in hypoxic vs normoxic synaptosomes. This increased accumulation may be due to an initial influx of Ca2+ via the altered NMDA receptor with subsequent release of Ca2+ from intracellular stores. Increase in intracellular calcium may initiate several pathways of free radical generation including cyclooxygenase, lipoxygenase, xanthine oxidase and nitric oxide synthase, and lead to membrane lipid peroxidation resulting in neuronal cell damage.

Oxygen free radical generation during in-utero hypoxia in the fetal guinea pig brain: the effects of maturity and of magnesium sulfate administration

Previous studies have shown, employing direct measurements with electron spin resonance (ESR) spectroscopy, that hypoxia induces an increased production of oxygen free radicals (OFR) in the brain of the guinea pig fetus. The present study using the same approach, investigated the effects of maturity and Mg2+-pretreatment on hypoxia-induced OFR formation in the guinea pig fetal brain. The normoxic and the hypoxic groups were exposed for 60 min to 21% or 7% oxygen, respectively. The control group consisted of term fetuses exposed to normoxia (n=7) and hypoxia (n=7). The experimental groups consisted of the following: (a) for the investigation on maturity effect, preterm fetuses (40 days) exposed to normoxia (n=6) or hypoxia (n=6); and (b) for the Mg2+-pretreatment investigation, term fetuses (60 days) exposed to normoxia (n=6) or hypoxia (n=6) following maternal pretreatment with Mg2+ which consisted of an initial bolus of MgSO4 (600 mg/kg, i.p.) 1 h prior to hypoxia followed by a second dose (300 mg/kg, i.p.). Oxygen free radicals were measured by ESR spectroscopy in the fetal cerebral cortical tissue utilizing phenyl-N-tert-butylnitrone (PBN) spin trapping. Fetal brain tissue hypoxia was documented biochemically by decreased tissue levels of ATP and phosphocreatine. In the control group of term fetuses, the cortical tissue from hypoxic fetuses showed a significant increase in spin adducts (71% increase, p<0.01). In the preterm group, the cortical tissue from hypoxic fetuses showed a 33% increase in spin adducts (p<0.001). The baseline free radical generation during normoxia was 22.5% higher at preterm than at term (41.4+/-3.5 units/g issue vs. 33.8+/-9.3 units/g tissue, p<0.05). In Mg2+-treated groups, spin adduct levels in cortical tissue from hypoxic fetuses did not significantly differ from those of the normoxic group (30.2+/-9.9 units/g tissue, normoxic-Mg2+ vs. 30. 6+/-8.1 units/g tissue, hypoxic-Mg2+). The results indicate that the fetal brain at term may be more susceptible to hypoxia-induced free radical damage than at preterm and that Mg2+ administration significantly decreased the hypoxia-induced increase in oxygen free radical generation in the term fetal guinea pig brain in comparison with non-treated hypoxic group.

Intraerythrocyte nonprotein-bound iron and plasma malondialdehyde in the hypoxic newborn

Intraerythrocyte nonprotein-bound iron (INPBI), malondialdehyde (MDA), and hypoxanthine plasma levels (HxPL), were determined by high-pressure liquid chromatography in 138 randomly selected newborn infants with gestational ages ranging from 23 to 42 weeks at birth and on fourth day of life. MDA plasma levels were significantly higher in cord and fourth-day blood samples of preterm babies than term infants as well as babies born by emergency Caesarean section than babies born by vaginal delivery and in intubated than in nonintubated newborns. Highly significant correlations both in cord blood and fourth-day blood samples were observed between MDA plasma levels and gestational age, birth weight, Apgar score at 1 min and 5 min, HxPL, pH, base deficit, and INPBI content. Multiple regression analysis identified HxPL as the best single predictor of MDA plasma levels in cord blood, and INPBI content in fourth-day blood as the best single predictor of MDA plasma levels in fourth-day blood. The results indicate that red cells and plasma lipoproteins are a common target of free radical-induced oxidative stress during hypoxia.

Direct measurement of oxygen free radicals during in utero hypoxia in the fetal guinea pig brain

The present study tested the hypothesis that maternal hypoxia induces oxygen free radical generation in the fetal guinea pig brain utilizing techniques of electron spin resonance spectroscopy and alpha-phenyl-tert-butyl nitrone (PBN) spin trapping. Pregnant guinea pigs of 60 days gestation were divided into normoxic and hypoxic groups and exposed to 21% or 7% oxygen for 60 min. Free radical generation was documented by measuring the signal of PBN spin adducts. Fluorescent compounds were determined as an index of lipid peroxidation and the activity of Na+,K+-ATPase was determined as an index of brain cell membrane function. Hypoxic fetal cerebral cortical tissue showed a significant increase in spin adducts (normoxic: 33.8+/-9.3 units/g tissue vs. hypoxic: 57.9+/-9.2 units/g tissue, p<0.01) and fluorescent compounds (normoxic: 0.639+/-0.054 microg quinine sulfate/g brain vs. 0.810+/-0.102 microg quinine sulfate/g brain, p<0.01) and a decrease in Na+,K+-ATPase activity (normoxic: 43.04+/-2.50 micromol Pi/mg protein/h vs. hypoxic: 33. 80+/-3.51 micromol Pi/mg protein/h, p<0.001). These results demonstrate an increased free radical generation during hypoxia in the fetal guinea pig brain. The spectral characteristics of the radicals were consistent with those of alkoxyl radicals. The increased level of fluorescent compounds and decreased activity of Na+,K+-ATPase indicated hypoxia induced brain cell membrane lipid peroxidation and dysfunction, respectively. These results directly demonstrate an increased oxygen free radical generation during hypoxia and suggest that hypoxia-induced increase in lipid peroxidation and decrease in membrane function, as indicated by a decrease in Na+,K+-ATPase activity, are consequences of increased free radicals. The nature of predominantly present alkoxyl radical indicates ongoing lipid peroxidation during hypoxia. The direct demonstration of oxygen free radical generation during hypoxia is the critical missing link in the mechanism of hypoxia-induced brain cell membrane dysfunction and damage.

Effect of induced hyperglycemia on brain cell membrane function and energy metabolism during the early phase of experimental meningitis in newborn piglets

This study was done to elucidate the mechanism of hypoglycorrhachia and elevated lactate concentrations leading to neuronal dysfunction in neonatal meningitis, and to determine the effects of induced hyperglycemia on these disturbances. Thirty-eight newborn piglets were divided into three groups: 12 in the control group (CG), 12 in the normoglycemic meningitis group (NG), and 14 in the hyperglycemic meningitis group (HG). Meningitis was induced by intracisternal injection of 108 cfu of Escherichia coli. Hyperglycemia (blood glucose 300-400 mg dl-1) was induced and maintained for 60 min before induction of meningitis and throughout the experiment using modified glucose clamp technique. CSF-to-blood glucose ratio decreased significantly in NG. In HG, baseline CSF-to-blood glucose ratio was lower than two other groups, but increased at 1 h after induction of meningitis. CSF lactate concentration was increased progressively in both meningitis groups, and positively correlated with CSF leukocyte numbers (r=0.41, p<0.001) and TNF-alpha level (r=0.43, p<0.001). Brain glucose concentration was significantly increased in HG and showed inverse correlation with CSF leukocyte numbers (r=-0.59, p<0.01). Brain lactate concentration was not significantly different among three groups and positively correlated with the CSF TNF-alpha level (r=0.51, p<0.05). Lipid peroxidation products were increased in NG. Na+,K+-ATPase activity, ATP/PCr concentrations were not different among three groups. Increased intracranial pressure, CSF pleocytosis (214+/-59 vs. 437+/-214/mm3, p<0.02) and increased lipid peroxidation products observed in NG were reduced in HG. These results suggest that hypoglycorrhachia and elevated lactate concentration in the CSF during meningitis originates primarily from the increased anaerobic glycolysis in the subarachnoid space, induced by TNF-alpha and leukocytes. Induced hyperglycemia attenuates the inflammatory responses of meningitis and might be beneficial by providing an increased glucose delivery to meet its increased demand in meningitis.

Effect of propentofylline on free radical generation during cerebral hypoxia in the newborn piglet

The present study tests the hypothesis that propentofylline, an adenosine re-uptake inhibitor, will reduce free radical generation during cerebral hypoxia. Ten newborn piglets were pretreated with propentofylline (10 mg/kg), five of which were subjected to hypoxia, while the other five were maintained at normoxia. Five untreated control piglets underwent the same conditions. Hypoxia was induced through a decrease in FiO2 to 0.11 and documented biochemically by a decrease in ATP and phosphocreatine levels. Free radical formation in the cortex was detected directly using electron spin resonance spectroscopy with a spin trap technique. Results demonstrate that free radicals, corresponding to the alkoxyl radical, increased significantly following hypoxia, and that this increase was inhibited by pretreatment with propentofylline. Conjugated dienes, a lipid peroxidation product, also increased following hypoxia and were subsequently inhibited by propentofylline. The administration of propentofylline also significantly limited the hypoxia-induced decrease in tissue levels of ATP and phosphocreatine. These data demonstrate that pretreatment with propentofylline decreased free radical generation and lipid peroxidation as well as preserved high energy phosphates during cerebral hypoxia.

Temporal and anatomical variations of brain water apparent diffusion coefficient in perinatal cerebral hypoxic-ischemic injury: relationships to cerebral energy metabolism

Cerebral apparent diffusion coefficients (ADCs) were determined in nine newborn piglets before and for 48 h after transient hypoxia-ischemia. Phosphorus MRS revealed severely reduced cerebral energy metabolism during the insult and an apparently complete recovery 2 h after resuscitation commenced. At this time, mean ADC over the imaging slice (ADCglobal) was 0.88 (0.04) x 10(-9) m2 x s(-1) (mean (SD)), which was close to the baseline value of 0.92 (0.4) x 10(-9) m2 x s(-1). In seven of the animals, a "secondary" failure of energy metabolism then evolved, accompanied by a decline in ADCglobal to 0.64 (0.17) x 10(-9) m2 x s(-1) at 46 h postresuscitation (P < 0.001 versus baseline). For these seven animals, ADCglobal correlated linearly with the concentration ratio [phosphocreatine (PCr)]/[inorganic phosphate (Pi)] (0.94 < r < 0.99; P < 0.001). A nonlinear relationship was demonstrated between ADCglobal and the concentration ratio [nucleotide triphosphate (NTP)]/[Pi + PCr + 3 NTP]. The ADC reduction commenced in the parasagittal cortex before spreading in a characteristic pattern throughout the brain. ADC seems to be closely related to cerebral energy status and shows considerable potential for the assessment of hypoxic-ischemic injury in the newborn brain.

Function of cell membranes in cerebral cortical tissue of newborn piglets after hypoxia and inhibition of nitric oxide synthase

Hypoxia-induced brain cell membrane lipid peroxidation can be caused by free radicals that are produced during hypoxia. Recently, the production of nitric oxide (NO), a free radical, has been shown to be increased during cerebral hypoxia-ischemia. The present study tested the hypothesis that inhibition of NO synthase (NOS) reduced hypoxia-induced modifications of Na+,K+-ATPase activity, lipid peroxidation, and [3H]MK-801 binding to the N-methyl-D-aspartate (NMDA) receptor in cerebral cortical tissue of newborn piglets. Studies were performed in 26 newborn piglets. Cerebral NOS was inhibited by the i.v. administration of 25 or 50 mg/kg N(omega)-nitro-L-arginine (NNLA) over 30 min. Control animals received normal saline. Six groups of piglets were thus created (normoxia, no NNLA; normoxia + NNLA 25 mg/kg; normoxia + NNLA 50 mg/kg; hypoxia, no NNLA; hypoxia + NNLA 25 mg/kg; hypoxia + NNLA 50 mg/kg). One hour after the start of NNLA or saline infusion, hypoxia was induced by lowering the FiO2 to 0.07 in the three hypoxia groups, whereas in the three other groups normoxia was maintained. After 60 min of hypoxia, the brain was taken out and frozen. NOS activity, Na+,K+-ATPase activity, conjugated dienes, and [3H]MK-801 binding to the NMDA receptor of cerebral cortical tissue were determined. NOS activity was reduced to 34% of its baseline value with NNLA 25 mg/kg, and to 19-27% of its baseline value with NNLA 50 mg/kg, respectively. Administration of NNLA did neither significantly alter the hypoxia-induced production of conjugated dienes, indicating lipid peroxidation nor the decrease of Na+,K+-ATPase activity after hypoxia. [3H]MK-801 binding studies of the NMDA receptor, however, showed that NNLA preserved Bmax and Kd after hypoxia. We conclude that inhibition of NOS does not change the hypoxia-induced decrease of Na+,K+-ATPase activity and production of conjugated dienes in brain cell membranes. Inhibition of NOS preserved the binding of [3H]MK-801 to the NMDA receptor after hypoxia.

Lipid peroxidation and modification of lipid composition in an endothelial cell model of ischemia and reperfusion

Among the changes that accompany the development of ischemia are alterations in the composition and turnover of membrane phospholipids. To study these effects, a cell culture model was developed to facilitate accurate measurements of lipids over varying intervals of ischemia and reperfusion (I/R). In order to mimic ischemia, rabbit aortic endothelial cells were grown to confluency on collagen coated beads and the bead cultures allowed to settle to the bottom of a conical test tube or spectrofluorometric cuvette. The cell-coated beads were then resuspended in media to simulate the process of reperfusion. Survival after ischemia/reperfusion, was determined by measurements of cellular replating efficiency, and found to decrease after periods longer than three hours of ischemia (followed by 24 h of reperfusion). Plating efficiencies were reduced to nearly 50% after 5 h of ischemia followed by reperfusion. Release of LDH inversely correlated with cell survival, and lactate production, ATP levels, and extracellular H2O2 concentration were all affected by the duration of ischemia. These changes could be directly related to rates of cellular oxygen consumption which decreased by 50% after 5 h of ischemia, while the percentage of oxygen consumption not be inhibitable by cyanide, increased. Release of esterified fatty acids, which was partly inhibited by the phospholipase A2 inhibitor, mepacrine, was stimulated by increasing periods of ischemia while the incorporation of free fatty acids into phospholipids was inhibited. The incorporation of arachidonic acid was inhibited to a lesser degree than that of oleic or linoleic acids with a resulting change in phospholipid fatty acyl composition favoring greater proportions of unsaturated fatty acids. In some experiments, the effects of vitamin E or ascorbic acid administered prior to ischemia were studied. The degree of fatty acid unsaturation, fatty acid incorporation into phospholipids, and release from phospholipids into the free fatty acid pool during ischemia/reperfusion were not affected by prior administration of vitamin E or ascorbic acid. However, the extent of lipid peroxidation during ischemia was inhibited by 100 mM ascorbic acid when present during the ischemia/reperfusion period, but not by vitamin E administered for 24 h prior to ischemia. Ascorbic acid treatment, but not vitamin E, also enabled cells to recover substantial amounts of the ATP lost following prolonged ischemia. The ATP recovery corresponded to an increased cell survival and decreased lipid peroxidation. Progressive intervals of ischemia followed by reperfusion result in compromised cell respiratory activity and decreased ATP production, and decreased phospholipid acylation leading to net hydrolysis. The associated changes in phospholipid composition, and specifically increased unsaturation appear to favor peroxidation of membrane phospholipids.

A piglet survival model of posthypoxic encephalopathy

The aim of this study was to produce a neonatal piglet model which, avoiding vessel ligation, exposed the whole animal to hypoxia and produced dose-dependent clinical encephalopathy and neuropathologic damage similar to that seen after birth asphyxia. Twenty-three piglets were halothane-anesthetized. Hypoxia was induced in 19 piglets by reducing the fractional concentration of inspired oxygen (FiO2) to the maximum concentration at which the EEG amplitude was below 7 microV (low amplitude) for 17-55 min. There were transient increases in Fio2 to correct bradycardia and hypotension. Posthypoxia, the piglets were extubated when breathing was stable. Four were sham-treated controls. We aimed at 72-h survival; seven died prematurely due to posthypoxic complications. EEG and a videotaped itemized neurologic assessment were recorded regularly. We found that 95% of the animals showed neuropathologic damage. The duration of low amplitude EEG during the insult and the arterial pH at the end of the insult correlated with cortical/white matter damage; r = 0.75 and 0.81, respectively. Early postinsult EEG background amplitude (r = 0.86 at 3 h) and neurologic score (r = 0.79 at 8 h) correlated with neuropathology. Epileptic seizures in seven animals were always associated with severe neuropathologic damage. We conclude that EEG-controlled hypoxia and subsequent intensive care enabled the animals to survive with an encephalopathy which correlated with the cerebral hypoxic insult. The encephalopathy was clinically, electrophysiologically, and neuropathologically similar to that in the asphyxiated term infant. This model is suitable for examining mechanisms of damage and evaluation of potential protective therapies after birth asphyxia.

Modification of the N-methyl-D-aspartate (NMDA) receptor in the brain of newborn piglets following hyperventilation induced ischemia

The present study tests the hypothesis that cerebral ischemia induced by severe hypocapnia modifies the N-methyl-D-aspartate (NMDA) receptor/ion channel complex in the cerebral cortical cell membranes of newborn piglets. Studies were performed in six newborn piglets subjected to ischemic hypoxia induced by hyperventilation (PaCO2, 9-11 mmHg) for 1 h. Comparisons were made to a normoxic group on room air (n = 6). Following hyperventilation, phosphocreatine decreased 80%, but ATP remained unchanged. NMDA receptor activation was determined by measuring [3H]MK-801 binding at concentrations varying from 2.5 to 50 nM. Following hyperventilation, Bmax decreased 52% to 0.50 +/- 0.04 pmol/mg protein (P = 0.001); however, the Kd value was unchanged at 7.45 +/- 0.79 nM. Spermine and magnesium dependent activation of the NMDA receptor was determined in the hyperventilated and control groups. With spermine concentrations increasing from 2.5 to 50 microM the maximal spermine dependent activation in the normoxic group was 13.7 +/- 7.93% which occurred at a concentration of 3.75 +/- 1.37 microM. In the hyperventilated group maximal activation was 32.4 +/- 23.5% (P = 0.095) at 4.58 +/- 2.46 microM (P = ns). With magnesium concentrations increasing from 2.5 to 100 microM the maximal magnesium dependent activation in the normoxic group was 17.0 +/- 13.6% which occurred at a concentration of 22.5 +/- 6.12 microM. In the hyperventilated group maximal activation was 26.3 +/- 14.9% (P = ns) at 4.58 +/- 2.92 microM (P < 0.0001). These data show that with less severe tissue hypoxia, as evidenced by conservation of ATP, there is less modification of the NMDA receptors. Ischemia induced by hyperventilation leads to an increase in spermine activation of the NMDA receptor, and the NMDA receptor is much more sensitive to magnesium as evidenced by the maximal activation occurring at a significantly lower magnesium concentration. Ischemia induced by hyperventilation modifies the spermine, magnesium, and MK-801 binding sites of the NMDA receptor and may result in increased NMDA receptor mediated neurotoxicity in the newborn brain.

Brain cell membrane Na+,K(+)-ATPase activity following severe hypoxic injury in the newborn piglet

This study tests the hypothesis that severe brain hypoxia causes decreased Na+,K(+)-ATPase activity, resulting in permanent alterations in the neuronal cell membranes. Seventeen anesthetized piglets (normoxic control (NC), no recovery after hypoxia (Group 1), 6 h normoxic recovery (Group 2), and 48 h normoxic recovery (Group 3)) were studied. Hypoxia was induced by lowering the FiO2 to maintain PCr/Pi ratio at 25% of baseline for 1 h as monitored by 31P-NMR spectroscopy. PCr/Pi returned to 57% of baseline by 6 h and was normal by 48 h. At termination, cortical tissue Na+,K(+)-ATPase activity was determined. Na+,K(+)-ATPase activity was measured in cortical membrane preparations by determining the rate of ATP hydrolysis. NC membranes had Na+,K(+)-ATPase activity of 58.3 +/- 1.3 microM Pi/mg protein/h (mean +/- S.E.M.). Na+,K(+)-ATPase activity was reduced in Groups 1, 2, and 3 (45.8 +/- 1.3, 47.4 +/- 3.6, 48.7 +/- 2.9 microM Pi/mg protein/h) (P < 0.05 compared to NC). There was no difference in enzyme activity among Groups 1, 2, or 3. The data show that in spite of recovery of neuronal oxidative phosphorylation (PCr/Pi) by 48 h, there is a permanent decrease in Na+,K(+)-ATPase activity in cells that have undergone severe hypoxic injury. The persistent decrease in Na+,K(+)-ATPase activity indicates ongoing cell injury following severe cerebral hypoxia, and that recovery of oxidative phosphorylation as indicated by PCr/Pi values cannot be used as an index of recovery of cell function.

Cytosolic and membrane-bound cerebral nitric oxide synthase activity during hypoxia in cortical tissue of newborn piglets

To determine the role of nitric oxide production during hypoxia, the presence of two forms of neuronal nitric oxide synthase, cytosolic (cNOS) and membrane-bound (memNOS), in cortical tissue of newborn piglets and the effects of hypoxia on the activity of these enzymes were studied. Experiments were performed in 12 anesthetized and ventilated Yorkshire piglets, 2-4 days of age. Hypoxia was induced by decreasing the FiO2 to 0.07. The control group was ventilated maintaining normoxia. After 1 h of normoxic or hypoxic ventilation brain tissue was removed and frozen immediately in liquid nitrogen. Tissue hypoxia was confirmed by analysis of adenosine triphosphate (ATP) and phosphocreatine (PCr): ATP was reduced to 52% and PCr to 28% of control values. cNOS activity was 35.3 +/- 13.7 pmol/mg protein per min in the control group and 28.3 +/- 7.0 in the hypoxia group; memNOS activity was 10.5 +/- 4.5 and 12.0 +/- 3.9 pmol/mg protein per min in the control and hypoxia groups, respectively. Differences in cNOS and memNOS activity between control and hypoxic animals were not significant. The results indicate that both cNOS and memNOS are present in cortical tissue of newborn piglets and that the activity is unaffected by 1 h of tissue hypoxia. We suggest that production of nitric oxide and its derivative peroxynitrite during hypoxia may therefore be a potential mechanism for hypoxia-induced brain cell membrane lipid peroxidation.

Brain peroxidative and glutathione status after moderate hypoxia in normal weight and intra-uterine growth-restricted newborn piglets

In order to investigate the pathogenetic factors causing the relatively frequent occurrence of brain injury in intrauterine growth-restricted newborns, lipid peroxidation products (TBAR), glutathione (GSH, GSSG) and in vitro production of reactive oxygen species (chemiluminescence, stimulated lipid peroxidation, H2O2 formation) were studied in the brain of normal weight (NW) and intra-uterine growth-restricted newborn piglets (IUGR) after 1 hour of hypoxia (FiO2 11%) and 90 min reoxygenation. Cardiocirculatory parameters and catecholamine release into the blood were also measured. In the cerebellum, higher GSH content, but also higher in vitro production of lucigenin amplified chemiluminescence were found in comparison to other brain regions, independent of growth restriction and hypoxia. Moderate hypoxia without acidosis and hypercapnia resulted in GSH depletion especially in the brain of IUGR, but no changes in GSSG concentrations were measured. Though TBAR decreased after hypoxia/reoxygenation, in some brain areas of IUGR higher TBAR values were found in comparison to NW. H2O2 formation, stimulated lipid peroxidation and lucigenin and luminol amplified chemiluminescence in the 9000 x/g supernatant of brain tissue did not reveal special response of IUGR to hypoxia/reoxygenation. Hypoxia-induced circulatory centralisation due to increased release of catecholamines into the plasma prevented oxygen deficiency also in the brain of IUGR. The role of brain monoamine metabolism in the production of reactive oxygen species, followed by greater GSH depletion and higher in vivo formation of lipid peroxides in IUGR is discussed.

Protective effect of alpha-tocopherol on brain cell membrane function during cerebral cortical hypoxia in newborn piglets

Protective effect of alpha-tocopherol on the structure and function of brain cell membranes was investigated by measuring Na+,K(+)-ATPase activity and products of lipid peroxidation (fluorescent compounds) in brain cell membranes obtained from newborn piglets. Four groups of anesthetized, ventilated piglets were studied: five hypoxic piglets and five normoxic piglets were pretreated with free alpha-tocopherol (20 mg/kg/dose i.m.), five additional hypoxic piglets received i.m. placebo and five normoxic piglets served as control. Placebo and alpha-tocopherol were given 48 and 3 h prior to onset of hypoxia. Hypoxic hypoxia was induced and cerebral hypoxia was documented as a decrease in the ratio of phosphocreatine to inorganic phosphate (PCr/P(i)) using 31P NMR spectroscopy. PCr/P(i) decreased from baseline of 2.62 +/- 0.54 to 1.05 +/- 0.27 in alpha-tocopherol-pretreated and from 2.44 +/- 0.48 to 1.14 +/- 0.30 in the placebo-pretreated group during hypoxia. Na+,K(+)-ATPase activity was unchanged in both normoxic and hypoxic alpha-tocopherol-pretreated groups. However, in placebo-pretreated hypoxic group, Na+,K(+)-ATPase activity decreased as compared with control (44.9 +/- 9.7 vs. 61.8 +/- 5.7 mumol P(i)/mg protein/h, P < 0.005). The level of fluorescent compounds increased in placebo-pretreated but not in alpha-tocopherol-pretreated group as compared with control. During hypoxia, serum alpha-tocopherol levels were higher in alpha-tocopherol-pretreated groups as compared with placebo-pretreated hypoxic group. The present data indicates that alpha-tocopherol protects brain cell membranes in newborn piglets from lipid peroxidative damage during tissue hypoxia probably by being incorporated in cell membrane and also as circulating antioxidant.

Protective effect of MgSO4 infusion on nmda receptor binding characteristics during cerebral cortical hypoxia in the newborn piglet

This study tests the hypothesis that magnesium, a selective non-competitive antagonist of the NMDA receptor, will attenuate hypoxia-induced alteration in NMDA receptors and preserve MK-801 binding characteristics during cerebral hypoxia in vivo. Anesthetized, ventilated and instrumented newborn piglets were divided into three groups: normoxic controls were compared to untreated hypoxic and Mg(2+)-treated hypoxic piglets. Cerebral hypoxia was induced by lowering the FiO2 to 5-7% and confirmed biochemically by a decrease in the levels of phosphocreatine (82% lower than control). The Mg(2+)-treated group received MgSO4 600 mg/kg over 30 min followed by 300 mg/kg administered during 60 min of hypoxia. Plasma Mg2+ concentrations increased from 1.6 +/- 0.1 mg/dl to 17.7 +/- 3.3 mg/dl. 3H-MK-801 binding was used as an index of NMDA receptor modification. The Bmax in control, hypoxic and Mg(2+)-treated hypoxic piglets was 1.09 +/- 0.17, 0.70 +/- 0.25 and 0.96 +/- 0.14 pmoles/mg protein, respectively. The Kd for the same groups were 10.02 +/- 2.04, 4.88 +/- 1.43 and 8.71 +/- 2.23 nM, respectively. The Bmax and Kd in the hypoxic group were significantly lower compared to the control and Mg(2+)-treated hypoxic groups, indicating a preservation of NMDA receptor number and affinity for MK-801 during hypoxia with Mg2+. The activity of Na+, K+ ATPase, a marker of neuronal membrane function, was lower in the hypoxic group compared to the control and Mg(2+)-treated hypoxic groups. These findings show that MgSO4 prevents the hypoxia-induced modification of the NMDA receptor and attenuates neuronal membrane dysfunction.(ABSTRACT TRUNCATED AT 250 WORDS)

Alteration of brain cell membrane function following cocaine exposure in the fetal guinea pig

The effect of cocaine on brain cell membrane structure and function was studied in the fetal guinea pig. We tested the hypothesis that cocaine, a potent vasoconstrictor, would result in brain cell membrane dysfunction as determined by altered activity of Na+,K(+)-ATPase and the appearance of products of membrane lipid peroxidation (conjugated dienes (CD) and fluorescent compounds (FC)). A total of 14 pregnant guinea pigs were studied at term (60 days). One hour prior to delivery, the pregnant guinea pigs were divided into 3 groups as follows: cocaine, 30 mg/kg i.p., saline placebo i.p., or 7% FiO2 for 1 h. Following cocaine, brain Na+,K(+)-ATPase activity decreased (mean +/- S.D., 25.6 +/- 9.2 vs. 54.6 +/- 3.4 mumol Pi/mg protein/h, cocaine vs. control, respectively, P < 0.01) and was similar to the hypoxia group (21.9 +/- 2.8 mumol Pi/mg protein/h). The products of lipid peroxidation did not change significantly following cocaine whereas hypoxia resulted in a rise in CD from 0 to 0.175 +/- 0.015 mumol/g brain, control vs. hypoxia, (P < 0.01), and FC from 1.13 +/- 0.15 to 1.88 +/- 0.13 micrograms quinine sulfate/g brain, control vs. hypoxia, (P < 0.01). These data show that acute fetal cocaine exposure, unlike hypoxia alone, results in a significant decrease in Na+,(K+)-ATPase activity without a significant increase in the products of lipid peroxidation, suggesting the mechanism by which cocaine affects brain cell membrane integrity is distinct from hypoxia. Inhibition of the enzyme activity may be due to a direct action of cocaine on the enzyme or due to enzyme regulation by cocaine-induced alterations in neurotransmitters.

Hypoxia-induced modification of the N-methyl-D-aspartate receptor in the brain of the newborn piglet

The effect of hypoxia on the N-methyl-D-aspartate (NMDA) receptor/ion channel complex in the brain cell membrane of the newborn piglet was studied. Experiments were conducted on newborn piglets, 2-4 days of age, that were anesthetized and mechanically ventilated. Hypoxic hypoxia was induced in the experimental group by lowering the FiO2 to 5-7%. The control group was ventilated under normoxic conditions. Tissue hypoxia was documented biochemically by decreased levels of ATP and phosphocreatine (PCr) in the hypoxic group (52% and 81% lower than the normoxic group, respectively). [3H]MK-801 binding characteristics (Bmax = number of receptors, Kd = dissociation constant) were used as an index of NMDA receptor modification. In hypoxic brains, Bmax decreased from the control level of 1.13 +/- 0.15 pmol/mg protein to 0.68 +/- 0.23 pmol/mg protein (P < 0.01) and the Kd value decreased (reflecting increased affinity) from 9.46 +/- 1.68 nM in the control brains to 4.87 +/- 1.42 nM (P < 0.01) in the hypoxic brains. The Na+,K(+)-ATPase activity, an index of brain cell membrane function, decreased from a control value of 46.5 +/- 0.4 to 40.5 +/- 2.3 mumol inorganic phosphate (Pi) mg protein/h (P < 0.005) during hypoxia. The results of this study indicate that hypoxia in newborn piglets modifies the NMDA receptor in the cerebral cortex, resulting in an increased affinity of the receptor channel. Hypoxia-induced modification of the NMDA ion/receptor complex may be a potential mechanism of cerebral excitotoxicity.

Selective sensitivity of synaptosomal membrane function to cerebral cortical hypoxia in newborn piglets

The effect of hypoxia on the structure and function of the synaptosomal membranes and myelin fraction (glial cells, neuronal cells bodies and axonal membranes) was investigated by measuring Na+,K(+)-ATPase activity and levels of lipid peroxidation products in cerebral cortical synaptosomal membranes and myelin fractions obtained from newborn piglets. Hypoxic hypoxia was induced and cerebral hypoxia was documented as a decrease in the ratio of phosphocreatine to inorganic phosphate (PCr/Pi) using 31P-NMR spectroscopy. PCr/Pi decreased from baseline of 2.93 +/- 0.76 to 0.61 +/- 0.36 during hypoxia. The synaptosomal membrane Na+,K(+)-ATPase activity decreased from a control value of 56.6 +/- 3.7 to 40.4 +/- 6.0 mumol Pi/mg protein/h during hypoxia. The level of conjugated dienes increased from zero (reference value) to 4.5 +/- 2.7 nmol/mg lipid and the level of fluorescent compounds increased from 23.5 +/- 2.2 to 92.6 +/- 46.4 ng quinine sulfate/mg lipid in the synaptosomal membranes during hypoxia. No change in myelin fraction Na+,K(+)-ATPase activity or levels of lipid peroxidation products were noted. These data indicate that synaptosomal membranes, rich in polyunsaturated fatty acids, are more susceptible to oxygen free radical mediated lipid peroxidative damage during hypoxia.

Pharmacologic management of neonatal cerebral ischemia and hemorrhage: old and new directions

New developments in pharmacologic management of cerebral ischemia and hemorrhage are reviewed. A number of agents with diverse modes of action have now been shown to be neuroprotective in adult and neonatal animal models when administered either before or after a hypoxic-ischemic insult. As experience improves with these agents in hypoxic-ischemic injury and periventricular-intraventricular hemorrhage in human neonates, there is reason to be optimistic that effective neuroprotective strategies will soon be clinically available.