Single dose of 17ß-estradiol provides transient neuroprotection in female juvenile mice after cardiac-arrest and cardiopulmonary resuscitation.

Each year there are approximately 7000 out of hospital cardiac arrests in the pediatric population, with 30% resuscitation rate and a 6-10% rate of survival to hospital discharge. Survivors of cardiac arrest exhibit learning and memory deficits that are devastating during the school years. Delayed neuronal cell death occurs in the hippocampus following cardiac arrest and likely contributes to memory impairments. Circulating endogenous estrogen in young adult females has been shown to provide protection against ischemic cell death, as does chronic exogenous administration of 17ß-estradiol (E2). Chronic estrogen benefit can have undesirable feminizing effects, particularly in pre-adolescents. Here, we tested if a single-dose of E2 is neuroprotective in our pediatric cardiac arrest mouse model performed in juvenile mice. We subjected P21P25 C57Blk6 male and female mice to 8 min of cardiac arrest followed by cardiopulmonary resuscitation (CA/CPR). This developmental stage preceded the hormonal onset and serum estradiol and testosterone levels were not different in males and females. A single dose of E2 (100µg/kg) or vehicle was administered 30 min after resuscitation. Neuronal cell death measured 3 days after CA/CPR showed reduced hippocampal cell death in E2-treated females, but not males. Benefit of E2 in females was blocked by the P38 MAPK inhibitor, SB203580. Hippocampal-dependent memory function was equally impaired in E2-and vehicle-treated females measured in the contextual fear conditioning task at 7 days. Our findings demonstrate female-specific transient neuroprotection with E2 that does not provide sustained functional benefit.

Therapeutic hypothermia protects against ischemia-induced impairment of synaptic plasticity following juvenile cardiac arrest in sex-dependent manner.

Pediatric cardiac arrest (CA) often leads to poor neurologic outcomes, including deficits in learning and memory. The only approved treatment for CA is therapeutic hypothermia, although its utility in the pediatric population remains unclear. This study analyzed the effect of mild therapeutic hypothermia after CA in juvenile mice on hippocampal neuronal injury and the cellular model of learning and memory, termed long-term potentiation (LTP). Juvenile mice were subjected to cardiac arrest and cardiopulmonary resuscitation (CA/CPR) followed by normothermia (37°C) and hypothermia (30°C, 32°C). Histological injury of hippocampal CA1 neurons was performed 3days after resuscitation using hematoxylin and eosin (H&E) staining. Field excitatory post-synaptic potentials (fEPSPs) were recorded from acute hippocampal slices 7days after CA/CPR to determine LTP. Synaptic function was impaired 7days after CA/CPR. Mice exposed to hypothermia showed equivalent neuroprotection, but exhibited sexually dimorphic protection against ischemia-induced impairment of LTP. Hypothermia (32°C) protects synaptic plasticity more effectively in females, with males requiring a deeper level of hypothermia (30°C) for equivalent protection. In conclusion, male and female juvenile mice exhibit equivalent neuronal injury following CA/CPR and hypothermia protects both males and females. We made the surprising finding that juvenile mice have a sexually dimorphic response to mild therapeutic hypothermia protection of synaptic function, where males may need a deeper level of hypothermia for equivalent synaptic protection.

Region-specific role for GluN2B-containing NMDA receptors in injury to Purkinje cells and CA1 neurons following global cerebral ischemia.

Motor deficits are present in cardiac arrest survivors and injury to cerebellar Purkinje cells (PCs) likely contribute to impairments in motor coordination and post-hypoxic myoclonus. N-Methyl-D-aspartic acid (NMDA) receptor-mediated excitotoxicity is a well-established mechanism of cell death in several brain regions, but the role of NMDA receptors in PC injury remains understudied. Emerging data in cortical and hippocampal neurons indicate that the GluN2A-containing NMDA receptors signal to improve cell survival and GluN2B-containing receptors contribute to neuronal injury. This study compared neuronal injury in the hippocampal CA1 region to that in PCs and investigated the role of NMDA receptors in PC injury in our mouse model of cardiac arrest and cardiopulmonary resuscitation (CA/CPR). Analysis of cell density demonstrated a 24% loss of PCs within 24 h after 8 min CA/CPR and injury stabilized to 33% by 7 days. The subunit promiscuous NMDA receptor antagonist MK-801 protected both CA1 neurons and PCs from ischemic injury following CA/CPR, demonstrating a role for NMDA receptor activation in injury to both brain regions. In contrast, the GluN2B antagonist, Co 101244, had no effect on PC loss while protecting against injury in the CA1 region. These data indicate that ischemic injury to cerebellar PCs progresses via different cell death mechanisms compared to hippocampal CA1 neurons.

Increasing small conductance Ca2+-activated potassium channel activity reverses ischemia-induced impairment of long-term potentiation.

Global cerebral ischemia following cardiac arrest and cardiopulmonary resuscitation (CA/CPR) causes injury to hippocampal CA1 pyramidal neurons and impairs cognition. Small conductance Ca(2+)-activated potassium channels type 2 (SK2), expressed in CA1 pyramidal neurons, have been implicated as potential protective targets. Here we showed that, in mice, hippocampal long-term potentiation (LTP) was impaired as early as 3 h after recovery from CA/CPR and LTP remained impaired for at least 30 days. Treatment with the SK2 channel agonist 1-Ethyl-2-benzimidazolinone (1-EBIO) at 30 min after CA provided sustained protection from plasticity deficits, with LTP being maintained at control levels at 30 days after recovery from CA/CPR. Minimal changes in glutamate release probability were observed at delayed times after CA/CPR, implicating post-synaptic mechanisms. Real-time quantitative reverse transcriptase-polymerase chain reaction indicated that CA/CPR did not cause a loss of N-methyl-D-aspartate (NMDA) receptor mRNA at 7 or 30 days after CA/CPR. Similarly, no change in synaptic NMDA receptor protein levels was observed at 7 or 30 days after CA/CPR. Further, patch-clamp experiments demonstrated no change in functional synaptic NMDA receptors at 7 or 30 days after CA/CPR. Electrophysiology recordings showed that synaptic SK channel activity was reduced for the duration of experiments performed (up to 30 days) and that, surprisingly, treatment with 1-EBIO did not prevent the CA/CPR-induced loss of synaptic SK channel function. We concluded that CA/CPR caused alterations in post-synaptic signaling that were prevented by treatment with the SK2 agonist 1-EBIO, indicating that activators of SK2 channels may be useful therapeutic agents to prevent ischemic injury and cognitive impairments.

A novel mouse model of pediatric cardiac arrest and cardiopulmonary resuscitation reveals age-dependent neuronal sensitivities to ischemic injury.

BACKGROUND: Pediatric sudden cardiac arrest (CA) is an unfortunate and devastating condition, often leading to poor neurologic outcomes. However, little experimental data on the pathophysiology of pediatric CA is currently available due to the scarcity of animal models. NEW METHOD: We developed a novel experimental model of pediatric cardiac arrest and cardiopulmonary resuscitation (CA/CPR) using postnatal day 20-25 mice. Adult (8-12 weeks) and pediatric (P20-25) mice were subjected to 6min CA/CPR. Hippocampal CA1 and striatal neuronal injury were quantified 3 days after resuscitation by hematoxylin and eosin (H&E) and Fluoro-Jade B staining, respectively. RESULTS: Pediatric mice exhibited less neuronal injury in both CA1 hippocampal and striatal neurons compared to adult mice. Increasing ischemia time to 8 min CA/CPR resulted in an increase in hippocampal injury in pediatric mice, resulting in similar damage in adult and pediatric brains. In contrast, striatal injury in the pediatric brain following 6 or 8 min CA/CPR remained extremely low. As observed in adult mice, cardiac arrest causes delayed neuronal death in pediatric mice, with hippocampal CA1 neuronal damage maturing at 72 h after insult. Finally, mild therapeutic hypothermia reduced hippocampal CA1 neuronal injury after pediatric CA/CPR. COMPARISON WITH EXISTING METHOD: This is the first report of a cardiac arrest and CPR model of global cerebral ischemia in mice. CONCLUSIONS: Therefore, the mouse pediatric CA/CPR model we developed is unique and will provide an important new tool to the research community for the study of pediatric brain injury.

Sexually dimorphic response of TRPM2 inhibition following cardiac arrest-induced global cerebral ischemia in mice.

Transient global cerebral ischemia due to cardiac arrest followed by resuscitation (CA/CPR) causes significant neurological damage in vulnerable neuron populations within the brain, such as hippocampal CA1 neurons. In recent years, we have implicated the transient receptor potential M2 (TRPM2) channel as a mediator of ischemic injury to neurons. We previously demonstrated that genetic and pharmacological strategies that reduce TRPM2 function preferentially protect male neurons in vitro and reduce infarct volume following experimental stroke. Due to the narrow therapeutic window for intervention following ischemic stroke, it is important to assess the role of TRPM2 in other models of cerebral ischemia. Therefore, this study utilized a modified mouse model of CA/CPR to mimic more accurately the clinical condition by maintaining body and head temperatures near the physiological range throughout. Here, we report that inhibition of TRPM2 activity with clotrimazole reduces hippocampal CA1 neuronal injury when administered 30 min after resuscitation from cardiac arrest. Consistent with our previous observations, neuroprotection was observed in male mice and no effect on injury was observed in the female. These findings provide further evidence for TRPM2 as a target for protection against cerebral ischemia in the male brain.

Unintended changes in cognition, mood, and behavior arising from cell-based interventions for neurological conditions: ethical challenges.

The prospect of using cell-based interventions (CBIs) to treat neurological conditions raises several important ethical and policy questions. In this target article, we focus on issues related to the unique constellation of traits that characterize CBIs targeted at the central nervous system. In particular, there is at least a theoretical prospect that these cells will alter the recipients' cognition, mood, and behavior-brain functions that are central to our concept of the self. The potential for such changes, although perhaps remote, is cause for concern and careful ethical analysis. Both to enable better informed consent in the future and as an end in itself, we argue that early human trials of CBIs for neurological conditions must monitor subjects for changes in cognition, mood, and behavior; further, we recommend concrete steps for that monitoring. Such steps will help better characterize the potential risks and benefits of CBIs as they are tested and potentially used for treatment.

Effect of glutamine synthetase inhibition on astrocyte swelling and altered astroglial protein expression during hyperammonemia in rats.

Inhibition of glutamine synthesis reduces astrocyte swelling and associated physiological abnormalities during acute ammonium acetate infusion in anesthetized rats. We tested the hypothesis that inhibition of glutamine accumulation during more prolonged ammonium acetate infusion in unanesthetized rats reduces cortical astrocyte swelling and immunohistochemical changes in astrocytic proteins. Rats received a continuous i.v. infusion of either sodium acetate or ammonium acetate for 24 h to increase plasma ammonia from about 30-400 mumol/l. Cohorts were pretreated with vehicle or l-methionine-S-sulfoximine (MSO; 0.83 mmol/kg). MSO reduced glutamine synthetase activity by 57% and glutamine synthetase immunopositive cell number by 69%, and attenuated cortical glutamine accumulation by 71%. Hyperammonemia increased the number of swollen astrocytes in cortex and MSO reduced this increase to control values. The number of glial fibrillary acidic protein immunopositive cells in cortex was greater in hyperammonemic rats and the increase in superficial cortical layers was attenuated by MSO. Immunoreactivity for the gap junction protein connexin-43 in the neuropil, assessed by optical density, was greater in the hyperammonemic group compared with controls, but this increase was not attenuated by MSO. No changes in the optical density of GLT1 glutamate transporter immunoreactivity in cortex were detected in any group. We conclude that glutamine synthetase inhibition reduces astrocyte swelling and ameliorates some of the reactive astroglial cytoskeletal alterations seen at 24 h of hyperammonemia, but that gap junction changes in astrocytes occur independently of glutamine accumulation and swelling.

Double-masked randomized trial comparing alternate combinations of intraoperative anesthesia and postoperative analgesia in abdominal aortic surgery.

BACKGROUND: Improvement in patient outcome and reduced use of medical resources may result from using epidural anesthesia and analgesia as compared with general anesthesia and intravenous opioids, although the relative importance of intraoperative versus postoperative technique has not been studied. This prospective, double-masked, randomized clinical trial was designed to compare alternate combinations of intraoperative anesthesia and postoperative analgesia with respect to postoperative outcomes in patients undergoing surgery of the abdominal aorta. METHODS: One hundred sixty-eight patients undergoing surgery of the abdominal aorta were randomly assigned to receive either thoracic epidural anesthesia combined with a light general anesthesia or general anesthesia alone intraoperatively and either intravenous or epidural patient-controlled analgesia postoperatively (four treatment groups). Patient-controlled analgesia was continued for at least 72 h. Protocols were used to standardize perioperative medical management and to preserve masking intraoperatively and postoperatively. A uniform surveillance strategy was used for the identification of prospectively defined postoperative complications. Outcome evaluation included postoperative hospital length of stay, direct medical costs, selected postoperative morbidities, and postoperative recovery milestones. RESULTS: Length of stay and direct medical costs for patients surviving to discharge were similar among the four treatment groups. Postoperative outcomes were similar among the four treatment groups with respect to death, myocardial infarction, myocardial ischemia, reoperation, pneumonia, and renal failure. Epidural patient-controlled analgesia was associated with a significantly shorter time to extubation (P = 0.002). Times to intensive care unit discharge, ward admission, first bowel sounds, first flatus, tolerating clear liquids, tolerating regular diet, and independent ambulation were similar among the four treatment groups. Postoperative pain scores were also similar among the four treatment groups. CONCLUSIONS: In patients undergoing surgery of the abdominal aorta, thoracic epidural anesthesia combined with a light general anesthesia and followed by either intravenous or epidural patient-controlled analgesia, offers no major advantage or disadvantage when compared with general anesthesia alone followed by either intravenous or epidural patient-controlled analgesia.

Social stress exacerbates stroke outcome by suppressing Bcl-2 expression.

The relationship between stressful life events and the onset of disease is well documented. However, the role of psychological stress as a risk factor for life-threatening cerebrovascular insults such as stroke remains unspecified, but could explain individual variation in stroke outcome. To discover the mechanisms through which psychological stress may alter stroke outcome, we modeled the effects of chronic social intimidation and stress on ischemia-induced bcl-2 expression and early neuronal cell loss resulting from cerebral artery occlusion in mice (C57BL/6). The bcl-2 protooncogene promotes cell survival and protects against apoptosis and cellular necrosis in numerous neurodegenerative disorders, including stroke. In our study, male mice were chronically exposed to aggressive social stimuli before induction of a controlled, mild ischemic insult. Stressed mice expressed approximately 70% less bcl-2 mRNA than unstressed mice after ischemia. In addition, social stress greatly exacerbated infarct in wild-type mice but not in transgenic mice that constitutively express increased neuronal bcl-2. Despite similar postischemic concentrations of corticosterone, the major stress hormone in mice, high corticosterone concentrations were significantly correlated with larger infarcts in wild-type mice but not bcl-2 transgenic mice. Thus, enhanced bcl-2 expression offsets the potentially deleterious consequences of high postischemic plasma corticosterone concentrations. Taken together, these data demonstrate that stressful prestroke social milieu strongly compromises an endogenous molecular mechanism of neuroprotection in injured brain and offer a new behavioral target for stroke therapy.

Estrogen and Bcl-2: gene induction and effect of transgene in experimental stroke.

Female rodents producing endogenous estrogens are protected from stroke damage in comparison with male counterparts. This natural protection is lost after ovariectomy or reproductive senescence. The aim of this study is to determine whether estrogen reduces early neuronal injury and cell loss after ischemia by increasing the expression of Bcl-2. Male, intact female, ovariectomized, and estrogen-repleted ovariectomized rats were subjected to middle cerebral artery occlusion, and 22 hr later the level and localization of Bcl-2 mRNA and protein were determined. The levels of post-ischemic bcl-2 mRNA and protein were increased exclusively in neurons within the peri-infarct region. Intact females and estrogen-treated castrates demonstrated increased bcl-2 mRNA and protein expression compared with males and estrogen-deficient females, accompanied by a decrease in infarct size. To test the hypothesis that the neuroprotective mechanism of estrogen functions via Bcl-2, we compared ischemic outcome in male, female, and ovariectomized wild-type mice and mice overexpressing Bcl-2 exclusively in neurons. Wild-type female mice sustained smaller infarcts compared with males. Bcl-2 overexpression reduced infarct size in males, but provided no added protection in the female. Moreover, ovariectomy exacerbated infarction in wild-type females, but had no effect in Bcl-2 overexpressors. These data indicate that overexpression of Bcl-2 simulates the protection against ischemic injury conferred by endogenous female sex steroids. We concluded that estrogen rescues neurons after focal cerebral ischemia by increasing the level of Bcl-2 in peri-infarct regions and that estrogen-induced bcl-2 gene expression is an important downstream component of neuronal protection in female stroke.

Cognitive and behavioral assessment in experimental stroke research: will it prove useful?

Stroke in humans is associated with deficits in sensorimotor and cognitive function. Consequently, many stroke researchers recently have expanded their techniques to assess cognitive and behavioral correlates of histologically-determined stroke damage in animal models. Although the incorporation of functional outcome assessment represents an important step forward in stroke research, reports of middle cerebral artery occlusion (MCAO) induced behavioral deficits often conflict, and a significant correlation between post-stroke histology and behavior has been reported in few stroke studies. Discrepancies in behavioral outcomes among studies may be due to several factors, such as method of MCAO, duration of occlusion, strain, the timing and method of the behavioral testing and the laboratory environment. Furthermore, proper experimental and control groups, necessary to rule out potential confounding factors during cognitive testing, often are not incorporated. The goal of this review is: (1) to provide a description of the techniques most commonly employed to assess functional outcome after (MCAO) in rodents and (2) to identify potential confounding factors that may interfere with a clear interpretation of the behavioral data.

Rapid three-dimensional diffusion MRI facilitates the study of acute stroke in mice.

MRI studies using mouse brain models of ischemia are becoming a valuable tool for understanding the mechanism of stroke, since transgenic models are now available. However, the small size of the mouse brain and the surgical complexity of creating ischemia in mice make it technically challenging to obtain high-quality MRI data. Therefore, there are few reports of MRI studies in murine cerebral ischemia. In this project a newly developed rapid 3D diffusion-weighted imaging (DWI) technique was applied to study experimental stroke in a mouse model of reversible middle cerebral artery occlusion (MCAO). Ischemic volumes were successfully delineated using this 3D whole-brain imaging technique with high spatial (0.34 x 0.5 x 1.0 mm(3) before zero-filling) and temporal (7 min) resolution. The 3D observation revealed the characteristic evolution of stroke after transient MCAO. There was a temporarily high diffusion constant in the cortex during early reperfusion, followed by a secondary energy failure in the cortex and caudate-putamen at 6 and 21 h of reperfusion. Magn Reson Med 46:183-188, 2001.

Fetal cerebral and peripheral circulatory responses to hypoxia after nitric oxide synthase inhibition.

The increase in cerebral blood flow (CBF) during hypoxia in fetal sheep at 0.6 gestation is less than the increase at 0.9 gestation when normalized for differences in baseline CBF and oxygen consumption. Nitric oxide (NO) synthase (NOS) catalytic activity increases threefold during this period of development. We tested the hypothesis that administration of the NOS inhibitor N(omega)-nitro-L-arginine methyl ester (L-NAME) decreases the CBF response to systemic hypoxia selectively at 0.9 gestation. We also tested whether any peripheral vasoconstriction during hypoxia is potentiated by L-NAME at 0.9 gestation. Administration of L-NAME increased arterial blood pressure and decreased microsphere-determined CBF during normoxia in fetal sheep at both 0.6 and 0.9 gestation. With subsequent reduction of arterial oxygen content by approximately 50%, the percent increase in forebrain CBF in a control group (57 +/- 11%; +/- SE) and L-NAME-treated group (51 +/- 6%) was similar at 0.6 gestation. Likewise, at 0.9 gestation, the increase in CBF was similar in control (90 +/- 25%) and L-NAME (80 +/- 28%) groups. At 0.9 gestation, L-NAME treatment attenuated the increase in coronary blood flow and increased gastrointestinal vascular resistance during hypoxia. We conclude that NO exerts a basal vasodilatory influence in brain as early as 0.6 gestation in fetal sheep but is not an important mechanism for hypoxic vasodilation in brain at either 0.6 or 0.9 gestation. Thus the developmental increase in NOS catalytic capacity does not appear to be responsible for developmental increases in the CBF response to hypoxia during this period. In contrast, NO modulates the vascular response to hypoxia in heart and gastrointestinal tract.

MK801 decreases glutamate release and oxidative metabolism during hypoglycemic coma in piglets.

Hypoglycemic coma increases extracellular excitatory amino acids, which mediate hypoglycemic neuronal degeneration. Cerebral oxygen consumption increases during hypoglycemic coma in piglets. We tested the hypothesis that the NMDA-receptor antagonist dizocilpine (MK801) attenuates the increase in cerebral oxygen consumption during hypoglycemia. We measured EEG, cerebral blood flow (CBF), cerebral oxygen consumption (CMRO(2)) and cortical microdialysate levels of glutamate, aspartate and glycine in pentobarbital-anesthetized piglets during 60 min of insulin-induced hypoglycemic coma. NMDA-receptor distribution was measured by autoradiography. MK801 (0.75 mg/kg i.v.) was given within 5 min after onset of isoelectric EEG. Saline- and MK801-treated normoglycemic control animals were also studied. Brain temperature was maintained at 38.5+/-0.5 degrees C. MK801 prevented the 5--10-fold increase in glutamate and aspartate occurring in saline-treated hypoglycemic animals, and attenuated the increase in CMRO(2). Increases in CBF of 200--400% during hypoglycemic coma were not affected by MK801. MK801 did not alter CBF, CMRO(2) or microdialysate amino acid levels in normoglycemic control animals. Parietal cortex corresponding to microdialysis sites was highly enriched in NMDA receptors, and the density and distribution overall of NMDA receptor binding sites were comparable to that reported in other species. We conclude that NMDA receptor activation plays a central role in hypoglycemia-induced glutamate release, and contributes to increased cerebral oxygen consumption. Neuroprotective effects of MK801 during hypoglycemia in piglets may involve inhibitory effects on glutamate release and oxidative metabolism.

Estrogen restores postischemic pial microvascular dilation.

Estrogen protects the brain from experimental cerebral ischemia, likely through both vascular and neuronal cellular mechanisms. The purpose of this study was to determine whether chronic estrogen treatment in males and repletion in ovariectomized (Ovx) females reverses abnormalities in pial arteriolar reactivity during reperfusion from global forebrain ischemia (4-vessel occlusion, 15 min) and whether the site of protection is vascular endothelium. Male and Ovx female rats were implanted with either placebo or a 25-microg 17 beta-estradiol pellet 10 days before ischemia. With the use of intravital microscopy, pial vessel dilation to ACh (10 microM) and S-nitroso-N-acetyl-penicillamine (SNAP; 1 microM) and vasoconstriction to serotonin (10 microM) was examined in situ at 30--60 min of reperfusion. Postischemic changes in vessel diameter were compared with preischemic values for each agent. Postischemic response to both ACh and SNAP was lost in males and Ovx females, but not in estrogen pellet-implanted males and estrogen-implanted Ovx females, suggesting that estrogen protects both endothelial and smooth muscle-mediated vasodilation. Ischemia blunted vessel constriction to serotonin regardless of treatment. These data demonstrate that estrogen acts as a vasoprotective agent within the cerebral circulation and can improve microvascular function under conditions of an acutely evolving ischemic pathology.

Blood-brain barrier permeability during dopamine-induced hypertension in fetal sheep.

Dopamine is often used as a pressor agent in sick newborn infants, but an increase in arterial blood pressure could disrupt the blood-brain barrier (BBB), especially in the preterm newborn. Using time-dated pregnant sheep, we tested the hypothesis that dopamine-induced hypertension increases fetal BBB permeability and cerebral water content. Barrier permeability was assessed in nine brain regions, including cerebral cortex, caudate, thalamus, brain stem, cerebellum, and spinal cord, by intravenous injection of the small tracer molecule [(14)C]aminoisobutyric acid at 10 min after the start of dopamine or saline infusion. We studied 23 chronically catheterized fetal sheep at 0.6 (93 days, n = 10) and 0.9 (132 days, n = 13) gestation. Intravenous infusion of dopamine increased mean arterial pressure from 38 +/- 3 to 53 +/- 5 mmHg in 93-day fetuses and from 55 +/- 5 to 77 +/- 8 mmHg in 132-day fetuses without a decrease in arterial O(2) content. These 40% increases in arterial pressure are close to the maximum hypertension reported for physiological stresses at these ages in fetal sheep. No significant increases in the brain transfer coefficient of aminoisobutyric acid were detected in any brain region in dopamine-treated fetuses compared with saline controls at 0.6 or 0.9 gestation. There was also no significant increase in cortical water content with dopamine infusion at either age. We conclude that a 40% increase in mean arterial pressure during dopamine infusion in normoxic fetal sheep does not produce substantial BBB disruption or cerebral edema even as early as 0.6 gestation.

Two-compartment exchange model for perfusion quantification using arterial spin tagging.

The original well-mixed tissue model for the arterial spin tagging techniques is extended to a two-compartment model of restricted water exchange between microvascular (blood) and extravascular (tissue) space in the parenchyma. The microvascular compartment consists of arterioles, capillaries, and venules, with the blood/tissue water exchange taking place in the capillaries. It is shown that, in the case of limited water exchange, the individual FAIR (Flow-sensitive Alternating Inversion Recovery) signal intensities of the two compartments are comparable in magnitude, but are not overlapped in time. It is shown that when the limited water exchange is assumed to be fast, flows quantified from the signal-intensity difference are underestimated, an effect that becomes more significant for larger flows and higher magnetic field strengths. Experimental results on cat brain at 4.7 T comparing flow data from the FAIR signal-intensity difference with those from microspheres over a cerebral blood flow range from 15 to 150 mL 100 g(-1) min(-1) confirm these theoretic predictions. FAIR flow values with correction for restricted exchange, however, correlate well with the radioactive microsphere flow values. The limitations of the approach in terms of choice of the intercompartmental exchange rates are discussed.

Early Neurodegeneration after Hypoxia-Ischemia in Neonatal Rat Is Necrosis while Delayed Neuronal Death Is Apoptosis.

We used silver staining to demonstrate neuronal cell body, axonal, and terminal degeneration in brains from p7 rat pups recovered for 0, 1.5, 3, 6, 24, 48, 72 h, and 6 days following hypoxia-ischemia. We found that initial injury is evident in ipsilateral forebrain by 3 h following hypoxia-ischemia, while injury in ventral basal thalamus develops at 24 h. A secondary phase of injury occurs at 48 h in ipsilateral cortex, but not until 6 days in basal ganglia. Initial injury in striatum and cortex is necrosis, but in thalamus the neurodegeneration is primarily apoptosis. Degeneration also occurs in bilateral white matter tracts, and in synaptic terminal fields associated with apoptosis in regions remote from the primary injury. These results show that hypoxia-ischemia in the developing brain causes both early and delayed neurodegeneration in specific systems in which the morphology of neuronal death is determined by time, region, and potentially by patterns of neuronal connectivity.

Failure to sustain recovery of Na,K-ATPase function is a possible mechanism for striatal neurodegeneration in hypoxic-ischemic newborn piglets.

Hypoxia-ischemia (HI) in the newborn can lead to a variety of sensorimotor abnormalities, including movement and posture disorders. Striatal neurons undergo necrosis after HI in piglets, but mechanisms for this neuronal death are not understood. We tested the hypothesis that Na,K-ATPase is defective in striatum early after HI. Piglets (1 week old) were subjected to 30 min hypoxia (arterial oxygen saturation 30%) and then 7 min of airway occlusion (oxygen saturation 5%), producing asphyxic cardiac arrest. Animals were resuscitated and recovered for 3, 6, 12, and 24 h, respectively. Neuronal necrosis in the striatum is progressive [14]. Na,K-ATPase activity (percent of control) was 60, 98, 51, and 54% at 3, 6, 12, and 24 h after HI, respectively. Intrastriatal differences in enzyme activity were detected histochemically, with the putamen showing greater loss of Na,K-ATPase activity than caudate after 12 h recovery. Immunoblotting showed that the levels of the alpha(3) isoform (localized exclusively to neurons) were 85, 115, 101, and 79% of sham control at 3, 6, 12, and 24 h, respectively. Levels of beta(1), the predominant beta isoform, were similar to alpha(3), while levels of the alpha(1) subunit, the catalytic isoform found in neurons and glia, were 182, 179, 226, and 153% at the same recovery times. We conclude that early inactivation of Na,K-ATPase function participates in the pathogenesis of striatal neuron necrosis, but that loss of enzyme function early after HI is not caused by depletion of composite alpha/beta subunits.