Focal protein synthesis inhibition in a model of neonatal hypoxic-ischemic brain injury

Regional metabolic status of the E-18 rat fetal brain following transient hypoxia/ischemia

Increasing evidence indicates that fetal metabolic stress may result in a variety of post-natal perturbations during brain development. The goal of the study was to determine the duration of hypoxia/ischemia that would elicit a demonstrable regional depression of metabolism in the fetal brain and further to examine several end-points to determine if the metabolic stress affects the developing brain. The uterine artery and uterine branch of the ovarian artery were occluded with aneurysm clamps for a period of 45 min, the clips removed and the metabolites in five regions of the perinatal brain were measured at 0, 2 and 6 h of reflow. Regional P-creatine, ATP and glucose levels were significantly depleted at the end of the 45 min occlusion. The levels of glycogen and glutamate at the end of the occlusion indicated a decreasing trend which was not significant. The concentration of citrate remained essentially unchanged at the end of the occlusion. To ensure that the insult was not lethal to the tissue, the recovery of the metabolites was examined at 2 and 6 h of reflow and generally the concentrations of the high-energy phosphates and glucose were normal or near-normal by 6 h of reperfusion in the five regions of the brain examined. The changes in the metabolites indicate that 45 min of hypoxia/ischemia is an appropriate model for studying neonatal development after fetal metabolic stress.

Down-regulation of Phospholipase D2 mRNA in Neonatal Rat Brainstem and Cerebellum after Hypoxia-Ischemia

Phospholipase D (PLD) and phosphatidylcholine (PC) were implicated in apoptosis and cancer. However, direct evidence on the role of PLD in the cause of apoptosis remains obscure. It was recently reported that apoptosis and necrosis could be induced in the cerebellum and brainstem after focal cerebral hypoxic-ischemic (HI) injury. It was found that apoptosis could be enhanced by farnesol inhibition of PLD signal transduction. Whereas it was shown that highly invasive cancer cell line depends on PLD activity for survival when deprived of serum growth factors. Based on these reports, it is postulated that apoptosis in the cerebellum and brainstem induced after focal cerebral HI treatment may be caused by faulty PLD expression. This is consistent with a report that PLD1 activity and mRNA levels were down-regulated during apoptosis. To test this hypothesis, Northern blotting was used to examine PLD2 mRNA expression after focal cerebral HI. The results show that both PLD2 mRNA 10.8 and 3.9 kb transcripts were significantly decreased by as much as 37% in the brainstem and cerebellum areas 3 h after HI compared to the control, concur with previous report of decreasing PLD activity after ischemia. These PLD2 transcripts, however, were not significantly different from the control 3 days after HI, indicating that the decrease in PLD2 transcription after HI maybe a transient phenomenon. This is the first report to show that the loss of membrane integrity resulting from deprivation of energy and growth factors after HI could cause decrease in PLD2 transcription that promotes apoptosis. The hypothetic role of PLD2 and the mechanism leading to apoptosis remains to be further elucidated.

Experimental model of pediatric asphyxial cardiopulmonary arrest in rats

OBJECTIVE

Develop a clinically relevant model of pediatric asphyxial cardiopulmonary arrest in rats.

DESIGN

Prospective interventional study.

SETTING

University research laboratory.

SUBJECTS

Postnatal day 16-18 rats (n = 9/group).

INTERVENTIONS

Anesthetized rats were endotracheally intubated and mechanically ventilated, and vascular catheters were inserted. Vecuronium was administered, and the ventilator was disconnected from the rats for 8 mins, whereupon rats were resuscitated with epinephrine, sodium bicarbonate, and chest compressions until spontaneous circulation returned. Shams underwent all procedures except asphyxia.

MEASUREMENTS AND MAIN RESULTS

Asphyxial arrest typically occurred by 1 min after the ventilator was disconnected. Return of spontaneous circulation typically occurred <30 secs after resuscitation. An isoelectric electroencephalograph was observed for 30 mins after asphyxia, and rats remained comatose for 12-24 hrs. Overall survival rate was 85%. Motor function measured using beam balance and inclined plane tests was impaired on days 1 and 2, but recovered by day 3, in rats after asphyxia vs. sham injury (p <.05). Spatial memory acquisition measured using the Morris-water maze on days 7-14 and 28-35 was also impaired in rats after asphyxia vs. sham injury (total latency 379 +/- 28 vs. 501 +/- 40 secs, respectively, p <.05). DNA fragmentation was detected in CA1 hippocampal neurons bilaterally 3-7 days after asphyxia. Neurodegeneration detected using Fluorojade B was seen in bilateral CA1 hippocampi and layer V cortical neurons 3-7 days after asphyxia, with persistent neurodegeneration in CA1 hippocampus detected up to 5 wks after asphyxia. CA1 hippocampal neuron survival after asphyxia was 39-43% (p <.001 vs. sham). Evidence of DNA or cellular injury was not detected in sham rats.

CONCLUSIONS

This model of asphyxial cardiopulmonary arrest in postnatal day 17 rats produces many of the clinical manifestations of pediatric hypoxic-ischemic encephalopathy. This model may be useful for the preclinical testing of novel and currently available interventions aimed at improving neurologic outcome in infants and children after cardiopulmonary arrest.

Hypoxia-ischemia induces thioredoxin expression and nitrotyrosine formation in new-born rat brain

Thioredoxin (TRX) is a 13 kDa protein with antioxidant effect and redox regulating functions. Peroxynitrite is a strong oxidizing and nitrating agent which can react with all classes of biomolecules. In the present study, we focused on the association between TRX and nitrotyrosine, which served as a marker of peroxynitrite formation, in the neonatal hypoxia-ischemia (HI) rat brain. At 4-16 h after HI, the immunoreactivity for TRX was diminished in the injured region in the cortex and striatum, whereas nitrotyrosine immunoreactivity was enhanced. In contrast, around the injured region, TRX immunoreactivity was enhanced in survival neurons at 4-24 h after HI, while the immunoreactivity for nitrotyrosine was mostly not detected. Northern blot analysis showed increased TRX mRNA induction in the cerebral hemisphere ipsilateral to the carotid ligation from 4-24 h after HI but not in the contralateral hypoxic hemisphere. These findings suggest that production of peroxynitrite is involved in HI brain injury, and that induced TRX plays a neuroprotective role against oxidative stress resulting from HI.

Protein synthesis inhibition in neocortical grafts evaluated by systemic amino acid uptake autoradiography

The temporal pattern of protein synthesis inhibition was examined in grafted neocortical neurons using [(3)H]valine in vivo autoradiography. Neuronal uptake levels of systemically administered (3)H-labeled amino acids which cross the blood-brain barrier (BBB) via endothelial cell neutral carriers have long been a hallmark in studies of experimental ischemic pathology; there is likely a strong correlation between persistent protein synthesis inhibition and the progression of cell damage. Because the grafting procedure involves the loss of blood flow and the subsequent reperfusion of the donor tissue there are, mechanistically, important similarities to reversible ischemia models. The effects of ischemic injury on grafted CNS neurons are not fully understood. Quantitative analysis of grain distribution in individual graft or control (adjacent host cortex) neurons indicated an initial breakdown of the amino acid barrier system, subsequent recovery, and progressive reduction of amino acid uptake by 1 year. Up to 3 weeks after surgery grafts were flooded with the [(3)H]valine tracer but individual neurons contained relatively few silver grains. After this time, the tracer was normally distributed within graft neurons but at significantly lower levels than in controls. Grain density gradually decreased over time such that 12-month grafted neurons had approximately half that compared to control and only 58% of that in 2-month grafts; the 12-month levels were comparable to those observed at early (10 days) postoperative times. Autoradiography of immunostained sections for MAP-2, SMI 311 (neurofilament marker), and neuron-specific enolase showed reduced expression of these proteins in neurons coupled with weak amino acid tracer uptake. The results further suggest that grafted neurons bear intriguing similarities to neurons placed at ischemic risk, particularly "penumbral" neurons, which are affected by reduced blood flow and are metabolically weakened. The loss of BBB properties in early grafts may also extend to the endothelial cell amino acid carrier system, and the delayed revascularization process could affect neuronal uptake mechanisms.

Dexamethasone effects on cerebral protein synthesis prior to and following hypoxia-ischemia in immature rat

We hypothesized that the neuroprotection against cerebral hypoxic-ischemic damage observed with dexamethasone treatment in immature rats is related to a change in cerebral protein synthesis. Six-day-old Wistar rats were injected with either vehicle (10 ml/kg) or dexamethasone (0.1 mg/kg) 24 h prior to cerebral hypoxia-ischemia. Local cerebral protein synthesis (incorporation of 14C-leucine into proteins) was measured in 7-day-old rats during normoxia, during hypoxia-ischemia, and after hypoxia-ischemia which was produced with right carotid artery ligation and 2-h exposure to 8% O2. In normoxic controls, cerebral protein synthesis was similar in dexamethasone and vehicle-treated animals. During hypoxia-ischemia, local cerebral protein synthesis decreased markedly (p < 0.0001) in ischemic regions ipsilateral to the occlusion, irrespective of treatment. After hypoxia-ischemia, protein synthesis declined even further in vehicle-treated animals. Reductions in protein synthesis were substantially more severe in vehicle- than dexamethasone-treated animals, particularly after hypoxia-ischemia (p < 0.0001). Thus, neuroprotection with dexamethasone is not related to a reduction in basal levels of cerebral protein synthesis, but is associated with an improved protein synthesis during and following hypoxia-ischemia.

Hypoxia-ischaemia model in the 7-day-old rat: possibilities and shortcomings

The Levene model in 7-day-old rats is the most often used model of hypoxia-ischaemia (HI) in immature animals. The rat central nervous system is immature at birth and corresponds neurodevelopmentally to the term human infant during the second postnatal week. The Levene model of HI differs from clinical asphyxia with respect to the unilateral distribution of brain injury and lack of multi-organ dysfunction. Furthermore, it does not allow cardiovascular monitoring or repeated blood sampling. On the other hand, the progressive nature of HI bears many similarities to birth asphyxia with regard to blood flow changes and cellular metabolic derangements. The model is well characterized, easy to carry out and the low cost allows inclusion of a sufficient number of animals for dose-response evaluation of neuroprotective agents. In addition, it provides the unique opportunity of long-term evaluation of neuropathological and functional outcome.

Hypoxia-ischemia, but not hypoxia alone, induces the expression of heme oxygenase-1 (HSP32) in newborn rat brain

Heme oxygenase (HO) is the rate-limiting enzyme in the degradation of heme to produce bile pigments and carbon monoxide. The HO-1 isozyme is induced by a variety of agents such as heat, heme, and hydrogen peroxide. Evidence suggests that the bile pigments serve as antioxidants in cells with compromised defense mechanisms. Because hypoxia-ischemia (HI) increases the level of oxygen free radicals, the induction of HO-1 expression in the brain during ischemia could modulate the response to oxidative stress. To study the possible involvement of HO-1 in neonatal hypoxia-induced ischemic tolerance, we examined the brains of newborn rat pups exposed to 8% O2 (for 2.5 to 3 hours), and the brain of chronically hypoxic rat pups with congenital cardiac defects (Wistar Kyoto; WKY/ NCr). Heme oxygenase-1 immunostaining did not change after either acute or chronic hypoxia, suggesting that HO-1 is not a good candidate for explaining hypoxia preconditioning in newborn rat brain. To study the role of HO-1 in neonatal HI, 1-week-old rats were subjected to right carotid coagulation and exposure to 8% O2/92% N2 for 2.5 hours. Whereas HO enzymatic activity was unchanged in ipsilateral cortex and subcortical regions compared with the contralateral hemisphere or control brains, immunocytochemistry and Western blot analysis showed increased HO-1 staining in ipsilateral cortex, hippocampus, and striatum at 12 to 24 hours up to 7 days after HI. Double fluorescence immunostaining showed that HO-1 was expressed mostly in ED-1 positive macrophages. Because activated brain macrophages have been associated with the release of several cytotoxic molecules, the presence of HO-1 positive brain macrophages may determine the tissue vulnerability after HI injury.

Enhanced expression of interleukin (IL)-1 and IL-6 messenger RNA and bioactive protein after hypoxia-ischemia in neonatal rats

The effect of hypoxia-ischemia (HI) on IL-1, and IL-6 bioactivity in relation to expression of IL-1 alpha, IL-1 beta, and IL-6 mRNA was studied, and the neuroprotective efficacy of IL-1 receptor antagonist (IL-1ra) was evaluated in neonatal rats. HI was induced in 7-d-old rats by unilateral carotid artery ligation and hypoxia for 70-100 min. Animals were killed at different time points up to 14 d after HI, and brains were analyzed for IL-1 and IL-6 bioactivity using bioassays and for mRNA for IL-1 alpha, IL-1 beta, and IL-6 with reverse transcription followed by a polymerase chain reaction. In separate animals, IL-1ra was administered intracerebrally before or after HI, and the extent of brain injury was assessed 14 d after HI. A transient increase of IL-1 bioactivity occurred after HI, reaching a peak at 6 h of recovery. IL-1 beta mRNA followed a similar time course but attained maximum expression at 3 h. IL-6 bioactivity and mRNA were also stimulated by HI and followed a similar time course as IL-1. Pretreatment with IL-1ra reduced HI brain damage from 54.4 +/- 9.3 to 41.4 +/- 10.0% (p < or = 0.01), and IL-1ra posttreatment increased the proportion of animals devoid of brain injury (40%) compared with vehicle-treated controls (13%) (p < or = 0.05). In conclusion, a transient activation of IL-1 and IL-6 occurred after HI, and IL-1ra reduced HI brain injury to a moderate degree.

Adaptive preservation of ATP and tolerance to hypoxia following carotid artery ligation in the immature rat

To investigate the adaptive mechanisms following carotid artery ligation in immature rats, histologic injury and tissue levels of ATP were compared after exposure to identical episodes of hypoxia induced either 3 or 24 h postligation. Histologic injury, assessed in both 9-day- and 23-day-postnatal animals after survival for 1 week, was markedly diminished in animals exposed to hypoxia 24 h postligation compared to that in animals exposed to hypoxia 3 h postligation. In 9-day-postnatal animals, ATP levels in the cerebral cortex ipsilateral to the ligation were depleted during hypoxia to 0.39 +/- 0.49 mmol/kg (mean +/- SD; N = 15) in animals exposed to hypoxia 3 h postligation but were maintained at 2.04 +/- 0.26 mmol/g (N = 18; p < 0.001) in animals exposed to hypoxia 24 h postligation. Thus, preservation of ATP may account for the diminution of cellular injury that results from delaying the onset of hypoxia from 3 to 24 h after carotid artery ligation in immature rats.

Regional alterations of ATP and heat-shock protein-72 mRNA following hypoxia-ischemia in neonatal rat brain

Neonatal rats, 7 days of age, underwent unilateral carotid artery ligation followed by exposure to hypoxia (8% O2) for 80 min. At the end of the period of hypoxia, and after recovery for 2 or 24 h, regional levels of ATP and heat-shock protein-72 (hsp72) mRNA were measured in adjacent brain sections using ATP-luminescence histochemistry and in situ hybridization, respectively. At the end of hypoxia, ATP levels were decreased in a patchy pattern within the hemisphere ipsilateral to the carotid ligation. In the parietal cortex, the reduction of ATP often occurred in columns oriented perpendicular to the cortical surface. Expression of hsp72 mRNA was not detected prior to recovery, except in the ventricular lining of the ipsilateral hemisphere. However, by 2 h of recovery, hsp72 mRNA was expressed in a diffuse pattern in the ipsilateral hemisphere, even in regions in which the distribution of ATP remained patchy. Although the regional extent of expression varied in different animals, hsp72 mRNA was expressed consistently in the subcortical white matter, which, in some animals, was the only region showing expression. In contrast to the diffuse pattern of expression at 2 h of recovery, expression of hsp72 mRNA at 24 h was highly localized in the superficial layers of cerebral cortex and the pyramidal cell layer of hippocampus. The present results demonstrate that hypoxia-ischemia causes regionally distinct alterations in ATP and hsp72 mRNA that may be related to cell injury in this model.

Changes in c-fos mRNA in the neonatal rat brain following hypoxic ischemia

We used quantitative in situ hybridization to study changes in the expression of c-fos following hypoxic-ischemia (H-I) in the neonatal rat brain. 7-day-old rat pups were subjected to a unilateral ligation of the common carotid artery followed by a 2 h 15 min hypoxic period (7.7% O2 in N2). This resulted in the expected ipsilateral infarction of cortex, lateral hippocampus, lateral-superior aspects of the striatum and the white matter of the corpus callosum. Brain damage was not seen in the contralateral hemisphere subjected only to hypoxia. c-fos mRNA levels increased in the contralateral hemisphere immediately after the hypoxia and had returned towards normal levels 2 h thereafter. In the ipsilateral hemisphere, the expression of c-fos was delayed but very marked at 2 h. Animals subjected only to hypoxia showed little or no increase in c-fos mRNA. Thus the earliest recorded increase in c-fos after hypoxic ischemia, which occurred on the non-ischemic, contralateral side, may represent a generalized response to a more localized insult.

Localization of c-fos, c-jun, and hsp70 mRNA expression in brain after neonatal hypoxia-ischemia

The sites of expression of early response mRNAs were determined in the brains of 7-day-old rat pups exposed to unilateral carotid artery ligation followed by 3 h of hypoxia. Pups were sacrificed after recovery periods ranging from 10 min to 24 h. In agreement with our previous northern blot analysis, in situ hybridization of coronal brain sections to probes for c-fos, c-jun, and heat-inducible hsp70 revealed a marked induction and subsequent disappearance of all three mRNAs during this time period. We observed co-localization of the 2 immediate early gene (IEG) mRNAs, c-fos and c-jun, which encode proteins that act in combination to regulate subsequent gene expression. These mRNAs were expressed in all regions known to be vulnerable to permanent injury in this model, such as the cortex, hippocampus, and striatum, as well as in other regions that are spared from permanent damage, such as contralateral cortex and lateral ventricular neuroepithelium. The temporal and regional co-localization of c-fos and c-jun suggests that the transcriptional regulatory activity of their protein products could play a role in plasticity associated with death or recovery from injury in the immature brain. Hsp70 mRNA expression was induced in nearly all of the animals that were positive for IEG mRNAs. Although the most frequent site of expression for all three mRNAs was the ipsilateral cerebral cortex, hsp70 expression was restricted to the ipsilateral hemisphere and absent from a number of structures that were positive for c-fos and c-jun. In addition, the patterns of expression of hsp70 within specific structures frequently differed from those of the IEGs, implying that although both cellular early response systems are activated in this model, their specific functions are carried out within different microenvironments.

Neuro-pathophysio-biochemical profiles of neonatal asphyxia

Neurological and neuroelectrophysio-biochemical profiles were evaluated in newborn lambs exposed to severe temporary asphyxia. Isoelectric EEG, marked disturbances of phosphorus magnetic resonance spectrum (31P-MRS), and significant brain intracellular acidosis (pHi) were noted during asphyxia. Following resuscitation, the presence of early postasphyxic blood-brain-barrier (BBB) opening was associated with a marked transient increase in intracranial pressure (ICP), a 50% neonatal mortality and a 67% incidence of severe asphyxic encephalopathy. In contrast, those lambs exposed to the same magnitude of asphyxia, but without early BBB opening experienced neither death nor severe neurological deficits. Further, these lambs showed a rapid progressive normalization of the 31P-MRS and pHi, despite, the lack of EEG recovery in the first hour following resuscitation. Thus, the present study depicts that the early postasphyxic BBB disruption following temporary neonatal asphyxia is associated with poor prognosis.

Dose-related effects of cycloheximide on delayed neuronal death in the gerbil hippocampus after bilateral transitory forebrain ischemia

Degeneration of dendrites followed by punctate chromatin condensation in the CA1 area of the hippocampus is a characteristic of delayed neuronal death following bilateral forebrain ischemia. The effects of the protein synthesis inhibitor cycloheximide on delayed neuronal death following 20 min of bilateral forebrain ischemia were examined in the gerbil hippocampus at the 4th day of reperfusion. Low doses of cycloheximide beginning 10 min after ischemia (1.0 microgram/g body weight in saline followed by 1.0 microgram/g every 24 h) reduced the number of dying cells in the CA1 area, whereas high doses (2.0 micrograms/g, followed by 1.0 microgram/g every 12 h) increased the number of dying cells. No effects were seen when a single dose of cycloheximide was injected 1 h before ischemia. These results indicate that the effects of cycloheximide are dose-dependent, low doses reduce, high doses increase cell death. These findings also indirectly suggest that protein synthesis may play a role in the extent of delayed neuronal death. Some involved proteins could be heat shock proteins, which are induced after ischemia and had been correlated with increased resistance to injury. However, changes of heat shock immunoreactivity in the postischemic hippocampus were not seen in the present study following cycloheximide injection.

Immediate early gene induction after neonatal hypoxia-ischemia

Immediate early gene (IEG) products, such as FOS and JUN, may partially mediate the long-term transcriptional response of CNS cells to specific changes in their environment. To determine whether IEG products might be involved in the immature brain's response to hypoxia-ischemia (H-I), 7-day-old rat pups were subjected to unilateral common carotid artery ligation followed by 3 h of hypoxia (8% O2/92% N2) at 37 degrees C, which results in pathological changes only in specific regions of the hemisphere ipsilateral to ligation. Time course experiments were performed, in which animals were sacrificed between 1 and 24 h after H-I. RNAs from several brain regions were analyzed by Northern blot hybridization for their relative concentrations of nine IEG mRNAs (c-fos, c-jun, junB, TIS 1 (nur77), TIS7, TIS8 (zif268), TIS10, TIS11, and TIS21). Induction of all IEGs, except TIS7 and TIS10, was observed in ipsilateral forebrain, and, less frequently, in contralateral forebrain, at 1, 2, and 3 h post-hypoxia. In some animals, lower levels of expression were also detected at 4, 18 and 24 h. With minor exceptions, co-induction of all seven IEGs was observed in a given RNA sample. Induction of two other mRNAs, representing the heat shock and astrocytic responses, were also observed. Hsp70 mRNA levels were increased only in the brains of animals exhibiting IEG induction. However, hsp70 induction was confined to the ipsilateral forebrain, implying a more direct relationship between its expression and permanent morphological damage. GFAP mRNA induction occurred predominantly in ipsilateral forebrain samples at 18 and 24 h post-hypoxia. Levels of B-actin and ubiquitin mRNAs were relatively constant in the same RNA samples. In control experiments c-fos mRNA induction was not detected after sham ligation with hypoxia, ligation with sham hypoxia, or hypoxia alone. These results suggest that the immature brain is highly responsive to H-I at the level of gene expression, involving at least three different rapid response systems.

Regional expression of c-fos and heat shock protein-70 mRNA following hypoxia-ischemia in immature rat brain

Cerebral ischemia induces the expression of a number of proteins that may have an important influence on cellular injury. The purpose of this study was to compare the regional effects of hypoxia-ischemia on the expression of the proto-oncogene, c-fos, and the heat shock protein-70 (HSP-70) gene in developing brain. Unilateral hypoxia-ischemia was produced in the brain of immature rats (7, 15, and 23 days after birth) using a combination of carotid artery ligation and systemic hypoxia (8% O2). After recovery for 2 and 24 h, the regional expression of c-fos and HSP-70 mRNA was determined using in situ hybridization. Littermates were permitted to recover for 1 week for assessment of histologic injury. Hypoxia-ischemia increased the expression of both c-fos and HSP-70 mRNA, but the topography of expression varied with the age of the animal as well as the mRNA species. In the 7-day-old group, expression of c-fos at 2 h increased in multiple regions of the ipsilateral hemisphere in nearly one-half of the animals, while HSP-70 mRNA was not expressed until 24 h and, then, predominantly in the hippocampus. In 15- and 23-day-old rats, expression of c-fos was increased at 2 h in the entorhinal cortex and in the dendritic field of the upper blade of the hippocampal dentate gyrus, while HSP-70 mRNA was prominently expressed in neocortex and the cell layers of the hippocampus. Interestingly, the strong expression of HSP-70 mRNA in dentate granule cells did not occur in the innermost layer of cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Heat Shock Proteins in Hypoxic-Ischemic Brain Injury: A Perspective

There is much to suggest that the induction of heat shock protein synthesis is an important response to injury and stress in the brain. The role of heat shock proteins in neurological disease has been approached from two points-of-view. First, the induction and synthesis of specific proteins after brain cell injury provide a window through which insight on the regulation of gene expression in pathological tissue can be obtained. These studies have broad implications for understanding pathophysiological mechanisms of disease. Second, putative cell protective effects of heat shock proteins in brain tissue provide insight into biochemical mechanisms of selective neuronal vulnerability. These studies have extremely important clinical implications since cell sensitivity to injury can seemingly be modified. The role of heat shock proteins in hypoxic-ischemic brain injury is discussed forthwith.

Intra- and extracellular changes of amino acids in the cerebral cortex of the neonatal rat during hypoxic-ischemia

Excitatory amino acids (EAAs) have been implicated to play a part in the development of hypoxic-ischemic brain injury in the neonate. The aim of the present study was to follow changes of intra- and extracellular (microdialysis) amino acids in the cerebral cortex in a model where cortical hypoxic-ischemic damage is produced consistently. Hypoxic-ischemia (unilateral ligation of the carotid artery + 2 h of exposure to 7.8% oxygen) caused a depletion of tissue ATP, phosphocreatine and glucose with a concomittant accumulation of AMP and lactic acid in cortical tissue. These changes were accompanied by a decrease of tissue aspartate and glutamine whereas the contents of gamma-aminobutyric acid (GABA), phenylalanine, leucine, isoleucine, valine and alanine increased. In the extracellular fluid GABA, glutamate, aspartate, taurine, glycine and alanine all increased multi-fold during hypoxic-ischemia. Aspartate and glutamate returned to near initial levels 2 h after the end of the insult, whereas the elevation of glycine persisted during recovery. In conclusion, the high extracellular levels of EAAs and glycine may exert injurious effects during and after hypoxic-ischemia.

Heat shock protein hsp72 induction in cortical and striatal astrocytes and neurons following infarction

Transient global and transient focal ischemia induced the 72 kDa heat shock protein (hsp72) in neurons in cortex, striatum, and other regions known to be injured during transient ischemia. A novel finding was the induction of hsp72 in islands (cylinders in three dimensions) of cells composed of astrocytes around the perimeter and neurons in the interior. Since histology showed pale staining in these regions, it is proposed that these islands represent areas of focal infarction in the distribution of small cortical and lenticulostriate arteries. Although the factors responsible for hsp72 induction during ischemia and infarction are unknown, these results suggest differences in mechanisms of hsp72 induction in astrocytes compared to neurons.

Synthesis of the major inducible heat shock protein in rat hippocampus after neonatal hypoxia-ischemia

Rats aged 7 days were exposed to 3.5 h of cerebral hypoxia-ischemia produced by unilateral common carotid artery ligation combined with hypoxia (8% oxygen). The major inducible heat-shock protein, HSP-68, was synthesized in ipsilateral but not contralateral (control) hippocampus during early recovery (1 and 3 h). HSP-68 synthesis was not detected during longer recovery periods. The presence of HSP-68 was confirmed by Western blotting and immunostaining with a polyclonal antibody to HSP-68.

Asymmetrical perfusion fixation in a rodent model of perinatal hypoxia-ischemia may lead to artifactual morphologic asymmetries

We have observed asymmetries in perfusion between the cerebral hemispheres in immature rats previously subjected to carotid ligation in a model of perinatal hypoxia-ischemia. These asymmetries are associated with marked differences in the number of neurons stained positive by immunoperoxidase protocols for cholinergic neurons utilizing a monoclonal antibody to choline acetyltransferase. These differences are likely to be spurious and due to the asymmetry of perfusion, because fewer stained neurons appear on the unligated side of control animals, in the absence of gliosis or neuron loss. We recommend that quantitative morphologic studies in this model be performed on immersion-fixed specimens.

Cerebral hypoxia-ischemia in immature rats: methodological considerations

We used a model of perinatal hypoxic/ischemic brain damage which combines unilateral common carotid artery ligation and hypoxia (8% O2). Protein synthesis inhibition and cell loss were found in the ipsilateral forebrain of 11-day-old rats when hypoxia was initiated 4 h but not 24 h after carotid ligation. [14C]Iodoantipyrine uptake studies suggest that compensating vascular changes which protect the ipsilateral forebrain occur within 24 h of carotid ligation.