Glucocorticoid prevention of neonatal hypoxic-ischemic damage: role of hyperglycemia and antioxidant enzymes

Bidirectional Crosstalk Between Hypoxia Inducible Factors and Glucocorticoid Signalling in Health and Disease

Glucocorticoid-induced (GC) and hypoxia-induced transcriptional responses play an important role in tissue homeostasis and in the regulation of cellular responses to stress and inflammation. Evidence exists that there is an important crosstalk between both GC and hypoxia effects. Hypoxia is a pathophysiological condition to which cells respond quickly in order to prevent metabolic shutdown and death. The hypoxia inducible factors (HIFs) are the master regulators of oxygen homeostasis and are responsible for the ability of cells to cope with low oxygen levels. Maladaptive responses of HIFs contribute to a variety of pathological conditions including acute mountain sickness (AMS), inflammation and neonatal hypoxia-induced brain injury. Synthetic GCs which are analogous to the naturally occurring steroid hormones (cortisol in humans, corticosterone in rodents), have been used for decades as anti-inflammatory drugs for treating pathological conditions which are linked to hypoxia (i.e. asthma, ischemic injury). In this review, we investigate the crosstalk between the glucocorticoid receptor (GR), and HIFs. We discuss possible mechanisms by which GR and HIF influence one another, in vitro and in vivo, and the therapeutic effects of GCs on HIF-mediated diseases.

Experimental neonatal hypoxia ischemia causes long lasting changes of oxidative stress parameters in the hippocampus and the spleen

Neonatal hypoxia ischemia (HI) is the main cause of mortality and morbidity in newborns. The mechanisms involved in its progression start immediately and persist for several days. Oxidative stress and inflammation are determinant factors of the severity of the final lesion. The spleen plays a major part in the inflammatory response to HI. This study assessed the temporal progression of HI-induced alterations in oxidative stress parameters in the hippocampus, the most affected brain structure, and in the spleen. HI was induced in Wistar rat pups in post-natal day 7. Production of reactive oxygen species (ROS), and the activity of the anti oxidant enzyme superoxide dismutase and catalase were assessed 24 h, 96 h and 38 days post-HI. Interestingly, both structures showed a similar pattern, with few alterations in the production of ROS species up to 96 h often combined with an increased activity of the anti oxidant enzymes. However, 38 days after the injury, ROS were at the highest in both structures, coupled with a decrease in the activity of the enzymes. Altogether, present results suggest that HI causes long lasting alterations in the hippocampus as well as in the spleen, suggesting a possible target for delayed treatments for HI.

Corticosteroids and perinatal hypoxic-ischemic brain injury

Perinatal hypoxic-ischemic (HI) brain injury is the major cause of neonatal mortality and severe long-term neurological morbidity. Yet, the effective therapeutic interventions currently available are extremely limited. Corticosteroids act on both mineralocorticoid (MR) and glucocorticoid (GR) receptors and modulate inflammation and apoptosis in the brain. Neuroinflammatory response to acute cerebral HI is a major contributor to the pathophysiology of perinatal brain injury. Here, we give an overview of current knowledge of corticosteroid-mediated modulations of inflammation and apoptosis in the neonatal brain, focusing on key regulatory cells of the innate and adaptive immune response. In addition, we provide new insights into targets of MR and GR in potential therapeutic strategies that could be beneficial for the treatment of infants with HI brain injury.

Antenatal dexamethasone before asphyxia promotes cystic neural injury in preterm fetal sheep by inducing hyperglycemia

Antenatal glucocorticoid therapy significantly improves the short-term systemic outcomes of prematurely born infants, but there is limited information available on their impact on neurodevelopmental outcomes in at-risk preterm babies exposed to perinatal asphyxia. Preterm fetal sheep (0.7 of gestation) were exposed to a maternal injection of 12 mg dexamethasone or saline followed 4 h later by asphyxia induced by 25 min of complete umbilical cord occlusion. In a subsequent study, fetuses received titrated glucose infusions followed 4 h later by asphyxia to examine the hypothesis that hyperglycemia mediated the effects of dexamethasone. Post-mortems were performed 7 days after asphyxia for cerebral histology. Maternal dexamethasone before asphyxia was associated with severe, cystic brain injury compared to diffuse injury after saline injection, with increased numbers of seizures, worse recovery of brain activity, and increased arterial glucose levels before, during, and after asphyxia. Glucose infusions before asphyxia replicated these adverse outcomes, with a strong correlation between greater increases in glucose before asphyxia and greater neural injury. These findings strongly suggest that dexamethasone exposure and hyperglycemia can transform diffuse injury into cystic brain injury after asphyxia in preterm fetal sheep.

Dexamethasone-induced neuroprotection in hypoxic-ischemic brain injury in newborn rats is partly mediated via Akt activation

Prior treatment with dexamethasone (Dex) provides neuroprotection against hypoxia ischemia (HI) in newborn rats. Recent studies have shown that the phosphatidylinositol-3-kinase/Akt (PI3K/Akt) pathway plays an important role in the neuroprotection. The objective of this study is to evaluate the role of the PI3K/Akt pathway in the Dex-induced neuroprotection against subsequent HI brain injury. Seven-day-old rat pups had the right carotid artery permanently ligated followed by 160min of hypoxia (8% oxygen). Rat pups received i.p. injection of either saline or Dex (0.25mg/kg) at 24 and 4h before HI exposure. To quantify the effects of a PI3K/Akt inhibitor, wortmannin (1μl of 1μg/μl) or vehicle was injected intracerebroventricularly in the right hemisphere on postnatal day 6 at 30min prior to the first dose of Dex or saline treatment. Dex pretreatment significantly reduced the brain injury following HI which was quantified by the decrease in cleaved caspase-3 protein as well as cleaved caspase-3 and TUNEL positive cells at 24h and percent loss of ipsilateral hemisphere weight at 22d after HI, while wortmannin partially reversed these effects. We conclude that Dex provides robust neuroprotection against subsequent HI in newborn rats in part via activation of PI3/Akt pathway.

Dexamethasone alleviates tumor-associated brain damage and angiogenesis

Children and adults with the most aggressive form of brain cancer, malignant gliomas or glioblastoma, often develop cerebral edema as a life-threatening complication. This complication is routinely treated with dexamethasone (DEXA), a steroidal anti-inflammatory drug with pleiotropic action profile. Here we show that dexamethasone reduces murine and rodent glioma tumor growth in a concentration-dependent manner. Low concentrations of DEXA are already capable of inhibiting glioma cell proliferation and at higher levels induce cell death. Further, the expression of the glutamate antiporter xCT (system X_c⁻; SLC7a11) and VEGFA is up-regulated after DEXA treatment indicating early cellular stress responses. However, in human gliomas DEXA exerts differential cytotoxic effects, with some human glioma cells (U251, T98G) resistant to DEXA, a finding corroborated by clinical data of dexamethasone non-responders. Moreover, DEXA-resistant gliomas did not show any xCT alterations, indicating that these gene expressions are associated with DEXA-induced cellular stress. Hence, siRNA-mediated xCT knockdown in glioma cells increased the susceptibility to DEXA. Interestingly, cell viability of primary human astrocytes and primary rodent neurons is not affected by DEXA. We further tested the pharmacological effects of DEXA on brain tissue and showed that DEXA reduces tumor-induced disturbances of the microenvironment such as neuronal cell death and tumor-induced angiogenesis. In conclusion, we demonstrate that DEXA inhibits glioma cell growth in a concentration and species-dependent manner. Further, DEXA executes neuroprotective effects in brains and reduces tumor-induced angiogenesis. Thus, our investigations reveal that DEXA acts pleiotropically and impacts tumor growth, tumor vasculature and tumor-associated brain damage.

Up-regulation of stomatin expression by hypoxia and glucocorticoid stabilizes membrane-associated actin in alveolar epithelial cells

Stomatin is an important lipid raft-associated protein which interacts with membrane proteins and plays a role in the membrane organization. However, it is unknown whether it is involved in the response to hypoxia and glucocorticoid (GC) in alveolar epithelial cells (AEC). In this study we found that hypoxia and dexamethasone (dex), a synthetic GC not only up-regulated the expression of stomatin alone, but also imposed additive effect on the expression of stomatin in A549 cells, primary AEC and lung of rats. Then we investigated whether hypoxia and dex transcriptionally up-regulated the expression of stomatin by reporter gene assay, and found that dex, but not hypoxia could increase the activity of a stomatin promoter-driven reporter gene. Further deletion and mutational studies demonstrated that a GC response element (GRE) within the promoter region mainly contributed to the induction of stomatin by dex. Moreover, we found that hypoxia exposure did not affect membrane-associated actin, but decreased actin in cytoplasm in A549 cells. Inhibiting stomatin expression by stomatin siRNA significantly decreased dense of peripheral actin ring in hypoxia or dex treated A549 cells. Taken all together, these data indicated that dex and/or hypoxia significantly up-regulated the expression of stomatin in vivo and in vitro, which could stabilize membrane-associated actin in AEC. We suppose that the up-regulation of stomatin by hypoxia and dex may enhance the barrier function of alveolar epithelia and mediate the adaptive role of GC to hypoxia.

Dexamethasone administration to the neonatal rat results in neurological dysfunction at the juvenile stage even at low doses

Dexamethasone (DEX), a synthetic glucocorticoid, has been widely used to prevent the development of a variety of poor health conditions in premature infants including chronic lung disease, inflammation, circulatory failure, and shock. Although there are some reports of neurologic complications related to DEX exposure, its full effects on the premature brain have not been examined in detail. To investigate the effects of DEX on neural development, we first administered low doses (0.2 mg/kg bodyweight or less) of the glucocorticoid to neonatal rats on a daily basis during the first postnatal week and examined subsequent behavioral alterations at the juvenile stage. DEX-treated rats exhibited not only a significant reduction in both somatic and brain weights but also learning disabilities as revealed in the shuttle avoidance test. The hippocampi of DEX-treated rats displayed a high apoptotic and a low mitotic cell density compared to control rats on day 7 after birth. In a subsequent experiment, neural stem/progenitor cells were cultured in the presence of DEX for 6 days. The glucocorticoid inhibited cell growth without an increase in cell death. These results suggest that administration of DEX to premature infants induces neurological dysfunction via inhibition of the proliferation of neural stem/progenitor cells.

Neonatal dexamethasone treatment exacerbates hypoxic-ischemic brain injury

Background

The synthetic glucocorticoid dexamethasone (DEX) is commonly used to prevent chronic lung disease in prematurely born infants. Treatment regimens usually consist of high doses of DEX for several weeks, notably during a critical period of brain development. Therefore, there is some concern about adverse effects of this clinical practice on fetal brain development. In this study, using a clinically relevant rat model, we examined the impact of neonatal DEX treatment on subsequent brain injury due to an episode of cerebral hypoxia-ischemia (HI).

Results

We found that a 3-day tapering course (0.5, 0.3 and 0.1 mg/kg) of DEX treatment in rat pups on postnatal days 1–3 (P1-3) exacerbated HI-induced brain injury on P7 by a glucocorticoid receptor-mediated mechanism. The aggravating effect of neonatal DEX treatment on HI-induced brain injury was correlated with decreased glutamate transporter-1 (GLT-1)-mediated glutamate reuptake. The expression levels of mRNA and protein of GLT-1 were significantly reduced by neonatal DEX treatment. We also found that the administration of β-lactam antibiotic ceftriaxone increased GLT-1 protein expression and significantly reduced HI-induced brain injury in neonatal DEX-treated rats.

Conclusions

These results suggest that early DEX exposure may lead the neonatal brain to be more vulnerable to subsequent HI injury, which can be ameliorated by administrating ceftriaxone.

Role of the pituitary–adrenal axis in granulocyte-colony stimulating factor-induced neuroprotection against hypoxia–ischemia in neonatal rats

Several reports indicate that the activity of the hypothalamic–pituitary–adrenal axis (HPA) is increased after a brain insult and that its down-regulation can improve detrimental outcomes associated with ischemic brain injuries.Granulocyte-colony stimulating factor (G-CSF) is a neuroprotective drug shown in the naïve rat to regulate hormones of the HPA axis. In this study we investigate whether G-CSF confers its neuroprotective properties by influencing the HPA response after neonatal hypoxia–ischemia (HI). Following the Rice–Vannucci model, seven day old rats (P7)were subjected to unilateral carotid ligation followed by 2.5 h of hypoxia. To test our hypothesis,metyrapone was administered to inhibit the release of rodent specific glucocorticoid, corticosterone, at the adrenal level. Dexamethasone, a synthetic glucocorticoid, was administered to agonize the effects of corticosterone.Our results show that both G-CSF and metyrapone significantly reduced infarct volume while dexamethasone treatment did not reduce infarct size even when combined with G-CSF. The protective effects of G-CSF do not include blood brain barrier preservation as suggested by the brain edema results. G-CSF did not affect the pituitary released adrenocorticotropic hormone (ACTH) levels in the blood plasma at 4 h, but suppressed the increase of corticosterone in the blood. The administration of G-CSF and metyrapone increased weight gain, and significantly reduced the Bax/Bcl-2 ratio in the brain while dexamethasone reversed the effects of G-CSF. The combination of G-CSF and metyrapone significantly decreased caspase-3 protein levels in the brain, and the effect was antagonized by dexamethasone.We report that G-CSF is neuroprotective in neonatal HI by reducing infarct volume, by suppressing the HI-induced increase of the Bax/Bcl-2 ratio, and by decreasing corticosterone in the blood. Metyrapone was able to confer similar neuroprotection as G-CSF while dexamethasone reversed the effects of G-CSF. In conclusion, we show that decreasing HPA axis activity is neuroprotective after neonatal HI, which can be conferred by administering G-CSF.

Upregulations of glucocorticoid-induced leucine zipper by hypoxia and glucocorticoid inhibit proinflammatory cytokines under hypoxic conditions in macrophages

Hypoxia and inflammation often develop concurrently in numerous diseases, and the influence of hypoxia on natural evolution of inflammatory responses is widely accepted. Glucocorticoid-induced leucine zipper (GILZ) is thought to be an important mediator of anti-inflammatory and immune-suppressive actions of glucocorticoid (GC). However, whether GILZ is involved in hypoxic response is still unclear. In this study, we investigated the effects of hypoxic exposure and/or the administration of dexamethasone (Dex), a synthetic GC on GILZ expression both in vitro and in vivo, and further explored the relationship between GILZ and proinflammatory cytokines IL-1β, IL-6, and TNF-α under normoxic and hypoxic conditions. We found that hypoxia not only remarkably upregulated the expression of GILZ, but also significantly enhanced Dex-induced expression of GILZ in macrophages and the spleen of rats. ERK activity is found involved in the upregulation of GILZ induced by hypoxia. Inhibiting the expression of GILZ in RAW264.7 cells using specific GILZ small interfering RNA led to a significant increase in mRNA production and protein secretion of IL-1β and IL-6 in hypoxia and abrogated the inhibitory effect of Dex on expression of IL-1β and IL-6 in hypoxia. We also found that adrenal hormones played pivotal roles in upregulation of GILZ expression in vivo. Altogether, data presented in this study suggest that GILZ has an important role not only in adjusting adaptive responses to hypoxia by negatively regulating the activation of macrophages and the expression of proinflammatory cytokines, but also in mediating the anti-inflammatory action of GC under hypoxic conditions.

Dexamethasone pre-treatment protects brain against hypoxic-ischemic injury partially through up-regulation of vascular endothelial growth factor A in neonatal rats

Dexamethasone (Dex) provides neuroprotection against subsequent hypoxia ischemia (HI) in newborn rats, but the mechanism of this neuroprotection is not well understood. It is known that vascular endothelial growth factor A (VEGF) has neuroprotective effects. The objective of this study was to evaluate the role of the VEGF signaling pathway in the Dex-induced neuroprotection in newborn rats. Seven-day-old rat pups had the right carotid artery permanently ligated followed by 140 or 160 min of hypoxia (8% oxygen). Rat pups received two i.p. injections of either saline or Dex (0.25 mg/kg) at 24 and 4 h before HI exposure. To quantify the effects of a glucocorticoid receptor (GR) blocker, on postnatal day (PD) 6 and 15 min prior to Dex treatment rat pups received s.c. vehicle or RU486 (GR blocker, 60 mg/kg). After 24 h at PD 7, all rat pups had HI as described earlier. To quantify the effects of a VEGFR 2 blocker, at 24 h after Dex/Veh treatment (PD7), SU5416, a VEGFR 2 inhibitor or vehicle was injected intracerebroventricularly in the right hemisphere at 30 min before and 2 h after HI. Dex pre-treatment reduced brain injury and enhanced the HI-induced brain VEGF protein while a GR blocker inhibited these effects. Treatment with VEGFR 2 blocker decreased Dex-induced neuroprotection also. Dex pre-treatment enhanced the HI-induced increase in mRNA expression of VEGF splice variants and decreased the HI-induced reduction of Akt phosphorylation. Additionally, it also decreased HI-induced increase of caspase-3 activity and DNA fragments in neonatal rat brain. We conclude that Dex provides robust neuroprotection against subsequent HI in newborn rats via GR likely with the partial involvement of VEGF signaling pathway.

Dexamethasone induces neurodegeneration but also up-regulates vascular endothelial growth factor A in neonatal rat brains

The use of dexamethasone (Dex) in premature infants to prevent and/or treat bronchopulmonary dysplasia can adversely affect early neurodevelopment and probably result in loss of cerebral volume. Vascular endothelial growth factor A (VEGF), specifically VEGF(164) isoform has neurotrophic, neuroprotective and neurogenesis enhancing effects. Previous studies have demonstrated that Dex usually down-regulates VEGF. In the present study we investigated the effect of Dex on brain growth and VEGF in the neonatal rat brain. The pups in each litter were divided into the vehicle (n=84) or Dex-treated (n=98) groups. Rat pups in the Dex group received one of three different regimens of i.p. Dex which included tapering doses on postnatal days 3-6 (0.5, 0.25, 0.125 and 0.06 mg/kg, respectively), or repeated doses of 0.5 or 1 mg/kg/day on postnatal days 4-6 or single dose of 0.031, 0.06, 0.125, 0.25 or 0.5 mg/kg on postnatal day 6. The total VEGF protein and mRNA expression of the three main VEGF splice variants (VEGF(120), VEGF(164), and VEGF(188)) were measured in the rat pup brain using enzyme-linked immunosorbent assay and real-time reverse transcription polymerase chain reaction, respectively. Treatment with Dex significantly decreased the gain of body and brain weight. The tapering and repeated doses of Dex significantly increased caspase-3 activity, VEGF protein and the expression of mRNA of VEGF(164) and VEGF(188) splice variants but the single dose did not. We conclude that Dex is neurodegenerative in the developing brain but also increases VEGF which may play a neurotrophic and neuroprotective role.

Bioenergetics of cerebral ischemia: a cellular perspective

In cerebral ischemia survival of neurons, astrocytes, oligodendrocytes and endothelial cells is threatened during energy deprivation and/or following re-supply of oxygen and glucose. After a brief summary of characteristics of different cells types, emphasizing the dependence of all on oxidative metabolism, the bioenergetics of focal and global ischemia is discussed, distinguishing between events during energy deprivation and subsequent recovery attempt after re-circulation. Gray and white matter ischemia are described separately, and distinctions are made between mature and immature brains. Next comes a description of bioenergetics in individual cell types in culture during oxygen/glucose deprivation or exposure to metabolic inhibitors and following re-establishment of normal aerated conditions. Due to their expression of NMDA and non-NMDA receptors neurons and oligodendrocytes are exquisitely sensitive to excitotoxicity by glutamate, which reaches high extracellular concentrations in ischemic brain for several reasons, including failing astrocytic uptake. Excitotoxicity kills brain cells by energetic exhaustion (due to Na(+) extrusion after channel-mediated entry) combined with mitochondrial Ca(2+)-mediated injury and formation of reactive oxygen species. Many (but not all) astrocytes survive energy deprivation for extended periods, but after return to aerated conditions they are vulnerable to mitochondrial damage by cytoplasmic/mitochondrial Ca(2+) overload and to NAD(+) deficiency. Ca(2+) overload is established by reversal of Na(+)/Ca(2+) exchangers following Na(+) accumulation during Na(+)-K(+)-Cl(-) cotransporter stimulation or pH regulation, compensating for excessive acid production. NAD(+) deficiency inhibits glycolysis and eventually oxidative metabolism, secondary to poly(ADP-ribose)polymerase (PARP) activity following DNA damage. Hyperglycemia can be beneficial for neurons but increases astrocytic death due to enhanced acidosis.

Glucose management during and after intensive delivery room resuscitation

Hypoxic-ischemic encephalopathy remains a major cause of morbidity and mortality in preterm and full-term infants. Experimental data from animal studies suggest that interventions that improve survival of injured neurons and prevent delayed neuronal loss may decrease hypoxic ischemic brain injury. Considerable attention has focused on optimizing management of newborns in the period immediately after resuscitation from perinatal asphyxia to minimize delayed neuronal death. The evidence regarding the role of glucose in modifying post-asphyxia brain injury and resuscitation was reviewed to better define optimal glucose management after perinatal asphyxia and resuscitation.

The role of glucose in brain injury following the combination of lipopolysaccharide or lipoteichoic acid and hypoxia-ischemia in neonatal rats

We have previously shown that lipopolysaccharide (LPS) sensitizes the immature rat brain to subsequent hypoxic-ischemic (HI) injury; however, the underlying mechanisms remain unclear. In this study, we examined the role of glucose in the sensitizing effects of LPS and lipoteichoic acid (LTA) in combination with HI in 7-day-old rats. LPS/HI resulted in hypoglycemia which lasted 24 h and lactate levels were increased from 6 to 10 h after LPS administration. LPS/HI induced severe brain injury, which persisted 2 weeks after LPS/HI. Administration of glucose to LPS-treated animals with HI reduced brain injury in the cerebral cortex and hippocampus, while striatal damage remained. LTA/HI did not affect blood glucose, lactate or brain injury. In conclusion, enhanced blood glucose levels during HI after LPS administration conferred protection in some brain regions but not in the striatum, suggesting that alterations in glucose can only partly explain the sensitizing effect of LPS.

Direct inner ear infusion of dexamethasone attenuates noise-induced trauma in guinea pig

The protective effect of dexamethasone (DEX) against noise-induced trauma, as reflected in hair cell destruction and elevation in auditory brainstem response (ABR) sensitivity, was assessed in guinea pigs. The animals were administered DEX (1, 10, 100, and 1000 ng/ml) or artificial perilymph (AP) via a mini-osmotic pump directly into scala tympani and, on the fourth day after pump implantation, exposed to 120 dB SPL octave band noise, centered at 4 kHz, for 24 h. Animals receiving DEX demonstrated a dose-dependent reduction in noise-induced outer hair cell loss (significant at 1, 10 and 100 ng/ml DEX animals compared to AP control animals) and a similar attenuation of the noise-induced ABR threshold shifts, observed 7 days following exposure (significant at 100 ng/ml DEX animals compared to AP control animals). These physiological and morphological results indicate that direct infusion of DEX into the perilymphatic space has protective effects against noise-induced trauma in the guinea pig cochlea.

Circulating adrenocorticotropic hormone (ACTH) and cortisol concentrations in normal, appropriate-for-gestational-age newborns versus those with sepsis and respiratory distress: Cortisol response to low-dose and standard-dose ACTH tests

In this crossover study, we compared the peak responses of cortisol to low-dose (1 microg/1.73 m(2)) and standard-dose (250 microg/1.73 m(2)) adrenocorticotropic hormone (ACTH) stimulation tests in 90 full-term newborns (37 to 42 weeks gestational age, birthweight > 2,500 g, aged 4 to 7 days): 30 with sepsis syndrome, 30 with respiratory distress (RD) and 30 normal infants. Basal cortisol and ACTH were measured in a fasting venous sample. Serum cortisol concentrations were measured 30 minutes after low-dose ACTH and 60 minutes after standard-dose ACTH by radioimmunoassay (RIA). The mean basal circulating cortisol concentration and peak cortisol responses to low-dose and standard-dose ACTH tests were higher in stressed infants with sepsis and RD compared to normal. Basal but not ACTH-stimulated cortisol concentrations were significantly higher in newborns with sepsis versus those with RD. Circulating cortisol concentrations after the low-dose ACTH test were correlated significantly with those obtained after the standard-dose ACTH test (r = 0.814, P <.001). Clinical subgrouping of septic newborns showed that those with leukopenia (5/10 died) and with meningitis (6/12 died) had significantly lower basal and peak cortisol responses to the low-dose ACTH test (but not the standard-dose ACTH test) versus those with leukocytosis (3/20 died) and without meningitis (2/18 died), respectively. In addition, septic newborns who died had significantly lower circulating cortisol concentrations and lower cortisol responses to the low-dose ACTH test (but not the standard-dose test) versus those who survived the stress. On an individual basis, only 2 septic newborns (both died) had low basal cortisol levels (<5 microg/dL) and cortisol responses less than 15 microg/dL after the low-dose ACTH test. Four more septic newborns had basal cortisol above 5 microg/dl but cortisol responses below 20 microg/dL after the low-dose ACTH test. These 4 newborns (4/30) with inadequate adrenocortical response to low-dose ACTH during sepsis had high mortality (3/4 died) and represented a subgroup of septic newborns that should be diagnosed, using a low-dose ACTH test, and treated early. These data suggest that the low-dose ACTH test may be more disciminatory than the standard-dose test among babies under stress. Increasing the cut-point level of basal cortisol in stressed infants to the lowest level of cortisol response to low-dose ACTH in normal newborns, followed by the use of a low-dose ACTH test, appears to select some newborns who need and may improve on corticosteroid therapy. Further studies are required to investigate whether supplementation with stress doses of hydrocortisone may improve the outcome in these patients.

Effects of antenatal steroids on ischemic brain injury in near-term ovine fetuses

BACKGROUND

Hypoxia/ischemia in utero can result in brain damage to the fetus and newborn. Antenatal steroids are a routine part of the management of women who develop premature labor. Pretreatment of young postnatal rats with dexamethasone before hypoxic/ischemic insults has been reported to attenuate brain injury. However, the effects of antenatal steroids on ischemic brain injury in fetuses have not been investigated.

OBJECTIVE

We examined the effects of maternally administered antenatal corticosteroids on ischemic brain injury in near-term ovine fetuses.

METHODS

Chronically instrumented fetuses at 122 days of gestation were studied 12 h after the last of four 4 mg dexamethasone, or placebo injections were given over 48 h to the ewes. Groups were dexamethasone/ischemic, placebo/ischemic and sham-treated control. Fetuses were exposed to 30 min of carotid occlusion (ischemia) or no occlusion (control) and 72 h of reperfusion. Whole brain coronal sections stained with Luxol fast blue-hematoxylin-eosin were scored for white matter and cerebral cortical lesions. Both areas received pathological scores of 0 to 5 reflecting the degree of injury (0=0%, 1=1-10%, 2=11-50%, 3=51-90%, 4=91-99% and 5=100%). Bilateral carotid blood flow also was measured before, during and after brain ischemia in the dexamethasone/ischemic and placebo/ischemic groups.

RESULTS

White matter (WM) and cerebral cortical scores did not differ between the dexamethasone/ischemic and placebo/ischemic (WM: 3.0+/-1.9 and 2.9+/-1.7; cortex: 3.1+/-1.7 and 2.6+/-1.8, mean+/-S.D.) groups. White matter and cerebral cortical scores were higher in the dexamethasone/ischemic (WM: 3.0+/-1.9, P<0.02; cortex: 3.1+/-1.7, P<0.005) and placebo/ischemic (WM: 2.9+/-1.7, P<0.006; cortex: 2.6+/-1.8, P<0.007) than control (WM: 0.2+/-0.4; cortex: 0.2+/-0.4) group. Carotid blood flow was relatively higher (P<0.05) after 24, 48 and 72 h of reperfusion in the dexamethasone/ischemic than placebo/ischemic group.

CONCLUSIONS

We conclude that maternal pretreatment with antenatal dexamethasone did not attenuate ischemic brain injury in the fetus, and that carotid blood flow was higher during reperfusion in fetuses of dexamethasone than placebo-treated ewes, most likely secondary to decreases in arterial oxygen tension.

Intra-cochlear administration of dexamethasone attenuates aminoglycoside ototoxicity in the guinea pig

This study demonstrates the attenuation of aminoglycoside ototoxicity by cochlear infusion of dexamethasone (Dex) using a microcannulation-osmotic pump delivery system. The results indicate that treating the cochlea with Dex both before and after kanamycin administration was more effective in preventing ototoxicity than Dex treatment only after kanamycin administration. A concentration of 1 ng/ml Dex showed the greatest protective effect on both kanamycin-induced threshold shift of the auditory brainstem response and outer hair cell survival. These results show that the Dex treatment attenuates both functional and structural damage of the inner ear from aminoglycoside toxicity.

Increased plasma beta-hydroxybutyrate, preserved cerebral energy metabolism, and amelioration of brain damage during neonatal hypoxia ischemia with dexamethasone pretreatment

Dexamethasone (DEX) pretreatment has been shown to be neuroprotective in a neonatal rat model of hypoxia ischemia (HI). The exact mechanism of this neuroprotection is still unknown. This study used 31P nuclear magnetic resonance spectroscopy to monitor energy metabolism during a 3-h episode of HI in 7-d-old rat pups in one of two groups. The first group was pretreated with 0.1 mL saline (i.p.) and the second group was treated with 0.1 mL of 0.1mg/kg DEX (i.p.) 22 h before HI. Animals pretreated with DEX had elevated nucleoside triphosphate and phosphocreatine levels during HI when compared with controls. Saline-treated animals had significant decreases in nucleoside triphosphate and phosphocreatine and increases in inorganic phosphate over this same period. 31P nuclear magnetic resonance data unequivocally demonstrate preservation of energy metabolism during HI in neonatal rats pretreated with DEX. Animals pretreated with DEX had little or no brain damage following 3 h of HI when compared with matched controls, which experienced severe neuronal loss and cortical infarction. These same pretreated animals had an increase in blood beta-hydroxybutyrate levels before ischemia, suggesting an increase in ketone bodies, which is the neonate's primary energy source. Elevation of ketone bodies appears to be one of the mechanisms by which DEX pretreatment provides neuroprotection during HI in the neonatal rat.

Preoperative high dose methylprednisolone attenuates the cerebral response to deep hypothermic circulatory arrest

OBJECTIVE

The aim of this study was to assess the effects of preoperative high dose methylprednisolone on cerebral recovery following a period of deep hypothermic circulatory arrest (DHCA).

METHODS

Sixteen 1-week-old piglets were randomized to placebo (n=8), or 30 mg/kg intramuscular methylprednisolone sodium succinate (MPRED) given at 8 and 2 h before induction of anaesthesia. All piglets underwent cardiopulmonary bypass, cooling to 18 degrees C, 60 min of circulatory arrest followed by 60 min of reperfusion and rewarming. The radiolabelled microsphere method was used to determine the global and regional cerebral blood flow (CBF) and cerebral oxygen metabolism (CMRO(2)) at baseline before DHCA and after 60 min of reperfusion.

RESULTS

In controls, mean global CBF (+/-1 standard error) before DHCA was 53.7+/-2.4 ml/100 g per min and fell to 23.8+/-1.2 ml/100 g per min following DHCA (P<0.0001). This represents a post-DHCA recovery to 45.1+/-3.3% of the pre-DHCA value. In the MPRED group recovery of global CBF post-DHCA was significantly higher at 63.6+/-5.2% of the pre-DHCA value (P=0.009). The regional recovery of CBF in the cerebellum, brainstem and basal ganglia was 80, 75 and 69% of pre-DHCA values in the MPRED group respectively compared to 66, 60 and 55% in controls (P<0.05). Global CMRO(2) in controls fell from 3.9+/-0.2 ml/100 g per min before to 2. 3+/-0.2 ml/100 g per min after DHCA (P=0.0001). This represents a post-DHCA recovery to 58.6+/-4.4% of the pre-DHCA value. In the MPRED group, however, recovery of global CMRO(2) post-DHCA was significantly higher at 77.9+/-7.1% of the pre-DHCA value (P=0.04).

CONCLUSIONS

Treatment with high dose methylprednisolone at 8 and 2 h preoperatively attenuates the normal cerebral response to a period of deep hypothermic ischaemia. This technique may therefore offer a safe and inexpensive strategy for cerebral protection during repair of congenital heart defects with the use of DHCA.

The effect of hypoxia from birth on the regulation of aldosterone in the 7-day-old rat: plasma hormones, steroidogenesis in vitro, and steroidogenic enzyme messenger ribonucleic acid

Adaptation to hypoxia in the neonate requires an appropriate adrenocortical response. The purpose of this study was to examine the adaptation of the aldosterone pathway in rat pups exposed to hypoxia in vivo from birth to 7 days of age. Neonatal rats (with their lactating dams) were exposed to normoxia (21% O2) or hypoxia (12% O2) continuously for 7 days from birth. Trunk blood was collected, and entire adrenal glands were processed from 7-day-old rats to study the activity of the steroidogenic pathway in dispersed cells and isolated mitochondria, for measurement of expression of the steroidogenic enzyme messenger RNAs (mRNAs) by RT-competitive PCR and in situ hybridization histochemistry, for measurement of zona glomerulosa width by immunohistofluorescent staining for P450c11AS protein, and for measurement of mitochondrial number and distribution by transmission electron microscopy. Exposure to hypoxia for 7 days from birth resulted in a marked increase in plasma ACTH, corticosterone, and aldosterone with no change in PRA. Aldosteronogenesis and P450c11AS activity were both augmented in dispersed cells; this effect was lost in isolated mitochondria (from entire adrenal glands) using a permeable substrate for P450c11AS. There was no significant effect of hypoxia on expression of the steroidogenic enzyme mRNAs measured by RT-competitive PCR or in situ hybridization histochemistry. Finally, hypoxia had no effect on mitochondrial number or stereology as assessed by transmission electron microscopy or on zona glomerulosa width as assessed by staining for P450c11AS protein. We conclude that, as opposed to that in adults, hypoxia in the neonate results in an augmentation of aldosteronogenesis. This effect is not accounted for by a change in steroidogenic enzyme mRNA expression, zona glomerulosa width (i.e. hyperplasia), or mitochondrial number or distribution. This functional augmentation of aldosteronogenesis may be due to a change in mitochondrial permeability to steroid substrates and/or the effect of cytosolic factors that control mitochondrial steroidogenesis.

Effect of exogenous corticosteroids on the developing central nervous system: a review

Corticosteroid therapy is used in a variety of developmental clinical settings. Prenatally, maternal administration of corticosteroids is used primarily in the prevention of respiratory distress syndrome. Postnatally, corticosteroids are used to treat a variety of infant diseases such as autoimmune hemolytic anemia and hypoglycemia. Treatment regimes often involve repeated administration, on a weekly basis prenatally and daily postnatally, despite an absence of safety data from randomized clinical trials. A large number of animal studies, the majority of which used rodents, have shown that both repeated prenatal or neonatal administration of exogenous corticosteroids has a wide range of detrimental effects on the structure and function of the developing central nervous system (CNS). None of these studies included long-term follow-up. Despite the reported detrimental effects on CNS development, a number of animal studies have shown that pretreatment with corticosteroids nevertheless protect the brain from hypoxia-ischemic injury; however, clinically such treatment is no longer favored. Studies using large animal models and with long-term follow-up should be undertaken to establish the relative risks and benefits of the repeated application of exogenous corticosteroids.

Neurotrophic action of lipocortin 1 derived from astrocytes on cultured rat cortical neurons

The lipocortins are a family of structurally related proteins, namely an annexin family, that exerts a variety of cellular functions through Ca2+-dependent binding to phospholipase A2 [EC 3.1. 1.4], including a crucial role in the central nervous system (CNS) such as antipyrogenic, thermoregulatory and neuroprotective agents in vivo. To elucidate the paradigm of lipocortin 1 functions in the CNS, we have first demonstrated (1) the induction and subsequent extracellular secretion of LC1 by glucocorticoid in cultured rat astrocytes, and (2) neurotrophic activities (survival-promoting, neuritogenic and synaptogenic actions on rat cortical neurons) of recombinant LC1. Time-and dose-dependent experiments of a synthetic glucocorticoid, dexamethasone (DEX), on rat cortical astrocytes in culture revealed that the expression of the intracellular LC1 mRNA and protein were significantly augmented by DEX (1 microM). In addition, DEX evoked an extracellular secretion of LC1 without its cytotoxic effects. Furthermore, the recombinant LC1 appeared to promote not only the survival and neurite outgrowth but also the synaptogenesis of embryonal rat cortical neurons. These results suggest that LC1 induced and selectively released from astrocytes by either endogenously or exogenously introduced glucocorticoids may play a specific and essential role on development and regeneration of the central nervous system.

Cell death and associated c-jun induction in perinatal hypoxia-ischemia. Effect of the neuroprotective drug dexamethasone

Previous studies in a model of unilateral hypoxia-ischemia in the developing rat brain have shown induction of the mRNAs of c-fos and c-jun and presence of apoptotic DNA fragmentation. In this same model, dexamethasone confers neuroprotection if given before the insult. Since c-fos and c-jun have been involved in several models of cell death, we investigated whether the neuroprotective effect of dexamethasone could be associated with changes in expression of these genes. Rat pups, pre-treated with either 0.5 mg/kg dexamethasone or vehicle 48 h, 24 h and immediately before the injury, were subjected to ligation of the left common carotid artery followed by 3 h hypoxia. Analysis of c-fos and c-jun expression at 2 h, by means of in situ hybridization, revealed diminished induction in dexamethasone-treated animals. Jun immunoreactivity, but not Fos, and DNA fragmentation, assessed by in situ end-labeling of fragmented DNA, were present at 24 h only in vehicle-injected animals. Electrophoresis of brain extracted DNA revealed a ladder pattern in all the animals. Our results show a relationship between Jun overexpression and cell-death in the hypoxic-ischemic developing brain and suggest that dexamethasone exerts its protective effect anteceding immediate early gene induction, at some early point in post-ischemic signal transduction.

A model of perinatal hypoxic-ischemic brain damage

In conclusion, our immature rat model has gained wide acceptance as the animal model of choice to study basic physiologic, biochemical, and molecular mechanisms of perinatal hypoxic-ischemic brain damage. In addition, the model has been used extensively to study those physiologic and therapeutic variables which either are deleterious or beneficial to the perinatal brain undergoing hypoxia-ischemia. As therapeutic interventions are tested in the animal setting, the results will provide important information regarding the effect of these agents in the human setting.

Vulnerability to cerebral hypoxic-ischemic insult in neonatal but not in adult rats is in parallel with disruption of the blood-brain barrier

BACKGROUND AND PURPOSE

Vulnerability to cerebral hypoxic-ischemic (H-I) insult and its relation to disruption of the blood-brain barrier were investigated in postnatal rats.

METHODS

Pups of postnatal day (P) 7, P14, and P21 underwent ligation of a unilateral carotid artery and were exposed to hypoxic conditions. For the detection of early-phase deterioration, brains were perfusion-fixed 24 hours after H-I insult and examined by argyrophil III method. For the detection of later infarction, animals were fixed at 72 hours after the H-I insult.

RESULTS

In either case, tissue damage was detected in the striatum, parietal cortex, and hippocampus. The vulnerability of P7 and P21 rats was remarkable, as compared with P14 rats. Although the developmental status of the vasculature was not significantly different at each age, the permeability of IgG after H-I injury was prominent in P7 rats and to a lesser extent in P14 rats. In P21 rats, however, there was little IgG leakage even 24 hours after the insult. Dexamethasone pretreatment blocked the extravasation of IgG and reduced the damaged tissue in P7 and P14 rats but not in P21 rats. Percentages of reduction in infarcted areas by the dexamethasone became smaller in proportion to ages.

CONCLUSIONS

The results suggest that in younger rats vulnerability to H-I insult was in parallel with permeability of the blood-brain barrier, whereas in adults in might be more dependent on cellular vulnerability.

The induction of ICAM-1 in human cerebromicrovascular endothelial cells (HCEC) by ischemia-like conditions promotes enhanced neutrophil/HCEC adhesion

Ischemic brain injury is exacerbated by leukocyte infiltration and formation of vasogenic edema. In this study we demonstrate that intercellular adhesion molecule-1 (ICAM-1) is dramatically (3 to 15-fold) up-regulated in human cerebromicrovascular endothelial cells (HCEC) by a 16 h exposure to the cytokine, IL-1 beta (50-200 u/ml), the phorbol ester, TPA (1-100 nM), or by simulated in vitro ischemia/reperfusion. These treatments also significantly increased the adhesion of allogeneic neutrophils to HCEC monolayers. Both IL-1 beta- and TPA-induced expression of ICAM-1 and increased neutrophil adhesion to HCEC were inhibited by the transcriptional inhibitor, actinomycin D (AcD; 1-10 micrograms/ml), and by an anti-ICAM-1 antibody (ICAM-1 Ab). By contrast, ischemia-induced neutrophil adhesion was only slightly affected by AcD and ICAM-1 Ab alone, but it was abolished by the combination of anti-ICAM-1 and anti-CD18 antibodies. The increase in surface expression of ICAM-1 and neutrophil adhesion by IL-1 beta, TPA and ischemia were significantly reduced by the cyclo-oxygenase (COX) inhibitors, indomethacin (100-300 microM) and dexamethasone (10-50 microM). These results indicate that ICAM-1 expression in HCEC can lead to enhanced neutrophil adhesion and that COX activation in HCEC likely plays a role in the processes by which leukocyte adhesion and recruitment take place in the brain during inflammation and ischemia in vivo.

Dexamethasone prevents apoptosis in a neonatal rat model of hypoxic-ischemic encephalopathy (HIE) by a reactive oxygen species-independent mechanism

It has previously been shown, in a neonatal rat model of hypoxic-ischemic encephalopathy (HIE), that neuronal injury can be attenuated by pretreatment with dexamethasone. The mechanism by which dexamethasone exerts this protective effect is not known. Using the same neonatal rat model of HIE, we found pretreatment with dexamethasone to have no effect on the generation of superoxide radical, products of lipid peroxidation, peroxynitrite-mediated tissue damage or bcl-2 protein expression. However, dexamethasone did inhibit the induction of c-fos transcription seen following HIE, and subsequent evidence of apoptosis. We conclude that it is possible to limit hypoxic-ischemic neuronal injury, despite the continued production of reactive oxygen species, by interventions which block the cascade of events culminating in apoptosis. The involvement of apoptosis in the neuronal injury of HIE, if confirmed in acutely asphyxiated human infants, suggests that there may be a post-injury 'window of opportunity' for neuroprotective interventions.

Animal models for the study of perinatal hypoxic-ischemic encephalopathy: a critical analysis

We critically evaluated various design features from 292 animal studies related to perinatal hypoxic-ischemic encephalopathy (HIE). Rodents were the most frequently used animals in HIE research (26%), followed by piglets (23%) and sheep (22%). Asphyxia with or without ischemia was the most predominant method of producing experimental brain damage, but there were significant variations in specific details, particularly regarding the method and duration of brain insult. In 71% (207/292) of studies the CNS outcomes were tested within 24 h of experimental insult and in 29% (85/292) they were tested 24 h or more after the insult. Acute CNS metabolic end-points were assessed in 82-100% of all studies. In 90% of studies the chronological age of the animal was equivalent to that of human term newborn infant. However, in only 23% (67/292) were clinical neurological, developmental or behavioral outcomes evaluated, and in only 26% (76/292) was neuropathology assessed. While no single animal model was found to be ideal for all HIE research, some models were distinctly superior to others, depending upon the specific research question. The fetal sheep, newborn lamb and piglet models are well suited for the study of acute and subacute metabolic and physiologic endpoints, whereas the rodent and primate models could be used for long-term neurological and behavioral outcome experiments as well. We also feel that standardizing the study design features, including an HI insult method that produces consistent and predictable brain damage is urgently needed. Studies in neuro-ethology should explore how well brains of various animals compare with that of the newborn human infant. There is also a need for developing animal models that mimic clinical entities in which long-term neuro-developmental and behavioral outcomes can be assessed.

Protection against hypoxic-ischemic damage with corticosterone and dexamethasone: inhibition of effect by a glucocorticoid antagonist RU38486

We investigated whether the neuroprotection provided by dexamethasone against neonatal hypoxic-ischemic damage can be inhibited by a glucocorticoid antagonist and whether corticosterone, the endogenous glucocorticoid in the rat, also provides protection. Rats (6 days old) were treated with either vehicle (0.1 ml/10 g), corticosterone (3.5-80 mg/kg, s.c.) or dexamethasone alone or in combination with RU38486 (20-80 mg/kg, s.c.) 15 min prior to dexamethasone (0.1 mg/kg, i.p.). At 7 days of age, cerebral hypoxia-ischemia was produced by right carotid artery ligation under anesthesia and subsequent exposure to 2 h of hypoxia. Damage was quantified from brains perfusion-fixed and processed 2 days later. The reduction in somatic growth, thymus weight and the relatively elevated blood glucose levels at the end of hypoxia-ischemia were inhibited by RU38486. The protective effect of dexamethasone was also prevented by RU38486 (P < 0.001). Similar to pre-treatment with dexamethasone, administration of corticosterone (40-80 mg/kg) markedly reduced the extent of infarction compared to vehicle-treated controls (P < 0.0001). Thus, the endogenous glucocorticoid in the rat also provides protection against hypoxic-ischemic damage. RU38486 inhibits the beneficial effects of dexamethasone demonstrating that the neuroprotection observed with dexamethasone is a glucocorticoid receptor-mediated effect.

Stress, Glucocorticoids, and Damage to the Nervous System: The Current State of Confusion

An extensive literature demonstrates that glucocorticoids (GCs), the adrenal steroids secreted during stress, can have a broad range of deleterious effects in the brain. The actions occur predominately, but not exclusively, in the hippocampus, a structure rich in corticosteroid receptors and particularly sensitive to GCs. The first half of this review considers three types of GC effects: a) GC-induced atrophy, in which a few weeks' exposure to high GC concentrations or to stress causes reversible atrophy of dendritic processes in the hippocampus; b) GC neurotoxicity where, over the course of months, GC exposure kills hippocampal neurons; c) GC neuroendangerment, in which elevated GC concentrations at the time of a neurological insult such as a stroke or seizure impairs the ability of neurons to survive the insult. The second half considers the rather confusing literature as to the possible mechanisms underlying these deleterious GC actions. Five broad themes are discerned: a) that GCs induce a metabolic vulnerability in neurons due to inhibition of glucose uptake; b) that GCs exacerbate various steps in a damaging cascade of glutamate excess, calcium mobilization and oxygen radical generation. In a review a number of years ago, I concluded that these two components accounted for the deleterious GC effects. Specifically, the energetic vulnerability induced by GCs left neurons metabolically compromised, and less able to carry out the costly task of containing glutamate, calcium and oxygen radicals. More recent work has shown this conclusion to be simplistic, and GC actions are shown to probably involve at least three additional components: c) that GCs impair a variety of neuronal defenses against neurologic insults; d) that GCs disrupt the mobilization of neurotrophins; e) that GCs have a variety of electrophysiological effects which can damage neurons. The relevance of each of those mechanisms to GC-induced atrophy, neurotoxicity and neuroendangerment is considered, as are the likely interactions among them.

Detection and regulation of Cu/Zn-SOD and Mn-SOD in rat cochlear tissues

Relative levels of copper/zinc-superoxide dismutase (Cu/Zn-SOD) and manganese-superoxide dismutase (Mn-SOD) in individual cochlear tissues were detected by the use of an enzyme-linked immunosorbent assay (ELISA). A heterogeneous distribution of Cu/Zn-SOD was observed in the individual tissues of control animals: high levels were measured in the stria vascularis (SV), intermediate levels of enzyme were measured in the spiral ligament (SL), and low levels were measured in the organ of Corti region (OC); collectively, these levels were not statistically significant (P = 0.0645). Levels of Mn-SOD in individual tissues of the control group were statistically significant (P < 0.05): high levels were measured in the SV, medium levels were detected in the SL, and low levels were identified in the OC. Following the administration of methylprednisolone (MP), a significant reduction of Cu/Zn-SOD in the SV (P < 0.05) and a non-significant, but noticeable, increase (> 30%) of Mn-SOD in the OC were observed. These results indicate that levels of SOD are tissue specific and that SOD is subject to glucorticoid regulation.

Hypoxia and brain development

Hypoxia threatens brain function during the entire life-span starting from early fetal age up to senescence. This review compares the short-term, long-term and life-spanning effects of fetal chronic hypoxia and neonatal anoxia on several behavioural paradigms including novelty-induced spontaneous and learning behaviours. Furthermore, it reveals that perinatal hypoxia is an additional threat to neurodegeneration and decline of cognitive and other behaviours during the aging process. Prenatal hypoxia evokes a temporary delay of ingrowth of cholinergic and serotonergic fibres into the hippocampus and neocortex, and causes an enhanced neurodegeneration of 5-HT-ir axons during aging. Neonatal anoxia suppresses hippocampal ChAT activity and up-regulates muscarinic receptor sites for 3H-QNB and 3H-pirenzepine binding in the hippocampus in the early postnatal age. The altered development of axonal arborization and pre- and postsynaptic cholinergic functions may be an important underlying mechanism to explain the behavioural deficits. As far as the cellular mechanisms of perinatal hypoxia is concerned, our primary aim was to study the putative importance of Ca2+ homeostasis of developing neurons by means of pharmacological interventions and by measuring the development of immunoexpression of Ca(2+)-binding proteins. We assessed that nimodipine, an L-type calcium channel blocker, prevented or attenuated the adverse behavioural and neurochemical effects of perinatal hypoxias, while it enhanced the early postnatal development of ir-Ca(2+)-binding proteins. The results are discussed in the context of different related research areas on brain development and hypoxia and ischaemia.

Prevention of hypoxic-ischemic damage with dexamethasone is dependent on age and not influenced by fasting

Pretreatment with the synthetic glucocorticoid dexamethasone prevents hypoxic-ischemic brain damage in 7-day-old neonatal rats. We presently characterize the response further by examining the effect of varying the age, the glucocorticoid, and the time of injection and by examining whether fasting can influence the response. Rats (n = 193) were randomized to one of 16 different treatment groups and subjected to hypoxia-ischemia (right carotid artery occlusion +8% O2 which was 3 h in duration for 7-day, 1 h for 2-week, and 30 min for 1-month-old animals). The brains were subsequently perfusion fixed and the area of infarction was measured from hematoxylin- and eosin-stained sections. Time dependence studies demonstrated that treatment with 0.1 mg/kg intraperitoneal dexamethasone 4 h prior to hypoxia reduced infarct size compared to vehicle-treated animals whereas pretreatment at either 48 h or 4 days was ineffective. Dexamethasone pretreatment (4 h) also provided neuroprotection against 4 h of hypoxia-ischemia. Fasted animals which received dexamethasone had reduced blood glucose levels yet markedly less damage than controls. Another glucocorticoid, methylprednisolone (0.7 mg/kg), also reduced infarction. In 2-week-old animals the area of infarction was reduced by pretreatment with dexamethasone, whereas in 1-month-old animals dexamethasone was ineffective. The results suggest that a glucocorticoid-mediated response intervenes in events leading to neuronal death in young animals but not older animals once myelination and synaptogenesis are complete.

A comparison of the protective effect of dexamethasone to other potential prophylactic agents in a neonatal rat model of cerebral hypoxia-ischemia

It has recently been reported that pretreatment with a single dose of dexamethasone (0.1 mg/kg) 24 hours before hypoxia in 7-day-old rat pups is protective against an hypoxic-ischemic insult (unilateral carotid artery occlusion followed by 3 hours of hypoxia in 8% O2). The authors now examine whether pretreatment 6 hours before insult is equally effective and compare other agents potentially suitable for prophylaxis in neonatal hypoxia-ischemia, including the calcium antagonists flunarizine (30 mg/kg pretreatment), nimodipine (0.5 mg/kg pretreatment), and the 21-aminosteroid U-74389F (10 mg/kg pre- and posttreatment). For each active agent, there was also a vehicle-treated control group. Comparison of the mean area of ipsilateral infarction on brain coronal sections showed that there was no statistically significant difference between the various control groups (mean area of infarction 66% +/- 4%). Pretreatment with dexamethasone 6 hours prior to hypoxia offered complete protection with no infarction. A beneficial effect was seen following pretreatment with flunarizine (mean area of infarction 33.6% +/- 7.8%), although this degree of damage was still significantly different from that seen with dexamethasone pretreatment. Pretreatment with nimodipine or U-74389F offered no protection (mean area of infarction 77.5% +/- 4% and 59% +/- 10%, respectively). Unlike findings in adult animals and clinical studies, the current studies show that dexamethasone may have a role in the treatment of neonatal hypoxia-ischemia and deserves reappraisal.