Dexamethasone prevents long-lasting learning impairment following neonatal hypoxic-ischemic brain insult in rats

Repression of the Glucocorticoid Receptor Increases Hypoxic-Ischemic Brain Injury in the Male Neonatal Rat

Hypoxic-ischemic encephalopathy (HIE) resulting from asphyxia is the most common cause of neonatal brain damage and results in significant neurological sequelae, including cerebral palsy. The current therapeutic interventions are extremely limited in improving neonatal outcomes. The present study tests the hypothesis that the suppression of endogenous glucocorticoid receptors (GRs) in the brain increases hypoxic-ischemic (HI) induced neonatal brain injury and worsens neurobehavioral outcomes through the promotion of increased inflammation. A mild HI treatment of P9 rat pups with ligation of the right common carotid artery followed by the treatment of 8% O₂ for 60 min produced more significant brain injury with larger infarct size in female than male pups. Intracerebroventricular injection of GR siRNAs significantly reduced GR protein and mRNA abundance in the neonatal brain. Knockdown of endogenous brain GRs significantly increased brain infarct size after HI injury in male, but not female, rat pups. Moreover, GR repression resulted in a significant increase in inflammatory cytokines TNF-α and IL-10 at 6 h after HI injury in male pups. Male pups treated with GR siRNAs showed a significantly worsened reflex response and exhibited significant gait disturbances. The present study demonstrates that endogenous brain GRs play an important role in protecting the neonatal brain from HI induced injury in male pups, and suggests a potential role of glucocorticoids in sex differential treatment of HIE in the neonate.

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.

Anoxia ameliorates the dexamethasone-induced neurobehavioral alterations in the neonatal male rat pups

Glucocorticoids and hypoxia are two essential factors affecting the brain development during labor and delivery. In addition to the neurobehavioral alterations induced separately by these factors, glucocorticoids can attenuate the deleterious consequences of severe hypoxia-ischemia on the brain development, acting as a neuroprotective agent in combination with hypoxia. The role of hypoxia in the combined action with corticosteroids is less clear. Severe hypoxia-ischemia results in the massive activation of caspase-3, masking any other effects of hypoxia on the neonatal brain exposed to glucocorticoids. As a result, the effects of mild hypoxia on the developing brain pretreated with glucocorticoids remain unclear. To analyze this problem, 2-day-old male rats were treated with dexamethasone (DEX) before the subsequent exposure to mild 10-min anoxia or normoxia. The treatment with only DEX resulted in the delay in the development of the negative geotaxis reaction and in the decrease in locomotor activity of the neonatal male pups. The mild anoxic event attenuated these DEX-induced neurobehavioral alterations. The treatment with DEX, but not the mild anoxic exposure alone, resulted in the delayed upregulation of active caspase-3 in the prefrontal cortex and in the brainstem of the male pups. This glucocorticoid-induced upregulation of active caspase-3 was prevented by the anoxic event. The present findings evidence that mild anoxia is capable of ameliorating the glucocorticoid-induced neurodevelopmental alterations in the neonatal rats if the artificial or the naturally occurring increase in the levels of glucocorticoids occurred just before the episode of hypoxia.

Intraperitoneal and intravenous deliveries are not comparable in terms of drug efficacy and cell distribution in neonatal mice with hypoxia-ischemia

BACKGROUND AND PURPOSE

Most therapeutic agents are administered intravenously (IV) in clinical settings and intraperitoneally (IP) in preclinical studies with neonatal rodents; however, it remains unclear whether intraperitoneal (IP) injection is truly an acceptable alternative for intravenous (IV) injection in preclinical studies. The objective of our study is to clarify the differences in the therapeutic effects of drugs and in the distribution of infused cells after an IP or IV injection in animals with brain injury.

METHODS

Dexamethasone or MK-801, an N-methyl-d-aspartate receptor antagonist was administered either IP or IV in a mouse model of neonatal hypoxic-ischemic encephalopathy. Green fluorescent protein-expressing mesenchymal stem cells (MSCs) or mononuclear cells (MNCs) were injected IP or IV in the mouse model. Two hours and 24h after the administration of the cells, we investigated the cell distributions by immunohistochemical staining. We also investigated distribution of IV administered MNCs labeled with 2-[18F]fluoro-2-deoxy-d-glucose in a juvenile primate, a macaque with stroke 1h after the administration.

RESULTS

IP and IV administration of dexamethasone attenuated the brain injury to a similar degree. IP administration of MK-801 attenuated brain injury, whereas IV administration of MK-801 did not. The IV group showed a significantly greater number of infused cells in the lungs and brains in the MSC cohort and in the spleen, liver, and lung in the MNC cohort compared to the IP group. In the macaque, MNCs were detected in the spleen and liver in large amounts, but not in the brain and lungs.

CONCLUSIONS

This study demonstrated that the administration route influences the effects of drugs and cell distribution. Therefore, a preclinical study may need to be performed using the optimal administration route used in a clinical setting.

Effects of maternal separation on behavior and brain damage in adult rats exposed to neonatal hypoxia-ischemia

Animal studies suggest that maternal separation, a widely used paradigm to study the effects of early life adversity, exerts a profound and life-long impact on both brain and behavior. The aim of the current study was to investigate whether adverse early life experiences interact with neonatal hypoxia-ischemia, affecting the outcome of this neurological insult at both functional and structural levels during adulthood. Rat pups were separated from their mothers during postnatal days 1-6, for either a short (15 min) or prolonged (180 min) period, while another group was left undisturbed. On postnatal day 7, a subgroup from each of the three postnatal manipulations was exposed to a hypoxic-ischemic episode. Behavioral examination took place approximately at three months of age and included tests of learning and memory (Morris water maze, novel object and novel place recognition), as well as motor coordination (rota-rod). We found that both prolonged maternal separation and neonatal hypoxia-ischemia impaired the animals' spatial learning and reference memory. Deficits in spatial but not visual recognition memory were detected only in hypoxic-ischemic rats. Interestingly, prolonged maternal separation prior to neonatal hypoxia-ischemia augmented the reference memory impairments. Histological analysis of infarct size, hippocampal area and thickness of corpus callosum did not reveal any exacerbation of damage in hypoxic-ischemic rats that were maternally separated for a prolonged period. These are the first data suggesting that an adverse postnatal environmental manipulation of just 6 days causes long-term effects on spatial learning and memory and may render the organism more vulnerable to a subsequent insult.

Long term creatine monohydrate supplementation, following neonatal hypoxic ischemic insult, improves neuromuscular coordination and spatial learning in male albino mouse

Creatine is known to rescue animals following brain damage. Present study was designed to demonstrate the effect of long term (15 week) supplementation of 2% creatine monohydrate (Cr), following neonatal hypoxic ischemic insult, on learning and memory formation in male albino mouse. Albino mice pups were subjected to right common carotid artery ligation followed by 8% hypoxia for 25 minutes. Following weaning, animals were separated and grouped on the basis of dietry supplementation for 15 weeks followed by a battery of neurological tests including Morris water maze, open field and rota rod. It was observed that HI mice fed on 2% Cr for 15 weeks performed better than their littermates mice on normal rodent diet during water maze (learning and memory) and rotating rod (neuro-muscular coordination and balance) test while the results of open field test remained unaffected. It was also observed that Cr treated animals had a reduced brain infarct volume than untreated but this difference did not reached statistical significance. We have also observed an overall increase in body weight in Cr treated mice during the study. Over all our results are indicating that long term Cr supplementation is beneficial for male albino following hypoxic ischemic insult.

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 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.

Hypoxic-ischemic neonatal encephalopathy: animal experiments for neuroprotective therapies

Hypoxic-ischemic neonatal encephalopathy and ensuing brain damage is still an important problem in modern perinatal medicine. In this paper, we would like to share some of the results of our recent studies on neuroprotective therapies in animal experiments, as well as some literature reviews. From the basic animal studies, we have now obtained some possible candidates for therapeutic measures against hypoxic-ischemic neonatal encephalopathy. For example, they are hypothermia, rehabilitation, free radical scavenger, neurotrophic factors and growth factors, steroid, calcium channel blocker, vagal stimulation, some anti apoptotic agents, pre- and post conditioning, antioxidants, cell therapy with stem cells, modulators of K(+)-ATP channels, and so on. Whether combination of these therapies may be more beneficial than any single therapy needs to be clarified. Hypoxia-ischemia is a complicated condition, in which the cause, severity, and time-course are different in each case. Likewise, each fetus has its own inherent potentials such as adaptation, preconditioning-tolerance, and intolerance. Therefore, further extensive studies are required to establish an individualized strategy for neuroprotection against perinatal hypoxic-ischemic insult.

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.

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.

Methadone-induced delayed posthypoxic encephalopathy: clinical, radiological, and pathological findings

Objective. To describe the clinical, radiological and pathological findings in a patient with methadone-induced delayed posthypoxic encephalopathy (DPHE). Case Report. A Thirty-eight-year-old man was found unconscious for an unknown duration after methadone and diazepam ingestion. His initial vitals were temperature 104 degree Fahrenheit, heart rate 148/minute, respiratory rate 50/minute, and blood pressure 107/72 mmhg. He developed renal failure, rhabdomyolysis, and elevated liver enzymes which resolved completely in 6 days. After 2 weeks from discharge he had progressive deterioration of his cognitive, behavioral and neurological function. Brain MRI showed diffuse abnormal T2 signal in the corona radiata, centrum semiovale, and subcortical white matter throughout all lobes. Extensive work up was negative for any metabolic, infectious or autoimmune disorder. Brain biopsy showed significant axonal injury in the white matter. He was treated successfully with combination of steroids and antioxidants. Follow up at 2 year showed no residual deficits. Conclusion. Our observation suggests that patients on methadone therapy should be monitored for any neurological or psychiatric symptoms, and in suspected cases MRI brain may help to make the diagnosis of DPHE. A trial of steroids and antioxidants may be considered in these patients.

Low dose dexamethasone reverses depressive-like parameters and memory impairment in rats submitted to sepsis

Sepsis is characterized by a systemic inflammatory response of the immune system against an infection, presenting with hypothalamic-pituitary-adrenal (HPA) axis dysfunction, behavior alterations, and high mortality. In this study, we aimed to evaluate the effects of dexamethasone on mortality, anhedonia, circulating corticosterone and adrenocorticotropin hormone (ACTH) levels, body and adrenal gland weight, and aversive memory in sepsis survivor rats. Male Wistar rats underwent sham operation or cecal ligation and perforation (CLP) procedure. Rats subjected to CLP were treated with "basic support" and dexamethasone (at 0.2 and 2mg/kg daily for 7 days after CLP, intraperitonially) or saline. After 10 days of sepsis procedure, it was evaluated aversive memory, sweet food consumption, and body and adrenal gland weight. Serum and plasma were also obtained. It was observed that low dose dexamethasone reverted anhedonia, normalized adrenal gland and body weight, corticosterone and ACTH levels, and decreased mortality and avoidance memory impairment, demonstrating that low doses of dexamethasone for moderate periods may be beneficial for sepsis treatment and its sequelae-depressive-like parameters and memory impairment.

NF-kappaB inhibition after neonatal cerebral hypoxia-ischemia improves long-term motor and cognitive outcome in rats

We recently demonstrated that inhibition of the NF-kappaB-pathway by the specific peptide inhibitor TAT-NBD markedly reduced cerebral injury in a rat model of perinatal hypoxic-ischemic (HI) brain damage. The aim of the current study was to assess whether neuroprotection by TAT-NBD is associated with long-term functional improvements after neonatal HI. Postnatal-day 7 rats subjected to HI showed motor deficits in the cylinder rearing test and adhesive removal task. HI-treated animals also showed cognitive impairments in a visuo-spatial learning task (modified hole board) as defined by an increased latency to complete this task and increased numbers of short- and long-term memory errors. HI animals treated with TAT-NBD [20mg/kg i.p.] at 0 and 3h post-HI did not show impairments in the cylinder rearing test, adhesive removal task and modified hole board. In conclusion, the almost complete reduction in lesion size observed after TAT-NBD treatment was associated with long-lasting normalization of sensorimotor and cognitive functions.

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.

Adverse neurodevelopmental effects of dexamethasone modeled in PC12 cells: identifying the critical stages and concentration thresholds for the targeting of cell acquisition, differentiation and viability

The use of dexamethasone (DEX) to prevent respiratory distress in preterm infants is suspected to produce neurobehavioral deficits. We used PC12 cells to model the effects of DEX on different stages of neuronal development, utilizing exposures from 24 h up to 11 days and concentrations from 0.01 to 10 microM, simulating subtherapeutic, therapeutic, and high-dose regimens. In undifferentiated cells, even at the lowest concentration, DEX inhibited DNA synthesis and produced a progressive deficit in the number of cells as evaluated by DNA content, whereas cell growth (evaluated by the total protein to DNA ratio) and cell viability (Trypan blue exclusion) were promoted. When cell differentiation was initiated with nerve growth factor, the simultaneous inclusion of DEX still produced a progressive deficit in cell numbers and promoted cell growth and viability while retarding the development of neuritic projections as monitored by the membrane/total protein ratio. Again, even 0.01 microM DEX was effective. We next assessed effects at mid-differentiation by introducing nerve growth factor for 4 days followed by coexposure to DEX. Although effects on cell number, growth, and neurite extension were still detectable, the outcomes were generally less notable. DEX also shifted the fate of PC12 cells away from the cholinergic phenotype and toward the adrenergic phenotype, with the maximum effect achieved at the outset of differentiation. Our results indicate that DEX directly disrupts neuronal cell replication, differentiation, and phenotype at concentrations below those required for the therapy of preterm infants, providing a mechanistic link between glucocorticoid use and neurodevelopmental sequelae.

Basic and translational research in neonatal pharmacology

Pharmacologic study is needed in the extremely immature newborns who currently survive. Study is needed of both the drug treatment previously established in more mature neonates and of novel drug therapy. Carefully controlled studies are needed to identify accurately both beneficial and harmful drug therapy and the mechanisms of that toxicity. Careful pharmacologic study of drug disposition and its mechanisms might lead to dosing paradigms or patient selection that minimize toxicity and maximize efficacy. In vivo, translational models of neonatal diseases are limited, but can be used to identify novel treatments and study mechanisms of established, successful therapy. Findings from such studies can generate hypotheses for study in humans leading to a continuing scientific interchange from bedside to bench to bedside. Similarly, clinical observations can generate hypotheses for study in translational models where more invasive analyses are possible. Specific areas of drug treatment should focus on neonatal disorders with long-term, adverse outcomes, such as chronic lung disease, that is amenable to translational study with animal models. National data show a progressive decrease in the clinician-scientist pool entering biomedical research. The future of neonatal pharmacology studies requires an increase in training programs for the physician-scientist whose clinical education in neonatology can be complemented by rigorous basic-science training. Success as a clinician-scientist will require collaboration with full-time basic scientists who can continue studies during periods of clinical work and provide critical study methodology to the overall study design. Such a work environment must be supported by academic institutions and may require more flexibility in the promotion and tenure schedule and process, such as the nature of what it rewards. To complement this, the NIH could modify its grant reporting process to identify co-investigators in studies who may provide unique input to the study concepts and design, such as clinical correlations or clinical investigations.

Endotoxin-induced hypoxic-ischemic tolerance is mediated by up-regulation of corticosterone in neonatal rat

Previous studies suggest that the endotoxin lipopolysaccharide (LPS) may have dual effects on brain damage induced by hypoxia-ischemia (HI) in 7-d-old rats, depending on the exposure paradigm. Although a 4-h interval between LPS administration and HI results in sensitization to HI brain injury, tolerance is observed when LPS is administered 24 h before HI. Our hypothesis is that endogenous corticosteroids are important in acquiring tolerance to HI. Neonatal rats received a single injection of LPS (1.0 mg/kg) either 4 h or 24 h before HI, or two LPS injections (4 h and 24 h) before HI. Increased brain injury was seen in animals subjected to a single LPS injection made 4 h before HI. In contrast, both the single 24-h exposure and the double injections of LPS resulted in tolerance to HI brain damage. To study the effects of corticosteroids on HI tolerance, RU486, a glucocorticoid receptor blocker, was subcutaneously injected at the same time as LPS (1.0 mg/kg), 24 h before HI stress. RU486-LPS treatment counteracted the LPS-induced tolerance effect, and aggravated the HI-induced brain injury compared with the vehicle-LPS-treated group. RU486 did not aggravate the HI-induced brain injury produced 24 h later in saline-injected animals. LPS (1.0 mg/kg) injected into 6-d-old rats transiently up-regulated serum corticosterone levels (119.6, 57.9, 56.8, and 28.3 ng/mL at 6, 12, 24, and 48 h after the LPS injection, respectively). We conclude that endotoxin-induced up-regulation of endogenous corticosterone appears to be critical for acquiring endotoxin-induced HI tolerance.

Neonatal novelty exposure ameliorates anoxia-induced hyperactivity in the open field

We investigated in an animal model of neonatal anoxia whether effects of oxygen deprivation on emotional reactivity can be reversed by neonatal novelty exposure, a behavioral method, involving daily 3min away from the home cage for the first 3 weeks of life. Male neonates were exposed to either 100% N2 gas (Anoxia) or room air (Control) for 25min on postnatal day 1. Within each of the two treatment conditions, one-half of the neonates were further individually exposed to relatively novel non-home cages for 3min daily during postnatal days 2-21 (Novel: NAnoxia=20; NControl=16), while the other half remained in the home cage (Home: NAnoxia=19; NControl=19). Emotional reactivity to an open field was evaluated on postnatal day 25 during four 20-s trials. Among home rats, temporal patterns of open-field activity across multiple trials and initial-trial activity significantly differed between the Anoxia and Control rats. In contrast, these differences were eliminated among the Novel rats. These results show that neonatal novelty exposure, an early-stimulation method that has recently been shown to enhance spatial and social memory, adaptive control of stress response, and hippocampal synaptic plasticity, can also eliminate neonatal anoxia-induced changes in emotional reactivity. These findings suggest that brief and repeated, but mild, changes in the postnatal environment may serve to counteract some of the aversive effects induced by neonatal trauma associated with oxygen deprivation.

Neurological reflexes and early motor behavior in rats subjected to neonatal hypoxic-ischemic injury

Severe perinatal hypoxia-ischemia is an important cause of brain injury in both full-term and premature newborns, with a high risk of future behavioral and neurological deficits. The most commonly used animal model of neonatal hypoxia-ischemia is the unilateral ligation of the common carotid artery followed by exposure to hypoxia in 7-day-old rats. In spite of the wide use of this model, lot of contradictions and discrepancies exist between the results obtained by different laboratories regarding behavioral deficits and there are no data regarding the possible delay of the appearance of neurological reflexes and the time-course of reflex performances following neonatal hypoxic-ischemic injury in rats. In the present study we showed that neonatal hypoxia-ischemia retarded the development of somatic growth and several neurological reflexes (ear twitch, grasping, gait and negative geotaxis). Hypoxic animals also displayed retarded performance in righting, geotaxis and gait reflexes. Although hypoxic pups performed worse in most tests for motor coordination, they reached normal levels by 5 weeks of age except in the footfault test. In the open-field, hypoxic animals were generally more active, except at 3 weeks, when activity of normal pups increased enormously as well. Brain areas were significantly reduced in hypoxic animals, but no close correlation was found with behavioral deficits.

Implantation of encapsulated glial cell line-derived neurotrophic factor-secreting cells prevents long-lasting learning impairment following neonatal hypoxic-ischemic brain insult in rats

OBJECTIVE

Implantation of encapsulated glial cell line-derived neurotrophic factor-secreting cells into brain parenchyma reduces histological brain damage following hypoxic-ischemic stress in neonatal rats. We examined the effect of glial cell line-derived neurotrophic factors on long-term learning and memory impairment and morphological changes up to 18 weeks after hypoxic-ischemic stress in neonatal rats.

STUDY DESIGN

Baby hamster kidney cells were transfected with expression vector either including (glial cell line-derived neurotrophic factor-hypoxic-ischemic group; n = 10) or not including (control-hypoxic-ischemic group; n = 8) human glial cell line-derived neurotrophic factor cDNA, encapsulated in semipermeable hollow fibers, and implanted into the left brain parenchyma of 7-day-old Wistar rats. Two days after implantation the rats received hypoxic-ischemic stress, and their behavior was then examined in several learning tasks: the 8-arm radial maze, choice reaction time, and water maze tasks, which examine short-term working memory, attention process, and long-term reference memory, respectively. The rats were killed 18 weeks after the hypoxic-ischemic insult for evaluation of brain damage. Two additional control groups were used: the control group (n = 15), which underwent no treatment, and the glial cell line-derived neurotrophic factor group (n = 6), which underwent implantation of the glial cell line-derived neurotrophic factor capsule but did not undergo hypoxic-ischemic stress.

RESULTS

The decrease in the size of the cerebral hemisphere was significantly less in the glial cell line-derived neurotrophic factor-hypoxic-ischemic group, compared with the control-hypoxic-ischemic group, and improved performance was observed in all three tasks for the glial cell line-derived neurotrophic factor-hypoxic-ischemic group: for the control-hypoxic-ischemic group versus the glial cell line-derived neurotrophic factor-hypoxic-ischemic group, respectively, in the 8-arm radial maze test, average number of correct choices was 6.2 +/- 0.1 versus 6.9 +/- 0.1 ( P < .01); in the choice reaction time test, average reaction time for a correct response was 2.35 +/- 0.1 seconds versus 1.97 +/- 0.09 seconds ( P < .01); in the water maze test, average swimming length was 1120.0 +/- 95.2 cm versus 841.6 +/- 92.1 cm ( P < .01). All results for the glial cell line-derived neurotrophic factor group were similar to those for the control group.

CONCLUSION

Glial cell line-derived neurotrophic factor treatment is effective in not only reducing brain damage but also inhibiting learning and memory impairment, following hypoxic-ischemic insult in neonatal rats. No adverse effects in learning and memory tests were observed in the glial cell line-derived neurotrophic factor group.

Dexamethasone prevents long-lasting learning impairment following a combination of lipopolysaccharide and hypoxia-ischemia in neonatal rats

OBJECTIVE

There are no established therapies for preventing or rescuing perinatal infection or inflammation-induced perinatal brain damage. We administered dexamethasone (DEX), a synthetic corticosteroid anti-inflammatory drug, to neonatal rats in a model of such damage induced by a combination of lipopolysaccharide (LPS) and hypoxia-ischemia (HI), which produces characteristic histologic and behavioral abnormalities.

STUDY DESIGN

Four hours after the injection of LPS (1 mg/kg, i.p.), 7-day-old Wistar rat pups were subjected to unilateral HI for 1 hour according to Levine's procedure. Injections of 0.5 mg/kg of dexamethasone (DEX-treated group, n = 15) or saline (saline-treated group, n = 15) were given 4 hours before HI. A sham-operated control group received neither LPS nor HI (n = 15). We chose rats of this age because their stage of brain maturation is similar to the human neonate. Over the 7 to 16 weeks after treatment, a choice reaction time (CRT) task was used for assessment of attention processes in each group, an 8-arm radial maze task was used to test short-term memory, and a water maze task was used to test long-term memory. In the CRT task, the reward food was released when the tested animal correctly pressed a lever on the side of an illuminating lamp. The correct and incorrect lever pressings were counted. In the 8-arm radial maze task, rats were allowed to move freely, seeking a reward of food placed at the end of 1 arm. An error was defined as the choice of an arm that had already been visited. In the water maze, rats had to swim to seek a concealed platform as aversive escape motivation. At 19 weeks, the rats were euthanized, the brain was removed, sectioned coronally, and the volume of each part was measured.

RESULTS

The striatum, cortex, and hippocampus showed reductions in volume in the saline-treated group (42.7%, 49.2%, and 34.9% decreases compared with the sham-operated controls, respectively), but this was not observed in the DEX-treated group. All learning and memory processes were impaired with the combination of LPS and HI treatment, but these deficits were almost completely prevented by DEX treatment.

CONCLUSION

Dexamethasone is a promising candidate for prevention of infection and inflammation-induced perinatal brain damage. The impact of dexamethasone identifies potential therapeutic pathways once the mechanism of dexamethasone's protection is determined.

Erythropoietin improves long-term spatial memory deficits and brain injury following neonatal hypoxia-ischemia in rats

It is well known that neonatal hypoxic-ischemic brain injury leads to mental retardation and deficits in cognitive abilities such as learning and memory in human beings. The ameliorative effect of erythropoietin (Epo) on experimental hypoxic-ischemic brain injury in neonatal rats has been recently reported. However, the effect of Epo on cognitive abilities in the hypoxic-ischemic brain injury model is unknown. The aim of this study is to investigate the effects of Epo on learning-memory, behavior and neurodegeneration induced by hypoxia-ischemia. Seven days old Wistar Albino rat pups have been used in the study (n = 28). Experimental groups in the study were: (1) saline-treated hypoxia-ischemia group, (2) Epo-treated (i.p., 1000 U/kg) hypoxia-ischemia group, (3) sham-operated group, (4) control group. In hypoxia-ischemia groups, left common carotid artery was ligated permanently on the seventh postnatal day. Two hours after the procedure, hypoxia (92% nitrogen and 8% oxygen) was induced for 2.5 h. Epo was administered as a single dose immediately after the hypoxia period. When pups were 22 days old, learning experiments were performed using Morris water maze. On the 20th week, when brain development is accepted to be complete, learning experiments were repeated. Rats were then perfused and brains removed for macroscopic and microscopic evaluation. Epo treatment immediately after hypoxic-ischemic insult significantly improved long-term neurobehavioral achievements when tested during the subsequent phase of brain maturation and even into adulthood. Histopathological evaluation demonstrated that Epo also significantly diminished brain injury and spared hippocampal CA1 neurons. In conclusion, Epo administrated as a single dose immediately after neonatal hypoxic-ischemic insult provides benefit over a prolonged period in the still developing rat brain. Since the wide use of Epo in premature newborns, this agent may be potentially beneficial in treating asphyxial brain damage in the perinatal period.

Effect of neonatal dexamethasone exposure on growth and neurological development in the adult rat

Until recently, the synthetic glucocorticoid dexamethasone was commonly used to lessen the morbidity of chronic lung disease in premature infants. This practice diminished as dexamethasone use was linked to an increased incidence of cerebral palsy and short-term neurodevelopmental delay. Of more concern is the fact that we know little regarding dexamethasone effects on long-term neurodevelopment. To study the effects of neonatal dexamethasone exposure on long-term neurodevelopment, we have developed a rat model where newborn pups are exposed to tapering doses of dexamethasone at time points corresponding to the neurodevelopmental age when human infants are traditionally exposed to this drug in the neonatal intensive care unit. Using a within-litter design, pups were assigned to one of three groups on postnatal day 2 (P2): handled controls, saline-injected controls, and animals receiving intramuscular dexamethasone between P3 and P6. Somatic growth was decreased in dexamethasone-treated animals. Dexamethasone-treated animals demonstrated slight delays in indexes of neurodevelopment and physical maturation at P7 and P14, but not P20. In adolescence (P45), there was no difference between groups in an open field test. However, as adult dexamethasone-treated animals were less active in the open field and spent more time in closed arms of the elevated plus maze. The serum corticosterone response to crowding stress in dexamethasone-treated animals was no different from controls, but they demonstrate a delay in return of corticosterone levels to baseline. These differences in behavior and hormonal stress responsiveness suggest that neonatal dexamethasone exposure may permanently alter function of the neuroendocrine stress axis.