Selective and long-term learning impairment following neonatal hypoxic-ischemic brain insult in rats

Therapeutic effect of caffeine treatment immediately following neonatal hypoxic-ischemic injury on spatial memory in male rats

Hypoxia Ischemia (HI) refers to the disruption of blood and/or oxygen delivery to the brain. Term infants suffering perinatal complications that result in decreased blood flow and/or oxygen delivery to the brain are at risk for HI. Among a variety of developmental delays in this population, HI injured infants demonstrate subsequent memory deficits. The Rice-Vannucci rodent HI model can be used to explore behavioral deficits following early HI events, as well as possible therapeutic agents to help reduce deleterious outcomes. Caffeine is an adenosine receptor antagonist that has recently shown promising results as a therapeutic agent following HI injury. The current study sought to investigate the therapeutic benefit of caffeine following early HI injury in male rats. On post-natal day (P) 7, HI injury was induced (cauterization of the right common carotid artery, followed by two hours of 8% oxygen). Male sham animals received only a midline incision with no manipulation of the artery followed by room air exposure for two hours. Subsets of HI and sham animals then received either an intraperitoneal (i.p.) injection of caffeine (10 mg/kg), or vehicle (sterile saline) immediately following hypoxia. All animals later underwent testing on the Morris Water Maze (MWM) from P90 to P95. Results show that HI injured animals (with no caffeine treatment) displayed significant deficits on the MWM task relative to shams. These deficits were attenuated by caffeine treatment when given immediately following the induction of HI. We also found a reduction in right cortical volume (ipsilateral to injury) in HI saline animals as compared to shams, while right cortical volume in the HI caffeine treated animals was intermediate. These findings suggest that caffeine is a potential therapeutic agent that could be used in HI injured infants to reduce brain injury and preserve subsequent cognitive function.

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.

Neuroprotective effect of human placental extract on hypoxic-ischemic brain injury in neonatal rats

We investigated the neuroprotective effects of human placental extracts (HPE) and the effects of HPE on recovery of cognitive and behavioral function on hypoxic-ischemic brain injury in the newborn rat. The right common carotid arteries of 7-day-old rats were coagulated, and rats were then exposed to 8% oxygen. Immediately before and again at three times after the hypoxia-ischemia (pre-treatment group), and immediately after and three times again after hypoxia-ischemia (post-treatment group), the rats were intraperitoneally injected with HPE (0.1, 0.25, or 0.5 mL/10 g/dose). No-treatment rats received saline only. On postnatal day 12, brains were removed and gross morphological damage was evaluated. To quantify the severity of brain injury, bilateral cross-sectional areas of the anterior commissural and posterior hippocampal levels were analyzed with NIH Image. Assessments of the open field activity levels at 2, 4, 6 and 8 week and, the Morris water maze test at 8 weeks after hypoxia-ischemia were carried out according to standard methods. HPE pre-treatment decreased the incidence of liquefactive cerebral infarction, at an optimally neuroprotective dose of 0.5 mL/10 g/dose (P<0.05). In the Morris water maze test, the group injected with HPE at 0.5 mL/10 g/dose concentration showed shorter escape latencies than the no-treatment group (P<0.05). These findings support a protective effect of the HPE treatment on neuronal integrity and cognitive function following hypoxic-ischemic brain injury. Injected at an appropriate dose prior to exposure, HPE may significantly reduce or prevent hypoxic-ischemic injury in the immature brain.

Mild neonatal hypoxia-ischemia induces long-term motor- and cognitive impairments in mice

To understand and potentially treat the lifelong cognitive and motor deficits in humans resulting from perinatal mild cerebral hypoxic-ischemic (HI) events, valid animal models are of high importance. Nowadays the murine model of neonatal cerebral HI-injury (unilateral carotid artery occlusion followed by hypoxia) is applied more frequently. In the present study we investigated motor, behavioral and cognitive functioning in mice with mild cerebral HI-injury (45 min of hypoxia; HI-45) in comparison to mice exposed to severe HI (HI-75) and sham-control mice. Lateralizing motor disturbances as measured using the cylinder rearing test developed in both HI-45 and HI-75 mice and was significantly more severe in HI-75 animals. To assess behavior and cognitive functions, we used the modified hole board (mHB) test in two stages. First, the ability of the animals to find the three food rewards in cued holes over time was determined. The results revealed an overall learning impairment in HI-75 mice, while HI-45 mice were not different from sham controls. In the second stage, a reversal test was performed with rewarded cylinders being non-cued and non-rewarded cylinders being cued. This reversal-task revealed impairments in cognitive flexibility in HI-45 mice as compared to sham-control animals. Our data indicate that both the cylinder rearing task and the two stages of the mHB are suitable behavioral approaches to differentiate consequences of neonatal mild and severe brain damage on executive functioning.

Lateralized and sex-dependent behavioral and morphological effects of unilateral neonatal cerebral hypoxia-ischemia in the rat

Neonatal cerebral hypoxia-ischemia (HI) is an important cause of neurological deficits. The Levine-Rice model of unilateral HI is a useful experimental tool, but the resulting brain damage is mainly restricted to one hemisphere. Since the rat presents morphological and biochemical asymmetries between brain hemispheres, behavioral outcome from this model is probably dependent on which hemisphere is damaged. We here investigated the effects of sex and lesioned hemisphere on the outcome of open field, plus maze, inhibitory avoidance and water maze tasks in adult rats previously submitted to neonatal unilateral HI. Females were more active than males in some of studied parameters and males presented better spatial learning. Hypoxia-ischemia caused spatial deficits independently of sex or damaged hemisphere. Right-HI increased locomotion only in males and caused working memory in females and on aversive learning in both males and females. Morphological analysis showed that right-HI animals presented greater reduction of ipsilateral striatum area, with females being more affected. Interestingly, males showed greater hippocampal volume. These results show that task performance and cerebral damage extension are lateralized and sex-dependent, and that the right hemisphere, irrespective of sex, is more vulnerable to neonatal cerebral hypoxia-ischemia.

IFATS collection: The conditioned media of adipose stromal cells protect against hypoxia-ischemia-induced brain damage in neonatal rats

Adipose tissue stroma contains a population of mesenchymal stem cells, which support repair when administered to damaged tissues, in large part through secreted trophic factors. We directly tested the ability of media collected from cultured adipose-derived stem cells (ASCs) to protect neurons in a rat model of brain hypoxic-ischemic (HI) injury. Concentrated conditioned medium from cultured rat ASCs (ASC-CM) or control medium was infused through the jugular vein of neonatal Sprague-Dawley rats subjected to HI injury. The ASC-CM was administered either 1 hour before or 24 hours after induction of injury. Analysis at 1 week indicated that administration at both time points significantly protected against hippocampal and cortical volume loss. Analysis of parallel groups for behavioral and learning changes at 2 months postischemia demonstrated that both treated groups performed significantly better than the controls in Morris water maze functional tests. Subsequent post-mortem evaluation of brain damage at the 2-month time point confirmed neuronal loss to be similar to that observed at 1 week for all groups. We have identified several neurotrophic factors in ASC-CM, particularly insulin-like growth factor-1 and brain-derived neurotrophic factor, which are important factors that could contribute to the protective effects of ASCs observed in studies with both in vitro and in vivo neuronal injury models. These data suggest that delivery of the milieu of factors secreted by ASCs may be a viable therapeutic option for treatment of HI, as well as other brain injuries.

A chemical chaperone, sodium 4-phenylbutyric acid, attenuates the pathogenic potency in human alpha-synuclein A30P + A53T transgenic mice

Aggregation and cytotoxicity of misfolded alpha-synuclein are postulated to be crucial in the disease processes of Parkinson's disease (PD) and other synucleinopathies. Mutations in the alpha-synuclein gene in some pedigrees of familial PD have been reported. The mutant alpha-synuclein has been reported to form fibrillar aggregates resulting in biochemical abnormalities that are responsible for the onset of familial PD. Thus, any agent that effectively prevents the development of misfolded and aggregated alpha-synuclein would be a disease modifying therapeutic candidate. We examined the efficacy of sodium 4-phenylbutyric acid (PBA), one of the chemical chaperons, in transgenic (Tg) mice overexpressing human alpha-synuclein containing a double mutation (A30P + A53T). To evaluate the therapeutic efficacy, bradykinesia and motor coordination were assessed using a pole test and a rotarod treadmill task, respectively. After PBA treatment, these motor deteriorations gradually improved. In immunohistochemical examinations, both a loss of tyrosine hydroxylase-positive neurons and an increase of phosphorylated alpha-synuclein in the substantia nigra were inhibited, resulting in no depletion of the striatal dopamine content. These data suggest that PBA might be one of the therapeutic reagents for neurodegenerative disorders.

Minocycline: a neuroprotective agent for hypoxic-ischemic brain injury in the neonate?

Minocycline is a second-generation tetracycline and a potential neuroprotective intervention following brain injury. However, despite the recognized beneficial effects of minocycline in a multitude of adult disease states, the clinical application of minocycline in neonates is contentious. Tetracyclines, as a class, are not usually administered to neonates, but there is compelling evidence that minocycline reduces brain injury after neonatal hypoxic-ischemic brain injury. This Review focuses on the evidence for minocycline use in neonates by considering aspects of pharmacology, drug regimens, functional outcomes, and mechanisms of action.

Inhibition of gelatinase activity reduces neural injury in an ex vivo model of hypoxia-ischemia

Perinatal hypoxia-ischemia (H-I) often manifests as cognitive and/or motor disturbances that appear early in development. Growing evidence indicates that neuroinflammation may exacerbate H-I injury. Resident microglia release proinflammatory cytokines and proteases in response to ischemia. Matrix metalloproteinases (MMPs), in particular, activate cytokines and degrade basement membrane proteins. These actions ultimately permit entry of peripheral leukocytes into the CNS neuropil, enhancing neuroinflammation and cell death. Currently, the relative contributions of resident and peripheral immune cells to ischemic brain injury are unclear. The present study employed an ex vivo model of H-I through oxygen glucose deprivation (OGD) to identify the cellular localization of MMP-9 in organotypic hippocampal slices from rat, and to determine whether inhibiting gelatin-degrading MMPs affords neuroprotection in the absence of peripheral immune cells. Immunohistochemistry revealed ubiquitous neuronal MMP-9 expression in both normoxic and hypoxic slices. Increased MMP-9 expression was detected in CD11b-positive microglia after 48 h exposure to OGD relative to normoxic controls. Consistent with these data, in situ zymography showed increased gelatinolytic activity after OGD. Gelatin-cleaved fluorescence localized to astrocytic processes and somata of various cellular morphologies. Treatment with either the MMP inhibitor AG3340 (prinomastat) or minocycline dampened OGD-induced gelatinolytic activity and neural injury, as measured by Fluoro-Jade staining, relative to vehicle controls. These results show that resident microglia, in the absence of peripheral immune cells, were sufficient to enhance neural injury after OGD in the organotypic hippocampal slice. Additionally, these effects were associated with upregulation or secretion of MMP-9, and were blocked after treatment with either the gelatinase-selective compound AG3340 or the anti-inflammatory compound minocycline. These data, coupled with the effectiveness of these compounds previously shown in vivo, support the selective targeting of gelatin-degrading MMPs and activated microglia as potential therapeutic approaches to combat neonatal H-I injury.

Delayed administration of a matrix metalloproteinase inhibitor limits progressive brain injury after hypoxia-ischemia in the neonatal rat

Background

Hypoxia-ischemia (H-I) can produce widespread neurodegeneration and deep cerebral white matter injury in the neonate. Resident microglia and invading leukocytes promote lesion progression by releasing reactive oxygen species, proteases and other pro-inflammatory mediators. After injury, expression of the gelatin-degrading matrix metalloproteinases (MMPs), MMP-2 and MMP-9, are thought to result in the proteolysis of extracellular matrix (ECM), activation of cytokines/chemokines, and the loss of vascular integrity. Thus, therapies targeting ECM degradation and progressive neuroinflammation may be beneficial in reducing H-I – induced neuropathy. Minocycline has MMP-inhibitory properties and is both anti-inflammatory and neuroprotective. AG3340 (prinomastat) is an MMP inhibitor with high selectivity for the gelatinases. The purpose of this study was to determine whether these compounds could limit H-I – induced injury when administered at a delayed time point.

Methods

Sprague-Dawley rats were exposed to H-I at postnatal day 7 (P7), consisting of unilateral carotid artery ligation followed by 90 min exposure to 8% O₂. Minocycline, AG3340, or vehicle were administered once daily for 6 days, beginning 24 hours after insult. Animals were sacrificed at P14 for neurohistological assessments. Immunohistochemistry was performed to determine the degree of reactive astrogliosis and immune cell activation/recruitment. Neural injury was detected using the Fluoro-Jade stain, a marker that identifies degenerating cells.

Results

CD11b and glial fibrillary acidic protein (GFAP) immunopositive cells increased in ipsilateral cortex after treatment with vehicle alone, demonstrating microglia/macrophage recruitment and reactive astrogliosis, respectively. Fluoro-Jade staining was markedly increased throughout the fronto-parietal cortex, striatum and hippocampus. Treatment with minocycline or AG3340 inhibited microglia/macrophage recruitment, attenuated astrogliosis and reduced Fluoro-Jade staining when compared to vehicle alone.

Conclusion

The selective gelatinase inhibitor AG3340 showed equal efficacy in reducing neural injury and dampening neuroinflammation when compared to the anti-inflammatory compound minocycline. Thus, MMP-2 and MMP-9 may be viable therapeutic targets to treat neonatal brain injury.

Intermittent hypoxia impairs performance of adult mice in the two-way shuttle box but not in the Morris water maze

We have previously found that neonatal intermittent hypobaric hypoxia exposure enhanced mouse spatial, but impaired associative, cognition. This study sought to investigate the effects of hypobaric hypoxia on adult mice cognition. Mice were exposed to 2, 5, 10, 15, or 25 days of intermittent hypoxia (IH; 4 hr/day) at 2 km (16.0% O2) or 5 km (10.8% O2) altitudes in a hypobaric chamber for the Morris water maze (MWM) test and exposed to IH for 2, 10, or 25 days for the shuttle-box test. Amino acid dynamics in vivo in the hippocampus and amygdala of mice exposed to 2 km hypoxia were analyzed by high-pressure liquid chromatography. The results in MWM task showed that IH-2d to -25d at 2 km or 5 km did not change the escape latencies of mice in the training test or the retention of platform in the probe test. In the shuttle-box task, however, IH-10d at 5 km significantly reduced mouse avoidances in the acquisition test on day 4, and IH-10d at 2 km reduced avoidances in the retention test; IH-25d at 5 km significantly reduced avoidances of mice throughout the acquisition days. Glutamate in the amygdala persisted in declining to 69% of baseline at 8 hr posthypoxia (P = 0.040 vs. GLU released during 30 min before hypoxia) during the posthypoxia stage. These results suggest that adult hypobaric IH impairs the hippocampal-independent, but not the hippocampal-dependent, task in mice. The different GLU releases in the hippocampus and amygdala in response to hypoxia are involved in the different behaviors.

Effects of daily environmental enrichment on memory deficits and brain injury following neonatal hypoxia-ischemia in the rat

Environmental enrichment (EE) results in improved learning and spatial memory, as well as attenuates morphological changes resulting from cerebral ischemia in adult animals. This study examined the effects of daily EE on memory deficits in the water maze and cerebral damage, assessed in the hippocampus and cerebral cortex, caused by neonatal hypoxia-ischemia. Male Wistar rats in the 7th postnatal day were submitted to the Levine-Rice model of neonatal hypoxia-ischemia (HI), comprising permanent occlusion of the right common carotid artery and a period of hypoxia (90 min, 8%O(2)-92%N(2)). Starting two weeks after the HI event, animals were stimulated by the enriched environment (1h/day for 9 weeks); subsequent to the stimulation, performance of animals in the water maze was assessed. HI resulted in spatial reference and working memory impairments that were completely reversed by EE. Following the behavioral study, animals were killed and the hippocampal volume and cortical area were estimated. There was a significant reduction of both hippocampal volume and cortical area, ipsilateral to arterial occlusion, in HI animals; environmental stimulation had no effect on these morphological measurements. Presented data indicate that stimulation by the daily environmental enrichment recovers spatial memory deficits caused by neonatal hypoxia-ischemia without affecting tissue atrophy in either hippocampus or cortex.

Minocycline attenuates hypoxia-ischemia-induced neurological dysfunction and brain injury in the juvenile rat

To investigate whether minocycline provides long-lasting protection against neonatal hypoxia-ischemia-induced brain injury and neurobehavioral deficits, minocycline was administered intraperitoneally in postnatal day 4 Sprague-Dawley rats subjected to bilateral carotid artery occlusion followed by exposure to hypoxia (8% oxygen for 15 min). Brain injury and myelination were examined on postnatal day 21 (P21) and tests for neurobehavioral toxicity were performed from P3 to P21. Hypoxic-ischemic insults resulted in severe white matter injury, enlarged ventricles, deficits in the hippocampus, reduction in numbers of mature oligodendrocytes and tyrosine hydroxylase-positive neurons, damage to axons and dendrites, and impaired myelination, as indicated by the decrease in myelin basic protein immunostaining in the P21 rat brain. Hypoxic-ischemic insult also significantly affected physical development (body weight gain and eye opening) and neurobehavioral performance, including sensorimotor and locomotor function, anxiety and cognitive ability in the P21 rat. Treatments with minocycline significantly attenuated the hypoxia-ischemia-induced brain injury and improved neurobehavioral performance. The protection of minocycline was associated with its ability to reduce microglial activation. The present results show that minocycline has long-lasting protective effects in the neonatal rat brain in terms of both hypoxia-ischemia-induced brain injury and the associated neurological dysfunction.

Intrahippocampal injection of endothelin-1 in immature rats results in neuronal death, development of epilepsy and behavioral abnormalities later in life

The direct injection of endothelin-1 (ET-1) into brain parenchyma was recently suggested as a suitable model of stroke. The present study was designed to assess whether intrahippocampal injection of ET-1 in immature rats causes neurodegeneration and immediate seizures, and results in impairment of motor development, cognitive decline, epilepsy and chronic hippocampal lesion. ET-1 was injected unilaterally into the dorsal hippocampus in doses of 20 or 40 pmol at the age of 12 (P12) or 25 (P25) days. Video-electroencephalographic monitoring performed during 100 min after the injection of ET-1 demonstrated the development of convulsive epileptic seizures in 75-100% of animals of individual age-and-dose groups. Long-term behavioral follow-up did not reveal impairment of motor development in any dose-and-age group. At 2 months after ET-1 injection, impairment of spatial memory occurred only in rats with 40 pmol of ET-1 at P12. At 3 months after ET-1 injection spontaneous electrographic seizures occurred in 62.5-100% animals of both ages with no relation to the dose used. Seizures were always non-convulsive. The total seizure duration per 24 h was higher in the P12 than the P25 group, suggesting more severe epilepsy. The extent of the hippocampal lesion increased with the dose of ET-1 and was significantly higher in the P12 than the P25 group. The severity of the ET-1-induced lesion correlated positively with total seizure duration per 24 h at both ages. Our results document that early intrahippocampal injection of ET-1 results in lesion development and both immediate seizures and chronic epilepsy in either age group. Cognitive impairment occurred only in rats with ET-1 injection at P12.

Rehabilitative training tasks improve spatial learning impairment in the water maze following hypoxic-ischemic insult in neonatal rats

We recently reported that hypoxic-ischemic (HI) insult to the brain of 7-d-old rats resulted in a slowly progressive learning and memory disability, which started at around 5 wk after HI, a time frame that is representative of human adolescence. The purpose of the present study was to examine whether physical or mental exercises can prevent this late-onset, slowly progressing disability. Wistar rats were subjected to left carotid ligation followed by 2 h of hypoxic stress (8% O2 and 92% N(2) at 33 degrees C). Sham-control rats were subjected to the same procedure without ligation and hypoxic stress. Six weeks after the HI, the animals were divided into four groups: pretraining control, no training control, pretraining HI, and no training HI groups. We used the plus maze, eight-arm radial maze, and choice reaction time task as the rehabilitative training. Sixteen weeks after the HI, the water maze task was performed over 5 d to evaluate spatial learning ability; thereafter, cerebral morphology of the animals was examined. There were no differences in swimming length and latency between the pretraining control and no training control groups. Swimming length and latency in the pretraining HI group were significantly shorter and swifter than those in the no training HI group. The infarct areas on the left cerebral hemisphere were equivalent between pretraining HI and no training HI groups at each sectional slice. Rehabilitative training tasks prevented the neonatal HI-induced late-onset slowly progressive learning and memory disability.

Neonatal exposure to intermittent hypoxia enhances mice performance in water maze and 8-arm radial maze tasks

Hypoxia has generally been reported to impair learning and memory. Here we established a hypoxia-enhanced model. Intermittent hypoxia (IH) was simulated at 2 km (16.0% O2) or 5 km (10.8% O2) in a hypobaric chamber for 4 h/day from birth to 1, 2, 3, or 4 week(s), respectively. Spatial learning and memory ability was tested in the Morris water maze (MWM) task at ages of postnatal day 36 (P36)-P40 and P85-89, respectively, and in the 8-arm maze task at P60-68. The long-term potentiation (LTP), synaptic density, and phosphorylated cAMP-responsive element-binding protein (p-CREB) level in the hippocampus were measured in mice at P36 under the IH for 4 weeks (IH-4w). The results showed that IH for 3 weeks (IH-3w) and IH-4w at 2 km significantly reduced the escape latencies of mice at P36-40 in the MWM task with significantly enhanced retention, and this spatial enhancement was further confirmed by the 8-arm maze test in mice at P60-68. The improvement in MWM induced by IH-4w at 2 km was still maintained in mice at P85-89. IH-4w at 2 or 5 km significantly increased amplitude of LTP, the number of synapse, and the p-CREB level in the hippocampus of P36 mice. These results indicated that IH (4 h/day) exposure to neonatal mice at 2 km for 3 or 4 weeks enhanced mice spatial learning and memory, which was related to the increased p-CREB, LTP, and synapses of hippocampus in this model.

Short-Term Administration of a New Free Radical Scavenger, Edaravone, Is More Effective Than its Long-Term Administration for the Treatment of Neonatal Hypoxic–Ischemic Encephalopathy

BACKGROUND AND PURPOSE

Edaravone (3-methyl-1-phenyl-2-pyrazolin-5-one) is a new free radical scavenger that is used for the treatment of adult acute cerebral infarction in Japan. We examined the effect of edaravone on the optimal duration of treatment, the long-term effect on the brain, and the effect on learning and memory disability in a rat model of neonatal hypoxic-ischemic encephalopathy.

METHODS

Seven-day-old Wistar rats were subjected to left common carotid artery ligation then 2 hours of hypoxic-ischemic insult or sham operation. Edaravone was administered intraperitoneally (9 mg/kg) after hypoxic-ischemic insult every 24 hours for 2, 5, or 10 consecutive days. The neuroprotective effect of edaravone was evaluated by behavioral test and histological analysis.

RESULTS

Two-day treatment with edaravone significantly gave protection to the learning and memory capability, as well as morphological recovery compared with control rats. Five-day treatment showed morphological improvement but no behavioral improvement. In contrast, 10-day treatment did not show either morphological or behavior improvement.

CONCLUSIONS

These findings indicate that edaravone is a promising candidate as a treatment of choice for neonatal hypoxic-ischemic encephalopathy, when its use is limited to the acute phase after hypoxia-ischemia.

Erythropoietin prevents long-term sensorimotor deficits and brain injury following neonatal hypoxia-ischemia in rats

Perinatal asphyxia accounts for behavioral dysfunctions that often manifest as sensorimotor, learning or memory disabilities throughout development and into maturity. Erythropoietin (Epo) has been shown to exert neuroprotective effects in different models of brain injury including experimental models of perinatal asphyxia. However, the effect of Epo on functional abilities following cerebral hypoxia-ischemia (HI) in neonatal rats is not known. The aim of the present study is to investigate the effect of Epo on sensorimotor deficits and brain injury induced by hypoxia-ischemia. Seven-day-old rats underwent unilateral, permanent carotid artery ligation followed by 1 h of hypoxia. Epo was administered as a single dose immediately after the hypoxic insult (2000 U/kg). The neuroprotective effect of Epo was evaluated at postnatal day 42 by using a battery of behavioral tests and histological analysis. The results of the present study suggest that Epo treatment immediately after HI insult significantly facilitated recovery of sensorimotor function. Consistently, histopathological evaluation demonstrated that Epo significantly attenuated brain injury and preserved the integrity of cerebral cortex. These findings indicate that long-term neuroprotective effect of Epo on neonatal HI-induced brain injury might be associated with the preservation of sensorimotor functions.

Mechanisms of hyperbaric oxygen and neuroprotection in stroke

Cerebral vascular diseases, such as neonatal encephalopathy and focal or global cerebral ischemia, all result in reduction of blood flow to the affected regions, and cause hypoxia-ischemia, disorder of energy metabolism, activation of pathogenic cascades, and eventual cell death. Due to a narrow therapeutic window for neuroprotection, few effective therapies are available, and prognosis for patients with these neurological injuries remains poor. Hyperbaric oxygen (HBO) has been used as a primary or adjunctive therapy over the last 50 years with controversial results, both in experimental and clinical studies. In addition, the mechanisms of HBO on neuroprotection remain elusive. Early applications of HBO within a therapeutic window of 3-6h or delayed but repeated administration of HBO can either salvage injured neuronal tissues or promote neurobehavioral functional recovery. This review explores the discrepancies between experimental and clinical observations of HBO, focusing on its therapeutic window in brain injuries, and discusses the potential mechanisms of HBO neuroprotection.

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.

Hypoxic preconditioning confers long-term reduction of brain injury and improvement of neurological ability in immature rats

Exposure to preconditioning (PC) hypoxia 24 h before a severe hypoxic-ischemic (HI) insult reduces development of injury in the immature brain. Several protective regimens have proved effective in the short-term but not in the long-term perspective. The aim of the present study, therefore, was to evaluate the PC effect on long-term morphologic and neurologic outcome in the developing brain. Six-day-old rats were subjected to hypoxia (36 degrees C, 8.0% O2; PC/HI group) and sham controls to normoxia (36 degrees C; HI group) for 3 h. Twenty-four hours later, all rats were exposed to cerebral HI produced by unilateral carotid artery occlusion combined with 1 h, 15 min of hypoxia (36 degrees C, 7.7% O2). A cylinder test was used to evaluate forelimb asymmetry to determine sensorimotor function at 4, 6, and 8 wk of age. Spatial/cognitive ability was assessed by Morris water maze trials at 7 wk of recovery. Neuropathologic analysis was performed 8 wk after insult. Brain damage was reduced (p<0.0001) in PC/HI (45.0+/-11.1 mm3) in comparison with HI (159.3+/-12.2 mm3) rats. A bias for using the ipsilateral forelimb in wall movements was observed in the cylinder test in HI compared with PC/HI rats at 4 (p<0.001), 6 (p<0.01), and 8 (p<0.0001) wk of age. Results of the Morris water maze test revealed differences (p<0.0001) in average path length between groups on the third and fourth day of trials. Hypoxic PC before HI reduced brain injury by 72% at 8 wk after the insult and provided long-term improvement of sensorimotor and spatial/cognitive functions.

Auditory processing deficits in rats with neonatal hypoxic-ischemic injury

Hypoxia-ischemia (HI) refers to reduced blood oxygenation and/or a diminished amount of blood perfusing the brain, and is associated with premature birth/very low birth weight (VLBW). HI represents a common cause of injury to the perinatal brain. Indeed, a significant number of premature/VLBW infants go on to demonstrate cognitive/behavioral deficits, with particularly high incidence of disruptions in language development. Auditory processing deficits, in turn, have been suggested to play a causal role in the development of language impairments. Specifically, the inability to identify fast elements in speech is purported to exert cascading detrimental effects on phonological discrimination, processing, and identification. Based on this convergent evidence, the current studies address auditory processing evaluation in a rodent model of HI injury induced on postnatal days 1, 7, or 10 (which in turn is well accepted as modeling HI-related injury to the perinatal human). Induced injuries were followed by a battery of auditory testing, and a spatial maze assessment, performed both during juvenile and adult periods. Results indicate that rats suffering from these early HI insults performed significantly worse than shams on tasks requiring rapid auditory processing, and on a test of spatial learning (Morris water maze (MWM)), although these effects were not seen on simpler versions of auditory tasks or on a water escape assessment (thus ruling out hearing/motor impairments). Correlations were found between performance on rapid auditory and spatial behavioral tasks and neuroanatomical measures for HI animals such as: the volume of the hippocampus, cerebral cortex, ventricles, and/or the area of the corpus callosum. Cumulative findings suggest that perinatal HI injury in the rat may lead to neurodevelopmental damage associated, in turn, with auditory processing and/or learning and memory impairments. As such, the current model may have critical implications for the study of neurophysiological underpinnings of cognitive deficits in premature/VLBW infants.

Effects of sensorimotor restriction and anoxia on gait and motor cortex organization: implications for a rodent model of cerebral palsy

Chronic or acute perinatal asphyxia (PA) has been correlated with the subsequent development of cerebral palsy (CP), a developmental neurological disorder characterized by spasticity and motor abnormalities often associated with cognitive deficits. Despite the prevalence of CP, an animal model that mimics the lifetime hypertonic motor deficits is still not available. In the present study, the consequences of PA on motor behavior, gait and organization of the primary motor cortex were examined in rats, and compared with the behavioral and neurological consequences of early postnatal movement-restriction with or without oxygen deprivation. Rats subjected to PA had mild increases in muscular tone accompanied by subtle differences in walking patterns, paralleled by significantly altered but relatively modest disorganization of their primary motor cortices. Movement-restricted rats, suffering PA or not, had reduced body growth rate, markedly increased muscular tone at rest and with active flexion and extension around movement-restricted joints that resulted in abnormal walking patterns and in a profoundly distorted representation of the hind limbs in the primary motor cortex. Within the sensorimotor-restricted groups, non-anoxic rats presented the most abnormal pattern and the greatest cortical representational degradation. This outcome further supports the argument that PA per se may represent a substrate for subtle altered motor behaviors, and that PA alone is sufficient to alter the organization of the primary motor cortex. At the same time, they also show that early experience-dependent movements play a crucial role in shaping normal behavioral motor abilities, and can make a powerful contribution to the genesis of aberrant movement abilities.

Hypoxia-ischemic insult in neonatal rats induced slowly progressive brain damage related to memory impairment

The present study was designed to determine potential associations between the brain damage induced by hypoxic-ischemic (HI) insult and spatial learning impairment in an eight-arm radial maze task. We first determined the pathological outcomes after 2, 5, 9, and 17 weeks of recovery following the HI insult. The results show that the brain damage progressed from 2 up to 17 weeks of recovery. To clarify the time course of the brain damage changes, we investigated the histological changes of the same individual with magnetic resonance imaging (MRI) after 5, 9, and 57 weeks of recovery following the HI insult. The MRI changes were similar to the histological changes, and the brain damages were exacerbated in the contralateral hemisphere after 57 weeks of recovery following the HI insult. To investigate whether alteration in brain function was correlated with MRI and histological changes, the rats were made to find their way through an eight-arm radial maze was performed at either 7th or 16th weeks of recovery. According to the results, the spatial learning impairments of rats in the maze starting at 16 weeks of recovery were more severe than those at 7 weeks of recovery, indicating that the impairments were progressive and depended on the degree of brain damage. The results of the present study are the first demonstration that the evolutional and specific brain damage following the HI insult is slowly and progressively exacerbated to the contralateral hemisphere and rats who experience the HI are at risk for showing a late impairment of brain function.

Combination treatment of neonatal rats with hypoxia-ischemia and endotoxin induces long-lasting memory and learning impairment that is associated with extended cerebral damage

OBJECTIVE

We assessed the long-term effects of perinatal hypoxia-ischemia and endotoxin on attention and short- and long-term memory in neonatal rats with the use of behavioral tasks and brain histologic results.

STUDY DESIGN

Four hours after injections of lipopolysaccharide (1 mg/kg, intraperitoneally) or saline solution, 7-day-old Wistar rat pups were subjected to unilateral hypoxia-ischemia for 1 hour. We studied 4 groups: controls (n = 43 rats), lipopolysaccharide alone (n = 12 rats), hypoxia-ischemia alone (n = 29 rats), and combined lipopolysaccharide + hypoxia-ischemia treatment (n = 34 rats). Seven to 16 weeks after the treatment, we measured attention with a choice reaction time task, short-term memory with an 8-arm radial maze task, and long-term memory with a water maze task. At 19 weeks of age, the brain was removed, fixed, and sectioned coronally; and the volume of each part was measured.

RESULTS

A loss of volume in the hippocampus was observed in the lipopolysaccharide, hypoxia-ischemia, and lipopolysaccharide + hypoxia-ischemia groups; a loss of striatum was observed in the hypoxia-ischemia and lipopolysaccharide + hypoxia-ischemia groups, but loss of cortex was observed only in the lipopolysaccharide + hypoxia-ischemia group. The lipopolysaccharide, hypoxia-ischemia, and lipopolysaccharide + hypoxia-ischemia groups showed significantly poorer performance (attention deficit) than controls in the choice reaction time task. Correct choices decreased, and error increased in the lipopolysaccharide + hypoxia-ischemia group compared with the other groups in the radial maze task, which shows short-term memory impairment. Swimming distance was significantly greater in the hypoxia-ischemia and lipopolysaccharide + hypoxia-ischemia groups than in the other 2 groups in the water maze test, which shows long-term memory impairment.

CONCLUSION

Combined lipopolysaccharide and hypoxia-ischemia treatment synergistically induced short-term memory impairment that is associated with loss of cortical volume.

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.

Late Measures of Brain Injury After Neonatal Hypoxia–Ischemia in Mice

BACKGROUND AND PURPOSE

This work was undertaken to determine to what degree long-term neurofunctional outcome of neonatal hypoxic-ischemic (HI) brain injury in mice correlates with anatomical extent of cerebral damage assessed by magnetic resonance imaging (MRI) and histopathology.

METHODS

On postnatal day 7, mice were subjected to HI. At 7 to 9 weeks after HI neurofunctional outcome was assessed by water-maze, rota-rod, and open-field test performance, followed by cerebral MRI and histopathology evaluation.

RESULTS

At 10 weeks after HI, MRI revealed ipsilateral brain atrophy alone or with porencephalic cyst formation and contralateral ventriculomegaly. Adult HI-affected mice, especially those that developed a porencephalic cyst, demonstrated significant neurofunctional deficit compared with age-matched naïve mice. HI-affected mice with ipsilateral cerebral atrophy but without porencephaly demonstrated no or an intermediate level of neurofunctional deficit. Neurobehavioral assessment of mice subjected to HI insult revealed a strong correlation between degree of brain injury and functional neurohandicap.

CONCLUSIONS

This is the first study to demonstrate that long-term neurofunctional outcome in mice after a neonatal HI correlates tightly with anatomical pattern/extent of cerebral damage, defined by MRI and histopathology.

Characteristics of behavioral abnormalities in α1d-adrenoceptors deficient mice

To investigate the functional role of alpha1d-adrenergic receptor (alpha1d-AR) in the CNS, we have generated mutant mice lacking the alpha1d-AR using a gene targeting approach and examined in detail the effects of alpha1d-AR knockout mice on motor function, sensory function, and learning and memory. alpha1d-AR knockout mice showed better motor coordination at the highest rotating speed of the rotarod performance and stronger muscle tone using the traction meter, but their locomotor activity and swimming ability in the water maze were not affected. In the water maze requiring reference memory, alpha1d-AR knockout mice showed normal spatial learning. In the Y-maze task requiring working memory or attention, alpha1d-AR knockout mice displayed an impaired spontaneous alternation performance. The alpha1d-AR knockout mice tended to display lower levels of acoustic startle responses than the wild-type group at lower pulse intensities, although the acoustic prepulse inhibition was not impaired in the alpha1d-AR knockout mice. Furthermore, the NMDA receptor antagonist, MK-801-induced deficits of acoustic prepulse inhibition were not observed in the alpha1d-AR knockout mice. These results clearly demonstrate that the alpha1d-AR receptor plays an important role in the process of auditory sensory function, attention or working memory rather than reference memory, and the sensorimotor gating deficits induced by the NMDA receptor antagonist.

V1a receptor knockout mice exhibit impairment of spatial memory in an eight-arm radial maze

In this study, we examined the performance of vasopressin V1a receptor (V1aR) and vasopressin V1b receptor (V1bR) knockout (KO) mice compared to wild-type (WT) mice in an eight-arm radial maze. V1aR KO mice exhibited an impairment of spatial memory in comparison to WT mice. By contrast, we did not observe any significant differences between the V1bR KO mice and the WT mice in the eight-arm radial maze. Moreover, OPC-21268, a selective V1aR antagonist, impaired spatial memory in the eight-arm radial maze in WT mice characterized by an increased number of errors. These results suggest that the V1aR controls spatial memory in mice.

Brain injury and neurofunctional deficit in neonatal mice with hypoxic-ischemic encephalopathy

Birth asphyxia accounts for the majority of developmental motor and cognitive deficits. Studies were undertaken to develop a reproducible murine model of perinatal hypoxic-ischemic encephalopathy (HIE) which would permit both anatomic and neurofunctional quantification of injury. Short-term neurofunctional outcomes consisted of three developmental reflexes (righting, cliff aversion and geotaxis) assessed in 7-day-old mouse pups 24 h after unilateral carotid artery ligation followed by inhalation of 8% oxygen. Cerebral infarct volume was dependent on duration of hypoxia, being approximately 2.5-fold greater with longer (60 min) versus shorter (30 min) hypoxia exposure (P=0.001). All three sensorimotor neonatal reflexes assessed at 24 h after HIE injury correlated significantly with long-term neurofunction evaluated using a water-maze test of navigational learning and memory assessed 8 weeks later in the same animals. Cerebral atrophy, a delayed consequence of HIE in this model, also correlated strongly with water-maze performance (r=0.86, P=0.002). These data demonstrate for the first time that murine neonatal sensorimotor reflex performance can be rigorously quantified in the acute phase of perinatal HIE and has strong predictive value not only for anatomic extent of cerebral injury, but also for long-term neurofunctional outcome.

Magnetic resonance imaging shows delayed ischemic striatal neurodegeneration

Brief focal ischemia leading to temporary neurological deficits induces delayed hyperintensity on T1-weighted magnetic resonance imaging (MRI) in the striatum of humans and rats. The T1 hyperintensity may stem from biochemical alterations including manganese (Mn) accumulation after ischemia. To clarify the significance of this MRI modification, we investigated the changes in the dorsolateral striatum of rats from 4 hours through 16 weeks after a 15-minute period of middle cerebral artery occlusion (MCAO), for MRI changes, Mn concentration, neuronal number, reactivities of astrocytes and microglia/macrophages, mitochondrial Mn-superoxide dismutase (Mn-SOD), glutamine synthetase (GS), and amyloid precursor protein. The cognitive and behavioral studies were performed in patients and rats and compared with striatal T1 hyperintensity to show whether alteration in brain function correlated with MRI and histological changes. The T1-weighted MRI signal intensity of the dorsolateral striatum increased from 5 days to 4 weeks after 15-minute MCAO, and subsequently decreased until 16 weeks. The Mn concentration of the dorsolateral striatum increased after ischemia in concert with induction of Mn-SOD and GS in reactive astrocytes. The neuronal survival ratio in the dorsolateral striatum decreased significantly from 4 hours through 16 weeks, accompanied by extracellular amyloid precursor protein accumulation and chronic glial/inflammatory responses. The patients and rats with neuroradiological striatal degeneration had late-onset cognitive and/or behavioral declines after brief focal ischemia. This study suggests that (1) the hyperintensity on T1-weighted MRI after mild ischemia may involve tissue Mn accumulation accompanied by Mn-SOD and GS induction in reactive astrocytes, (2) the MRI changes correspond to striatal neurodegeneration with a chronic inflammatory response and signs of oxidative stress, and (3) the subjects with these MRI changes are at risk for showing a late impairment of brain function even though the transient ischemia is followed by total neurological recovery.

Neonatal cerebral hypoxia-ischemia causes lateralized memory impairments in the adult rat

Neonatal hypoxia-ischemia (HI) has been extensively studied in a rat model characterized by unilateral brain damage (Rice-Vannucci Model). However, as well as in humans, each rat brain hemisphere is distinctly involved in cognitive functions, as for example retrieval of emotionally based memory, and neurochemical asymmetries have been described. In this paper we investigated whether hypoxia-ischemia could cause distinct cognitive deficits depending on which hemisphere is damaged. Seven-day-old male Wistar rats were submitted to permanent occlusion of left or right common carotid artery and were exposed to a mixture of 8% oxygen-92% nitrogen for 2.5 h. On adulthood, these rats were trained in step-down inhibitory avoidance and in two tasks in the Morris water maze. Both experimental groups (right and left lesioned) showed a deficit of retrieval in the inhibitory avoidance task compared to controls, although rats with right hemisphere lesion showed a significantly greater deficit than the left damaged group (P<0.05). In the Morris maze, both damaged groups presented cognitive deficits in the reference memory task (P<0.05), however only the right damaged group had an impairment in the working memory task. Brain coronal areas, at levels +1.20 and -3.30 mm from bregma of both HI groups were smaller than those of control, with no differences between the right and left damaged groups (P<0.05). These results show that cerebral hypoxia-ischemia in neonatal rats causes asymmetric behavioral outcomes depending on which of the hemispheres is lesioned and support the hypothesis of lateralization of cognitive functions in the rodent brain.

The pharmacological characterization of attentional processes using a two-lever choice reaction time task in rats

Activating the noradrenergic and cholinergic systems is known to enhance attentional processes, while stimulating dopaminergic, serotonergic, and GABAergic systems suppresses them. The objective of the present study was to investigate the pharmacological characterization in the attentional processes of a two-lever choice reaction time (CRT) task using different centrally acting drugs. We designed seven parameters in this task: the correct response (CR) rate; error response rate; nonresponse (NR) rate; differential reinforcement of other behavior (DRO) responses; number of incorrect lever pressings during both the intertrial interval and DRO periods; the mean CRT of CR; and activity during 30 trials. The compounds produced different profiles at each dose. 1) Facilitative and disruptive effects on attentional processes occurred with changes in CRT alone. Scopolamine (0.1 mg/kg) and prazosin (0.3-1 mg/kg) prolonged the CRT, whereas methamphetamine (0.3 mg/kg) shortened the CRT. 2) Attentional deficits occurred with abnormal behavior showing premature response or perseverative behavior. Scopolamine (0.2-1 mg/kg), methamphetamine (3 mg/kg), delta(9)-tetrahydrocannabinol (10 mg/kg), and MK-801 (0.1-0.3 mg/kg) produced a marked increase in the number of total lever pressings. 3) Motor function deficits rather than attentional deficits occurred. 8-OH DPAT (1 mg/kg) and muscimol (1 mg/kg) produced a decrease in CR and an increase in NR with a marked decrease in activity and prolonged the CRT. Activating noradrenergic alpha(1) receptors was found to enhance the attentional processes, while blocking muscarinic receptors, alpha(1) receptors, and NMDA receptors, and stimulating cannabinoid receptors and the dopaminergic systems impaired the attentional processes in the two-lever CRT task.

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

We examined for 18 weeks the effect of dexamethasone treatment on learning and memory impairment produced by hypoxic-ischemic stress at postnatal day 7 in rat in addition to brain histological study. Dexamethasone of 0.5 mg/kg was injected i.p. 4 h before hypoxic-ischemic stress, in which the left carotid artery was ligated followed by 2 h hypoxia (8% oxygen). Dexamethasone treatment improved behavior in each learning task: in choice reaction time tasks relating to the attention process, in 8-arm radial maze task examining working and reference memory, and in water maze task relating to reference memory. Improvement to the extent of the sham-control level was observed. Dexamethasone treatment also completely prevented histological brain damage. No adverse effect in learning and memory tests was observed in the animals treated with dexamethasone without hypoxic-ischemic stress. It is concluded that dexamethasone treatment is significantly effective in prevention not only of histological brain damage but also of learning and memory impairment occasioned by subsequent hypoxic-ischemic insult, warranting further clinical investigation.

Hyperbaric oxygenation prevented brain injury induced by hypoxia-ischemia in a neonatal rat model

The occurrence of hypoxia-ischemia (HI) during early fetal or neonatal stages of an individual leads to the damaging of immature neurons resulting in behavioral and psychological dysfunctions, such as motor or learning disabilities, cerebral palsy, epilepsy or even death. No effective treatment is currently available and this study is the first to use hyperbaric oxygen (HBO) as a treatment for neonatal HI. Herein, we sought out to determine if HBO is able to offer neuroprotectivity against an HI insult. Seven-day-old rat pups were subjected to unilateral carotid artery ligation followed by 2.5 h of hypoxia (8% O(2) at 37 degrees C). HBO treatment was administered by placing pups in a chamber (3 ATA for 1 h) 1 h after hypoxia exposure. Brain injury was assessed based on ipsilateral hemispheric weight divided by contralateral hemispheric weight, light microscopy, and EM. Sensorimotor functional tests were administered at 5 weeks after hypoxia exposure. After HI, the ipsilateral hemisphere was 52.65 and 57.64% (P<0.001) of the contralateral hemisphere at 2 and 6 weeks, respectively. In HBO treated groups, the ipsilateral hemisphere was 77.77 and 84.19% (P<0.001) at 2 and 6 weeks. There was much less atrophy and apoptosis in HBO treated animals under light or electron microscopy. Sensorimotor function was also improved by HBO at 5 weeks after hypoxia exposure (Chi-square, P<0.050). The results suggest that HBO is able to attenuate the effects of HI on the neonatal brain by reducing the progression of neuronal injury and increasing sensorimotor function.

Huperzine A attenuates cognitive deficits and brain injury in neonatal rats after hypoxia-ischemia

The protective effects of huperzine A, a novel acetylcholinesterase inhibitor, on hypoxic-ischemic (HI) brain injury were investigated in neonatal rats. A unilateral HI brain injury was produced by the ligation of left common carotid artery followed by 1 h hypoxia with 7.7% oxygen in 7-day-old rat pups. After 5 weeks, HI brain injury in rat pups resulted in working memory impairments shown by increased escape latency in a water maze and reduced time spent in the target quadrant. The combination of common carotid artery ligation and exposure to a hypoxic environment caused the damage in the striatum, cortex, and hippocampus in the ipsilateral hemisphere, and the neuronal loss in the CA1 region. Huperzine A was administrated daily at the dose of 0.05 or 0.1 mg/kg i.p. for 5 weeks after HI injury. The significant protection against HI injury on behavior and neuropathology was produced by huperzine A at the dose of 0.1 mg/kg. These findings suggest that huperzine A might be beneficial in the treatment of hypoxic-ischemic encephalopathy in neonates.