The stress of being restrained reduces brain damage after a hypoxic-ischaemic insult in the 7-day-old rat

Neuroprotective efficacy of hypothermia and Inter-alpha Inhibitor Proteins after hypoxic ischemic brain injury in neonatal rats

Therapeutic hypothermia is the standard of care for hypoxic-ischemic (HI) encephalopathy. Inter-alpha Inhibitor Proteins (IAIPs) attenuate brain injury after HI in neonatal rats. Human (h) IAIPs (60 ​mg/kg) or placebo (PL) were given 15 ​min, 24 and 48 ​h to postnatal (P) day-7 rats after carotid ligation and 8% oxygen for 90 ​min with (30 ​°C) and without (36 ​°C) exposure to hypothermia 1.5 ​h after HI for 3 ​h. Hemispheric volume atrophy (P14) and neurobehavioral tests including righting reflex (P8-P10), small open field (P13-P14), and negative geotaxis (P14) were determined. Hemispheric volume atrophy in males was reduced (P ​< ​0.05) by 41.9% in the normothermic-IAIP and 28.1% in the hypothermic-IAIP compared with the normothermic-PL group, and in females reduced (P ​< ​0.05) by 30.3% in the normothermic-IAIP, 45.7% in hypothermic-PL, and 55.2% in hypothermic-IAIP compared with the normothermic-PL group after HI. Hypothermia improved (P ​< ​0.05) the neuroprotective effects of hIAIPs in females. The neuroprotective efficacy of hIAIPs was comparable to hypothermia in female rats (P ​= ​0.183). Treatment with hIAIPs, hypothermia, and hIAIPs with hypothermia decreased (P ​< ​0.05) the latency to enter the peripheral zone in the small open field test in males. We conclude that hIAIPs provide neuroprotection from HI brain injury that is comparable to the protection by hypothermia, hypothermia increases the effects of hIAIPs in females, and hIAIPs and hypothermia exhibit some sex-related differential effects.

Inter-Alpha Inhibitor Proteins Modify the Microvasculature after Exposure to Hypoxia-Ischemia and Hypoxia in Neonatal Rats

Microvasculature develops during early brain development. Hypoxia-ischemia (HI) and hypoxia (H) predispose to brain injury in neonates. Inter-alpha inhibitor proteins (IAIPs) attenuate injury to the neonatal brain after exposure to HI. However, the effects of IAIPs on the brain microvasculature after exposure to HI have not been examined in neonates. Postnatal day-7 rats were exposed to sham treatment or right carotid artery ligation and 8% oxygen for 90 min. HI comprises hypoxia (H) and ischemia to the right hemisphere (HI-right) and hypoxia to the whole body, including the left hemisphere (H-left). Human IAIPs (hIAIPs, 30 mg/kg) or placebo were injected immediately, 24 and 48 h after HI/H. The brains were analyzed 72 h after HI/H to determine the effects of hIAIPs on the microvasculature by laminin immunohistochemistry and calculation of (1) the percentage area stained by laminin, (2) cumulative microvessel length, and (3) density of tunneling nanotubes (TNTs), which are sensitive indicators of the earliest phases of neo-vascularization/collateralization. hIAIPs mainly affected the percent of the laminin-stained area after HI/H, cumulative vessel length after H but not HI, and TNT density in females but not males. hIAIPs modify the effects of HI/H on the microvasculature after brain injury in neonatal rats and exhibit sex-related differential effects. Our findings suggest that treatment with hIAIPs after exposure to H and HI in neonatal rats affects the laminin content of the vessel basal lamina and angiogenic responses in a sex-related fashion.

Restraint stress during neonatal hypoxia-ischemia alters brain injury following normothermia and hypothermia

Rodent models of neonatal hypoxic-ischemic (HI) injury require a subset of animals to be immobilized for continuous temperature monitoring during the insult and subsequent treatment. Restrained animals are discarded from the analysis due to the effect of restraint on the brain injury as first demonstrated by Thoresen et al 1996. However, the effects of restraint on responses to hypothermic (HT) post-insult therapy are not well described. We examine the effects of restraint associated with different probe placements on HI brain injury. We have conducted a meta-analysis of 23 experiments comparing probe rats (skin n = 42, rectal n = 35) and free-moving matched non-probe controls (n = 80) that underwent HI injury (left common carotid artery ligation and 90 min 8% O₂ ) at postnatal day 7 (P7), followed by 5 h of NT (37°C) or HT (32°C). On P14, brain regions were analyzed for injury (by neuropathology and area loss), microglial reactivity and brain-derived neurotrophic factor (BDNF). HI injury was mitigated in NT skin and rectal probe rats, with greater neuroprotection among the rectal probe rats. Following HT, the skin probe rats maintained the restraint-associated neuroprotection, while brain injury was significantly exacerbated among the rectal probe rats. Microglial reactivity strongly correlated with the acquired injury, with no detectable difference between the groups. Likewise, we observed no differences in BDNF signal intensity. Our findings suggest a biphasic neuroprotection from restraint stress, which becomes detrimental in combination with HT and the presumed discomfort from the rectal probe. This finding is useful in highlighting unforeseen effects of common experimental designs or routine clinical management.

Inter-alpha Inhibitor Proteins Ameliorate Brain Injury and Improve Behavioral Outcomes in a Sex-Dependent Manner After Exposure to Neonatal Hypoxia Ischemia in Newborn and Young Adult Rats

Hypoxic-ischemic (HI) brain injury is a major contributor to neurodevelopmental morbidities. Inter-alpha inhibitor proteins (IAIPs) have neuroprotective effects on HI-related brain injury in neonatal rats. However, the effects of treatment with IAIPs on sequential behavioral, MRI, and histopathological abnormalities in the young adult brain after treatment with IAIPs in neonates remain to be determined. The objective of this study was to examine the neuroprotective effects of IAIPs at different neurodevelopmental stages from newborn to young adults after exposure of neonates to HI injury. IAIPs were given as 11-sequential 30-mg/kg doses to postnatal (P) day 7-21 rats after right common carotid artery ligation and exposure to 90 min of 8% oxygen. The resulting brain edema and injury were examined by T2-weighted magnetic resonance imaging (MRI) and cresyl violet staining, respectively. The mean T2 values of the ipsilateral hemisphere from MRI slices 6 to 10 were reduced in IAIP-treated HI males + females on P8, P9, and P10 and females on P8, P9, P10, and P14. IAIP treatment reduced hemispheric volume atrophy by 44.5 ± 29.7% in adult male + female P42 rats and improved general locomotor abilities measured by the righting reflex over time at P7.5, P8, and P9 in males + females and males and muscle strength/endurance measured by wire hang on P16 in males + females and females. IAIPs provided beneficial effects during the learning phase of the Morris water maze with females exhibiting beneficial effects. IAIPs confer neuroprotection from HI-related brain injury in neonates and even in adult rats and beneficial MRI and behavioral benefits in a sex-dependent manner.

The deleterious effect of crossfostering in rat pups on hypoxic-ischemic injury tolerance and hypothermic neuroprotection

We study the effect of hypothermia (HT) following hypoxic-ischemic (HI) brain injury in postnatal day 7 (P7) rats. In 2015, new European Union animal transport regulations prompted a change in practice at the breeding facility, which henceforth crossfostered P3 litters to P8 older lactating dam prior to transportation. It is generally assumed that crossfostering does not significantly affect the experimental results. The aim of this study was to examine whether crossfostering affects our model consistency by modifying injury susceptibility and hypothermic neuroprotection. We analysed 219 pups (56 litters) from 11 experiments conducted between 2013 and 2015: 73 non-crossfostered and 146 crossfostered pups. At P7, all pups underwent unilateral common carotid artery ligation followed by 50min of hypoxia (8% O2, 36°C). Immediately after this mild insult, the pups were randomised to post-insult normothermia (NT) or HT treatment. Pups were culled at P14. Injury was assessed by area loss of the ipsilateral hemisphere and histopathology scoring of hippocampus, cortex, thalamus, and basal ganglia. Crossfostered pups had double the injury compared to non-crossfostered pups irrespective of treatment group. Hypothermic neuroprotection was statistically significant, but with a smaller and less consistent effect in crossfostered pups (relative neuroprotection 16% vs. 31% in non-crossfostered). These results demonstrate hypothermic neuroprotection following a mild HI insult. A representative subset of 41 animals were also assessed for evidence of microglial reactivity, however no detectable difference in microglial reactivity was observed between any of the groups. In conclusion, crossfostering alters outcomes in our established model through reduced insult tolerance and variable neuroprotection. Crossfostering as a common breeding practice is a largely unexplored variable in animal research that may result in invalid research conclusions if inadequately adjusted for by larger group sizes. As a result, crossfostering is likely to be inconsistent with the principles of replacement, reduction, and refinement.

Pharmacokinetics of Inter-Alpha Inhibitor Proteins and Effects on Hemostasis After Hypoxic-Ischemic Brain Injury in Neonatal Rats

BACKGROUND

Hypoxic-ischemic (HI) brain injury is a leading cause of long-term neurodevelopmental morbidities in neonates. Human plasma-derived Inter-Alpha Inhibitor Proteins (hIAIPs) are neuroprotective after HI brain injury in neonatal rats. The light chain (bikunin) of hIAIPs inhibits proteases involved in the coagulation of blood. Newborns exposed to HI can be at risk for significant bleeding in the brain and other organs.

OBJECTIVE

The objectives of the present study were to assess the pharmacokinetics (PK) and the duration of bleeding after intraperitoneal (IP) administration of hIAIPs in HI-exposed male and female neonatal rats.

METHODS

HI was induced with the Rice-Vannucci method in postnatal (P) day-7 rats. After the right common carotid artery ligation, rats were exposed to 90 min of 8% oxygen. hIAIPs (30 mg/kg, IP) were given immediately after Sham or HI exposure in the PK study and serum was collected 1, 6, 12, 24, or 36 h after the injections. Serum hIAIP concentrations were measured with a competitive ELISA. ADAPT5 software was used to fit the pooled PK data considering first-order absorption and disposition. hIAIPs (60 mg/kg, IP) were given in the bleeding time studies at 0, 24 and 48 h after HI with tail bleeding times measured 72 h after HI.

RESULTS

IP administration yielded significant systemic exposure to hIAIPs with PK being affected markedly including primarily faster absorption and reduced elimination as a result of HI and modestly of sex-related differences. hIAIP administration did not affect bleeding times after HI.

CONCLUSION

These results will help to inform hIAIP dosing regimen schedules in studies of neuroprotection in neonates exposed to HI.

Effects of inter-alpha inhibitor proteins on brain injury after exposure of neonatal rats to severe hypoxia-ischemia

Hypoxic-ischemic (HI) brain injury is one of the most common neurological problems occurring in premature and full-term infants after perinatal complications. Hypothermia is the only treatment approved for HI encephalopathy in newborns. However, this treatment is only partially protective, cannot be used to treat premature infants, and has limited efficacy to treat severe HI encephalopathy. Inflammation contributes to the evolution of HI brain injury in neonates. Inter-alpha Inhibitor Proteins (IAIPs) are immunomodulatory proteins that have neuroprotective properties after exposure to moderate HI in neonatal rats. The objective of the current study was to determine the neuroprotective efficacy of treatment with IAIPs starting immediately after or with a delay of one hour after exposure to severe HI of 120 min duration. One hundred and forty-six 7-day-old rat pups were randomized to sham control, HI and immediate treatment with IAIPs (60 mg/kg) or placebo (PL), and sham, HI and delayed treatment with IAIPs or PL. IAIPs or PL were given at zero, 24, and 48 h after HI or 1, 24 and 48 h after HI. Total brain infarct volume was determined 72 h after exposure to HI. Treatment with IAIPs immediately after HI decreased (P < 0.05) infarct volumes by 58.0% and 44.5% in male and female neonatal rats, respectively. Delayed treatment with IAIPs after HI decreased (P < 0.05) infarct volumes by 23.7% in male, but not in female rats. We conclude that IAIPs exert neuroprotective effects even after exposure to severe HI in neonatal rats and appear to exhibit some sex-related differential effects.

Variability and sex-dependence of hypothermic neuroprotection in a rat model of neonatal hypoxic-ischaemic brain injury: a single laboratory meta-analysis

Therapeutic hypothermia (HT) is standard care for term infants with hypoxic–ischaemic (HI) encephalopathy. However, the efficacy of HT in preclinical models, such as the Vannucci model of unilateral HI in the newborn rat, is often greater than that reported from clinical trials. Here, we report a meta-analysis of data from every experiment in a single laboratory, including pilot data, examining the effect of HT in the Vannucci model. Across 21 experiments using 106 litters, median (95% CI) hemispheric area loss was 50.1% (46.0–51.9%; n = 305) in the normothermia group, and 41.3% (35.1–44.9%; n = 317) in the HT group, with a bimodal injury distribution. Median neuroprotection by HT was 17.6% (6.8–28.3%), including in severe injury, but was highly-variable across experiments. Neuroprotection was significant in females (p < 0.001), with a non-significant benefit in males (p = 0.07). Animals representing the median injury in each group within each litter (n = 277, 44.5%) were also analysed using formal neuropathology, which showed neuroprotection by HT throughout the brain, particularly in females. Our results suggest an inherent variability and sex-dependence of the neuroprotective response to HT, with the majority of studies in the Vannucci model vastly underpowered to detect true treatment effects due to the distribution of injury.

Neuroprotective exendin-4 enhances hypothermia therapy in a model of hypoxic-ischaemic encephalopathy

Hypoxic-ischaemic encephalopathy remains a global health burden. Despite medical advances and treatment with therapeutic hypothermia, over 50% of cooled infants are not protected and still develop lifelong neurodisabilities, including cerebral palsy. Furthermore, hypothermia is not used in preterm cases or low resource settings. Alternatives or adjunct therapies are urgently needed. Exendin-4 is a drug used to treat type 2 diabetes mellitus that has also demonstrated neuroprotective properties, and is currently being tested in clinical trials for Alzheimer's and Parkinson's diseases. Therefore, we hypothesized a neuroprotective effect for exendin-4 in neonatal neurodisorders, particularly in the treatment of neonatal hypoxic-ischaemic encephalopathy. Initially, we confirmed that the glucagon like peptide 1 receptor (GLP1R) was expressed in the human neonatal brain and in murine neurons at postnatal Day 7 (human equivalent late preterm) and postnatal Day 10 (term). Using a well characterized mouse model of neonatal hypoxic-ischaemic brain injury, we investigated the potential neuroprotective effect of exendin-4 in both postnatal Day 7 and 10 mice. An optimal exendin-4 treatment dosing regimen was identified, where four high doses (0.5 µg/g) starting at 0 h, then at 12 h, 24 h and 36 h after postnatal Day 7 hypoxic-ischaemic insult resulted in significant brain neuroprotection. Furthermore, neuroprotection was sustained even when treatment using exendin-4 was delayed by 2 h post hypoxic-ischaemic brain injury. This protective effect was observed in various histopathological markers: tissue infarction, cell death, astrogliosis, microglial and endothelial activation. Blood glucose levels were not altered by high dose exendin-4 administration when compared to controls. Exendin-4 administration did not result in adverse organ histopathology (haematoxylin and eosin) or inflammation (CD68). Despite initial reduced weight gain, animals restored weight gain following end of treatment. Overall high dose exendin-4 administration was well tolerated. To mimic the clinical scenario, postnatal Day 10 mice underwent exendin-4 and therapeutic hypothermia treatment, either alone or in combination, and brain tissue loss was assessed after 1 week. Exendin-4 treatment resulted in significant neuroprotection alone, and enhanced the cerebroprotective effect of therapeutic hypothermia. In summary, the safety and tolerance of high dose exendin-4 administrations, combined with its neuroprotective effect alone or in conjunction with clinically relevant hypothermia make the repurposing of exendin-4 for the treatment of neonatal hypoxic-ischaemic encephalopathy particularly promising.

Rectal temperature in the first five hours after hypoxia-ischemia critically affects neuropathological outcomes in neonatal rats

BackgroundHyperthermia after hypoxia-ischemia (HI) in newborn infants is associated with worse neurological outcomes. Loss of thermoregulation may also be associated with greater injury.MethodsIn the postnatal-day 7 (P7) rat, the effect of 5 h of graded hyperthermia (38 °C or 39 °C) immediately after unilateral HI was compared with normothermia (NT, 37 °C) and therapeutic hypothermia (TH, 32 °C). Early (negative geotaxis) and late (staircase test) behavioral testing was performed, as well as neuropathology scoring in adulthood. Separately, P7 rats were exposed to HI, and individual nesting temperatures were monitored before analysis of neuropathology at P14.ResultsMortality increased as temperature was increased from 38 °C (0%) to 39 °C (50%) after HI. Hyperthermia also resulted in early behavioral deficits compared with NT. In adulthood, pathology scores in the thalamus, basal ganglia, cortex, and hippocampus increased as post-hypoxic temperature increased above NT. Significant global neuroprotection was seen in the TH group. However, no significant difference was seen between HI groups in the staircase test. One hour after HI, the core temperature of pups was inversely correlated with global pathology scores at P14.ConclusionEarly temperature is a significant determinant of injury after experimental HI. Spontaneous decreases in core temperature after HI may confound neuroprotection studies.

Vitamin D improves functional outcomes in neonatal hypoxic ischemic male rats treated with N-acetylcysteine and hypothermia

Hypothermia treatment neuroprotects approximately 50% of neonates who present with moderate to severe hypoxic ischemic encephalopathy (HIE). N-acetylcysteine (NAC), a potent antioxidant, is neuroprotective in combination with hypothermia in neonatal hypoxia-ischemia (HI) female rats, but less protective in males. Vitamin D is a neurosteroid, which may provide immunomodulation and improve outcomes for both sexes. We investigated the efficacy of this combination of drugs with hypothermia after severe HI, as well as potential mechanisms of vitamin D effects in the transition to chronic inflammation. DOL 7 rats were randomized to sham, or HI and hypothermia treated with either saline (HYPO), NAC (50 mg/kg/d, HNAC), or HNAC plus 1,25-dihydroxy-vitamin D₃ (0.1 μg/kg/d, HNAC + VitD) daily for 2 weeks. A second set of animals were randomized and treated for 11 days to investigate vitamin D metabolism and inflammatory mediators. Rats treated with HNAC + VitD performed significantly better on tests of strength and use of affected limb, adaptive sensorimotor skills, motor sequence learning, and working memory than either HYPO or HNAC, particularly benefiting male rats. Significantly fewer rats in the HNAC + VitD group had severe hemispheric volume loss. HI injury decreased serum vitamin D at 11 days and induced the enzyme that deactivates vitamin D in the hippocampus, particularly in males. Persistent vitamin D dysregulation was seen in both hippocampi in males, which was not reversed by hypothermia. Vitamin D in combination with hypothermia and NAC supports functional recovery in both sexes of neonatal rats significantly better than hypothermia alone or hypothermia and NAC in this severe HI model.

Therapeutic Hypothermia Provides Variable Protection against Behavioral Deficits after Neonatal Hypoxia-Ischemia: A Potential Role for Brain-Derived Neurotrophic Factor

BACKGROUND

Despite treatment with therapeutic hypothermia (TH), infants who survive hypoxic ischemic (HI) encephalopathy (HIE) have persistent neurological abnormalities at school age. Protection by TH against HI brain injury is variable in both humans and animal models. Our current preclinical model of hypoxia-ischemia (HI) and TH displays this variability of outcomes in neuropathological and neuroimaging end points with some sexual dimorphism. The detailed behavioral phenotype of this model is unknown. Whether there is sexual dimorphism in certain behavioral domains is also not known. Brain-derived neurotrophic factor (BDNF) supports neuronal cell survival and repair but may also be a marker of injury. Here, we characterize the behavioral deficits after HI and TH stratified by sex, as well as late changes in BDNF and its correlation with memory impairment.

METHODS

HI was induced in C57BL6 mice on postnatal day 10 (p10) (modified Vannucci model). Mice were randomized to TH (31°C) or normothermia (NT, 36°C) for 4 h after HI. Controls were anesthesia-exposed, age- and sex-matched littermates. Between p16 and p39, growth was followed, and behavioral testing was performed including reflexes (air righting, forelimb grasp and negative geotaxis) and sensorimotor, learning, and memory skills (open field, balance beam, adhesive removal, Y-maze tests, and object location task [OLT]). Correlations between mature BDNF levels in the forebrain and p42 memory outcomes were studied.

RESULTS

Both male and female HI mice had an approximately 8-12% lower growth rate (g/day) than shams (p ≤ 0.01) by p39. TH ameliorated this growth failure in females but not in males. In female mice, HI injury prolonged the time spent at the periphery (open field) at p36 (p = 0.004), regardless of treatment. TH prevented motor impairments in the balance beam and adhesive removal tests in male and female mice, respectively (p ≤ 0.05). Male and female HI mice visited the new arm of the Y-maze 12.5% (p = 0.05) and 10% (p = 0.03) less often than shams, respectively. Male HI mice also had 35% lower exploratory preference score than sham (p ≤ 0.001) in the OLT. TH did not prevent memory impairments found with Y-maze testing or OLT in either sex (p ≤ 0.01) at p26. At p42, BDNF levels in the forebrain ipsilateral to the HI insult were 1.7- to 2-fold higher than BDNF levels in the sham forebrain, and TH did not prevent this increase. Higher BDNF levels in the forebrain ipsilateral to the insult correlated with worse performance in the Y-maze in both sexes and in OLT in male mice (p = 0.01).

CONCLUSIONS

TH provides benefit in specific domains of behavior following neonatal HI. In general, these benefits accrued to both males and females, but not in all areas. In some domains, such as memory, no benefit of TH was found. Late differences in individual BDNF levels may explain some of these findings.

Monitoring of cerebral blood flow during hypoxia-ischemia and resuscitation in the neonatal rat using laser speckle imaging

Neonatal hypoxic-ischemic encephalopathy (HIE) is associated with alterations in cerebral blood flow (CBF) as a result of perinatal asphyxia. The extent to whichCBFchanges contribute to injury, and whether treatments that ameliorate these changes might be neuroprotective, is still unknown. Higher throughput techniques to monitorCBFchanges in rodent models ofHIEcan help elucidate the underlying pathophysiology. We developed a laser speckle imaging (LSI) technique to continuously monitorCBFin six postnatal-day 10 (P10) rats simultaneously before, during, and after unilateral hypoxia-ischemia (HI, ligation of the left carotid artery followed by hypoxia in 8% oxygen). After ligation,CBFto the ligated side fell by 30% compared to the unligated side (P < 0.0001). Hypoxia induced a bilateral 55% reduction inCBF, which was partially restored by resuscitation. Compared to resuscitation in air, resuscitation in 100% oxygen increasedCBFto the ligated side by 45% (P = 0.033). Individual variability inCBFresponse to hypoxia between animals accounted for up to 24% of the variability in hemispheric area loss to the ligated side. In both P10 and P7 models of unilateralHI, resuscitation in 100% oxygen did not affect hemispheric area loss, or hippocampalCA1 pyramidal neuron counts, after 1-week survival. ContinuousCBFmonitoring usingLSIin multiple rodents simultaneously can screen potential treatment modalities that affectCBF, and provide insight into the pathophysiology ofHI.

Treatment temperature and insult severity influence the neuroprotective effects of therapeutic hypothermia

Therapeutic hypothermia (HT) is standard care for moderate and severe neonatal hypoxic-ischaemic encephalopathy (HIE), the leading cause of permanent brain injury in term newborns. However, the optimal temperature for HT is still unknown, and few preclinical studies have compared multiple HT treatment temperatures. Additionally, HT may not benefit infants with severe encephalopathy. In a neonatal rat model of unilateral hypoxia-ischaemia (HI), the effect of five different HT temperatures was investigated after either moderate or severe injury. At postnatal-day seven, rat pups underwent moderate or severe HI followed by 5 h at normothermia (37 °C), or one of five HT temperatures: 33.5 °C, 32 °C, 30 °C, 26 °C, and 18 °C. One week after treatment, neuropathological analysis of hemispheric and hippocampal area loss, and CA1 hippocampal pyramidal neuron count, was performed. After moderate injury, a significant reduction in hemispheric and hippocampal loss on the injured side, and preservation of CA1 pyramidal neurons, was seen in the 33.5 °C, 32 °C, and 30 °C groups. Cooling below 33.5 °C did not provide additional neuroprotection. Regardless of treatment temperature, HT was not neuroprotective in the severe HI model. Based on these findings, and previous experience translating preclinical studies into clinical application, we propose that milder cooling should be considered for future clinical trials.

Therapeutic hypothermia and hypoxia-ischemia in the term-equivalent neonatal rat: characterization of a translational preclinical model

BACKGROUND

Hypoxic-ischemic encephalopathy (HIE) is a major cause of morbidity in survivors. Therapeutic hypothermia (TH) is the only available intervention, but the protection is incomplete. Preclinical studies of HIE/TH in the rodent have relied on the postnatal day (P) 7 rat whose brain approximates a 32-36 wk gestation infant, less relevant for these studies. We propose that HIE and TH in the term-equivalent P10 rat will be more translational.

METHODS

P10-11 rat pups were subjected to unilateral hypoxia-ischemia (HI) and 4 h recovery in normothermic (N) or hypothermic (TH) conditions. Brain damage was assessed longitudinally at 24 h, 2 wk, and 12 wk. Motor function was assessed with the beam walk; recognition memory was measured by novel object recognition.

RESULTS

Neuroprotection with TH was apparent at 2 and 12 wk in both moderately and severely damaged animals. TH improved motor function in moderate, but not severe, damage. Impaired object recognition occurred with severe damage with no evidence of protection of TH.

CONCLUSION

This adaptation of the immature rat model of HI provides a reproducible platform to further study HIE/TH in which individual animals are followed up longitudinally to provide a useful translational preclinical model.

The effect of resuscitation in 100% oxygen on brain injury in a newborn rat model of severe hypoxic-ischaemic encephalopathy

AIM

Infants with birth asphyxia frequently require resuscitation. Current guidance is to start newborn resuscitation in 21% oxygen. However, infants with severe hypoxia-ischaemia may require prolonged resuscitation with oxygen. To date, no study has looked at the effect of resuscitation in 100% oxygen following a severe hypoxic-ischaemic insult.

METHODS

Postnatal day 7 Wistar rats underwent a severe hypoxic-ischaemic insult (modified Vannucci unilateral brain injury model) followed by immediate resuscitation in either 21% or 100% oxygen for 30 min. Seven days following the insult, negative geotaxis testing was performed in survivors, and the brains were harvested. Relative ipsilateral cortical and hippocampal area loss was assessed histologically.

RESULTS

Total area loss in the affected hemisphere and area loss within the hippocampus did not significantly differ between the two groups. The same results were seen for short-term neurological assessment. No difference was seen in weight gain between pups resuscitated in 21% and 100% oxygen.

CONCLUSION

Resuscitation in 100% oxygen does not cause a deleterious effect on brain injury following a severe hypoxic-ischaemic insult in a rat model of hypoxia-ischaemia. Further work investigating the effects of resuscitation in 100% oxygen is warranted, especially for newborn infants with severe hypoxic-ischaemic encephalopathy.

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.

Combined treatment of xenon and hypothermia in newborn rats--additive or synergistic effect?

BACKGROUND

Breathing the inert gas Xenon (Xe) enhances hypothermic (HT) neuroprotection after hypoxia-ischemia (HI) in small and large newborn animal models. The underlying mechanism of the enhancement is not yet fully understood, but the combined effect of Xe and HT could either be synergistic (larger than the two effects added) or simply additive. A previously published study, using unilateral carotid ligation followed by hypoxia in seven day old (P7) rats, showed that the combination of mild HT (35°C) and low Xe concentration (20%), both not being neuroprotective alone, had a synergistic effect and was neuroprotective when both were started with a 4 h delay after a moderate HI insult. To examine whether another laboratory could confirm this finding, we repeated key aspects of the study.

DESIGN/METHODS

After the HI-insult 120 pups were exposed to different post-insult treatments: three temperatures (normothermia (NT) NT37°C, HT35°C, HT32°C) or Xe concentrations (0%, 20% or 50%) starting either immediately or with a 4 h delay. To assess the synergistic potency of Xe-HT, a second set (n = 101) of P7 pups were exposed to either HT35°C+Xe0%, NT+Xe20% or a combination of HT35°C+Xe20% starting with a 4 h delay after the insult. Brain damage was analyzed using relative hemispheric (ligated side/unligated side) brain tissue area loss after seven day survival.

RESULTS

Immediate HT32°C (p = 0.042), but not HT35°C significantly reduced brain injury compared to NT37°C. As previously shown, adding immediate Xe50% to HT32°C increased protection. Neither 4 h-delayed Xe20%, nor Xe50% at 37°C significantly reduced brain injury (p>0.050). In addition, neither 4 h-delayed HT35°C alone, nor HT35°C+Xe20% reduced brain injury. We found no synergistic effect of the combined treatments in this experimental model.

CONCLUSIONS

Combining two treatments that individually were ineffective (delayed HT35°C and delayed Xe20%) did not exert neuroprotection when combined, and therefore did not show a synergistic treatment effect.

Hypothermia is not neuroprotective after infection-sensitized neonatal hypoxic-ischemic brain injury

BACKGROUND

Therapeutic hypothermia (HT) is the standard treatment after perinatal hypoxic-ischemic (HI) injury. Infection increases vulnerability to HI injury, but the effect of HT on lipopolysaccharide (LPS) sensitized HI brain injury is unknown.

DESIGN/METHODS

P7 rat pups were injected either with vehicle or LPS, and after a 4h delay they were exposed to left carotid ligation followed by global hypoxia inducing a unilateral stroke-like HI injury. Pups were randomized to the following treatments: (1) vehicle treated HI-pups receiving normothermia treatment (NT) (Veh-NT; n=30); (2) LPS treated HI-pups receiving NT treatment (LPS-NT; n=35); (3) vehicle treated HI-pups receiving HT treatment (Veh-HT; n=29); or (4) LPS treated HI-pups receiving HT treatment (LPS-HT; n=46). Relative area loss of the left/right hemisphere and the areas of hippocampi were measured at P14.

RESULTS

Mean brain area loss in the Veh-NT group was 11.2±14%. The brain area loss in LPS-NT pups was 29.8±17%, which was significantly higher than in the Veh-NT group (p=0.002). The Veh-HT group had a significantly smaller brain area loss (5.4±6%), when compared to Veh-NT group (p=0.043). The LPS-HT group showed a brain area loss of 32.5±16%, which was significantly higher than in the Veh-HT group (p<0.001). LPS-HT group also had significantly smaller size of the left hippocampus, which was not found in other groups. LPS-sensitization significantly decreased the sizes of the right, unligated-hemispheres, independent of post-HI treatment.

CONCLUSIONS

Therapeutic hypothermia is not neuroprotective in this LPS-sensitized unilateral stroke-like HI brain injury model in newborn rats. Lack of neuroprotection was particularly seen in the hippocampus. Pre-insult exposure to LPS also induced brain area loss in the unligated hemisphere, which is normally not affected in this model.

Combined effect of hypothermia and caspase-2 gene deficiency on neonatal hypoxic-ischemic brain injury

INTRODUCTION

[corrected] Hypoxia-ischemia (HI) injury in term infants develops with a delay during the recovery phase, opening up a therapeutic window after the insult. Hypothermia is currently an established neuroprotective treatment in newborns with neonatal encephalopathy (NE), saving one in nine infants from developing neurological deficits. Caspase-2 is an initiator caspase, a key enzyme in the route to destruction and, therefore, theoretically a potential target for a pharmaceutical strategy to prevent HI brain damage.

METHODS

The aim of this study was to explore the neuroprotective efficacy of hypothermia in combination with caspase-2 gene deficiency using the neonatal Rice-Vannucci model of HI injury in mice.

RESULTS

HI brain injury was moderately reduced in caspase-2(-/-) mice as compared with wild-type (WT) mice. Five hours of hypothermia (33 °C ) vs. normothermia (36 °C) directly after HI provided additive protection overall (temperature P = 0.0004, caspase-2 genotype P = 0.0029), in the hippocampus and thalamus, but not in other gray matter regions or white matter. Delayed hypothermia initiated 2 h after HI in combination with caspase-2 gene deficiency reduced injury in the hippocampus, but not in other brain areas.

DISCUSSION

In conclusion, caspase-2 gene deficiency combined with hypothermia provided enhanced neuroprotection as compared with hypothermia alone.

Resuscitation with 100% oxygen increases injury and counteracts the neuroprotective effect of therapeutic hypothermia in the neonatal rat

INTRODUCTION

Mild therapeutic hypothermia (HT) reduces brain injury in survivors after perinatal asphyxia. Recent guidelines suggest that resuscitation of term infants should be started with air, but supplemental oxygen is still in use. It is not known whether supplemental oxygen during resuscitation affects the protection offered by subsequent HT.

RESULTS

Wilcoxon median (95% confidence interval) hippocampal injury scores (range 0.0-4.0; 0 to ≥90% injury) were 21% O(2) normothermia (NT): 2.00 (1.25-2.50), 21% O(2) HT: 1.00 (0.50-1.50), 100% O(2) NT: 2.50 (1.50-3.25), and 100% O(2) HT: 2.00 (1.25-2.50). Although HT significantly reduced hippocampal injury (B = -0.721, SEM = 0.297, P = 0.018), reoxygenation with 100% O(2) increased injury (B = +0.647, SEM = 0.297, P = 0.033). Regression constant B = 1.896, SEM = 0.257 and normally distributed residuals.

DISCUSSION

We confirm an ~50% neuroprotective effect of therapeutic HT in the neonatal rat. Reoxygenation with 100% O(2) increased injury and worsened reflex performance. HT was neuroprotective whether applied after reoxygenation with air or 100% O(2). However, HT after 100% O(2) gave no net neuroprotection.

METHODS

In an established neonatal rat model, hypoxia-ischemia (HI) was followed by 30-min reoxygenation in either 21% O(2) or 100% O(2) before 5 h of NT (37 °C) or HT (32 °C). The effects of HT and 100% O(2) on histopathologic injury in the hippocampus, basal ganglia, and cortex, and on postural reflex performance 7 d after the insult, were estimated by linear regression.

Antioxidant enzymes are differently changed in experimental ischemic hippocampal CA1 region following repeated restraint stress

Restraint stress induces physiological changes in the brain. In the present study, we observed the effects of repeated stress on ischemic damage associated with oxidative stress in gerbils. Animals were placed into restrainers for 5h (between 09:30 h and 14:30 h) for 21 consecutive days prior to 5 min of transient cerebral ischemia. Experimental groups were divided into 4 groups; 1) sham-operated control-group (sham-group), 2) ischemia-operated control-group (ischemia-group), 3) sham-operated stress-group (stressed-sham-group), and 4) ischemia-operated stress-group (stressed-ischemia-group). Serum corticosterone level in the ischemia-group was highest (330% vs the sham-group) at 12h post-ischemia, and serum corticosterone levels in the stressed-ischemia-group were significantly lower than the ischemia-group. Locomotor activity in the ischemia-group was significantly increased (300% vs the sham-group) at 1 day post-ischemia; however, locomotor activity in the stressed-ischemia-group was less increased compared to the ischemia-group. A few NeuN (neuron-specific soluble nuclear antigen)-positive ((+)) cells were found in the stratum pyramidale (SP) of the hippocampal CA1 region (CA1) 4 days post-ischemia in the ischemia-group; however, in the stressed-ischemia-group at 4 days post-ischemia, 83.8% of NeuN(+) neurons were found. In addition, we found a few Fluro-Jade B (a marker for neuronal degeneration)(+) and TUNEL(+) cells in the stressed-ischemia-group at 4 days post-ischemia. In gliosis, glial fibrillary acidic protein(+) astrocytes in the stressed-ischemia-groups was similar to the ischemia-groups; however, ionized calcium-binding adapter molecule 1(+) microglia in the stressed-ischemia-groups were much less activated than the ischemia-groups. Among antioxidants, Cu,Zn-superoxide dismutase (SOD1) immunoreactivity in the SP was higher in the stressed-ischemia-groups than the ischemia-groups. Catalase immunoreactivity in the SP of the stressed-ischemia-groups was similar to the ischemia-groups. However, Mn-superoxide dismutase and glutathione peroxidase immunoreactivity were lower than the ischemia-groups. In brief, our results indicate that repeated restraint stress significantly attenuates ischemic neuronal damage and locomotor activity following ischemia. In addition, SOD1 among antioxidants significantly increases in the stressed-ischemia-groups.

Changes in corticosteroid hormone receptors in the ischemic gerbil hippocampal CA1 region following repeated restraint stress

Restraint stress produces physiological changes including suppression of long-term potentiation in the brain. We observed the effects of repeated stress on ischemic damage associated with corticosteroid hormone receptors in gerbils. Animals were placed into restrainers for 5 h (between 09:30 h and 14:30 h) for 21 consecutive days prior to induction of transient cerebral ischemia. The animals were divided into 4 groups; (1) sham-operated-control-group (sham-group), (2) ischemia-operated-control-group (ischemia-group), (3) sham-operated-stress-group (stressed-sham-group), and (4) ischemia-operated-stress-group (stressed-ischemia-group). We found that serum corticosterone level in the ischemia-group was highest (374% of the sham-group) 12 h after ischemia/reperfusion and its level in the stressed-ischemia-group was significantly lower than the ischemia-group. Locomotor activity in the ischemia-group was significantly increased (295% of the sham-group) at 1 day post-ischemia; however, the locomotor activity in the stressed-ischemia-group was less increased compared to the ischemia-group. Cresyl violet positive (CV(+)) cells were significantly decreased in the stratum pyramidale (SP) of the hippocampal CA1 region (CA1) of the 4 days post-ischemia-group, while 79.4% of CV(+) cells were detected in the CA1 of the stressed-ischemia-group. Also, a few NeuN (neuron-specific soluble nuclear antigen)(+) cells were detected in the SP of the 4 days post-ischemia-group; however, in the 4 days stressed-post-ischemia-group, 77.2% of NeuN(+) neurons were found in the SP. Glial fibrillary acidic protein(+) astrocytes in the CA1 in the stressed-ischemia-groups were similar to those in the ischemia-groups; however, ionized calcium-binding adapter molecule 1(+) microglia in the stressed-ischemia-groups were less activated compared to the ischemia-groups. Mineralocorticoid receptor (MCR) and glucocorticoid receptor (GR) immunoreactivity in the SP of the stressed-ischemia-group were higher than the ischemia-group; at 4 days post-ischemia, MCR and GR immunoreactivity were expressed in non-pyramidal cells. In brief, our results indicate that repeated restraint stress significantly increase levels of corticosteroid hormone receptors and attenuates neuronal damage in the ischemic hippocampal CA1 region.

The effect of stress on stroke recovery in a photothrombotic stroke animal model

BACKGROUND AND AIMS

Several studies have provided convincing evidence that psychosocial factors, chronic stress and emotional factors are all independent predictors of atherosclerosis and cardiovascular events as well. However, psychosocial factors have received little attention in the medical setting. The purpose of this study is to evaluate the influence of stress on photothrombotic ischemic cortical injury in an animal model.

METHODS

Sprague-Dawley rats were assigned to the four groups and cortical photothrombosis was induced in the sensorimotor cortex. The stress groups were subjected to restraint stress for five days. We evaluate the behavioral function, infarct volume, apoptotic cell death and the activations of mitogen-activated protein kinases (MAPK: Erk1/Erk2, and p38MAPK) for the evaluation of stress effects on stroke.

RESULTS

There was a significant increase in cortical infarct volume and apoptotic cell death at the stroke group subjected to restraint stress (p<0.05, and p<0.01, respectively). The functional recovery was worst in restraint stress group during five days (p<0.05). The activation of Erk1 and Erk2 were increased by restraint stress in sham operation group but decreased in stroke-stress group than stroke control group (p<0.01). The activation of p38MAPK was increased by stroke but this effect was decreased by restraint stress (p<0.05, and p<0.01, respectively). Our data demonstrates that restraint stress increases infarction volume and decreases functional recovery in rat stroke models by modulation of the MAPK pathway.

Phenobarbital augments hypothermic neuroprotection

Seizures are associated with adverse outcome in infants with hypoxic-ischemic encephalopathy. We hypothesized that early administration of the anticonvulsant phenobarbital after cerebral hypoxia ischemia could enhance the neuroprotective efficacy of delayed-onset hypothermia. We tested this hypothesis in a neonatal rodent model. Seven-d-old rats (n = 104) underwent right carotid ligation, followed by 90 min 8% O2 exposure; 15 min later, they received injections of phenobarbital (40 mg/kg) or saline. One or 3 h later, all were treated with hypothermia (30 degrees C, 3 h). Function and neuropathology were evaluated after 7 d (early outcomes) or 1 mo (late outcomes). Early outcome assessment demonstrated better sensorimotor performance and less cortical damage in phenobarbital-treated groups; there were no differences between groups in which the hypothermia delay was shortened from 3 to 1 h. Late outcome assessment confirmed sustained benefits of phenobarbital + hypothermia treatment; sensorimotor performance was better (persistent attenuation of contralateral forepaw placing deficits and absence of contralateral forepaw neglect); neuropathology scores were lower (median, phenobarbital 2 and saline 8.5, p < 0.05); and less ipsilateral cerebral hemisphere %Damage (mean +/- SD, 11 +/- 17 versus 28 +/- 22, p < 0.05). These results suggest that early posthypoxia-ischemia administration of phenobarbital may augment the neuroprotective efficacy of therapeutic hypothermia.

Docosahexaenoic acid confers neuroprotection in a rat model of perinatal hypoxia-ischemia potentiated by Escherichia coli lipopolysaccharide-induced systemic inflammation

OBJECTIVE

Lipopolysaccharide pretreatment potentiates hypoxic ischemic injury. We hypothesized that docosahexaenoic acid pretreatment would improve function and reduce brain volume loss in this rat model of perinatal brain injury and inflammation.

STUDY DESIGN

Seven-day-old rats were divided into 3 groups: intraperitoneal docosahexaenoic acid 1 mg/kg and lipopolysaccharide 0.1 mg/kg, 25% albumin and lipopolysaccharide, and normal saline. Injections were given 2.5 hours before carotid ligation, followed by 90 minutes 8% O2. Rats underwent sensorimotor function testing and brain volume loss assessment on postnatal day 14.

RESULTS

Docosahexaenoic acid pretreatment improved vibrissae forepaw placing scores compared with albumin/lipopolysaccharide (mean+/-standard deviation weighted score/20: 17.72+/-0.92 docosahexaenoic acid/lipopolysaccharide vs 13.83+/-0.82 albumin/lipopolysaccharide; P<.007). Albumin/lipopolysaccharide rats scores were worse than those of the normal saline/normal saline rats (13.83+/-0.82 vs 17.21+/-0.71; P=.076). No significant differences in brain volume loss were observed among groups.

CONCLUSION

Lipopolysaccharide inflammatory stimulation in conjunction with hypoxic ischemic resulted in poorer function than hypoxic ischemic alone. Docosahexaenoic acid pretreatment had significantly improved function in neonatal rats exposed to lipopolysaccharide and hypoxic ischemic.

Effects of repeated restraint stress on platelet endothelial cell adhesion molecule-1 immunoreactivity and protein levels in the gerbil hippocampus after transient cerebral ischemia

Stress has long been known to be a causative factor of various disease states. In this study, we investigated the effects of repeated restraint stress on platelet endothelial cell adhesion molecule-1 (PECAM-1), a very important mediator in inflammation, immunoreactivity and protein levels as well as neuronal damage, in the gerbil hippocampus after 5 minutes of transient cerebral ischemia. Transient ischemia-induced neuronal death was shown in CA1 pyramidal cells 4 days after ischemia/reperfusion. However, repeated restraint stress protected neuronal death induced by ischemic damage. In the ischemia-group, PECAM-1 immunoreactivity and its protein levels were significantly increased in all the hippocampal subregions 4 days after ischemia/reperfusion. However, PECAM-1 immunoreactivity and its protein levels did not change significantly in the hippocampus of the stress-ischemia-group compared to the sham-groups. These results indicate that repeated restraint stress protects neuronal damage induced by transient cerebral ischemia, and this may be associated with maintenance of PECAM-1levels.

Cooling combined with immediate or delayed xenon inhalation provides equivalent long-term neuroprotection after neonatal hypoxia-ischemia

Hypothermia (HT) improves outcome after neonatal hypoxia-ischemia. Combination therapy may extend neuroprotection. The noble anesthetic gas xenon (Xe) has an excellent safety profile. We have shown earlier that 3 h of 50% Xe plus HT (32 degrees C) additively gives more protection (72%) than either alone (HT=31.1%, Xe=10.2%). Factors limiting clinical use include high-cost and specialist administration requirements. Thus, combinations of 1 h of 50% Xe were administered concurrently for either the first (1 h(Immediate)Xe) or last (1 h(Delayed)Xe) of 3 h of posthypoxic-ischemic HT as compared with 3 h of 50%Xe/HT to investigate how brief Xe exposure with a delay would affect efficacy. An established neonatal rat hypoxia-ischemia model was used. Serial functional neurologic testing into adulthood was performed, followed by neuropathological examination. Xenon with HT was more effective with longer Xe duration (3 h versus 1 h) (P=0.015). However, 1 h Xe/3 h HT resulted in better neuroprotection than 3 h HT alone (P=0.03), this significant effect was also present with 1 h Xe after a 2-h delay. One (immediate or with a delay) or 3 h Xe also significantly improved motor function (P=0.024). Females had significantly better motor scores than males, but no sex-dependent difference in pathology results. The neuroprotection of short, delayed Xe treatment would allow transport to specialist facilities to receive Xe.

Xenon and hypothermia combine additively, offering long-term functional and histopathologic neuroprotection after neonatal hypoxia/ischemia

BACKGROUND AND PURPOSE

Hypoxic/ischemic (HI) brain injury affects 1 to 6 per 1000 live human births, with a mortality of 15% to 20%. A quarter of survivors have permanent disabilities. Hypothermia is the only intervention that improves outcome; however, further improvements might be obtained by combining hypothermia with additional treatments. Xenon is a noble anesthetic gas with an excellent safety profile, showing great promise in vitro and in vivo as a neuroprotectant. We investigated combinations of 50% xenon (Xe(50%)) and hypothermia of 32 degrees C (HT(32 degrees C)) as a post-HI therapy.

METHODS

An established neonatal rat HI model was used. Serial functional neurologic testing into adulthood 10 weeks after injury was performed, followed by global and regional brain histopathology evaluation.

RESULTS

In the combination Xe(50%)HT(32 degrees C) group, complete restoration of long-term functional outcomes was seen. Hypothermia produced improvement on short- (P<0.001) and long- (P<0.001) term functional testing, whereas Xe(50%) alone predominantly improved long-term function (P<0.05), suggesting that short-term testing does not always predict eventual outcome. Similarly, the Xe(50%)HT(32 degrees C) combination produced the greatest (71%) improvement in global histopathology scores, a pattern mirrored in the regional scores, whereas Xe(50%) and HT(32 degrees C) individually produced smaller improvements (P<0.05 and P<0.001, respectively). The interaction between the 2 treatments was additive.

CONCLUSIONS

The xenon/hypothermia combination additively confers greater protection after HI than either treatment alone. The functional improvement is almost complete, is sustained long term, and is accompanied by greatly improved histopathology. The unique safety profile differentiates xenon as an attractive combination therapy with hypothermia to improve the otherwise bleak outcome from neonatal HI.

Involvement of IL-1beta in acute stress-induced worsening of cerebral ischaemia in rats

Stress is known to be one of the risk factors of stroke. Most of the knowledge on the effects of stress on cerebrovascular disease in humans is restricted to catecholamines and glucocorticoids effects on blood pressure and/or development of atherosclerosis. However, few experimental studies have examined the possible mechanisms by which stress may affect stroke outcome. We have used an acute stress protocol consisting of the exposure of male Fischer rats to an acute, single exposure immobilisation protocol (6 h) prior to permanent middle cerebral artery occlusion (MCAO), and we have found that stress worsens behavioural and neurological outcomes and increased infarct size after MCAO. The possible regulatory role of the TNFalpha and IL-1beta was studied by looking at the release of these cytokines in brain. The results of the present study showed an increase in IL-1beta release in cerebral cortex after exposure to acute stress. Brain levels of IL-1beta are also higher in previously stressed MCAO rats than in MCAO animals without stress. Pharmacological blockade of IL-1beta with an antibody anti-IL-1beta led to a decrease in the infarct size as well as in neurological and behavioural deficits after MCAO. In summary, our results indicate that IL-1beta, but not TNFalpha, accounts at least partly for the worsening of MCAO consequences in brain of rats exposed to acute stress.

The role of tumor necrosis factor-alpha in stress-induced worsening of cerebral ischemia in rats

Whereas stress is known to be one of the risk factors of stroke, few experimental studies have examined the possible mechanisms by which stress may affect stroke outcome. Most of the knowledge on the effects of stress on cerebrovascular disease in humans is restricted to catecholamines and glucocorticoids effects on blood pressure and/or development of atherosclerosis. By using an experimental paradigm consisting of the exposure of Fischer rats to repeated immobilization sessions (1 h daily during seven consecutive days) prior to permanent middle cerebral artery occlusion (MCAO), we have found that stress worsens behavioral outcome and increases infarct size after MCAO. These changes occur concomitantly to an increase in inducible nitric oxide synthase (iNOS) expression and to the accumulation of lipid peroxidation markers in brain tissue. The possible regulatory role of TNFalpha was studied by looking at the mechanisms of release of this cytokine as well as to the expression of its receptors (TNFR1 and 2). The results of the present study suggest an increase in TNFalpha expression and release after stress, as well as an increase in the expression of TNFR1. Pharmacological blockade of TNFalpha with anti-TNFalpha led to a decrease in the infarct size as well as in the oxidative/nitrosative biochemical parameters seen after ischemia. In summary, our results indicate that TNFalpha accounts, at least partly, for the worsening of MCAO consequences in brain of rats exposed to stress. Furthermore, the data presented here provide evidence that stress can increase brain ischemic damage and support a possible protective effect of treatment of stressful situations before and during the development of the brain ischemia.

Effect of subacute and chronic immobilisation stress on the outcome of permanent focal cerebral ischaemia in rats

The aim of this study was to determine the effect of mood disorders, including psychological distress and depression, on stroke outcome. Male Fischer rats were exposed to immobilisation stress, an animal paradigm of psychological stress, major depression and post-traumatic stress disorder. Either a subacute (1 h for 7 days) or a chronic (6 h for 21 days) exposure to stress was applied 24 h before permanent middle cerebral artery occlusion (MCAO). Stroke outcome was assessed by measurement of infarct size and behavioural characterisation. Serum glutamate and brain ATP levels as well as brain glutamate transporter function and expression were studied in the search for the molecular mechanisms involved. Subacute stress exposure increased infarct size and decreased behavioural scores after stroke. On the contrary, chronic stress exposure decreased infarct size. Peak serum glutamate levels correlated with infarct size after MCAO. Expression of glutamate transporters was decreased by subacute stress, whereas the expression of EAAT1, a glial glutamate carrier, was increased after the chronic stress protocol. Our results indicate that distinct patterns of stress determine different stroke outcomes, and that expressional changes of brain glutamate transporters, able to affect glutamate release after stroke, are involved.

Improved neuroprotection with hypothermia delayed by 6 hours following cerebral hypoxia-ischemia in the 14-day-old rat

Since hypothermia may be a potential treatment for perinatal cerebral hypoxic-ischemic injury, we used an established neonatal model of hypoxia-ischemia to determine the time after injury at which cooling had the best protective effect. Fourteen-day-old Wistar rats were subjected to right carotid artery ligation and hypoxia (8% O(2) for 90 min). Immediately at the end of hypoxia (defined as 0h), animals were either maintained at normal body temperature until sacrifice (normothermia) or subjected to hypothermia. In a preliminary study, the effects of a reduction in temperature and the duration of such cooling were investigated; animals were cooled (until brain temperature reached 33 degrees C or 30 degrees C) for 2, 4, or 6 h commencing immediately after hypoxia. In a second study, animals were cooled (brain temperature 30 degrees C) for 6 h commencing at either 0, 2, 4, or 6 h after the end of hypoxia. Sham-operated animals were used as controls. Twenty-four hours after hypoxia-ischemia, cerebral energy metabolism was measured by phosphorus magnetic resonance spectroscopy, and at 5 d cerebral infarction was measured by planimetry. In normothermic animals the ratio of phosphocreatine/inorganic phosphate (PCr/Pi) had fallen markedly 24 h following hypoxia-ischemia. In contrast, animals cooled between 6 and 12 h displayed high PCr/Pi ratios similar to those in control animals. Similarly, after 5 d, infarct area was significantly reduced only in animals cooled between 6 and 12 h after injury. These results indicate that cooling between 6 and 12 h after hypoxia-ischemia is more effective in reducing cerebral injury than other cooling regimes and suggest that the physiologic events during this period are critical for understanding cerebral infarction.

Neuroprotective effects of mild hyperthermia prior to focal ischemia in conscious rats

Hyperthermia during or after stroke is known to worsen neuronal damage. Paradoxically, when hyperthermia precedes stroke, it can protect against a subsequent ischemic insult. Other stressors including restraint also have a similar pre-conditioning effect. In the present study, we report the unanticipated finding that conscious rats, restrained for the purpose of intravenous infusion, had markedly reduced neuronal and functional deficits after middle cerebral artery occlusion compared with unrestrained rats. Restrained rats had significantly higher body temperature prior to stroke than unrestrained rats. The findings suggest restraint leading to mild hyperthermia may be sufficient to induce adaptive processes which protect against subsequent ischemia.