Apoptosis in the preterm and near term ovine fetal brain and the effect of intermittent umbilical cord occlusion

Systemic infusions of anti-interleukin-1β neutralizing antibodies reduce short-term brain injury after cerebral ischemia in the ovine fetus

Perinatal hypoxic-ischemic reperfusion (I/R)-related brain injury is a leading cause of neurologic morbidity and life-long disability in children. Infants exposed to I/R brain injury develop long-term cognitive and behavioral deficits, placing a large burden on parents and society. Therapeutic strategies are currently not available for infants with I/R brain damage, except for hypothermia, which can only be used in full term infants with hypoxic-ischemic encephalopathy (HIE). Moreover, hypothermia is only partially protective. Pro-inflammatory cytokines are key contributors to the pathogenesis of perinatal I/R brain injury. Interleukin-1β (IL-1β) is a critical pro-inflammatory cytokine, which has been shown to predict the severity of HIE in infants. We have previously shown that systemic infusions of mouse anti-ovine IL-1β monoclonal antibody (mAb) into fetal sheep resulted in anti-IL-1β mAb penetration into brain, reduced I/R-related increases in IL-1β expression and blood-brain barrier (BBB) dysfunction in fetal brain. The purpose of the current study was to examine the effects of systemic infusions of anti-IL-1β mAb on short-term I/R-related parenchymal brain injury in the fetus by examining: 1) histopathological changes, 2) apoptosis and caspase-3 activity, 3) neuronal degeneration 4) reactive gliosis and 5) myelin basic protein (MBP) immunohistochemical staining. The study groups included non-ischemic controls, placebo-treated ischemic, and anti-IL-1β mAb treated ischemic fetal sheep at 127days of gestation. The systemic intravenous infusions of anti-IL-1β mAb were administered at fifteen minutes and four hours after in utero brain ischemia. The duration of each infusion was two hours. Parenchymal brain injury was evaluated by determining pathological injury scores, ApopTag® positive cells/mm², caspase-3 activity, Fluoro-Jade B positive cells/mm², glial fibrillary acidic protein (GFAP) and MBP staining in the brains of fetal sheep 24h after 30min of ischemia. Treatment with anti-IL-1β mAb reduced (P<0.05) the global pathological injury scores, number of apoptotic positive cells/mm², and caspase-3 activity after ischemia in fetal sheep. The regional pathological scores and Fluoro-Jade B positive cells/mm² did not differ between the placebo- and anti-IL-1β mAb treated ischemic fetal sheep. The percent of the cortical area stained for GFAP was lower (P<0.05) in the placebo ischemic treated than in the non-ischemic group, but did not differ between the placebo- and anti-IL-1β mAb treated ischemic groups. MBP immunohistochemical expression did not differ among the groups. In conclusion, infusions of anti-IL-1β mAb attenuate short-term I/R-related histopathological tissue injury, apoptosis, and reduce I/R-related increases in caspase-3 activity in ovine fetal brain. Therefore, systemic infusions of anti-IL-1β mAb attenuate short-term I/R-related parenchymal brain injury in the fetus.

Apoptosis in the Ovine Fetal Brain Following Placental Embolization and Intermittent Umbilical Cord Occlusion

The purpose of this study was to compare the regional distribution of apoptotic cells in the near term ovine fetal brain caused by prolonged moderate hypoxia, as seen in placental insufficiency, and intermittent severe hypoxia, as seen in umbilical cord compression, which may then contribute to adverse neurodevelopment in the postnatal life. We hypothesized that apoptosis in the fetal brain will be increased in response to both prolonged moderate hypoxia and intermittent severe hypoxia. Twenty-one near term (126-127 days) sheep were divided into 3 groups: control (CON; n = 7), placental embolization (EMB; n = 7), and umbilical cord occlusion (UCO; n = 8). The EMB group had microsphere injections into the umbilical arterial circulation until the oxygen content was at 50% of baseline value. The UCO group had complete cord occlusion for 2 minutes every hour, 6 times a day for 2 consecutive days. At 4 pm on day 2, the animals were euthanized; fetal brains were fixed and prepared for apoptosis staining using the terminal uridine deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay method. In the cerebellar white matter, there was a 3-fold increase in the number of TUNEL positive cells per 1000 cells in both EMB and UCO animals as compared to CON (P = .017). There was also a significant increase in the frontal cortical grey matter (layers 1-3) in EMB animals as compared to CON (P = .014). As such, apoptosis in the near term fetal sheep brain is altered with both sustained moderate hypoxia and intermittent severe hypoxia in the latter part of pregnancy, with potential for long-term neurological sequelae.

Microtubule-associated protein 2 and synaptophysin in the preterm and near-term ovine fetal brain and the effect of intermittent umbilical cord occlusion

We have determined the change in immunoreactivity (IR) for microtubule-associated protein 2 (MAP-2) and synaptophysin (SYN) as markers for dendritic and presynaptic nerve development, respectively, in the ovine fetal brain with advancing gestation and in response to intermittent umbilical cord occlusion (UCO), which might then contribute to adverse neurodevelopment. Fetal sheep (control and experimental groups preterm at 111-115 and near term at 132-138 days of gestation; term = 145 days) were studied over 4 days with UCOs performed by inflation of an occluder cuff for 90 seconds every 30 minutes for 3 to 5 hours each day. Animals were then euthanized and fetal brains assessed for IR of MAP-2 and SYN. In control animals, the IR of SYN increased in the gray matter with advancing gestation consistent with a developmental increase in presynaptic vesicles and/or nerve terminals as expected; however, the IR of MAP-2 decreased in all brain regions studied, suggesting concurrent refinement in dendritic branching and spine development. Intermittent UCO as studied with marked but limited hypoxemia resulted in a decrease in IR of SYN for the brain regions of the preterm animals when protein turnover is higher and indicates decreased presynaptic vesicle formation; whereas, MAP-2 IR was selectively increased in the hippocampus CA1 and thalamus of the near-term animals, consistent with reactive dendritic change and heightened vulnerability for neuronal injury. As such, intermittent cord compressions in the ovine fetus can impact protein markers for dendritic and presynaptic nerve development depending on their timing, which might then lead to alterations in synapse formation and neuronal circuitry.

Antenatal allopurinol reduces hippocampal brain damage after acute birth asphyxia in late gestation fetal sheep

Free radical-induced reperfusion injury is a recognized cause of brain damage in the newborn after birth asphyxia. The xanthine oxidase inhibitor allopurinol reduces free radical synthesis and crosses the placenta easily. Therefore, allopurinol is a promising therapeutic candidate. This study tested the hypothesis that maternal treatment with allopurinol during fetal asphyxia limits ischemia-reperfusion (I/R) damage to the fetal brain in ovine pregnancy. The I/R challenge was induced by 5 repeated measured compressions of the umbilical cord, each lasting 10 minutes, in chronically instrumented fetal sheep at 0.8 of gestation. Relative to control fetal brains, the I/R challenge induced significant neuronal damage in the fetal hippocampal cornu ammonis zones 3 and 4. Maternal treatment with allopurinol during the I/R challenge restored the fetal neuronal damage toward control scores. Maternal treatment with allopurinol offers potential neuroprotection to the fetal brain in the clinical management of perinatal asphyxia.

The impact of intermittent umbilical cord occlusions on the inflammatory response in pre-term fetal sheep

Fetal hypoxic episodes may occur antepartum with the potential to induce systemic and cerebral inflammatory responses thereby contributing to brain injury. We hypothesized that intermittent umbilical cord occlusions (UCOs) of sufficient severity but without cumulative acidosis will lead to a fetal inflammatory response. Thirty-one chronically instrumented fetal sheep at ∼0.85 of gestation underwent four consecutive days of hourly UCOs from one to three minutes duration for six hours each day. Maternal and fetal blood samples were taken for blood gases/pH and plasma interleukin (IL)-1β and IL-6 levels. Animals were euthanized at the end of experimental study with brain tissue processed for subsequent counting of microglia and mast cells. Intermittent UCOs resulted in transitory fetal hypoxemia with associated acidemia which progressively worsened the longer umbilical blood flow was occluded, but with no cumulative blood gas or pH changes over the four days of study. Fetal arterial IL-1β and IL-6 values showed no significant change regardless of the severity of the UCOs, nor was there any evident impact on the microglia and mast cell counts for any of the brain regions studied. Accordingly, intermittent UCOs of up to three minutes duration with severe, but limited fetal hypoxemia and no cumulative acidemia, do not result in either a systemic or brain inflammatory response in the pre-term ovine fetus. However, fetal IL-1B and IL-6 values were found to be well correlated with corresponding maternal values supporting the placenta as a primary source for these cytokines with related secretion into both circulations. Female fetuses were also found to have higher IL-1β levels than males, indicating that gender may impact on the fetal inflammatory response to various stimuli.

The instrumented fetal sheep as a model of cerebral white matter injury in the premature infant

Despite advances in neonatal intensive care, survivors of premature birth remain highly susceptible to unique patterns of developmental brain injury that manifest as cerebral palsy and cognitive-learning disabilities. The developing brain is particularly susceptible to cerebral white matter injury related to hypoxia-ischemia. Cerebral white matter development in fetal sheep shares many anatomical and physiological similarities with humans. Thus, the fetal sheep has provided unique experimental access to the complex pathophysiological processes that contribute to injury to the human brain during successive periods in development. Recent refinements have resulted in models that replicate major features of acute and chronic human cerebral injury and have provided access to complex clinically relevant studies of cerebral blood flow and neuroimaging that are not feasible in smaller laboratory animals. Here, we focus on emerging insights and methodologies from studies in fetal sheep that have begun to define cellular and vascular factors that contribute to white matter injury. Recent advances include spatially defined measurements of cerebral blood flow in utero, the definition of cellular maturational factors that define the topography of injury and the application of high-field magnetic resonance imaging to define novel neuroimaging signatures for specific types of chronic white matter injury. Despite the higher costs and technical challenges of instrumented preterm fetal sheep models, they provide powerful access to clinically relevant studies that provide a more integrated analysis of the spectrum of insults that appear to contribute to cerebral injury in human preterm infants.

Early Cerebral Hemodynamic, Metabolic, and Histological Changes in Hypoxic-Ischemic Fetal Lambs during Postnatal Life

The hemodynamic, metabolic, and biochemical changes produced during the transition from fetal to neonatal life may be aggravated if an episode of asphyxia occurs during fetal life. The aim of the study was to examine regional cerebral blood flow (RCBF), histological changes, and cerebral brain metabolism in preterm lambs, and to analyze the role of oxidative stress in the first hours of postnatal life following severe fetal asphyxia. Eighteen chronically instrumented newborn lambs were randomly assigned to either a control group or the hypoxic-ischemic (HI) group, in which case fetal asphyxia was induced just before delivery. All the animals were maintained on intermittent positive pressure ventilation for 3 h after delivery. During the HI insult, the injured group developed acidosis, hypoxia, hypercapnia, lactic acidosis, and tachycardia (relative to the control group), without hypotension. The intermittent positive pressure ventilation transiently improved gas exchange and cardiovascular parameters. After HI injury and during ventilatory support, there continued to be an increased RCBF in inner regions among the HI group, but no significant differences were detected in cortical flow compared to the control group. Also, the magnitude of the increase in TUNEL positive cells (apoptosis) and antioxidant enzymes, and decrease of ATP reserves was significantly greater in the brain regions where the RCBF was not higher. In conclusion, our findings identify early metabolic, histological, and hemodynamic changes involved in brain damage in premature asphyxiated lambs. Such changes have been described in human neonates, so our model could be useful to test the safety and the effectiveness of different neuroprotective or ventilation strategies applied in the first hours after fetal HI injury.

Effects of maternal antenatal glucocorticoid treatment on apoptosis in the ovine fetal cerebral cortex

We examined the effects of single and multiple maternal glucocorticoid courses on apoptosis in the cerebral cortices of ovine fetuses (CC). Ewes received single dexamethasone or placebo courses at 104-106 or 133-135 days or multiple courses between 76-78 and 104-106 days gestation. In the single-course groups, ewes received four 6 mg dexamethasone or placebo injections every 12 hr for 48 hr. Multiple-course groups received the same treatment once per week for 5 weeks. Neuronal and nonneuronal apoptotic cell numbers per square millimeter were determined with TUNEL and NeuN staining and with caspase-3 enzyme activity on CC tissues harvested at 106-108 (70%) or 135-137 (90%) days of gestation. Apoptotic cell numbers and caspase-3 activity were 50% lower (P < 0.02) after single placebo courses at 90% than 70% gestation; 90% of apoptotic cells were (P < 0.01) nonneuronal at both ages. Nonneuronal apoptotic cells and caspase-3 activity were 40% and 20% lower (P < 0.02) after single dexamethasone than placebo courses at 70%, but not 90%, gestation. Caspase-3 activity was 20% lower (P < 0.01) after multiple dexamethasone than placebo courses, but apoptotic cell number did not differ. We conclude that nonneuronal apoptosis represents the major form of apoptosis in the CC at both 70% and 90% of gestation. Apoptosis in nonneuronal cells decreases with maturity and after a single course of dexamethasone at 70%, but not at 90%, gestation and not after multiple courses at 70% gestation. We speculate that a single course of glucocorticoids exerts maturational changes on the rate of apoptosis in the cerebral cortex of preterm ovine fetuses.

BDNF and TrkB in the preterm and near-term ovine fetal brain and the effect of intermittent umbilical cord occlusion

We have determined the developmental change in immunoreactivity for brain-derived neurotrophic factor and its high-affinity tyrosine kinase receptor, TrkB, in the ovine fetal brain with advancing gestation and in response to intermittent umbilical cord occlusion, which might then contribute to adverse neurodevelopment. Fetal sheep (control and experimental groups at 0.75 and 0.90 of gestation) were studied over 4 days with umbilical cord occlusions performed in the experimental group animals by complete inflation of an occluder cuff for 90 seconds every 30 minutes for 3 to 5 hours each day. Animals were then euthanized and the fetal brains perfusion fixed and prepared for subsequent histology with the distribution of brain-derived neurotrophic factor and tyrosine kinase receptor immunoreactivity determined by immunohistochemistry. In the control group animals brain-derived neurotrophic factor immunoreactivity decreased in the gray matter, thalamus, and hippocampus but increased in the white matter, while tyrosine kinase receptor immunoreactivity decreased in all regions (most P < .01), with advancing gestation consistent with the developmental change from neurogenesis/gliagenesis to myelination over this time period. Intermittent umbilical cord occlusion as studied with severe but limited hypoxemia resulted in a variable decrease in brain-derived neurotrophic factor and tyrosine kinase receptor immunoreactivity for all brain regions in the preterm animals (most P < .01) when protein turnover is higher, but a selective increase in brain-derived neurotrophic factor immunoreactivity in the hippocampus of the near-term animals consistent with a heightened vulnerability for necrotic/apoptotic injury at this time. As such, brain-derived neurotrophic factor-tyrosine kinase receptor in the ovine fetal brain may be altered with intermittent hypoxic insults over the latter part of pregnancy with potential for longer term neurologic consequences.

Cerebral blood flow heterogeneity in preterm sheep: lack of physiologic support for vascular boundary zones in fetal cerebral white matter

Periventricular white matter (PVWM) injury is the leading cause of neurologic disability in survivors of prematurity. To address the role of ischemia in PVWM and cerebral cortical injury, we hypothesized that immaturity of spatially distal vascular 'end zones' or 'border zones' predisposes PVWM to greater decreases in cerebral blood flow (CBF) than more proximal structures. We quantified regional CBF with fluorescently labeled microspheres in 0.65 gestation fetal sheep in histopathologically defined three-dimensional regions by post hoc digital dissection and coregistration algorithms. Basal flow in PVWM was significantly lower than in gyral white matter and cortex, but was equivalent in superficial, middle, and deep PVWM. Absolute and relative CBF (expressed as percentage of basal) did not differ significantly during ischemia or reperfusion between PVWM, gyral white matter, or cortex. Moreover, CBF during ischemia-reperfusion was equivalent in three adjacent PVWM levels and was not consistent with the magnitude of severity of PVWM injury, defined by TUNEL (terminal deoxynucleotidyltransferase-mediated dUPT nick end labeling) staining. However, the magnitude of ischemia was predicted by the severity of discrete cortical lesions. Hence, unlike cerebral cortex, unique CBF disturbances did not account for the distribution of PVWM injury. Previously defined cellular maturational factors, thus, appear to have a greater influence on PVWM vulnerability to ischemic injury than the presence of immature vascular boundary zones.

Perinatal hypoxia induces subsequent retinal degeneration in the offspring of ovoviviparous fish, Xiphophorous maculates

OBJECTIVE

This experiment evaluated the perinatal hypoxic effect on the retina of offspring of the ovoviviparous fish.

ANIMAL STUDIED

The ovoviviparous fish Xiphophorous maculates was used for the experiment.

PROCEDURE

The mothers were kept in a hypoxic environment of 3.5% oxygen for 6 h, starting 30 h before hatching. Subsequently, the retinae of the offspring were fixed, sectioned at 6 microm and evaluated microscopically from the age of 1 to 35 days.

RESULTS

Degeneration of the outer nuclear layer of the retina was noted on the 3rd day and severe retinal degeneration was observed on the 35th day. Immunocytochemistry confirmed apoptosis by TUNEL reaction. There was no difference in neovascularization, as revealed by vascular endothelial growth factor, between controls (group 1) and hypoxic fish (group 2).

CONCLUSIONS

Perinatal hypoxia could have long-lasting effects on the central nervous system in some species.

Early cell death in the brain of fetal preterm lambs after hypoxic-ischemic injury

The objective of the present study was to evaluate using premature fetal lambs the effect of cerebral hypoxia-ischemia induced by partial occlusion of the umbilical cord on the type of cell death which occurs in different brain regions and to ascertain some of the neural pathways which may underlie the associated pathologies. Lambs were sacrificed either immediately after a 1 h hypoxic-ischemic insult or 3 h later. Brains were fixed by perfusion and blocks of the different brain territories were processed for light microscopy (hematoxylin-eosin, Nissl staining), electron transmission microscopy and quantification of apoptosis by the TUNEL method. Other fixed brains were dissociated and labeled by nonyl acridine orange to determine mitochondrial integrity. Non-fixed brains were also used for membrane asymmetry studies, in which cell suspensions were analyzed by flow cytometry to quantify apoptosis. In both hypoxic-ischemic groups, necrotic-like neurons were observed mainly in the mesencephalon, pons, deep cerebellar nuclei and basal nuclei, whereas apoptotic cells were extensively found both in white and gray matter and were not limited to regions where necrotic neurons were present. The 3 h post-partial cord occlusion group, but not the 0 h group, showed a generalized alteration of cell membrane asymmetry and mitochondrial integrity as revealed by Annexin V/PI flow cytometry and nonyl acridine orange studies, respectively. Our results show that the apoptotic/necrotic patterns of cell death occurring early after hypoxic-ischemic injury are brain-region-specific and have distinct dynamics and suggest that therapeutic strategies aimed at rescuing cells from the effects of hypoxia/ischemia should be aimed at blocking the apoptotic components of brain damage.

The effect of repeated umbilical cord occlusions on pulmonary surfactant protein mRNA levels in the ovine fetus

OBJECTIVES

In this study we sought to determine the effect of brief repeated umbilical cord occlusions (rUCO) on surfactant protein (SP) mRNA levels in the fetal sheep lung at two different gestational ages.

METHODS

Fourteen fetuses at 112 to 115 days' gestation (control n = 7, rUCO n = 7) and 15 fetuses at 130 to 133 days' gestation (control n = 7, rUCO n = 8) were studied over 4 successive days with rUCO of 90 seconds duration performed every 30 minutes for 3 to 5 hours each day in the rUCO animals. Blood samples were collected for corticotrophin (ACTH) and cortisol measurements. Animals were killed within 1 hour of the final cord occlusion. SP-A, -B, -C, and -D mRNA levels were determined in lung tissue using a ribonuclease protection assay.

RESULTS

Cord occlusions resulted in temporary increases in circulating ACTH on day 1 with both gestational ages, but the elevations were blunted by day 4. Plasma cortisol levels increased transiently with the larger effect being observed on day 4, in particular with the near-term group. With advancing gestational age there was a significant (P < .05) increase in the level of SP-A (control 112-115 days: 0.01 +/- 0.01 vs control 130-133 days: 0.07 +/- 0.02 fmol/mg RNA), SP -B (control 112-115 days: 0.02 +/- 0.01 vs control 130-133 days: 0.07 +/- 0.01 fmol/mg RNA) and SP-C (control 112-115 days: 0.13 +/- 0.09 vs control 130-133 days: 0.51 +/- 0.10 fmol/mg RNA), but not SP-D mRNA levels (control 112-115 days: 0.002 +/- 0.002 vs control 130-133 days: 0.01 +/- 0.002 fmol/mg RNA). At 112 to 115 days, there was no significant change in any of the SP mRNA levels following rUCO compared to controls. However, the same regime of rUCO at 130 to 133 days resulted in an 85% reduction in SP-A and SP-B mRNA content and a 66% reduction in SP-C mRNA levels compared to controls.

CONCLUSION

The surprising decrease in SP-A and SP-B mRNA levels, which contrasts with other studies, suggests intermittent asphyxial episodes impact differently on surfactant apoprotein mRNA expression than does prolonged hypoxia.

Fetal hypoxic and ischemic injuries

PURPOSE OF REVIEW

The principles of neonatal neurological protection following intrapartum hypoxia are briefly reviewed. The physiological principles behind the use of cardiotocograph patterns in defining the timing and mechanism of fetal hypoxia and injury are then demonstrated.

RECENT FINDINGS

Fetal neurological injury may result from progressive hypoxemia, acidosis, diminished cardiac output and cerebral ischemia, manifested at birth as low Apgar scores, multisystem compromise, severe acidosis and encephalopathy. More commonly, however, intrapartum injury results from often intermittent, regional ischemia secondary to umbilical cord or head compression resulting in hemorrhage or infarction. Under these circumstances, the amount of umbilical acidosis and neonatal encephalopathy varies and the potential candidate for neuroprotection may escape recognition and timely treatment. Selecting infants likely to benefit from neuroprotection requires information on the timing, duration and mechanism of hypoxia. Neonatal parameters, including low Apgar scores, acidosis, even seizures, lack sensitivity and specificity. Cardiotocograph patterns are capable of determining the duration, mechanism and severity of hypoxia and occasionally, the timing of neurological injury.

SUMMARY

Protecting the newborn from the neurological consequences of intrapartum hypoxia requires critical definition of the mechanism and timing of this exposure. cardiotocograph tracings offer the opportunity to refine the selection of candidates for neonatal rescue.

Spatial heterogeneity in oligodendrocyte lineage maturation and not cerebral blood flow predicts fetal ovine periventricular white matter injury

Although periventricular white matter injury (PWMI) is the leading cause of chronic neurological disability and cerebral palsy in survivors of premature birth, the cellular-molecular mechanisms by which ischemia-reperfusion contributes to the pathogenesis of PWMI are not well defined. To define pathophysiologic relationships among ischemia, acute cerebral white matter damage, and vulnerable target populations, we used a global cerebral ischemia-reperfusion model in the instrumented 0.65 gestation fetal sheep. We developed a novel method to make repeated measurements of cerebral blood flow using fluorescently labeled microspheres to resolve the spatial heterogeneity of flow in situ in three-dimensional space. Basal flow in the periventricular white matter (PVWM) was significantly lower than in the cerebral cortex. During global cerebral ischemia induced by carotid occlusion, flow to all regions was reduced by nearly 90%. Ischemia of 30 or 37 min duration generated selective graded injury to frontal and parietal PVWM, two regions of predilection for human PWMI. Injury was proportional to the duration of ischemia and increased markedly with 45 min of ischemia to extensively damage cortical and subcortical gray matter. Surprisingly, the distribution of PVWM damage was not uniform and not explained by heterogeneity in the degree of white matter ischemia. Rather, the extent of white matter damage coincided with the presence of a susceptible population of late oligodendrocyte progenitors. These data support that although ischemia is necessary to generate PWMI, the presence of susceptible populations of oligodendrocyte progenitors underlies regional predilection to injury.

The Scottish Perinatal Neuropathology Study-clinicopathological correlation in stillbirths

OBJECTIVE

To examine the neuropathology of fetuses dying before birth, to determine the timing of any brain damage seen and to ascertain clinical associations of pre-existing brain damage.

DESIGN

Population-based observational study.

SETTING

All 22 delivery units within Scotland, 1995-1998.

SAMPLE

All stillborn fetuses > or =24 weeks of gestation excluding those with chromosomal abnormality or central nervous system/cardiothoracic malformation.

METHODS

Clinical detail was collected on all stillborn fetuses. Requests for postmortem included separate request for detailed neuropathological examination. Stillborn fetuses were classified as full term antepartum (normal growth/growth restricted), preterm antepartum (normal growth/growth restricted), intrapartum (full term/preterm), multiple births and stillborn fetuses following abruptions. Clinicopathological correlation attempted to define the timing of brain insult. Placentas were examined for each case where available.

MAIN OUTCOME MEASURES

Presence of established and/or recent brain damage. RESULTS Clinical details were available for 471 stillborn fetuses, and detailed neuropathology was possible in 191 cases. Of these 191, 13 were multiple births, 9 died following abruption, 12 were intrapartum deaths and 157 were antepartum stillborn fetuses (99 preterm and 58 full term). Recent or established brain damage was seen in 66% of the entire cohort. Thirty-five percent of all cases showed well-established hypoxic damage predating the last evidence of fetal life, and this was more common in preterm fetuses (P = 0.015), those fetuses with evidence of recent damage (P < 0.001), in pregnancies complicated by pregnancy-induced hypertension (P = 0.044) and those in whom the placenta was <10th centile (P = 0.002).

CONCLUSIONS

Brain damage is commonly seen in stillborn infants, and in around one-third of cases, damage predates the period immediately before death. Factors suggesting suboptimal placental function are associated with such damage. Early identification of placental impairment may lead to improved pregnancy outcome.

General anesthesia improves fetal cerebral oxygenation without evidence of subsequent neuronal injury

Anesthetic exposure during pregnancy is viewed as a relatively routine medical practice. However, recent rodent studies have suggested that common anesthetic agents can damage the developing brain. Here we assessed this claim in a higher order species by exposing previously instrumented near-term pregnant sheep at gestational day 122 (+/-1) to a combination of midazolam, sodium thiopental, and isoflurane at clinically relevant doses and means of anesthetic delivery (i.e., active ventilation). Four hours of maternal general anesthesia produced an initial increase in fetal systemic oxygenation and a sustained increase in fetal cerebral oxygenation, as determined by in utero near-infrared spectroscopy. Postexposure monitoring failed to identify changes in physiologic status that could be injurious to the fetal brain. Finally, through the histologic assessment of noninstrumented sheep at the same gestational time point, we found no evidence for a direct fetal neuro-toxic effect of our triple-drug regimen. Collectively, these results appear to corroborate the presumed safety of inhalational anesthetic use during pregnancy.

The CTG and the timing and mechanism of fetal neurological injuries

Defining the relationship between the cardiotocograph (CTG) pattern and subsequent neurological injury is confounded by the requirement that certain clinical and biochemical perinatal findings are essential for relating intrapartum events to subsequent neurological injury. Similarly, the value of CTG analysis in these cases has been compromised by antiquated terminology focused on hypoxia but not neurological behavior. Strong evidence suggests that the evaluation of umbilical artery acidosis, low Apgar score and neonatal encephalopathy are limited in their ability to either include or exclude intrapartum injury. Proper evaluation of the CTG requires that trends and the rapidity of changes in patterns of decelerations are necessary to confidently define the normal-behaving fetus, the hypoxemic but uninjured fetus, the injured but non-hypoxic fetus, and finally to distinguish ischemic events from other forms of hypoxia. A newly defined CTG pattern, the 'conversion' pattern, appears to be a specific marker of ischemic injury and could help to redefine the role of CTG monitoring.

Preterm fetal hypoxia-ischemia causes hypertonia and motor deficits in the neonatal rabbit: a model for human cerebral palsy?

Prenatal hypoxia-ischemia to the developing brain has been strongly implicated in the subsequent development of the hypertonic motor deficits of cerebral palsy (CP) in premature and full-term infants who present with neonatal encephalopathy. Despite the enormous impact of CP, there is no animal model that reproduces the hypertonia and motor disturbances of this disorder. We report a rabbit model of in utero placental insufficiency, in which hypertonia is accompanied by marked abnormalities in motor control. Preterm fetuses (67-70% gestation) were subjected to sustained global hypoxia. The dams survived and gave spontaneous birth. At postnatal day 1, the pups that survived were subjected to a battery of neurobehavioral tests developed specifically for these animals, and the tests were videotaped and scored in a masked manner. Newborn pups of hypoxic groups displayed significant impairment in multiple tests of spontaneous locomotion, reflex motor activity, and the coordination of suck and swallow. Increased tone of the limbs at rest and with active flexion and extension were observed in the survivors of the preterm insult. Histopathological studies identified a distinct pattern of acute injury to subcortical motor pathways that involved the basal ganglia and thalamus. Persistent injury to the caudate putamen and thalamus at P1 was significantly correlated with hypertonic motor deficits in the hypoxic group. Antenatal hypoxia-ischemia at preterm gestation results in hypertonia and abnormalities in motor control. These findings provide a unique behavioral model to define mechanisms and sequelae of perinatal brain injury from antenatal hypoxia-ischemia.

Chronic intermittent hypoxia decreases the expression of Na/H exchangers and HCO3-dependent transporters in mouse CNS

Chronic intermittent hypoxia (CIH) is a component of several disease states, including obstructive sleep apnea, which results in neurocognitive and cardiovascular morbidity. Because chronic hypoxia can induce changes in metabolism and pH homeostasis, we hypothesized that CIH induces changes in the expression of acid-base transporters. Two- to three-day-old mice, exposed to alternating cycles of 2 min of hypoxia (6.0-7.5% O2) and 3 min of normoxia (21% O2) for 8 h/day for 28 days, demonstrated decreases in specific acid-base transport protein expression in most of the central nervous system (CNS). Sodium/hydrogen exchanger isoform 1 (NHE1) and sodium-bicarbonate cotransporter expression were decreased in all regions of the CNS but especially so in the cerebellum. NHE3, which is only expressed in the cerebellum, was also significantly decreased. Anion exchanger 3 protein was decreased in most brain regions, with the decrease being substantial in the hippocampus. These results indicate that CIH induces downregulation of the major acid-extruding transport proteins, NHE1 and sodium-bicarbonate cotransporter, in particular regions of the CNS. This downregulation in acid-extruding capacity may render neurons more prone to acidity and possibly to injury during CIH, especially in the cerebellum and hippocampus. Alternatively, it is possible that O2 consumption in these regions is decreased after CIH, with consequential downregulation in the expression of certain cellular proteins that may be less needed under such circumstances.