Etiologies and distribution of neonatal leukomalacia

The consequences of chorioamnionitis: preterm birth and effects on development

Preterm birth is a major cause of perinatal mortality and long-term morbidity. Chorioamnionitis is a common cause of preterm birth. Clinical chorioamnionitis, characterised by maternal fever, leukocytosis, tachycardia, uterine tenderness, and preterm rupture of membranes, is less common than subclinical/histologic chorioamnionitis, which is asymptomatic and defined by inflammation of the chorion, amnion, and placenta. Chorioamnionitis is often associated with a fetal inflammatory response. The fetal inflammatory response syndrome (FIRS) is defined by increased systemic inflammatory cytokine concentrations, funisitis, and fetal vasculitis. Clinical and epidemiological studies have demonstrated that FIRS leads to poor cardiorespiratory, neurological, and renal outcomes. These observations are further supported by experimental studies that have improved our understanding of the mechanisms responsible for these outcomes. This paper outlines clinical and experimental studies that have improved our current understanding of the mechanisms responsible for chorioamnionitis-induced preterm birth and explores the cellular and physiological mechanisms underlying poor cardiorespiratory, neural, retinal, and renal outcomes observed in preterm infants exposed to chorioamnionitis.

Intrauterine inflammation and preterm delivery

Spontaneous preterm delivery, prematurity, and low birth weight due to prematurity account for a great part of neonatal morbidity and mortality. Specifically, chronic amniotic fluid inflammation may cause preterm labor, with the involvement of different mediators that produce diverse aspects of the inflammatory response. Although bacteria are considered to be the main trigger for intrauterine infection/inflammation, viral infections also appear to be involved. Recently, molecular genetic techniques have helped us better understand the underlying pathophysiologic processes. This is especially important because epidemiological and experimental studies indicate that intrauterine infection and inflammation constitute a risk factor for adverse neurological outcome in preterm infants. Chronic subclinical chorioamnionitis associated with preterm birth can also modify lung development. Although no current clinical strategy is aimed at adapting the maternofetal inflammatory response, immunomodulators may serve as a future intervention in preterm embryos.

A history of our understanding of cerebral vascular development and pathogenesis of perinatal brain damage over the past 30 years

This article reviews our studies focusing on cerebral vascular development, the pathogenesis of subependymal/intraventricular hemorrhage (SEH/IVH), periventricular leukomalacia (PVL), and pontosubicular neuron necrosis (PSN). Their pathogenesis consists of predisposing developmental and causal factors. SEH/IVH may be caused by reperfusion or overperfusion following ischemia in the subependymal germinal matrix with characteristic vasculature. The cause of PVL is multifactorial (ie, ischemia and inflammation), predisposed by the maturational status of the vasculature and oligodendroglia in the white matter. Focal PVL is ischemic necrosis, and diffuse PVL or white matter injury may include cytotoxic damage. PSN has an apoptotic character, and may be induced by ischemic and oxidative stress on specific immature neurons. Further studies on preventive and therapeutic measures are necessary in clinical, pathologic, and experimental fields. The monitoring and control methods of brain hemodynamics and cellular stability should be more developed to prevent brain damages.

Permissive hypercapnia to decrease lung injury in ventilated preterm neonates

Lung injury in ventilated premature infants occurs primarily through the mechanism of volutrauma, often due to the combination of high tidal volumes in association with a high end-inspiratory volume and occasionally end-expiratory alveolar collapse. Tolerating a higher level of arterial partial pressure of carbon dioxide (PaCO2) is considered as 'permissive hypercapnia' and when combined with the use of low tidal volumes may reduce volutrauma and lead to improved pulmonary outcomes. Permissive hypercapnia may also protect against hypocapnia-induced brain hypoperfusion and subsequent periventricular leukomalacia. However, extreme hypercapnia may be associated with an increased risk of intracranial hemorrhage. It may therefore be important to avoid large fluctuations in PaCO2 values. Recent randomized clinical trials in preterm infants have demonstrated that mild permissive hypercapnia is safe, but clinical benefits are modest. The optimal PaCO2 goal in clinical practice has not been determined, and the available evidence does not currently support a general recommendation for permissive hypercapnia in preterm infants.

The fetal inflammatory response syndrome

The fetal inflammatory response syndrome (FIRS) is a condition characterized by systemic inflammation and an elevation of fetal plasma interleukin-6. This syndrome has been observed in fetuses with preterm labor with intact membranes, preterm prelabor rupture of the membranes, and also fetal viral infections such as cytomegalovirus. FIRS is a risk factor for short-term perinatal morbidity and mortality after adjustment for gestational age at delivery and also for the development of long-term sequelae such as bronchopulmonary dysplasia and brain injury. Multiorgan involvement in FIRS has been demonstrated in the hematopoietic system, thymus, adrenal glands, skin, kidneys, heart, lung, and brain. This article reviews the fetal systemic inflammatory response as a mechanism of disease. Potential interventions to control an exaggerated inflammatory response in utero are also described.

Maternal plasma interleukin-6, interleukin-1beta and C-reactive protein as indicators of tocolysis failure and neonatal outcome after preterm delivery

OBJECTIVE

To investigate whether maternal serum interleukin-6 (IL-6), interleukin-1beta (IL-1beta) and high sensitive C-reactive protein (CRP) could be used as markers of tocolysis failure and adverse neonatal outcome in pregnancies with preterm labor (PL).

METHODS

Forty-seven maternal blood samples taken because of PL at admission and delivery were analyzed. Control samples were taken from 20 gravidas with normal pregnancies. Differences in interleukins and CRP levels with or without chorioamnionitis, connatal infection or periventricular leukomalacia (PVL) were analyzed. Cut-off values were estimated for prediction of tocolysis failure and adverse neonatal outcome.

RESULTS

All three parameters were significantly higher in patients delivering prematurely than in patients delivering at term. All three parameters were significantly higher with than without histologic chorioamnionitis (p < 0.001), with than without connatal infection (p < 0.01), with than without PVL (p < 0.01 for IL-6 and IL-1beta, p < 0.05 for CRP), and in pregnancies with preterm premature rupture of membranes (PPROM) delivered within 48 hours compared to those more prolonged (p < 0.01). Choosing 50.9 pg/mL of IL-6 and a CRP of 19.7 as cut-offs in maternal blood admission concentrations for neonatal PVL, resulted in sensitivity of 81% and specificity of 91% and sensitivity of 91% and specificity of 81%, respectively. At respective maternal blood admission cut-off levels of 27.8 pg/mL of IL-6 and 8.9 of CRP, both parameters were effective predictors of connatal infection.

CONCLUSIONS

Maternal blood IL-6 and CRP could become useful in predicting tocolysis failure and intrauterine treat for the fetus.

Minimising neonatal brain injury: how research in the past five years has changed my clinical practice

With improving neonatal survival for extremely premature babies, the challenge for neonatology is to improve outcome of surviving babies. This review concentrates on best evidence emerging in recent years on prevention of brain damage by early administration of drugs as well as avoidance of induced brain damage by hyperventilation and dexamethasone therapy given postnatally for chronic lung disease.

Prenatal glucocorticoid exposure and postnatal adaptation in premature newborn baboons ventilated for six days

OBJECTIVE

Renal and cardiovascular function is improved during the first 24 hours of life in preterm ventilated baboons exposed to prenatal betamethasone (BETA). We hypothesized BETA-induced effects would be sustained through day 6 of life. Study design Pregnant baboons received saline or BETA (6 mg) 48 and 24 hours before preterm delivery at 125 days' gestation. The newborn baboons were ventilated for 6 days, and assessed for renal, cardiovascular, and endocrine function.

RESULTS

Mean arterial blood pressure (MAP) and glomerular filtration rate (GFR) values 24 hours after delivery were higher in the BETA group. Kidney Na, K-ATPase activity was higher in the BETA group by day 6. All other measures were similar in both groups by day 6.

CONCLUSION

Prenatal BETA exposure in the premature baboon: (1) increases MAP and GFR on day 1 without measurable effects by day 6 and (2) increases kidney Na, K-ATPase activity.

Update on extracorporeal membrane oxygenation

Extracorporeal membrane oxygenation (ECMO) consists of the application of intermediate-term cardiopulmonary bypass for the treatment of potentially reversible heart and/or lung failure in the neonate, child, and adult. Applications in the neonate include congenital diaphragmatic hernia, pulmonary hypertension, meconium aspiration syndrome, and pre- and post-operative congenital heart surgery support. In the older child, myocarditis, infections, and respiratory failure (RSV and ARDS) are the most frequent indications, in addition to peri-operative cardiac surgical support. A review of the institutional experiences at the University of Louisville spanning a 15-year period and comparison international data will be presented, along with a pertinent review of the literature. Technical considerations, complications, and long-term outcomes will be reviewed, and the potential interface between ECMO and other, less invasive technologies, i.e., high-frequency ventilation, replacement surfactant, and nitric oxide, will be discussed.

Single and multiple prenatal glucocorticoid exposures improve preterm newborn lamb cardiovascular and renal function similarly

OBJECTIVE

Renal and cardiovascular function improves in preterm newborn lambs after a single prenatal betamethasone treatment. We hypothesized that multiple betamethasone exposures would further improve renal and cardiovascular adaptation.

STUDY DESIGN

Pregnant ewes were chosen randomly to receive saline solution, one dose of 0.5 mg/kg betamethasone at 104 days of gestation, or three doses of 0.5 mg/kg betamethasone at 104, 111, and 118 days of gestation. Lambs were delivered at 125 days of gestation (preterm) or 145 days of gestation (term). Renal and cardiovascular responses to phenylephrine were evaluated at 2 hours of age.

RESULTS

The preterm single and multiple betamethasone-treated lambs comparably increased glomerular filtration rate, urinary flow and osmolar clearance, and sodium excretion in response to phenylephrine. Term responses were similar and not influenced by betamethasone exposure.

CONCLUSION

Multiple courses of betamethasone do not further improve renal and cardiovascular responses from a single betamethasone dose. Renal and cardiovascular function at term is not affected by early prenatal betamethasone exposure.

Permissive hypercapnia

Although lifesaving, mechanical ventilation can result in lung injury and contribute to the development of bronchopulmonary dysplasia. The most critical determinants of lung injury are tidal volume and end-inspiratory lung volume. Permissive hypercapnia offers to maintain gas exchange with lower tidal volumes and thus decrease lung injury. Further physiologic benefits include improved oxygen delivery and neuroprotection, the latter through both avoidance of accidental hypocapnia, which is associated with a poor neurologic outcome, and direct cellular effects. Clinical trials in adults with acute respiratory failure indicated improved survival and reduced incidence of organ failure in subjects managed with low tidal volumes and permissive hypercapnia. Retrospective studies in low birth weight infants found an association of bronchopulmonary dysplasia with low PaCO(2). Randomized clinical trials of low birth weight infants did not achieve sufficient statistical power to demonstrate a reduction of BPD by permissive hypercapnia, but strong trends indicated the possibility of important benefits without increased adverse events. Herein, we review the mechanisms leading to lung injury, the physiologic effects of hypercapnia, the dangers of hypocapnia, and the available clinical data.

Periventricular leukomalacia, inflammation and white matter lesions within the developing nervous system

Periventricular leukomalacia (PVL) occurring in premature infants, represents a major precursor for neurological and intellectual impairment, and cerebral palsy in later life. The disorder is characterized by multifocal areas of necrosis found deep in the cortical white matter, which are often symmetrical and occur adjacent to the lateral ventricles. There is no known cure for PVL. Factors predisposing to PVL include birth trauma, asphyxia and respiratory failure, cardiopulmonary defects, premature birth/low birthweight, associated immature cerebrovascular development and lack of appropriate autoregulation of cerebral blood flow in response to hypoxic-ischemic insults. The intrinsic vulnerability of oligodendrocyte precursors is considered as central to the pathogenesis of PVL. These cells are susceptible to a variety of injurious stimuli including free radicals and excitotoxicity induced by hypoxic-ischemic injury (resulting from cerebral hypoperfusion), lack of trophic stimuli, as well as secondary associated events involving microglial and astrocytic activation and the release of pro-inflammatory cytokines TNF-alpha and IL-6. It is yet unclear whether activated astrocytes and microglia act as principal participants in the development of PVL lesions, or whether they are representatives of an incidental pathological response directed towards repair of tissue injury in PVL. Nevertheless, the accumulated evidence points to a pathological contribution of microglia towards damage. The topography of lesions in PVL most likely reflects a combination of the relatively immature cerebrovasculature together with a failure in perfusion and/or hypoxia during the greatest period of vulnerability occurring around mid-to-late gestation. Mechanisms underlying the pathogenesis of PVL have so far been related to prenatal ischemic injury to the brain initiated within the third trimester, which result in global cognitive and developmental delay and motor disturbances. Over the past few years, several epidemiological and experimental studies have implicated intrauterine infection and chorioamnionitis as causative in the pathogenesis of PVL. In particular, recent investigations have shown that inflammatory responses in the fetus and neonate can contribute towards neonatal brain injury and development-related disabilities including cerebral palsy. This review presents current concepts on the pathogenesis of PVL and emphasizes the increasing evidence for an inflammatory pathogenic component to this disorder, either resulting from hypoxic-ischemic injury or from infection. These findings provide the basis for clinical approaches targeted at protecting the premature brain from inflammatory damage, which may prove beneficial for treating PVL, if identified early in pathogenesis.

The effects of hypoxia and hyperoxia on fetal-placental vascular tone and inflammatory cytokine production

OBJECTIVE

To determine the effects of fetal hypoxia and hyperoxia on placental vascular tone and production of interleukin-6 and tumor necrosis factor-alpha.

STUDY DESIGN

The maternal and fetal circulation of 2 cotyledons from 5 human placentas were perfused for 4 hours. The fetal circulation of 1 cotyledon was perfused with hypoxic Hanks' balanced salt solution; the other was perfused with hyperoxic Hanks' balanced salt solution. Fetal vascular pressures were recorded every 10 minutes, and fetal vein effluents were collected hourly.

RESULTS

Fetal-placental vascular perfusion pressure was reduced from baseline during hypoxic conditions. Cytokine concentrations were elevated during hyperoxic conditions compared with hypoxic conditions, with significant differences achieved at 2, 3, and 4 hours for interleukin-6 and at 4 hours for tumor necrosis factor-alpha.

CONCLUSION

Fetal-placental vasodilation may be a compensatory mechanism to improve hypoxic conditions. Supraphysiologic oxygenation may contribute to the fetal inflammatory response syndrome and to the development of cerebral palsy.

Characteristic neuropathology and plasticity in periventricular leukomalacia

The brains of extremely low-birth-weight infants with periventricular leukomalacia, who survived for more than 30 days, were examined by means of neuropathologic and immunohistochemical methods. The characteristic neuropathology of the brain is comprised of spongy changes with astrogliosis, a widespread distribution (i.e., in the deep to intermediate white matter), and a diffuse distribution of associated recent lesions. Also, these lesions, both remote and recent, are located in the frontal to occipital lobes. Regarding the correlation between the lesions and transneuronal connecting fibers, the lesions involved fibers of the motor, sensory, visual, and higher cerebral functions. This involvement may cause motor and intellectual disabilities. Furthermore, immunohistochemistry demonstrated nestin-positive astrocytes, and neurons increased around the lesions, suggesting the plasticity of the brains.

Hypocapnia and hypercapnia in respiratory management of newborn infants

Recent experimental and clinical data demonstrate that both hypocapnia and hypercapnia during the neonatal period may result in beneficial or adverse consequences. Multiple retrospective studies report a strong association between PaCO2 levels less than 25 to 30 mm Hg and an increased incidence of cystic PVL and CP in preterm infants. Prolonged exposure to PaCO2 values less than 25 to 30 mm Hg is also associated with hearing loss in term and near-term infants. A low tidal volume strategy combined with permissive hypercapnia is potentially a strategy that could prevent lung injury. Clearly, more randomized, controlled trials are needed before this latter strategy or that of permissive hypercapnia can be recommended routinely for preterm, near-term, or term gestation infants with respiratory disorders.

Is periventricular leucomalacia a result of hypoxic-ischaemic injury? Hypocapnia and the preterm brain

Decrease in the arterial partial pressure of carbon dioxide (PaCO(2)) causes a reduction in cerebral blood flow in humans and in most animal species; in adults as well as in newborns and even in fetal life. Severely decreased PaCO(2) increases cerebral lactate production, modifies spontaneous electric brain activity, and may decrease the metabolic rate of oxygen. A relation between very low PaCO(2) and brain injury, however, has not been shown in adult humans or full-term newborn infants, nor in perinatal animals. In contrast, an association between low PaCO(2) and cerebral palsy and white matter injury in preterm infants has been reported repeatedly. A cause-and-effect relation is suggested by data from the immature rat: brain damage induced by ligation of a carotid artery can be reduced by adding CO(2) to the inspired gas and hence avoiding the consequences of spontaneous hyperventilation. This may be relevant for the clinical care of preterm infants, since PaCO(2) to a large extent is a function of respiratory management. The questions to be addressed are whether hypocapnia sensitizes the brain to hypoxaemia, and also whether the escape mechanisms are less effective in the preterm human brain.

Cerebral palsy births in eastern Denmark, 1987--90: implications for neonatal care

The Cerebral Palsy Register in eastern Denmark has collected cases using a uniform data sampling procedure since birth year 1979. We have investigated changes in the rate of cerebral palsy, related to gestational age, mortality and perinatal risk factors in children born 1983--90. The total cerebral palsy birth prevalence decreased from 3.0 in the birth year period 1983--86 to 2.4 per 1000 live births (P < 0.01) in 1987--90, owing to a decrease among all preterm infants (29--19 per 1000, P < 0.001). The perinatal and early neonatal mortality in preterm infants was unchanged from 1983--86 to 1987--90. The rate of cerebral palsy in term infants was 1.5 per 1000 in all birth-year periods from 1979--90. Among the cerebral palsy infants, the proportion of very preterm babies treated with mechanical ventilation in the neonatal period decreased from 95% in 1983--86 to 61% in 1987--90 (P < 0.001), while the group treated with CPAP among the moderately preterm babies increased from 61% to 78% (P < 0.05). The significant decline in cerebral palsy rate in preterm infants born 1987--90 may be due to a change in treatment at the neonatal intensive care units using less mechanical ventilation, a hypothesis which needs further investigation.

Topography of cerebral white-matter disease of prematurity studied prospectively in 1607 very-low-birthweight infants

The objective of this study was to evaluate to what extent (1) the characteristics of localization, distribution, and size of echodense and echolucent abnormalities enable individuals to be designated as having either periventricular hemorrhagic infarction or periventricular leukomalacia and (2) the characteristics of periventricular hemorrhagic infarction and periventricular leukomalacia are independent occurrences. The population for this study consisted of 1607 infants with birthweights of 500 to 1500 g, born between January 1991 and December 1993, who had at least one cranial ultrasound scan read independently by at least two ultrasonographers. The ultrasound data collection form diagrammed six standard coronal views. The cerebrum was divided into 17 zones in each hemisphere. All abnormalities were described as being echodense or echolucent and were classified on the basis of their size, laterality, location, and evolution. Eight percent (134/1607) of infants had at least one white-matter abnormality. The prevalence of white-matter disease decreased with increasing gestational age. Most abnormalities were small or medium sized and unilateral; only large echodensities tended to be bilateral and asymmetric. Large abnormalities, whether echodense or echolucent, were more likely than smaller abnormalities to be widespread, and the extent of cerebral involvement was independent of whether abnormalities were unilateral or bilateral. Large abnormalities were relatively more likely than small abnormalities to involve anterior planes. Small abnormalities, whether echodense or echolucent, or whether unilateral or bilateral, preferentially occurred near the trigone. Using the characteristics of location, size, and laterality/symmetry, we were able to allocate only 53% of infants with white-matter abnormalities to periventricular hemorrhagic infarction or periventricular leukomalacia. Assuming that periventricular leukomalacia and periventricular hemorrhagic infarction are independent and do not share risk factors, and that each occurs in approximately 5% of infants, we would have expected 0.25%, or about 4 individuals, to have abnormalities with characteristics of both periventricular leukomalacia and periventricular hemorrhagic infarction, whereas we found 63 such infants. Most infants with white-matter disease could not be clearly designated as having periventricular hemorrhagic infarction or periventricular leukomalacia only. Periventricular hemorrhagic infarction contributes to the risk of periventricular leukomalacia occurrence, or the two sorts of abnormalities share common risk antecedent factors. The descriptive term echodense or echolucent and the generic term white-matter disease of prematurity should be used instead of periventricular leukomalacia or periventricular hemorrhagic infarction when referring to sonographically defined white-matter abnormalities.

Hypocapnia under hypotension induces apoptotic neuronal cell death in the hippocampus of newborn rabbits

We investigated the adverse effect of hypocapnia on the neonatal rabbit brain. Two-week-old Japanese white rabbits were assigned to three groups, hyperventilation (H group), ischemia (I group), or hypocapnia with ischemia (HI group) and then subjected for 1.5 h with simultaneous measurement of the mean arterial blood pressure (MABP) and intracranial Hb concentration changes. Marked reductions of PaCO2 and MABP were induced in the hyperventilation-loaded groups and the ischemia-loaded groups, respectively. The intracranial oxyhemoglobin and total Hb concentrations decreased slightly in the H group and markedly in the I and HI groups after the start of experimental protocols, although there were no statistical differences between the I and HI groups. Animals were killed at 24 h after experiments and then subjected to pathologic examination. Damaged neurons with shrunken cell bodies and nuclear changes were found on light microscopic examination, mainly in the pyramidal cell layer of the subiculum and cornu ammonis 1. The numerical density of damaged neurons was significantly higher in the HI group than those in the H or I groups (p < 0.05). These damaged neurons were positive on DNA nick end labeling. A DNA ladder was detected on electrophoresis with a DNA sample extracted from hippocampal tissue in the HI group, but not in the other two groups. On electron microscopic examination, not only condensation of the nucleus but also disruption of mitochondria and the cell membrane were detected. These results suggested that hypocapnia under hypotension might cause neuronal cell death in the hippocampus of neonatal rabbit. Not only ischemia but also a metabolic change induced by hypocapnia might contribute to this apoptotic neuronal cell damage.

Antenatal glucocorticoids alter postnatal preterm lamb renal and cardiovascular responses to intravascular volume expansion

We assessed renal and cardiovascular function in preterm newborn lambs after antenatal glucocorticoid exposure. Pregnant ewes were randomly assigned to receive betamethasone or saline via either direct fetal or maternal injection at 122 d gestation. Lambs were delivered 15 h later, and cardiovascular and renal function was assessed. Two hours after delivery, baseline urine flow, urinary sodium excretion, and urinary osmolar clearance were similar in all groups. Volume expansion (saline, 2.5% of body weight, for 10 min) increased values for urine flow (0.23 +/- 0.04 to 0.58 +/- 0.09 mL x min(-1) x kg(-1)), urinary sodium excretion (29.7 +/- 5.8 to 76.2 +/- 12.3 microEq x min(-1) x kg(-1)), and osmolar clearance (12.2 +/- 1.2 to 24.3 +/- 1.6 mL/100 mL GFR) in the fetal group. Increases in urine values were also observed in the maternal group, but control values did not change significantly. Mean arterial pressure was increased in both betamethasone-treated groups relative to controls. Short-term antenatal betamethasone exposure 1) augments preterm newborn kidney adaptive responses to acute volume expansion, and 2) increases postnatal blood pressure in preterm newborn lambs.

Oxidative damage in fetal rat brain induced by ischemia and subsequent reperfusion. Relation to arachidonic acid peroxidation

To determine whether ischemia followed by subsequent reperfusion can induce fetal cerebral oxidative damage, we created a model of fetal ischemia/reperfusion using rats at day 19 of pregnancy. Fetal ischemia was induced by unilateral occlusion of the utero-ovarian artery for 20 min. Reperfusion was achieved by releasing the occlusion and restoring the circulation for 30 min. The opposite uterine horn was used as control. We measured brain mitochondrial respiratory control index (RCI) and the concentration of thiobarbituric acid-reactive substances (TBARS) in each group. Arachidonic acid (AA) peroxidation induced by the incubation of brain microvessel fraction and AA was measured. AA peroxidation was also evaluated with and without aspirin, an inhibitor of cyclooxygenase and phenidone, which inhibits both of cyclooxygenase and lipoxygenase. The RCI significantly decreased by the occlusion with (p < 0.01) or without reperfusion (p < 0.05). The TBARS level significantly increased with occlusion plus reperfusion (p < 0.01). AA peroxidation was significantly greater in the occlusion and occlusion plus reperfusion groups than in the control groups (p < 0. 01). Aspirin did not affect peroxidation, while phenidone significantly inhibited it in a concentration-dependent manner (p < 0.001). Accordingly, ischemia followed by reperfusion is likely to induce fetal cerebral lipid peroxidation, which may inhibit mitochondrial respiratory activity. The phenidone-inhibited enzyme lipoxygenase may participate importantly in this peroxidation.

Early axonal and glial pathology in fetal sheep brains with leukomalacia induced by repeated umbilical cord occlusion

We conducted a chronic preparation experiment involving near term fetal sheep to evaluate the contribution of umbilical cord occlusion to fetal brain injury. In experimental groups (n = 11), complete cord occlusion for 3 min followed by 5 min release, repeated 5 times were performed at 3 days after initial surgery. Instrumental cases without cord occlusion (n = 3) and uninstrumental twins (n = 6) were also examined as controls. Multiple necrotic foci predominantly in the periventricular white matter were found in the fetal brains examined at 1-3 days after cord occlusion. To estimate the contribution of early axonal and glial reaction to brain injury the following immunohistochemical study was performed. In the lesions, coagulation necrosis, axonal swelling and microglial activation were demonstrated with amyloid precursor protein or ionized calcium binding adapter molecule 1 immunohistochemistry. The induction of tumor necrosis factor alpha and inducible nitric oxide synthase were also detected immunohistochemically in the microglia at 1 and 3 days after cord occlusion. In contrast, the reaction of glial fibrillary acidic protein positive astrocytes was faint at 1 day after occlusion, but the induction of cyclooxygenase-2 was observed. These findings suggest the glial reaction of cytokines and free radicals induced by fetal hypoxia may contribute to the occurrence of brain injury.

Expression of transforming growth factor-beta 1 in periventricular leukomalacia

The expression of transforming growth factor-beta 1, which has neurotrophic effects, was investigated in 25 neonates with periventricular leukomalacia using immunohistochemistry. In controls, transforming growth factor-beta 1 immunoreactivity was not detected in the cerebral white matter or cortex. Of the 25 cases of periventricular leukomalacia, transforming growth factor-beta 1 immunoreactivity was found in 16, and was distributed mainly in the cytoplasm of astrocytes, being prominent around necrotic foci in the white matter. The immunoreactivity was negative or weak at the acute stage of periventricular leukomalacia, and increased at the subacute stage and then decreased or was absent at the chronic stage. Astrocytes that were moderately or markedly positive for transforming growth factor-beta 1 were not found before 27 weeks' gestation, but were observed after 32 weeks' gestation in the white matter of the brains of neonates with periventricular leukomalacia. Transforming growth factor-beta 1 expression tended to be more obvious in focal periventricular leukomalacia than in widespread or diffuse periventricular leukomalacia. Our results suggest that transforming growth factor-beta 1 could be involved in the delayed glial response rather than the initial glial activation, and could play a role in the inhibition and repair of injury in periventricular leukomalacia. Exogenous transforming growth factor-beta 1 could have therapeutic potential for periventricular leukomalacia.

Periventricular leukomalacia: relation to gestational age and axonal injury

Eighty-five infants ranging from 22 to 41 weeks gestation were diagnosed as having periventricular leukomalacia (PVL) using traditional neuropathologic methods. The lesions were also studied by immunocytochemistry for beta-amyloid precursor protein (beta-APP), a glycoprotein that has been observed in PVL. Using this technique, the distribution of white matter tissue necrosis was defined as focal, widespread, and diffuse. The type of PVL correlated with the gestational age at birth. The youngest infants tended to demonstrate widespread necrosis, and the oldest infants exhibited more focal necrosis. beta-APP immunopositivity was present in the axons around the foci of white matter necrosis in 76% of the patients and in the neurons of the adjacent cortex in 66% of the patients. In age-matched control patients, there was no beta-APP reactivity in the cerebral white matter or the cortex. In most patients the distribution of beta-APP-positive axons proved to be a useful marker for demonstrating the type of PVL; however, the relationship of beta-APP to the pathogenesis of PVL requires further study.

West syndrome with periventricular leukomalacia: a morphometric MRI study

A morphometric magnetic resonance imaging study was performed, and the results were compared among three groups (group 1, periventricular leukomalacia patients with West syndrome; group 2, periventricular leukomalacia patients without West syndrome; and group 3, control patients) to clarify the characteristics and cause of West syndrome. This study included 21 infants (11 males and 10 females, 7 months to 2 years 8 months old) born at 24-32 weeks of gestation and weighing 625-1,908 gm. The Evans ratio, ratio of the posterior horns, Cella media index, width of the third ventricle, and the areas of the midbrain, pons, and medulla oblongata were measured and compared among the three groups. There were no differences of gestation or birth weight among the three groups. The Evans ratio, ratio of the posterior horns, Cella media index, and width of the third ventricle were larger in group 1 than in groups 2 and 3. The ratio of the posterior horns and Cella media index were larger in group 2 than in group 3, although the width of the third ventricle was not. Myelination was delayed in all patients in group 1 and in two patients in group 2. In group 1 the areas of the midbrain and pons were smaller than in groups 2 and 3 and the medulla oblongata was smaller than in group 3, although there were no differences in midbrain, pons, and medulla oblongata between groups 2 and 3. Although the infants with periventricular leukomalacia and West syndrome frequently demonstrated marked ventricular dilatation and delayed myelination, the atrophy of midbrain and pons was the most characteristic, and the damage may cause West syndrome.

[Periventricular leukomalacia. I. Histological and pathophysiological aspects]

The term 'periventricular leukomalacia' (PVL) usually covers necrotic and/or gliotic lesions from perinatal origin occurring in the periventricular ring of telencephalic white matter. PVLs are found post-mortem in one third of brains from autopsies of premature infants; PVLs are diagnosed in 4 to 10% of infants born before 33 weeks of gestation and remaining alive more than 3 days after birth. PVL is very rare in at term infants. The proportion of PVLs from prenatal origin is estimated between one third and one half of cases. Recent progresses in neuroepidemiology, developmental neurobiology and imaging methods permit to revisit the pathophysiology of PVLs on a multifactorial basis. The final result of these multiple factors seem to be calcium influx due to glutamatergic overactivation triggered by cytokines, infection and inflammation, and deficit in neurotrophic factors. Periventricular topography can be explained by properties of intracerebral vascular wall at this stage of angiogenesis and by perfusion failure/hypoxia.

Characteristic neuropathology of leukomalacia in extremely low birth weight infants

Extremely low birth weight (ELBW) infants with periventricular leukomalacia (PVL) were examined by neuropathological and immunohistochemical methods. Thirteen ELBW infants of 85 infants with PVL, born at 23 to 27 weeks of gestation, showed a widespread type of distribution of PVL from the deep to intermediate white matter. Immunohistochemistry demonstrated glial fibrillary acidic protein (GFAP)-positive astrocytes to be increased in the deep white matter, often spreading to the intermediate white matter, in all cases of PVL. Tumor necrosis factor-alpha (TNF-alpha)-positive cells were found in the deep to intermediate white matter in 69% of PVL cases and appeared earlier, from 23 weeks of gestation, than in controls. beta-Amyloid precursor protein (beta APP)-positive axons were found around PVL in the deep to intermediate white matter in 85% of the cases. In age-matched control ELBW infants, GFAP-, TNF-alpha-, or beta APP-positive cells were never found. Therefore, in ELBW infants, widespread axonal damage and glial activation with cytokine production occur in the progression in characteristic PVL lesions.

Interleukin-6 concentrations in umbilical cord plasma are elevated in neonates with white matter lesions associated with periventricular leukomalacia

OBJECTIVE

Periventricular leukomalacia, a common brain white matter lesion in preterm neonates, is a major risk factor for cerebral palsy. Recently, cytokines (i.e., tumor necrosis factor and interleukin-1(beta)) have been implicated as mediators for the development of periventricular leukomalacia. The purpose of this study was to examine the relationship between umbilical cord plasma levels of tumor necrosis factor-alpha, interleukin-1(beta), interleukin-6, and interleukin-1 receptor antagonist and the occurrence of periventricular leukomalacia in preterm neonates.

STUDY DESIGN

Umbilical cord blood was collected from 172 consecutive preterm births (25 to 36 weeks). Periventricular leukomalacia-associated lesions were diagnosed by brain ultrasonography within the first 3 days of life. Tumor necrosis factor-alpha, interleukin-1(beta) interleukin-6, and interleukin-1 receptor antagonist were measured by sensitive and specific enzyme-linked immunoassay methods. Umbilical cord arterial pH was measured at birth. Statistical analysis was performed with multiple logistic regression and receiver operating characteristic curve analysis.

RESULTS

Periventricular leukomalacia-associated lesions were present in 14.5% (25/172) of infants. Plasma concentrations of interleukin-6 but not of tumor necrosis factor-alpha, interleukin-1(beta), and interleukin-1 receptor antagonist were significantly higher in neonates with periventricular leukomalacia-associated lesions than in those without these lesions (median 718, range < 226 to 32,000 pg/ml vs median < 226, range < 226 to 43,670 pg/ml; p < 0.0001). An interleukin-6 value > or = 400 pg/ml had a sensitivity of 72% (18/25) and a specificity of 74% (108/147) in the identification of periventricular leukomalacia-associated lesions. Multivariate analysis showed that umbilical cord interleukin-6 was an independent risk factor for periventricular leukomalacia (odds ratio 6.2, p < 0.002) after correction for known confounding variables (i.e., gestational age at birth, umbilical artery pH, chorioamnionitis).

CONCLUSIONS

Interleukin-6 concentrations in umbilical cord plasma are elevated in neonates with periventricular leukomalacia-associated lesions. Our data support the hypothesis that periventricular leukomalacia may be the result of cytokine-mediated brain injury.

Immunohistochemical expression of tumor necrosis factor alpha in neonatal leukomalacia

The expression of tumor necrosis factor alpha (TNF alpha) was examined in infants with leukomalacia by means of immunohistochemical methods with an antihuman TNF alpha monoclonal antibody. We studied 23 patients with neonatal leukomalacia, classified as having "focal," "widespread," or "diffuse" disease according to the distribution of the lesions, and 18 age-matched controls. TNF alpha immunoreactivity was positive in 19 of the 23 (83%) patients with leukomalacia, and in 7 of the 18 (39%) controls. TNF alpha was expressed mainly in glial cells in the deep white matter in both groups, and was most abundant around the necrotic foci in the focal group. TNF alpha immunoreactivity appeared earlier in patients with leukomalacia than in controls, being first detected at 25 and 29 weeks gestation, respectively. Immunofluorescence double-labeling revealed the TNF alpha -immunoreactive cells were Ricinus communis agglutinin-1 (RCA-1)-positive microglial cells. Thus, our study revealed increasing expression of TNF alpha in the normally developing brain during the late fetal period, and overproduction of TNF alpha by microglial cells associated with the pathogenesis of neonatal leukomalacia.

Immunohistochemical study of myelination and oligodendrocyte in infants with periventricular leukomalacia

Eighteen patients with periventricular leukomalacia (PVL) of the focal or widespread type were immunohistochemically studied with respect to myelination and ferritin-containing oligodendrocytes and compared with 23 controls. Morphometric examination of myelination and ferritin-containing oligodendrocytes revealed normal development in the nonnecrotic cerebral white matter of the focal PVL brains. Myelination was mainly impaired in the necrotic or gliotic periventricular white matter of the widespread PVL brains. The expression of lipid components was poorer than that of myelin basic protein and the number of ferritin-containing oligodendrocytes was decreased in the necrotic or diffuse gliotic region of the widespread PVL brains compared to the controls. There was a significant relationship between the number of ferritin-containing oligodendrocytes and the degree of myelination. The impaired myelination in the PVL brains occurred in the necrotic as well as gliotic regions in the cerebral white matter, and may be related to the decrease of normal oligodendrocytes.

Periventricular leukomalacia, glial development and myelination

In perinatal leukomalacia, the brain pathology exhibits several different distribution patterns, according to cerebrovascular and glial maturity or various causal factors. Periventricular leukomalacia occurs in the prenatal as well as the postnatal period, and is caused by, in addition to predisposing factors, cerebral hypoperfusion which is in turn caused by systemic hypotension or intracranial vascular constriction and circulatory disturbance. Oligodendroglial damage or diffuse astrogliosis associated with leukomalacia may lead to delayed or reduced myelination in the cerebral white matter.

Cerebral hemodynamics on near-infrared spectroscopy in hypoxia and ischemia in young animal studies

Using near-infrared spectroscopy the changes of intracranial oxyhemoglobin, deoxyhemoglobin, total hemoglobin and cytochrome aa3, which show the progression of intracranial oxygenation, hemodynamics and cell metabolism, were recorded during prolonged partial hypoxia induced by carbon dioxide (CO2) and nitrogen (N2), ischemia induced by hyperventilation, and hypoxia during hypoglycemia in neonatal and young rabbits. The reduction of cytochrome aa3 during the terminal stage of CO2-induced prolonged hypoxia, hyperventilation and hypoxia in hypoglycemia suggests that the redox state of cytochrome aa3 will be changed by several combined factors such as oxygen delivery, ATP demand and substrate (glucose) delivery.

The effects of corticosteroids and thyrotropin-releasing hormone on newborn adaptation and sympathoadrenal mechanisms in preterm sheep

OBJECTIVES

We examined the effect of prenatal corticosteroids and thyrotropin-releasing hormone on postnatal adaptation and sympathoadrenal function in preterm lambs.

STUDY DESIGN

Catheterized fetal lambs received saline solution (n = 6), corticosteroids alone (n = 8), or corticosteroids plus thyrotropin-releasing hormone (n = 6) for 60 hours. The lambs were delivered by cesarean section at a gestational age of 130 +/- 1 days. Ventilatory, cardiovascular, and metabolic responses and plasma catecholamine concentrations were measured for 2 hours after birth. Statistical analysis was performed by use of independent t tests or analysis of variance.

RESULTS

Ventilatory function and cardiac contractility were significantly improved in both corticosteroid and corticosteroid plus thyrotropin-releasing hormone animals. Lambs treated with corticosteroid plus thyrotropin-releasing hormone had significantly higher aortic pressure and left ventricular blood pressure than either of the other groups. The postnatal norepinephrine and epinephrine surge was blunted in response to corticosteroid and corticosteroid plus thyrotropin-releasing hormone treatment. There were no differences in metabolic responses among the three groups.

CONCLUSIONS

In premature lambs prenatal exposure to corticosteroids and thyrotropin-releasing hormone improves postnatal cardiovascular adaptation more than corticosteroids alone.

Developmental expression of copper, zinc-superoxide dismutase in human brain by chemiluminescence

Copper, zinc-superoxide dismutase (Cu,Zn-SOD) activities were determined by the chemiluminescence method using the cypridina luciferin analog (MCLA) in 22 human brains from fetuses to adults. Cu,Zn-SOD activity of the cerebral cortex and white matter increased from 15% in fetuses to 50% of adult levels in neonates. The activity of the white matter was higher than that in the cortex in the fetal period, but was essentially the same as those of the cortex in the postnatal period. Cu,Zn-SOD activity in the central nervous system was highest in the spinal cord and higher in the order pons, medulla oblongata > cerebellum, midbrain, thalamus > putamen, pallidum and cerebrum. These low activities may be related to the vulnerability of cerebral cortex and white matter in premature infants.

Neuropathologic study of newborns with prenatal-onset leukomalacia

The distribution of leukomalacia and glial fibrillary acidic protein (GFAP)-positive glial cells in prenatal- and postnatal-onset leukomalacia were compared and diagnosed histologically in 128 autopsied infants and the different pathogeneses were examined. Prenatal-onset leukomalacia was diagnosed in 12 of 71 still-births and neonates surviving less than 3 days (16.9%). All 4 preterm infants of less than 32 gestational weeks had widespread white matter necrosis and 4 of 5 term infants had focal necrosis. GFAP-positive glial cells were more increased in the deep and intermediate white matter in both forms of leukomalacia than in the controls, although in the subcortical white matter they were less increased in prenatal- than postnatal-onset leukomalacia. These differences may indicate different pathogeneses, including vascular maturity and causal factors, in prenatal- and postnatal-onset leukomalacia.