Brain injury in the premature infant: Neuropathology, clinical aspects, and pathogenesis

Neuroprotective and Regenerative Effects of Growth Hormone (GH) in the Embryonic Chicken Cerebral Pallium Exposed to Hypoxic-Ischemic (HI) Injury

Prenatal hypoxic−ischemic (HI) injury inflicts severe damage on the developing brain provoked by a pathophysiological response that leads to neural structural lesions, synaptic loss, and neuronal death, which may result in a high risk of permanent neurological deficits or even newborn decease. It is known that growth hormone (GH) can act as a neurotrophic factor inducing neuroprotection, neurite growth, and synaptogenesis after HI injury. In this study we used the chicken embryo to develop both in vitro and in vivo models of prenatal HI injury in the cerebral pallium, which is the equivalent of brain cortex in mammals, to examine whether GH exerts neuroprotective and regenerative effects in this tissue and the putative mechanisms involved in these actions. For the in vitro experiments, pallial cell cultures obtained from chick embryos were incubated under HI conditions (<5% O2, 1 g/L glucose) for 24 h and treated with 10 nM GH, and then collected for analysis. For the in vivo experiments, chicken embryos (ED14) were injected in ovo with GH (2.25 µg), exposed to hypoxia (12% O2) for 6 h, and later the pallial tissue was obtained to perform the studies. Results show that GH exerted a clear anti-apoptotic effect and promoted cell survival and proliferation in HI-injured pallial neurons, in both in vitro and in vivo models. Neuroprotective actions of GH were associated with the activation of ERK1/2 and Bcl-2 signaling pathways. Remarkably, GH protected mature neurons that were particularly harmed by HI injury, but was also capable of stimulating neural precursors. In addition, GH stimulated restorative processes such as the number and length of neurite outgrowth and branching in HI-injured pallial neurons, and these effects were blocked by a specific GH antibody, thus indicating a direct action of GH. Furthermore, it was found that the local expression of several synaptogenic markers (NRXN1, NRXN3, GAP-43, and NLG1) and neurotrophic factors (GH, BDNF, NT-3, IGF-1, and BMP4) were increased after GH treatment during HI damage. Together, these results provide novel evidence supporting that GH exerts protective and restorative effects in brain pallium during prenatal HI injury, and these actions could be the result of a joint effect between GH and endogenous neurotrophic factors. Also, they encourage further research on the potential role of GH as a therapeutic complement in HI encephalopathy treatments.

MRI for premature neonatal brain injury: a case report

This case report aims to extend analytical thinking and clinical reasoning of clinicians and radiographers when presented with diagnosing premature neonatal brain injuries (PNBI). The report considers the uses and merit of magnetic resonance imaging (MRI) in the primary assessment of PNBI. The traditional technique of cranial ultrasound as the first modality of choice can have several limitations, which includes a lower temporal resolution in its ability to differentiate grey-white matter distribution patterns, lower spatial resolution in its ability to accurately map white matter fibre tracts and distribution patterns which are critical in white matter injury pathological events. In this specific case report, MRI was useful for the assessment of haemorrhagic brain injury post partum.Therefore, should MRI be considered, the primary imaging modality in these cases when the concerns about PNBI is presented? This case study explores the current trends in MRI neonatal brain imaging and advancements being made in this field.

Disruption of the serotonergic system after neonatal hypoxia-ischemia in a rodent model

Identifying which specific neuronal phenotypes are vulnerable to neonatal hypoxia-ischemia, where in the brain they are damaged, and the mechanisms that produce neuronal losses are critical to determine the anatomical substrates responsible for neurological impairments in hypoxic-ischemic brain-injured neonates. Here we describe our current work investigating how the serotonergic network in the brain is disrupted in a rodent model of preterm hypoxia-ischemia. One week after postnatal day 3 hypoxia-ischemia, losses of serotonergic raphé neurons, reductions in serotonin levels in the brain, and reduced serotonin transporter expression are evident. These changes can be prevented using two anti-inflammatory interventions; the postinsult administration of minocycline or ibuprofen. However, each drug has its own limitations and benefits for use in neonates to stem damage to the serotonergic network after hypoxia-ischemia. By understanding the fundamental mechanisms underpinning hypoxia-ischemia-induced serotonergic damage we will hopefully move closer to developing a successful clinical intervention to treat neonatal brain injury.

Anti-oxidant strategies

Oxidative stress plays an important role in causing organ injury in the compromised fetus and neonate. Recent experimental research and clinical studies have clarified important pathways in the production of reactive oxygen and nitrogen species. Free radicals are involved in causing cerebral damage after perinatal hypoxia-ischemia affecting membrane lipids, proteins, and DNA. Anti-oxidant strategies can be used as add-on neuroprotective therapy after perinatal oxidative stress. Selective inhibitors of neuronal and inducible nitric oxide synthase, allopurinol, melatonin, and erythropoietin are among the first compounds that are ready for clinical trials.

Magnetic resonance imaging of the neonatal brain

Neonatal magnetic resonance (MR) imaging is rapidly becoming the preferred modality for the evaluation of central nervous system disorders in the newborn. Recent literature supports the value of this imaging technique in diagnosing ischemic, hemorrhagic and infectious disease processes in the premature and full-term neonatal brain. Recent data in premature newborns with neurological injury also suggest a role for MR imaging in determining long-term neurodevelopmental outcomes. This review article provides a framework and overview on neonatal MR imaging techniques and examines the literature or radiological disease patterns and prognostic implications in common neurological disorders.

Astrocytes and developmental white matter disorders

There is an increasing awareness that the astrocytes in the immature periventricular white matter are vulnerable to ischemia and respond to inflammation. Here we provide a synopsis of the articles that have evaluated the causes and consequences of developmental brain injuries to white matter astrocytes as well as the consequences of several genetic mutations that result in abnormal astrocyte development. Emerging data suggest that the astrocytes are not simply responding to the injury but are likely victims as well as culprits. Given the important roles that astrocytes play in maintaining ionic, neurotransmitter, and metabolic homeostasis in the brain, a more thorough understanding of the mechanisms that lead to their incapacitation, demise, or reactions as well as a better understanding of the stimuli that regulate their neuroprotective and regenerative properties will enable these cells to be manipulated to preserve the integrity of white matter and to potentially provide therapeutics to enhance neonatal regeneration and recovery from brain injury.

Imaging of the neonatal CNS

Imaging of the central nervous system is one of the major tasks of Paediatric Radiology, particularly in newborns, who present with a variety of conditions that need more or less urgent imaging. Imaging is usually performed primarily by bedside US, in rare cases supplemented by a skull or spine radiograph. For more detailed information and preoperatively, MRI has become the neuroimaging tool. Thus, CT today is only used for acute trauma assessment, for assessment of potential cerebral calcifications or when MRI is not available. In cases with vascular anomalies or unsuccessful punctures, image guided interventions (embolisation) or image guidance for access (lumbar puncture, puncture of skull collections ...) may become necessary. This article tries to give a brief overview on the common disease entities, their typical imaging features in the major modalities applied and the implications of imaging potential for indication and choice of imaging method. In general, acute assessment may become everywhere and major features of important diseases should be recognised not to miss conditions which need urgent treatment or referral to a dedicated paediatric unit. Many other conditions will only be seen at centres with a dedicated neonatal care unit and dedicated paediatric radiologist who then also will be able to provide proper imaging with adapted protocols and methods for these partially severely sick babies. As these specific features and adapted capabilities as well as dedicated training and clinical experience are necessary for providing best results and proper handling in neonates, many neonatal conditions will not be imaged at a peripheral site, but primarily should be referred to a paediatric (radiology) centre.

MR imaging of the neonatal brain

The advent of modern neuroimaging tools and methods has revolutionized the evaluation of the brain in neonates. The development of magnetic resonance (MR)-compatible monitoring tools and incubators has alleviated concerns regarding transportation of these unstable infants. The development of dedicated neonatal imaging coils has increased signal-to-noise ratios dramatically in images of the neonatal brain; this has made high-quality anatomic imaging, diffusion tensor imaging, and proton MR spectroscopy feasible in a normal imaging time. In centers that are equipped properly for neonatal MR imaging, MR is now unquestionably the study of choice for neonates who have encephalopathy or suspected brain injury. This article discusses the application of modern MR techniques to some of the causes of encephalopathy in neonates.

Maturational effects of lipopolysaccharide on white-matter injury in fetal sheep

White-matter damage has been associated with the development of cerebral palsy in children born both prematurely and at term, and it has been suggested that intrauterine infection can contribute to the brain injury. However, the relative importance of age on white-matter injury following infectious exposure in utero remains unclear. In this study, fetal sheep were exposed to systemic endotoxemia by administration of Escherichia coli lipopolysaccharide (88.7 +/- 7.7 ng/kg) at 65% or 85% of gestation. These gestational ages approximately correspond to human brain development in preterm and near-term infants respectively. White-matter injury was evaluated 3 days after lipopolysaccharide exposure with regard to microglia activation and loss of neurofilament and myelin basic protein. The expression of oligodendrocytes at different maturational stages was demonstrated in preterm and near-term fetuses with the oligodendroglial markers O4 and 2 ,3 -cyclic nucleotide 3 -phospodiesterase. Forty percent of the fetuses in the preterm group and 22% in the near-term group died within 8 hours of the endotoxin exposure. Three of six preterm and two of seven near-term surviving fetuses demonstrated pathologic changes in the brain with regard to increased microglia activation and loss of neurofilament staining. The number of activated microglia was enhanced in the subcortical white matter in both the preterm lipopolysaccharide-exposed fetuses (lipopolysaccharide: 235 +/- 64 cells/mm2; control: 72 +/- 28 cells/mm2; P = .0374) and the near-term fetuses (lipopolysaccharide: 180 +/- 40 cells/mm2; control 23 +/- 16 cells/mm2; P = .0152). There was a loss of neurofilament staining in both preterm fetuses (lipopolysaccharide: 2.20 +/- 0.77 pixel units; control: 0.20 +/- 0.10 pixel units; P = .0306) and near-term fetuses (lipopolysaccharide: 1.15 +/- 0.48 pixel units; control: 0.06 +/- 0.06 pixel units; P = .0285). O4-positive cells were detected at both gestational ages, whereas 2,3-cyclic nucleotide 3-phospodiesterase-positive cells and myelin basic protein staining were mainly detected in the near-term fetuses. In summary, we found white-matter injury in a proportion of both preterm and near-term fetuses after administration of lipopolysaccharide. These results are in agreement with clinical evidence suggesting that both preterm and term infants are at risk of periventricular leukomalacia in association with intrauterine infection.

White matter injury after repeated endotoxin exposure in the preterm ovine fetus

Intrauterine infection has been linked to neurologic injury in preterm infants. However, a reproducible model of white matter injury in the preterm fetus in a long gestation species that can be monitored in utero is currently unavailable. Thus, our objective was to determine the effects of bacterial endotoxin (lipopolysaccharide, LPS) on physiologic and inflammatory responses and brain structure in the preterm ovine fetus. At 0.7 of gestation, six catheterized fetuses received three to five intravenous injections of LPS (1 micro g/kg) over 5 d; seven fetuses served as controls. Fetal responses were monitored and brain tissue examined 10-11 d after the initial LPS injection. After LPS on d 1 and 2, fetuses became transiently hypoxemic and hypotensive and blood IL-6 levels were increased, but these responses were smaller or absent after subsequent LPS exposures. Neural injury was observed in all LPS-exposed fetuses, most prominently in the cerebral white matter. Injury ranged from diffuse subcortical damage to periventricular leukomalacia, and in the brainstem the cross-sectional area of the corticospinal tract was reduced by 30%. Thus, repeated exposure of the preterm ovine fetus to LPS causes neuropathology resembling that of cerebral palsy and provides a robust model for exploring the etiology, prevention, and treatment of white matter damage.

Educational neuroimaging: a proposed neuropsychological application of near-infrared spectroscopy (nIRS)

OBJECTIVE

To provide a description of an emerging neuroimaging methodology, near-infrared spectroscopy (nIRS), and a potential educational application of the unique aspects of this technology.

SUMMARY

nIRS is documented for its potential as a personal, portable, brain imaging system that may prove useful for cerebral monitoring in applied settings such as home, school, and work. The basis of nIRS brain imaging is reviewed, with summary descriptions of optical and neurovascular issues as well as a brief comparison to other brain imaging methodologies. Recent developments in nIRS technology are discussed, including ongoing validation efforts and potential applications for neuropsychologists. We describe one potential application of nIRS (i.e., educational neuroimaging) as an illustration of the use of nIRS technology and the potential expansion of the neuropsychologist's role in the educational setting.

CONCLUSION

nIRS holds the potential of opening new clinical questions and opportunities for neuropsychologists, and may provide a low-cost means of repeatable, neurovascular monitoring in nonmedical settings.

The variety of visual perceptual impairments in pre-school children with perinatal brain damage

To study the selectivity of visual perceptual impairment in children with early brain injury, eight visual perceptual tasks (L94), were administered to congenitally disabled children both with and without risk for cerebral visual impairment (CVI). The battery comprised six object-recognition and two visuoconstructive tasks. Seven tasks were newly designed. For these normative data are presented (age 2.75-6.50 years). Because the recognition tasks required object naming, each item included a canonical control drawing and visual perceptual ability was evaluated relative to the non-verbal intelligence level, instead of chronological age. In 22 multiple disabled children with no indications of CVI, the frequency of impairment did not exceed that in the reference sample for any L94 task. In contrast, in 57 5-year-old children who were at risk for CVI due to pre-maturity or birth asphyxia, a significant increase in the frequency of impairment was seen on six L94 tasks (range 12-38%). However, only five children had more than two impairments, indicating that the deficits were selective, not pervasive. We conclude that early brain lesions interfere with the functioning of particular visual subsystems, yet leave other subsystems intact and functioning within the normal range.

Controversies in the diagnosis and management of hypotension in the newborn infant

Although close to half of the newborns admitted to neonatal intensive care units receive treatment for "hypotension," the normal physiologic blood pressure range ensuring appropriate organ perfusion in the neonate is unknown. Thus, the decision to treat hypotension in the newborn is based on statistically defined gestational and postnatal age-dependent normative blood pressure values and physicians' beliefs rather than on data bearing physiologic reference. Dopamine is the most widely used sympathomimetic amine in the treatment of neonatal hypotension, and it is more effective than dobutamine in raising blood pressure. Volume administration is less effective in the immediate postnatal period, and its extensive use is associated with significant untoward effects, especially in preterm infants. During the course of their disease, some of the sickest hypotensive newborns become unresponsive to volume and pressor administration. This phenomenon is caused by the desensitization of the cardiovascular system to catecholamines by the critical illness and relative or absolute adrenal insufficiency. The findings that steroids rapidly up-regulate cardiovascular adrenergic receptor expression and serve as hormone substitution in cases of adrenal insufficiency explain their effectiveness in stabilizing the cardiovascular status and decreasing the requirement for pressor support in the critically ill newborn with volume-and pressor-resistant hypotension. Finally, despite recent advances in our understanding of the pathophysiology and management of neonatal hypotension, there are few data on the impact of the treatment on organ blood flow and tissue perfusion and on neonatal morbidity and mortality.

Exposure of developing oligodendrocytes to cadmium causes HSP72 induction, free radical generation, reduction in glutathione levels, and cell death

Primary cultures of oligodendrocytes were used to study the toxic effects of cadmium chloride. Cell viability was evaluated by the mitochondrial dehydrogenase activity and confirmed by propidium iodide (PI) fluorescence staining. The expression of the 72 kDa stress protein, HSP72, was assayed by Western blot analysis. The results showed that Cd(2+)-induced toxicity was dependent on the time and dose of exposure, as well as on the developmental stage of the cultures. Oligodendrocyte progenitors were more vulnerable to Cd(2+) toxicity than were mature oligodendrocytes. Mature oligodendrocytes accumulated relatively higher levels of Cd(2+) than did progenitors, as determined by (109)CdCl(2) uptake; treatment with the metal ion caused a more pronounced reduction in intracellular glutathione levels and significantly higher free radical accumulation in progenitors. The latter could explain the observed differences in Cd(2+) susceptibility. HSP72 protein expression was increased both in progenitors and in mature cells exposed to Cd(2+). Pretreatment with N-acetylcysteine, a thiocompound with antioxidant activity and a precursor of glutathione, prevented Cd(2+)-induced (i) reduction in glutathione levels and (ii) induction of HSP72 and diminished (i) Cd(2+) uptake and (ii) Cd(2+)-evoked cell death. In contrast, buthionine sulfoximine, an inhibitor of gamma-glutamyl-cysteine synthetase, depleted glutathione, and potentiated the toxic effect of Cd(2+). These results strongly suggest that Cd(2+)-induced cytotoxicity in oligodendrocytes is mediated by reactive oxygen species and is modulated by glutathione levels.

Cerebral intravascular oxygenation correlates with mean arterial pressure in critically ill premature infants

OBJECTIVES

Premature infants experience brain injury, ie, germinal matrix-intraventricular hemorrhage (GMH-IVH) and periventricular leukomalacia (PVL), in considerable part because of disturbances in cerebral blood flow (CBF). Because such infants are susceptible to major fluctuations in mean arterial blood pressure (MAP), impaired cerebrovascular autoregulation would increase the likelihood for the changes in CBF that could result in GMH-IVH and PVL. The objectives of this study were to determine whether a state of impaired cerebrovascular autoregulation could be identified reliably and conveniently at the bedside, the frequency of any such impairment, and the relation of the impairment to the subsequent occurrence of severe GMH-IVH and PVL.

PATIENTS AND METHODS

To monitor the cerebral circulation continuously and noninvasively, we used near-infrared spectroscopy (NIRS) to determine quantitative changes in cerebral concentrations of oxygenated hemoglobin (HbO(2)) and deoxygenated hemoglobin (Hb) from the first hours of life. Our previous experimental study showed a strong correlation between a measure of cerebral intravascular oxygenation (HbD), ie, HbD = HbO(2) - Hb, determined by NIRS, and volemic CBF, determined by radioactive microspheres. We studied 32 very low birth weight premature infants (gestational age: 23-31 weeks; birth weight: 605-1870 g) requiring mechanical ventilation, supplemental oxygen, and invasive blood pressure monitoring by NIRS from 1 to 3 days of age. MAP measured by arterial catheter pressure transducer and arterial oxygen saturation measured by pulse oximetry were recorded simultaneously. The relationship of MAP to HbD was quantitated by coherence analysis.

RESULTS

Concordant changes (coherence scores >. 5) in HbD and MAP, consistent with impaired cerebrovascular autoregulation, were observed in 17 of the 32 infants (53%). Eight of the 17 infants (47%) developed severe GMH-IVH or PVL or both. Of the 15 infants with apparently intact autoregulation, ie, coherence scores <.5, only 2 (13%) developed severe ultrasonographic lesions. Thus, for the entire study population of 32 infants, 8 of the 10 with severe lesions exhibited coherence scores >.5.

CONCLUSIONS

We conclude that NIRS can be used in a noninvasive manner at the bedside to identify premature infants with impaired cerebrovascular autoregulation, that this impairment is relatively common in such infants, and that the presence of this impairment is associated with a high likelihood of occurrence of severe GMH-IVH/PVL.