Developmental changes of glial fibrillary acidic protein and myelin basic protein in perinatal leukomalacia: relationship to a predisposing factor

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.

Respiratory inhibition after crying in infants

BACKGROUND

Among full-term neonates, the authors discovered infants who showed respiratory inhibition after crying which involved a marked decrease in SpO2. The infants were found to present increased echogenicity or a cyst in a cranial region termed the ganglionic eminence, or to have a subependymal cyst. The authors prospectively examined the relationship between respiratory inhibition after crying and these changes to examine the prevention and treatment of the episode.

METHODS

The authors conducted cranial ultrasonography to screen 381 full-term neonates who showed no abnormalities at birth and whose parents requested ultrasonographic screening of the head, followed by polygraphy of infants who showed increased echogenicity or a cyst in ganglionic eminence, or had a subependymal cyst. The authors similarly conducted polygraphy for 50 neonates without cranial ultrasound abnormalities; the former constituted the control group. Respiratory inhibition was defined to be central apnea immediately after crying with a decrease in SpO2 to <60%.

RESULTS

Among 381 neonates examined, 104 showed cranial ultrasound abnormalities; 60 of the 104 neonates indicated respiratory inhibition after crying. Oxygenation failed to improve the episode in 17 neonates with severe respiratory inhibition. However, theophylline alleviated the episode, and SpO2 no longer decreased to <60%. Theophylline was discontinued successfully by 6 months after birth, while 50 neonates in the control group showed no respiratory inhibition after crying.

CONCLUSION

Respiratory inhibition after crying which involved a marked decrease in SpO2 was observed in full-term neonates who showed no abnormalities after birth. These neonates could be screened by cranial ultrasonography.

Apnea, glial apoptosis and neuronal plasticity in the arousal pathway of victims of SIDS

Of 27,000 infants whose sleep-wake characteristics were studied under the age of 6 months, 38 died unexpectedly 2-12 weeks after the sleep recording in a pediatric sleep laboratory. Of these infants, 26 died of sudden infant death syndrome (SIDS), and 12 of definitely identified causes. The frequency and duration of sleep apneas were analysed. Sleep recordings and brainstem histopathology were studied to elucidate the possible relationship between sleep apnea and neuropathological changes within the arousal system. Immunohistochemical analyses were conducted using tryptophan hydroxylase (TrypH), a serotonin synthesizing enzyme, and growth-associated phosphoprotein 43 (GAP43), a marker of synaptic plasticity. The terminal-deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) method was used for apoptosis. The pathological and physiological data were correlated for each infant. In the SIDS victims, statistically significant positive correlations were seen between the number of TrypH-positive neurons in the dorsal raphe nucleus of the midbrain and the duration of central apneas (p = 0.03), between the number of TUNEL-positive glial cells in the pedunculopontine tegmental nucleus (PPTN) and the average number of spines in GAP43-positive neurons in the PPTN (p = 0.04). These findings in the dorsal raphe nucleus of the midbrain and PPTN, that play important roles in the arousal pathway suggest a possible link between changes in arousal and SIDS.

The correlation between ubiquitin in the brainstem and sleep apnea in SIDS victims

BACKGROUND

The sudden infant death syndrome (SIDS) is still the main cause of postneonatal infant death and its etiology has stimulated many competing theories, among which is the role of hypoxia and brainstem abnormalities. One report claims an increased in ubiquitin in the liver of SIDS victims, ubiquitin being one of the heat-shock proteins. The correlation between ubiquitin in the brainstem and sleep apnea in SIDS was investigated here.

MATERIALS AND METHODS

Among 27,000 infants studied prospectively to characterize their sleep-wake behavior, 38 infants died under 6 months of age, including 26 cases of SIDS. All the infants had been recorded during one night in a pediatric sleep laboratory some 3-12 weeks before death. The frequency and duration of sleep apnea were analyzed. Brainstem material was collected at autopsy and examined immunohistochemically for ubiquitin. The density of ubiquitin-positive elements was measured semiquantitatively. Correlation analyses were carried out between the density of ubiquitin-positive elements and the data on sleep apnea.

RESULTS

In the victims of SIDS, a statistically significant positive correlation was found between the density of ubiquitin-positive neuronal factors in the pons and the frequency of obstructive apnea (p=0.001) and statistically significant negative correlations were seen between the density of ubiquitin-positive cells in the ependyma in the pons and the duration of obstructive apnea (p=0.044) and between the density of ubiquitin-positive cells in the subependyma in the medulla and the frequency of central apnea (p=0.024).

CONCLUSIONS

It was found that three significant associations existed between the pathological data referring to ubiquitin and physiological data in SIDS victims. These facts are in agreements with the association of sleep apnea in SIDS.

The relationship between neuronal plasticity and serotonergic neurons in the brainstem of SIDS victims

BACKGROUND

The sudden infant death syndrome (SIDS) is still the main cause of postneonatal infant death and its cause is still unknown. Recently, the medullary serotonergic network deficiency theory has been proposed and an association between SIDS and neuronal plasticity has also been suggested. The growth-associated phosphoprotein 43 (GAP43) is a marker of synaptic plasticity and is critical for normal development of the serotonergic innervation. Therefore, the characteristics of GAP43-positive elements and their association with serotonergic neurons were here investigated in the brainstem of SIDS victims.

MATERIALS AND METHODS

The materials of this study included 26 cases of SIDS and 12 control cases. The brainstem material was collected and the immunohistochemistry of GAP43 and tryptophan hydroxylase (TrypH) carried out. The density of GAP43-positive neurons and dendrites and of TrypH-positive neurons were measured quantitatively. Nonparametric analyses of GAP43 between SIDS and non-SIDS and correlation analyses between GAP43 and TrypH were performed.

RESULTS

No significant difference in GAP43-associated findings was found between SIDS and non-SIDS nor any significant correlation between GAP43-associated findings and TrypH-positive neurons.

CONCLUSIONS

The results of this study were not in agreement with the association of GAP43 with SIDS and with serotonergic innervation in SIDS.

Clinicopathological correlation between brainstem gliosis using GFAP as a marker and sleep apnea in the sudden infant death syndrome

BACKGROUND

Chronic hypoxia, leading to brainstem gliosis, has been postulated as a factor in the sudden infant death syndrome (SIDS), which is still the main cause of postneonatal infant death. Gliosis detected by immunohistochemistry of glial fibrillary acidic protein (GFAP) is a marker of apoptosis. The correlation between GFAP-positive reactive astrocytes in the brainstem and sleep apnea in SIDS was investigated.

MATERIALS AND METHODS

Among 27,000 infants studied prospectively to characterize their sleep-wake behavior, 38 infants died under 6 months of age, including 26 cases of SIDS. The frequency and duration of sleep apnea were analyzed. Brainstem material was collected and immunohistochemistry of GFAP carried out. The density of GFAP-positive reactive astrocytes was measured quantitatively. Correlation analyses were carried out between the data on gliosis and the physiological data of sleep apnea.

RESULTS

A SIDS-specific negative correlation between the density of gliosis in the dorsal vagus nucleus in the medulla oblongata and the frequency of obstructive apnea (p=0.022) was found.

CONCLUSIONS

A significant SIDS-specific correlation with gliosis in the dorsal vagus nucleus and the characteristics of sleep apnea might invite the cardiorespiratory changes in SIDS.

Pathological data on apoptosis in the brainstem and physiological data on sleep apnea in SIDS victims

The sudden infant death syndrome (SIDS) is still the main cause of postneonatal infant death and its cause is still unknown. A chronic hypoxic situation has been shown to exist in the brains of SIDS victims and apoptosis has been demonstrated in hypoxic situations. In this study, the correlation between apoptotic neurons or glias and sleep apnea in SIDS was investigated in the brainstem of SIDS victims.

MATERIALS AND METHODS

In a cohort of 27,000 infants studied prospectively to characterize their sleep-wake behavior, 38 infants died under 6 months of age. They included 26 cases of SIDS. The frequency and duration of sleep apnea were analyzed. The brainstem material was collected and terminal-deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL) method was carried out. The density of TUNEL-positive neurons or glias was measured quantitatively. Correlation analyses were carried out between the apoptosis-associated pathological data and the physiological data of sleep apnea.

RESULTS

No significant negative or positive correlation between the density of TUNEL-positive neurons or glias and the characteristics of sleep apnea was observed in SIDS victims. No statistically significant differences associated with apoptotic neurons and glias were observed between SIDS and non-SIDS.

CONCLUSIONS

The pathological findings of apoptosis were not in agreement with the hypothesis refer to apnea and arousal phenomenon in pathophysiology of SIDS.

The presence of TATA-binding protein in the brainstem, correlated with sleep apnea in SIDS victims

BACKGROUND

Recent reports have indicated that the presence of transcription factors and RNA polymerase decreases in rat brains that suffer perinatal asphyxia from hypoxia. As hypoxia has been proposed as a causative factor in the Sudden Infant Death Syndrome (SIDS), the correlation between TATA-binding protein (TBP) in the brainstem of SIDS victims as a marker of transcription and the incidence of sleep apnea was investigated.

MATERIALS AND METHODS

A total of 38 infants, including 26 cases of SIDS, died under 6 months of age, in a cohort of 27,000 infants studied prospectively to characterize their sleep-wake behavior. The frequency and duration of sleep apnea was analyzed. Brainstem material was collected and immunohistochemistry of TBP was carried out. The density of TBP-positive neurons was measured quantitatively. Correlation analyses were carried out between the density of TBP-positive neurons and the data concerning sleep apnea.

RESULTS

One SIDS-specific positive correlation occurred between the density of TBP-positive neurons in the dorsal raphe nucleus of the midbrain and the duration of central apnea (p=0.049) and two SIDS-specific negative correlations between the density of TBP-positive neurons in the pars compacta and dissipata of the pedunculopontine tegmentum nucleus (PPTNc, PPTNd) in the midbrain and the duration of apnea (p=0.035).

CONCLUSIONS

The significant correlation between the findings of TBP-positive neurons in the midbrain arousal pathway and the characteristics of sleep apnea in SIDS victims is in agreement with the both association of apnea and arousal phenomenon in pathophysiology of SIDS.

Investigation into the correlation in SIDS victims between Alzheimer precursor protein A4 in the brainstem and sleep apnea

BACKGROUND

Recently, the appearance of beta-amyloid precursor protein (APP) has been demonstrated in the neonatal brain following hypoxic-ischaemic injury. As chronic hypoxia is one of the favoured theories of causation in the sudden infant death syndrome (SIDS), the correlation between APP in the brainstem and sleep apnea in SIDS was investigated.

MATERIALS AND METHODS

Among 27,000 infants studied prospectively to characterize their sleep-wake behavior, 38 infants died under 6 months of age, which included 26 cases of SIDS. All the infants had been recorded during one night in a pediatric sleep laboratory, some 3 to 12 weeks before death. The frequency and duration of sleep apnea were analyzed. The brainstem material was collected and immunohistochemistry with anti-Alzheimer precursor protein A4 (APP) was carried out. The density of APP-positive elements was measured semi-quantitatively. Correlation analyses were carried out between the density of APP-positive elements and the data on sleep apnea.

RESULTS

No correlation was found.

CONCLUSION

No correlation between pathological data of APP and physiological data of sleep apnea was not in agreement with the association of sleep apnea in pathophysiology of SIDS.

The correlation between microtubule-associated protein 2 in the brainstem of SIDS victims and physiological data on sleep apnea

BACKGROUND

Microtubule-associated protein 2(MAP2), a cytoskeletal protein of the neuron, is a marker of early ischemic neuronal damage. As a chronic hypoxic situation exists in the brains of victims of the sudden infant death syndrome (SIDS), the correlation between MAP2-positive neurons or dendritic spines in the brainstem and sleep apnea was investigated in SIDS, which is still the main cause of postneonatal infant death.

MATERIALS AND METHODS

27,000 infants were studied prospectively to characterize their sleep-wake behavior and amongst these, 38 infants died under 6 months of age. They included 26 cases of SIDS. The frequency and duration of sleep apneae were analyzed. The brainstem material was collected and immunohistochemistry of MAP2 was carried out. The density of MAP2-positive neurons, dendrites and dendritic spines were measured quantitatively. Correlation analyses were carried out between the MAP2-associated pathological data and the physiological data of sleep apnea.

RESULTS

One negative correlation between the density of MAP2-positive dendrites in the pars compacta of pedunculo-pontine tegmentum nucleus (PPTNc) and the duration of obstructive apnea (p=0.017) and two SIDS-specific positive correlations between the density of MAP2-positive dendrites in the pars dissipata of pedunculo-pontine tegmentum nucleus (PPTNd) and the duration of central apnea (p=0.005) and between the dorsal raphe and the frequency of obstructive apnea were found in SIDS victims. The density of MAP2-positive dendritic spines in PPTNc was significantly higher in SIDS than in control (p=0.034).

CONCLUSIONS

The significant correlations with the MAP2-positive findings in the midbrain arousal pathway and the characteristics of sleep apnea in SIDS victims were in agreement with the association with apnea and arousal-deficiency in SIDS.

Correlation between the Ki-67 antigen in the brainstem and physiological data on sleep apnea in SIDS victims

BACKGROUND

The Ki-67 antigen appears in all human proliferating cells during late G1, S, M and G2 phases of the cell cycle, but is consistently absent in the Go phase (noncycling) cells. The correlation between Ki-67 in the brainstem and sleep apnea in victims of the sudden infant death syndrome (SIDS) was investigated to elucidate cell kinetics in the brainstem of this condition, which is still the main cause of postneonatal infant death.

MATERIALS AND METHODS

Twenty-six cases of SIDS occurred among 38 infants dying under 6 months of age in a cohort of 27,000 infants studied prospectively to characterize their sleep-wake behavior. All the infants had been recorded during one night in a pediatric sleep laboratory some 3 to 12 weeks before death. The frequency and duration of sleep apnea were analyzed. At autopsy, brainstem material was collected and immunohistochemistry for Ki-67 was carried out. The density of Ki-67-positive neurons was measured semiquantitatively. Correlation analyses were carried out between the density of Ki-67-positive neurons and the data on sleep apnea.

RESULTS

Except in two cases in SIDS victims and in one control, the detection of Ki-67 was negative. No correlation analysis between the Ki-67 and of sleep apnea was found.

CONCLUSIONS

There were no abnormal cell kinetics detected by the demonstration of Ki-67 antigen in the brainstems of SIDS victims.

The correlation between serotonergic neurons in the brainstem and sleep apnea in SIDS victims

BACKGROUND

In the Sudden Infant Death Syndrome (SIDS), a medullary serotonergic network deficiency theory has been proposed, amongst many other hypotheses. The correlation between serotonergic neurons or dendritic spines in the brainstem of SIDS and sleep apnea was investigated here.

MATERIALS AND METHODS

Twenty-seven thousand infants were studied prospectively to characterize their sleep-wake behavior. Of these, 38 infants died under 6 months of age, including 26 cases of SIDS. The frequency and duration of sleep apnea were analyzed. Brainstem material was collected and immunohistochemistry for tryptophan hydroxylase (TrypH) carried out. The density of TrypH-positive neurons was measured quantitatively. Correlation analyses were carried out between the TrypH-associated pathological data and the physiological data of sleep apnea.

RESULTS

One significant positive correlation between the density of TrypH-positive neurons in the dorsal raphe nucleus of the midbrain and the duration of central apnea (p=0.027) was found in SIDS victims.

CONCLUSIONS

Some of serotonergic facts could be involved in the pathophysiology of SIDS.

The correlation between tau protein in the brainstem and sleep apnea in SIDS victims

BACKGROUND

Recently, it has been reported that neuronal plasticity in the brainstem arousal pathway is related to the sudden infant death syndrome (SIDS). Tau protein may contribute to axonal development and neural plasticity; therefore, the correlation between tau protein in the brainstem and sleep apnea in SIDS was investigated here.

MATERIALS AND METHODS

Among 27,000 infants studied prospectively to characterize their sleep-wake behavior, 38 infants died under 6 months of age, including 26 cases of SIDS. The frequency and duration of sleep apnea were analyzed on all the infants, having been recorded during one night in a pediatric sleep laboratory some 3-12 weeks before death. The brainstem material was collected and immunohistochemistry of tau was carried out. The density of tau-positive elements was measured semiquantitatively. Correlation analyses were carried out between the density of tau-positive elements and the data of sleep apnea.

RESULTS

In the 26 SIDS cases, tau-positive findings were observed in the sub-pia mater in two cases, in the colloid plexus in one case, in the ependyma and subependyma in five cases, in neurons in two cases and as a general diffusion in one case. In 12 control cases, tau-positive findings were observed in the sub-pia mater in one case and in neuronal elements in three cases. No correlation was found on analysis.

CONCLUSIONS

There was no correlation between the finding of tau in the brainstem of SIDS victims and the incidence of sleep apnea.

In vivo quantitative ultrasonic evaluation of neonatal brain with a real time integrated backscatter imaging system

We applied the integrated backscatter (IBS) imaging system to the evaluation of the normal neonatal brain of different birth-weights: extremely low-birth-weight (N=13), very-low-birth-weight (N=14), low-birth weight (N=14), and normal birth weight (N=19). The IBS values in six regions of interest, the deep white matter, subcortical white matter, choroid plexus, thalamus, lateral ventricle, and occipital bone, were compared among groups of different birth weights, gestational age, and postnatal age: at the date of birth and 28 approximately 30 days after birth. The IBS values were higher in the order of bone>choroid plexus>deep white matter>subcortical white matter>thalamus>lateral ventricle and were significantly different except for the lateral ventricle in all the groups at days 0 and 28 approximately 30. The IBS values increased with the decrease of birth weight and gestational age. There was a decrease of IBS values at day 28 compared to that of day 0 in the extremely low birth weight and very low birth weight groups; however, they remained the same in infants with low birth weights and in the normal birth weight group. Further studies to evaluate the significance of this technique for the objective diagnosis of brain insults in neonates are necessary.

Myelin transcription factor 1 (MyT1) immunoreactivity in infants with periventricular leukomalacia

Myelin transcription factor 1 (MyT1) is a zinc-dependent, DNA-binding protein, and is known to be expressed in early progenitors of oligodendrocytes. We examined the immunoreactivity of MyT1 in developing human brains and brains with periventricular leukomalacia (PVL) to understand the relationship between the expression of MyT1 and myelination in PVL brains. MyT1-positive glial cells were first detected at 19 gestational weeks (GWs) and then gradually increased until 26-29 GWs in the control group. Then they decreased and became very rare at 1 year of age. The expression of MyT1 immunoreactivity shifted from the nucleus to the cytoplasm of the glial cells in the developmental time course. In the chronic stage of PVL, MyT1-positive cells were significantly increased around necrotic foci and some of the regions were coincident with increasing MBP and PLP immunoreactivity. These results may reflect myelin repair on dysmyelination around PVL areas. Therefore, MyT1 may play an important role in the myelin repair in PVL regions.

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.

White matter injury in the preterm infant: an important determination of abnormal neurodevelopment outcome

Periventricular white matter injury, specifically cystic periventricular leukomalacia (PVL) and ipsilateral hemorrhage into white matter associated with periventricular-intraventricular hemorrhage (PV-IVH), contribute significantly to neonatal mortality and long-term neurodevelopmental deficits in the premature infant. The first lesion PVL occurs in approximately 3-4% of infants of birth weight (BW) < 1500 grams. It manifests either as a focal or diffuse lesion within white matter. Although the pathogenesis of PVL is complex and likely multifactorial, principle contributors include vascular factors which markedly increase the risk for ischemia during periods of systemic hypotension and the intrinsic vulnerability of the oligodendrocyte to neurotoxic factors such as free radicals or cytokines. Clinical associations with PVL include a history of chorioamnionitis, prolonged rupture of membranes, asphyxia, sepsis, hypocarbia, etc. The vast majority of infants exhibit long-term neurodevelopmental deficits that affect motor, cognitive and visual function. The second lesion, the ipsilateral hemorrhage into white matter lesion associated with PV-IVH, occurs in approximately 10-15% of infants of BW < 1000 grams. The white matter injury appears to be a venous infarction with hemorrhage occurring as a secondary phenomenon. Prevention of this lesion has to include prevention of the associated PV-IVH. In this regard, the antenatal administration of glucocorticoids has been associated with a significant reduction in the sonographic incidence of severe IVH and the associated white matter involvement. The postnatal administration of indomethacin to high risk infants appears to hold the most promise at the current time in preventing this lesion. The neurodevelopmental outcome with extensive white matter injury is universally poor, affecting long-term motor and cognitive deficits; the long-term outcome is more favorable with lesser involvement. A clearer understanding of pathogenesis of both conditions is essential so as to provide targeted preventative strategies.

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.

Ventriculomegaly, delayed myelination, white matter hypoplasia, and "periventricular" leukomalacia: how are they related?

Preterm infants, including some who have sustained intracranial hemorrhage, appear to be at increased risk of lateral ventricular enlargement. Although some occurrences might be due to an impairment of cerebrospinal fluid flow or absorption, many instances of ventriculomegaly without accompanying macrocephaly reflect diffuse white matter damage resulting in diminished (i.e., hypoplastic) white matter or an inadequate density of axons. Perinatally acquired widespread white matter damage is sometimes associated with the focal white matter necrosis. We hypothesize that in some infants both ventriculomegaly and delayed myelination are consequences of disturbances to myelinogenesis that result from an impairment of cells destined to become oligodendroglia or of disturbances to rapidly growing axons. The vulnerability of developing white matter in preterm newborns might, in part, reflect the diminished availability of growth/ survival factors, or a vulnerability to toxins or physiologic perturbations. Awareness that some ventriculomegaly reflects widely distributed white matter damage should prevent overtreatment of what might appear to be hydrocephalus, but is not due to impaired cerebrospinal fluid dynamics. Increased understanding of the phenomena leading to ventriculomegaly related to paucity of white matter should lead to successful efforts to prevent white matter damage in preterm newborns.

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.

Visual and neurological outcome of infants with periventricular leukomalacia

Visual acuity, visual fields and neurological status were assessed in 10 infants with periventricular leukomalacia (PVL), tested at 16, 36, 48 and 72 weeks from the expected date of confinement. Monocular acuity development was normal in eight of the 10 infants, but was below normal in one infant at eight months and in another at 18 months. Over half the infants tested at 16, 36 and 48 weeks had smaller visual fields than those of 95 per cent of healthy preterm infants tested at the same ages, but by 72 weeks only two of six infants tested had restricted visual fields. Nine of the 10 infants were neurologically abnormal at ages under one year, but only four remained so beyond one year. These results indicate more favourable outcomes for visual acuity and neurological status in infants with non-cavitary PVL than have been reported in infants with cavitary PVL. The most compromised infants were one with cavitary PVL and another with extensive non-cavitary PVL who had the longest-lasting EEG abnormalities of all 10 infants.

Infantile subcortical leukohypodensity demonstrated by computed tomography

We reviewed the computed tomography scans of 126 term infants, ages 1-6 months; leukohypodensity was found just under the cerebral cortex (subcortical leukohypodensity [SLD]) in 3 infants (2.4%) at 1-3 months of age. On subsequent computed tomography at over 4 months of age, SLD had disappeared and anterior horn predominant dilatation of the lateral ventricles had appeared. Only 1 patient with a distinct SLD had a poor neurodevelopmental outcome: spastic diplegia. SLD in our patients is believed to be closely related to subcortical leukomalacia because of the similar location and age distribution. Transient SLD may be a mild form of cystic SLD which would require careful computed tomography follow-up examination in early infancy.

Endotoxin, cerebral blood flow, amino acids and brain damage in young rabbits

The effects of bacterial endotoxin (lipopolysaccharide; LPS) on the cerebral blood flow (CBF), amino acid levels and brain histology were studied in young rabbits. The CBF was slightly decreased in the cerebral cortex and markedly decreased in the cerebral white matter at 60 and 120 min after LPS administration. Histological examination revealed only slightly pyknotic neurons around small vessels at 24 hours, and multifocal necrosis in the deep cerebral cortex and white matter at 72 hours. Some amino acids were increased in the plasma and brain regions at 24 hours after LPS administration, most of which were essential amino acids. GABA in the cerebral white matter was decreased at 24 hours. At 72 hours, most non-essential and glucogenic amino acids were decreased. These results suggest that the brain histological changes are related mainly to hypoperfusion and vascular damage in the brain. The amino acid changes may also be related to inappropriate amino acid metabolism associated with brain cell damage.