The clinical outcomes of deep gray matter injury in children with cerebral palsy in relation with brain magnetic resonance imaging

In the present study we investigated the nature and extent of clinical outcomes using various classifications and analyzed the relationship between brain magnetic resonance imaging (MRI) findings and the extent of clinical outcomes in children with cerebral palsy (CP) with deep gray matter injury. The deep gray matter injuries of 69 children were classified into hypoxic ischemic encephalopathy (HIE) and kernicterus patterns. HIE patterns were divided into four groups (I-IV) based on severity. Functional classification was investigated using the gross motor function classification system-expanded and revised, manual ability classification system, communication function classification system, and tests of cognitive function, and other associated problems. The severity of HIE pattern on brain MRI was strongly correlated with the severity of clinical outcomes in these various domains. Children with a kernicterus pattern showed a wide range of clinical outcomes in these areas. Children with severe HIE are at high risk of intellectual disability (ID) or epilepsy and children with a kernicterus pattern are at risk of hearing impairment and/or ID. Grading severity of HIE pattern on brain MRI is useful for predicting overall outcomes. The clinical outcomes of children with a kernicterus pattern range widely from mild to severe.

WHAT THIS PAPER ADDS

Delineation of the clinical outcomes of children with deep gray matter injury, which are a common abnormal brain MRI finding in children with CP, is necessary. The present study provides clinical outcomes for various domains in children with deep gray matter injury on brain MRI. The deep gray matter injuries were divided into two major groups; HIE and kernicterus patterns. Our study showed that severity of HIE pattern on brain MRI was strongly associated with the severity of impairments in gross motor function, manual ability, communication function, and cognition. These findings suggest that severity of HIE pattern can be useful for predicting the severity of impairments. Conversely, children with a kernicterus pattern showed a wide range of clinical outcomes in various domains. Children with severe HIE pattern are at high risk of ID or epilepsy and children with kernicterus pattern are at risk of hearing impairment or ID. The strength of our study was the assessment of clinical outcomes after 3 years of age using standardized classification systems in various domains in children with deep gray matter injury.

Bilirubin-Induced Audiologic Injury in Preterm Infants

Although hyperbilirubinemia is extremely common among neonates and is usually mild and transient, it sometimes leads to bilirubin-induced neurologic damage (BIND). The auditory pathway is highly sensitive to the effects of elevated total serum/plasma bilirubin (TB) levels, with damage manifesting clinically as auditory neuropathy spectrum disorder. Compared to full-term neonates, preterm neonates are more susceptible to BIND and suffer adverse effects at lower TB levels with worse long-term outcomes. Furthermore, although standardized guidelines for management of hyperbilirubinemia exist for term and late preterm neonates, similar guidelines for neonates less than 35 weeks gestational age are limited.

Audiologic impairment associated with bilirubin-induced neurologic damage

Hyperbilirubinemia occurs commonly in neonates and is usually mild and transient, with no long-lasting sequelae. However, bilirubin-induced neurologic damage may occur in some infants. The auditory pathway is the most sensitive part of the central nervous system to bilirubin-induced toxicity, and permanent sequelae may result from only moderately elevated total serum/plasma bilirubin levels. The damage to the auditory system occurs primarily within the brainstem and cranial nerve VIII, and manifests clinically as auditory neuropathy spectrum disorder.

Are the neuromotor disabilities of bilirubin-induced neurologic dysfunction disorders related to the cerebellum and its connections?

Investigators have hypothesized a range of subcortical neuropathology in the genesis of bilirubin-induced neurologic dysfunction (BIND). The current review builds on this speculation with a specific focus on the cerebellum and its connections in the development of the subtle neuromotor disabilities of BIND. The focus on the cerebellum derives from the following observations: (i) the cerebellum is vulnerable to bilirubin-induced injury; perhaps the most vulnerable region within the central nervous system; (ii) infants with cerebellar injury exhibit a neuromotor phenotype similar to BIND; and (iii) the cerebellum has extensive bidirectional circuitry projections to motor and non-motor regions of the brainstem and cerebral cortex that impact a variety of neurobehaviors. Future study using advanced magnetic resonance neuroimaging techniques have the potential to shed new insights into bilirubin's effect on neural network topology via both structural and functional brain connectivity measurements.

[Diagnostic value of amplitude-integrated electroencephalography in predicting outcome of newborn patients in neonatal intensive care unit]

OBJECTIVE

To assess the diagnostic value of amplitude-integrated electroencephalography (aEEG) in predicting outcome of newborns who were at high risk for central nervous system without severe hypoxic-ischemic encephalopathy.

METHODS

Forty-two consecutive patients at risks for neurological disorders referred to our level-III NICU were prospectively enrolled in the study over a period of 3 years. They were classified on the basis of their primary diagnoses including hypoglycemic brain damage, meningoencephalitis, bilirubin encephalopathy, and metabolic disease. Clinical data were collected. Amplitude-integrated and raw EEG tracings were assessed for background pattern, sleep-wake cycling, and epileptiform activity. The neuromotor development of survivors was assessed by using the Infant Neurological International Battery (INFANIB).

RESULT

The characteristic of aEEG tracings in 42 infants showed continuous normal voltage (CNV)(n = 15), discontinuous voltage (DC)(n = 9), burst-suppression (BS) BS(+) (n = 6), BS(-)(n = 7), flat (FT, n = 5); mature sleep-wake cycling (SWC, n = 4), immature SWC (n = 14), no SWC (n = 24); 30 infants (71.4%) had electrical seizures: single seizure (n = 6); repetitive seizures (n = 7), and status epilepticus (SE) (n = 17).aEEG of 20 infants who had poor outcome showed FT (n = 5), BS(-)/SE (n = 6), BS(-)/ repetitive seizures (n = 1) , BS(+)/SE (n = 1), BS(+)/repetitive seizures (n = 1), DC/SE(n = 6). Chi-square analysis and Spearman rank correlation analysis showed the classification of aEEG background pattern, SWC and comprehensive score (score system was developed by evaluation of the above 3 variables) were correlated with the outcome of these infants at high neurological risks.

CONCLUSION

Amplitude-integrated electroencephalography can provide important information of the status of cerebral function in neonates at high neurological risk and help to predict their outcome.

[Amplitude-integrated electroencephalographic changes in neonates with acute bilirubin encephalopathy]

OBJECTIVE

To characterize amplitude-integrated electroencephalo graphic (aEEG) traces in neonates with acute bilirubin encephalopathy (ABE), explore the value of aEEG in early diagnosis and prediction of neurological outcome of ABE.

METHOD

aEEG records of 10 cases with ABE (Oct 2009-Nov 2011) were reviewed to identify neonates with a diagnosis of ABE. Clinical data were collected. The aEEG traces were classified according to background activity (normal, moderate, or severely abnormal), presence of seizures and sleep-wake cycling (SWC). Brainstem auditory evoked potential (BAEP) and magnetic resonance imaging (MRI) were studied. The neuromotor development of survivors with ABE was assessed by using the Infant Neurological International Battery (INFANIB).

RESULT

The characteristics of aEEG tracings in these infants with ABE were shown continuous normal voltage (CNV, n = 5), discontinuous voltage (DNV, n = 4), discontinuous voltage with burst-suppression (BS)BS+ (n = 1); mature SWC (n = 2), immature SWC (n = 5), no SWC (n = 3); 8 infants (80%) had electrical seizures: single seizure (n = 2); repetitive seizures (n = 2), and status epilepticus (SE) (n = 4). Among the 10 infants with ABE, no infants had normal aEEG, 3 had mildly abnormal aEEG, and 7 had severely abnormal aEEG. Eight infants accepted BAEP test, 2 were mildly abnormal and 6 were severely abnormal. Six infants accepted MRI, 1 was normal and 5 were abnormal. By chi-square analysis and Spearman rank correlation analysis, the results of aEEG classification were correlated with the phase of ABE and the severity of BAEP. These infants were followed up for more than 6 months (range 6 months to 1 year). In 3 infants with mildly abnormal aEEG, 2 were normal and 1 was transit in infanib score at 6 months of age. Of 7 infants with severely abnormal aEEG, 1 died, 3 were abnormal (2 Spastic dyskinesia and 1 hypotonia), 2 were transit in infanib score at 6 months old. 1 lost to follow-up.

CONCLUSION

Amplitude-integrated electroencephalography can provide important information of the status of cerebral function in neonates with ABE and help to predict its neurological outcome.

Influence of hypoxia and ischemia preconditioning on bilirubin damage to astrocytes

Hypoxia-ischemia in the perinatal period is a common cause of neurologic disability in children and is often associated with neonatal morbidity and mortality. Another frequent condition of the newborn is hyperbilirubinemia and it is well known that deposition of unconjugated bilirubin (UCB) in the central nervous system can damage nerve cells and cause encephalopathy. Interestingly, some studies report the onset of cerebral hypoxia-ischemia as a risk factor for UCB encephalopathy, since that condition often precedes neonatal hyperbilirubinemia. However, the cellular mechanisms triggered by hypoxia-ischemia that may enforce UCB deleterious effects are not well elucidated. Therefore, we designed this study to investigate whether hypoxia (HP) or combined oxygen-glucose deprivation (OGD) followed by reoxygenation, modifies glial cell susceptibility to UCB injury. Thus, cultured astrocytes were exposed to HP or OGD for 4 h and returned to normoxic conditions for another 12 h prior to incubation with UCB for 4 h. HP and OGD effects in UCB toxicity were compared to normoxic conditions. Our results demonstrate that HP and OGD preconditioning increase the vulnerability of glial cells to UCB damage by enhancing some of the deleterious effects of UCB, namely cell death by both apoptosis and necrosis. This preconditioning also augments the UCB-induced stimulation of an inflammatory response by an effect that involves the activation of the nuclear factor kappaB activation. These findings provide a novel basis for the increased risk of brain damage in jaundiced newborns that were previously exposed to hypoxia or ischemia during the perinatal period, namely during delivery.

Role of multidrug resistance-associated protein 1 expression in the in vitro susceptibility of rat nerve cell to unconjugated bilirubin

Nerve cell injury by unconjugated bilirubin (UCB) has been implicated in brain damage during neonatal hyperbilirubinemia, particularly in the preterm newborn. Recently, it was shown that UCB is a substrate for the multidrug resistance-associated protein 1 (Mrp1), an ATP-dependent efflux pump, which may decrease UCB intracellular levels. To obtain a further insight into the role of Mrp1 in the increased vulnerability of immature cells to UCB, we evaluated the mRNA and the protein levels of Mrp1 throughout differentiation in primary cultures of rat neurons and astrocytes. Furthermore, in order to provide supportive evidence for the role of Mrp1 in the protection of nerve cells from UCB-induced effects, we evaluated cell susceptibility to UCB when Mrp1 was inhibited with MK571 ((E)-3-[[[3-[2-(7-chloro-2-quinolinyl) ethenyl]phenyl]-[[3-dimethylamino)-3-oxopropyl]thio]methyl]thio]-propanoic acid). The results are the first to demonstrate that Mrp1 is expressed in neurons and that both mRNA and protein levels of Mrp1 increase with cell differentiation. Additionally, inhibition of Mrp1 was associated with an increase in UCB toxic effects, namely cell death, cell dysfunction, and secretion of interleukin (IL)-1beta, tumor necrosis factor (TNF)-alpha, as well as of glutamate. These results point to a novel role of Mrp1 in the susceptibility of premature babies to UCB encephalopathy, and provide a startup point for the development of a new therapeutic strategy.

NMDA channel antagonist MK-801 does not protect against bilirubin neurotoxicity

BACKGROUND

Bilirubin encephalopathy or kernicterus is a potentially serious complication of neonatal hyperbilirubinemia. The mechanism of bilirubin-induced neurotoxicity is not known. Many neurological insults are mediated through NMDA receptor activation.

OBJECTIVE

We assessed the effect of the NMDA channel antagonist, MK-801 on bilirubin neurotoxicity in vivo and in vitro.

METHODS

Bilirubin toxicity in vitro was assessed using trypan blue staining. Sulfadimethoxine injected (i.p.) jaundiced Gunn rat pups exhibit many neurological sequelae observed in human hyperbilirubinemia. Brainstem auditory-evoked potentials (BAEPs), a noninvasive sensitive tool to assess auditory dysfunction due to bilirubin neurotoxicity, were used to assess neuroprotection with MK-801 (i.p.) in vivo.

RESULTS

In primary cultures of hippocampal neurons, 20 min exposure to 64:32 microM bilirubin:human serum albumin reduced the cell viability by approximately 50% ten hours later. MK-801 treatment did not protect the cells. MK-801 pretreatment doses ranging from 0.1-4.0 mg/kg did not protect against BAEP abnormalities in Gunn rat pups 6 h after sulfadimethoxine injection.

CONCLUSION

Our findings suggest that bilirubin neurotoxicity is not mediated through NMDA receptor activation.

Minocycline blocks acute bilirubin-induced neurological dysfunction in jaundiced Gunn rats

BACKGROUND

Extreme hyperbilirubinemia is treated with double volume exchange transfusion, which may take hours to commence. A neuroprotective agent that could be administered immediately might be clinically useful. Minocycline, an anti-inflammatory and anti-apoptotic semisynthetic tetracycline, prevents hyperbilirubinemia-induced cerebellar hypoplasia in Gunn rats. Acute brainstem auditory evoked potential (BAEP) abnormalities occur after giving sulfadimethoxine to 16-day-old jaundiced Gunn rats to displace bilirubin into tissue including brain.

OBJECTIVE

To assess whether minocycline is neuroprotective in this model of acute bilirubin encephalopathy.

METHODS

We recorded BAEPs at baseline and 6 h after injecting sulfadimethoxine. Minocycline 0.5 mg/kg (n = 4), 5 mg/kg (n = 9), 50 mg/kg (n = 9) or 500 mg/kg (n = 3, all died) was administered 15 min before sulfadimethoxine (0 h). Controls received saline followed by either sulfadimethoxine (n = 13) or saline (n = 7).

RESULTS

At 6 h total plasma bilirubin decreased from 10.84 +/- 0.88 mg/dl (mean +/- SD) to 0.70 +/- 0.35 mg/dl (p <10(-9)) in all sulfadimethoxine-injected groups. At 6 h, there was complete protection against decreased amplitudes of BAEP waves II and III and increased I-II and I-III interwave intervals (brainstem conduction times corresponding to I-III and I-V in humans) with 50 mg/kg minocycline, and partial protection with lower doses.

CONCLUSIONS

Minocycline 50 mg/kg 15 min prior to an intervention that normally produces acute bilirubin neurotoxicity is neuroprotective in jaundiced Gunn rat pups. Further studies are needed to investigate the temporal course and mechanism of neuroprotection. Minocycline, administered immediately, may be clinically useful in treating extreme neonatal hyperbilirubinemia and preventing kernicterus. We believe our model provides an efficient in vivo model to screen and evaluate new agents that are neuroprotective against bilirubin toxicity and kernicterus.

Neurodevelopmental outcome of the late preterm infant

There is very limited information about the developmental outcome of the late preterm infant. The developing brain is vulnerable to injury during this very active and important stage of fetal brain development; therefore, it is important to carefully monitor the neurologic outcome of these infants. This article discusses gestational brain development and complications of late preterm birth that contribute to the overall risk of brain injury.

Hyperbilirubinemia and kernicterus

This article describes new findings concerning the basic science of bilirubin neurotoxicity, new considerations of the definition of clinical kernicterus, and new and useful tools to diagnose kernicterus in older children, and discusses treatments for kernicterus beyond the newborn period and why proper diagnosis is important.

Toward understanding kernicterus: a challenge to improve the management of jaundiced newborns

PURPOSE

We sought to evaluate the sensitivity and specificity of total serum bilirubin concentration (TSB) and free (unbound) bilirubin concentration (Bf) as predictors of risk for bilirubin toxicity and kernicterus and to examine consistency between these findings and proposed mechanisms of bilirubin transport and brain uptake.

METHODS

A review of literature was undertaken to define basic principles of bilirubin transport and brain uptake leading to neurotoxicity. We then reviewed experimental and clinical evidence that relate TSB or Bf to risk for bilirubin toxicity and kernicterus.

RESULTS

There are insufficient published data to precisely define sensitivity and specificity of either TSB or Bf in determining risk for acute bilirubin neurotoxicity or chronic sequelae (kernicterus). However, available laboratory and clinical evidence indicate that Bf is better than TSB in discriminating risk for bilirubin toxicity in patients with severe hyperbilirubinemia. These findings are consistent with basic pharmacokinetic principles involved in bilirubin transport and tissue uptake.

CONCLUSIONS

Experimental and clinical data strongly suggest that measurement of Bf in newborns with hyperbilirubinemia will improve risk assessment for neurotoxicity, which emphasizes the need for additional clinical evaluation relating Bf and TSB to acute bilirubin toxicity and long-term outcome. We speculate that establishing risk thresholds for neurotoxicity by using newer methods for measuring Bf in minimally diluted serum samples will improve the sensitivity and specificity of serum indicators for treating hyperbilirubinemia, thus reducing unnecessary aggressive intervention and associated cost and morbidity.

Bilirubin-induced inflammatory response, glutamate release, and cell death in rat cortical astrocytes are enhanced in younger cells

Unconjugated bilirubin (UCB) encephalopathy is a predominantly early life condition resulting from the impairment of several cellular functions in the brain of severely jaundiced infants. However, only few data exist on the age-dependent effects of UCB and their association with increased vulnerability of premature newborns, particularly in a sepsis condition. We investigated cell death, glutamate efflux, and inflammatory cytokine dynamics after exposure of astrocytes at different stages of differentiation to clinically relevant concentrations of UCB and/or lipopolysaccharide (LPS). Younger astrocytes were more prone to UCB-induced cell death, glutamate efflux, and inflammatory response than older ones. Furthermore, in immature cells, LPS exacerbated UCB effects, such as cell death by necrosis. These findings provide a basis for the increased susceptibility of premature newborns to UCB deleterious effects, namely when associated with sepsis, and underline how crucial the course of cell maturation can be to UCB encephalopathy during moderate to severe neonatal jaundice.

Minocycline blocks bilirubin neurotoxicity and prevents hyperbilirubinemia-induced cerebellar hypoplasia in the Gunn rat

Encephalopathy induced by hyperbilirubinemia in infants has been described in the medical literature for over a century but neither the cellular nor molecular mechanisms underlying bilirubin neurotoxicity are well understood. In this study, we have demonstrated that minocycline potently protects primary cultured rat cerebellar granule neurons against bilirubin neurotoxicity (IC50 approximately 2 microm) and almost completely blocks cerebellar hypoplasia and the profound loss of Purkinje and granule neurons observed in homozygous Gunn rats, a genetic model of hyperbilirubinemia-induced neurotoxicity. Minocycline-treated newborn Gunn rats had nearly equivalent numbers of viable Purkinje and granule neurons in the cerebellum as did control animals. Moreover, minocycline inhibits the bilirubin-induced phosphorylation of p38 mitogen-activated protein kinase both in vivo as well as in vitro. Taken together our data demonstrate that minocycline is able to greatly reduce bilirubin-induced neurotoxicity and suggest that minocycline's neuroprotective effects may be due in part to an inhibition of p38 mitogen-activated protein kinase activity. Our findings may lead to novel approaches for treating bilirubin-induced encephalopathy.

Transient bilirubin encephalopathy and apnea of prematurity in 28 to 32 weeks gestational age infants

OBJECTIVE

Apnea of prematurity (AoP) is, in part, a reflection of brainstem-mediated respiratory control system maturation. We previously demonstrated changes in brainstem function in relation to hyperbilirubinemia (bilirubin encephalopathy, (BE)) as evaluated by auditory brainstem evoked responses (ABR) in infants 28 to 32 weeks gestational age (GA). We hypothesized that in this population, as bilirubin increases and causes auditory brainstem dysfunction, respiratory control system may also be adversely affected leading to increased frequency of AoP.

STUDY DESIGN

We studied 100, 28 to 32 weeks GA infants and identified 66 with normal and 34 with abnormal ABR progression in temporal relation to hyperbilirubinemia (BE). The abnormal ABR progression was associated with elevated bilirubin, specifically elevated unbound bilirubin levels. A blinded, retrospective chart review quantified the amount of weekly apnea and bradycardia events during the hospital stay, total duration of methylxanthine treatment, total duration of mechanical ventilation, CPAP, and/or nasal cannula, and risk factors for apnea (sepsis, IVH grade >II, asphyxia). Since mechanical ventilation confounds the identification of apnea, infants requiring mechanical ventilation were excluded from further review (n = 60; 21 with BE and 39 with normal ABR progression). Data from the remaining 40 infants were analyzed. Student's t-test was used to analyze continuous variables if the distribution was normal otherwise Wilcoxon-ranked-sum test was used. chi(2) was used to analyze nominal variables. A p < or =0.05 was considered significant.

RESULTS

There was no difference in risk factors between infants with and without BE. BE was identified on day 3 (median; range 1 to 6 days). Patients with BE had significantly more apneic events (15 vs 2, p = 0.0009), bradycardic events (14 vs 1, p = 0.02), and required more prolonged treatment with CPAP (2.2 vs 0.5 days, p = 0.007), nasal cannula (6.6 vs 2.2 days, p = 0.02), and methylxanthines (9.5 vs. 1.9 days, p = 0.002) than those with normal ABR progression. The difference in the incidence of apnea and bradycardia between infants with and without BE was most pronounced during the first week.

CONCLUSIONS

Premature infants with transient bilirubin encephalopathy as defined by abnormal ABR progression in relation to hyperbilirubinemia have more concurrent apneic events and require more prolonged respiratory support and medications.

Kernicterus: still a concern

The presence of yellow staining and damage to the brain caused by unconjugated bilirubin was first described by Hervieux in 1847. Kernicterus, the technical term used to describe the intense yellow staining in the basal ganglia of the brain, was first used by Schmorl in 1903. Perhaps as many as 60 percent of all babies born each year in the U.S. are diagnosed with clinical jaundice. Kernicterus is a preventable brain injury caused by severe jaundice, yet it remains a threat today. Because of this, anyone caring for newborns must be aware of the risks and treatment for hyperbilirubinemia and the sequelae of this seemingly benign entity.

Kernicterus as a 'Never-Event': a newborn safety standard?

Kernicterus, preventable in most cases but with untreatable and tragic sequelae, is a matter of public health concern that requires implementation of safer community healthcare standards to prevent its occurrence.

Definition of the clinical spectrum of kernicterus and bilirubin-induced neurologic dysfunction (BIND)

Kernicterus, currently used to describe both the neuropathology of bilirubin-induced brain injury and its associated clinical findings, is a complex syndrome. The neurobiology of kernicterus, including the determinants and mechanisms of neuronal injury, is discussed along with traditional and evolving definitions ranging from classical kernicterus with athetoid cerebral palsy, impaired upward gaze and deafness, to isolated conditions, for example, auditory neuropathy or dys-synchrony (AN/AD), and subtle bilirubin-induced neurological dysfunction (BIND). The clinical expression of BIND varies with location, severity, and time of assessment, influenced by the amount, duration and developmental age of exposure to excessive free bilirubin. Although total serum bilirubin (TSB) is important, kernicterus cannot be defined based solely on TSB. For study purposes kernicterus may be defined in term and near-term infants with TSB > or = 20 mg/dl using abnormal muscle tone on examination, auditory testing diagnostic of AN/AD, and magnetic resonance imaging showing bilateral lesions of globus pallidus+/-subthalamic nucleus.

Clinical assessment of bilirubin-induced neurotoxicity in premature infants

The clinical assessment of bilirubin-induced neurotoxicity in premature infants remains difficult in the absence of a gestational age-specific total or free (unbound) bilirubin level that predicts bilirubin-induced neurotoxicity. Because the total serum bilirubin concentration is an unreliable predictor of bilirubin-induced neurotoxicity in premature infants, alternative mean for predicting bilirubin-induced neurotoxicity in jaundiced preterm newborns is needed. Over the last few years, we have witnessed substantial gain in our knowledge involving usefulness of bilirubin-binding variables (total bilirubin, free bilirubin, bilirubin:albumin molar ratio) for clinical assessment of bilirubin-induced neurotoxicity in preterm infants. The knowledge gained has provided impetus for more clinical studies that are geared toward confirming the usefulness of free bilirubin as a predictor of bilirubin-induced neurotoxicity and identifying the gestational age-specific free bilirubin level that may increase the risk of bilirubin-induced neurotoxicity in premature infants. The paper has attempted to provide an overview of bilirubin-induced auditory toxicity along with the existing clinical evidence in favor of free bilirubin assay and usefulness of auditory brainstem evoked response for evaluation of bilirubin-induced neurotoxicity in premature infants. In addition, the author has described findings that suggest an association of apnea, a clinical manifestation, with acute bilirubin encephalopathy in premature infants.

New concepts in bilirubin encephalopathy

Revised concepts of bilirubin encephalopathy have been revealed by studies of bilirubin toxicity in cultured CNS cells and in congenitally jaundiced Gunn rats. Bilirubin neurotoxicity is related to the unbound (free) fraction of unconjugated bilirubin (Bf), of which the dominant species at physiological pH is the protonated diacid, which can passively diffuse across cell membranes. As the binding affinity of plasma albumin for bilirubin decreases strikingly as albumin concentration increases, previously reported Bf values were underestimated. Newer diagnostic tests can detect reversible neurotoxicity before permanent damage occurs from precipitation of bilirubin (kernicterus). Early toxicity can occur at Bf only modestly above aqueous saturation and affects astrocytes and neurons, causing mitochondrial damage, resulting in impaired energy metabolism and apoptosis, plus cell-membrane perturbation, which causes enzyme leakage and hampers transport of neurotransmitters. The concentrations of unbound bilirubin in the cerebro-spinal fluid and CNS cells are probably limited mainly by active export of bilirubin back into plasma, mediated by ABC transporters present in the brain capillary endothelium and choroid plexus epithelium. Intracellular bilirubin levels may be diminished also by oxidation, conjugation and binding to cytosolic proteins. These new concepts may explain the varied susceptibility of neonates to develop encephalopathy at any given plasma bilirubin level and the selective distribution of CNS lesions in bilirubin encephalopathy. They also can suggest better strategies for predicting, preventing and treating this syndrome.

Bilirubin toxicity in the developing nervous system

Bilirubin toxicity remains a significant problem despite recent advances in the care of jaundiced (hyperbilirubinemic) neonates. A recent surge in reported cases of classical kernicterus, due in part to earlier hospital discharge and relaxation of treatment criteria for hyperbilirubinemia, and new reports of hyperbilirubinemia-induced auditory dysfunction using evoked potential based infant testing and hearing screening, underscore the need to better understand how hyperbilirubinemia causes brain damage in some infants, especially because the damage is preventable. Recent progress in understanding bilirubin binding and neurotoxicity resulting from unbound or "free" unconjugated bilirubin, how bilirubin affects the central nervous system in vivo and in vitro, and the use of new clinical tools in neonates, for example magnetic resonance imaging revealing bilateral lesions in globus pallidus and subthalamus, and abnormal brainstem auditory evoked potentials with normal inner ear function, may lead to improved detection and prevention of neurologic dysfunction and damage from bilirubin. Finally, the concern is raised that partial or isolated neurologic sequelae, for example auditory neuropathy and other central auditory processing disorders, may result from excessive amount and duration of exposure to free, unconjugated bilirubin at different stages of neurodevelopment.

Somatosensory and brainstem auditory evoked potentials in the Gunn rat model of acute bilirubin neurotoxicity

Brainstem auditory evoked potentials (BAEPs) are a sensitive indicator of bilirubin neurotoxicity. Somatosensory evoked potentials (SEPs) have been proposed as another measure of toxicity, though the lemniscal pathways that generate the SEP are not involved in kernicterus. In 16 to 17-d-old jaundiced (jj) Gunn rats, serial BAEPs and SEPs were obtained up to 8 h after acute bilirubin toxicity. jjs were injected with 150 mg/kg sulfadimethoxine to displace bilirubin into brain tissue (n = 8); littermate controls were jjs given saline (n = 4) and nonjaundiced given sulfadimethoxine or saline (n = 7). After anesthesia, BAEP and SEP recordings were obtained at baseline and serially after injection. SEPs to median nerve stimulation were recorded from surface electrodes over the brachial plexus (Erb's) and contralateral parietal cortex, and subtracted to obtain central conduction time (CCT). There were no statistically significant different baseline values between groups. Baseline BAEP I, I-II, and I-III were 1.22 +/- 0.13, 1.11 +/- 0.12, and 2.10 +/- 0.15 ms, and SEP Erb's and CCT were 1.48 +/- 0.20 and 5.59 +/- 0.50 ms, respectively (n = 19). At 6.8 +/- 1.5 h after injection BAEP I, I-II, and I-III increased 0.10 +/- 0.08, 0.18 +/- 0.17, and 0.56 +/- 0.33 ms over baseline, respectively (p = 0.005, 0.01, and 0.001, respectively, paired, 1-tailed t-tests), in experimental but not control groups. SEP Erb's decreased slightly, -0.06 +/- 0.04 ms in experimental and -0.08 +/- 0.08 ms in control groups, while CCT did not change significantly. BAEPs were completely abolished in two jjs with no SEP changes. When injection of sulfonamide induced significant peripheral and central BAEP abnormalities in jaundiced rats, no SEP abnormalities occurred. SEPs assess proprioception but not other somatosensory function or sensory integration. The results demonstrate the selectivity of acute bilirubin toxicity for the auditory nervous system.

[The toxicity of bilirubin to the central nervous system]

Whatever the causes of its accumulation, excessive production and/or insufficient elimination, unconjugated bilirubin when it reaches a certain concentration threshold, is responsible for neurones and astrocytes death. In this paper the mechanisms involved in this process of cellular death, from hemolysis to oxydation in neurons and neuroglial cells, are reviewed.

[Combined neuronal toxicity of bilirubin and hypoxia. Study of cultured rat neurons]

Clinical observations suggest that bilirubin encephalopathy is often seen in newborn infants presenting not only with hyperbilirubinemia but also with alterations in oxygen transport like in severe anaemia. Since bilirubin and hypoxia have been shown to be detrimental to the central nervous system, the present study was designed to test the additional effects of the two insults on the outcome of cultured neurons from the forebrain of 14 day-old embryos. After 6 days in vitro, neurons were exposed either to bilirubin (0.5 microM) or to bilirubin and hypoxia for 6 hours. Thereafter, cells were reoxygenated for 96 hours in standard conditions. Control cells were kept in normoxia. Cell viability was assessed by the methyltetrazolium method. Cell death (apoptosis or necrosis) was characterized by fluorescent nuclear staining with DAPI. Rates of protein synthesis and energy metabolism in neurons were measured by [3H]leucine and [3H]2-deoxyglucose incorporation, respectively. Data are reported as percentages of change as compared to controls. Each experiment involved 5 to 10 dishes per time point and was repeated 2 to 4 times.

RESULTS

Bilirubin reduced cell viability by 24.5% vs controls (p < 0.001) at 96 h while 16% of the neurons exhibited morphological features of apoptosis (p < 0.001). The combination of hypoxia with bilirubin induced a 34% decrease in cell viability (p < 0.001) and the percentage of apoptotic cells was higher than after the exposure to hypoxia or to bilirubin alone. The rate of protein synthesis increased significantly in all experimental conditions as early as 1 h after the onset of the insult and at 48 h post reoxygenation. It increased again at 72 h in the cells exposed to bilirubin or to bilirubin and hypoxia. These sequential changes in synthesis of specific proteins seem to be involved in delayed neuronal death. Bilirubin decreased significantly [3H]2-deoxyglucose incorporation at 24 h while it increased when the neurons were exposed to both bilirubin and hypoxia (+60%, p < 0.001) and decreased thereafter. These data confirm the deleterious effects of bilirubin on neuronal viability, on protein synthesis and metabolic rates. The combination of bilirubin with hypoxia resulted in stronger detrimental effects on neurons than bilirubin alone.

Breast-feeding, neonatal jaundice and kernicterus

Despite the many advantages of breast-feeding, there is ample documentation of the strong association between breast-feeding and an increase in the risk of neonatal hyperbilirubinaemia. Breast-fed infants have higher bilirubin levels than formula-fed infants. Suggested mechanisms for these findings include poor fluid and caloric intake, inhibition of hepatic excretion of bilirubin, and intestinal absorption of bilirubin (enterohepatic circulation). On rare occasions, breast-fed infants without evidence of haemolysis have developed extreme hyperbilirubinaemia and kernicterus. Because almost all of the cases of kernicterus reported in the last 15 years have occurred in fully or partially breast-fed newborns, it is important that these infants be followed closely. Appropriate support and advice must be provided to the lactating mother so that successful breast-feeding can be established and the risk of severe hyperbilirubinaemia reduced.

Effect of hypothermia on bilirubin-induced alterations in brain cell membrane function and energy metabolism in newborn piglets

The aim of this study was to evaluate the effects of hypothermia on bilirubin-induced alterations in brain cell membrane function and energy metabolism in the developing brain. Thirty-seven newborn piglets were divided randomly into four groups: normothermic control (NC, n=9); hypothermic control (HC, n=7); normothermic bilirubin infusion (NB, n=11); and hypothermic bilirubin infusion (HB, n=10) groups. In bilirubin infusion groups (NB and HB), a loading dose of bilirubin (35 mg/kg) was given over 5 min, followed by a continuous infusion (25 mg/kg/h) for 4 h. The control groups (NC, HC) received a bilirubin-free buffer solution. Sulfadimethoxine was administered to animals in all experimental groups. Rectal temperature was maintained between 38.0 and 39.0 degrees C in normothermic groups, and between 34.0 and 35.0 degrees C in hypothermic groups for 4 h after the start of bilirubin infusion. The final blood and brain bilirubin concentrations in the bilirubin infusion groups (NB and HB) were not significantly different. Decreased cerebral cortical cell membrane Na(+),K(+)-ATPase activity and increased lipid peroxidation products observed in the NB group, indicative of bilirubin-induced brain damage, were significantly attenuated in the HB group. Hypothermia also significantly improved the bilirubin-induced reduction in brain ATP and phosphocreatine levels and increase in blood and brain lactate levels. In summary, hypothermia significantly attenuated the bilirubin-induced alterations in brain cell membrane function and energy metabolism in the newborn piglet. These findings suggest the possibility that hypothermia could be a good neuroprotective therapeutic modality in neonatal bilirubin encephalopathy.

Bilirubin-albumin binding and free bilirubin

The relevance of plasma bilirubin-albumin binding and, in particular, the nonalbumin-bound or "free" bilirubin concentration to neonatal bilirubin toxicity is controversial. The pivotal role that "free" bilirubin played in the bilirubin toxicity that occurred following administration of sulfisoxazole or benzyl alcohol to jaundiced newborns, and the correlation of "free" bilirubin with bilirubin-induced changes in the auditory brainstem response are strong support for measuring "free" bilirubin when evaluating neonatal jaundice. Reliable methods for measuring "free bilirubin" are available, and population reference values are needed to help determine its proper clinical use.

Bilirubin and the auditory system

The auditory system is highly sensitive to bilirubin toxicity. Damage to the auditory nervous system includes auditory neuropathy or auditory dyssynchrony and auditory processing problems which may occur with or without deafness, hearing loss. Auditory dysfunction may occur in children with or without other signs of classical kernicterus. Bilirubin selectively damages the brainstem auditory nuclei, and may also damage the auditory nerve and spiral ganglion containing cell bodies of primary auditory neurons. The inner ear, thalamic and cortical auditory pathways appear to be spared. Noninvasive auditory neurophysiological tests such as the auditory brainstem response (ABR) or brainstem auditory response (BAER) play an important role in the early detection of bilirubin-induced auditory and central nervous system dysfunction in the neonate.

Spectrum of outcome in infants with extreme neonatal jaundice

The increasing number of case reports on neurologic sequelae related to hyperbilirubinaemia may represent a re-emergence of kernicterus in the industrialized world. However, not much has been written about infants who survived extreme levels of serum bilirubin without neurologic damage. We present three cases of extreme neonatal hyperbilirubinaemia, all with peak serum bilirubin levels >600 micromol/L. Two of the infants developed neurologic sequelae, but the third infant did not. In contrast to the two with sequelae, the infant without sequelae was female, had a positive Coombs' test, less clinical signs compatible with bilirubin encephalopathy, and a shorter exposure to serum bilirubin values >400 micromol/L.

CONCLUSION

The basic mechanism of bilirubin neurotoxicity remains unknown, and it is not clear why some infants do not develop neurologic injury at serum bilirubin levels at which others do. We speculate that a comparison between patients with sequelae and those without may yield important information.

Effect of bilirubin on the activity and thermokinetic characteristics of brain (synaptosomal) membrane NO synthase

NO synthase activity was found in the plasma (synaptosomal) membrane particles isolated from the homogenate of adult rat brain (without cerebellum) under conditions preventing the protease attack and formation of reactive oxygen species. The NO synthase discovered exhibited some properties of a neuronal constitutive integral membrane enzyme and was inhibited by N-nitro-L-arginine. NO synthase activity decreased when bilirubin entered the synaptosomal membrane in vitro. Bilirubin caused the shift of the transition temperature in the temperature dependence of NO synthase activity in Arrhenius plots. The incorporation of bilirubin into synaptosomal membranes resulted in an increase in the apparent activation energy for NO synthase within a temperature range of 10-30 degrees C. The membrane NO synthase was susceptible to the photodynamic effect of membrane-bound bilirubin molecules. Monomeric human serum albumin without organophilic ligands exerted a protective effect on NO synthase in bilirubin-containing membrane particles.

The blood-brain barrier and bilirubin encephalopathy

1. The pathogenesis of bilirubin encephalopathy is multifactorial, involving the transport of bilirubin or albumin/bilirubin across the blood-brain barrier and delivering bilirubin to target neurons. 2. The relative importance of the blood-brain barrier, unconjugated bilirubin levels, serum binding, and tissue susceptibility in this process is only partially understood. Even at dangerously high serum levels, bilirubin traverses the intact blood-brain barrier slowly, requiring time for encephalopathy to occur, although deposition of bilirubin can be rapid if a surge in plasma unbound bilirubin is produced by administering a drug which competes with bilirubin for binding to albumin. 3. There may be maturational changes in permeability both in the fetus and postnatally which protect the brain from bilirubin. 4. Disruption or partial disruption of the blood-brain barrier by disease or hypoxic ischemic injury will facilitate transport of bilirubin/albumin into brain, but the relative affinities of albumin and target neurons will determine whether the tissue bilirubin load is sufficient for toxicity to occur.

Transcutaneous bilirubinometry: its role in the assessment of neonatal jaundice

OBJECTIVE

To review the literature on transcutaneous bilirubinometry so that its exact role in the prevention of kernicterus or bilirubin encephalopathy could be determined.

DESIGN AND METHODS

Literature searches were done in Medline and Current Contents.

RESULTS

It is estimated that about 50% of newborns have an episode of jaundice in the first few days of life. Six percent of newborns may develop hyperbilirubinemia (> 220 mumol/L), which can potentially cause bilirubin encephalopathy or kernicterus, a severe neonatal disease. In the past, serum bilirubin (SB) has been the preferred method of detecting hyperbilirubinemia in newborns. The ordering of SB in neonates is based on visual evaluation by either physicians or nursing staff. Skin puncture collection of blood exposes the neonate to trauma and risk of infection. A noninvasive device for predicting serum bilirubin levels in newborns diminishes the need to do skin punctures. One such device that has been very extensively studied is the Minolta AirShields Jaundice Meter. It is a portable light-weight instrument that uses reflectance measurements on the skin to determine the amount of yellow color present in the skin, namely transcutaneous bilirubin (TcB). Although the TcB measurements correlate well with serum bilirubin (SB) levels, they cannot accurately predict serum bilirubin because of error related to a variety of factors.

CONCLUSIONS

TcB cannot be used directly to make decisions about transfusions or phototherapy in neonates. It is a good tool for screening neonates to determine when a laboratory measurement of serum bilirubin is needed. Such a practice requires careful selection of the decision level so that false-negative TcB values do not prevent appropriate serum bilirubin tests from being done.

Bilirubin metabolism and kernicterus

Neonatal jaundice continues to be a common problem. Kernicterus, although rare, continues to be a very real concern in both full-term and preterm infants. The diagnosis of kernicterus requires not only bilirubin staining in a characteristic pattern in the brain but also neuronal damage. With careful pathologic evaluation, kernicterus should be distinguishable from the brain damage associated with asphyxia and hypoxia. Early hospital discharge is a risk factor for the development of kernicterus. Combining the use of traditional phototherapy from above and a fiberoptic blanket from below has improved the effectiveness of phototherapy. Clinical trials with SnMP as an inhibitor of heme oxygenase appear encouraging; no adverse effects were noted, except for mild, occasional photosensitization manifest by erythema in babies receiving phototherapy. One theoretical toxicity of inhibitors of heme oxygenase involves the recent observation that carbon monoxide (CO) is a neurotransmitter in certain regions of the brain, possibly comparable to nitric oxide (NO), and the consequences of such inhibition are unknown. More research is needed to improve our understanding about the entry of bilirubin into the brain, the predilection of bilirubin for certain brain regions, and the cytotoxicity of bilirubin. In the United States, there is currently no generally accepted method to predict hyperbilirubinemia or kernicterus. Brain stem auditory evoked responses and MRI can both be used effectively to monitor the effects of severe hyperbilirubinemia.

Postnatal development of somatosensory evoked potential in jaundiced Gunn rats and effects of sulfadimethoxine administration

Bilirubin encephalopathy results from the entry of bilirubin into the brain and is expressed by motor, sensory, and/or behavioral impairment. The jaundiced (jj) Gunn rat is a valuable animal model for studying the kinetics of bilirubin-induced neurotoxicity. This is often done by recording evoked potentials, which are also used as indices of brain damage in infants who develop neonatal jaundice, as is the case with the auditory nerve and brainstem evoked response (ABR). The present study describes the postnatal development of the somatosensory evoked potential (SEP) in Gunn rats. No effects of jaundice on the SEP were found in young jj rats (16-28 d). However, adult (3-4 mo) jj rats had prolonged latencies and decreased amplitudes of the P2 component of the SEP compared with adult nonjaundiced (Jj) rats. These changes in the SEP of jaundiced rats may reflect a synaptic lesion in these animals, possibly due to cumulative and/or progressive damage induced by bilirubin during the first 3 mo of life. After sulfadimethoxine administration, marked latency prolongations (2-6%) were observed in the early components of SEP in young (3-wk-old) jj (but not Jj) rats, as early as 2 h after injection. These changes, which became more severe (4-10%) with time, seem to be mostly peripheral. The present results suggest that the SEP may be a sensitive marker for the massive entry of bilirubin into the nervous system, and could serve as part of an evoked potential battery (in addition to visual evoked potential and ABR) in assessing bilirubin-induced neurotoxicity in jaundiced newborns and infants.

[Kernicterus in a full term infant]

This article describes a case history of a term infant who developed extreme hyperbilirubinaemia and neurological manifestations of kernicterus during the first postnatal week. Signs of haemolysis (AB0) were found, and in addition the infant suffered from hypernatremic dehydration. The current hypothesis for the development of kernicterus is described.

Changes in piglet auditory brainstem response amplitudes without increases in serum or cerebrospinal fluid neuron-specific enolase

We studied the relationship between changes in auditory brainstem responses (ABR) and serum and cerebrospinal fluid levels of neuron-specific enolase (NSE) in hyperbilirubinemic 2- to 8-d-old piglets. Infusion of a stabilized solution of bilirubin resulted in serum bilirubin levels of 571.1 +/- 48.8 mumol/L (mean +/- SEM) after 6 h. ABR were obtained at baseline and then hourly until the piglets were killed. We measured peak amplitudes and latencies for waves I-V, as well as latency for the post-V trough. Changes in amplitudes and latencies were analyzed as slopes because of heterogeneous variances. Over time, a significant reduction was observed in peak II-V amplitudes of bilirubin-infused piglets, but not in those of corresponding controls. No change was observed in latencies. NSE was analyzed by RIA. Serum NSE remained stable throughout the experiment (means 5.1-6.6 micrograms/L) and did not differ between the groups. Cerebrospinal fluid NSE values also remained stable, and no differences that could be ascribed to hyperbilirubinemia were detected. We conclude that hyperbilirubinemia induced significant changes in piglet ABR amplitudes without concomitant evidence of severe neuronal compromise, as might have been indicated by significant increases in serum and/or cerebrospinal fluid NSE levels. This provides further support to the clinical impression that early ABR changes during hyperbilirubinemia may be reversible.

Neonatal jaundice and bilirubin encephalopathy: a clinical and experimental reappraisal

Hyperbilirubinemia and bilirubin encephalopathy are well-known occurrences in the neonatal period. The fact that bilirubin might be toxic to neural cells stems from the neurological picture that has emerged and the associated hyperbilirubinemia. Studies of the relationship between hyperbilirubinemia in healthy full-term infants and the long-term consequences showed little or no effect of bilirubin. Nevertheless, bilirubin is still considered toxic to premature infants and infants with hemolysis. In addition, in spite of a fairly detailed understanding of the chemistry of bilirubin and the biochemistry of bilirubin metabolism, the primary target of its toxic effect is still not known. The difficulties in analyzing the results are due to the variation in experimental designs, the use of different animal models and cell systems and the use of unstable bilirubin solutions. We review some of the problems related to clinical and experimental studies of bilirubin toxicity.

Morphological changes in the cochlear nucleus and nucleus of the trapezoid body in Gunn rat pups

Mechanisms underlying bilirubin encephalopathy and hearing loss remain poorly understood, including the way bilirubin enters the nervous system and how bilirubin accumulates in circumscribed regions of the brain. The present experiments examined the auditory brainstem in heterozygous (Nj) and homozygous (jj) Gunn rats at an age when serum bilirubin levels were highest, and after brain bilirubin concentration was artificially raised by sulfadimethoxine administration. In four litters of 11-12 days old Gunn rats, Nj and jj littermates received a single intraperitoneal injection of sulfadimethoxine (100 mg/kg) or a comparable volume of saline. At 16-17 days of age, brainstem auditory evoked potentials were recorded to assess the severity of bilirubin toxicity in the Nj and jj animals. Following the recordings, each animal was perfusion-fixed and frozen sections of the brainstem were cut in the transverse plane from medullary through mesencephalic levels. Sections were mounted on slides, stained with thionin and coded to avoid observer bias. Quantitative analysis revealed no differences between saline and sulfa-treated Nj rats for cochlear nucleus volume, or for cell size in the cochlear nucleus or superior olive. In the sulfa-treated jj rats, cochlear nucleus volume, and cross-sectional areas of spherical cells in the anteroventral cochlear nucleus and principal cells in the nucleus of the trapezoid body, were all significantly smaller than in the combined groups of Nj animals. The affected areas in the cochlear nucleus and superior olive are innervated by large axosomatic end-bulbs of Held or calyceal endings, and were associated with bilirubin staining of glia in the most severely jaundiced jj sulfa-treated rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Brainstem auditory evoked potentials correlate with morphological changes in Gunn rat pups

The relationship of brainstem structure and function in bilirubin encephalopathy is incompletely understood. The present experiments compare quantitative measures of brainstem structures with brainstem auditory evoked potentials (BAEPs) in infant jaundiced (jj) and nonjaundiced (Nj) Gunn rats. Ten jj's from 4 litters were injected with sulfadimethoxine at 11-12 days of age to raise their brain bilirubin concentration. Littermate controls were jj's given saline, and Nj's given sulfadimethoxine or saline. At 15-17 days of age BAEPs were recorded, and rats were prepared for histological examination, as was reported in the previous paper (Conlee and Shapiro, 1991). Significant differences between groups were seen for BAEP wave I latency (P = 0.002). I-II interwave interval (P = 0.001), and amplitudes of waves I, II, III, and IV (each P less than 0.0005) due to increased latencies and decreased amplitudes in the jj-sulfa group. Animals with the most severe BAEP abnormalities had the most severe histological abnormalities. Cochlear nucleus volume had a positive linear correlation with the amplitude of BAEP waves I, II, and IV, and an inverse correlation with wave I latency and I-II interwave interval (P less than or equal to 0.001). The highest correlations were BAEP I-II interwave interval and amplitude of waves I and II with cochlear nucleus volume (r = -0.78, 0.71 and 0.70, respectively, P less than 0.0005).(ABSTRACT TRUNCATED AT 250 WORDS)

The neurotoxicity of bilirubin

Recent clinical and research findings on kernicterus and bilirubin toxicity are reviewed. Bilirubin binds to cell membranes and appears to interfere with the metabolism, depolarization, and transmitter functions of neurons. The neurobehavioral and clinical findings associated with bilirubin encephalopathy and low bilirubin kernicterus are presented and evaluated. Cardiorespiratory stabilization, avoidance of displacing drugs, and preventive use of phototherapy appear to have decreased the incidence of low bilirubin kernicterus in high-risk newborns.

Assessing the risk of kernicterus using nuclear magnetic resonance

Kernicterus is the end result of injury to the central nervous system by bilirubin and other factors. Serum bilirubin levels alone are poor predictors of kernicterus especially in sick preterm infants. We need a rapid noninvasive indicator of neurotoxicity and impending cell injury. Bilirubin first seems to affect neuronal conduction before energy metabolism is impaired. Unchecked, this may lead to failure of ATP synthesis, resulting in the breakdown of all active intracellular processes. It is now possible to measure energy metabolism in vivo and noninvasively by surface coil 31P NMR spectroscopy. Recent animal studies demonstrate perturbations in energy metabolism when hyperbilirubinemia is associated with an open BBB. Perhaps the further developments in NMR spectroscopy and imaging will permit regional assessment of impending or actual bilirubin neurotoxicity and allow us to identify those infants in need of immediate treatment.

Controversial topics in kernicterus

The physiology of the blood-brain barrier and its disruption by a variety of pathophysiologic processes in the development of experimental and clinical kernicterus are reviewed. The use of currently available methods for measuring free and bound bilirubin in developing strategies for the prevention of kernicterus and more subtle sequelae of hyperbilirubinemia also are presented.

The effects of brain blood flow on brain bilirubin deposition in newborn piglets

Since kernicteric lesions are usually found in the subcortical regions of the brain and these areas also receive the highest blood flow during asphyxia and hypercapnia, we hypothesized that increases in brain bilirubin deposition may be related to increases in brain blood flow. Fourteen piglets underwent a 3-h infusion of bilirubin to maintain total serum bilirubin at approximately 8 mg/dl, during which time blood gases, hemodynamic variables, and brain blood flow were determined. After sacrificing the animals, regional brain bilirubin content was determined. Ten piglets underwent the same protocol; in addition, hypercapnia was induced during the last hour of study (PaCO2 approximately 70 mm Hg). The regional brain blood flow and bilirubin deposition were significantly increased over control values (p less than 0.05) following hypercapnia in the subcortical region and significantly so in the midbrain and cerebellum. In separate groups of control (n = 6) and hypercapnia (n = 6) piglets, 125I-labeled albumin was infused and demonstrated that hypercapnia was not associated with increased regional brain albumin content. We conclude that hypercapnia-induced augmentation in regional brain blood flow is associated with increased deposition brain blood flow is associated with increased deposition of unbound bilirubin. Although the causal relationship between these two observations has not been firmly established, the findings deserve future investigation to clarify the role of brain blood flow, brain bilirubin deposition, and the production of kernicterus in high risk infants.