Impairment of perinatal hypoxia-ischemia to the preterm brainstem

Altered maturation in brainstem neural conduction in very premature babies with fetal growth restriction

BACKGROUND

Using maximum length sequence brainstem auditory evoked response (MLS BAER) to study brainstem neural conduction and maturation in fetal growth restriction (FGR) babies born very prematurely and assess the effect of FGR on brainstem neural maturation.

METHODS

MLS BAER was recorded and analyzed at a mean 40 week postmenstrual age in babies born at 27-32 week gestation without other major perinatal conditions or problems. The data were compared between babies with FGR (n = 30) and age-matched babies without FGR (n = 34) to define any differences.

RESULTS

A notable difference in MLS BAER was found in interpeak intervals between the babies with FGR and those without FGR. The FGR babies manifested significantly shortened I-III interval, moderately prolonged III-V interval, and significantly decreased III-V/I-III interval ratio. The slope of the I-III interval-rate function in FGR babies was moderately decreased, relative to that in the babies without FGR.

CONCLUSION

FGR babies born very prematurely are associated with accelerated or precocial neural maturation at caudal brainstem regions, but moderately delayed maturation at rostral brainstem regions. The altered brainstem neural maturation is different from previously reported mildly delayed maturation in FGR babies born less prematurely, and may have important implication for neurodevelopmental outcome.

IMPACT

This first MLS BAER study in FGR found that brainstem neural maturation in very premature FGR babies differed from age-matched non-FGR babies. Neural maturation in very premature FGR babies is accelerated or precocial at caudal brainstem regions but moderately delayed at rostral brainstem regions. The altered maturation is different from previously reported mild delay in brainstem neural maturation in FGR babies born less prematurely. FGR exerts a major and differential effect on brainstem neural maturation in babies born very prematurely. This alteration in very premature FGR babies may have important implication for their neurodevelopment.

Neurovascular responses to neuronal activity during sensory development

Understanding the development of intercellular communication in sensory regions is relevant to elucidate mechanisms of physiological and pathological responses to oxygen shortage in the newborn brain. Decades of studies in laboratory rodents show that neuronal activity impacts sensory maturation during two periods of postnatal development distinguished by the maturation of accessory structures at the sensory periphery. During the first of these developmental periods, angiogenesis is modulated by neuronal activity, and physiological levels of neuronal activity cause local tissue hypoxic events. This correlation suggests that neuronal activity is upstream of the production of angiogenic factors, a process that is mediated by intermittent hypoxia caused by neuronal oxygen consumption. In this perspective article we address three theoretical implications based on this hypothesis: first, that spontaneous activity of sensory neurons has properties that favor the generation of intermittent tissue hypoxia in neonate rodents; second, that intermittent hypoxia promotes the expression of hypoxia inducible transcription factors (HIFs) in sensory neurons and astrocytes; and third, that activity-dependent production of angiogenic factors is involved in pathological oxygen contexts.

Towards detection of brain injury using multimodal non-invasive neuromonitoring in adults undergoing extracorporeal membrane oxygenation

Extracorporeal membrane oxygenation (ECMO) is a form of cardiopulmonary bypass that provides life-saving support to critically ill patients whose illness is progressing despite maximal conventional support. Use in adults is expanding, however neurological injuries are common. Currently, the existing brain imaging tools are a snapshot in time and require high-risk patient transport. Here we assess the feasibility of measuring diffuse correlation spectroscopy, transcranial Doppler ultrasound, electroencephalography, and auditory brainstem responses at the bedside, and developing a cerebral autoregulation metric. We report preliminary results from two patients, demonstrating feasibility and laying the foundation for future studies monitoring neurological health during ECMO.

Defining the relationship between maternal care behavior and sensory development in Wistar rats: Auditory periphery development, eye opening and brain gene expression

Defining the relationship between maternal care, sensory development and brain gene expression in neonates is important to understand the impact of environmental challenges during sensitive periods in early life. In this study, we used a selection approach to test the hypothesis that variation in maternal licking and grooming (LG) during the first week of life influences sensory development in Wistar rat pups. We tracked the onset of the auditory brainstem response (ABR), the timing of eye opening (EO), middle ear development with micro-CT X-ray tomography, and used qRT-PCR to monitor changes in gene expression of the hypoxia-sensitive pathway and neurotrophin signaling in pups reared by low-LG or high-LG dams. The results show the first evidence that the transcription of genes involved in the hypoxia-sensitive pathway and neurotrophin signaling is regulated during separate sensitive periods that occur before and after hearing onset, respectively. Although the timing of ABR onset, EO, and the relative mRNA levels of genes involved in the hypoxia-sensitive pathway did not differ between pups from different LG groups, we found statistically significant increases in the relative mRNA levels of four genes involved in neurotrophin signaling in auditory brain regions from pups of different LG backgrounds. These results suggest that sensitivity to hypoxic challenge might be widespread in the auditory system of neonate rats before hearing onset, and that maternal LG may affect the transcription of genes involved in experience-dependent neuroplasticity.

Brainstem auditory pathway function at four months of corrected postnatal age in preterm infants born below 30 week gestation

OBJECTIVE

Functional status of the brainstem auditory pathway was examined at four months of corrected postnatal age in infants born below 30 week gestation to assess the effect of very or extremely preterm birth on postnatal development of the pathway.

METHODS

Thirty-four preterm infants born at 24-29 week gestation (GA24-29w) were studied at four months of corrected postnatal age. Normal controls were 38 postnatal age-matched term infants. Maximum length sequence brainstem auditory evoked response (MLS BAER) were recorded and analysed with 60 dB nHL clicks.

RESULTS

Compared with term control group, GA24-29w group manifested higher BAER threshold (p < 0.05), longer MLS BAER wave latencies at all click rates 91-910/s (p < 0.01-0.001), and lower wave amplitudes at most click rates (p < 0.05-0.01). No significant differences were found between the two groups in I-V interval at any click rates. I-III interval was shorter while III-V interval was longer in GA24-29w group than in term group at higher rates (all p < 0.05). III-V/I-III interval ratio in GA24-29w group was greater at 455 and 910/s clicks (p < 0.05 and 0.01). These interval variables showed similar changes when 4 GA24-29w infants with threshold elevation were excluded.

CONCLUSIONS

At four months of corrected postnatal age, infants born below 30 week gestation manifested elevated BAER threshold, increased wave latencies, and reduced amplitude. They also manifested a small decrease in I-III interval but a small increase in III-V interval at high rates. Very or extremely preterm birth exerts a mild or moderate effect on postnatal development of the brainstem auditory pathway.

Brainstem shape is affected by clinical course in the neonatal intensive care unit

The brainstem, critical for motor function, autonomic regulation, and many neurocognitive functions, undergoes rapid development from the third trimester. Accordingly, we hypothesized it would be vulnerable to insult during this period, and that a difficult clinical course in the neonatal intensive care unit (NICU) would affect development, and be reflected through atypical shape. Our study population consisted of 66 neonates - all inpatients from the NICU at Victoria Hospital, London Health Sciences Centre, ON, Canada, of which 45 entered the final analysis. The cohort varied in gestational age (GA) and ranged from neurologically healthy to severely brain-injured. Structural MRI was used to quantify brainstem shape at term-equivalent age. From these images, brainstems were semi-automatically segmented and co-registered across subjects. The anterior-posterior dimensions on a sagittal maximum intensity projection were used as the basis for shape comparison. Factor analysis was used to summarize variation in shape and in clinical course to determine three shape factors and three clinical factors, and their relationship assessed using correlation. A factor driven by low GA and associated complications correlated with alterations in the posterior medulla, while a factor driven by complications independent of GA correlated with alterations in the midbrain. Additionally, single clinical measures most representative of their respective clinical factor (days in NICU; days on ventilation) predicted the changes. Thus, different clinical courses in the NICU may have different effects on the shape of the brainstem, and may mediate some of the distinct neurodevelopmental profiles observed in premature and brain-injured neonates.

Birth Asphyxia and Hypoxic-Ischemic Brain Injury in the Preterm Infant

Birth asphyxia, also termed perinatal hypoxia-ischemia, is a modifiable condition as evidenced by improved outcomes of infants ≥36 weeks' gestation provided hypothermia treatment in randomized trials. Preterm animal models of asphyxia in utero demonstrate that hypothermia can provide short-term neuroprotection for the developing brain, supporting the interest in extending therapeutic hypothermia to preterm infants. This review focuses on the challenge of identifying preterm infants with perinatal asphyxia; the neuropathology of hypoxic-ischemic brain injury across extreme, moderate, and late preterm infants; and patterns of brain injury, use of therapeutic hypothermia, and approach to patient selection for neuroprotective treatments among preterm infants.

Antioxidant Treatments Recover the Alteration of Auditory-Evoked Potentials and Reduce Morphological Damage in the Inferior Colliculus after Perinatal Asphyxia in Rat

Maturation of the auditory pathway is dependent on the central nervous system myelination and it can be affected by pathologies such as neonatal hypoxic ischemic (HI) encephalopathy. Our aim was to evaluate the functional integrity of the auditory pathway and to visualize, by histological and cellular methods, the damage to the brainstem using a neonatal rat model of HI brain injury. To carry out this morphofunctional evaluation, we studied the effects of the administration of the antioxidants nicotine, melatonin, resveratrol and docosahexaenoic acid after hypoxia-ischemia on the inferior colliculus and the auditory pathway. We found that the integrity of the auditory pathway in the brainstem was altered as a consequence of the HI insult. Thus, the auditory brainstem response (ABR) showed increased I-V and III-V wave latencies. At a histological level, HI altered the morphology of the inferior colliculus neurons, astrocytes and oligodendricytes, and at a molecular level, the mitochondria membrane potential and integrity was altered during the first hours after the HI and reactive oxygen species (ROS) activity is increased 12 h after the injury in the brainstem. Following antioxidant treatment, ABR interpeak latency intervals were restored and the body and brain weight was recovered as well as the morphology of the inferior colliculus that was similar to the control group. Our results support the hypothesis that antioxidant treatments have a protective effect on the functional changes of the auditory pathway and on the morphological damage which occurs after HI insult.

Effect of neonatal asphyxia on the impairment of the auditory pathway by recording auditory brainstem responses in newborn piglets: a new experimentation model to study the perinatal hypoxic-ischemic damage on the auditory system

INTRODUCTION

Hypoxia-ischemia (HI) is a major perinatal problem that results in severe damage to the brain impairing the normal development of the auditory system. The purpose of the present study is to study the effect of perinatal asphyxia on the auditory pathway by recording auditory brain responses in a novel animal experimentation model in newborn piglets.

METHOD

Hypoxia-ischemia was induced to 1.3 day-old piglets by clamping 30 minutes both carotid arteries by vascular occluders and lowering the fraction of inspired oxygen. We compared the Auditory Brain Responses (ABRs) of newborn piglets exposed to acute hypoxia/ischemia (n = 6) and a control group with no such exposure (n = 10). ABRs were recorded for both ears before the start of the experiment (baseline), after 30 minutes of HI injury, and every 30 minutes during 6 h after the HI injury.

RESULTS

Auditory brain responses were altered during the hypoxic-ischemic insult but recovered 30-60 minutes later. Hypoxia/ischemia seemed to induce auditory functional damage by increasing I-V latencies and decreasing wave I, III and V amplitudes, although differences were not significant.

CONCLUSION

The described experimental model of hypoxia-ischemia in newborn piglets may be useful for studying the effect of perinatal asphyxia on the impairment of the auditory pathway.