Effect of graded hypoxia on the high-affinity CPP binding site of the NMDA receptor in the cerebral cortex of newborn piglets

Transcutaneous carbon dioxide monitoring for the prevention of neonatal morbidity and mortality

BACKGROUND

Carbon dioxide (CO2) measurement is a fundamental evaluation in a neonatal intensive care unit (NICU), as both low and high values of CO2 might have detrimental effects on neonatal morbidity and mortality. Though measurement of CO2 in the arterial blood gas is the most accurate way to assess the amount of CO2, it requires blood sampling and it does not provide a continuous monitoring of CO2.

OBJECTIVES

To assess whether the use of continuous transcutaneous CO2 (tcCO2) monitoring in newborn infants reduces mortality and improves short and long term respiratory and neurodevelopmental outcomes.

SEARCH METHODS

We used the standard search strategy of the Cochrane Neonatal Review group to search the Cochrane Central Register of Controlled Trials (CENTRAL 2015, Issue 11), MEDLINE via PubMed (1966 to November 1, 2015), EMBASE (1980 to November 1, 2015), and CINAHL (1982 to November 1, 2015). We also searched clinical trials databases, conference proceedings, and the reference lists of retrieved articles for randomized controlled trials and quasi-randomized trials.

SELECTION CRITERIA

Randomized, quasi-randomized and cluster randomized controlled trials comparing different strategies regarding tcCO2 monitoring in newborns. Three comparisons were considered, that is, continuous tcCO2 monitoring versus 1) any intermittent modalities to measure CO2; 2) other continuous CO2 monitoring; and 3) with or without intermittent CO2 monitoring.

DATA COLLECTION AND ANALYSIS

We used the standard methods of the Cochrane Neonatal Review Group. Two review authors independently assessed studies identified by the search strategy for inclusion.

MAIN RESULTS

Our search strategy yielded 106 references. Two review authors independently assessed all references for inclusion. We did not find any completed studies for inclusion, nor ongoing trials.

AUTHORS' CONCLUSIONS

There was no evidence to recommend or refute the use of transcutaneous CO2 monitoring in neonates. Well-designed, adequately powered randomized controlled studies are necessary to address efficacy and safety of transcutaneous CO2 monitoring in neonates.

Pathophysiology of an hypoxic–ischemic insult during the perinatal period

Hypoxia-ischemia is a leading cause of morbidity and mortality in the perinatal period with an incidence of 1/4000 live births. Biochemical events such as energy failure, membrane depolarization, brain edema, an increase of neurotransmitter release and inhibition of uptake, an increase of intracellular Ca(2+), production of oxygen-free radicals, lipid peroxidation, and a decrease of blood flow are triggered by hypoxia-ischemia and may lead to brain dysfunction and neuronal death. These abnormalities can result in mental impairments, seizures, and permanent motor deficits, such as cerebral palsy. The physical and emotional strain that is placed on the children affected and their families is enormous. The care that these individuals need is not only confined to childhood, but rather extends throughout their entire life span, so it is very important to understand the pathophysiology that follows a hypoxic-ischemic insult. This review will highlight many of the mechanisms that lead to neuronal death and include the emerging area of white matter injury as well as the role of inflammation and will provide a summary of therapeutic strategies. Hypothermia and oxygen will also be discussed as treatments that currently lack a specific target in the hypoxic/ischemic cascade.

Correlations between brainstem NMDA receptor changes and active neuronal cell death after intermittent hypercapnic hypoxia in the developing piglet

The role of the N-methyl-D-aspartate (NMDA) receptor in cell death was evaluated in the piglet brainstem after exposure to intermittent hypercapnic hypoxia (IHH). Study groups comprised controls (n=6) and piglets exposed to IHH on 2 (n=6) or 4 (n=5) successive days prior to euthanasia. All piglets had the caudal medulla evaluated at 13-14 days of age using double immunohistochemistry for TUNEL and the NMDA receptor 1 (NR1) subunit. The percent of TUNEL positive neurons amongst NR1 (% TUN in NR1) and non-NR1 neurons (% TUN in non-NR1) was determined in eight nuclei. After 2 days of IHH, %TUN in NR1 was increased in the dorsal motor nucleus of the vagus (DMNV, P=0.007) and the inferior olivary nucleus (ION, P=0.05). After 2 days IHH, %TUN in non-NR1 neurons was increased in the lateral reticular nucleus (LRt, P=0.05), nucleus of the solitary tract (NTS, P=0.004) and gracile nucleus (P=0.05). After 4days IHH, the increase of %TUN in NR1 was sustained in the ION (P=0.05), while %TUN in non-NR1 neurons was sustained in NTS (P=0.04) and LRt (P=0.006). Daily IHH exposure induces neuronal death within NR1 and non-NR1 neurons, but the neuronal phenotype is consistent within affected brainstem nuclei. Involvement of the NMDA receptor tended to occur in nuclei with higher basal NR1 expression, and thus occurred in nuclei relevant to cardiorespiratory function. We speculate that IHH exposures, such as occurs during obstructive apnea or facial entrapment in prone sleeping during infancy, can induce abnormalities of cardiorespiratory control.

Distribution and quantification of NMDA R1 mRNA and protein in the piglet brainstem and effects of intermittent hypercapnic hypoxia (IHH)

The first aim of this study was to determine the cellular distribution of NR1 in the piglet brainstem. Documentation of NR1 mRNA was by non-radioactive in situ hybridisation (non-RISH) and of NR1 protein by immunohistochemistry. We found that all neurons expressed mRNA but not all had NR1 protein. Application of non-RISH has permitted us, for the first time, to document the cellular localization of NR1 mRNA showing that it was present in the cytoplasm and nucleolus of motor neurons but dispersed throughout the cellular compartments of sensory neurons. NR1 protein on the other hand, was localized to the cytoplasm only. The second aim of this study was to quantify the distribution of NR1 mRNA and protein. Using image analysis software, we used optical density (OD) to quantify the non-RISH signal for mRNA and cellular counting for protein (expressed as % positive). Results show that NR1 expression is greater in motor than sensory nuclei; for mRNA: 0.46+/-0.04 vs. 0.31+/-0.02 OD units (P<0.001), for protein: 75.9+/-3.1 vs. 58.4+/-2.5% positive (P<0.001). The third aim of this study was to determine the effects of intermittent hypercapnic hypoxia (IHH) on NR1 expression. Chronic IHH exposure caused differential changes in mRNA and protein expression. NR1 mRNA expression increased while the number of neurons expressing NR1 protein showed no change. This finding suggests that NMDA pathways are activated by exposure to IHH.