Neonatal exposure to high concentration of carbon dioxide produces persistent learning deficits with impaired hippocampal synaptic plasticity

Hypercapnia Causes Injury of the Cerebral Cortex and Cognitive Deficits in Newborn Piglets

In critically ill newborns, exposure to hypercapnia (HC) is common and often accepted in neonatal intensive care units to prevent severe lung injury. However, as a "safe" range of arterial partial pressure of carbon dioxide levels in neonates has not been established, the potential impact of HC on the neurodevelopmental outcomes in these newborns remains a matter of concern. Here, in a newborn Yorkshire piglet model of either sex, we show that acute exposure to HC induced persistent cortical neuronal injury, associated cognitive and learning deficits, and long-term suppression of cortical electroencephalogram frequencies. HC induced a transient energy failure in cortical neurons, a persistent dysregulation of calcium-dependent proapoptotic signaling in the cerebral cortex, and activation of the apoptotic cascade, leading to nuclear deoxyribonucleic acid fragmentation. While neither 1 h of HC nor the rapid normalization of HC was associated with changes in cortical bioenergetics, rapid resuscitation resulted in a delayed onset of synaptosomal membrane lipid peroxidation, suggesting a dissociation between energy failure and the occurrence of synaptosomal lipid peroxidation. Even short durations of HC triggered biochemical responses at the subcellular level of the cortical neurons resulting in altered cortical activity and impaired neurobehavior. The deleterious effects of HC on the developing brain should be carefully considered as crucial elements of clinical decisions in the neonatal intensive care unit.

Phenobarbital does not worsen outcomes of neonatal hypoxia on hippocampal LTP on rats

Introduction

Neonatal hypoxia is a common cause of early-life seizures. Both hypoxia-induced seizures (HS), and the drugs used to treat them (e.g., phenobarbital, PB), have been reported to have long-lasting impacts on brain development. For example, in neonatal rodents, HS reduces hippocampal long-term potentiation (LTP), while PB exposure disrupts GABAergic synaptic maturation in the hippocampus. Prior studies have examined the impact of HS and drug treatment separately, but in the clinic, PB is unlikely to be given to neonates without seizures, and neonates with seizures are very likely to receive PB. To address this gap, we assessed the combined and separate impacts of neonatal HS and PB treatment on the development of hippocampal LTP.

Methods

Male and female postnatal day (P)7 rat pups were subjected to graded global hypoxia (or normoxia as a control) and treated with either PB (or vehicle as a control). On P13-14 (P13+) or P29-37 (P29+), we recorded LTP of the Schaffer collaterals into CA1 pyramidal layer in acute hippocampal slices. We compared responses to theta burst stimulation (TBS) and tetanization induction protocols.

Results

Under the TBS induction protocol, female rats showed an LTP impairment caused by HS, which appeared only at P29+. This impairment was delayed compared to male rats. While LTP in HS males was impaired at P13+, it normalized by P29+. Under the tetanization protocol, hypoxia produced larger LTP in males compared to female rats. PB injection, under TBS, did not exacerbate the effects of hypoxia. However, with the tetanization protocol, PB - on the background of HS - compensated for these effects, returning LTP to control levels.

Discussion

These results point to different susceptibility to hypoxia as a function of sex and age, and a non-detrimental effect of PB when administered after hypoxic seizures.

Review of pediatric hypercarbia and intraoperative management

PURPOSE OF REVIEW

Hypercarbia in pediatric patients is an important component of intraoperative management. Despite marked advances in medicine and technology, it is uncertain what the physiological CO2 range in neonates, infants and small children. This data is extrapolated from the adult population. We are going to review advantages and disadvantages of CO2 measurement techniques, causes and systemic effects of hypercarbia. We are going to discuss how to approach management of intraoperative hypercarbia.

RECENT FINDINGS

Although physiological range in this patient population may not be fully understood, it is known that any rapid change from a child's baseline increases risks of complications. Any derangements in CO2 are further compromised by hypoxia, hypotension, hypothermia, anemia, all of which may occur in a dynamic operating room environment.

SUMMARY

Pediatric anesthesiologists and their teams must remain vigilant and anticipate these developments. Care must be taken to avoid any rapid changes in these vulnerable patients to minimize risks of adverse outcomes.

Neonatal isoflurane exposure disturbs granule cell migration in the rat dentate gyrus

It has been reported that neonatal isoflurane exposure causes behavioral abnormalities following neurodegeneration in animals and gamma-aminobutyric acid type A (GABA_A) receptor activation during the synaptogenesis is considered to be one possible trigger. Additionally, the inhibitory effect of excitatory GABA_A receptor signaling on the granule cell (GC) migration in the neonatal rat dentate gyrus (DG) was reported in a febrile seizure model. Then, we hypothesized that neonatal isoflurane exposure, which activates GABA_A receptor, causes GC migration disturbances in the neonatal rat. Rat pups were injected with 5-bromo-2'-deoxyuridine (BrdU) and divided into five treatment groups, and double immunofluorescent staining targeting BrdU and homeobox prospero-like protein 1 (Prox1) was performed to examine the localization of BrdU/Prox1 colabeled cells, and then the GC migration was assessed. As a result, we found that the ectopic migration of GC after 2% isoflurane exposure on postnatal day 7 significantly increased after P21. The number of hilar ectopic GCs was influenced by the concentration of isoflurane and the exposure day but not by carbon dioxide exposure. Our main finding is that neonatal isoflurane anesthesia disturbs the migration of GCs in the rat DG, which may be one possible mechanism underlying the neurotoxicity following neonatal isoflurane anesthesia.

Perioperative management of esophageal atresia/tracheo-esophageal fistula: An analysis of data of 101 consecutive patients

BACKGROUND

The perioperative management of esophageal atresia/tracheo-esophageal fistula by open or thoracoscopic approach can be complicated by metabolic derangements. Little is known, however, about the severity of derangements of vital and metabolic parameters in the perioperative period.

AIM

The aim of this study is to describe the perioperative courses of vital and metabolic parameters in 101 consecutive neonates undergoing surgical repair of esophageal atresia type C.

METHOD

In a retrospective cohort study, we extracted all data from the electronic anesthetic and medical charts of patients who underwent esophageal atresia type C repair within 30 days of life (2007-2017). We distinguished three types of surgery: primary open, primary thoracoscopic, and primary thoracoscopic surgery converted to open surgery. Descriptive analysis was applied.

RESULTS

The charts of 117 patients were reviewed: data of 101 were included. The perioperative anesthetic management was not standardized; various methods and medications were used for anesthesia induction and maintenance. Intraoperative blood gas analysis data of 72 patients were available and showed derangements regardless of type of surgery. The median pH-value decreased to 7.21 [IQR 7.14-7.30] and a pH-value below 7.20 was found in 29 patients; in four cases below 7.0, with the lowest value 6.83. The median PaCO₂ reached an upper level of 7.5kPa [IQR 5.8-9.2]; in 13 cases above 10.0kPa, with a peak value of 25.8kPa. These high PaCO₂ levels fluctuated with lowest measured PaCO₂ of median 5.6 [IQR 4.5-6.6], with the lowest value 2.8kPa. The median PaO₂ level reached an upper level of 16.9kPa [IQR 11.8-25.7], in 22 cases above 20.0kPa, with a peak value of 50.0kPa. These high levels fluctuated with lowest measured PaO₂ levels of median 8.3kPa [IQR 6.73-10.5]; the lowest PaO₂ value was 4.7 kPa.

CONCLUSION

Open and thoracoscopic correction of esophageal atresia were associated with periods of severe metabolic derangements. These events need to be taken into account for the evaluation of esophageal atresia (surgical) care and in evaluations of short- and long-term outcomes.

Functional roles of three cues that provide nonsynaptic modes of communication in the brain: electromagnetic field, oxygen, and carbon dioxide

The integrative actions of the brain depend on the exchange of information among its computational elements. Hence, this phenomenon plays the key role in driving the complex dynamics of the central nervous system, in which true computations interact with noncomputational dynamical processes to generate brain representations of the body and of the body in the external world, and hence the finalistic behavior of the organism. In this context, it should be pointed out that, besides the intercellular interactions mediated by classical electrochemical signals, other types of interactions, namely, "cues" and "coercions," also appear to be exploited by the system to achieve its function. The present review focuses mainly on cues present in the environment and on those produced by cells of the body, which "pervade" the brain and contribute to its dynamics. These cues can also be metabolic substrates, and, in most cases, they are of fundamental importance to brain function and the survival of the entire organism. Three of these highly pervasive cues will be analyzed in greater detail, namely, oxygen, carbon dioxide, and electromagnetic fields (EMF). Special emphasis will be placed on EMF, since several authors have suggested that these highly pervasive energy fluctuations may play an important role in the global integrative actions of the brain; hence, EMF signaling may transcend classical connectionist models of brain function. Thus the new concept of "broadcasted neuroconnectomics" has been introduced, which transcends the current connectomics view of the brain.

Consequences of a Chronic Exposure of Cultured Brain Astrocytes to the Anti-Retroviral Drug Efavirenz and its Primary Metabolite 8-Hydroxy Efavirenz

Efavirenz is a widely prescribed non-nucleoside reverse transcriptase inhibitor for the treatment of HIV infections. To test for potential long-term consequences of efavirenz on brain cells, cultured primary astrocytes were incubated with this substance or with its primary metabolite 8-hydroxy efavirenz for up to 7 days. Both, efavirenz and 8-hydroxy efavirenz caused time- and concentration-dependent cell toxicity and stimulated in subtoxic concentrations the glycolytic flux (glucose consumption and lactate release) in astrocytes. As 8-hydroxy efavirenz was less toxic than efavirenz and stimulated glycolysis in lower concentrations we tested for a potential hydroxylation of efavirenz to 8-hydroxy efavirenz in astrocytes. Analysis of media and cell lysates by HPLC-UV and mass spectrometry revealed that after 3 days of incubation viable astrocytes had accumulated about 17 and 7 % of the applied efavirenz and 8-hydroxy efavirenz, respectively. However, in cultures treated with efavirenz neither 8-hydroxy efavirenz nor any other known metabolite of efavirenz was detectable. These data demonstrate that cultured rat astrocytes efficiently accumulate, but not metabolize, efavirenz and 8-hydroxy efavirenz and that the observed chronic stimulation of glycolysis is mediated by both efavirenz and 8-hydroxy efavirenz.

Anesthesia and the developing brain: relevance to the pediatric cardiac surgery

Anesthetic neurotoxicity has been a hot topic in anesthesia for the past decade. It is of special interest to pediatric anesthesiologists. A subgroup of children potentially at greater risk for anesthetic neurotoxicity, based on a prolonged anesthetic exposure early in development, are those children receiving anesthesia for surgical repair of congenital heart disease. These children have a known risk of neurologic deficit after cardiopulmonary bypass for surgical repair of congenital heart disease. Yet, the type of anesthesia used has not been considered as a potential etiology for their neurologic deficits. These children not only receive prolonged anesthetic exposure during surgical repair, but also receive repeated anesthetic exposures during a critical period of brain development. Their propensity to abnormal brain development, as a result of congenital heart disease, may modify their risk of anesthetic neurotoxicity. This review article provides an overview of anesthetic neurotoxicity from the perspective of a pediatric cardiac anesthesiologist and provides insight into basic science and clinical investigations as it relates to this unique group of children who have been studied over several decades for their risk of neurologic injury.

Neonatal exposure to sevoflurane causes significant suppression of hippocampal long-term potentiation in postgrowth rats

BACKGROUND

The inhaled anesthetic sevoflurane is commonly used for neonates in the clinical setting. Recent studies have indicated that exposure of neonatal rodents to sevoflurane causes acute widespread neurodegeneration and long-lasting neurocognitive dysfunction. Although acute toxic effects of sevoflurane on cellular viability in the hippocampus have been reported in some studies, little is known about the effects of neonatal sevoflurane exposure on long-term hippocampal synaptic plasticity, which has been implicated in the processes of learning and memory formation. Our study is the first to examine the long-term electrophysiological impact of neonatal exposure to a clinically relevant concentration of sevoflurane.

METHODS

On postnatal day 7, rats were exposed to sevoflurane (1% or 2% for 2 hours) with oxygen. To eliminate the influence of blood gas abnormalities caused by sevoflurane-induced respiratory suppression, a group of rats were exposed to a high concentration of carbon dioxide (8% for 2 hours) to duplicate respiratory disturbances caused by 2% sevoflurane exposure.

RESULTS

Exposure of neonatal rats to 2% sevoflurane for 2 hours caused significant suppression of long-term potentiation (LTP) induction in the postgrowth period. There was no significant difference between the control group and the CO2-exposed group in LTP induction, indicating that sevoflurane-induced LTP suppression was not caused by blood gas abnormalities.

CONCLUSION

Our present findings indicate that neonatal exposure to sevoflurane at a higher concentration can cause alterations in the hippocampal synaptic plasticity that persists into adulthood.

The effect of blood glucose and pCO2 on spectral EEG of premature infants during the first three days of life

BACKGROUND

Spectral EEG analysis using automated quantification of total absolute band power (tABP) expresses brain function. We hypothesized that pCO2 or blood glucose affects tABP during the critical first days of life in premature infants.

OBJECTIVE

To use automated tABP quantification to determine whether EEG background activity in premature infants during the first 3 days of life is influenced by pCO2 or blood glucose levels.

METHODS

Preterm infants, group 1 [gestational age (GA) = 24-27 weeks] and group 2 (GA = 28-30 weeks), underwent continuous EEG monitoring for 3 days after birth. Biochemical data were extracted from the observational datasheet used during monitoring. Blood samples were taken at the request of the attending physician. Statistical analyses were performed as repeated measurements using linear mixed models with a random intercept. The effect of time was treated as a fixed covariate and the GA groups as a fixed factor in all models. Continuous data were described using the mean ± SD or median and range, and categorical data were described using the number of patients and percentages unless otherwise indicated.

RESULTS

There was an association between increased pCO2 and tABP and between increased blood glucose and tABP. Further, there were no differences in the responses between groups 1 and 2.

CONCLUSION

Both hyperglycemia and hypercapnia showed a negative effect on brain activity decreasing tABP during the first 3 days of life in premature infants.