Elsevier

Neurobiology of Disease

Volume 50, February 2013, Pages 69-75
Neurobiology of Disease

Neurodevelopmental impairment following neonatal hyperoxia in the mouse

https://doi.org/10.1016/j.nbd.2012.10.005Get rights and content

Abstract

Extremely premature infants are often exposed to supra-physiologic concentrations of oxygen, and frequently have hypoxemic episodes. These preterm infants are at high risk (~ 40%) for neurodevelopmental impairment (NDI) even in the absence of obvious intracranial pathology such as intraventricular hemorrhage or periventricular leukomalacia. The etiology for NDI has not been determined, and there are no animal models to simulate neurodevelopmental outcomes of prematurity. Our objectives were to develop and characterize a mouse model to determine long-term effects of chronic hypoxia or hyperoxia exposure on neurodevelopment. Newborn C57BL/6 mice were exposed to hypoxia (12% O2) or hyperoxia (85% O2) from postnatal days 1 to 14 and then returned to air. At 12–14 weeks of age, neurobehavioral assessment (Water Maze test, Novel Object Recognition test, Open Field test, Elevated Plus Maze, and Rotarod test) was performed, followed by MRI and brain histology. Neurobehavioral testing revealed that hyperoxia-exposed mice did poorly on the water maze and novel object recognition tests compared to air-exposed mice. MRI demonstrated smaller hippocampi in hyperoxia- and hypoxia-exposed mice with a greater reduction in hyperoxia-exposed mice, including a smaller cerebellum in hyperoxia-exposed mice. Brain histology showed reduced CA1 and CA3 and increased dentate gyral width in hippocampus. In conclusion, neonatal hyperoxia in mice leads to abnormal neurobehavior, primarily deficits in spatial and recognition memory, associated with smaller hippocampal sizes, similar to findings in ex-preterm infants. This animal model may be useful to determine mechanisms underlying developmental programming of NDI in preterm infants, and for evaluation of therapeutic strategies.

Highlights

► Adult mice exposed to hyperoxia in the newborn period had impaired spatial and recognition memory. ► Adult hyperoxia- and hypoxia-exposed mice had smaller hippocampi by MRI and histology ► Adult mice exposed to hyperoxia in the newborn period had reduced cerebellar area but performance on the Rotorod test was not affected. ► Neonatal hyperoxia exposure increased exploratory behavior and decreased anxiety in adult mice.

Introduction

Extremely low birth weight infants are at high risk (~ 40%) for neurodevelopmental impairment (NDI) even in the absence of known intracranial complications of prematurity such as intraventricular hemorrhage or periventricular leukomalacia (Broitman et al., 2007, Laptook et al., 2005, Neubauer et al., 2008). The etiology for NDI in the absence of such obvious intracranial pathology is not clear, and there are no animal models to simulate neurodevelopmental outcomes of prematurity. Preterm infants are often exposed to supraphysiological levels of oxygen supplementation, sometimes alternating with periods of hypoxemia, that are known to affect normal lung and retinal development (Auten et al., 2009, Dorfman et al., 2008, Londhe et al., 2011). Impairment of lung development (bronchopulmonary dysplasia) or abnormal retinal development (retinopathy of prematurity) in extremely preterm infants are associated with an increased risk of NDI (Anderson and Doyle, 2006, Hintz et al., 2005a, Schmidt et al., 2003). It is important to determine if oxygen supplementation also alters developmental programming of brain development, leading to neurodevelopmental impairment and alterations in neurobehavior. Our objective in this project was to test the hypothesis that exposure of newborn mice to chronic hypoxia or hyperoxia during the first two postnatal weeks would lead to permanent impairment of brain development and function, when assessed in adult life.

Section snippets

Materials and methods

All protocols were approved by the Institutional Animal Care and Use Committee (IACUC) of UAB, and were consistent with the PHS policy on Humane Care and Use of Laboratory Animals (Office of Laboratory Animal Welfare, Aug 2002) and the Guide for the Care and Use of Laboratory Animals (National Research Council, National Academy Press, 1996). All experiments, unless otherwise specified, were done with a minimum of six mice of either gender from at least two litters for each experimental

Neurobehavioral studies

As described previously by Van Groen (Handattu et al., 2009, Perry et al., 2010) and others (Rogers et al., 1999, Rogers et al., 2001), a modified comprehensive phenotyping protocol (SHIRPA) was used at 12 weeks of age. Mice were assessed for locomotor activity (Open field test), balance and coordination (Rotarod test) anxiety (Elevated Plus Maze), spatial learning and memory (Novel Object Recognition test, Morris Water Maze Task), and vision (Cliff test). All the behavioral tests described

Neonatal hyperoxia exposure decreased adult spatial learning and memory in adult mice

Air- and hypoxia-exposed mice were able to find the submerged platform in the Morris water maze task in a comparable reduced amount of time with successive trials. However, neonatal hyperoxia markedly impaired the ability of mice to find the platform (Fig. 1). Neonatal hyperoxia also decreased performance in the novel object recognition, with less time spent on exploring the new objects compared to air-exposed mice (Fig. 2A).

Neonatal hyperoxia exposure increased exploratory behavior and decreased anxiety in adult mice

In the elevated plus maze test, hyperoxia-exposed (but not

Discussion

The present study is the first to determine the effect of neonatal exposure to chronic hypoxia or hyperoxia on adult neurobehavior and brain structure in a mouse model. The major finding of our study was that exposure of newborn mice to chronic hyperoxia led to deficits in spatial and recognition memory associated with smaller hippocampi in adult mice. This finding is important and highly clinically relevant as human preterm infants, despite a relatively uncomplicated neonatal intensive care

Conclusions

In conclusion, neonatal exposure to chronic hyperoxia leads to impaired spatial learning and memory deficits associated with reduced hippocampal size in adult mice. Neonatal exposure to chronic hypoxia also reduces hippocampal size, and may lead to more subtle neurological effects. These mouse models may be useful to investigate the mechanisms underlying abnormal neurodevelopment in preterm infants who are often exposed to hyperoxia or have hypoxemic episodes.

Disclosure

None.

Conflict of interest statement

None.

Acknowledgments

This work was partially funded by NIH P30 NS47466, NIH R01 HL092906, NIH C06 RR15490, IKARIA, and Division of Neonatology, Department of Pediatrics, University of Alabama at Birmingham, Birmingham, AL, USA.

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