Neonatal mouse models of apnea of prematurity: Early postnatal hypoxia, defense responses and behavioral outcome

Preterm birth, affecting roughly 10% of all infants, is an important health problem that puts children at risk for long-term morbidity and developmental disabilities. We will focus on one aspect of preterm infants complex pathology, namely respiratory instability. Respiratory instability, characterized by frequent apneas, and resultant intermittent hypoxia (IH) that can persist for weeks to months, is a common problem in preterm infants. Epidemiological studies suggest that it is related to poor developmental outcome. However, pinpointing causal relationships between respiratory instability and developmental outcome is difficult in infants because of numerous confounding comorbidities and ethical considerations that render clinical studies in this population difficult. Newborn animal models are necessary for this purpose. In this dissertation we have integrated physiological and behavioral techniques in newborn mice to tackle research questions about respiratory instability related to preterm birth and its consequences on neurobehavioral development.First, to be able to assess cognitive performance early in development, we developed a new conditioning procedure suitable for neonatal mouse pups, using artificial odors as conditioned stimuli and ambient temperature as the unconditioned stimulus. Second, we investigated the short- and long-term behavioral consequences of frequent apneas during the postnatal period in two mouse models, using an experimental and a genetic approach. In adult mice postnatally exposed to IH, we found evidence for hyperactivity in a novel environment. In male mice, we observed working memory impairment and alterations in social behavior. Phox2b+/- mice were studied as an alternative to IH. This genetic mouse model shows spontaneous apneas specifically during the postnatal period. We found evidence for emotional alterations in Phox2b+/-mice. These results indicate that newborns' ability to adequately respond to hypoxia is a key factor for developmental outcome. We consequently focused on the repertoire of defense reactions a newborn mouse exhibits to cope with hypoxia. We studied a broad range of both physiological and behavioral defense reactions to hypoxia in both a thermoneutral and a cold environment. The latter increases metabolic rate and aggravates hypoxic stress. We showed that newborn mice cope with hypoxia using a context-dependent strategy. Furthermore, based on conditioning studies using odors as conditioned stimuli and hypoxia as the unconditioned stimulus, we found that the defense response to hypoxia in newborn mice may be shaped by past experience. Finally, we investigated whether the group III metabotropic glutamate receptors mGluR4, mGluR7 and mGluR8, which are differentially implicated in anxiety and stress, are also involved in the defense response to hypoxia. This was done using genetic knockout (KO) mouse models. We observed a blunted ventilatory response to cold and hypoxia in mGluR7 KO mouse pups, while mGluR8 KO pups exhibited an enhanced response. This suggests that these receptors are differentially involved in the defense response to hypoxic stress.nrpages: 180status: publishe

Olfactory classical conditioning in neonatal mouse pups using thermal stimuli

Mouse models are increasingly used to investigate genetic contributions to developmental disorders in children, especially newborns. In particular, early cognitive assessment in newborn mice is critical to evaluate pediatric drug efficacy and toxicity. Unfortunately, methods for behavioral tests in newborn mice are scarce. Therefore, developing such tests for newborn mice is a priority challenge for neurogenetics and pharmacological research. The aim of the present study was to develop a conditioning method well suited to high-throughput cognitive screening in newborn mice. To this end, we developed an odor-preference conditioning test using ambient temperature as an unconditioned stimulus (US) and artificial odors as conditioned stimuli (CS). First, we showed that mouse pups move toward the thermoneutral temperature when offered a choice between a thermoneutral and cold environment, thus showing thermotaxis. Second, we conducted a classical conditioning paradigm in pups aged six to ten days. In terms of central nervous system development, this period corresponds to extreme prematurity to early post-term period in humans. During acquisition, the pups were alternatively exposed to odor CS paired with either cold or warm temperatures. Immediately after acquisition, the pups underwent a two-odor choice test, which showed preference for the odor previously paired with the warm temperature, thus showing conditioning. The proposed paradigm is easy to conduct, and requires modest experimenter interference. The method is well suited for high-throughput screening of early associative disorders in newborn mice.status: publishe

Olfactory classical conditioning in neonatal mouse pups using thermal stimuli

International audienceMouse models are increasingly used to investigate genetic contributions to developmental disorders in children, especially newborns. In particular, early cognitive assessment in newborn mice is critical to evaluate pediatric drug efficacy and toxicity. Unfortunately, methods for behavioral tests in newborn mice are scarce. Therefore, developing such tests for newborn mice is a priority challenge for neurogenetics and pharmacological research. The aim of the present study was to develop a conditioning method well suited to high-throughput cognitive screening in newborn mice. To this end, we developed an odor-preference conditioning test using ambient temperature as an unconditioned stimulus (US) and artificial odors as conditioned stimuli (CS). First, we showed that mouse pups move toward the thermoneutral temperature when offered a choice between a thermoneutral and cold environment, thus showing thermotaxis. Second, we conducted a classical conditioning paradigm in pups aged six to ten days. In terms of central nervous system development, this period corresponds to extreme prematurity to early post-term period in humans. During acquisition, the pups were alternatively exposed to odor CS paired with either cold or warm temperatures. Immediately after acquisition, the pups underwent a two-odor choice test, which showed preference for the odor previously paired with the warm temperature, thus showing conditioning. The proposed paradigm is easy to conduct, and requires modest experimenter interference. The method is well suited for high-throughput screening of early associative disorders in newborn mice

Learned defense response to hypoxia in newborn mice

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A Bradycardia-Based Stress Calculator for the Neonatal Intensive Care Unit: A Multisystem Approach

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A Bradycardia-Based Stress Calculator for the Neonatal Intensive Care Unit: A Multisystem Approach

Early life stress in the neonatal intensive care unit (NICU) can predispose premature infants to adverse health outcomes and neurodevelopment delays. Hands-on-care and procedural pain might induce apneas, hypoxic events, and sleep-wake disturbances, which can ultimately impact maturation, but a data-driven method based on physiological fingerprints to quantify early-life stress does not exist. This study aims to provide an automatic stress detector by investigating the relationship between bradycardias, hypoxic events and perinatal stress in NICU patients. EEG, ECG, and SpO2 were recorded from 136 patients for at least 3 h in three different monitoring groups. In these subjects, the stress burden was assessed using the Leuven Pain Scale. Different subspace linear discriminant analysis models were designed to detect the presence or the absence of stress based on information in each bradycardic spell. The classification shows an area under the curve in the range [0.80-0.96] and a kappa score in the range [0.41-0.80]. The results suggest that stress seems to increase SpO2 desaturations and EEG regularity as well as the interaction between the cardiovascular and neurological system. It might be possible that stress load enhances the reaction to respiratory abnormalities, which could ultimately impact the neurological and behavioral development.status: publishe

Emotional disorders in adult mice heterozygous for the transcription factor Phox2b

Phox2b is an essential transcription factor for the development of the autonomic nervous system. Mice carrying one invalidated Phox2b allele (Phox2b(+/-)) show mild autonomic disorders including sleep apneas, and impairments in chemosensitivity and thermoregulation that recover within 10days of postnatal age. Because Phox2b is not expressed above the pons nor in the cerebellum, this mutation is not expected to affect brain development and cognitive functioning directly. However, the transient physiological disorders in Phox2b(+/-) mice might impair neurodevelopment. To examine this possibility, we conducted a behavioral test battery of emotional, motor, and cognitive functioning in adult Phox2b(+/-) mice and their wildtype littermates (Phox2b(+/+)). Adult Phox2b(+/-) mice showed altered exploratory behavior in the open field and in the elevated plus maze, both indicative of anxiety. Phox2b(+/-) mice did not show cognitive or motor impairments. These results suggest that also mild autonomic control deficits may disturb long-term emotional development.publisher: Elsevier articletitle: Emotional disorders in adult mice heterozygous for the transcription factor Phox2b journaltitle: Physiology & Behavior articlelink: http://dx.doi.org/10.1016/j.physbeh.2015.01.012 content_type: article copyright: Copyright © 2015 Elsevier Inc. All rights reserved.status: publishe

Impact of inhaled nitric oxide on white matter damage in growth-restricted neonatal rats

Fetal growth restriction is the second leading cause of perinatal morbidity and mortality, and neonates with intrauterine growth retardation (IUGR) have increased neurocognitive and neuropsychiatric morbidity. These neurocognitive impairments are mainly related to injury of the developing brain associated with IUGR. Growing evidence from preclinical models of brain injury in both adult and neonatal rodents supports the view that nitric oxide can promote neuroprotection