Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
DNA vaccination wikipedia , lookup
Microevolution wikipedia , lookup
Saethre–Chotzen syndrome wikipedia , lookup
Genomic imprinting wikipedia , lookup
Designer baby wikipedia , lookup
Epigenetics of depression wikipedia , lookup
Epigenetics of neurodegenerative diseases wikipedia , lookup
History of genetic engineering wikipedia , lookup
Nutriepigenomics wikipedia , lookup
Epigenetics in learning and memory wikipedia , lookup
Transgenic Models to Study Disorders of Respiratory Control in Newborn Mice Claude Gaultier, Boris Matrot, and Jorge Gallego Abstract Recent studies described the in vivo respiratory phenotype of mutant newborn mice with targeted deletions of genes involved in respiratory control development. Whole-body flow barometric plethysmography is the noninvasive method of choice for studying unrestrained newborn mice. The main characteristics of the early postnatal development of respiratory control in mice are reviewed, including available data on breathing patterns and on hypoxic and hypercapnic ventilatory responses. Mice are very immature at birth, and their instable breathing is similar to that of preterm infants. Breathing pattern abnormalities with prolonged apneas occur in newborn mice that lack genes involved in the development of rhythmogenesis. Some mutant newborn mice have blunted hypoxic and hypercapnic ventilatory responses whereas others exhibit impairments in responses to hypoxia or hypercapnia. Furthermore, combined studies in mutant newborn mice and in humans have helped to provide pathogenic information on genetically determined developmental disorders of respiratory control in humans. Key Words: chemosensitivity; congenital central hypoventilation syndrome; genetics; human newborns; hypercapnia; hypoxia; newborn mice; plethysmography Investigating the Respiratory Control Phenotype in Newborn Mice Introduction G enetic research into respiratory control is finding new paths for investigating developmental respiratory control disorders in humans, such as apneas of prematurity, sudden infant death syndrome, and congenital central hypoventilation syndrome (CCHS1) (Gaultier et al. Claude Gaultier, M.D., Ph.D., Boris Matrot, Eng., and Jorge Gallego, Ph.D., are Professor of Physiology, Project Manager, and Researcher, respectively, in the Service de Physiologie and Inserm U676, Hôpital Robert Debré, Paris, France. 1 Abbreviations used in this article: CCHS, congenital central hypoventilation syndrome; Ece1, endothelin-converting enzyme 1; Edn1, endothelin 1; Ednra, endothelin receptor a; HVD, hypoxic ventilatory decline; preBötzC, pre-Bötzinger complex; Bdnf, brain-derived neurotrophic factor; Mash-1, mammalian achaete-scute homologous 1 gene; PACAP, pituitary adenylcyclase-activating polypeptide; Ret, rearranged-during-transfection gene; Phox2b, paired-like homeobox 2b gene. Volume 47, Number 1 2004). Studies in newborn mice with targeted gene deletions have started to establish links among the expressions of specific genes involved in the development of individual respiratory-control components, such as rhythmogenesis and chemosensitivity for oxygen and carbon dioxide. Furthermore, combined studies in mutant newborn mice and in humans have helped to provide pathogenic information on genetically determined disorders of respiratory control development in humans. Pulmonary gas exchange provides oxygen to developing cells in all mammalian species (with the exception of skin breathing in some species [Mortola et al. 1999]). Respiratory control impairments at early stages of development compromise brain oxygenation and are thought to account for irreversible motor and cognitive disorders. This review focuses on in vivo studies of respiratory phenotype in mutant newborn mice. First, methods for testing respiratory control are described briefly. Second, the main characteristics of the early postnatal development of respiratory control in mice are reviewed. In mice, the developmental stage at birth roughly matches that of human preterm neonates born at 25 wk of gestational age (Marret et al. 1995). Finally, the respiratory phenotype of mutant newborn mice with targeted deletion of genes involved in the development of respiratory control is detailed. 2006 Breathing is usually quantified based on breath duration, inspiratory and expiratory duration, tidal volume, and ventilation. These variables are measured not only while the animals breathe air but also during exposure to hypercapnia, hypoxia, or hyperoxia to test for chemosensitivity. In addition, the number and duration of apneas and periodic breathing episodes are indicators of respiratory instability, a characteristic of the neonatal period in newborn mammals. Analyzing the respiratory phenotype of mutant mice at birth is of crucial importance for two main reasons. First, null mutants for most genes of interest die within a few hours after birth, possibly from respiratory failure, which leaves very little time to investigate respiratory function. Second, breathing control is the outcome of numerous adaptation processes, including plasticity and learning. These processes may lead to resolution of respiratory impairment present early after birth, thereby masking the effects of a gene mutation (Dauger et al. 1999b, 2003). 15 The small birth weight (1.3 g) and tidal volume (3-4 L/g) in newborn mice preclude the use of measurement devices that are widely accepted for adult mice or larger animals (e.g., pneumotachometers, thermistors, respiratory inductance spirometers, magnetometers). Two methods provide valid measurements in newborn mice: head-out plethysmography (e.g., Burton et al. 1997) and whole-body plethysmograpy (e.g., Dauger et al. 1999a,b, 2003). In head-out plethysmography, the newborn mouse is placed in a chamber and its head is slipped outside the chamber through an opening with an airtight seal around the neck. The amount of air that moves in and out of the chamber as a result of breathing is roughly proportional to the changes in chest volume. This method provides a relatively direct measurement of breathing. Its main drawback is that the animal must be tightly restrained to ensure that no air leakage occurs around the neck. As a rule, restraint is a potent stressor that has marked effects on the baseline breathing pattern in adult mice (Dauger et al. 1998). Although the effects have not been studied in newborn mice, stress probably exerts a major influence on ventilatory data collected using head-out plethysmography. Whole-body flow barometric plethysmography consists of placing the animal in a chamber and measuring the pressure changes inside the box. The pressure in the chamber increases during inspiration because of the addition of water vapor to the inspired gas and because of the warming of the inspired gas from the temperature in the chamber to that in the alveoli. Conversely, pressure diminishes during expiration because of condensation of water vapor and cooling of expired gas. This method provides an indirect semiquantitative measure of breathing variables. It has been validated against pneumotachography in adult mice (Onodera et al. 1997) but not in newborns. In newborn mice, whole-body plethysmography provides semiquantitative measurements of tidal volume and ventilation while allowing valid measurement of breathing frequency and apnea. It is important to control for body temperature, which can influence the results, most notably when stimuli may affect metabolism (typically hypoxia or hyperoxia). The zone of thermoneutrality is known for rat pups (Blumberg and Sokoloff 1998) but not for mice pups. However, it may be assumed that the temperature inside the litter (32-33°C) is appropriate for respiratory measurements. Furthermore, this limitation does not preclude genotype group comparisons, which form the basis of phenotype studies. The flow bias through the plethysmograph allows continuous measurement without CO2 accumulation over long periods, which is crucial when studying the time-course of ventilatory responses, delayed effects (e.g., posthypoxic period after switching back to normoxia), repeated stimulations, and effects of behavioral states (Durand et al. 2004). At present, whole-body flow barometric plethysmography is the only noninvasive method and is therefore the method of choice for studying unrestrained newborn mice. Apneas, sighs, and gasps can be identified by visual examination of the plethysmographic signal. However, au16 tomatic detection methods based on spectral analysis for apnea detection facilitate phenotyping of large numbers of mutant animals (Matrot et al. 2005). Behavioral states (wakefulness, active sleep, quiet sleep, or undetermined sleep) were determined recently using nuchal muscle tone, coordinated limb movements, and motor twitches in newborn mice (Durand et al. 2005). It is not possible to determine sleep states by electroencephalogram or electrooculogram in newborn rodents (Karlsson and Blumberg 2002). Maturation of Respiratory Control and Arousal Responses to Chemical Stimuli in Newborn Mice Rapid changes occur postnatally in baseline breathing pattern and ventilatory responses to hypercapnia and hypoxia in newborn mice (Renolleau et al. 2001a). Newborn mice show an extremely immature pattern of breathing reminiscent of the respiratory instability in human preterm infants. At birth, breathing is characterized by numerous apneas, which disappear gradually as age increases (Matrot et al. 2005). The ventilatory response to hypoxia increases sharply after birth due to peripheral chemoreceptor resetting in newborn mammals (Gaultier and Gallego 2005). This resetting occurs approximately 2 to 12 hr after birth in newborn mice (Renolleau et al. 2001a). The time-course of the hypoxic ventilatory responses in wild-type newborn mice during the first 24 hr after birth is reported in Figure 1. During sustained hypoxia, newborn mammals exhibit a biphasic ventilatory response with an initial hyperpneic phase followed by a decline in ventilation to below the normoxic level (hypoxic ventilatory decline [HVD1]) (Gaultier and Gallego 2005). Furthermore, ventilation remains decreased and apneas may occur during the posthypoxic period after switching back to normoxia in some newborn mice (Figure 2). The ventilatory response to hypercapnia is present and vigorous at birth (Renolleau et al. 2001a) and then increases steadily until adulthood (Robinson et al. 2000). Behavioral arousal has been defined as a stereotyped motor response characterized by sudden neck and forepaw extension. At 48 hr of postnatal age, this stereotyped pattern of motor activity is followed by head-raising (Durand et al. 2004). Arousal from sleep in response to hypoxia is a critical defense reflex that is triggered by afferent messages from mechanoreceptors and/or oxygen-sensitive chemoreceptors. Few studies have addressed the development of the hypoxic arousal response during the early postnatal period. In mice, arousal has been shown to occur during the hypoxic decline in all age groups, indicating that mechanoreceptor input was not sufficient to trigger arousal (Dauger et al. 2001). Arousal may therefore contribute to the hypoxic ventilatory response in the early postnatal period in mice, and it thus deserves consideration in studies of respiratory control maturation in newborns. In particular, abnormal developILAR Journal Figure 1 Hypoxic ventilatory response from 1 hr (H1) to 24 hr (H24) after birth in wild-type newborn mice. Newborn mice were exposed to 10% O2, 3% CO2, and 87% N2 during 4 min within a whole-body flow barometric plethysmograph. The hypoxic ventilatory response (VE) is expressed as a percentage of the baseline VE in normoxia-normocapnia. The time-course of the hypoxic ventilatory response shows an initial increase in VE (hyperpneic ventilatory response [HVR]) followed by a decrease in VE (hypoxic ventilatory decline [HVD]). At H1, the hypoxic HVR is weak, and VE falls below the baseline level during the HVD. At H12 and H24, the HVR is stronger than at H1, whereas the HVD is less marked. The data suggest that resetting of the peripheral chemoreceptors may occur around H6-H12. Values are group means ± s.e.m. Reprinted with permission from Renolleau S, Dauger S, Autret F, Vardon G, Gaultier C, Gallego J. 2001a. Maturation of baseline breathing and of hypercapnic and hypoxic ventilatory resonses in newborn mice. Am J Physiol Integr Comp Physiol 281:R1746-R1753. ment of the central mechanisms of arousal may account for the impaired responsiveness to hypoxia observed in some newborn mutant mice (Renolleau et al. 2001b). Furthermore, studies of arousal latency are helpful for examining habituation to a chemical stimulus. Experiments in newborn mice have shown that intermittent hypoxia rapidly and reversibly lengthens arousal latency from baseline levels increased after the first hypoxic stimulus, thereby delaying arousal in newborn mice (Durand et al. 2004). Respiratory Phenotype in Mutant Newborn Mice Survival differs across mutant newborn mice. Examples of homozygous mutant mice that have died in utero include paired-like homeobox 2b (Phox2b 1 ) and endothelinconverting enzyme 1 (Ece11) mouse embryos (Pattyn et al. 1999; Yanagisawa et al. 1998). Among mutant mice born Volume 47, Number 1 2006 alive, many die within a few hours. In general, heterozygous mutant newborn mice develop normally, which allows for longitudinal testing. However, irrespective of the targeted gene deletion, surviving mutant newborn mice usually weigh less than wild-type pups and require normalization of ventilation for body weight. Genotype-related differences in breathing variables can be further examined in weightmatched groups of mutant and wild-type pups. Yet one or more respiratory control abnormalities may occur in mutant newborn mice, which complicates the interpretation of deficiencies in each individual component of respiratory control. Finally, the problem of appropriate genetic controls for comparison with genetically modified newborn mice is an important issue. The phenotypic effects of a mutation probably depend on the genetic background, as demonstrated in other settings (Nadeau 2001). The modifier genes responsible for this respiratory phenotype variability could perhaps be identified by interstrain comparisons. To date, no such experiment has been reported in newborn mutant mice. Mutant Newborn Mice with Abnormal Baseline Breathing Studies of breathing rhythmicity in mutant newborn mice have yielded new information about the genes that control rhythmogenesis. Pioneer studies demonstrated that loss of genes responsible for hindbrain segmentation during the early embryonic stages, such as Krox20, led to severe breathing instability at birth that usually resulted in death (Borday et al. 2004). However, studies have shown that neurotrophic factors, such as the brain-derived neurotrophic factor (Bdnf1), play a pivotal role in respiratory rhythm development in mice (Erickson et al. 1996). Bdnf nullmutant newborn mice exhibit severe disruption of respiratory rhythmogenesis, with bradypnea and numerous apneas (Erickson et al 1996). Recording of brainstem-spinal cord preparations from Bdnf newborn mutant mice have shown discharge frequency attenuation, which has been more marked in homozygous than in heterozygous newborns (Erickson et al. 2001). Bdnf appears critical to respiratory rhythmogenesis in neonatal mice through the Bdnf receptor tyrosine kinase B in neurons of the pre-Bötzinger complex (preBötzC1) (Thoby-Brisson et al. 2003). The preBötzC complex is thought to underlie rhythmogenesis (Feldman et al. 2003). Another group of studies has focused on the role of respiratory drive modulation by the A5 and A6 noradrenergic nuclei in mutant newborn mice lacking one of the genes that control noradrenergic neuronal development (Hilaire et al. 2004). Loss of the inhibitory influence of A5 (Errchidi et al. 1991) leads to abnormally fast breathing, as observed in null-mutant newborn mice lacking the mammalian achaete-scute homologous 1 gene (Mash-11) (Dauger et al. 1999a), the respiratory neuron homeobox gene Rnx (Shirasawa et al. 2000), or the glial cell line-derived neuro17 Figure 2 Examples of breathing pattern in normoxia, hypoxia, and posthypoxic normoxia in a heterozygous Ret mutant newborn (c-ret +/-) (top) and a wild-type newborn (c-ret+/+) (bottom). The traces during hypoxia corresponded to the hyperpneic phase of the hypoxic response. The traces during posthypoxic normoxia were selected 2 min after switching back to air. In both pups, breathing was depressed and irregular during posthypoxic normoxia, but only the Ret +/- pup exhibited apneas and periodic breathing. Reprinted with the permission of Elsevier from Aizenfisz S, Dauger S, Durand E, Vardon G, Levacher B, Simonneau M, Gaultier C, Gallego J. 2002. Ventilatory responses to hypercapnia and hypoxia in heterozygous c-ret +/- newborn mice. Respir Physiol 131:213-222. trophic factor gene (Gdnf1) (Huang et al. 2005); all these mutant mice die shortly after birth. Recent evidence suggests that the A6 pontine noradrenergic center may be essential for normal respiratory rhythmogenesis in neonatal mice (Viemari et al. 2004). Phox2a null-mutant neonatal mice, which lack A6 neurons, exhibit numerous apneas and gasps and die shortly after birth. Recent studies have shed light on the genes involved in preBötzC development. Deficiency of the transcription factor MafB causes defective respiratory rhythmogenesis in neonatal mutant mice, which manifests as gasps and fatal apneas shortly after birth (Blanchi et al. 2003). The human orthologue of the Necdin gene is mutated in patients with Prader-Willi syndrome, which is characterized by abnormal respiratory control, and null-mutant mice for Necdin exhibit respiratory rhythm instability, which is fatal within a few hours after birth (Ren et al. 2003). Medullary slice preparations from the preBötzC regions of these null-mutant embryos on embryonic day 18.5 show abnormal rhythmic discharges that suggest loss or alteration of the function of preBötzC rhythmic neurons (Ren et al. 2003). Finally, newborn mice that lack the transcription factor Nurr1, which governs the development of midbrain dopaminergic neurons, exhibit disturbed breathing patterns with numerous apneas and die shortly after birth (Nsegbe et al. 2004). Mutant Newborn Mice with Abnormal Chemosensitivity (Table 1) Abnormal Ventilatory Response to Hypoxia and Hypercapnia Abnormal ventilatory responses to both sustained hypoxia and sustained hypercapnia have been reported in mutant newborn mice lacking endothelin pathway genes that encode endothelin (Edn11) and the endothelin receptor a 18 (Ednra1) (Kuwaki et al. 1999). These mutant newborn mice die shortly after birth (Kuwaki et al. 1999). In contrast, the ventilatory responses to hypoxia and hypercapnia are normal in mutant mice that lack genes for the endothelin 3 signaling pathway (Kuwaki et al. 1999). Recent evidence shows that null-mutant newborn mice deficient in pituitary adenylcyclase-activating polypeptide (PACAP1), a member of the vasoactive intestinal peptide superfamily, have blunted ventilatory responses to both hypoxia and hypercapnia. This evidence suggests that the PACAP signaling pathway may contribute to both hypoxic and hypercapnic chemosensitivity (Cummings et al. 2003). Abnormal Ventilatory Response to Hypoxia or to Hyperoxia Other gene disruptions alter only the hypoxic ventilatory response in mutant newborn mice. Heterozygous mutant newborn mice lacking Ece1 survive after birth and exhibit an abnormal hyperpneic ventilatory response to hypoxia that persists during adulthood (Renolleau et al. 2001b). Nurr1 null-mutant newborn mice have deficient ventilatory responses to hypoxia and die shortly after birth (Nsegbe et al. 2004). Because Nurr1 is expressed in the nucleus tractus solitarius, which is the first central relay of the arterial chemoreflex, loss of function of this gene may explain the deficient ventilatory response to hypoxia in mutant mice. Hyperpneic ventilatory responses to hypoxia at birth are not affected by heterozygous disruption of genes involved in the development of the autonomic nervous system, such as the rearranged-during-transfection gene (Ret1) or Phox2b (Aizenfisz et al. 2002; Dauger et al. 2003). However, the HVD is exaggerated in these mutant newborn mice. Conversely, the HVD is attenuated by disruption of other genes; thus, the HVD is weak in null-mutant mice lacking the beta-2 subunit of the nicotinic acetylcholine receptors ILAR Journal Table 1 Ventilatory responses to hypoxia and hypercapnia in knock-out newborn micea Hypoxic Newborn mice Age at study Hypercapnic VR␣ Ret−/− Ret+/− Mash+/− Phox2b+/− Edn1−/− Ednra−/− Ecel+/− Nurr−/− Bdnf−/− PACA−/− Beta− 2nAChR−/− A few hours 12 hr ⬙⬙ 48 hr First day First day A few hours First day First 4 days Day 4 48 hr Decreased*a NSa Decreased †a Decreased Decreased Decreased NS NS Present Decreased HVRa NS NS NS NS Decreased Decreased Decreased Decreased HVDa Hyperoxic VR Increased Increased Absent Decreased NS Decreased References (see text) Burton et al. 1997 Aizenfisz et al. 2002 Dauger et al. 1999a,b Dauger et al. 2003 Kuwaki et al. 1999 Kuwaki et al. 1999 Renolleau et al. 2001 Nsegbe et al. 2004 Erickson et al. 1996 Cummings et al. 2004 Dauger et al. 2004 a VR, ventilatory response; HVR, hyperpneic ventilatory response; HVD, hypoxic ventilatory decline; beta-2nAChR, beta-2 subunit of the nicotinic acetylcholine receptors; NS, not significantly different from wild-type littermates; *, significantly decreased compared with wild-type littermates; †, significantly decreased in males; for other abbreviations, see text. (Dauger et al. 2004). These findings suggest alterations in the inhibitory processes that affect the ventilatory response to hypoxia in neonates. Ventilatory responses to hyperoxia, which reflect peripheral chemoreceptor function, are absent in Bdnf null-mutant newborn mice (Table 1) (Erickson et al. 1996), presumably due to loss of chemoafferent neurons (Erickson et al. 2001). Phox2b mutant mice (Dauger et al. 2003) and is no longer present in adult Mash-1 mice (Dauger et al. 1999b). Compensatory mechanisms and/or plasticity processes may explain the recovery of ventilatory responses to hypercapnia in these mutant mice, although the underlying mechanisms remain unexplored. Conclusion and Perspectives Abnormal Ventilatory Response to Hypercapnia Abnormal ventilatory responses to hypercapnia have been reported in newborn mice that lack genes of the Mash-1Ret-Phox2b pathway, which is involved in the development of the autonomic nervous system. Null-mutant newborn mice lacking the Ret gene, but not mice heterozygous for this mutation, have blunted ventilatory responses to hypercapnia (Aizenfisz et al. 2002; Burton et al. 1997). Male heterozygous Mash-1 mutant newborn mice show decreased ventilatory responses to hypercapnia (Dauger et al. 1999b). Finally, heterozygous mutant mice that lack the Phox2b gene, whose human orthologue is mutated in CCHS patients (Amiel et al. 2003; Trochet et al. 2005), exhibit a reduced ventilatory response to hypercapnia on postnatal day 2 (Figure 3). Furthermore, these mutants have sleep apneas (Durand et al. 2005). Ret, Mash-1, and Phox2b are expressed in central chemosensitive areas, such as the nucleus tractus solitarius and the locus coeruleus in newborn mice (Dauger et al. 1999a, 2003). Loss of expression of these factors may explain the deficient ventilatory response to hypercapnia in mutant mice. Interestingly, the deficiency in ventilatory responses to hypercapnia resolves on postnatal day 10 in Volume 47, Number 1 2006 Studies of the respiratory phenotype of mutant newborn mice have been helpful in understanding how gene disruption may disturb one or several components of respiratory control during postnatal development. Although many genes involved in respiratory control have been identified, none of the genetically engineered mice developed to date fully replicate the phenotype of human disorders in respiratory control development. However, studies of the respiratory phenotype of mutant newborn mice combined with studies in humans have provided valuable pathogenic information on genetically determined disorders of respiratory control development in humans (e.g., congenital central hypoventilation syndrome and Prader-Willi syndrome). It is thus clearly important to extend these studies to early disturbances of respiratory control, including apneas of prematurity and sudden infant death syndrome. In vivo studies of the respiratory phenotype should be combined with in vitro studies of brainstem-spinal cord preparations and/or brain slices in culture to describe in full the consequences of gene disruption in isolated neurons, isolated brainstem, and live animals. Furthermore, technological improvements should allow integrative approaches that encompass not only respiration but also all vital func19 Figure 3 Hypercapnic ventilatory responses in heterozygous newborn mice lacking Phox2b and in wild-type pups on postnatal day 2. Newborn mice were exposed to 8% CO2, 21% O2, and 71% N2 during 3 min within a whole-body flow barometric plethysmograph. Panel a: Ventilatory tracings of one Phox2b +/+ pup (top) and one Phox2b +/- pup (bottom); both pups had similar baseline ventilation, but the Phox2b+/- pup exhibited a weaker ventilatory response to hypercapnia. Panel b: The ventilatory increase during hypercapnia in Phox2b+/pups was approximately half that in Phox2b+/+ pups, because of a smaller increase in breathing frequency. Values are group means ± s.e.m. Reprinted with permission from Dauger S, Pattyn A, Lofaso F, Gaultier C, Goridis C, Gallego J, Brunet JF. 2003. Phox2b controls the development of peripheral chemoreceptors and afferent visceral pathways. Development 130:6635-6642. tions of mutant newborn mice. Recordings of respiratory variables should be combined with recordings of heart rate, temperature, and behavioral states (Durand et al. 2005). Research into the respiratory phenotype of newborn mice is an important component of current international efforts to determine the function of genes and their role in human diseases and to design new treatment strategies. Neonatal phenotyping is mandatory for exploring the molecular mechanisms of early disturbances in respiratory control, which are not faithfully reflected by the adult phenotype, and their impact on neurodevelopment. References Aizenfisz S, Dauger S, Durand E, Vardon G, Levacher B, Simonneau M, Gaultier C, Gallego J. 2002. Ventilatory responses to hypercapnia and hypoxia in heterozygous c-ret +/- newborn mice. Respir Physiol 131: 213-222. Amiel J, Laudier B, Attie-Bitach T, Trang H, De Pontual L, Gener B, Trochet D, Etchevers H, Ray P, Simonneau M, Vekemans M, Munnich 20 A, Gaultier C, Lyonnet S. 2003. Polyalanine expansion and frameshift mutations of the paired-like homeobox gene PHOX2B in congenital central hypoventilation syndrome. Nat Genet 33:459-461. Blanchi B, Kelly LM, Viemari JC, Lafon I, Burnet H, Bevengut M, Tillmans S, Daniel L, Graf T, Hilaire G, Sieweke MH. 2003. MafB deficiency causes defective respiratory rhythmogenesis and fatal central apnea at birth. Nat Neurosci 6:1091-1100. Blumberg MS, Sokoloff G. 1998. Thermoregulatory competence and behavioural expression in young of altricial species-revisited. Dev Psychobiol 33:107-123. Borday C, Wrobe, L, Fortin G, Champagnat J, Thaëron-Antôno C, ThobyBrisson M. 2004. Developmental gene control of brainstem function: Views from the embryo. Prog Biophys Mol Biol 84:89-106. Burton MD, Kawashima A, Brayer JA, Kazemi H, Shannon DC, Schuchardt A, Costantini F, Pachnis V, Kinane TB. 1997. RET protooncogene is important for the development of respiratory CO2 sensitivity. J Autonom Nerv Syst 63:137-143. Cummings KJ, Pendlebury JD, Sherwood NM, Wilson RJA. 2003. Sudden neonatal death in PACAP-deficient mice is associated with reduced respiratory chemoresponse and susceptibility to apnoea. J Physiol 555: 15-26. Dauger S, Aizenfisz S, Renolleau S, Durand E, Vardon G, Gaultier C, Gallego J. 2001. Arousal response to hypoxia in newborn mice. Respir Physiol 128:235-240. ILAR Journal Dauger S, Durand E, Cohen G, Lagercrantz H, Changeux JP, Gaultier C, Gallego J. 2004. Control of breathing in newborn mice lacking the beta-2nAChR subunit. Acta Physiol Scand 181:1-8. Dauger S, Guimiot F, Renolleau S, Levacher B, Boda B, Mas C, Nepote V, Simonneau M, Gaultier C, Gallego J. 1999a. Mash-1/Ret pathway involvement in development of brain stem control of respiratory frequency in newborn mice. Physiol Genomics 7:49-157. Dauger S, Nsegbe E, Vardon G, Gaultier C, Gallego J. 1998. The effects of restraint on ventilatory responses to hypercapnia and hypoxia in adult mice. Respir Physiol 112:215-252. Dauger S, Pattyn A, Lofaso F, Gaultier C, Goridis C, Gallego J, Brunet JF. 2003. Phox2b controls the development of peripheral chemoreceptors and afferent visceral pathways. Development 130:6635-6642. Dauger S, Renolleau S, Nepote V, Mas C, Simonneau M, Gaultier C, Gallego J. 1999b. Ventilatory responses to hypercapnia and to hypoxia in Mash-1 heterozygous newborn and adult mice. Pediatr Res 46:535542. Durand E, Dauger S, Pattyn A, Gaultier C, Goridis C, Gallego J. 2005. Sleep-disordered breathing in newborn mice heterozygous for the transcription factor Phox2b. Am J Respir Crit Care Med: Apr 28 (Epub ahead of print). Durand E, Lofaso F, Dauger S, Vardon G, Gaultier C, Gallego J. 2004. Intermittent hypoxia induces transient arousal delay in newborn mice. J Appl Physiol 96:1216-1222. Erickson JT, Conover JC, Borday V, Champagnat J, Barbacid M, Yancopoulos G, Katz DM. 1996. Mice lacking brain-derived neurotrophic factor exhibit visceral sensory neuron losses distinct from mice lacking NT4 and display a severe developmental deficit in control of breathing. J Neurosci 16:5361-5371. Erickson JT, Brosenitsch TA, Katz DM. 2001. Brain-derived neurotrophic factor and glial cell line-derived neurotrophic factor are required simultaneously for survival of dopaminergic primary sensory neurons in vivo. J Neurosci 15:581-589. Errchidi S, Monteau R, Hilaire G. 1991. Noradrenergic modulation of the medullary respiratory rhythm generator in the newborn rat: An in vitro study. J Physiol 443:477-498. Feldman JL, Mitchell GS, Nattie EE. 2003 Breathing: Rhythmicity, plasticity, chemosensitivity. Annu Rev Neurosci 26:239-266. Gaultier C, Amiel J, Dauger S, Trang H, Lyonnet S, Gallego J, Simonneau M. 2004. Genetics and early disturbances of breathing control. Pediatr Res 55:729-733. Gaultier C, Gallego J. 2005. Development of respiratory control: Evolving concepts and perspectives. Respir Physiol Neurobiol June 4, 2005 (Epub ahead of print). Hilaire G, Viemari JC, Coulon P, Simonneau M, Bévengut M. 2004. Modulation of the respiratory rhythm generator by the pontine noradrenergic A5 and A6 groups in rodents. Respir Physiol Neurobiol 143: 187-197. Huang L, Guo H, Hellard DT, Katz DM. 2005. Glial cell line-derived neurotrophic factor (GDNF) is required for differentiation of pontine noradrenergic neurons and patterning of central respiratory output. Neuroscience 130:95-105. Karlsson KA, Blumberg MS. 2002. The union of the state: Myoclonic twitching is coupled with nuchal atonia in infants rats. Behav Neurosci 116:912-917. Kuwaki T, Ling GY, Onodera M, Ishii T, Nakamura A, Ju KH, Cao Wh, Kumada M., Kurihara H, Kurihara Y, Yazaki Y, Ohuchi T, Yanagisawa M, Fukuda Y. 1999. Endothelin in the central control of cardio- Volume 47, Number 1 2006 vascular and respiratory functions. Clin Exp Pharmacol Physiol 26: 989-994. Marret S, Mukendi R, Gadisseux JF, Gressens P, Evrard P. 1995. Effect of ibotenate on brain development: An excitotoxic mouse model of microgyria and posthypoxic-like lesions. J Neuropathol Exp Neurol 54: 358-370. Matrot B, Durand E, Dauger S, Vardon, Gaultier, Gallego J. 2005. Automatic classification of activity and apneas using whole-body plethysmography in newborn mice. J Appl Physiol 98:365-370. Mortola JP, Frappell PB, Woolley PA. 1999. Breathing through skin in a newborn mammal. Nature 397:660. Nadeau JH. 2001. Modifiers genes in mice and humans. Nat Rev 2:165174. Nsegbe E, Wallen-Mackensie A, Dauger S, Roux JC, Shvarev Y, Lagercrantz H, Perlman T, Herlenius E. 2004. Congenital hypoventilation hypoxic response in Nurr1 mutant mice. J Physiol 556:43-59. Onodera M, Kuwaki T, Kumada M, Masuda Y. 1997. Determination of ventilatory volume in mice by whole body plethysmography. Jpn J Physiol 47:317-326. Pattyn A, Morin X, Cremer H, Goridis C, Brunet JF. 1999. The homeobox gene Phox2b is essential for the development of autonomic neural crest derivatives. Nature 399:366-370. Ren J, Lee S, Pagliardini S, Gerard M, Stewart CL, Greer JJ, Wevrick R. 2003. Absence of Ndn, encoding the Prader-Willi syndrome-deleted gene necdin, results in congenital deficiency of central respiratory drive in neonatal mice. J Neurosci 23:1569-1573. Renolleau S, Dauger S, Autret F, Vardon G, Gaultier C, Gallego J. 2001a. Maturation of baseline breathing and of hypercapnic and hypoxic ventilatory responses in newborn mice. Am J Physiol Integr Comp Physiol 281:R1746-R1753. Renolleau S, Dauger S, Vardon G, Levacher B, Simonneau M, Yanagisawa M, Gaultier C, Gallego J. 2001b. Impaired ventilatory responses to hypoxia in mice deficient in endothelin-converting-enzyme-1. Pediatr Res 49:705-712. Robinson DM, Kwork H, Adams BM, Peebles KC, Funk GD. 2000. Development of the ventilatory response to hypoxia in Swiss CD-1 mice J Appl Physiol 88:1907-1914. Shirasawa S, Arata A, Onimaru H, Roth KA, Brown GA, Horning S, Arata S, Okumura K, Sasazuki T, Korsmeyer SJ. 2000. Rnx deficiency results in congenital hypoventilation. Nat Genet 24:287-290. Thoby-Brisson M, Cauli B, Champagnat J, Fortin G, Katz DM. 2003. Expression of functional tyrosine kinase B receptors by rhythmically active respiratory neurons in the pre-Bötzinger complex of neonatal mice. J Neurosci 23:7685-7689. Trochet D, O’Brien LM, Gozal D, Nordenskjold A, Laudier B, Svensson PJ, Uhrig S, Cole T, Munnich A, Gaultier C, Lyonnet S, Amiel J. 2005. PHOX2B genotype allows for prediction of tumour risk in congenital central hypoventilation syndrome. Am J Hum Genet 76:421-426. Viemari JC, Bevengut M, Burnet H, Coulon P, Pequignot JM, Tiveron MC, Hilaire G. 2004. Phox2a gene, A6 neurons, and noradrenaline are essential for development of normal respiratory rhythm in mice. J Neurosci 24:928-937. Yanagisawa H, Yanakisawa M, Kapur RP, Richardson JA, Williams SC, Clouthier DE, de Wit D, Emoto N, Hammer RE. 1998. Dual genetic pathway of endothelin-mediated intracellular signaling revealed by targeted disruption of endothelin converting enzyme-1 gene. Development 125:825-836. 21