Biomedical subjects

Jorge Gallego

Publications and source records attributed to Jorge Gallego.

17 recordsLinked to original sources

PubMed2006

Air hunger and ventilation in response to hypercapnia: effects of repetition and anxiety.

We investigated the effects of anxiety on the intensity of air hunger during gradually increasing levels of CO2 until the end-tidal fractional concentration of CO2 was 7.9% or air hunger was intolerable. Normal high and low (trait) anxious participants (N=23) went through three rebreathing trials (15 min interval). Breathing behaviour was continuously monitored and air hunger was rated every 12 s. The threshold for responding to the increased CO2 was always lower for the subjective rating than for the ventilatory response. Habituation across trials was observed for both the ventilatory response and the air hunger rating regardless of anxiety. However, beyond the threshold, the slope in air hunger ratings decreased across trials in low anxious persons and tended to increase in high anxious persons (interaction P<0.05). No differences occurred in the slopes of the breathing responses. The findings documented uncoupling of the physiological and subjective responses during CO2-induced air hunger.

Adolescent↗

PubMed2006

Transgenic models to study disorders of respiratory control in newborn mice.

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.

Animals↗

PubMed2005

Development of respiratory control: evolving concepts and perspectives.

The mechanisms underlying respiratory system immaturity in newborns have been investigated, both in vivo and in vitro, in humans and in animals. Immaturity affects breathing rhythmicity and its modulation by suprapontine influences and by afferents from central and peripheral chemoreceptors. Recent research has moved from bedside tools to sophisticated technologies, bringing new insights into the plasticity and genetics of respiratory control development. Genetic research has benefited from investigations of newborn mice having targeted deletions of genes involved in respiratory control. Genetic variability may govern the normal programming of development and the processes underlying adaptation to homeostasis disturbances induced by prenatal and postnatal insults. Studies of plasticity have emphasized the role of neurotrophic factors. Improvements in our understanding of the mechanistic effects of these factors should lead to new neuroprotective strategies for infants at risk for early respiratory control disturbances, such as apnoeas of prematurity, sudden infant death syndrome and congenital central hypoventilation syndrome.

Animals↗

PubMed2005

Pediatric disorders with autonomic dysfunction: what role for PHOX2B?

Hirschsprung disease, neuroblastomas, and congenital central hypoventilation syndrome can occur in combination, and familial cases have been reported in all three conditions. This suggests variable expression of a single genetic abnormality as the common cause to these neural crest disorders. Because the PHOX2B gene is pivotal in the development of most relays of the autonomic nervous system, including all autonomic neural crest derivatives, it was considered a candidate gene for the above conditions. Recent studies have shown that 1) PHOX2B is the main disease-causing gene for congenital central hypoventilation syndrome, an autosomal dominant disorder with incomplete penetrance; 2) PHOX2B is the first gene for which germline mutations have been demonstrated to predispose to neuroblastoma; and 3) Hirschsprung disease was associated with an intronic single-nucleotide polymorphism of the PHOX2B gene in a case-control study. For clarifying the variable clinical expression of the autonomic nervous system dysfunction observed in neural crest disorders, international databases of clinical symptoms and molecular test results should be established. Furthermore, the development of genetic mouse models should help to improve our understanding of the molecular mechanisms underlying neural crest disorders.

Animals↗

PubMed2005

Sleep-disordered breathing in newborn mice heterozygous for the transcription factor Phox2b.

RATIONALE: Central congenital hypoventilation syndrome (CCHS) is a rare autosomal dominant syndrome present from birth, and characterized by depressed ventilation during sleep. Heterozygous mutations of the homeobox gene Phox2b were recently found in a very high proportion of patients. OBJECTIVES: To determine whether newborn mice with heterozygous targeted deletion of the transcription factor Phox2b would display sleep-disordered breathing. METHODS: We measured breathing pattern using whole-body plethysmography in wild-type and mutant 5-day-old mice, and we classified sleep-wake states using nuchal EMG and behavioral scores. RESULTS: We found that sleep apnea total time was approximately six times longer (8.9 +/- 12 vs. 1.5 +/- 2.2 seconds, p < 0.0015), and ventilation during active sleep was 21% lower (18.4 +/- 5.1 vs. 23.3 +/- 5.5 ml/g/second, p < 0.006) in mutant than in wild-type pups. During wakefulness, apnea time and ventilation were not significantly different between mutant and wild-type pups. Mutant and wild-type pups showed highly similar sleep-wake states. CONCLUSION: Although their respiratory phenotype was much less severe than CCHS, the Phox2b(+/-) mutant mice showed sleep-disordered breathing, which partially modeled the key feature of CCHS.

Animals↗

PubMed2005

Olfactory classical conditioning in newborn mice.

Determining the behavioural phenotype of genetically altered mice is a valuable approach for elucidating the function of genes and their role in cognitive disorders. Methods for phenotyping newborn mice are scarce and generally confined to sensorimotor reflexes. Here, we describe a simple method for assessing associative abilities in newborn mice. We used a two-odour-choice classical conditioning paradigm in mice from the day of birth (post-natal age 0, P0) to P6. Acquisition required 20 trials: 10 trials during which the pups were placed over the conditioned stimulus (CS+) odour (lemon or peppermint) for 30s and simultaneously stroked gently with a paintbrush and 10 trials during which the pups were placed over the other odour (CS-) for 30s, without stroking. Then, the pups were subjected to five odour-preference trials to test for conditioning. This sequence of five trials was repeated after 5 and 24h to assess retention of the conditioned odour preference. During the immediate post-acquisition sequence, the pups spent significantly more time over the CS+ than over the CS- (p<0.0001). No extinction of the conditioned preference was observed during this test. No preference was observed after 5 or 24h, indicating that the conditioned response was promptly lost. Conditioning was effective as soon as P0-P1. Thus, conditioning may emerge in newborn mice sooner than previously reported. This paradigm is well suited to phenotyping of large samples of genetically altered mice and may shed light on the role for genes in paediatric cognitive impairments.

Age Factors↗

PubMed2004

A simple method for short-term controlled anesthesia in newborn mice.

In this study, we describe a simple and inexpensive method for inducing short-term anesthesia and rapid recovery in newborn mice. Litters of Swiss mice pups were randomly allocated to testing on postnatal days 2, 5, and 8. Anesthesia was induced by placing the pup in a syringe and adding a volume of isoflurane-saturated gas that produced an estimated level of 32% isoflurane. Exposure to isoflurane lasted 30 s. All the pups survived the anesthesia. At all study ages, this method abolished the nociceptive response to tail clamp without inducing mortality, thus showing effective anesthesia. Recovery from anesthesia was assessed immediately after isoflurane exposure, based on two nonnoxious behavioral tests: the defensive response to a drop of water (10 tests, 1 min apart) and 10 min later the righting reflex, i.e., the time to recovery of the prone position (five tests, 10 min apart). The water drop test scores increased during the recovery phase toward the control values in all age groups. Treatment and time had no significant effect on righting reflex scores. The initial volume in the syringe, the volume of added isoflurane-saturated gas, and the duration of exposure may be adjusted according to postnatal age and specific strains or species (e.g., rats). This method is well suited to behavioral or physiological phenotype studies in developing mice, in which noxious procedures must precede functional testing, making rapid recovery from anesthesia a key requirement.

Age Factors↗

PubMed2004

Genetics and early disturbances of breathing control.

Early disturbances in breathing control, including apneas of prematurity and apparently life-threatening events, account for some cases of sudden infant death syndrome and for a rare disorder called congenital central hypoventilation syndrome (CCHS). Data suggesting a genetic basis for CCHS have been obtained. Recently, we found heterozygous de novo mutations of the PHOX2B gene in 18 of 29 individuals with CCHS. Most mutations consisted of five to nine alanine expansions within a 20-residue polyalanine tract, probably resulting from nonhomologous recombination. Other mutations, generally inherited from one of the parents, in the coding regions of genes involved in the endothelin and RET signaling pathways and in the brain-derived-neurotrophic factor (BDNF) gene have been found in a few CCHS patients. Interestingly, all these genes are involved in the development of neural crest cells. Targeted disruption of these genes in mice has provided information on the pathophysiological mechanisms underlying CCHS. Despite the identification of these genes involved in breathing control, none of the genetically engineered mice developed to date replicate the full human CCHS respiratory phenotype. Recent insights into the genetic basis for CCHS may shed light on the genetics of other early disturbances in breathing control, such as apnea of prematurity and sudden infant death syndrome.

Animals↗

PubMed2003

Phox2b controls the development of peripheral chemoreceptors and afferent visceral pathways.

We report that the afferent relays of visceral (cardiovascular, digestive and respiratory) reflexes, differentiate under the control of the paired-like homeobox gene Phox2b: the neural crest-derived carotid body, a chemosensor organ, degenerates in homozygous mutants, as do the three epibranchial placode-derived visceral sensory ganglia (geniculate, petrosal and nodose), while their central target, the nucleus of the solitary tract, which integrates all visceral information, never forms. These data establish Phox2b as an unusual 'circuit-specific' transcription factor devoted to the formation of autonomic reflex pathways. We also show that Phox2b heterozygous mutants have an altered response to hypoxia and hypercapnia at birth and a decreased tyrosine hydroxylase expression in the petrosal chemosensory neurons, thus providing mechanistic insight into congenital central hypoventilation syndrome, which is associated with heterozygous mutations in PHOX2B.

Afferent Pathways↗

PubMed2003

Genes modulating chemical breathing control: lessons from mutant animals.

Genetic factors influence breathing control. Respiratory phenotypes of mutant mice may help to better understand these factors. Congenital central hypoventilation syndrome (CCHS) is a rare disorder defined as failure of chemical control of breathing causing central alveolar hypoventilation, especially during sleep. A genetic basis for CCHS is supported by several arguments, mainly the identification, in a few CCHS patients, of heterozygous mutations of genes contributing to neural crest cell development, namely, genes involved in the endothelin and c-ret pathways. Furthermore, plethysmography studies of the respiratory phenotypes of newborn heterozygous mutant mice have shown that genes in both pathways are involved in breathing control at birth. Nevertheless, no single gene mutation in newborn mice reproduces the human CCHS phenotype. Avenues for future research into the genetics of CCHS include (i) testing of mutant newborn mice for genes in other pathways and (ii) use of microarrays to identify gene clusters that should be associated with abnormal chemical breathing control.

Animals↗

PubMed2003

Neonatal exposure to 65% oxygen durably impairs lung architecture and breathing pattern in adult mice.

STUDY OBJECTIVE: To test the hypothesis that exposure to hyperoxia during the postnatal period of rapid alveolar multiplication by septation would cause permanent impairments, even with moderate levels of hyperoxia. DESIGN: We exposed mouse pups to 65% O(2) (hyperoxic mice) or normoxia (normoxic mice) during their first postnatal month, and we analyzed lung histology, pulmonary mechanics, blood gas, and breathing pattern during normoxia or in response to chemical stimuli in adulthood, when they reached 7 to 8 months of postnatal age. RESULTS: Hyperoxic mice had fewer and larger alveoli than normoxic mice (number of alveoli per unit surface area of parenchyma, 266 +/- 62/mm(2) vs 578 +/- 77/mm(2), p < 0.0001) [mean +/- SD], the cause being impaired alveolarization (radial alveolar count, 5.8 +/- 0.2 in hyperoxic mice vs 10.5 +/- 0.5 in normoxic mice, p < 0.0001). Respiratory system compliance was higher in hyperoxic mice (0.098 +/- 0.006 mL/cm H(2)O) than in normoxic mice (0.064 +/- 0.006 mL/cm H(2)O, p < 0.016). Baseline tidal volume (VT) and breath duration (TTOT]) measured noninvasively by whole-body plethysmography were larger in hyperoxic mice than in normoxic mice (VT, + 15%, p < 0.01; TTOT, + 12%, p < 0.01). Despite these impairments, blood gas, baseline minute ventilation E, and E responses to hypoxia and hypercapnia were normal in hyperoxic mice, compared with normoxic mice. CONCLUSION: Hyperoxic exposure during lung septation in mice may cause irreversible lung injury and breathing pattern abnormalities in adulthood at O(2) concentrations lower than previously thought. However, ventilatory function and body growth were preserved, and ventilatory function showed no major abnormalities, at least at rest, despite early oxygen-induced injuries.

Animals↗

PubMed2002

beta 2 nicotinic acetylcholine receptor subunit modulates protective responses to stress: A receptor basis for sleep-disordered breathing after nicotine exposure.

Nicotine exposure diminishes the protective breathing and arousal responses to stress (hypoxia). By exacerbating sleep-disordered breathing, this disturbance could underpin the well established association between smoking and the increased risk of sudden infant death syndrome. We show here that the protective responses to stress during sleep are partially regulated by particular nicotinic acetylcholine receptors (nAChRs). We compared responses of sleeping wild-type and mutant mice lacking the beta2 subunit of the nAChR to episodic hypoxia. Arousal from sleep was diminished, and breathing drives accentuated in mutant mice indicating that these protective responses are partially regulated by beta2-containing nAChRs. Brief exposure to nicotine significantly reduced breathing drives in sleeping wild-type mice, but had no effect in mutants. We propose that nicotine impairs breathing (and possibly arousal) responses to stress by disrupting functions normally regulated by beta2-containing, high-affinity nAChRs.

Animals↗

PubMed2002

Ventilatory responses to hypercapnia and hypoxia in heterozygous c-ret newborn mice.

The c-ret proto-oncogene encodes a tyrosine-kinase receptor involved in survival and differentiation of neural crest cell lineages. Previous studies have shown that homozygous c-ret-/- mice die soon after birth and have impaired ventilatory responses to hypercapnia. Heterozygous c-ret +/- mice develop normally, but their respiratory phenotype has not been described in detail. We used whole-body flow plethysmography to compare baseline breathing and ventilatory and arousal responses to chemical stimuli in unrestrained heterozygous c-ret +/- newborn mice and their wild-type c-ret +/+ littermates at 10-12 h of postnatal age. The hyperpnoeic and arousal responses to hypoxia and hypercapnia were not significantly different in these two groups. However, the number and total duration of apnoeas and periodic breathing episodes were significantly higher in c-ret +/- than in c-ret +/+ pups during hypoxia and post-hypoxic normoxia. These results are further evidence that respiratory control at birth is heavily dependent on genes involved in the neural determination of neural crest cells.

Animals↗

PubMed2002

Depression of hypoxic arousal response in adolescent mice following antenatal vasoactive intestinal polypeptide blockade.

Late-gestation blockade of vasoactive intestinal polypeptide (VIP) activity in pregnant mice produces discrete morphological abnormalities in the somatosensory cortex of offspring. We investigated the functional implications of this lesion on the behavioural arousal response to moderate hypoxia. Pregnant mice received twice-daily injections of 200 microl saline (control), or saline + 50 microg VIP antagonist (anti-VIP) on embryonic days 17 and 18. Offspring were studied unrestrained at 6-7 weeks after birth, in a bias-flow whole-body plethysmograph during behavioural quiet sleep. Arousal was defined by movement (MVT) lasting > or =1 s. Hypoxic ventilatory (HVR) and arousal responses were measured during a 5 min exposure to 10 % O(2)-3 % CO(2) (hypoxia); peripheral chemoreflex drive was estimated by transient hyperoxia administered at rest and end-hypoxia (Dejours-type test). MVTs increased in all mice during hypoxia, but in anti-VIP mice: (a) MVT onset was delayed (174 +/- 90 vs. 108 +/- 59 s from the start of hypoxia, anti-VIP vs. control; P = 0.008); and (b) MVTs were less frequent, and total MVT time in hypoxia was less (8 +/- 7 vs. 15 +/- 9 %; P = 0.03). The HVR, and peripheral drive at rest and end-hypoxia were comparable in control and anti-VIP mice. In conclusion, a significant arousal deficit was evident in anti-VIP mice. This was not associated with obviously deranged peripheral or brainstem-mediated responses to hypoxia during sleep. This may signal a general deficit in the way hypoxic distress is monitored and processed, and arousal initiated and sustained in these mice.

Animals↗

PubMed2002

Comparison of the hyperoxic test and the alternate breath test in infants.

Peripheral chemoreceptor function has been tested using either the hyperoxic test (HT), which decreases minute ventilation (V E) by causing physiologic chemodenervation, or the alternate breath test (ABT), which induces V E alternations by delivering rapid hypoxic stimuli through breath-by-breath alternations in fractional inspired O(2) between normoxia (0.21) and hypoxia (0.15). No previous studies have compared ventilatory responses to both tests in the same infants. We hypothesized that the V E decrease during HT would be significantly related to V E alternations during ABT. Eighteen infants (postnatal age 21 +/- 14 d) underwent two 30-s HTs and two ABTs (quiet sleep, face mask, and pneumotachograph; mass spectrometry measurement of inspired and expired O(2) and CO(2) fractions; and breath-by-breath analysis). The tests were done in random order. Decreases in V E and mean inspiratory flow (tidal volume over inspiratory time, VT/TI) during HTs were significantly correlated to their respective percentage coefficients of alternation during ABTs (r = 0.69 and 0.70, respectively, p < 0.01). Principal components analysis showed that the V E and VT/TI decreases during HTs were due chiefly to a fall in VT, whereas V E and VT/TI alternations were ascribable to alternations in both VT and TI. Intraindividual coefficients of variation of V E changes were significantly lower during HTs than during ABTs. We conclude that (1) ventilatory responses to HT and ABT are significantly correlated despite differences in the mechanisms of the V E changes; (2) the better reproducibility of the V E response to HT as compared with ABT may be an advantage in clinical practice.

Breath Tests↗

PubMed2002

Ventilatory control in newborn mice prenatally exposed to cocaine.

Infants born to mothers who used cocaine during pregnancy are at increased risk for neonatal death and respiratory impairments. Confounding factors such as multiple substance abuse make it difficult to isolate the effects of cocaine. We used a murine model to test the hypothesis that prenatal cocaine exposure may impair ventilatory responses to chemical stimuli in newborns. Seventy-two pregnant mice were randomly assigned to three groups: cocaine (COC), saline (SAL), and untreated (UNT). COC and SAL mice received subcutaneous injections of either 20 mg/kg of cocaine or a saline solution twice a day from gestational days 8-17. Ventilation (V'(E)) and tidal volume (V(T)), both divided by body weight, and breath duration (T(TOT)) were measured using whole-body plethysmography in freely moving COC (n = 47), SAL (n = 123), and UNT (n = 93) pups on postnatal day 2.The comparison between SAL and UNT pups showed significant differences in baseline breathing and in V'(E) responses to hypoxia, suggesting that maternal stress caused by injections affected the development of ventilatory control in pups. Baseline T(TOT) was significantly longer in COC than in SAL pups. V'(E) responses to hypoxia were significantly smaller in COC than in SAL pups (+27 +/- 35% vs. +38 +/- 25%), but V'(E) responses to hypercapnia were similar (29 +/- 15% vs. 25 +/- 23%).Thus, breathing control was impaired by prenatal cocaine exposure, possibly because of abnormal development of neurotransmitter systems, such as the dopamine and serotonin systems.

Animals↗

PubMed2002

The formation of structurally relevant units in artificial grammar learning.

A total of 78 adult participants were asked to read a sample of strings generated by a finite state grammar and, immediately after reading each string, to mark the natural segmentation positions with a slash bar. They repeated the same task after a phase of familiarization with the material, which consisted, depending on the group involved, of learning items by rote, performing a short-term matching task, or searching for the rules of the grammar. Participants formed the same number of cognitive units before and after the training phase, thus indicating that they did not tend to form increasingly large units. However, the number of different units reliably decreased, whatever the task that participants had performed during familiarization. This result indicates that segmentation was increasingly consistent with the structure of the grammar. A theoretical account of this phenomenon, based on ubiquitous principles of associative memory and learning, is proposed. This account is supported by the ability of a computer model implementing those principles, PARSER, to reproduce the observed pattern of results. The implications of this study for developmental theories aimed at accounting for how children become able to parse sensory input into physically and linguistically relevant units are discussed.

Adult↗