Periodic breathing in patients with NALCN mutations.

Biallelic mutations in NALCN are responsible for infantile hypotonia with psychomotor retardation and characteristic facies 1 (IHPRF1). Common features of this condition include severe neonatal-onset hypotonia and profound global developmental delay. Given the rarity of this condition, long-term natural history studies are limited. Here, we present a 9-year-old male with a homozygous nonsense mutation in NALCN (c.3910C>T, p.Arg1304X) leading to profound intellectual disability, seizures, feeding difficulties, and significant periodic breathing. Breathing irregularity was also reported in three previous patients; similar to our patient, those children demonstrated periodic breathing that was characterized by alternating apneic periods with deep, rapid breathing. As the phenotype associated with NALCN mutations continues to be delineated, attention should be given to abnormal respiratory patterns, which may be an important distinguishing feature of this condition.

Arginase 1 deletion in myeloid cells affects the inflammatory response in allergic asthma, but not lung mechanics, in female mice.

BACKGROUND: (Over-)expression of arginase may limit local availability of arginine for nitric oxide synthesis. We investigated the significance of arginase1 (ARG1) for the development of airway hyperresponsiveness (AHR) and lung inflammation in female mice with ovalbumin (OVA)-induced allergic asthma. METHODS: Arg1 was ablated in the lung by crossing Arg1 fl/fl and Tie2Cre tg/- mice. OVA sensitization and challenge were conducted, and AHR to methacholine was determined using the Flexivent system. Changes in gene expression, chemokine and cytokine secretion, plasma IgE, and lung histology were quantified using RT-qPCR, ELISA, and immunohistochemistry, respectively. RESULTS: Arg1 ablation had no influence on the development of OVA-induced AHR, but attenuated OVA-induced increases in expression of Arg2 and Nos2, Slc7a1, Slc7a2, and Slc7a7 (arginine transporters), Il4, Il5 and Il13 (TH2-type cytokines), Ccl2 and Ccl11 (chemokines), Ifng (TH1-type cytokine), Clca3 and Muc5ac (goblet cell markers), and OVA-specific IgE. Pulmonary IL-10 protein content increased, but IL-4, IL-5, IL-13, TNFα and IFNγ content, and lung histopathology, were not affected. Arg1 elimination also decreased number and tightness of correlations between adaptive changes in lung function and inflammatory parameters in OVA/OVA-treated female mice. OVA/OVA-treated female mice mounted a higher OVA-IgE response than males, but the correlation between lung function and inflammation was lower. Arg1-deficient OVA/OVA-treated females differed from males in a more pronounced decline of arginine-metabolizing and -transporting genes, higher plasma arginine levels, a smaller OVA-specific IgE response, and no improvement of peripheral lung function. CONCLUSION: Complete ablation of Arg1 in the lung affects mRNA abundance of arginine-transporting and -metabolizing genes, and pro-inflammatory genes, but not methacholine responsiveness or accumulation of inflammatory cells.

Genome-wide association study of short-acting ß2-agonists. A novel genome-wide significant locus on chromosome 2 near ASB3.

RATIONALE: ß2-Agonists are the most common form of treatment of asthma, but there is significant variability in response to these medications. A significant proportion of this responsiveness may be heritable. OBJECTIVES: To investigate whether a genome-wide association study (GWAS) could identify novel pharmacogenetic loci in asthma. METHODS: We performed a GWAS of acute bronchodilator response (BDR) to inhaled ß2-agonists. A total of 444,088 single-nucleotide polymorphisms (SNPs) were examined in 724 individuals from the SNP Health Association Resource (SHARe) Asthma Resource Project (SHARP). The top 50 SNPs were carried forward to replication in a population of 444 individuals. MEASUREMENTS AND MAIN RESULTS: The combined P value for four SNPs reached statistical genome-wide significance aftercorrecting for multiple comparisons. Combined P values for rs350729, rs1840321, rs1384918, and rs1319797 were 2.21 × 10(-10), 5.75 × 10(-8), 9.3 × 10(-8), and 3.95 × 10(-8), respectively. The significant variants all map to a novel genetic region on chromosome 2 near the ASB3 gene, a region associated with smooth muscle proliferation. As compared with the wild type, the presence of the minor alleles reduced the degree of BDR by 20% in the original population and by a similar percentage in the confirmatory population. CONCLUSIONS: These GWAS findings for BDR in subjects with asthma suggest that a gene associated with smooth muscle proliferation may influence a proportion of the smooth muscle relaxation that occurs in asthma.

Plp1 gene duplication inhibits airway responsiveness and induces lung inflammation.

Mice with Plp1 gene duplication model the most common form of Pelizaeus-Merzbacher disease (PMD), a CNS disease in which patients may suffer respiratory complications. We hypothesized that affected mice would lack airway responsiveness compared to wild-type and carrier mice during methacholine challenge. Wild-type (n = 10), carrier female (n = 6) and affected male (n = 8) mice were anesthetized-paralyzed, tracheostomized and ventilated. Respiratory mechanics were recorded at baseline and during escalating doses of nebulized methacholine followed by albuterol. Lung resistance (RL) was the primary endpoint. Lung tissues were assayed for inflammatory and histological differences. At baseline, phase angles were higher in carrier and affected mice than wild-type. Dose-response RL curves in affected and carrier mice indicated a lack of methacholine response. Albuterol reduced RL in wild-type and carrier, but not affected mice. Affected mice exhibited lower interleukin (IL)-6 tissue levels and alveolar inflammatory infiltrates. Affected and carrier mice, compared to wild-type, lacked airway reactivity during methacholine challenge, but only affected mice exhibited decreased lung tissue levels of IL-6 and inflammation.

Role of rostral medulla in serotonin-induced changes of respiratory rhythm in newborn rat brainstem-spinal cord preparations.

Abnormalities of the serotonin (5-hydroxytryptamine, 5-HT) system may induce respiratory disorders. We examined which regions in the rostral medulla are important for the effect of 5-HT on the frequency of respiratory-like nerve (fR-like) activity by transecting the preparations at different levels near the facial nucleus (nVII) in newborn rat brainstem-spinal cord preparations. The fR-like activity at the fourth cervical ventral root (C4) of the Pons-medulla-spinal cord preparations in 2-3-day-old rats (n=25) was monitored at 26°C, and the change in fR-like activity in response to application of 10µM 5-HT before and after transection was compared among three groups, in which nVII was retained (group A, n=10), partially retained (group B, n=7), or eliminated (group C, n=8) by the transection. Before transection, the resting fR-like activity (set to 100%) and stimulant effect of 5-HT (+101-143%) were similar among the groups. After transection, resting fR-like activity increased in all groups, but the facilitatory effects of 5-HT on the fR-like activity were abolished in groups A and C (fR-like activity of -4% and +7%, respectively). In group B, 5-HT became inhibitory (fR-like activity of -28%). In conclusion, a distinct part of the rostral medulla in the absence of pontine influences may mediate the inhibitory effects of 5-HT on the respiratory rhythm.

Age-related increases in ozone-induced injury and altered pulmonary mechanics in mice with progressive lung inflammation.

In these studies we determined whether progressive pulmonary inflammation associated with aging in surfactant protein D (Sftpd)-/- mice leads to an exacerbated response to ozone. In Sftpd-/- mice, but not wild-type (WT) mice, age-related increases in numbers of enlarged vacuolated macrophages were observed in the lung, along with alveolar wall rupture, type 2 cell hyperplasia, and increased bronchoalveolar lavage protein and cell content. Numbers of heme oxygenase+ macrophages also increased with age in Sftpd-/- mice, together with classically (iNOS+) and alternatively (mannose receptor+, YM-1+, or galectin-3+) activated macrophages. In both WT and Sftpd-/- mice, increasing age from 8 to 27 wk was associated with reduced lung stiffness, as reflected by decreases in resistance and elastance spectra; however, this response was reversed in 80-wk-old Sftpd-/- mice. Ozone exposure (0.8 ppm, 3 h) caused increases in lung pathology, alveolar epithelial barrier dysfunction, and numbers of iNOS+ macrophages in 8- and 27-wk-old Sftpd-/-, but not WT mice at 72 h postexposure. Conversely, increases in alternatively activated macrophages were observed in 8-wk-old WT mice following ozone exposure, but not in Sftpd-/- mice. Ozone also caused alterations in both airway and tissue mechanics in Sftpd-/- mice at 8 and 27 wk, but not at 80 wk. These data demonstrate that mild to moderate pulmonary inflammation results in increased sensitivity to ozone; however, in senescent mice, these responses are overwhelmed by the larger effects of age-related increases in baseline inflammation and lung injury.

Decreased Hering-Breuer input-output entrainment in a mouse model of Rett syndrome.

Rett syndrome, a severe X-linked neurodevelopmental disorder caused by mutations in the gene encoding methyl-CpG-binding protein 2 (Mecp2), is associated with a highly irregular respiratory pattern including severe upper-airway dysfunction. Recent work suggests that hyperexcitability of the Hering-Breuer reflex (HBR) pathway contributes to respiratory dysrhythmia in Mecp2 mutant mice. To assess how enhanced HBR input impacts respiratory entrainment by sensory afferents in closed-loop in vivo-like conditions, we investigated the input (vagal stimulus trains) - output (phrenic bursting) entrainment via the HBR in wild-type and MeCP2-deficient mice. Using the in situ perfused brainstem preparation, which maintains an intact pontomedullary axis capable of generating an in vivo-like respiratory rhythm in the absence of the HBR, we mimicked the HBR feedback input by stimulating the vagus nerve (at threshold current, 0.5 ms pulse duration, 75 Hz pulse frequency, 100 ms train duration) at an inter-burst frequency matching that of the intrinsic oscillation of the inspiratory motor output of each preparation. Using this approach, we observed significant input-output entrainment in wild-type mice as measured by the maximum of the cross-correlation function, the peak of the instantaneous relative phase distribution, and the mutual information of the instantaneous phases. This entrainment was associated with a reduction in inspiratory duration during feedback stimulation. In contrast, the strength of input-output entrainment was significantly weaker in Mecp2 (-/+) mice. However, Mecp2 (-/+) mice also had a reduced inspiratory duration during stimulation, indicating that reflex behavior in the HBR pathway was intact. Together, these observations suggest that the respiratory network compensates for enhanced sensitivity of HBR inputs by reducing HBR input-output entrainment.

Endogenous distal airway progenitor cells, lung mechanics, and disproportionate lobar growth following long-term postpneumonectomy in mice.

Using a model of postpneumonectomy (PNY) compensatory lung growth in mice, we previously observed an increase in numbers of a putative endogenous distal airway progenitor cell population (CCSP(pos) /pro-SPC(pos) cells located at bronchoalveolar duct junctions [BADJs]), at 3, 7, and 14 days after pneumonectomy, returning to baseline at 28 days post-PNY. As the origin of these cells is poorly understood, we evaluated whether bone marrow cells contributed to the pool of these or other cells during prolonged post-PNY lung regrowth. Naïve and sex-mismatched chimeric mice underwent left PNY and were evaluated at 1, 2, and 3 months for numbers of BADJ CCSP(pos) /pro-SPC(pos) cells and presence of donor-derived marrow cells engrafted as airway or alveolar epithelium. Nonchimeric mice were also examined at 12 months after PNY for numbers of BADJ CCSP(pos) /pro-SPC(pos) cells. Notably, the right accessory lobe (RAL) continued to grow disproportionately over 12 months, a novel finding not previously described. Assessment of lung mechanics demonstrated an increase in lung stiffness following PNY, which significantly diminished over 1 year, but remained elevated relative to 1-year-old naïve controls. However, the number of CCSP(pos) /pro-SPC(pos) BADJ cells ≥1-month following PNY was equivalent to that found in naïve controls even after 12 months of continued RAL growth. Notably, no donor bone marrow-derived cells engrafted as airway or alveolar epithelial cells, including those at the BADJ, up to 3 months after PNY. These studies suggest that lung epithelial cells, including CCSP(pos) /pro-SPC(pos) cells, are not replenished from marrow-derived cells during post-PNY lung growth in mice.

Stable respiratory activity requires both P/Q-type and N-type voltage-gated calcium channels.

P/Q-type voltage-gated calcium channels (Ca(v)2.1) play critical presynaptic and postsynaptic roles throughout the nervous system and have been implicated in a variety of neurological disorders. Here we report that mice with a genetic ablation of the Ca(v)2.1 pore-forming α(1A) subunit (α(1A)⁻/⁻) encoded by CACNA1a (Jun et al., 1999) suffer during postnatal development from increasing breathing disturbances that lead ultimately to death. Breathing abnormalities include decreased minute ventilation and a specific loss of sighs, which was associated with lung atelectasis. Similar respiratory alterations were preserved in the isolated in vitro brainstem slice preparation containing the pre-Bötzinger complex. The loss of Ca(v)2.1 was associated with an alteration in the functional dependency on N-type calcium channels (Ca(v)2.2). Blocking N-type calcium channels with conotoxin GVIA had only minor effects on respiratory activity in slices from control (CT) littermates, but abolished respiratory activity in all slices from α(1A)⁻/⁻ mice. The amplitude of evoked EPSPs was smaller in inspiratory neurons from α(1A)⁻/⁻ mice compared with CTs. Conotoxin GVIA abolished all EPSPs in inspiratory neurons from α(1A)⁻/⁻ mice, while the EPSP amplitude was reduced by only 30% in CT mice. Moreover, neuromodulation was significantly altered as muscarine abolished respiratory network activity in α(1A)⁻/⁻ mice but not in CT mice. We conclude that excitatory synaptic transmission dependent on N-type and P/Q-type calcium channels is required for stable breathing and sighing. In the absence of P/Q-type calcium channels, breathing, sighing, and neuromodulation are severely compromised, leading to early mortality.

High frequency mechanical ventilation affects respiratory system mechanics differently in C57BL/6J and BALB/c adult mice.

We tested the hypothesis that high frequency ventilation affects respiratory system mechanical functions in C57BL/6J and BALB/c mice. We measured respiratory mechanics by the forced oscillation technique over 1h in anesthetized, intubated, ventilated BALB/c and C57BL/6J male mice. We did not detect any change in airway resistance, Rn, tissue damping, G, tissue elastance, H and hysteresivity, eta in BALB/c mice during 1h of ventilation at 150 or at 450 breaths/min; nor did we find a difference between BALB/c mice ventilated at 150 breaths/min compared with 450 breaths/min. Among C57BL/6J mice, except for H, all parameters remained unchanged over 1h of ventilation in mice ventilated at 150 breaths/min. However, after 10 and 30 min of ventilation at 450 breaths/min, Rn, and respiratory system compliance were lower, and eta was higher, than their starting value. We conclude that high frequency mechanical ventilation affects respiratory system mechanics differently in C57BL/6J and BALB/c adult mice.

A TrkB small molecule partial agonist rescues TrkB phosphorylation deficits and improves respiratory function in a mouse model of Rett syndrome.

Rett syndrome (RTT) results from loss-of-function mutations in the gene encoding the methyl-CpG-binding protein 2 (MeCP2) and is characterized by abnormal motor, respiratory and autonomic control, cognitive impairment, autistic-like behaviors and increased risk of seizures. RTT patients and Mecp2-null mice exhibit reduced expression of brain-derived neurotrophic factor (BDNF), which has been linked in mice to increased respiratory frequency, a hallmark of RTT. The present study was undertaken to test the hypotheses that BDNF deficits in Mecp2 mutants are associated with reduced activation of the BDNF receptor, TrkB, and that pharmacologic activation of TrkB would improve respiratory function. We characterized BDNF protein expression, TrkB activation and respiration in heterozygous female Mecp2 mutant mice (Het), a model that recapitulates the somatic mosaicism for mutant MECP2 found in typical RTT patients, and evaluated the ability of a small molecule TrkB agonist, LM22A-4, to ameliorate biochemical and functional abnormalities in these animals. We found that Het mice exhibit (1) reduced BDNF expression and TrkB activation in the medulla and pons and (2) breathing dysfunction, characterized by increased frequency due to periods of tachypnea, and increased apneas, as in RTT patients. Treatment of Het mice with LM22A-4 for 4 weeks rescued wild-type levels of TrkB phosphorylation in the medulla and pons and restored wild-type breathing frequency. These data provide new insight into the role of BDNF signaling deficits in the pathophysiology of RTT and highlight TrkB as a possible therapeutic target in this disease.

Raphé tauopathy alters serotonin metabolism and breathing activity in terminal Tau.P301L mice: possible implications for tauopathies and Alzheimer's disease.

Tauopathies, including Alzheimer's disease are the most frequent neurodegenerative disorders in elderly people. Patients develop cognitive and behaviour defects induced by the tauopathy in the forebrain, but most also display early brainstem tauopathy, with oro-pharyngeal and serotoninergic (5-HT) defects. We studied these aspects in Tau.P301L mice, that express human mutant tau protein and develop tauopathy first in hindbrain, with cognitive, motor and upper airway defects from 7 to 8 months onwards, until premature death before age 12 months. Using plethysmography, immunohistochemistry and biochemistry, we examined the respiratory and 5-HT systems of aging Tau.P301L and control mice. At 8 months, Tau.P301L mice developed upper airway dysfunction but retained normal respiratory rhythm and normal respiratory regulations. In the following weeks, Tau.P301L mice entered terminal stages with reduced body weight, progressive limb clasping and lethargy. Compared to age 8 months, terminal Tau.P301L mice showed aggravated upper airway dysfunction, abnormal respiratory rhythm and abnormal respiratory regulations. In addition, they showed severe tauopathy in Kolliker-Fuse, raphé obscurus and raphé magnus nuclei but not in medullary respiratory-related areas. Although the raphé tauopathy concerned mainly non-5-HT neurons, the 5-HT metabolism of terminal Tau.P301L mice was altered. We propose that the progressive raphé tauopathy affects the 5-HT metabolism, which affects the 5-HT modulation of the respiratory network and therefore the breathing pattern. Then, 5-HT deficits contribute to the moribund phenotype of Tau.P301L mice, and possibly in patients suffering from tauopathies, including Alzheimer's disease.

Morphological analysis of the trachea and pattern of breathing in ßENaC-Tg mice.

Cystic fibrosis (CF) is caused by mutations in the CFTR (cystic fibrosis transmembrane conductance regulator) gene which is a Cl- channel and a regulator of the epithelial Na+ channel (ENaC). We have recently shown that newborn CFTR-deficient mice exhibit abnormalities of the tracheal cartilage leading to altered ventilation (Bonvin et al., 2008). However, the mechanism by which a lack of CFTR causes tracheal cartilage defects remains unknown. The main goal of the present study was to determine whether the development of airway cartilage defects is related to ENac channel dysfunction. We thus performed macroscopic analysis of the trachea and explored ventilatory function in adult ßENaC-overexpressing (ßENaC-Tg) mice with airway Na+ hyperabsorption and "CF-lung" lung disease, at 2 and 5 month of age. Only minor cartilaginous abnormalities were observed in 8 out of 16 ßENaC-Tg mice and in 2 out of 20 littermate controls. Breathing pattern was progressively altered in ßENaC-Tg mice as evidenced by a significant decrease in respiratory frequency. Our results suggest that Na+ hyperabsorption alone is not a major contributor to the development of tracheal malformation observed in CF mice and that breathing pattern changes in ßENaC-Tg mice likely reflect airflow limitation due to airway mucus obstruction.

Physiological definition of upper airway obstructions in mouse model for Rett syndrome.

Rett syndrome is a neuro-developmental disease accompanied by breathing symptoms including breath-hold events, and is caused by mutation of the transcriptional repressor methyl-CpG-binding protein 2 (MeCP2). Males of Mecp2-deficient mice (Mecp2(-/y)) also develop breathing symptoms, with erratic rhythm and life-threatening apnoeas from postnatal day 30 (P30), leading to respiratory distress and premature death at around P60. We investigated the respiratory function of conscious Mecp2(-/y) mice at P40-P60 using conventional whole-body plethysmography, double-chamber plethysmography and chest EMG recordings. Double-chamber plethysmography revealed a persistent increase in respiratory work-load with enlarged chest movements, but no subsequent increase of tidal volume thus revealing a mismatch between airflow and muscle work-load. Apnoeas occurred with cessation of both chest movements and ventilation, but some (40%) developed with persisting rhythmic chest EMG discharges or chest movements without respiratory airflow, suggesting respiratory efforts against obstructed airways. Airway obstruction was maintained even when the respiratory drive increased significantly, triggering large chest EMG discharges and movements. Whole-body plethysmography of Mecp2(-/y) mice revealed significant increases of spirograms, reflecting forced chest movements against partially obstructed airways. The persisting chest EMG discharges and rhythmic chest movements without respiratory airflow suggest that Mecp2 inactivation alters neural circuits controlling the upper airway dilator muscles. The observed breath-hold events in Mecp2(-/y) mice might imply disturbance of neural circuits attached to voluntary control of breathing.

Early abnormalities of post-sigh breathing in a mouse model of Rett syndrome.

Rett syndrome is a neurodevelopmental disease accompanied by complex, disabling symptoms, including breathing symptoms. Because Rett syndrome is caused by mutations in the transcriptional repressor methyl-CpG-binding protein 2 (MeCP2), Mecp2-deficient mice have been generated as experimental model. Males of Mecp2-deficient mice (Mecp2(-/y)) breathe normally at birth but show abnormal respiratory responses to hypoxia and hypercapnia from postnatal day 25 (P25). After P30, Mecp2(-/y) mice develop breathing symptoms reminiscent of Rett syndrome, aggravating until premature death at around P60. Using plethysmography, we analyzed the sighs and the post-sigh breathing pattern of unrestrained wild type male mice (WT) and Mecp2(-/y) mice from P15 to P60. Sighs are spontaneous large inspirations known to prevent lung atelectasis and to improve alveolar oxygenation. However, Mecp2(-/y) mice show early abnormalities of post-sigh breathing, with long-lasting post-sigh apnoeas, reduced tidal volume when eupnoea resumes and lack of post-sigh bradypnoea which develop from P15, aggravate with age and possibly contribute to breathing symptoms to come.

Transgenic mice lacking serotonin neurons have severe apnea and high mortality during development.

Central serotonin (5-HT) neurons modulate many vital brain functions, including respiratory control. Whether breathing depends critically on 5-HT neurons, or whether their influence is excitatory or inhibitory, remains controversial. Here we show that neonatal Lmx1b(flox/flox;ePet-Cre/+) mice (also called Lmx1b(f/f/p) mice), which selectively lack serotonin neurons, display frequent and severe apnea lasting as long as 55 s. This was associated with a marked decrease in ventilation to less than one-half of normal. These respiratory abnormalities were most severe during the postnatal period, markedly improving by the time the pups were 2-4 weeks old. Despite the severe breathing dysfunction, many of these mice survived, but there was a high perinatal mortality, and those that survived had a decrease in growth rate until the age at which the respiratory defects resolved. Consistent with these in vivo observations, respiratory output was markedly reduced in isolated brainstem-spinal cord preparations from neonatal Lmx1b(f/f/p) mice and completely blocked in perfused brain preparations from neonatal rats treated with selective antagonists of 5-HT(2A) and neurokinin 1 (NK-1) receptors. The ventilatory deficits in neonatal Lmx1b(f/f/p) mice were reversed in vitro and in vivo with agonists of 5-HT(2A) and/or NK-1 receptors. These results demonstrate that ventilatory output in the neonatal period is critically dependent on serotonin neurons, which provide excitatory drive to the respiratory network via 5-HT(2A) and NK-1 receptor activation. These findings provide insight into the mechanisms of sudden infant death syndrome, which has been associated with abnormalities of 5-HT neurons and of cardiorespiratory control.

Breathing and sleep: measurement methods, genetic influences, and developmental impacts.

Sleep-disordered breathing comprises alterations in respiratory rate, rhythm, and depth that present during sleep and may or may not be recognizable in breathing during wakefulness. Primary disorders include repetitive apneas, near apneas (hypopneas), or reductions in overall ventilation during sleep (hypoventilation), all of which lead to reductions in pulmonary gas exchange resulting in arousals, arrhythmia, hypercapnia, acidosis, and/or hypoxic stress responses such as pulmonary hypertension or polycythemia. Because the underlying mechanisms resulting in sleep-disordered breathing and its resulting comorbidities remain unclear, researchers use a variety of animal models to better understand the disorder. These models allow for conditioning paradigms, more detailed measurements of respiratory control, and the use of fewer preparations to provide a detailed picture of the individual components that contribute to breathing patterns. Both noninvasive and reduced methods are applicable with conditioned, inbred, and/or genetically manipulated animals to determine effect size and imply mechanisms. Research in animals has established preclinical models showing that intermediate traits of breathing pattern (e.g., responses to hypoxia, hypercapnia, and reoxygenation) vary according to genetic background and conditioning. Such findings permit new ideas about pathogenesis and prevention and form the rationale for observational and interventional studies in the human population. In this article we focus on methods of investigating respiratory control and applicable rodent models.

Interstrain variation in cardiac and respiratory adaptation to repeated ozone and particulate matter exposures.

Increased ambient particulate matter (PM) is associated with adverse cardiovascular and respiratory outcomes, as demonstrated by epidemiology studies. Several studies have investigated the role of copollutants, such as ozone (O(3)), in this association. It is accepted that physiological adaptation involving the respiratory system occurs with repeated exposures to O(3). We hypothesize that adaptation to PM and O(3) varies among different inbred mouse strains, and cardiopulmonary adaptation to O(3) is a synchronized response between the cardiac and respiratory systems. Heart rate (HR), HR variability (HRV), and the magnitude and pattern of breathing were simultaneously measured by implanted telemeters and by plethysmography in three inbred mouse strains: C57Bl/6J (B6), C3H/HeJ (HeJ), and C3H/HeOuJ (OuJ). Physiological responses were assessed during dual exposures to filtered air (FA), O(3) (576 +/- 32 parts/billion), and/or carbon black (CB; 556 +/- 34 mug/m(3)). Exposures were repeated for 3 consecutive days. While each strain showed significant reductions in HR during CB with O(3) preexposure (O(3)CB) on day 1, prominent HRV responses were observed in only HeJ and OuJ mice. Each strain also differed in their adaptation profile in response to repeated O(3)CB exposures. Whereas B6 mice showed rapid adaptation in HR after day 1, HeJ mice generally showed more moderate HR and HRV adaptation after day 2 of exposure. Unlike either B6 or HeJ strains, OuJ mice showed little evidence of HR or HRV adaptation to repeated O(3)CB exposure. Adaptation profiles between HR regulation and breathing characteristics were strongly correlated, but these associations also varied significantly among strains. These findings suggest that genetic factors determine the responsivity and adaptation of the cardiac and respiratory systems to repeated copollutant exposures. During O(3)CB exposure, adaptation of cardiac and respiratory systems is markedly synchronized, which may explain a potential mechanism for adverse effects of PM on heart function.