Respiratory dysfunction progresses with age in Kcna1-null mice, a model of sudden unexpected death in epilepsy.

OBJECTIVE: Increased breathing rate, apnea, and respiratory failure are associated with sudden unexpected death in epilepsy (SUDEP). We recently demonstrated the progressive nature of epilepsy and mortality in Kcna1-/- mice, a model of temporal lobe epilepsy and SUDEP. Here we tested the hypothesis that respiratory dysfunction progresses with age in Kcna1-/- mice, thereby increasing risk of respiratory failure and sudden death (SD). METHODS: Respiratory parameters were determined in conscious mice at baseline and following increasing doses of methacholine (MCh) using noninvasive airway mechanics (NAM) systems. Kcna1+/+ , Kcna1+/- , and Kcna1-/- littermates were assessed during 3 age ranges when up to ~30%, ~55%, and ~90% of Kcna1-/- mice have succumbed to SUDEP: postnatal day (P) 32-36, P40-46, and P48-56, respectively. Saturated arterial O2 (SaO2 ) was determined with pulse oximetry. Lung and brain tissues were isolated and Kcna1 gene and protein expression were evaluated by reverse transcriptase quantitative polymerase chain reaction (RT-qPCR) and Western blot techniques. Airway smooth muscle responsiveness was assessed in isolated trachea exposed to MCh. RESULTS: Kcna1-/- mice experienced an increase in basal respiratory drive, chronic oxygen desaturation, frequent apnea-hypopnea (A-H), an atypical breathing sequence of A-H-tachypnea-A-H, increased tidal volume, and hyperventilation induced by MCh. The MCh-provoked hyperventilation was dramatically attenuated with age. Of interest, only Kcna1-/- mice developed seizures following exposure to MCh. Seizures were provoked by lower concentrations of MCh as Kcna1-/- mice approached SD. MCh-induced seizures experienced by a subset of younger Kcna1-/- mice triggered death. Respiratory parameters of these younger Kcna1-/- mice resembled older near-SD Kcna1-/- mice. Kcna1 gene and protein were not expressed in Kcna1+/+ and Kcna1+/- lungs, and MCh-mediated airway smooth muscle contractions exhibited similar half-maximal effective concentration( EC50 ) in isolated Kcna1+/+ and Kcna1-/- trachea. SIGNIFICANCE: The Kcna1-/- model of SUDEP exhibits progressive respiratory dysfunction, which suggests a potential increased susceptibility for respiratory failure during severe seizures that may result in sudden death.

Predicting neonatal respiratory morbidity by lamellar body count and gestational age.

AIMS: To develop a predictive model for assessing the risk of developing neonatal respiratory morbidity using lamellar body counts (LBCs) and gestational age (GA) to provide a more patient-specific assessment. METHODS: Retrospective cohort study of patients' ≥32 weeks' gestation who received amniocentesis with LBC analysis over a 9-year period. Respiratory morbidity was defined as respiratory distress syndrome, transient tachypnea of the newborn or oxygen requirement for >24 h. Logistic regression analyses were used to predict the absolute risk and odds of respiratory morbidity as a function of GA and lamellar body count. RESULTS: Two hundred and sixty-seven mother-infant pairs included in the analysis with 32 cases (12.0%) of respiratory morbidity. When compared to those without respiratory morbidity, neonates with respiratory morbidity had amniocentesis performed at an earlier median GA, had lower mean birthweight and had lower median LBC (P<0.01). The GA specific absolute risks and odds ratios for the presence of respiratory morbidity were calculated. The predicted absolute risks of neonatal respiratory morbidity ranged from 38% at 32 weeks to 6% at 40 weeks when LBC were 35,000/µL. CONCLUSION: GA specific predicted risk of neonatal respiratory morbidity using LBC provides a statistical model, which can aid clinicians in individually counseling patients regarding the absolute risk of their neonate developing respiratory morbidity.

The cessation of breathing in the chicken embryo during cold-hypometabolism.

The avian embryo toward end-incubation combines gas exchange through the chorioallantoic membrane (CAM) and pulmonary ventilation (V˙E). The main experiments examined breathing activity during cold-hypometabolism. Chicken embryos close to hatching were prepared for simultaneous measurements of oxygen consumption ( [Formula: see text] ) and carbon dioxide production ( [Formula: see text] ; open-flow methodology) and breathing frequency (f; barometric technique). As ambient (Ta) and egg temperature (Tegg) dropped, breathing eventually ceased at ∼18°C, when [Formula: see text] and [Formula: see text] were 22-28% of the normothermic values. With the eggshell experimentally covered to reduce CAM gas exchange breathing ceased at slightly lower [Formula: see text] and [Formula: see text] (17-18% of normothermia). Once breathing had stopped, egg exposure to hypoxia (10% or 5% O2) or hypercapnia (3% or 8% CO2) did not resume breathing, which recovered with re-warming. In normothermia, 10% O2 caused hypometabolism and tachypnea; differently, in 5% O2 [Formula: see text] dropped as much as with hypothermia and breathing stopped, to recover upon return in air. Correlation analysis among Ta, Tegg, [Formula: see text] , [Formula: see text] and f during cooling and re-warming indicated that f followed more closely the changes in [Formula: see text] and, especially, in [Formula: see text] than the changes in Ta or Tegg. Some considerations suggest that in this experimental model the cessation of breathing in hypothermia or severe hypoxia may be due to hypometabolism, while the lack of chemo-responses may have a different mechanistic basis.

Excitatory amino acid receptors in the dorsomedial hypothalamic area contribute to the chemoreflex tachypneic response.

This study evaluated the effect of blockade of the excitatory amino acid (EAA) receptors in the dorsomedial hypothalamic (DMH) area on the ventilatory and cardiovascular responses of the chemoreflex activation in conscious rats. Bilateral microinjection of kynurenic acid (2.7 nmol, n = 6) into the DMH area reduced the tachypneic (+ 264 ± 13 versus + 204 ± 14 cpm, P < 0.05) and pressor (+ 52 ± 5 versus + 31 ± 6 mmHg, P < 0.05) components of chemoreflex but had no effect on the bradycardic component (-214 ± 7 versus -244 ± 17 bpm) of the chemoreflex. The magnitudes of the reduction in pressor and tachypneic chemoreflex responses were not significantly correlated (r = 0.308, P = 0.330). These data indicate that neurons located in the DMH area are activated by chemoreflex; that this activation is mediated via EAA receptors; and that it is essential for the full expression of the respiratory component of the chemoreflex.