Sue Runciman

Postnatal development of the lung parenchyma in a marsupial: The Tammar wallaby

Marsupials are born at an early stage of development, and lung development from an air‐sac stage to maturity occurs in the air‐breathing environment, the pouch.

Role of sphingosine kinase 1 in allergen-induced pulmonary vascular remodeling and hyperresponsiveness

BACKGROUND Immunologic processes might contribute to the pathogenesis of pulmonary arterial hypertension (PAH), a fatal condition characterized by progressive pulmonary arterial remodeling, increased pulmonary vascular resistance, and right ventricular failure. Experimental allergen-driven lung inflammation evoked morphologic and functional vascular changes that resembled those observed in patients with PAH. Sphingosine kinase 1 (SphK1) is the main pulmonary contributor to sphingosine-1-phosphate (S1P) synthesis, a modulator of immune and vascular functions. OBJECTIVE We sought to investigate the role of SphK1 in allergen-induced lung inflammation. METHODS SphK1-deficient mice and C57Bl/6 littermates (wild-type [WT] animals) were subjected to acute or chronic allergen exposure. RESULTS After 4 weeks of systemic ovalbumin sensitization and local airway challenge, airway responsiveness increased less in SphK1(-/-) compared with WT mice, whereas pulmonary vascular responsiveness was greatly increased and did not differ between strains. Acute lung inflammation led to an increase in eosinophils and mRNA expression for S1P phosphatase 2 and S1P lyase in lungs of WT but not SphK1(-/-) mice. After repetitive allergen exposure for 8 weeks, airway responsiveness was not augmented in SphK1(-/-) or WT mice, but pulmonary vascular responsiveness was increased in both strains, with significantly higher vascular responsiveness in SphK1(-/-) mice compared with that seen in WT mice. Increased vascular responsiveness was accompanied by remodeling of the small and intra-acinar arteries. CONCLUSION : The data support a role for SphK1 and S1P in allergen-induced airway inflammation. However, SphK1 deficiency increased pulmonary vascular hyperresponsiveness, which is a component of PAH pathobiology. Moreover, we show for the first time the dissociation between inflammation-induced remodeling of the airways and pulmonary vasculature.

Symmorphosis and the insect respiratory system: allometric variation

SUMMARY Taylor and Weibels theory of symmorphosis predicts that structures of the respiratory system are matched to maximum functional requirements with minimal excess capacity. We tested this hypothesis in the respiratory system of the migratory locust, Locusta migratoria, by comparing the aerobic capacity of the jumping muscles with the morphology of the oxygen cascade in the hopping legs using an intraspecific allometric analysis of different body mass (Mb) at selected juvenile life stages. The maximum oxygen consumption rate of the hopping muscle during jumping exercise scales as Mb1.02±0.02, which parallels the scaling of mitochondrial volume in the hopping muscle, Mb1.02±0.08, and the total surface area of inner mitochondrial membrane, Mb0.99±0.10. Likewise, at the oxygen supply end of the insect respiratory system, there is congruence between the aerobic capacity of the hopping muscle and the total volume of tracheoles in the hopping muscle, Mb0.99±0.16, the total inner surface area of the tracheoles, Mb0.99±0.16, and the anatomical radial diffusing capacity of the tracheoles, Mb0.99±0.18. Therefore, the principles of symmorphosis are upheld at each step of the oxygen cascade in the respiratory system of the migratory locust.

Scaling of resting and maximum hopping metabolic rate throughout the life cycle of the locust Locusta migratoria

SUMMARY The hemimetabolous migratory locust Locusta migratoria progresses through five instars to the adult, increasing in size from 0.02 to 0.95 g, a 45-fold change. Hopping locomotion occurs at all life stages and is supported by aerobic metabolism and provision of oxygen through the tracheal system. This allometric study investigates the effect of body mass (Mb) on oxygen consumption rate (, μmol h–1) to establish resting metabolic rate (), maximum metabolic rate during hopping () and maximum metabolic rate of the hopping muscles () in first instar, third instar, fifth instar and adult locusts. Oxygen consumption rates increased throughout development according to the allometric equations , , and, if adults are excluded, and . Increasing body mass by 20–45% with attached weights did not increase mass-specific significantly at any life stage, although mean mass-specific hopping was slightly higher (ca. 8%) when juvenile data were pooled. The allometric exponents for all measures of metabolic rate are much greater than 0.75, and therefore do not support West, Brown and Enquists optimised fractal network model, which predicts that metabolism scales with a ¾-power exponent owing to limitations in the rate at which resources can be transported within the body.

Developmental allometry of pulmonary structure and function in the altricial Australian pelican Pelecanus conspicillatus

SUMMARY Quantitative methods have been used to correlate maximal oxygen uptake with lung development in Australian pelicans. These birds produce the largest altricial neonates and become some of the largest birds capable of flight. During post-hatching growth to adults, body mass increases by two orders of magnitude (from 88 g to 8.8 kg). Oxygen consumption rates were measured at rest and during exposure to cold and during exercise. Then the lungs were quantitatively assessed using morphometric techniques. Allometric relationships between body mass (M) and gas exchange parameters (Y) were determined and evaluated by examining the exponents of the equation Y=aMb. This intraspecific study was compared to interspecific studies of adult birds reported in the literature. Total lung volume scales similarly in juvenile pelicans (b=1.05) as in adult birds (b=1.02). However, surface area of the blood–gas barrier greatly increases (b=1.25), and its harmonic mean thickness does not significantly change (b=0.02), in comparison to exponents from adult birds (b=0.86 and 0.07, respectively). As a result, the diffusing capacity of the blood–gas tissue barrier increases much more during development (b=1.23) than it does in adult birds of different sizes (b=0.79). It increases in parallel to maximal oxygen consumption rate (b=1.28), suggesting that the gas exchange system is either limited by lung development or possibly symmorphic. The capacity of the oxygen delivery system is theoretically sufficient for powered flight well in advance of the birds need to use it.

Recruiting problem‐based learning (PBL) tutors for a PBL‐based curriculum: the Flinders University experience

To examine the contribution made to problem‐based learning (PBL) by individual teachers and by departments in years 1 and 2 of a new graduate‐entry medical programme (GEMP) with a PBL‐based curriculum.

Symmorphosis and the insect respiratory system: a comparison between flight and hopping muscle

SUMMARY Weibel and Taylors theory of symmorphosis predicts that the structural components of the respiratory system are quantitatively adjusted to satisfy, but not exceed, an animals maximum requirement for oxygen. We tested this in the respiratory system of the adult migratory locust Locusta migratoria by comparing the aerobic capacity of hopping and flight muscle with the morphology of the oxygen cascade. Maximum oxygen uptake by flight muscle during tethered flight is 967±76 μmol h−1 g−1 (body mass specific, ±95% confidence interval CI), whereas the hopping muscles consume a maximum of 158±8 μmol h−1 g−1 during jumping. The 6.1-fold difference in aerobic capacity between the two muscles is matched by a 6.4-fold difference in tracheole lumen volume, which is 3.5×108±1.2×108 μm3 g−1 in flight muscle and 5.5×107±1.8×107 μm3 g−1 in the hopping muscles, a 6.4-fold difference in tracheole inner cuticle surface area, which is 3.2×109±1.1×109 μm2 g−1 in flight muscle and 5.0×108±1.7×108 μm2 g−1 in the hopping muscles, and a 6.8-fold difference in tracheole radial diffusing capacity, which is 113±47 μmol kPa−1 h−1 g−1 in flight muscle and 16.7±6.5 μmol kPa−1 h−1 g−1 in the hopping muscles. However, there is little congruence between the 6.1-fold difference in aerobic capacity and the 19.8-fold difference in mitochondrial volume, which is 3.2×1010±3.9×109 μm3 g−1 in flight muscle and only 1.6×109±1.4×108 μm3 g−1 in the hopping muscles. Therefore, symmorphosis is upheld in the design of the tracheal system, but not in relation to the amount of mitochondria, which might be due to other factors operating at the molecular level.

Moulting of insect tracheae captured by light and electron-microscopy in the metathoracic femur of a third instar locust Locusta migratoria

The insect tracheal system is an air-filled branching network of internal tubing that functions to exchange respiratory gases between the tissues and the environment. The light and electron-micrographs presented in this study show tracheae in the process of moulting, captured from the metathoracic hopping femur of a juvenile third instar locust (Locusta migratoria). The images provide evidence for the detachment of the cuticular intima from the tracheal epithelial cells, the presence of moulting fluid between the new and old cuticle layers, and the withdrawal of the shed cuticular lining through larger upstream regions of the tracheal system during moulting. The micrographs also reveal that the cuticular intima of the fine terminal branches of the tracheal system is cast at ecdysis. Therefore, the hypothesis that tracheoles retain their cuticle lining at each moult may not apply to all insect species or developmental stages.

Gas transfer by the neonate in the pouch of the tammar wallaby, Macropus eugenii

The gas exchange characteristics of, and gaseous environment within, the wallaby pouch containing a single neonate (joey) (age 3–33 d) was determined in conscious animals from pouch gas samples obtained via an indwelling catheter. Pouch gas tensions were constant, with O2 approximately 3 torr below, and CO2 4 torr above, ambient values. For a surgically closed and sealed pouch without a joey, the equilibrium values of O2 and CO2 were approximately 70 and 40 torr, respectively. For joeys 3–33 d old, O2 uptake and CO2 excretion rates were approx. 0.60 and 0.52 ml · g−1 · h−1, and the respiratory exchange ratio averaged 0.94. Of the O2 from the atmosphere entering the pouch containing a 3-d joey, only 15% was consumed by the Joey, the remainder being removed by the pouch wall; similarly, 85% of CO2 leaving the pouch was added to the pouch gas from the pouch wall. Histological studies confirmed that the maternal skin lining the pouch was well vascularized and the joey lung highly vascularized, but that the joey skin was poorly vascularized. Gas exchange in neonatal joeys must be almost totally pulmonary, given the markedly poorer skin vascularity and longer diffusion distances from skin capillaries across its epithelium, compared to that of the capillary network of the lung.