Stereological analysis of individual lung lobes during normal and aberrant mouse lung alveolarisation

The quantitative assessment of the lung architecture forms the foundation of many studies on lung development and lung diseases, where parameters such as alveoli number, alveolar size, and septal thickness are quantitatively influenced by developmental or pathological processes. Given the pressing need for robust data that describe the lung structure, there is currently much enthusiasm for the development and refinement of methodological approaches for the unbiased assessment of lung structure with improved precision. The advent of stereological methods highlights one such approach. However, design-based stereology is both expensive and time-demanding. The objective of this study was to examine whether 'limited' stereological analysis, such as the stereological analysis of a single mouse lung lobe, may serve as a surrogate for studies on whole, intact mouse lungs; both in healthy lungs and in diseased lungs, using an experimental animal model of bronchopulmonary dysplasia (BPD). This served the dual-function of exploring BPD pathobiology, asking whether there are regional (lobar) differences in the responses of developing mouse lungs to oxygen injury, by examining each mouse lung lobe separately in the BPD model. Hyperoxia exposure resulted in decreased alveolar density, alveoli number, and gas-exchange surface area in all five mouse lung lobes, and increased the arithmetic mean septal thickness in all mouse lung lobes except the lobus cardialis. The data presented here suggest that - in healthy developing mice - a single mouse lung lobe might serve as a surrogate for studies on whole, intact mouse lungs. This is not the case for oxygen-injured developing mouse lungs, where a single lobe would not be suitable as a surrogate for the whole, intact lung. Furthermore, as the total number of alveoli can only be determined by an analysis of the entire lung, and given regional differences in lung structure, particularly under pathological conditions, the stereological assessment of the whole, intact lung remains desirable.