Abstract
The morphometric analysis of lung structure using the principles of stereology has emerged as a powerful tool to describe the structural changes in lung architecture that accompany the development of lung disease that is experimentally modelled in adult mice. These stereological principles are now being applied to the study of the evolution of the lung architecture over the course of prenatal and postnatal lung development in mouse neonates and adolescents. The immature lung is structurally and functionally distinct from the adult lung, and has a smaller volume than does the adult lung. These differences have raised concerns about whether the inflation fixation of neonatal mouse lungs with the airway pressure (Paw) used for the inflation fixation of adult mouse lungs may cause distortion of the neonatal mouse lung structure, leading to the generation of artefacts in subsequent analyses. The objective of this study was to examine the impact of a Paw of 10, 20 and 30 cmH2O on the estimation of lung volumes and stereologically assessed parameters that describe the lung structure in developing mouse lungs. The data presented demonstrate that low Paw (10 cmH2O) leads to heterogeneity in the unfolding of alveolar structures within the lungs, and that high Paw (30 cmH2O) leads to an overestimation of the lung volume, and thus, affects the estimation of volume-dependent parameters, such as total alveoli number and gas-exchange surface area. Thus, these data support the use of a Paw of 20 cmH2O for inflation fixation in morphometric studies on neonatal mouse lungs.
Highlights
Lung organogenesis occurs over a protracted period in mammals that starts in the early embryonic period, and continues into adolescence (Schittny 2017)
The objective of the present study was to determine whether a Paw of 20 cmH2O for inflation fixation—the Paw employed in studies with mature, adult mouse lungs—is suitable for the stereological analysis of immature, developing mouse lungs
The lungs of children and adolescents have fewer alveoli compared to adults, which increase in number during early life and adolescence (Herring et al 2014), to ≈480 million alveoli in adults (Ochs et al 2004)
Summary
Lung organogenesis occurs over a protracted period in mammals that starts in the early embryonic period, and continues into adolescence (Schittny 2017). The study of structural changes that occur during lung development rely on quantitative information about the lung structure, such as morphometric stereological methods (Weibel et al 2007) that permit estimation of the density and number of alveoli, the gas-exchange surface area, and septal thickness, amongst other parameters. The reliability of these estimations is critically dependent upon proper inflation of lungs during embedding and sectioning (Hsia et al 2010). This approach is widely used to study the microscopic structure of adult healthy and diseased mouse lungs
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