Quantitative study on the hygroscopic expansion of spurr resin to obtain a high-resolution atlas of the mouse brain

Abstract

Ultra-thin section-based microscopic imaging is considered one of the most realistic techniques for determining fine architectures of a brain-wide neural network. In this kind of method, the sample is usually embedded in resin and then immersed in water for sectioning and imaging. The effect of resin hygroscopic expansion on data accuracy and integrity is important as it may lead to inconsistent image qualities or degeneration of sectioning properties. But few studies have been conducted on this issue. Here, we have used surface profile measurements combined with sectioning and imaging by micro-optical sectioning tomography (MOST) to quantitatively study the sectioned surface expansion of spurr resin blocks as a result of water immersion for a short time period. The expansion effect on MOST imaging is also presented. The results revealed significant differences in the surface expansion of pure resin blocks with different immersion time durations (P < 0.001). During an eight-minute immersion, the surface expansion of the experimental specimens exhibited an approximately linear increase with immersion duration, while MOST images suffered a correlated decrease in brightness. Expansion was restricted to the submicron level with immersion duration of four minutes or less, and the mean and standard deviation of the expansion measurements both reached a maximum at eight minutes. When the immersion duration exceeded eight minutes, the expansion value decreased, which was most likely related to the degeneration of mechanical properties of the resin material on the block surface. This study indicates that it is necessary to select a specific sectioning mode according to the hygroscopic expansion properties of resin materials for maintaining the accuracy and integrity of whole brain atlas data.