Changes in size and shape during histochemical preparation for light and electron microscopy of neurons intracellularly labelled with horseradish peroxidase

In this study we show that neurons labelled intracellularly with horseradish peroxidase react differently from surrounding unlabelled neurons in vibratome sections during histological preparations for light and electron microscopy. The diameters and cross-sectional area of the cell bodies of intracellularly horseradish peroxidase-labelled neurons increased by about 6 and 11% respectively, while the surrounding unlabelled neurons decreased by the same amount. Also, the caliber of the proximal dendrites of horseradish peroxidase-labelled neurons increased during the histological preparation while dendritic path lengths remained unchanged. Since the surrounding tissue shrunk, the dendritic path shapes became more tortuous during histological processing. The demonstrated reaction of horseradish peroxidase-labelled neurons is suggested to be caused by the horseradish peroxidase reaction product.