ABSTRACT
Objective To improve the fixation method of the transmission electron microscope for better morphological preservation of mitochondria and lipid droplets in mouse brown adipose tissue. Methods The fixation method for mouse brown adipose tissue was optimized, mainly including an increased concentration of paraformaldehyde from 2% to 4% in the pre-fixative, employment of transcardial perfusion followed by immersion fixation in pre-fixation, and using imidazole-buffered osmium tetroxide as the post-fixative. The ultrastructures of brown adipocytes prepared by the improved method were observed and compared with those of a known standard protocol (3 mice in each group). The improved method was further validated in the quantitative analysis of mitochondrial cristae density and lipid droplets. Results The mitochondrial cristae and membrane structure of other organelles of brown adipocytes were better preserved using the optimized method compared with those of the standard method. Lipid droplets were presented as round structures with high electron density instead of vacuolated appearances. Using this method, we observed that the density of mitochondrial cristae and the content of lipid droplets increased in brown adipocytes after cold adaptation. Conclusion The optimized method can better preserve the ultrastructure of organelles in brown adipocytes, especially mitochondria and lipid droplets, and ma)' be applicable for studying the ultrastructures remodeling of brown adipose tissue under different physiological or pathological conditions.