Fluorescence polarization study of lipids and membranes prepared from brain hemispheres of a hibernating mammal

The physical behavior of total lipids, microsomes and microsomal lipids prepared from brain hemispheres of European Hamsters ($\text{Cricetus cricetus}$) was approached by the measure of the fluorescence polarization of the probe 1,6-diphenyl 1,3,5-hexatriene. We compare in this study the results obtained for two critical periods for a hibernator: winter (torpid state) and summer (active state). An increase in fluidity was noticed in the winter lipid and membrane preparations. The difference was however of very low magnitude, suggesting that only the microenvironment of some proteins was involved, rather than the bulk membrane fluidity.