Quantitative ultrastructural changes of hepatocyte constituents in euthermic, hibernating and arousing dormice (Muscardinus avellanarius).

Hibernating animals represent a suitable model for investigating the structural effects of drastic changes in cell activity under physiological conditions. In this study we investigated by means of electron microscopy and morphometrical analysis the fine structural counterpart of functional rest in hepatocytes of the hibernating dormouse, Muscardinus avellanarius, in comparison with arousing and euthermic dormice. Our observations demonstrate that during hibernation several structural constituents of the hepatocyte undergo modifications. In particular, during deep hibernation, the total cell and cytoplasm area significantly reduced, as well as the total and percent glycogen and residual body area, and the Golgi apparatus almost disappeared. Upon arousal, the amount of glycogen was minimal, whereas total cell and cytoplasm area significantly increased towards the euthermic value as well as total and percent residual body area. In comparison with the euthermic condition, the total and percent cell lipid area significantly increased in early hibernation, reduced in deep hibernation and almost disappeared during arousal. Taken together, our findings give quantitative ultrastructural support to the marked reduction found in hepatocyte functional activities during hibernation. Such a reduced activity involves profound rearrangement of the euthermic cell structure, which is rapidly resumed upon arousal.