Animals at the extremes: Hibernation and torpor
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# 4.5 Summary

Molecular approaches to the study of hibernation have combined largely non-hypothetical analytical and targeted methods. The analytical approach shows changes in the expression patterns of novel genes, often with unforeseen or unknown functions in hibernation, whilst indicating that the scale of the full range of adaptive genetic changes is small. The targeted approach has confirmed an important role for gene products normally involved in maintaining biological rhythms and energy-generating metabolic reactions.

The basis for the slowing of metabolic processes is the arrest of protein synthesis in hibernating cells through changes that inhibit the initiation of messenger RNA translation and polysome assembly. Although the mechanism operates in hibernating cells at any temperature once initiated, it is triggered during entry to torpor at a critical T b. Changes that occur in the structure of hepatocytes, their fuel deposits and mitochondria during the transition from carbohydrate to lipid metabolism, are indicative of enduring adaptations at microscopic level.

Hibernators have a system of protection against cellular injury or death resulting from the actions of reactive oxygen species (ROS) produced during the respiratory burst that accompanies arousal. Protective mechanisms include an increase in the level of ROS-neutralizing compounds in the blood and regulators that inhibit biochemical pathways leading to the death of individual cells.

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