ABSTRACT
A new hypothesis postulates that mechanisms of sleep are inhibited during torpor, and that hibernating animals become progressively sleep-deprived. Arctic ground squirrels prevented from sleeping in the early stages of arousal prolonged euthermic periods longer than those allowed to sleep in the stages. Because periodic arousals from hibernation are so energetically expensive and because all investigated species of hibernators arouse, it can be argued that arousals serve an essential function, common to all species, that cannot take place during hibernation. There is little doubt that hibernation in mammals evolved as a physiological adaptation for energy conservation in times of seasonal cold and food shortage. Being a phenomenon of modified thermoregulation involving a lowered central nervous system (CNS) set-point, the onset and termination of hibernation must involve CNS neurochemical regulation. Premature arousal can be induced by injection of naloxone, a non-specific opioid receptor antagonist, and heightened CNS met-enkephalin concentration and met-enkephalin immunoreactivity.
