Deep hypothermia and its effect on the 24-hour clock of rats and hamsters

Intensive hypothermia in rats and hamsters whose breathing and heartbeat had stopped for 1-4 hours was used as a setting in which to study the 24-hour biological clock. Pre- and post-hypothermia analyses depended on behavior wherein spontaneous running activity in revolving drums was used as a "hand" of the biological clock. Hypothermia had various effects. In some cases the clock was temporaily stopped, i.e., reset. In others it was simply slowed. Some clocks were both reset and slowed. Others ran without interruption even though breathing and heartbeat had stopped for 3-4 hours.