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Articles in PresS, published online ahead of print January 17, 2002
Am J Physiol Regu Physiol, 10.1152/ajpregu.00562.2001
Submitted on September 17, 2001
Accepted on December 7, 2001
1 Department of Psychology and Neuroscience, The Ohio State University, Columbus, OH, USA
2 Department of Psychology, University of California at Berkeley, Berkeley, CA, USA
3 Department of Psychology, University of California at Berkeley, Berkeley, CA, USA; Department of Integrative Biology, University of California at Berkeley, Berkeley, CA, USA
* To whom correspondence should be addressed. E-mail: prendergast{at}psy.ohio-state.edu.
Golden-mantled ground squirrels (Spermophilus lateralis) undergo seasonal hibernation during which core body temperatures (Tb) are maintained 1-2°C above ambient temperatures (Ta). Hibernation is not continuous. Squirrels arouse at approximately 7 day intervals, during which Tb increases to 37°C for ~16 h; thereafter they return to hibernation and sustain low Tbs until the next arousal. Over the course of the hibernation season, arousals consume 60-80% of a squirrel's winter energy budget, but their functional significance is unknown and disputed. Host-defense mechanisms appear to be downregulated during the hibernation season and preclude normal immune responses. These experiments assessed immune function during periodic arousals. The acute-phase response to bacterial lipopolysaccharide (LPS) was arrested during hibernation and fully restored upon arousal to normothermia in golden-mantled ground squirrels. LPS injection (i.p.) resulted in a 1 to 1.5°C fever in normothermic animals that was sustained for >8 h. LPS was without effect in hibernating squirrels, neither inducing fever nor provoking arousal, but a fever did develop several days later, when squirrels next aroused from hibernation; the duration of this arousal was increased 6-fold above baseline values. Intra-cerebroventricular infusions of prostaglandin E2 provoked arousal from hibernation and induced fever, suggesting that neural signaling pathways that mediate febrile responses are functional during hibernation. Periodic arousals may activate a dormant immune system which can then combat pathogens that may have been introduced immediately prior to or during hibernation.
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