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SLEEP AND TEMPERATURE REGULATION

Body temperature, behavior, and plasma cortisol changes induced by chronic infusion of Staphylococcus aureus in goats

¹School of Physiology, University of the Witwatersrand, Parktown 2193, South Africa; and ²Veterinary-Physiology, Justus-Liebig-University Giessen, Giessen D-35392, Germany

Submitted 29 January 2004 ; accepted in final form 22 June 2004

Most experimentally induced fevers are acute, usually lasting 6–12 h, and thus do not mimic chronic natural fevers, which can extend over several days or more. To produce a model of chronic natural fever, we infused eight goats (Capra hircus) intravenously with 2 ml of 2 x 10¹¹ cell walls of Staphylococcus aureus (S. aureus) for 6 days using osmotic infusion pumps (10 µl/h) while measuring changes in body temperature, behavior, and plasma cortisol concentration. Seven control animals were infused with sterile saline. Abdominal temperature-sensitive data loggers and osmotic infusion pumps were implanted under halothane anesthesia. To compare our new model with existing models of experimental fever, we also administered 2-ml bolus intravenous injections of 2 x 10¹¹ S. aureus cell walls, 0.1 µg/kg lipopolysaccharide (Escherichia coli, serotype 0111:B4), and sterile saline in random order to six other goats. Bolus injection of lipopolysaccharide and S. aureus induced typical acute phase responses, characterized by fevers lasting 6 h, sickness behavior, and increased plasma cortisol concentration. Infusion of S. aureus evoked prolonged fevers, which lasted for 3 days, starting on day 4 of infusion (ANOVA, P < 0.05), and did not disrupt the normal circadian rhythm of body temperature. However, pyrogen infusion did not cause plasma cortisol concentration to rise (ANOVA, P > 0.05) or the expression of sickness behavior. In conclusion, infusion of S. aureus produced a fever response resembling that of sustained natural fevers but did not elicit the cortisol and behavioral responses that often are described clinically and during short-term experimental fevers.

osmotic infusion pumps; lipopolysaccharide; circadian rhythm

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