Alpha-melanocyte-stimulating hormone conditioned suppression of a lipopolysaccharide-induced fever

Recent investigations have demonstrated the susceptibility of various components of the immune system to behavioral conditioning, using a conditioned taste aversion (CTA) paradigm. In Experiment 1 the effective antipyretic dose (40 micrograms/kg) and duration of antipyretic action (up to 4 hr) of alpha-melanocyte-stimulating hormone (alpha-MSH) was determined in rats tested with lipopolysaccharide (LPS). In the second experiment, alpha-MSH was used as the unconditioned stimulus (UCS) and paired with a novel-tasting saccharin solution (0.1%) to elicit a conditioned antipyretic response to a fever induced one hour previously by LPS. Both the antipyretic effect of alpha-MSH and the pyrogenic effect of LPS were found to be significantly conditionable. The conditioning of fever/antipyretic responses demonstrates for the first time that still another aspect of the host response can be influenced by conditioning procedures.