The conditioned stimulus elicits taste aversion but not sickness behavior in conditioned mice

This article extends previous reports on (i) elicitation of taste aversion after pairing a flavored beverage (saccharin solution) with a disease-provoking microbial product (lipopolysaccharide, LPS, or polyinosinic:polycytidylic acid, poly I:C); (ii) elicitation of sickness behavior (assessed as diminished ingestion of water and food) by the conditioned stimulus, and (iii) development of tolerance to those microbial products.

Mice of the CD1 strain were conditioned by pairing ingestion of 0.15% saccharin solution with injection of LPS (100 mug/mouse) or poly I:C (6 mg/kg). A few days later, some mice were offered saccharin solution and were injected with saline, whereas other mice were offered saccharin solution and were injected with the microbial product.

Regardless of the nature of the unconditioned stimulus (LPS or poly I:C), (i) taste aversion to saccharin ensued, (ii) tolerance ensued to sickness elicitation by a second administration of the microbial component, and (iii) saccharin taste did not evoke sickness.

Symptoms of infectious sickness in the absence of infection are hardly explained by exposure to the conditioned stimulus.