Taste aversions conditioned by the aversiveness of insulin and formalin: role of CS specificity.

Abstract

Experimenters in the past have reported that when insulin is used as the unconditioned stimulus (US), rats will learn an aversion to a sodium chloride but not a sucrose solution, whereas with formalin as the US, they will learn an aversion to a sucrose but not a saline solution. The present experiments failed to confirm these findings. Aversions to sucrose were conditioned with insulin and aversions to sodium chloride were conditioned with formalin. The use of a more concentrated sucrose solution in the present study may have been responsible for the successful sucrose-aversion conditioning with insulin. Although the source of the discrepancy in findings concerning aversion conditioning with formalin remains unclear, experiments ruled out numerous possibilities. These experiments also showed that sodium chloride aversion conditioning with formalin is a highly robust phenomenon that occurs with a variety of conditioned stimulus durations and formalin doses, with distributed and massed training, in male and female rats, and even if saline is not the only novel solution presented during conditioning. Furthermore, the aversion can be detected with both single-stimulus and choice test procedures.