Nutrient-conditioned flavor preference and acceptance in rats: effects of deprivation state and nonreinforcement

Rats acquire strong preferences for flavors paired with intragastric (IG) Polycose infusions. The present study investigated the ingestive responses to these flavors when they were no longer reinforced. All rats were first trained to associate a CS+ flavor with IG 32% Polycose and a CS- flavor with IG water during 23 h/day sessions. Experiment 1 examined the effects of deprivation on short-term (4 h/day) CS intakes under nonreinforcement conditions. Food deprivation selectively enhanced CS+ intake whereas water deprivation increased both CS+ and CS- intakes. The results also suggested that extinction training differentially affects CS+ preference and acceptance as measured by relative and absolute intakes. This was confirmed in a second experiment. The rats' absolute intake of the CS+ solution during 4 h/day sessions significantly decreased when it was no longer paired with IG Polycose infusions; yet the rats continued to show a strong preference for the CS+ over the CS- in both 4 h and 23 h/day tests. Experiment 3 examined the effects of extensive long-term extinction training on the CS+ preference. When the alternative was plain water, the CS+ preference extinguished over 12 days. Yet the same rats continued to prefer the CS+ to the CS- during 12 additional extinction days and during 16 extinction days that followed a 1-month rest period. The CS+ preference relative to the CS- was blocked only when the CS+ was paired with food deprivation and the CS- was paired with food repletion. These experiments confirm earlier reports of the resistance of Polycose-conditioned flavor preferences to extinction but also show that flavor acceptance is more susceptible to extinction. Flavor acceptance was not completely extinguished, however, and remained responsive to deprivation state.