Nutrient-conditioned intake stimulation does not require a distinctive flavor cue in rats

The postoral actions of nutrients in rodents can stimulate intake and condition flavor preferences through an appetition process. Appetition is revealed in rodents by their increased intake of and preference for a flavored solution paired with intragastric (IG) nutrient infusions. Here we determined if IG 16% maltodextrin (MD) infusions can stimulate intake and preference in the absence of a distinctive flavor cue. Rats implanted with IG catheters were given chow and water 2 h/day followed, 2 h later, by 20-h oral access to water paired with IG MD infusions. Other rats were given bitter sucrose octaacetate solution (SOA) paired with IG MD infusions 20 h/day. Over 8 test days, the SOA rats increased their total 20-h fluid intake (oral + IG) from 26 to 119 g/20 h and Water rats increased their intake from 31 to 96 g/20 h. When infused IG with water instead of MD in a 4-day extinction test, the SOA and Water groups reduced their fluid intakes to 45-48 g/20 h. When oral fluids were again paired with IG MD infusions, the SOA and Water groups increased their intakes to 115 and 109 g/20 h, respectively. In two-bottle tests, the SOA rats drank more SOA paired with IG MD than water paired with IG water. Water rats given the choice of a water bottle paired with IG MD and water bottle paired with IG water did not consistently prefer the H2O/ID MD bottle. Instead they displayed side or sipper tube preferences although neither cue was consistently paired with IG MD during one-bottle training.