Experiment 2

Brief-access two-bottle lick tests were conducted in 10 plastic cages with stainless-steel perforated floors (35). Fluid was available from two stainless-steel sipper spouts through slots (5 × 20 mm, 32 mm apart) in a stainless steel plate at the front of the cage. The sipper spouts had a 2.5-mm hole and were attached to 50-ml glass tubes mounted on motorized bottle holders (ENV-252M; Med Associates, Georgia, VT). The bottle holders positioned the spouts 1 mm in front of the cage at the start of a session and retracted them away from the cage 3 min after the animal had emitted 10 licks. Licking behavior was monitored with electronic lickometers (ENV-250B, Med Associates) interfaced to a microcomputer.

The soybean oil emulsions were prepared as in the first experiment using 2.5 and 5% soybean oil concentrations. Note that the 5% soybean oil emulsion infused in experiment 1 was diluted to 2.5% in the stomach by the ingested CS+ solution. After the soybean oil and 0.15% Emplex was processed in the Ultra-Turrax T25 disperser, 0.3% xanthan gum (Sigma) was added to the emulsion and mixed with a handheld blender (Braun Model 4169) for 5 min. A vehicle emulsion was prepared in the same manner but contained no soybean oil. The orlistat and control groups were tested with soybean oil emulsions with and without orlistat (4 mg/g of fat), respectively. In pretraining sessions, the mice were given a 4% sucrose solution (Domino Foods, Yonkers, NY) containing 0.3% xanthan gum and a gum vehicle (0.3% xanthan gum in water). These sessions served to train the animals to sample both spouts and accustom them to gum while keeping them naïve to oil.

Naive, adult male B6 mice (n = 20) were singly housed as in the first experiment. The mice were water deprived overnight and trained to drink water in the test cages from two sipper tubes in a 5-min session. They were then trained 3 min/day to drink 4% sucrose-gum versus gum for 4 days. After the 5-min and first 3-min sessions, the mice were given 1-h access to water in their home cages and then following all subsequent sessions they were given unlimited water and a food ration in their home cages that maintained them at 85–90% of ad libitum body weight. The mice were divided into two groups (n = 10 each) equated for their sucrose preference during the last two sessions. The control group was given two 3 min/day sessions with 2.5% soybean oil versus vehicle followed by another two sessions with 5% soybean oil versus vehicle. The orlistat group was similarly tested but with orlistat added to the soybean oil emulsions.