Novelty-induced hypophagia (NIH) test

The NIH test was performed as previously described [²⁵]. Briefly, NIH training and testing consisted of exposing mice to a highly palatable food (Reese’s peanut butter chips (Nestle, Glendale, CA (ingredients: partially defatted peanuts, sugar partially hydrogenated vegetable oil, corn syrup solids, dextrose, reduced minerals whey, salt vanillin, artificial flavor, soy lecithin)) and latency to consume was measured. One week before NIH training and for the duration of the experiment, mice were housed in groups of two. Training consisted of daily sessions in which mice were exposed to Reese’s peanut butter chips in a clear plastic dish. Plastic dividers (dividing the standard mouse cage lengthwise) were placed inside each cage to separate the mice during the training and home cage testing periods. Mice were acclimated to the barriers for 1 h before placement of food. Food was placed in the cage for 15 min, and latency to consume was measured. By the 10th day, a baseline latency to approach and consume the food was reached such that there was <20% variability between mice. After the last training session, the amount consumed was recorded as grams of peanut butter chips to ensure there were no appetitive treatment effects. Following training, mice were implanted with 14-day osmotic minipumps filled with pulsatile nicotine (12 mg/kg/day) or 0.9% pulsatile saline. Testing in the home cage (Home Test Day) and novel environment (Novel Test Day) occurred on the last 2 days of minipump viability. On Home Test Day, following testing, minipumps were surgically removed for the WD groups, and sham surgeries were performed on the chronic nicotine group as well as saline animals. Twenty-four hours later, on the Novel Test Day, mice were removed from the home cage and placed in an empty standard cage with no bedding that had been wiped with a cleanser (Pine-Sol, 1:10 dilution) to emit a novel odor and placed in a white box with bright light illumination (2150 lux). Latency to consume the palatable food was recorded on both days.