Cue-Induced Potentiation of Feeding

General Overview
This task is used to assess the influence of various types of conditioned stimuli on food consumption. Food deprived C57/Bl6 mice undergo an appetitive pavlovian training procedure during which they first learn to associate an auditory stimulus with food delivery (CS). During the second phase of training, CS trials are interrupted at random times. This intermission is signaled by a second auditory stimulus (meal interruption signal or IS). After one week of free access to chow, food consumption is tested in the presence of the CS, IS or in the absence of any discrete food-related signals. Both CS and IS enhance feeding, but in different ways. The former cue modulates feeding bout distribution, while the latter potentiates overall food consumption.

Apparatus
Training and testing is conducted in standard mouse conditioning chambers located inside sound attenuating enclosures. A fan can be utilized to provide constant ventilation and low-level background noise to each chamber. An incandescent house light is used to mildly illuminate the chambers. Each chamber is equipped with a fluid well recessed in one wall and a small speaker in the opposing wall. An optical lickometer provides automated measures of food consumption and allows controlling its delivery.

Procedure

Both training and testing is conducted during the light phase of the day. Before training, mice are food-restricted to 85-90% of their free-feeding weight. Restriction is maintained for the duration of training. Prior to testing, animals have free access to lab chow for 7-10 days. Free feeding is maintained throughout testing days.

Habituation
Training begins with two sessions of magazine training that serve to shape mice to the well by delivering sucrose at random time intervals once per minute over 30 minutes.

Training
Following magazine training animals are presented with a 2-minute auditory stimulus (tone, white noise or clicker) during which they receive four deliveries of a 10% sucrose solution at random times. Each session is 60-minute long and consists of 12 CS+ trials. After 80-90 trials, 80% of CS+ trials are interrupted with a 10 second auditory stimulus, such that the CS+ is terminated and future sucrose deliveries cancelled until the next trial. This interruption occurs 30 to 90 seconds after CS+ onset. Reward density (i.e. 1 food delivery/30seconds) is maintained. This form of training is continued for 170 trials.

Testing
After the last day of training animals are returned to their home cages and have free access to chow for 7-10 days. Testing consists of three sessions during which CS, IS or no cue are presented for short periods of time (20sec), while making sucrose freely available. Each test session is preceded by 2 minutes of unlimited access to sucrose. Total sucrose consumption and meal bout distribution are measured.