Document Type

Thesis

Degree Name

Master of Science (MSc)

Department

Psychology

Faculty/School

Faculty of Science

First Advisor

Rudy Eikelboom

Advisor Role

Thesis Supervisor

Abstract

While feeding is rewarding, the feeling of satiation has been theorized to be aversive under certain conditions. Using a food-restriction model of overeating developed in our laboratory the results presented here suggest that overeating, and the resulting experience of satiation, is capable of supporting a conditioned taste avoidance.

Rats had either ad lib (n=8) or restricted (n=24) food access (receiving 50% of the food eaten by ad lib fed rats) for 8 days. All rats were then given 24 hr access to a 0.1% saccharin solution, and two groups of food-restricted rats were given access to either 100% of the food eaten by the ad lib rats, or ad lib food access. This cycle was given once in Experiment 1 and three times (with 4 days between cycles) in Experiment 2. Rats were then returned to their previous feeding schedules for 1 day before being placed on ad lib food access until feeding was approximately equal for all groups. Rats were then tested for saccharin consumption in a two-bottle choice test of saccharin and water. Rats that were overeating at the time of the one-bottle saccharin acquisition trial(s) were expected to experience a change in internal state as a result of the influx in calories and associate this with the novel saccharin solution. This change in state should result in an avoidance of the saccharin at the two-bottle test.

In Experiment 1, at the two-bottle test, the restricted-ad lib feeding rats (those that overate) showed reduced saccharin consumption compared to the ad lib control rats, although these results were not significant. In Experiment 2, after three acquisition trials, the restricted-ad lib feeding group showed significantly reduced saccharin consumption compared to all other groups.

Experiment 3 sought to understand the learning component of the taste avoidance by making the saccharin familiar. Half of the rats were given 8 days of pre-exposure to the saccharin solution, after which they underwent the experimental procedure used in Experiment 2, with half the rats on food restriction. Because they had previously shown the largest difference in saccharin consumption, only the rest-adlib (n=32) and adlib-adlib (n=32) groups were used in this experiment. After 8 days, all rats received 24 hr access to the saccharin solution, and the food restricted rats received access to ad lib food. Non-restricted rats received the saccharin without a change in feeding.

Saccharin consumption was measured and it was found that at the time of the two-bottle test, prior saccharin exposure attenuated the decreased saccharin consumption seen in the rest-adlib group in Experiments 1 and 2.

Overall, the results of these studies showed that the experimental design was successful in inducing overeating in previously restricted rats. When this bout of overeating was paired with a novel saccharin solution, rats later showed reduced consumption of the solution even after feeding levels returned to baseline. This reduced consumption was attenuated by pre-exposure to the saccharin solution.

Convocation Year

2009

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