AbstractsPsychology

The modern diet contains a variety of energy-rich, highly palatable and readily available foods. The consumption of such foods may have contributed to the increased prevalence of obesity. This thesis investigated the effects of the modern human diet on feeding behavior and its neural correlates in the rat. The aim of the first set of experiments was to investigate the effects of a highly palatable diet (relative to a less palatable diet) on licking responses to several concentrations of a sweet non-nutritious solution, saccharin. Rats were placed on either standard laboratory chow or a highly palatable cafeteria diet that contained chow supplemented by some of the energy-rich foods eaten by people. We recorded lick responses to different concentrations of non-caloric saccharin during 10 minute drinking sessions over two different periods of diet exposure. Cafeteria-fed rats consumed more energy than chow fed rats, and gained weight at a faster rate. Exposure to the cafeteria diet produced an overall depression in clusters and licks per cluster to saccharin solution, and was associated with a shift in preference toward low concentrations of saccharin. These results suggest that an energy-rich diet may have the potential to affect the hedonic value of a tastant and further, that cafeteria-fed rats may have become hypersensitive to the bitter component of the saccharin. The second set of experiments aimed to examine the effects of switching between an energy-rich palatable diet and a lower-energy less palatable diet, typically known as ‘yo-yo’ dieting. Specifically, these experiments investigated the effects of cycling rats between the cafeteria and chow diets on: intake; feeding behavior following a shift from the cafeteria diet to chow; and licking responses to saccharin and caloric sucrose solutions following a shift from chow to the cafeteria diet and vice versa. Cycled rats developed binge-like eating behavior (i.e., rats switched to the cafeteria diet ate more than rats maintained on the cafeteria diet), and weighed more than chow-fed rats, but less than cafeteria-fed rats. When withdrawn from the cafeteria diet, cycled rats consumed significantly less chow than rats maintained on chow. Moreover, cycled rats withdrawn from the cafeteria diet consumed less of a novel palatable biscuit than chow-fed rats, which was due to shorter bout durations. This suggests that withdrawal from the cafeteria diet produced stress. Chow-fed rats, cafeteria-fed rats, and rats that were diet cycled equally ‘liked’ the saccharin solution, but cafeteria-fed and cycled rats were less motivated to obtain it. This was evidenced by a comparable number of licks per cluster between the groups, but fewer clusters in cafeteria-fed and cycled rats relative to chow-fed rats. In contrast, chow-fed rats and cycled rats ‘liked’ (i.e., had more licks per cluster) sucrose solution more than cafeteria-fed rats, but all three groups were equally motivated to obtain it (i.e., groups had a similar number of clusters). Licking responses in cycled rats were…