The Effects of Stress and Emotionality on Eating Patterns in Rats.
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Eating is 'over-determined': it is influenced by many factors, ranging from food resources to metabolism to stress. The present work explores the interaction of these factors. Occidental high-saccharin (HiS) and low-saccharin (LoS) rats have been selectively bred for differential saccharin intake, with LoS rats consuming less. In addition, LoS rats score higher than HiS rats on common measures of emotionality. This apparent linkage between taste and emotionality is consistent with research with humans on anxiety, depression, and eating disorders. It implies that LoS and HiS rats should differ in the behavioral regulation of feeding behavior. In this experiment, LoS and HiS rats earned food pellets on six fixed ratio schedules of reinforcement ( cyclic ratio schedule). The data yield information about reward palatability (elevation of function) and responsiveness to the 'cost' of food (slope of function). Prior work showed that in normal rats, stress selectively increases the slope of the function; thus, our prediction was that the more anxious LoS rats would have a steeper function than HiS rats. This prediction was confirmed. Additional tests after a moderate stressor suggested complex interactions involving line and sex. These results imply that people with higher levels of emotionality may have stronger behavioral regulation of food intake, and that these individual differences may be clearer and more consistent under everyday, 'normal' conditions than under stressful conditions.