The Effect of Activity Anorexia on Analgesia in Rats.
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In a culture emphasizing physical attractiveness and body image, Anorexia Nervosa is gaining more attention. A subtype of Anorexia Nervosa, Activity Anorexia (AA) involves great increases in activity coupled with substantial decreases in food intake. Giving rats access to running wheels and half of their average food intake simulates AA. Limiting their diet and activity serves as a stressor, one symptom of which is stress-induced analgesia. The present study explored individual differences in this effect across nine Occidental High (HiS) and nine Low (LoS) Saccharin rats. Each rat was observed under four conditions differing in food access (ad lib and restricted) and exercise (wheel access and limited access). Hot plate tests followed: the rats remained there until licking their hind paw (indicating heat perception). Their paw-lick latencies were recorded. It was predicted that rats with limited food and limited activity would have longer paw-lick latencies due to stress-induced analgesia. Furthermore, because LoS rats are more sensitive to stress, it was predicted that a restricted diet and limited activity would produce longer paw-lick latencies in LoS rats. A within-subjects analysis showed that HiS and LoS rats did react differently but in an unpredicted pattern to the combination of conditions. Further testing is needed to explain this phenomenon. Future studies may look at differences in HiS and LoS opoid receptors and/or corticosterone levels, possibly uncovering more genetic differences across lines, thus increasing our knowledge of AA.