Tolerance pattern of the anorexigenic action of amphetamine in rats

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Abstract
1 When food intake in fasted male rats was recorded daily for two consecutive 2 h periods it revealed a characteristic pattern. 2 In the control rats the food intake was greater during the first than the second 2 h period. Following (±)-amphetamine 5 mg/kg s.c. 30 min before food for 7 days there was a reversal of this normal food pattern. The rats consumed much less during the first 2 h period but progressively more during the second 2 h period. 3 The first 2 h food intake remained low throughout the treatment period and there was no evidence of development of tolerance despite continuation of treatment. 4 The second 2 h food intake steadily increased, contributing to the appearance of tolerance when only total 4 h food intake was recorded. 5 On withdrawal of amphetamine, there was immediate recovery of the first 2 h food intake. The second 2 h food intake, though decreased, remained high compared to the pretreatment level and may be responsible for the production of the ‘rebound’ phenomenon following withdrawal of amphetamine.