Ontogeny of amphetamine anorexia in rats: a behavioral analysis

These experiments were conducted to ascertain the effects of amphetamine on the behaviors associated with feeding in weanling and preweanling rats. The first two experiments produced the following results. (a) In 5-day-old pups, amphetamine increased speed of approach to an anesthetized dam but had no effect on other food-related behaviors, such as latency to attach to the nipple, time spent with the mother, duration of suckling, or weight gain. (b) At 15 days of age, amphetamine increased speed of approach to the dam but did not affect time spent in contact with the dam. However, it produced marked weight loss (relative to the weight of controls), slowed or reduced frequency of attachment to the nipple, and decreased time spent nursing. (c) AT 25 days of age, amphetamine disrupted all aspects of the feeding process except initial approach to the dam. Weight gain, time spent in contact with the dam, time spent nursing, and time attached to the nipple were all reduced by the drug. In Experiments 3 and 4, milk was delivered to pups 5, 15, and 25 days of age through tongue cannulas, which allowed ingestion without suckling. Under these circumstances amphetamine produced clear-cut weight loss (anorexia) in pups of all three ages. This developmental analysis shows that the feeding process consists of a complex and changing sequence of behavioral events which ae differentially affected by amphetamine at each age studied. Early in development the anorectic effects of amphetamine are overridden by the strong suckling response which is not disrupted by the drug.