Microstructural analysis of the involvement of beta-receptors in amphetamine anorexia.

Rats were trained to take food by pushing the door of the pellet dispenser in an operant chamber. Log survivor analysis of the inter-response time frequency distribution was used to determine whether or not an animal was eating, at any time during a thirty minute session. This information was used to compute eating time, eating rate, and the mean length of bouts of eating and gaps between eating bouts. Video-recordings confirmed that the method discriminated eating from not eating with an accuracy of approximately ninety percent. Amphetamine (0.5 mg/kg) significantly reduced total food intake and eating time, and increased gap length; propranolol (5 mg/kg) significantly increased eating time and bout length. Following propranolol pretreatment, amphetamine significantly reduced eating time and bout length but also significantly increased eating rate; as a result there was no significant decrease in total food intake. The possible mediation of these effects by beta-adrenergic and dopaminergic systems is discussed.