Amphetamine: differential effects on defensive flight and motor behavior in the rat

As in previous research, hooded rats treated with an acute high dose of d-amphetamine sulfate (5 mg/kg free base) showed a dramatic defensive flight reaction to a novel stimulus (mechanical robot) that did not elicit flight from saline controls. Both the defense response and stereotypy behavior (repetitive movements and oral, licking chewing) were assessed at eight time periods after injection: 1, 15, 30, 45, 75, 105, 135, and 165 min. The defense response peaked early (15-30 min) after injection and showed a significant decline by 75 min, with no reemergence as stereotypy subsided. Stereotypy peaked later (45 min) and did not decline until 105 min. Tests in the absence of the robot provided a control for motor effects of the drug. Whereas stereotypy occurred in both Robot and No Robot conditions, the defense response occurred only in the Robot condition. These results were thought to provide further evidence that the effects of amphetamine on defensive flight could not be attributed to purely motor reactions. Thus, amphetamine-induced defensive flight may be an appropriate pharmacological model of affective psychosis. As such, it may be helpful in establishing differential pharmacological profiles for affective versus motor potencies of potential antipsychotic compounds.