Because of their ability to alter a wide variety of behaviors in rats, we conclude that low doses of d-AMP are in the 0.1-0.4 mg/kg range. Doses within this range typically: 1) constitute the ED50 in most drug discrimination/generalization procedures; 2) increase a variety of consummatory behaviors; 3) increase a variety of unconditioned or spontaneous motor activities; 4) increase low rate schedule-controlled behavior while exerting variable effects on high rate schedule controlled behavior; and 5) improve performance on some choice tasks, particularly those requiring sustained attention. Our analyses also indicate that, with respect to behavior, investigators do not always agree on what constitutes a low dose of amphetamine in rats and that doses assumed to be low for this species often are relatively high.

No abstract

Previous studies from this laboratory have demonstrated that a variety of psychostimulant drugs can improve the performance of rats trained in a 2-choice stimulus detection task in which the correct responses are indicated by a briefly illuminated light. To enhance the construct validity of the task for assessing sustained attention, the procedure was modified so that the precue interval across trials varied unpredictably between 3, 7, and 11 s. After training rats (N = 17) so that their baseline accuracy levels stabilized between 75% and 88% correct, their performance was assessed after administration of d-amphetamine (0.125-0.75 mg/kg sc), nicotine (0.25-0.75 mg/kg sc), and pemoline (5.0-30.0 po). At certain doses all 3 drugs induced performance improvements in mean choice accuracy and choice response time. Because the precue intervals varied unpredictably and the cue durations used to maintain the rats' baseline accuracy levels were typically short (range = 70-500 ms), the task conforms to most conditions typically required for assessing sustained attention. Results verify the proposal that psychostimulant drugs can enhance the attentiveness of animals in a fashion similar to that documented in humans.

No abstract

The effects of 2 and 4 mg/kg morphine sulfate, 0.5 and 1 mg/kg d-amphetamine sulfate, and 6 and 12 mg/kg pentobaribital sodium were tested in rats in two different discrete-trial two-choice discrimination tasks. The discriminative stimuli for one task were high and low intensity shocks. In the other, correct choices were signaled by the position of a brief light flash. Morphine (4 mg/kg) significantly disrupted performance of both tasks, with more reliable disturbance occurring in the shock discrimination animals. Pentobarbital (12 mg/kg), while exerting noticeable effects on gross motor behavior, had little effect on discrimination performance; d-amphetamine (1 mg/kg) was disruptive of discrimination performance in only some animals. The results indicate that much of the effect of relatively low doses of morphine on the shock discrimination performance of rats may be due not to its putative specific antinociceptive properties, but to alterations in conceptual-judgmental processes or decreases in motivation (e.g., hunger) unrelated to pain.