Attentional effects of nicotine and amphetamine in rats at different levels of motivation.

RATIONALE

The effects of drugs on performance of tasks used to assess attention might be confounded with changes in motivation. Few studies have investigated the role of motivational factors in such situations.

OBJECTIVES

To determine how changes in motivation for food influence performance of the 5-choice serial reaction time task and whether the effects of nicotine and amphetamine can be explained by motivational changes.

METHODS

Male hooded Lister rats were trained to respond to a 1-s light stimulus presented randomly in one of five apertures in order to obtain food reinforcers. For three groups of rats (n=9-10), access to food was restricted to maintain body weights at 80, 90 or 95% of control weights. Saline and nicotine (0.025-0.2 mg/kg) were tested in each group, with and without pre-feeding (5 g). In a second experiment, saline and amphetamine (0.03-0.9 mg/kg s.c.) were tested without pre-feeding.

RESULTS

High levels of motivation for food were associated with increases in anticipatory responses, fewer omission errors, shorter response latencies and completion of more trials, without change in accuracy. Nicotine, but not amphetamine, increased accuracy and the number of trials completed; whereas amphetamine, but not nicotine, increased omission errors. Both drugs decreased anticipatory responding at the largest doses tested. There were few interactions of motivational level with drug effects.

CONCLUSIONS

The improvements in performance produced by nicotine did not resemble the effect of increased motivation, but some effects of amphetamine resembled those of reducing the level of motivation for food. Motivational levels did not confound assessments of the attentional effects of the drugs in terms of response accuracy.