A comparison of the effects of amphetamine, apomorphine and white noise on response switching in the rat.

The effects of d-amphetamine, apomorphine and white noise on response switching in the rat were examined using a schedule of reinforcement which resulted in the subjects displaying a range of different probabilities of switching. The procedure was analogous to the use of a fixed interval schedule of reinforcement for examining the rate-dependent effects of drugs. d-Amphetamine (0.4-4.0 mg/kg) increased response switching in a manner dependent both upon the dose of drug and the baseline probability of switching. Apomorphine (0.01-0.3 mg/kg) increased switching in a manner which depended upon dose but which was independent of the baseline probability of switching. Neither drug increased response rate, although both drugs reduced response rate at the highest doses. In contrast, continuous white noise (85-105 dB) increased response rate without affecting switching. The results indicate that different activating stimuli may have qualitatively different effects on behaviour.