Effects of dexamphetamine, amylobarbitone sodium and their mixture on sensory contingent bar pressing behaviour in the rat

The effects of the chronic administration of dexamphetamine, (one of five doses from 0.1 to 1.6 mg/kg), amylobarbitone sodium, (one of five doses from 1.0 to 16.0 mg/kg) and a mixture of the two (all of five doses, all at a constant ratio of 1.10 by weight) on sensory contingent bar pressing (SCBP) were investigated. 144 female Wistar rats bar pressed for 3 sec light and sound change as the only reward for their behaviour. The dose-response relationship under both dexamphetamine and the mixture took the form of an inverted U shaped function. Responding was not affected by amylobarbitone. The optimum doses of dexamphetamine and the mixture produced the same significant increase in SCBP, an effect which emerged over the initial trails. The results suggest that response feedback from the environment is magnified and thereby increases the reward value of SCBP. SCBP seems to have a number of advantages for the study of psychoactive drugs and intrinsic motivation.