Methylphenidate and nicotine focus responding to an informative discrete CS over successive sessions of appetitive conditioning

Methylphenidate (MP) and nicotine would be expected to improve associative learning, though previous evidence suggests that they should reduce the selectivity with which associations are formed. Here we tested their effects on learning the association between a conditioned stimulus (CS) and food (unconditioned stimulus, UCS) in male Wistar rats. The UCS was delivered immediately (0s) following CS offset or after a 10s trace. In addition to the measures of discrete CS conditioning, contextual and trace responding was measured in the inter-trial- and the inter-stimulus-interval, respectively. In all cases, conditioning was measured as nose poking for food. Both MP and nicotine improved the acquisition of discrete cue conditioning. Acquisition was accelerated (compared to saline) under 5 but not 1 mg/kg MP and 0.6, but not 0.4 mg/kg nicotine. In each case, this effect was observed in 0s but not 10s conditioned groups. For comparison, some earlier published data obtained following the same procedure with D-amphetamine were re-analysed in the same way. Amphetamine similarly improved conditioning in the 0s group, in this case at 0.5, but not 1.5 mg/kg. Thus three different dopamine agonists increased the ability to focus responding to CS presentations over successive sessions of appetitive acquisition.