Suppression of fixed-interval responding by flavour-amphetamine pairings in rats

Amphetamine is a potent and very effective drug for conditioning taste aversions, but much less is known about the possible effects of flavour-amphetamine pairings on aspects of behaviour other than eating and drinking. Rats were trained to press bars for water reinforcers delivered on a fixed-interval one-min schedule. Flavoured reinforcers were then substituted for the water and post-session injections of amphetamine (1 mg/kg) were given. Even a single flavour-amphetamine pairing produced some disruption of responding for that flavour, whereas 3 pairings almost completely suppressed responding (both bar-pressing and drinking). In the same rats, flavours paired with saline injections did not suppress responding. Amphetamine (1mg/kg) injected before sessions of responding for plain water disrupted the temporal pattern of fixed interval responding without affecting the total numbers of bar-presses or the amounts of liquid consumed. Omitting primary reinforcement (water) throughout a single session also failed to suppress responding. The conditioned effects of the flavour were therefore different from the effects of either the unconditioned stimulus (amphetamine) or of an extinction procedure.