Note
Rats administered amphetamine prior to access to milk in bottles develop tolerance to the hypophagic effect of the drug by learning to suppress stereotyped behaviours that interfere with feeding. When tolerant rats are later allowed to drink milk from a bottle in an unintoxicated state, tolerance is lost, even when drug exposure is held constant by administration of the drug after the test. In the present experiment, we show that tolerance can also be lost in the face of continued administration of amphetamine prior to milk tests, as a result of changes in the contingencies of reinforcement that govern the suppression of stereotypy. Rats were injected with 2 mg/kg amphetamine and given access to milk in bottles for 16 trials.