A comparison of the effects of nicotine and (+)-amphetamine on rat behaviour in an unsignalled Sidman avoidance...

In agreement with the results of previous studies, the withdrawal of nicotine from rats trained on an unsignalled Sidman avoidance schedule under the influence of the drug (0.4 mg kg-1 given subcutaneously 3 min before each training session) was associated with a reduction in lever-pressing responses (P less than 0.05) and an increase in the number of shocks received (P less than 0.01). The number of shocks received by the withdrawn rats was also greater (P less than 0.05) than the number of shocks received by rats trained and tested with saline, whereas the number of lever-pressing responses recorded for saline-treated rats was not influenced significantly by the drug used during training. The subcutaneous administration of (+)-amphetamine (0.5 mg kg-1 30 min before the test session) stimulated lever-pressing in rats trained with saline or nicotine and abolished the increase in the number of shocks received by the nicotine-withdrawn rats, but had no significant effect on the number of shocks received by rats trained with saline. The number of shocks received by the rats trained on the schedule with (+)-amphetamine but tested after an injection of saline was also greater (P less than 0.05) than the number of shocks received by rats trained and tested with saline. It is concluded that the disruption in shock avoidance performance observed for the nicotine- and (+)-amphetamine-withdrawn rats may reflect the development of dependence upon the stimulant properties of these drugs.