Aversive environmental stimuli as a factor in the psychostimulant response to nicotine.

Saline-treated rats tested on an elevated open platform were less active (p less than 0.01) than those tested on an enclosed platform of the same dimensions. Acute nicotine (0.05, 0.1 and 0.4 mg/kg SC) increased the activity (p less than 0.01) of rats tested on the open platform but had no effect on activity measured on the enclosed platform. When injected chronically, the highest dose tested increased the activity of rats tested on both platforms, whereas the two lower doses continued to exert selective effects on the activity of rats tested on the open platform. d-Amphetamine (0.1 to 0.5 mg/kg SC) and cocaine (5 and 15 mg/kg IP) evoked dose-dependent increases in activity which were independent of the test environment used. It is concluded that nicotine appeared to be a more effective psychostimulant in the rats tested on the open platform because, at doses lower than those needed to evoke general psychostimulation, it attenuated the reduction in activity caused by exposure to the more aversive environment.