Comparison of the ability of (+)-amphetamine and caffeine to produce environment-specific conditioning

Animals with a history of receiving psychomotor stimulants in a specific environment show enhanced activity when injected with saline and placed there. In the present study, a Pavlovian paradigm was used to compare the unconditioned and conditioned activity effects of (+)-amphetamine (0.1, 0.5, 1.0, and 5.0 mg/kg), caffeine (0.1, 1.0, 10.0, and 30.0 mg/kg), and a saline group (n's=6–12). Rats experienced conditioning days with either drug or saline injected IP prior to a 60-min session in the activity monitor and the alternate saline or drug injected in the home cage following the session. On test days, all animals received saline in the activity monitors. Results revealed that amphetamine produced environment-specific conditioning in a dose-dependent manner; previous experience with 0.5, 1.0, and 5.0 but not 0.1 mg/kg in the activity monitor resulted in conditioned activity. A caffeine dose of 10.0 mg/kg produced stimulant effects on conditioning days and previous experience with the 1.0, 10.0, or 30.0 mg/kg dose in the activity monitor led to conditioned activity on test days. However, on test days the control groups as well as the 30.0 mg/kg experimental group showed significantly reduced activity as compared to the saline group. Thus, it appeared that caffeine produced hypoactivity 23 h after injection. Amphetamine produced conditioning in a dose-dependent manner, and the appearance of significant unconditioned activity during conditioning sessions was not necessary or sufficient to produce a conditioned effect. For caffeine there was some evidence of environment-specific conditioning, but it appears that between-group differences for caffeine may be accounted for by hypoactivity 23 h following injection.