INFLUENCE OF NOVEL VERSUS HOME ENVIRONMENTS ON SENSITIZATION TO THE PSYCHOMOTOR STIMULANT EFFECTS OF COCAINE AND AMPHETAMINE

The acute psychomotor response (rotational behavior in rats with a uni lateral 6-OHDA lesion), and the development of sensitization, were stu died in rats that received seven consecutive daily injections of amphe tamine (Experiment 1) or cocaine (Experiment 2) either at home or in a 'novel' test environment. The home (HOME) and novel (NOVEL) cages wer e physically identical, but one group lived and was tested in these ca ges, whereas the rats in the other group were transported from the sta inless steel hanging cages where they lived, to these NOVEL test cages , for each test session. In Expt. 1, the acute psychomotor response to 3.0 mg/kg of amphetamine i.p. and the development of sensitization (i ncrease in the rotational response between the first and the seventh t est session) were greater in the NOVEL than in the HOME environment. I n Expt. 2, there were no significant group differences in the acute re sponse to 20 mg/kg of cocaine i.p., but the animals tested in the NOVE L environment showed greater sensitization than animals tested in the HOME environment. In addition, the animals pretreated with cocaine in the NOVEL environment, but not those pretreated with cocaine in the HO ME environment, showed conditioned rotational behavior in response to an injection of saline. These data indicate that: (i) sensitization to the psychomotor activating effects of both amphetamine and cocaine is enhanced in a NOVEL environment; (ii) this phenomenon appears to be i ndependent of the effects of the NOVEL environment on the acute respon se to these drugs; (iii) a robust conditioned psychomotor response to contextual cues develops only when cocaine treatments are given in the NOVEL test environment.