Administration of morphine during exposure to a sensory cue-defined environment (special characteristics of the box) could result in preferences for previously non-preferred side of a test box (conditioned place preference). Two of three compartments of the test box were identical in size, but differed in shading (black or white) and floor texture (smooth or textured). The third "choice" compartment was adjecent to the rear of the two big compartments, access to which through guillotine doors. During the 12 days conditioning phase, three groups of rats (following sham exposure or electromagnetic fieldexposure) were placed in this sensory cue-defined environment (i.e. confinement to one compartment) paired with morphine (10 mg/kg). Rats were also placed in another sensory cue-defined environment (confinement to another compartment) paired with physiological saline without exposure to electromagnetic fields. After finishing conditioning, preference tests were performed during a 10-day withdrawal period: Animals were placed in the "choice" compartment with doors open and were allowed free access for 15 minutes.
Rats were placed in a non metallic plastic bucket which was placed in the middle of the exposure area (60 cm x 30 cm x 43 cm) provided by the coil. Sham exposedrats were kept in the same set-up as used for exposure but the coil was not energized.
