Conditioned Fos expression following morphine-paired contextual cue exposure is environment specific.

Environmental cues associated with drug administration elicit neural activation in circuits involved in cognitive processes and emotional regulation. An important question is whether the neural activation observed is specific to the drug-paired environment or is due to a generalized activation induced by previous drug treatment or changes in arousal state. Rats were treated with morphine (5 mg/kg i.p.) in one environment and saline in an alternative environment, and their brains were later examined for conditioned Fos expression after placement in one of these environments without drug administration. Increases in neural activation after drug-paired environmental exposure were dependent on exposure to the specifically paired environment; exposure to an alternative environment in morphine-treated rats did not elicit similar increases in Fos expression.