Morphine administered post-trial can induce potent conditioned morphine effects

Publication date: Available online 27 February 2019Source: Pharmacology Biochemistry and BehaviorAuthor(s): Lucas Rangel de Oliveira, Breno Garone dos Santos, João Marcos de Mello Bastos, Richard Ian Samuels, Robert J. Carey, Marinete Pinheiro CarreraAbstractMorphine has substantial pro-dopamine effects and in rodents, this is expressed in behavior as increased locomotor activation. Here we administered post-trial 3 dose levels of morphine (3.0, 5.0 and 10.0 mg/kg) or vehicle either immediately or after a 15 min delay to different groups of rats following a brief (5 min) exposure to a novel test environment. Three post-trial injections were administered on three successive days. One day after the first post-trial morphine injections, the non-drug activity levels in the immediate post-trial morphine treatment groups were selectively increased compared to vehicle groups. The activity effects were potentiated with repeated immediate post-trial morphine treatments but the same morphine treatments given after a 15 min post-trial delay did not increase activity in any tests and did not differ from vehicle. Subsequently, all groups were given 5 daily non-drug test sessions as an extinction protocol. The increased activity levels in the 5.0 and 10.0 mg/kg immediate post-trial morphine groups were sustained over the five extinction sessions. Two days later all groups were given a 30 min non-drug test and the 5.0 and 10.0 immediate post-trial groups continued to exhibit a ...
Source: Pharmacology Biochemistry and Behavior - Category: Biochemistry Source Type: research