Conditioned Place Preference and Behavioral Analysis to Evaluate Nicotine Reinforcement Properties in Zebrafish

Abstract

Studies with mice and rats have demonstrated that nicotine induces a Pavlovian conditioning denominated conditioned place preference (CPP). This behavioral paradigm is performed by exposing an animal to a drug in a particular environment. If the animal associates the drug (unconditioned stimulus) with the place where the drug is administrated (conditioned stimulus), a CPP is established. Similarly, zebrafish have also been used as a model system to identify factors infl uencing nicotine-associated reward. The protocol described here was designed to establish nicotine-CPP in zebrafi sh by using a biased approach. Moreover, pros and cons of using biased vs. unbiased design are also discussed. The protocol design is based in the establishment of nicotine/environment associations (nicotine-paired group). Since nicotine exerts anxiolytic effects, we used a counterbalanced nicotine-exposed control group, which did not show a significantplace preference shift, providing evidence that the preference shift in the nicotine-paired group was not due to a reduction of aversion for the initially aversive compartment. Nicotine-induced place preference in zebrafish was corroborated by behavioral analysis of several indicators of drug preference, such as time spent in the drug-paired side, number of entries to the drug paired side, and distance traveled. This method provided further evidence that zebrafish actually develop a preference for nicotine, although the drug was administrated in an aversive place for the fish. This methodology offers an incremental value to the drug addiction field, because it describes behavioral features associated to nicotine-induced CPP in zebrafish. Therefore, this model is useful to screen for exogenous and endogenous molecules involved in nicotine-associated reward in vertebrates.