Rev. Neurosci., Vol. 22(1): 95–105, 2011 • Copyright © by Walter de Gruyter • Berlin • New York. DOI 10.1515/RNS.2011.011 Zebrafish models to study drug abuse-related phenotypes Adam Stewart a , Keith Wong a , Jonathan Cachat, Siddharth Gaikwad, Evan Kyzar, Nadine Wu, Peter Hart, Valerie Piet, Eli Utterback, Marco Elegante, David Tien and Allan V. Kalueff* Department of Pharmacology and Neuroscience Program, Zebrafish Neuroscience Research Consortium (ZNRC), Tulane University Medical School, 1430 Tulane Ave., New Orleans, LA 70112, USA *Corresponding author e-mail address: avkalueff@gmail.com Abstract Mounting evidence implicates the zebrafish ( Danio rerio) as a promising model species for reward and addiction research. Modeling drug abuse-related behavior in both adult and lar- val zebrafish produced a wealth of clinically translatable data, also demonstrating their sensitivity to various drugs of abuse and the ability to develop tolerance. Several studies have also applied withdrawal paradigms to model the adverse effects of drug abuse in zebrafish. In this review, we summarize recent findings of a wide spectrum of zebrafish drug abuse-related behavioral and physiological phenotypes, discuss the existing challenges, and outline potential future directions of research in this field. Keywords: anxiety; drug abuse; cortisol; stress tolerance; withdrawal; zebrafish. Introduction Drug abuse and addiction are serious mental health and societal problems (Larson and Bammer, 1996; Banken, 2004; Aceijas et al., 2006; Brady et al., 2008). They rep- resent complex brain disorders with multiple symptoms (Figure 1) caused by both genetic and environmental fac- tors (Brunette et al., 2003; Sareen et al., 2004; Busto et al., 2010; Cheung et al., 2010; Hamilton, 2010). Various experimental (animal) models have been introduced to tar- get different aspects of drug abuse (Brady , 1991; Markou et al., 1993; Crabbe et al., 1994; Friedman and Eisenstein, 2004; Jentsch, 2008). Zebrafish ( Danio rerio) continue to emerge as a new promising model for reward and addiction research (Gerlai et al., 2000; Ninkovic and Bally-Cuif, 2006; Webb et al., 2009; Cachat et al., 2010). Dopaminergic projections to zebrafish forebrain parallel the mesolimbic system (impli- cated in drug addiction in mammals; Rink and Wullimann, 2002), representing a pathway that is highly conserved and develops at early ontogenesis (Boehmler et al., 2004). Various behavioral paradigms have been particularly useful in zebrafish addiction research (Table 1 ). For example, con- ditioned place preference (CPP) and similar models reveal strong rewarding properties of different drugs in zebrafish (Kily et al., 2008; Webb et al., 2009). Genetic factors also contribute to zebrafish behavioral responses (Egan et al., 2009), demonstrating the link between individual genes and reward phenotypes (Ninkovic et al., 2006; Webb et al., 2009). Modeling zebrafish behavior traditionally utilizes both adults and younger animals, including ‘larvae’ and older, free-feeding ‘fry’. Although the distinction between lar- vae and fry is important, for the purposes of this article we will apply the term ‘larvae’ to both these stages. Overall, zebrafish larvae display robust drug-evoked neurobehav- ioral phenotypes (Best and Alderton, 2008) and offer the ability to study multiple animals simultaneously within a high-throughput battery (Best and Alderton, 2008; Best et al., 2008; Creton, 2009). However, larval models do not always display the complex behavior of their adult coun- terparts and lack fully established mediatory and endocrine systems (Kimmel et al., 1995), neural circuits (Kastenhuber et al., 2010), and neuromuscular systems (Dou et al., 2008). Therefore, both models should be used complementarily to study drug abuse-related neurobehavioral domains (Figure 1). Particular focus must be given to selecting the drug con- centrations for zebrafish studies. First, background litera- ture is lacking for many psychotropic drugs, because the zebrafish is a new model in behavioral pharmacology (Zon and Peterson, 2005; Rubinstein, 2006; Liang, 2009). Second, although zebrafish possess all major ‘mammalian’ neurotrans- mitters, peptides, and hormones (Egan et al., 2009; Mueller and Neuhauss, 2010), species differences in animal physiol- ogy play a role. For example, unlike humans and rodents, zebrafish have two forms of the serotonin transporter (SERT A and B) (Wang et al., 2006; Norton et al., 2008; Severinsen et al., 2008). Furthermore, the blood-brain barrier of teleost fish is less exclusive than in mammals, enabling serotonin to pass through it and affect both central and peripheral mechanisms (Genot et al., 1981; Khan and Deschaux, 1997; Stoddard et al., 2003). Thus, zebrafish might be differentially sensitive to various serotonergic drugs, compared to other model species. Third, discrepancies are probable within different zebrafish studies, because it is difficult to translate drug concentra- tions from larval into adult fish models. Finally, because the a These authors contributed equally. AUTHOR’S COPY | AUTORENEXEMPLAR AUTHOR’S COPY | AUTORENEXEMPLAR