Anxiolytic effects of nicotine in zebrafish Edward D. Levin ⁎ , Zachary Bencan, Daniel T. Cerutti Department of Psychiatry and Behavioral Sciences, Duke University Medical Center, USA Received 6 February 2006; received in revised form 15 August 2006; accepted 28 August 2006 Abstract Anxiolytic effects of nicotine have been documented in studies with rodents and humans. Understanding the neural basis of nicotine-induced anxiolysis can help both with developing better aids for smoking cessation as well as with the potential development of novel nicotinic ligands for treating anxiety. Complementary non-mammalian models may be useful for determining the molecular bases of nicotine effects on neurobehavioral function. The current project examined whether a zebrafish model of anxiety would be sensitive to nicotine. When zebrafish are placed in a novel environment, they dive to the bottom of the tank. In the wild, diving could help to escape predation. We tested the anxiolytic effect of nicotine on the novelty-elicited diving response and subsequent habituation. Zebrafish placed in a novel tank spent the majority of time at the bottom third of the tank during the first minute of a 5-min session and then show a gradual decrease in time spent at the tank bottom. Nicotine treatment at 100 mg/l for 3 min by immersion before testing caused a significant decrease in diving throughout the session, while 50 mg/l was effective during the first minute when the greatest bottom dwelling was seen in controls. Nicotine effects were reversed by the nicotinic antagonist mecamylamine given together with nicotine, but not when administered shortly before the test session after prior nicotine dosing. This implies that the effect of nicotine on diving was due to net stimulation at nicotinic receptors, an effect that is blocked by mecamylamine; and that once invoked, this effect is no longer dependent on continuing activation of nicotinic receptors. The effect of nicotine on diving did not seem to be the result of a general disorientation of the fish. The 100 mg/ml nicotine dose was shown in our earlier study to significantly improve spatial- discrimination learning in zebrafish. Nicotine-induced anxiolytic effects can be modeled in the zebrafish. This preparation will help in the investigation of the molecular bases of this effect. © 2006 Elsevier Inc. All rights reserved. Keywords: Nicotine; Mecamylamine; Zebrafish; Anxiolysis 1. Introduction Nicotine has a wide variety of effects on the central nervous system which impact behavioral function (reviews in [11,13,14,20,21,24]). Three main effects which seem to promi- nently underlie cigarette smoking are reward, cognitive enhance- ment, and anxiolysis [3]. Rodent models of have classically been used to assess nicotinic receptor roles in reinforcement, cognitive function and anxiety. Recently, zebrafish, Danio rerio, have emerged as a useful complementary model for the study of a variety of neurobehavioral functions including reward and cognitive function [6,10,15–18]. Anxiolysis was studied in the present experiment using the zebrafish model of nicotine effects, because it is thought to play a role in nicotine addiction and remission, and a demonstration that nicotine affects anxiety in the zebrafish would open new avenues of investigation in nicotinic receptor function. With a rapid and inexpensive model system many novel compounds could be efficiently screened for further study in mammalian models. Molecular mechanisms for the critical neuropharmacological effects could be readily studied in the great array of mutant zebrafish strains. Zebrafish behavioral assays are becoming increasingly versatile and utilized in studies of genetic and neural under- pinnings of cognitive function [1,7,22,27]. A dose–effect nicotine study on zebrafish in a delayed alternation task [16] found results consistent with rats, monkeys, and humans [19]: low doses improve memory, while high doses are detrimental. Nicotine has varied effects on anxiety in humans and animals [25]; these effects are frequently correlated with tobacco addiction [8]. In humans, stress increases the rate of smoking [12]; this relation between stress and nicotine seeking is also Physiology & Behavior 90 (2007) 54 – 58 ⁎ Corresponding author. Department of Psychiatry, Neurobehavioral Research Laboratory, Box #3412, Duke University Medical Center, Durham, NC 27710, USA. Tel.: +1 919 681 6273; fax: +1 919 681 3416. E-mail address: edlevin@duke.edu (E.D. Levin). 0031-9384/$ - see front matter © 2006 Elsevier Inc. All rights reserved. doi:10.1016/j.physbeh.2006.08.026