Zebrafish (Danio rerio) are quickly becoming an important model organism in behavioural neuroscience and drug addiction research. Conditioned place preference studies show that drugs of abuse produce responses in zebrafish that are similar to mammalian animal models. Repeated administration of ethanol in zebrafish results in withdrawal-induced behavioural responses that vary with dose and exposure duration, requiring additional investigation. Here, we examine the effects of ethanol withdrawal on anxiety-like behaviours in adult zebrafish after a 21-day ethanol dosing schedule at either 0.4% or 0.8%. Anxiety-like behaviour was measured with the novel object approach test; this test involves placing a fish in a circular arena with a novel object in the centre and observing the amount of exploration of the object. We found increased anxiety-like behaviour during ethanol withdrawal. This study adds to the growing body of literature that validates the zebrafish as a model organism in the field of behavioural neuroscience and addiction.

Nicotine is an addictive compound that activates neuronal nicotinic acetylcholine receptors (nAChRs) and causes behavioural effects that vary with dose, schedule of administration, and animal model. In zebrafish (Danio rerio), acute doses of nicotine have been consistently found to have anxiolytic properties, whereas, chronic exposure elicits anxiogenic effects. To date, however, studies on repeated nicotine administration and the effects of nicotine withdrawal have not been well explored using this model. In this study, we administered nicotine with three different dosing regimens: 1. Single exposures of a "high" dose (25, 50, 100, or 400 mg/L) for 3 minutes. 2. Single exposures to a "low" dose (2.5, 5, or 20 mg/L) for one hour. 3. Repeated one-hour exposure to a "low" dose (2.5, 5, or 20 mg/L) for 21 days. The novel object approach test was used to examine boldness based on the tendency of the fish to explore a novel object. Acutely, nicotine significantly increased the time spent approaching the object with both three-minute and onehour durations of exposure, indicating increased boldness. Conversely, after repeated nicotine exposure for 21 days, fish spent less time approaching the object suggesting a decrease in boldness. Distance moved was unaffected one hour after repeated nicotine exposure, yet decreased after a two-day withdrawal period. Our work suggests that nicotine can have opposing effects on boldness that vary based on dosage and schedule of exposure. The global prevalence of tobacco smoking among adults has declined in recent decades, however, the number of daily smokers has increased due to population growth 1. The harmful effects of repeated tobacco use (e.g. cancer, stroke and heart disease) result in tobacco use being the leading cause of preventable deaths worldwide 2 at about 7 million per year 3. When tobacco is consumed, most commonly by smoking, nicotine enters the central nervous system and binds to neuronal nicotinic acetylcholine receptors (nAChRs) that are normally activated by endogenous acetylcholine 4. Repeated nicotine use results in modifications to dopamine and acetylcholine pathways on reinforcement circuits in the midbrain and cortex 5 and causes a pleasurable experience via the activation of these circuits which reinforces self-administration 6. Contributing to the addictive nature of nicotine is the effect it has on emotion in humans 7,8. The acute effect of nicotine on anxiety, however, seems to depend on dose and varies across animal models. In rodent models, low doses of nicotine have anxiolytic effects on social interaction, whereas, high doses have an anxiogenic effect 7. Low doses of nicotine have also been shown to increase the amount of time some strains of mice spend in a mirrored chamber 9 as well as the time they spend in the white side of a white/black test box 10 , supporting an increase in boldness at low doses. Other studies, however, have failed to produce evidence that nicotine impacts anxiety and/ or boldness levels. For example, mice tested in an elevated ...

No abstract

The suitability of a traditional testing paradigm (e.g. choice chamber) for assessing chemosensory behaviour in the Pacific hagfish, Eptatretus stoutii, was examined. Actively-swimming hagfish, tested at night, showed no preference for any region of a T-maze in the absence of a stimulus, but in the presence of an olfactory food cue, spent significantly more time in the zone where the cue was placed. Conversely, hagfish avoided spending time in the zone the fish anaesthetic 3-amino benzoic acid ethylester (MS-222) was placed, and demonstrated significantly more reversal responses in which the fish moved its body backwards. These data suggest that hagfish are an amenable model species for laboratory testing of behaviour.

Cadmium (Cd2+) bioaccumulates in tissue in a dose-dependent manner after a 24 h exposure in green shore crabs (Carcinus maenas), but this has no impact on basic behaviour.