Effect of Acute and Chronic Nicotine Exposure on Anxiety-like Behaviour in Zebrafish

Abstract

Nicotine is an addictive compound that acts through the activation of nicotinic acetylcholine receptors (nAChRs ). Zebrafish (Danio rerio) are becoming an increasingly important animal model for pharmacological research and demonstrate varied effects of acute nicotine exposure on behaviour. For example, nicotine enhanced spatial position discrimination learning and increased object recognition memory. However, there have been opposing results on nicotine's action on anxiety-like behaviour and no studies examining the impact of withdrawal following chronic nicotine administration. In order to examine the effects of chronic and acute nicotine exposure on anxiety-like behaviour in wild-type adult zebrafish, we administered single doses of 25, 50, 100, or 400mg/L for acute experiments, or 2.5 , 5, or 20mg/L one-hour doses per day for 21 days for chronic experiments. Anxiety-like behaviours were observed using the novel object approach test which involves placing a fish in a circular arena containing a novel object placed in the center. Time spent in the outer (thigmotaxis), middle (transition), and inner zones, distance moved, and immobility were measured with a motion tracking software. Acute doses of nicotine significantly increased time spent in the transition zone, and significantly decreased time spent in the thigmotaxis zone indicating decreased anxiety. On the contrary, chronic nicotine exposure at 20 mg/L significantly increased anxiety as indicated by an increased time spent in the thigmotaxis zone. This study demonstrates that acute nicotine exposure decreases anxiety-like behaviour whereas chronic exposure causes increased anxiety-like behaviour during withdrawal.

Discipline: Psychology (Honours)

Faculty Mentor: Dr. Trevor Hamilton