Animated bird silhouette above the tank: Acute alcohol diminishes fear responses in zebrafish

Abstract

Alcohol dependence and alcohol abuse represent major unmet medical needs. The zebrafish is considered to be a promising vertebrate species with which the effects of alcohol on brain function and behavior and the mechanisms underlying these effects may be studied. Alcohol is known to induce alterations in motor function as well as fear and anxiety. Here we present a recently developed fear paradigm in which we employ an animated (moving) image of a bird silhouette. We measure the effect of acute alcohol administration (dose range employed: 0.00 – 0.75 vol/vol percentage, bath exposure for 60 minutes) on the behavioral responses of zebrafish. We test these responses during a pre-stimulus, stimulus and post-stimulus period of the task using both a video-tracking and an observation based quantification method. The fear inducing stimulus was found to decrease the distance of the zebrafish from the bottom of the tank, to increase number of erratic movements, and to increase the number of jumps in alcohol exposed fish (versus control fish). Alcohol attenuated these fear responses in a dose dependent manner. In addition, alcohol decreased general activity at the highest dose, an effect that was independent of the presentation of the stimulus. We discuss the similarities and differences between observation and video-tracking based results and conclude that fear paradigms will be useful in revealing alcohol induced functional changes in the brain of zebrafish.

Individual differences in activity levels in zebrafish (Danio rerio)

“…Also occasionally observed in zebrafish is the initial preference for the bottom of the tank within the first few minutes of being exposed to a new place, a response that subsequently may dissipate as the fish becomes habituated to the environment [22, 30 – 31]. Notably, however, this response has been argued to be less of a reliable indicator of fear due to its context dependence [2, 23, 36]. We report no changes in depth preference in the 37 L tank over the first 7 testing days but we detected a significant habituation of activity especially robust between days 1 and 2.…”

“…Total distance travelled was used as a measure of locomotor activity. Distance from bottom was used as a measure of fear, commonly used in previous studies [22 – 23]. …”

N-acetylcysteine prevents stress-induced anxiety behavior in zebrafish

“…On the other hand, time spent in the lower half increases when fish are exposed to threat, chronic unpredictable stress highdose caffeine and to alarm pheromone (Egan et al 2009;Piato et al 2011;Luca and Gerlai 2012). Taken together, these studies suggest that increased exploration of the upper zone may be related to a more 'elevated mood state' or less anxiety, and staying in the bottom zone may reflect avoidance, depressivelike or fear-related behavior.…”

Recent advances with a novel model organism: Alcohol tolerance and sensitization in zebrafish (Danio rerio)

“…These low doses, which have been reported to fall within the range of alcohol consumption in humans (Dlugos & Rabin, 2003; Rosemberg et al, 2012), exert stimulatory effects on zebrafish locomotor activity quantified as increased distance travelled, velocity, or number of zones crossed (Blaser & Penalosa, 2011; Gerlai et al, 2000; Rosemberg et al, 2012; Tran & Gerlai, 2013a). Anxiolytic effects are also observed in response to exposure to low and moderate concentrations of alcohol and they may manifest as reduced frequency or duration of erratic movement (Tran & Gerlai, 2013), freezing (Blaser & Penalosa, 2011), jumping (Luca & Gerlai, 2012), bottom dwelling (Mathur & Guo, 2011; Sackerman et al, 2010; Egan et al, 2009; Tran & Gerlai, 2013; Wong et al, 2010), preference for darkness (Mathur & Guo, 2011), shoaling, (Dlugos & Rabin, 2003; Damodaran et al, 2006; Gerlai et al, 2009), aggression (Echevarria et al, 2010), and distance to a predator (Luca & Gerlai, 2012). …”