Browsing by Author "Holcombe, Adam"

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    A novel method of drug administration to multiple zebrafish (Danio rerio) and the quantification of withdrawal
    (2014) Holcombe, Adam; Schalomon, Melike; Hamilton, Trevor
    Anxiety testing in zebrafish is often studied in combination with the application of pharmacological substances. In these studies, fish are routinely netted and transported between home aquaria and dosing tanks. In order to enhance the ease of compound administration, a novel method for transferring fish between tanks for drug administration was developed. Inserts that are designed for spawning were used to transfer groups of fish into the drug solution, allowing accurate dosing of all fish in the group. This increases the precision and efficiency of dosing, which becomes very important in long schedules of repeated drug administration. We implemented this procedure for use in a study examining the behavior of zebrafish in the light/dark test after administering ethanol with differing 21 day schedules. In fish exposed to daily-moderate amounts of alcohol there was a significant difference in location preference after 2 days of withdrawal when compared to the control group. However, a significant difference in location preference in a group exposed to weekly-binge administration was not observed. This protocol can be generalized for use with all types of compounds that are water-soluble and may be used in any situation when the behavior of fish during or after long schedules of drug administration is being examined. The light/dark test is also a valuable method of assessing withdrawal-induced changes in anxiety.
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    CO2-induced ocean acidification increases anxiety in rockfish via alteration of GABAA receptor functioning
    (2013) Hamilton, Trevor; Holcombe, Adam; Tresguerres, Martin
    The average surface pH of the ocean is dropping at a rapid rate due to the dissolution of anthropogenic CO2, raising concerns for marine life. Additionally, some coastal areas periodically experience upwelling of CO2-enriched water with reduced pH. Previous research has demonstrated ocean acidification (OA)-induced changes in behavioural and sensory systems including olfaction, which is due to altered function of neural gamma-aminobutyric acid type A (GABAA) receptors. Here, we used a camera-based tracking software system to examine whether OA-dependent changes in GABAA receptors affect anxiety in juvenile Californian rockfish (Sebastes diploproa). Anxiety was estimated using behavioural tests that measure light/dark preference (scototaxis) and proximity to an object. After one week in OA conditions projected for the next century in the California shore (1125 ± 100 µatm, pH 7.75), anxiety was significantly increased relative to controls (483 ± 40 µatm CO2, pH 8.1). The GABAA-receptor agonist muscimol, but not the antagonist gabazine, caused a significant increase in anxiety consistent with altered Cl− flux in OA-exposed fish. OA-exposed fish remained more anxious even after 7 days back in control seawater; however, they resumed their normal behaviour by day 12. These results show that OA could severely alter rockfish behaviour; however, this effect is reversible.
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    Object recognition memory in zebrafish
    (2016) May, Zacnicte; Morrill, Adam; Holcombe, Adam; Johnston, Travis; Gallup, Joshua; Fouad, Karim; Schalomon, Melike; Hamilton, Trevor
    The novel object recognition, or novel-object preference (NOP) test is employed to assess recognition memory in a variety of organisms. The subject is exposed to two identical objects, then after a delay, it is placed back in the original environment containing one of the original objects and a novel object. If the subject spends more time exploring one object, this can be interpreted as memory retention. To date, this test has not been fully explored in zebrafish (Danio rerio). Zebrafish possess recognition memory for simple 2- and 3-dimensional geometrical shapes, yet it is unknown if this translates to complex 3-dimensional objects. In this study we evaluated recognition memory in zebrafish using complex objects of different sizes. Contrary to rodents, zebrafish preferentially explored familiar over novel objects. Familiarity preference disappeared after delays of 5 mins. Leopard danios, another strain of D. rerio, also preferred the familiar object after a 1 min delay. Object preference could be re-established in zebra danios by administration of nicotine tartrate salt (50 mg/L) prior to stimuli presentation, suggesting a memory-enhancing effect of nicotine. Additionally, exploration biases were present only when the objects were of intermediate size (2 × 5 cm). Our results demonstrate zebra and leopard danios have recognition memory, and that low nicotine doses can improve this memory type in zebra danios. However, exploration biases, from which memory is inferred, depend on object size. These findings suggest zebrafish ecology might influence object preference, as zebrafish neophobia could reflect natural anti-predatory behaviour.
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    Preferences for achromatic horizontal, vertical, and square patterns in zebrafish (Danio rerio)
    (2017) Rimstad, Lisa; Holcombe, Adam; Pope, Alicia; Hamilton, Trevor; Schalomon, Melike
    The zebrafish (Danio rerio) is gaining popularity as a laboratory organism and is used to model many human diseases. Many behavioural measures of locomotion and cognition have been developed that involve the processing of visual stimuli. However, the innate preference for vertical and horizontal stripes in zebrafish is unknown. We tested the preference of adult zebrafish for three achromatic patterns (vertical stripes, horizontal stripes, and squares) at three different size conditions (1, 5, and 10 mm). Each animal was tested once in a rectangular arena, which had a different pattern of the same size condition on the walls of either half of the arena. We show that zebrafish have differential preferences for patterned stimuli at each of the three size conditions. These results suggest that zebrafish have naïve preferences that should be carefully considered when testing zebrafish in paradigms using visual stimuli.
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    Reversed scototaxis during withdrawal after daily- moderate, but not weekly-binge, administration of ethanol in zebrafish
    (2013) Holcombe, Adam; Howorko, Adam; Powell, Russell A.; Schalomon, Melike; Hamilton, Trevor
    Alcohol abuse can lead to severe psychological and physiological damage. Little is known, however, about the relative impact of a small, daily dose of alcohol (daily-moderate schedule) versus a large, once per week dose (weekly-binge schedule). In this study, we examined the effect of each of these schedules on behavioural measures of anxiety in zebrafish (Danio rerio). Adult wild-type zebrafish were administered either 0.2% ethanol on a daily-moderate schedule or 1.4% ethanol on a weekly-binge schedule for a period of 21 days, and then tested for scototaxis (preference for darkness) during withdrawal. Compared to a control group with no alcohol exposure, the daily-moderate group spent significantly more time on the light side of the arena (indicative of decreased anxiety) on day two of withdrawal, but not day 9 of withdrawal. The weekly-binge group was not significantly different from the control group on either day of withdrawal and showed no preference for either the light or dark zones. Our results indicate that even a small dose of alcohol on a daily basis can cause significant, though reversible, changes in behaviour.