Behavioral responses to novel situations often vary and can belong to a suite of correlated behaviors. Characteristic behaviors of different personality types (e.g. stress coping styles) are generally consistent across contexts and time. Here, we compare the repeatability and reliability of exploratory behaviors between zebrafish strains selectively bred to display contrasting behavioral responses to stressors that represent the proactive-reactive axis. Specifically, we measure exploratory behavior of individual fish in an open field test over five weeks. We quantified the stationary time, average swimming speed and time spent by a fish in the center area. We found a number of strain differences for each behavioral measure. Stationary time was the most repeatable and reliable measure for assessing proactive-reactive behavioral differences. Reactive zebrafish generally showed the highest reliability and repeatability of exploratory behavior compared to proactive zebrafish and a separate wild caught strain. Given the increased interest in the evolutionary consequences and proximate mechanisms of consistent individual differences, it will be important to continue to investigate how different selective pressures may influence expression of stress coping styles and their effects on the consistency of an animal’s behavior.

Variation in stress responses between individuals are linked to factors ranging from stress coping styles to sensitivity of neurotransmitter systems. Many anxiolytic compounds (e.g. ethanol) can increase stressor engagement through modulation of neurotransmitter systems and are used to investigate stress response mechanisms. There are two alternative suites of correlated behavioral and physiological responses to stressors (stress coping styles) that differ in exploration tendencies: proactive and reactive stress coping styles. By chronically treating individuals differing in stress coping style with ethanol, a GABA-acting drug, we assessed the role of the GABAergic system on the behavioral stress response. Specifically, we investigated resulting changes in stress-related behavior (i.e. exploratory behavior) and whole-brain GABA A receptor subunits ( gabra1 , gabra2 , gabrd , & gabrg2 ) in response to a novelty stressor. We found that ethanol-treated proactive individuals showed lower stress-related behaviors than their reactive counterparts. Proactive individuals showed significantly higher expression of gabra1 , gabra2, and gabrg2 compared to reactive individuals and ethanol treatment resulted in upregulation of gabra1 and gabrg2 in both stress coping styles. These results suggest that impacts of ethanol on stress-related behaviors vary by stress coping style and that expression of select GABA A receptor subunits may be one of the underlying mechanisms.

21Variation in stress responses between individuals is linked to factors ranging from stress coping 22 styles to sensitivity of neurotransmitter systems. Many anxiolytic compounds (e.g. ethanol) can 23 increase stressor engagement through modulation of neurotransmitter systems and are used to 24 investigate stress response mechanisms. Here we assessed the role of the GABAA system on the 25 variation of the behavioral stress response by comparing individuals differing in stress coping 26 styles that were chronically treated with ethanol. Specifically, we investigated resulting changes 27 in stress-related behavior and whole-brain GABAA receptor subunits (gabra1, gabra2, gabrd, & 28 gabrg2) in response to a novelty stressor. There were significant main and interaction effects on 29 two stress-related behaviors, where the ethanol-treated proactive individuals showed lower 30 stress-related behaviors than their reactive counterparts. Proactive individuals showed 31 significantly higher expression of gabra1, gabra2, and gabrg2 compared to reactive individuals 32 and ethanol treatment resulted in upregulation of gabra1 and gabrg2 in both stress coping styles. 33These results show that differences in stress-related behaviors between stress coping styles may 34 be facilitated in part by expression of select GABAA receptor subunits.GABAA receptor (GABAAR) agonists, such as ethanol, allow for positive modulation of the 52 GABAergic system to produce an anxiolytic response, while antagonists result in an anxiogenic 53 response 13,16,[21][22][23][24][25][26][27][28] . GABA-acting drugs influence the expression of the protein subunits that make 54 up the receptor subtype as well 29,30 . For example, rodents exposed to GABAA agonists show an 55 increase in expression of the α1-, α2-, and δ-subunits of the GABAAR, while expression of the 56 γ2-subunit decreases 31-34 . Studies utilizing zebrafish similarly show that ethanol administration 57 produces anxiolytic behavioral effects 13,23,24,26,35,36 . While there are baseline differences in