Differential adenosine signaling and effects of acute caffeine exposure on alternative stress coping styles in zebrafish (Danio rerio)

Changes within neurotransmitter systems are associated with variation in anxiety-related behavior. The adenosine signaling pathway has been associated with anxiety and caffeine has been utilized as a modulator. However, studies have not considered the impact of an individuals stress coping style (e.g. proactive, reactive) and corresponding differences in neuromolecular signaling that can influence the behavioral responses. To assess the role of adenosine signaling, we acutely treated reactive and proactive zebrafish with 50 mg/L caffeine and evaluated anxiety-like behavior using a novel tank diving test (NTDT). We then quantified whole-brain gene expression of genes representing distinct parts of the adenosine signaling pathway: adenosine receptors A1B, A2Aa, A2Ab, and A2B (adora1b, adora2aa, adora2ab, and adora2b, respectively) and enzymes adenosine deaminase (ada) and ecto-5-nucleotidase (nt5e). We found significant main effects of coping style, sex, treatment, and coping style by sex by treatment interaction effect on stress behaviors. Specifically, compared to controls, caffeine reduced stress behavior in only reactive males. We also observed significant differential baseline gene expression within the adenosine signaling pathway between the reactive and proactive strains, where reactive zebrafish expressed higher levels of adenosine receptors A1B, A2Ab, A2B, and adenosine deaminase and lower levels of adenosine receptor A2Aa than proactive zebrafish. These findings indicate that variation in adenosine signaling between the stress coping styles and sexes may be contributing to differences in anxiety-related behavior.