Research reportInteraction between handling induced stress and anxiolytic effects of ethanol in zebrafish: A behavioral and neurochemical analysis

- Handling induced stress increases anxiety-like behavior and decreases 5-HIAA levels.
- Handling x ethanol interaction is detected for behavioral responses.
- Handling x ethanol interaction is detected for dopamine levels.

Stress is often considered an important factor in the development of alcohol addiction. In rodents, various types of stressors have been shown to potentiate the effects of alcohol on behavioral responses, and to increase consumption of this substance. However, few have investigated the interaction between stress and alcohol in zebrafish. In the current study we present a repeated handling stress paradigm we developed for zebrafish, and examine whether stress alters alcohol induced behavioral and neurochemical responses. Our results show that repeated handling of zebrafish conducted for 2 consecutive days is sufficient to increase anxiety-like behavioral responses quantified 24 h post-stressor. Repeatedly handled zebrafish also exhibited a reduction in the levels of serotonin's metabolite, 5-hydroxyindole acetic acid (quantified by high precision liquid chromatography) compared to unhandled controls. A 60-min acute exposure to 1% ethanol was found to significantly increase locomotor activity and decrease anxiety-like behavioral responses in stressed zebrafish but not in controls. Furthermore, unhandled control zebrafish exhibited a significant increase in whole-brain dopamine levels following exposure to ethanol but the increase was not observed in repeatedly handled fish. Our findings suggest that ethanol induced locomotor activity and anxiolysis is potentiated by handling stress and may be partially mediated by changes in dopaminergic and serotonergic activity. Overall, we demonstrate the validity of our repeated handling stressor paradigm for zebrafish, which can be used to investigate the interaction between stress and ethanol.