Drinking in the morning versus evening: Time-dependent differential effects of acute alcohol administration on the behavior of zebrafish

Alcohol (ethanol) abuse remains to be a leading cause of medical, including mental, problems throughout the world. Whether alcohol consumption leads to chronic use, and subsequent alcohol dependency and abuse is known to be influenced by the acute effects of this drug. Numerous factors may influence how alcohol administered acutely affects the individual. For example, the mechanisms engaged by drugs of abuse, e.g. cocaine as well as alcohol, have been shown to overlap with those underlying circadian rhythm, and conversely, the effects of these drugs may be dependent upon the time of day of their consumption. To investigate the interaction between circadian rhythm and alcohol, here we employ a simple vertebrate model organism that was previously successfully utilized in other aspects of alcohol research, the zebrafish. We expose zebrafish to alcohol for 20 min in the morning or in the evening, and analyze the effects of this treatment by comparing 1% (vol/vol) alcohol-treated and control (alcohol naive) zebrafish. We record numerous swim path parameters, and report, for the first time, that the time of day of alcohol administration differentially affects certain behavioral parameters, enhancing some while blunting others. Our results suggest a complex interaction between circadian dependent and alcohol engaged mechanisms, findings that represent both practical complications as well as opportunities for understanding how alcohol affects brain function and behavior of vertebrates.