Modeling Fetal Alcohol Spectrum Disorders in Zebrafish to Characterize the Impact of an Adverse Embryonic Environment on Adult Social Behavior

Prenatal alcohol exposure can lead to a variety of birth defects collectively known as fetal alcohol spectrum disorders (FASD)¹. Impaired behavior, such as social difficulties, are common birth defects associated with FASD^2,3. Unfortunately, social difficulties frequently result in serious mental health issues⁴, which can adversely affect the quality of life for individuals with FASD. Thus, understanding the mechanisms responsible for ethanol-induced social defects is paramount.

Zebrafish have biological and behavioral characteristics which make them well suited to advancing our understanding of the mechanisms responsible for ethanol-induced social defects. For instance, zebrafish produce large quantities of transparent externally fertilized eggs; these biological characteristics allow researchers to easily create precise and replicable FASD phenotypes⁵. To expose embryos to ethanol at 24 h postfertilization (hpf), one simply has to use a dissecting microscope to examine the transparent egg and stage the embryo based on previously published work such as Kimmel et al.⁶, then place the egg in the desired ethanol concentration for the desired duration. Since the chorion is a weak barrier to alcohol⁷, the ethanol readily bathes the embryo. To stop the exposure, one simply has to remove the eggs from the ethanol solution. Besides providing researchers with a simple yet accurate method for creating FASD phenotypes, zebrafish also allow researchers to make genetic comparisons to humans because 70% of human genes have a zebrafish orthologue, thus they are a valuable tool for understanding human diseases-related genes⁸. Additionally, unlike other animal models zebrafish form social groups⁹ called shoals¹⁰. Shoaling behavior can be used to characterize the effects embryonic ethanol exposure has on social behavior¹¹. Furthermore, in zebrafish a social response can be elicited by using computer controlled social stimuli¹² or a live social stimulus¹³.

Previous works have characterized the social response of adult zebrafish in groups¹⁴, however a limitation of this approach is the inability to correlate the behavior of an individual fish with a specific measure such as changes in neurotransmitter levels¹¹. The following protocol will give users the ability to characterize the social behavior of an individual adult zebrafish. Since social behavior is acquired for individual fish, users of the protocol can now correlate the acquired behavioral profile of each fish with a dependent outcome. For example, previous work has shown that embryonic ethanol exposure impairs the dopaminergic response to a social stimulus¹¹. While the data shown here has used embryonic ethanol exposure as the independent variable, protocol users can characterize the effects other pharmacological treatments or genetic mutations have on social behavior. Furthermore, protocol users are not limited to examine how embryonic treatments alter behavior but can also determine how acute pharmacological treatments in adult zebrafish impact social behavior¹⁵.