Abnormal brain development of monoamine oxidase mutant zebrafish and impaired social interaction of heterozygous fish.

Monoamine oxidase (MAO) deficiency and imbalanced levels of brain monoamines have been associated with developmental delay, neuropsychiatric disorders and aggressive behavior. Animal models are valuable tools to gain mechanistic insight into outcomes associated with MAO deficiency. Here, we report a novel genetic model to study the effects of mao loss of function in zebrafish. Quantitative PCR, in situ hybridization and immunocytochemistry were used to study neurotransmitter systems and expression of relevant genes for brain development in zebrafish mao mutants. Larval and adult fish behavior was evaluated through different tests. Stronger serotonin immunoreactivity was detected in mao+/- and mao-/- larvae compared with their mao+/+ siblings. mao-/- larvae were hypoactive, and presented decreased reactions to visual and acoustic stimuli. They also had impaired histaminergic and dopaminergic systems, abnormal expression of developmental markers and died within 20 days post-fertilization. mao+/- fish were viable, grew until adulthood, and demonstrated anxiety-like behavior and impaired social interactions compared with adult mao+/+ siblings. Our results indicate that mao-/- and mao+/- mutants could be promising tools to study the roles of MAO in brain development and behavior. This article has an associated First Person interview with the first author of the paper.