Understanding the Role of Oxytocin in Autism: Establishment of Zebrafish MODEL

Background: Oxytocin is a neuropeptide that regulates a wide range of mammalian social and non-social behaviors relevant to autism, such as bonding, social recognition, anxiety, and aggression. Recently, intranasal administration of oxytocin has been reported to improve social function in autistic patients and has shown promise as a potential treatment of social impairments seen in autism. Since the mechanisms underlying autism and oxytocin’s role in allaying social symptoms in autistic patients are not well-understood, animal models with capacity for sophisticated genetic manipulation are necessary. Zebrafish (Danio rerio) is a highly social vertebrate with phylogenetic conservation in oxytocin and key neurotransmitter systems and we exploit these features to develop an animal model of autism in zebrafish.

Objectives: Importance of the oxytocinergic system in mammalian social behavior is well-established, but less is known about its homologous system in zebrafish. Our aim is to investigate social interaction and neurochemistry in zebrafish mutants with genetically manipulated oxytocin system.

Methods: Using adult male and female CRISPR-Cas9-mutants lacking either of the two zebrafish oxytocin receptor genes, oxtr and oxtrl, we performed a battery of tests for social and non-social behaviors. We measured behavioral responses (n ≥ 16 for each group) to experimentally-induced aggression and anxiety-related behavior, and ability to recognize previously encountered social stimulus in mutant and wildtype control fish. We also quantified the levels of neurotransmitters (dopamine, serotonin, norepinephrine, glutamate, glycine, GABA) in multiple brain regions of these mutants using high precision liquid chromatography.

Results: Our data show that zebrafish lacking oxytocin receptors display impairments in aggressive, social, and anxiety-related behavior, in a receptor-specific and sex-dependent manner. We also found significant differences in neurotransmitter levels in the measured brain regions (olfactory bulbs and telencephalon, mesencephalon, diencephalon, cerebellum & hindbrain), indicating a role of oxytocin in regulation of other neurotransmitters.

Conclusions: These results advance our understanding of neural mechanisms underlying oxytocin-regulated social interaction in zebrafish and further highlight the potential of future investigation of zebrafish oxytocin system towards generating better therapeutic treatments for autism.