Zebrafish embryonically exposed to valproic acid present impaired retinal development and sleep behavior

Abstract

Prenatal exposure to valproic acid (VPA), a drug widely used to treat epilepsy and bipolar disorder, is an environmental risk factor for autism spectrum disorder (ASD). VPA has been used to reproduce the core symptoms of ASD in animal model organisms, including zebrafish. Visual system functioning is essential in the interpretation of social conditions and plays an important role of several behavioral responses. We hypothesized that behavioral deficits displayed by ASD patients may involve impaired visual processing. We used zebrafish as model organism to investigate the visual system after embryonic exposure to VPA using histological, behavioral and gene expression analysis. We analyzed the pineal gland of zebrafish and sleep-like behavior to study how VPA exposure alters photo-sensibility of zebrafish. VPA-exposed zebrafish showed a delay in the development of the retina and optic nerve, which normalized at five days post fertilization. At larval stage, VPA-exposed zebrafish showed sleep disturbances associated with a reduced number of serotonin-producing cells of the pineal gland. In addition, the number of hypocretin/orexin (hcrt) expressing neurons in the rostral hypothalamus at 6 and 14 days post fertilization was reduced. In conclusion, we demonstrated that although VPA exposure leads to a delay in visual system development, it does not affect larval visual function. The novel finding that VPA alters significantly cells involved in sleep regulation and the sleep-like state itself may be relevant for understanding sleep disturbances in ASD patients.