VALPROIC ACID AFFECTS NEURONAL SPECIFICATION AND DIFFERENTIATION DURING EARLY OPTIC TECTUM DEVELOPMENT OF ZEBRAFISH

The mammalian superior colliculus and its non-mammalian homolog, the optic tectum (OT), are midbrain structures that integrate multimodal sensory inputs and guide non-voluntary movements in response to prevalent stimuli. Recent studies have implicated this structure as a possible site affected in Autism Spectrum Disorder (ASD). Interestingly, fetal exposure to valproic acid (VPA) has also been associated with an increased risk of ASD in humans and animal models. Therefore, we took the approach of determining the effects of VPA treatment on zebrafish OT development as a first step in identifying the mechanisms that allow its formation. We describe the normal OT development during the first 5 days of development and show that in VPA treated embryos, while proliferation of the OT neuroepithelium continued, neuronal specification stalled. This was followed by impairment of neurite extension and complexity, suggesting that in addition to neurogenesis, VPA treatment affects axonogenesis and dendritogenesis. VPA treatment was most detrimental during the first three days of development and did not appear to be linked to oxidative stress. In conclusion, our work provides a foundation for research into mechanisms driving OT development, as well as the relationship between the OT, VPA, and ASD.