Inorganic arsenic alters the development of dopaminergic neurons but not serotonergic neurons and induces motor neuron development via Sonic hedgehog pathway in zebrafish

•Sodium arsenite significantly reduced acetylcholinesterase activity.•Sodium arsenite increased dopaminergic neurons, but not 5-HT (serotonergic) neurons in the brain.•In hb9-GFP transgenic zebrafish, sodium arsenite induced generation of supernumerary motor neurons in the spinal cord potentially through Shh signaling pathway.•Anomalous motor neuron development may explain why arsenic exposure causes motor neuron disease/death and Shh could be a potential plasma biomarker of arsenic toxicity.