title: Chlorpyrifos-oxon disrupts zebrafish axonal growth and motor behavior.
abstract: Axonal morphology is a critical determinant of neuronal connectivity, and perturbation of the rate or extent of axonal growth during development has been linked to neurobehavioral deficits in animal models and humans. We previously demonstrated that the organophosphorus pesticide (OP) chlorpyrifos (CPF) inhibits axonal growth in cultured neurons. In this study, we used a zebrafish model to determine whether CPF, its oxon metabolite (CPFO), or the excreted metabolite trichloro-2-pyridinol (TCPy) alter spatiotemporal patterns of axonal growth in vivo. Static waterborne exposure to CPFO, but not CPF or TCPy, at concentrations ≥ 0.03 μM from 24- to 72-h post fertilization significantly inhibited acetylcholinesterase, and high-performance liquid chromatography detected significantly more TCPy in zebrafish exposed to 0.1 μM CPFO versus 1.0 μM CPF. These data suggest that zebrafish lack the metabolic enzymes to activate CPF during these early developmental stages. Consistent with this, CPFO, but not CPF, significantly inhibited axonal growth of sensory neurons, primary motoneurons, and secondary motoneurons at concentrations ≥ 0.1 μM. Secondary motoneurons were the most sensitive to axonal growth inhibition by CPFO, which was observed at concentrations that did not cause mortality, gross developmental defects, or aberrant somatic muscle differentiation. CPFO effects on axonal growth correlated with adverse effects on touch-induced swimming behavior, suggesting the functional relevance of these structural changes. These data suggest that altered patterns of neuronal connectivity contribute to the developmental neurotoxicity of CPF and demonstrate the relevance of zebrafish as a model for studying OP developmental neurotoxicity.
authors.affiliation: Department of Molecular Biosciences, University of California Davis School of Veterinary Medicine, Davis, California 95616, USA.
authors.forename: Dongren
authors.initials: D
authors.lastname: Yang
authors.forename: Holly
authors.initials: H
authors.lastname: Lauridsen
authors.forename: Kalmia
authors.initials: K
authors.lastname: Buels
authors.forename: Lai-Har
authors.initials: LH
authors.lastname: Chi
authors.forename: Jane
authors.initials: J
authors.lastname: La Du
authors.forename: Donald A
authors.initials: DA
authors.lastname: Bruun
authors.forename: James R
authors.initials: JR
authors.lastname: Olson
authors.forename: Robert L
authors.initials: RL
authors.lastname: Tanguay
authors.forename: Pamela J
authors.initials: PJ
authors.lastname: Lein
mesh_terms: D000818:Animals; D001369:Axons; D004390:Chlorpyrifos / Q000031:analogs & derivatives; D002851:Chromatography, High Pressure Liquid; D007150:Immunohistochemistry; D009043:Motor Activity / Q000187:drug effects*; D013550:Swimming; D015027:Zebrafish / Q000254:growth & development* / Q000502:physiology
chemical_list: C009618:O,O-diethyl O-3,5,6-trichloro-2-pyridyl phosphate; D004390:Chlorpyrifos