Chick embryo dorsal root ganglia (DRG) cultures were used to explore early pathological events associated with exposure to neuropathy-inducing organophosphorus (OP) compounds. This approach used an in vitro neuronal system from the species that provides the animal model for OP-induced delayed neuropathy (OPIDN). DRG were obtained from 9-day-old chick embryos, and grown for 14 days in minimal essential medium (MEM) supplemented with bovine and human placental sera and growth factors. Cultures were then exposed to 1 microM of the OP compounds phenyl saligenin phosphate (PSP) or mipafox, which readily elicit OPIDN in hens, paraoxon, which does not cause OPIDN, or the DMSO vehicle. The medium containing these toxicants was removed after 12 h, and cultures maintained for 4-7 days post-exposure. Morphometric analysis of neurites was performed by inverted microscopy, which demonstrated that neurites of cells treated with mipafox or PSP but not with paraoxon had decreased length-to-diameter ratios at day 4 post-exposure. Ultrastructural alterations of neurons treated with PSP and mipafox included dissolution of microtubules and neurofilaments and degrading mitochondria. Paraoxon-treated and DMSO control neuronal cell cultures did not show such evident ultrastructural changes. This study demonstrates that chick DRG show pathological changes following exposure to neuropathy-inducing OP compounds.