Quantitative analysis of neuronal damage induced by tri-ortho-cresyl phosphate in Wistar rats

A quantitative analysis of neuronal damage was performed on the fasciculus gracilis (FG) of the cervical spinal cord in male Wistar rats that received orally a single dose of tri-ortho-cresyl phosphate (TOCP) at 1500 mg/kg. FG tissues were sampled at 1, 2, and 3 weeks after treatment and examined histopathologically. Wallerian degeneration of myelinated nerve fibers was observed in FG at 2 weeks. Morphological changes were most evident at 3 weeks after treatment and the number of fibers was reduced. Ultrastructurally, axonal swelling due to the accumulation of cytoplasmic contents was observed near the node of Ranvier in the affected animals, indicating paranodal degeneration. Axonal atrophy and swelling in organophosphorus-induced delayed neuropathy (OPIDN) were evaluated quantitatively using a computer-assisted image analyzer. Morphometric examinations on semi-thin sections and frozen sections stained with Nauta's method were demonstrated to be useful for objective evaluation of OPIDN in the rat.