Organophosphorus compound-induced delayed neurotoxicity in white leghorn hens assessed by Fluoro-Jade

Certain organophosphorus (OP) compounds can induce a delayed neuropathy, termed OPIDN, that involves central and peripheral nervous system axons, terminals, and perikarya. Historically, OPIDN has been characterized by staining neural sections with silver or hematoxylin and eosin (H and E). This study utilized a novel staining method, Fluoro-Jade, for evaluating the distribution and extent of OPIDN in the central nervous system of hens. Results were then compared to synoptically sectioned and stained H and E preparations. White Leghorn hens were injected with phenyl saligenin phosphate (PSP, 2.5 mg/kg, intramuscular [im]), triphenyl phosphite (TPPi, 500 mg/kg, subcutaneous [sc]), or dimethyl sulfoxide vehicle (DMSO, 0.5 ml/kg, im or sc) and evaluated clinically for signs of neurological dysfunction associated with OPIDN. Hens were sacrificed 7, 14, and 21 days post dosing. Brains and spinal cords were removed immediately following sacrifice, fixed in formalin, and embedded in paraffin. Microtome-cut sections (7 micro m) were then stained with Fluoro-Jade (0.001%, w/v) or H&E. Staining with Fluoro-Jade revealed time-dependent degeneration of nerve fibers and terminals (with PSP and TPPi), or cell bodies (with TPPi) in lamina VII, spinocerebellar, and medial pontine-spinal tracts of the lumbar spinal cord, in white matter and mossy fibers of foliae I-V and IX of the cerebellum, and in medullary, pontine, and midbrain nuclei and paleostriatal fibers surrounding the optic tract. TPPi-induced degeneration was more extensive than that induced by PSP and affected additional cerebellar folia, medullary, pontine, midbrain, and forebrain nuclei and fiber tracts. H&E-stained sections revealed fewer sites of neurodegeneration when compared to Fluoro-Jade. These results demonstrate that Fluoro-Jade is a sensitive method for staining neural tissue affected by OPIDN.