Altered expression of neurofilament subunits in diisopropyl phosphorofluoridate-treated hen spinal cord and their presence in axonal aggregations.

Diisopropyl phosphorofluoridate (DFP) is an organophosphorus ester, which produces organophosphorus ester-induced delayed neuropathy (OPIDN) in hen and other sensitive species. A single dose of DFP (1.7 mg/kg, sc.) produces mild ataxia in 7-14 days in hens, which develops into severe ataxia or paralysis with the progression of disease. OPIDN is associated with axonal swellings and degeneration of axons. This study was carried out to investigate the expression of neurofilament (NF) subunits in the spinal cord of DFP-treated hens. Hens were treated with a single dose of DFP and sacrificed 1, 5, 10, and 20 days post-treatment. Western blot analysis showed increased expression of middle molecular weight neurofilament protein (NF-M), and decreased expression of high molecular weight (NF-H) and low molecular weight (NF-L) neurofilament proteins in the 2 M urea extracts of spinal cord particulate fraction. These changes were observed within 24 h of DFP administration and persisted for 10-20 days. Thus, there was increase in the stoichiometry of NF-M:NF-L in the spinal cord of DFP-treated hens. Immunoprecipitation, cross-linking, and two-dimensional polyacrylamide gel electrophoresis showed the presence of heterodimers, but not heterotetramers, in the hen spinal cord extract. Immunohistochemical staining revealed the presence of all three NF subunits in the cytoskeletal inclusions in DFP-treated hen spinal cord cross-sections. The results suggested that each NF subunit might be accumulated by a different mechanism in the axonal aggregations of DFP-treated hen.