Organophosphorus induced delayed neurotoxicity (OPIDN) has occurred in factory workers exposed in production of organophosphorus chemicals, which are used as plasticizers, lubricants, fire-retardants, or pesticides. Certain animal species (i.e., cats, dogs, cows, and chickens) are also susceptible, while others (rodents and some primates) are not. Although the chicken is the animal of choice to study this effect, it has many drawbacks. Our previous studies suggest the cat may be a better animal model to study the mechanisms of OPIDN. Although the mechanisms of OPIDN are not known, it is generally believed that the initial event is the phosphorylation of a protein (e.g. neurotoxic esterase, NTE) at the neurotoxicity target. We have postulated that subsequent changes in cellular Ca++ content leads to either enhanced phosphorylation of tubulin or a dissolution of neurofilaments. Both consequences lead to a disruption of axoplasmic transport and larger accumulations of Ca++ resulting in focal internodal swelling and Ca++ dependent proteolysis. Our preliminary studies have shown that in the cat brain, proteins relevant to OPIDN are concentrated in the synaptosomal fraction. Also, phosphorylation of brain synaptosomal protein with Gamma 32p-ATP was altered in cats as a result of TOCP treatment. We propose to study the effect of the neurotoxic organophosphorus esters (OP), TOCP, EPN, and DFP in comparison with the non-neurotoxic parathion on the normal phosphorylating mechanisms of neuronal proteins and on Ca++ concentrations of the axoplasm of neuronal organelles, as well as the isolation and characterization of tubulin and neurofilaments. In the beginning, we will examine the [Gamma 32p]ATP phosphorylatable proteins in brain and spinal cord synaptosomal cytosol and membrane fractions of normal cats. Optimum phosphorylating conditions will be established including the effect of calcium ions and calmodulin. The effect of in vivo protein phosphorylation will be determined. The effect of TOCP, EPN, DFP and parathion on slow and fast axoplasmic transport of radiolabeled proteins as well as NTE will be investigated. The characterization of tubulin and neurofilaments using electron microscopy as well as SDS-PAGE in TOCP treated cats will be studied. Electron microscopy will also be used to study cellular Ca++ levels in various organelles using x-ray energy spectrometry for the demonstration of calcium ions in swollen and degenerating axons. Finally, cats administered glucocorticoids in combination with OP's will be used to examine the reported benefit of glucocorticoid therapy in relation to the postulated mechanisms.

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Damodaran, T V; Attia, M K; Abou-Donia, M B (2011) Early differential cell death and survival mechanisms initiate and contribute to the development of OPIDN: a study of molecular, cellular, and anatomical parameters. Toxicol Appl Pharmacol 256:348-59
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