2001 Clinical and Scientific Meeting

Mohamed B. Abou-Donia

Department of Pharmacology and Cancer Biology,
Duke University Medical Center,
Durham, North Carolina,

Stress and Combined Exposure to Low Daily Doses of Pyridostigmine Bromide, DEET, and Permethrin in Adult Rats Causes Blood Brain Barrier Disruption and Neurochemical and Neuropathological Alterations in the Brain

A combined exposure to high doses of pyridostigmine bromide (PB), N,N-diethyl m-toluamide (DEET), and Permethrin leads to a significant toxicity and neurological dysfunction (Abou-Donia et al., J. Toxicol. Environ. Health, 48: 35-56, 1996). We investigated the effects following combined exposure to low doses of these chemicals with stress, simulating the daily exposure experienced by veterans to these chemicals during Persian Gulf War. Two groups of male Sprague-Dawley rats were administered PB (1.3mg/kg/d, oral), DEET (40mg/kg/d, dermal), and permethrin (0.13mg/kg/d, dermal) for 28 days. Animals in one of the above two groups were subjected to stress every day for the duration of the experiment by placing them in a Plexiglas® restraint tube for 5 minutes. Two additional groups of animals (one subjected to stress and vehicle treatment, and another treated with vehicle alone) served as controls. Three sets of five animals from each of the above four groups were processed for: 1) evaluation of the blood brain barrier (BBB) permeability using injections of [3H]hexamethonium iodide and 10% type IV horseradish peroxidase (HRP); 2) acetylcholinesterase (AChE) activity and m2 muscarinic ACh receptor biochemical assays; and (3) Hematoxylin and Eosin (H&E) staining and microtubule associated protein-2 (MAP-2) immunostaining. Animals subjected to either chemical treatment or stress alone did not show changes in body weight, brain [3H]hexamethonium iodide uptake, brain AChE, plasma ChE but exhibited a slight increase in BBB permeability by HRP and a decreased m2- muscarinic ACh receptor ligand binding, in comparison to control animals. In addition, these animals exhibited either no or minimal neuronal cell death. In contrast, animals subjected to both chemical treatment and stress exhibited a dramatic increase in BBB permeability (with focal perivascular accumulation of HRP in both cerebrum and the brainstem), a significant decrease in brain AChE activity, a decrease in m2 muscarinic ACh receptor ligand binding density in midbrain and cerebellum, and a significant neuronal cell death associated with a reduced MAP-2 expression in the cerebral cortex and the hippocampus. These results underscore that, when combined with stress, exposure to even low doses of PB, DEET, and permethrin, that produce minimal effects by themselves, leads to a significant brain injury.


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